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Tomiatti V, Istvánffy R, Pietschmann E, Kratzat S, Hoellein A, Quintanilla-Fend L, von Bubnoff N, Peschel C, Oostendorp RAJ, Keller U. Cks1 is a critical regulator of hematopoietic stem cell quiescence and cycling, operating upstream of Cdk inhibitors. Oncogene 2014; 34:4347-57. [DOI: 10.1038/onc.2014.364] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 08/06/2014] [Accepted: 09/02/2014] [Indexed: 01/14/2023]
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102
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The activity and stability of the intrinsically disordered Cip/Kip protein family are regulated by non-receptor tyrosine kinases. J Mol Biol 2014; 427:371-386. [PMID: 25463440 DOI: 10.1016/j.jmb.2014.11.011] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2014] [Revised: 11/07/2014] [Accepted: 11/10/2014] [Indexed: 12/21/2022]
Abstract
The Cip/Kip family of cyclin-dependent kinase (Cdk) inhibitors includes p21(Cip1), p27(Kip1) and p57(Kip2). Their kinase inhibitory activities are mediated by a homologous N-terminal kinase inhibitory domain. The Cdk inhibitory activity and stability of p27 have been shown to be regulated by a two-step phosphorylation mechanism involving a tyrosine residue within the kinase inhibitory domain and a threonine residue within the flexible C-terminus. We show that these residues are conserved in p21 and p57, suggesting that a similar phosphorylation cascade regulates these Cdk inhibitors. However, the presence of a cyclin binding motif within its C-terminus alters the regulatory interplay between p21 and Cdk2/cyclin A, as well as its responses to tyrosine phosphorylation and altered p21:Cdk2/cyclin A stoichiometry. We also show that the Cip/Kip proteins can be phosphorylated in vitro by representatives of many non-receptor tyrosine kinase (NRTK) sub-families, suggesting that NRTKs may generally regulate the activity and stability of these Cdk inhibitors. Our results further suggest that the Cip/Kip proteins integrate signals from various NRTK pathways and cell cycle regulation.
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103
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Chen XM, Xie XB, Zhao Q, Wang F, Bai Y, Yin JQ, Jiang H, Xie XL, Jia Q, Huang G. Ampelopsin induces apoptosis by regulating multiple c-Myc/S-phase kinase-associated protein 2/F-box and WD repeat-containing protein 7/histone deacetylase 2 pathways in human lung adenocarcinoma cells. Mol Med Rep 2014; 11:105-12. [PMID: 25333250 PMCID: PMC4237074 DOI: 10.3892/mmr.2014.2733] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 09/12/2014] [Indexed: 01/20/2023] Open
Abstract
Ampelopsin (AMP), a plant flavonoid, has been reported to inhibit cell growth and/or induce apoptosis in various types of tumor. The aim of the present study was to assess the apoptosis-inducing activity of AMP in A549 human lung adenocarcinoma epithelial cells and the associated underlying mechanism. A549 cells were incubated with different concentrations of AMP in culture medium. Cell growth and apoptosis were evaluated by MTT assay and Annexin V/propidium iodide double staining and flow cytometry, respectively. In addition, western blotting and reverse transcription quantitative polymerase chain reaction analysis were used to examine the time-dependent changes in protein expression. Certain changes in apoptotic protein expression were detected following exposure to AMP, including X-linked inhibitor of apoptosis protein release, reduced B-cell lymphoma 2, myeloid cell leukemia 1 and survivin expression levels, increased Bcl-2-associated X protein expression levels and cleaved-poly ADP ribose polymerase expression. The results revealed that AMP was a potent inhibitor of A549 cell proliferation. The c-Myc/S-phase kinase-associated protein 2 (Skp2) and histone deacetylase (HDAC)1/2 pathways were found to exert an important role in AMP-induced A549 cell apoptosis, as increased levels of c-Myc mRNA and reduced levels of c-Myc/Skp2 and HDAC1 and 2 proteins following AMP treatment were observed. The levels of F-box and WD repeat-containing protein 7α (Fbw7α), Fbw7β, Fbw7γ, phosphorylated-(p-)c-Myc (Thr58) and glycogen synthase kinase 3β (GSK3β) proteins involved in c-Myc ubiquitin-dependent degradation were also analyzed. Following exposure to AMP, the expression levels of Fbw7α, Fbw7γ and GSK3β were reduced and p-c-Myc (Thr58) expression levels were increased. The results suggest that AMP exerts an anticancer effect, which is associated with the degradation of c-Myc, Skp2 and HDAC1 and 2. The ability of AMP to induce apoptosis independently of Fbwα and Fbw7γ suggests a possible use in drug-resistant cancer associated with Fbw7 deficiency. Understanding the exact underlying mechanism requires further investigation of the association between c-Myc and Fbw7α/γ reversal, and analysis of whether Thr58 phosphorylation of c-Myc is dependent on GSK3β.
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Affiliation(s)
- Xin-Mei Chen
- Department of Biochemistry, School of Basic Science, Guangzhou Medical University, Guangzhou, Guangdong 510182, P.R. China
| | - Xian-Biao Xie
- Department of Musculoskeletal Oncology, The First Affiliated Hospital of Sun Yat‑Sen University, Guangzhou, Guangdong 510080, P.R. China
| | - Qing Zhao
- Department of Biochemistry, School of Basic Science, Guangzhou Medical University, Guangzhou, Guangdong 510182, P.R. China
| | - Fang Wang
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou 550009, P.R. China
| | - Yang Bai
- Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, Guangdong 510230, P.R. China
| | - Jun-Qiang Yin
- Department of Musculoskeletal Oncology, The First Affiliated Hospital of Sun Yat‑Sen University, Guangzhou, Guangdong 510080, P.R. China
| | - Hong Jiang
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou 550009, P.R. China
| | - Xiao-Lin Xie
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou 550009, P.R. China
| | - Qiang Jia
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou 550009, P.R. China
| | - Gang Huang
- Department of Musculoskeletal Oncology, The First Affiliated Hospital of Sun Yat‑Sen University, Guangzhou, Guangdong 510080, P.R. China
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Mishra S, Lin CL, Huang THM, Bouamar H, Sun LZ. MicroRNA-21 inhibits p57Kip2 expression in prostate cancer. Mol Cancer 2014; 13:212. [PMID: 25216674 PMCID: PMC4168249 DOI: 10.1186/1476-4598-13-212] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 09/09/2014] [Indexed: 01/07/2023] Open
Abstract
Background p57Kip2, a cyclin-dependent kinase inhibitor, is considered to be a candidate tumor suppressor gene that has been implicated in Beckwith-Wiedemann syndrome and sporadic cancers. In addition, decreased expression of p57Kip2 protein has been frequently observed in pancreatic, lung, breast, bladder, gastrointestinal tract and prostate cancers. However, p57Kip2 gene mutations are rare in these cancers suggesting that other unknown mechanisms might be at play in reducing its expression. The aim of this study was to investigate the molecular mechanism of down-regulation of p57Kip2 in prostate cancer. Findings We observed a significant negative correlation between the expression of p57Kip2 and microRNA-21 (miR-21) in prostate cancer samples and after androgen deprivation with castration in the CWR22 human prostate cancer xenograft model. We report that miR-21 targeted the coding region and decreased p57Kip2 mRNA and protein levels in prostate cancer cells. Conversely, inhibition of endogenous miR-21 by an anti-miR-21 inhibitor strongly induced p57Kip2 expression. Furthermore, we found that knockdown of p57Kip2 reversed the effects of the anti-miR-21 inhibitor on cell migration and anchorage-independent cell growth. Conclusions Our results indicate that miR-21 is able to downregulate p57Kip2 expression by targeting the coding region of the gene and is also able to attenuate p57Kip2 mediated functional responses. This is the first report demonstrating that p57Kip2 is a novel target of miR-21 in prostate cancer and revealing a novel oncogenic function of this microRNA. Electronic supplementary material The online version of this article (doi:10.1186/1476-4598-13-212) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | | | - Lu-Zhe Sun
- Department of Cellular and Structural Biology, University of Texas Health Science Center, 7703 Floyd Curl Drive, Mail Code 7762, San Antonio, TX 78229-3900, USA.
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105
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MDM2 mediates nonproteolytic polyubiquitylation of the DEAD-Box RNA helicase DDX24. Mol Cell Biol 2014; 34:3321-40. [PMID: 24980433 DOI: 10.1128/mcb.00320-14] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
MDM2 mediates the ubiquitylation and thereby triggers the proteasomal degradation of the tumor suppressor protein p53. However, genetic evidence suggests that MDM2 contributes to multiple regulatory networks independently of p53 degradation. We have now identified the DEAD-box RNA helicase DDX24 as a nucleolar protein that interacts with MDM2. DDX24 was found to bind to the central region of MDM2, resulting in the polyubiquitylation of DDX24 both in vitro and in vivo. Unexpectedly, however, the polyubiquitylation of DDX24 did not elicit its proteasomal degradation but rather promoted its association with preribosomal ribonucleoprotein (pre-rRNP) processing complexes that are required for the early steps of pre-rRNA processing. Consistently with these findings, depletion of DDX24 in cells impaired pre-rRNA processing and resulted both in abrogation of MDM2 function and in consequent p53 stabilization. Our results thus suggest an unexpected role of MDM2 in the nonproteolytic ubiquitylation of DDX24, which may contribute to the regulation of pre-rRNA processing.
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106
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Yang Q, Huang J, Wu Q, Cai Y, Zhu L, Lu X, Chen S, Chen C, Wang Z. Acquisition of epithelial-mesenchymal transition is associated with Skp2 expression in paclitaxel-resistant breast cancer cells. Br J Cancer 2014; 110:1958-67. [PMID: 24642627 PMCID: PMC3992499 DOI: 10.1038/bjc.2014.136] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2013] [Revised: 02/16/2014] [Accepted: 02/19/2014] [Indexed: 01/23/2023] Open
Abstract
Background: Breast cancer is the most common female malignant disease, and the second leading cause of cancer-related death in the United States. Acquired resistance to chemotherapeutic drugs is a pivotal reason that leads to worse treatment outcome of breast cancer. Therefore, it is urgent to elucidate the mechanism of drug resistance in breast cancer. Methods: To investigate the underlying molecular basis of the acquired resistant cells to paclitaxel in breast cancer, we used multiple methods including real-time RT–PCR, western blotting analysis, migration and invasion assays, wound healing assay, and transfection. Results: We found that epithelial–mesenchymal transition (EMT) is involved in paclitaxel-resistant (PR) breast cancer cells. The resistant cells with EMT features exhibit increased migration and invasion activities. Mechanistically, high expression of Skp2 was found to be associated with EMT in PR cells. Notably, depletion of Skp2 in PR cells led to partial reversal of EMT phenotype. Conclusions: These findings suggest that Skp2 was critically involved in PR-mediated EMT. Skp2 could be a potential therapeutic target for breast cancer.
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Affiliation(s)
- Q Yang
- Department of Biochemistry and Molecular Biology, Bengbu Medical College, Anhui 233030, China
| | - J Huang
- Clinical Testing and Diagnose Experimental Center of Bengbu Medical College, Anhui 233000, China
| | - Q Wu
- Department of Medical Oncology, First Affiliated Hospital of Bengbu Medical College, Bengbu, Anhui 233004, China
| | - Y Cai
- Clinical Testing and Diagnose Experimental Center of Bengbu Medical College, Anhui 233000, China
| | - L Zhu
- Clinical Testing and Diagnose Experimental Center of Bengbu Medical College, Anhui 233000, China
| | - X Lu
- Clinical Testing and Diagnose Experimental Center of Bengbu Medical College, Anhui 233000, China
| | - S Chen
- Department of Biochemistry and Molecular Biology, Bengbu Medical College, Anhui 233030, China
| | - C Chen
- Department of Biochemistry and Molecular Biology, Bengbu Medical College, Anhui 233030, China
| | - Z Wang
- Cyrus Tang Hematology Center, Jiangsu Institute of Hematology, First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215123, China
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Abstract
Cell division is controlled by a highly regulated program to accurately duplicate and segregate chromosomes. An important feature of the cell cycle regulatory program is that key cell cycle proteins are present and active during specific cell cycle stages but are later removed or inhibited to maintain appropriate timing. The ubiquitin-proteasome system has emerged as an important mechanism to target cell cycle proteins for degradation at critical junctures during cell division. Two key E3 ubiquitin ligase complexes that target key cell cycle proteins are the Skp1-Cul1-F-box protein complex and the anaphase-promoting complex/cyclosome. This chapter focuses on the role of these E3 ubiquitin ligases and how ubiquitin-dependent degradation of central cell cycle regulatory proteins advances the cell cycle.
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Affiliation(s)
- Deanna M Koepp
- Department of Genetics, Cell Biology and Development, University of Minnesota, 6-160 Jackson Hall, 321 Church St SE, Minneapolis, MN, 55455, USA,
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108
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Alexander A, Keyomarsi K. Exploiting Cell Cycle Pathways in Cancer Therapy: New (and Old) Targets and Potential Strategies. NUCLEAR SIGNALING PATHWAYS AND TARGETING TRANSCRIPTION IN CANCER 2014. [DOI: 10.1007/978-1-4614-8039-6_14] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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109
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Yuan X, Srividhya J, De Luca T, Lee JHE, Pomerening JR. Uncovering the role of APC-Cdh1 in generating the dynamics of S-phase onset. Mol Biol Cell 2013; 25:441-56. [PMID: 24356446 PMCID: PMC3923637 DOI: 10.1091/mbc.e13-08-0480] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Premature S-phase entry due to Cdh1 ablation results from premature loss of the CDK inhibitor p27 and a reduced requirement for cyclin E1. This prolonged S phase coincides with slowed replication fork elongation and fewer replication terminations, both of which could contribute to genome instability. Cdh1, a coactivator of the anaphase-promoting complex (APC), is a potential tumor suppressor. Cdh1 ablation promotes precocious S-phase entry, but it was unclear how this affects DNA replication dynamics while contributing to genomic instability and tumorigenesis. We find that Cdh1 depletion causes early S-phase onset in conjunction with increase in Rb/E2F1-mediated cyclin E1 expression, but reduced levels of cyclin E1 protein promote this transition. We hypothesize that this is due to a weakened cyclin-dependent kinase inhibitor (CKI)–cyclin-dependent kinase 2 positive-feedback loop, normally generated by APC-Cdh1–mediated proteolysis of Skp2. Indeed, Cdh1 depletion increases Skp2 abundance while diminishing levels of the CKI p27. This lowers the level of cyclin E1 needed for S-phase entry and delays cyclin E1 proteolysis during S-phase progression while corresponding to slowed replication fork movement and reduced frequency of termination events. In summary, using both experimental and computational approaches, we show that APC-Cdh1 establishes a stimulus–response relationship that promotes S phase by ensuring that proper levels of p27 accumulate during G1 phase, and defects in its activation accelerate the timing of S-phase onset while prolonging its progression.
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Affiliation(s)
- Xi Yuan
- Department of Biology, Indiana University, Bloomington, IN 47405-7003 Biocomplexity Institute, Department of Physics, Indiana University, Bloomington, IN 47405-7003 Department of Environmental Health, School of Public Health, Indiana University, Bloomington, IN 47408-2671 Department of Statistics, Indiana University, Bloomington, IN 47408-3825
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110
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Zhang SN, Pei DS, Zheng JN. The COP9 signalosome subunit 6 (CSN6): a potential oncogene. Cell Div 2013; 8:14. [PMID: 24286178 PMCID: PMC4175502 DOI: 10.1186/1747-1028-8-14] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 11/18/2013] [Indexed: 01/11/2023] Open
Abstract
CSN6 is one subunit of the constitutive photomorphogenesis 9 (COP9) signalosome (CSN), which is an evolutionarily conserved multiprotein complex found in plants and animals and originally described as a repressor of light-dependent growth and transcription in Arabidopsis. CSN is homologous to the 19S lid subcomplex of the 26S proteasome, thus it has been postulated to be a regulator of the ubiquitin-proteasome pathway. In mammalian cells, it consists of eight subunits (CSN1-CSN8). Among the CSN subunits, CSN5 and CSN6 are the only two that each contains an MPN (Mpr1p and Pad1p N-terminal) domain. The deneddylating activity of an MPN domain toward cullin-RING ubiquitin ligases (CRL) may coordinate CRL-mediated ubiquitination activity. More and more studies about CSN6 are emerging, and its overexpression is found in many types of cancers. Evidence has shown that CSN6 is a molecule platform between protein degradation and signal transduction. Here, we provide a summary of human CSN6, especially its roles in cancer, hoping that it can lay the groundwork for cancer prevention or therapy.
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Affiliation(s)
| | - Dong-Sheng Pei
- Jiangsu Key Laboratory of Biological Cancer Therapy, Xuzhou Medical College, 84 West Huai-hai Road, Xuzhou, Jiangsu, P,R, China.
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111
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Kotoshiba S, Gopinathan L, Pfeiffenberger E, Rahim A, Vardy LA, Nakayama K, Nakayama KI, Kaldis P. p27 is regulated independently of Skp2 in the absence of Cdk2. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:436-45. [PMID: 24269842 DOI: 10.1016/j.bbamcr.2013.11.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Revised: 10/25/2013] [Accepted: 11/13/2013] [Indexed: 10/26/2022]
Abstract
Cyclin-dependent kinase 2 (Cdk2) is dispensable for mitotic cell cycle progression and Cdk2 knockout mice are viable due to the compensatory functions of other Cdks. In order to assess the role of Cdk2 under limiting conditions, we used Skp2 knockout mice that exhibit increased levels of Cdk inhibitor, p27(Kip1), which is able to inhibit Cdk2 and Cdk1. Knockdown of Cdk2 abrogated proliferation of Skp2(-/-) mouse embryonic fibroblasts, encouraging us to generate Cdk2(-/-)Skp2(-/-) double knockout mice. Cdk2(-/-)Skp2(-/-) double knockout mice are viable and display similar phenotypes as Cdk2(-/-) and Skp2(-/-) mice. Unexpectedly, fibroblasts generated from Cdk2(-/-)Skp2(-/-) double knockout mice proliferated at normal rates. The increased stability of p27 observed in Skp2(-/-) MEFs was not observed in Cdk2(-/-)Skp2(-/-) double knockout fibroblasts indicating that in the absence of Cdk2, p27 is regulated by Skp2-independent mechanisms. Ablation of other ubiquitin ligases for p27 such as KPC1, DDB1, and Pirh2 did not restore stability of p27 in Cdk2(-/-)Skp2(-/-) MEFs. Our findings point towards novel and alternate pathways for p27 regulation.
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Affiliation(s)
- Shuhei Kotoshiba
- Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore; Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute-Frederick, Bldg. 560, 1050 Boyles Street, Frederick, MD 21702-1201, USA
| | - Lakshmi Gopinathan
- Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore
| | - Elisabeth Pfeiffenberger
- Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore
| | - Anisa Rahim
- Institute of Medical Biology (IMB), A*STAR (Agency for Science, Technology and Research), 8A Biomedical Grove, Immunos, Singapore 138648, Republic of Singapore
| | - Leah A Vardy
- Institute of Medical Biology (IMB), A*STAR (Agency for Science, Technology and Research), 8A Biomedical Grove, Immunos, Singapore 138648, Republic of Singapore; School of Biological Sciences, Nanyang Technological University, Singapore 639798, Republic of Singapore
| | - Keiko Nakayama
- Tohoku University, Department of Developmental Genetics, Center for Translational and Advanced Animal Research, Graduate School of Medicine, Aoba-ku, Sendai, Japan
| | - Keiichi I Nakayama
- Kyushu University, Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan; CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Philipp Kaldis
- Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore; National University of Singapore (NUS), Department of Biochemistry, Singapore 117597, Republic of Singapore; Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute-Frederick, Bldg. 560, 1050 Boyles Street, Frederick, MD 21702-1201, USA.
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112
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Chen XM, Bai Y, Zhong YJ, Xie XL, Long HW, Yang YY, Wu SG, Jia Q, Wang XH. Wogonin has multiple anti-cancer effects by regulating c-Myc/SKP2/Fbw7α and HDAC1/HDAC2 pathways and inducing apoptosis in human lung adenocarcinoma cell line A549. PLoS One 2013; 8:e79201. [PMID: 24265759 PMCID: PMC3827163 DOI: 10.1371/journal.pone.0079201] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2013] [Accepted: 09/20/2013] [Indexed: 12/05/2022] Open
Abstract
Wogonin is a plant monoflavonoid which has been reported to inhibit cell growth and/or induce apoptosis in various tumors. The present study examined the apoptosis-inducing activity and underlying mechanism of action of wogonin in A549 cells. The results showed that wogonin was a potent inhibitor of the viability of A549 cells. Apoptotic protein changes detected after exposure to wogonin included decreased XIAP and Mcl-1 expression, increased cleaved-PARP expression and increased release of AIF and cytotchrome C. Western blot analysis showed that the activity of c-Myc/Skp2 and HDAC1/HDAC2 pathways, which play important roles in tumor progress, was decreased. Quantitative PCR identified increased levels of c-Myc mRNA and decreased levels of its protein. Protein levels of Fbw7α, GSK3β and Thr58-Myc, which are involved in c-Myc ubiquitin-dependent degradation, were also analyzed. After exposure to wogonin, Fbw7α and GSK3β expression decreased and Thr58-Myc expression increased. However, MG132 was unable to prevent c-Myc degradation. The present results suggest that wogonin has multiple anti-cancer effects associated with degradation of c-Myc, SKP2, HDAC1 and HDAC2. Its ability to induce apoptosis independently of Fbw7α suggests a possible use in drug-resistance cancer related to Fbw7 deficiency. Further studies are needed to determine which pathways are related to c-Myc and Fbw7α reversal and whether Thr58 phosphorylation of c-Myc is dependent on GSK3β.
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Affiliation(s)
- Xin-mei Chen
- Guangzhou Medical University, Guangzhou, Guangdong, PR China
| | - Yang Bai
- Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, Guangdong, PR China
| | - Yu-jian Zhong
- Guangzhou Medical University, Guangzhou, Guangdong, PR China
| | - Xiao-lin Xie
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou, PR China
| | - Han-wu Long
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou, PR China
| | - Yu-yin Yang
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou, PR China
| | - Shi-gen Wu
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou, PR China
| | - Qiang Jia
- Institute of Biology, Guizhou Academy of Sciences, Guiyang, Guizhou, PR China
- Fanjingshan Forest Ecosystem Research Station, Guizhou Academy of Sciences, Jiangkou, Guizhou, PR China
- * E-mail: (QJ); (XHW)
| | - Xiao-hua Wang
- Guangzhou Medical University, Guangzhou, Guangdong, PR China
- * E-mail: (QJ); (XHW)
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113
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Hamajima N, Johmura Y, Suzuki S, Nakanishi M, Saitoh S. Increased protein stability of CDKN1C causes a gain-of-function phenotype in patients with IMAGe syndrome. PLoS One 2013; 8:e75137. [PMID: 24098681 PMCID: PMC3787065 DOI: 10.1371/journal.pone.0075137] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2013] [Accepted: 08/09/2013] [Indexed: 11/18/2022] Open
Abstract
Mutations in the proliferating cell nuclear antigen (PCNA)-binding domain of the CDKN1C gene were recently identified in patients with IMAGe syndrome. However, loss of PCNA binding and suppression of CDKN1C monoubiquitination by IMAGe-associated mutations hardly explain the reduced-growth phenotype characteristic of IMAGe syndrome. We demonstrate here that IMAGe-associated mutations in the CDKN1C gene dramatically increased the protein stability. We identified a novel heterozygous mutation, c.815T>G (p.Ile272Ser), in the CDKN1C gene in three siblings manifesting clinical symptoms associated with IMAGe syndrome and their mother (unaffected carrier). PCNA binding to CDKN1C was disrupted in the case of p.Ile272Ser, and for two other IMAGe-associated mutations, p.Asp274Asn and p.Phe276Val. Intriguingly, the IMAGe-associated mutant CDKN1C proteins were fairly stable even in the presence of cycloheximide, whereas the wild-type protein was almost completely degraded via the proteasome pathway, as shown by the lack of degradation with addition of a proteasome inhibitor, MG132. These results thus suggested that the reduced-growth phenotype of IMAGe syndrome derives from CDKN1C gain-of-function due to IMAGe-associated mutations driving increased protein stability.
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Affiliation(s)
- Naoki Hamajima
- Department of Pediatrics, Nagoya City West Medical Center, Nagoya, Aichi, Japan
- * E-mail:
| | - Yoshikazu Johmura
- Department of Cell Biology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi, Japan
| | - Satoshi Suzuki
- Department of Pediatrics, Nagoya City West Medical Center, Nagoya, Aichi, Japan
| | - Makoto Nakanishi
- Department of Cell Biology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi, Japan
| | - Shinji Saitoh
- Department of Pediatrics and Neonatology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi, Japan
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Yumimoto K, Matsumoto M, Onoyama I, Imaizumi K, Nakayama KI. F-box and WD repeat domain-containing-7 (Fbxw7) protein targets endoplasmic reticulum-anchored osteogenic and chondrogenic transcriptional factors for degradation. J Biol Chem 2013; 288:28488-502. [PMID: 23955342 DOI: 10.1074/jbc.m113.465179] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Although identification of substrates for an enzyme is a key step in elucidation of its biological functions, detection of the interaction between enzymes and substrates remains challenging. We recently developed a new approach, termed differential proteomics-based identification of ubiquitylation substrates (DiPIUS), for the discovery of substrates of ubiquitin ligases. We have now applied this approach to Fbxw7, the F-box protein component of an Skp1-Cul1-F-box protein-type ubiquitin ligase and, thereby, identified two similar transcription factors, old astrocyte specifically induced substance (OASIS) and BBF2 human homolog on chromosome 7 (BBF2H7), as candidate substrates. Coimmunoprecipitation analysis confirmed that the α and γ isoforms of Fbxw7 interact with OASIS and BBF2H7 in vivo. Sustained overexpression of Fbxw7 resulted in marked down-regulation of OASIS and BBF2H7, whereas RNAi-mediated Fbxw7 depletion stabilized both proteins. Mutation of a putative Cdc4 phosphodegron in OASIS and BBF2H7 attenuated their association with Fbxw7 and resulted in their stabilization. Depletion of Fbxw7 promoted the differentiation of mouse C2C12 mesenchymal cells into osteoblasts in association with the accumulation of OASIS. Conversely, overexpression of Fbxw7 in C2C12 cells resulted in down-regulation of Col1A1 mRNA, a target of OASIS. Conditional ablation of Fbxw7 in primary mouse mesenchymal cells promoted chondrogenesis in association with up-regulation of BBF2H7, whereas overexpression of Fbxw7 inhibited chondrogenesis in ATDC5 cells. Collectively, our results suggest that OASIS and BBF2H7 are bona fide substrates of Fbxw7 and that Fbxw7 controls osteogenesis and chondrogenesis by targeting OASIS and BBF2H7, respectively, for degradation.
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Affiliation(s)
- Kanae Yumimoto
- From the Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan
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115
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Qu X, Shen L, Zheng Y, Cui Y, Feng Z, Liu F, Liu J. A signal transduction pathway from TGF-β1 to SKP2 via Akt1 and c-Myc and its correlation with progression in human melanoma. J Invest Dermatol 2013; 134:159-167. [PMID: 23792459 DOI: 10.1038/jid.2013.281] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Revised: 10/12/2012] [Accepted: 10/29/2012] [Indexed: 12/31/2022]
Abstract
Both SKP2 (S-phase kinase-associated protein 2) and transforming growth factor-β1 (TGF-β1) play important roles in cancer metastasis through different mechanisms: TGF-β1 via induction of epithelial-mesenchymal transition (EMT) and SKP2 via downregulating p27(kip1). Recent studies indicated that c-Myc and Akt1 were active players in metastasis. In this study we demonstrated a crosstalk between these pathways. Specifically, we found that TGF-β1 treatment increased SKP2 expression accompanied with increased phosphorylation of Akt1 and c-Myc protein accumulation during EMT. We demonstrated that Akt1 was required for TGF-β1-mediated SKP2 upregulation and that c-Myc transcription factor specifically bound to the promoter of SKP2 for its enhanced transcription. Analysis of 25 samples of normal human skin, nevi, and melanomas revealed a positive correlation between c-Myc and SKP2 accumulation. Furthermore, accumulation of SKP2 and c-Myc proteins was significantly higher in metastatic melanoma samples as compared with that in primary melanomas, which again was higher than that in normal skin or nevi. In summary, our results integrated TGF-β1 signals to SKP2 via Akt1 and c-Myc during EMT, and provided, to our knowledge, a previously unreported mechanistic molecular event for TGF-β1-induced metastasis in human melanoma.
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Affiliation(s)
- Xuan Qu
- Institute of Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, Xi'an Jiaotong University School of Life Science and Technology, Xi'an, China
| | - Liangliang Shen
- Department of Biochemistry and Molecular Biology, The State Key Laboratory of Cancer Biology, The Fourth Military Medical University, Xi'an, China
| | - Yan Zheng
- Department of Dermatology, The Second Affiliated Hospital, Xi'an Jiaotong University, Xi'an, China
| | - Yang Cui
- Institute of Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, Xi'an Jiaotong University School of Life Science and Technology, Xi'an, China
| | - Zhihui Feng
- Center for Mitochondrial Biology and Medicine, Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an, China.
| | - Feng Liu
- Department of Medicine, University of California Irvine Medical School, Irvine, California, USA; Chao Family Comprehensive Cancer Center, University of California Irvine Medical School, Irvine, California, USA.
| | - Jiankang Liu
- Institute of Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, Xi'an Jiaotong University School of Life Science and Technology, Xi'an, China
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Wu L, Grigoryan AV, Li Y, Hao B, Pagano M, Cardozo TJ. Specific small molecule inhibitors of Skp2-mediated p27 degradation. ACTA ACUST UNITED AC 2013; 19:1515-24. [PMID: 23261596 DOI: 10.1016/j.chembiol.2012.09.015] [Citation(s) in RCA: 177] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 09/17/2012] [Accepted: 09/24/2012] [Indexed: 10/27/2022]
Abstract
In the ubiquitin proteasome system, the E3 ligase SCF-Skp2 and its accessory protein, Cks1, promote proliferation largely by inducing the degradation of the CDK inhibitor p27. Overexpression of Skp2 in human cancers correlates with poor prognosis, and deregulation of SCF-Skp2-Cks1 promotes tumorigenesis in animal models. We identified small molecule inhibitors specific to SCF-Skp2 activity using in silico screens targeted to the binding interface for p27. These compounds selectively inhibited Skp2-mediated p27 degradation by reducing p27 binding through key compound-receptor contacts. In cancer cells, the compounds induced p27 accumulation in a Skp2-dependent manner and promoted cell-type-specific blocks in the G1 or G2/M phases. Designing SCF-Skp2-specific inhibitors may be a novel strategy to treat cancers dependent on the Skp2-p27 axis.
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Affiliation(s)
- Lily Wu
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA
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117
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Bisteau X, Paternot S, Colleoni B, Ecker K, Coulonval K, De Groote P, Declercq W, Hengst L, Roger PP. CDK4 T172 phosphorylation is central in a CDK7-dependent bidirectional CDK4/CDK2 interplay mediated by p21 phosphorylation at the restriction point. PLoS Genet 2013; 9:e1003546. [PMID: 23737759 PMCID: PMC3667761 DOI: 10.1371/journal.pgen.1003546] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Accepted: 04/22/2013] [Indexed: 01/24/2023] Open
Abstract
Cell cycle progression, including genome duplication, is orchestrated by cyclin-dependent kinases (CDKs). CDK activation depends on phosphorylation of their T-loop by a CDK–activating kinase (CAK). In animals, the only known CAK for CDK2 and CDK1 is cyclin H-CDK7, which is constitutively active. Therefore, the critical activation step is dephosphorylation of inhibitory sites by Cdc25 phosphatases rather than unrestricted T-loop phosphorylation. Homologous CDK4 and CDK6 bound to cyclins D are master integrators of mitogenic/oncogenic signaling cascades by initiating the inactivation of the central oncosuppressor pRb and cell cycle commitment at the restriction point. Unlike the situation in CDK1 and CDK2 cyclin complexes, and in contrast to the weak but constitutive T177 phosphorylation of CDK6, we have identified the T-loop phosphorylation at T172 as the highly regulated step determining CDK4 activity. Whether both CDK4 and CDK6 phosphorylations are catalyzed by CDK7 remains unclear. To answer this question, we took a chemical-genetics approach by using analogue-sensitive CDK7(as/as) mutant HCT116 cells, in which CDK7 can be specifically inhibited by bulky adenine analogs. Intriguingly, CDK7 inhibition prevented activating phosphorylations of CDK4/6, but for CDK4 this was at least partly dependent on its binding to p21cip1. In response to CDK7 inhibition, p21-binding to CDK4 increased concomitantly with disappearance of the most abundant phosphorylation of p21, which we localized at S130 and found to be catalyzed by both CDK4 and CDK2. The S130A mutation of p21 prevented the activating CDK4 phosphorylation, and inhibition of CDK4/6 and CDK2 impaired phosphorylations of both p21 and p21-bound CDK4. Therefore, specific CDK7 inhibition revealed the following: a crucial but partly indirect CDK7 involvement in phosphorylation/activation of CDK4 and CDK6; existence of CDK4-activating kinase(s) other than CDK7; and novel CDK7-dependent positive feedbacks mediated by p21 phosphorylation by CDK4 and CDK2 to sustain CDK4 activation, pRb inactivation, and restriction point passage. In the cell cycle, duplication of all the cellular components and subsequent cell division are governed by a family of protein kinases associated with cyclins (CDKs). Related CDK4 and CDK6 bound to cyclins D are the first CDKs to be activated in response to cell proliferation signals. They thus play a central role in the cell multiplication decision, especially in most cancer cells in which CDK4 activity is highly deregulated. We have identified the activating T172 phosphorylation instead of cyclin D expression as the highly regulated step determining CDK4 activation. This finding contrasts with the prevalent view that the only identified metazoan CDK-activating kinase, CDK7, is constitutively active. By using human cells genetically engineered for specific chemical inhibition of CDK7, we found that CDK7 activity was indeed required for CDK4 activation. However, this dependence was conditioned by CDK4 binding to the CDK inhibitory protein p21, which increased in response to CDK7 inhibition. Further investigation revealed that CDK7 inhibition affects a major phosphorylation of p21, which we found to be required for CDK4 activation and performed by CDK4 itself and CDK2. Thus, depending on CDK7 activity, CDK4 and CDK2 facilitate CDK4 activation, generating novel positive feedbacks involved in the cell cycle decision.
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Affiliation(s)
- Xavier Bisteau
- WELBIO and Institute of Interdisciplinary Research (IRIBHM), Université Libre de Bruxelles, Brussels, Belgium
| | - Sabine Paternot
- WELBIO and Institute of Interdisciplinary Research (IRIBHM), Université Libre de Bruxelles, Brussels, Belgium
| | - Bianca Colleoni
- WELBIO and Institute of Interdisciplinary Research (IRIBHM), Université Libre de Bruxelles, Brussels, Belgium
| | - Karin Ecker
- Division of Medical Biochemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria
| | - Katia Coulonval
- WELBIO and Institute of Interdisciplinary Research (IRIBHM), Université Libre de Bruxelles, Brussels, Belgium
| | - Philippe De Groote
- Department for Molecular Biomedical Research, VIB, and Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium
| | - Wim Declercq
- Department for Molecular Biomedical Research, VIB, and Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium
| | - Ludger Hengst
- Division of Medical Biochemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria
| | - Pierre P. Roger
- WELBIO and Institute of Interdisciplinary Research (IRIBHM), Université Libre de Bruxelles, Brussels, Belgium
- * E-mail:
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Hirano A, Yumimoto K, Tsunematsu R, Matsumoto M, Oyama M, Kozuka-Hata H, Nakagawa T, Lanjakornsiripan D, Nakayama KI, Fukada Y. FBXL21 regulates oscillation of the circadian clock through ubiquitination and stabilization of cryptochromes. Cell 2013; 152:1106-18. [PMID: 23452856 DOI: 10.1016/j.cell.2013.01.054] [Citation(s) in RCA: 192] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 12/03/2012] [Accepted: 01/30/2013] [Indexed: 11/26/2022]
Abstract
In the mammalian circadian clockwork, CRY1 and CRY2 repressor proteins are regulated by posttranslational modifications for temporally coordinated transcription of clock genes. Previous studies revealed that FBXL3, an F-box-type E3 ligase, ubiquitinates CRYs and mediates their degradation. Here, we found that FBXL21 also ubiquitinates CRYs but counteracts FBXL3. Fbxl21(-/-) mice exhibited normal periodicity of wheel-running rhythms with compromised organization of daily activities, while an extremely long-period phenotype of Fbxl3(-/-) mice was attenuated in Fbxl3/Fbxl21 double-knockout mice. The double knockout destabilized the behavioral rhythms progressively and sometimes elicited arrhythmicity. Surprisingly, FBXL21 stabilized CRYs and antagonized the destabilizing action by FBXL3. Predominantly cytosolic distribution of FBXL21 contrasts with nuclear localization of FBXL3. These results emphasize the physiological importance of antagonizing actions between FBXL21 and FBXL3 on CRYs, and their combined actions at different subcellular locations stabilize oscillation of the circadian clock.
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Affiliation(s)
- Arisa Hirano
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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119
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Zhu XN, Kim DH, Lin HR, Budhavarapu VN, Rosenbaum HB, Mueller PR, Yew PR. Proteolysis of Xenopus Cip-type CDK inhibitor, p16Xic2, is regulated by PCNA binding and CDK2 phosphorylation. Cell Div 2013; 8:5. [PMID: 23607668 PMCID: PMC3655096 DOI: 10.1186/1747-1028-8-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 04/17/2013] [Indexed: 11/10/2022] Open
Abstract
Background Cell division is positively regulated by cyclin-dependent kinases (CDKs) partnered with cyclins and negatively regulated by CDK inhibitors. In the frog, Xenopus laevis, three types of CDK inhibitors have been described: p27Xic1 (Xic1) which shares sequence homology with both p21Cip1 and p27Kip1 from mammals, p16Xic2 (Xic2) which shares sequence homology with p21Cip1, and p17Xic3 (Xic3) which shares sequence homology with p27Kip1. While past studies have demonstrated that during DNA polymerase switching, Xic1 is targeted for protein turnover dependent upon DNA, Proliferating Cell Nuclear Antigen (PCNA), and the ubiquitin ligase CRL4Cdt2, little is known about the processes that regulate Xic2 or Xic3. Methods We used the Xenopus interphase egg extract as a model system to examine the regulation of Xic2 by proteolysis and phosphorylation. Results Our studies indicated that following primer synthesis during the initiation of DNA replication, Xic2 is targeted for DNA- and PCNA-dependent ubiquitin-mediated proteolysis and that Cdt2 can promote Xic2 turnover. Additionally, during interphase, Xic2 is phosphorylated by CDK2 at Ser-98 and Ser-131 in a DNA-independent manner, inhibiting Xic2 turnover. In the presence of double-stranded DNA ends, Xic2 is also phosphorylated at Ser-78 and Ser-81 by a caffeine-sensitive kinase, but this phosphorylation does not alter Xic2 turnover. Conversely, in the presence or absence of DNA, Xic3 was stable in the Xenopus interphase egg extract and did not exhibit a shift indicative of phosphorylation. Conclusions During interphase, Xic2 is targeted for DNA- and PCNA-dependent proteolysis that is negatively regulated by CDK2 phosphorylation. During a response to DNA damage, Xic2 may be alternatively regulated by phosphorylation by a caffeine-sensitive kinase. Our studies suggest that the three types of Xenopus CDK inhibitors, Xic1, Xic2, and Xic3 appear to be uniquely regulated which may reflect their specialized roles during cell division or early development in the frog.
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Affiliation(s)
- Xi-Ning Zhu
- Department of Molecular Medicine, Institute of Biotechnology, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
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Satija YK, Bhardwaj A, Das S. A portrayal of E3 ubiquitin ligases and deubiquitylases in cancer. Int J Cancer 2013; 133:2759-68. [PMID: 23436247 DOI: 10.1002/ijc.28129] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 02/14/2013] [Indexed: 02/03/2023]
Abstract
E3 ubiquitin ligases and deubiquitylating enzymes (DUBs) are the key components of ubiquitin proteasome system which plays a critical role in cellular protein homeostasis. Any shortcoming in their biological roles can lead to various diseases including cancer. The dynamic interplay between ubiquitylation and deubiquitylation determines the level and activity of several proteins including p53, which is crucial for cellular stress response and tumor suppression pathways. In this review, we describe the different types of E3 ubiquitin ligases including those targeting tumor suppressor p53, SCF ligases and RING type ligases and accentuate on biological functions of few important E3 ligases in the cellular regulatory networks. Tumor suppressor p53 level is tightly regulated by multiple E3 ligases including Mdm2, COP1, Pirh2, etc. SCF ubiquitin ligase complexes are key regulators of cell cycle and signal transduction. BRCA1 and VHL RING type ligases function as tumor suppressors and play an important role in DNA repair and hypoxia response respectively. Further, we discuss the biological consequences of deregulation of the E3 ligases and the implications for cancer development. We also describe deubiquitylases which reverse the process of ubiquitylation and regulate diverse cellular pathways including metabolism, cell cycle control and chromatin remodelling. As the E3 ubiquitin ligases and DUBs work in a substrate specific manner, an improved understanding of them can lead to better therapeutics for cancer.
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Affiliation(s)
- Yatendra Kumar Satija
- Molecular Oncology Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, 110067, India
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121
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Sistrunk C, Kim SH, Wang X, Lee SH, Kim Y, Macias E, Rodriguez-Puebla ML. Skp2 deficiency inhibits chemical skin tumorigenesis independent of p27(Kip1) accumulation. THE AMERICAN JOURNAL OF PATHOLOGY 2013; 182:1854-64. [PMID: 23474082 DOI: 10.1016/j.ajpath.2013.01.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Revised: 12/18/2012] [Accepted: 01/14/2013] [Indexed: 01/11/2023]
Abstract
S-phase kinase-associated protein 2 (Skp2) functions as the receptor component of the Skp-Cullin-F-box complex and is implicated in the degradation of several cell cycle regulators, such as p21(Cip1), p27(Kip1), p57(Kip2), and cyclin E. Numerous studies in human and experimental tumors have demonstrated low p27(Kip1) levels and elevated Skp2 expression. However, a direct association between the inverse correlation of Skp2 and p27(Kip1) with tumorigenesis has not been demonstrated. Herein, we provide evidence that skin tumorigenesis is inhibited in Skp2(-/-) mice. An analysis of mouse keratinocytes indicates that increased p27(Kip1) levels in Skp2(-/-) epidermis cause reduced cell proliferation that is alleviated in the epidermis from Skp2(-/-)/p27(-/-) compound mice. In contrast, we establish that a p27(Kip1) deficiency does not overturn the reduced skin tumorigenesis experienced by Skp2(-/-) mice. In addition, Skp2(-/-) epidermis exhibits an accumulation of p53-cofactor CBP/p300 that is associated with elevated apoptosis in hair follicles and decreased skin tumorigenesis. We conclude that p27(Kip1) accumulation is responsible for the hypoplasia observed in normal tissues of Skp2(-/-) mice but does not have a preponderant function in reducing skin tumorigenesis.
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Affiliation(s)
- Christopher Sistrunk
- Department of Molecular Biomedical Sciences and the Center for Comparative Medicine and Translational Research, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA
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Bassermann F, Eichner R, Pagano M. The ubiquitin proteasome system - implications for cell cycle control and the targeted treatment of cancer. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:150-62. [PMID: 23466868 DOI: 10.1016/j.bbamcr.2013.02.028] [Citation(s) in RCA: 191] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 02/07/2013] [Accepted: 02/22/2013] [Indexed: 01/21/2023]
Abstract
Two families of E3 ubiquitin ligases are prominent in cell cycle regulation and mediate the timely and precise ubiquitin-proteasome-dependent degradation of key cell cycle proteins: the SCF (Skp1/Cul1/F-box protein) complex and the APC/C (anaphase promoting complex or cyclosome). While certain SCF ligases drive cell cycle progression throughout the cell cycle, APC/C (in complex with either of two substrate recruiting proteins: Cdc20 and Cdh1) orchestrates exit from mitosis (APC/C(Cdc20)) and establishes a stable G1 phase (APC/C(Cdh1)). Upon DNA damage or perturbation of the normal cell cycle, both ligases are involved in checkpoint activation. Mechanistic insight into these processes has significantly improved over the last ten years, largely due to a better understanding of APC/C and the functional characterization of multiple F-box proteins, the variable substrate recruiting components of SCF ligases. Here, we review the role of SCF- and APC/C-mediated ubiquitylation in the normal and perturbed cell cycle and discuss potential clinical implications of SCF and APC/C functions. This article is part of a Special Issue entitled: Ubiquitin-Proteasome System. Guest Editors: Thomas Sommer and Dieter H. Wolf.
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Affiliation(s)
- Florian Bassermann
- Department of Medicine III, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, 81675 Munich, Germany.
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Postow L, Funabiki H. An SCF complex containing Fbxl12 mediates DNA damage-induced Ku80 ubiquitylation. Cell Cycle 2013; 12:587-95. [PMID: 23324393 DOI: 10.4161/cc.23408] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The Ku heterodimer, composed of Ku70 and Ku80, is the initiating factor of the nonhomologous end joining (NHEJ) double-strand break (DSB) repair pathway. Ku is also thought to impede the homologous recombination (HR) repair pathway via inhibition of DNA end resection. Using the cell-free Xenopus laevis egg extract system, we had previously discovered that Ku80 becomes polyubiquitylated upon binding to DSBs, leading to its removal from DNA and subsequent proteasomal degradation. Here we show that the Skp1-Cul1-F box (SCF) E3 ubiquitin ligase complex is required for Ku80 ubiquitylation and removal from DNA. A screen for DSB-binding F box proteins revealed that the F box protein Fbxl12 was recruited to DNA in a DSB- and Ku-sensitive manner. Immunodepletion of Fbxl12 prevented Cul1 and Skp1 binding to DSBs and Ku80 ubiquitylation, indicating that Fbxl12 is the F box protein responsible for Ku80 substrate recognition. Unlike typical F box proteins, the F box of Fbxl12 was essential for binding to both Skp1 and its substrate Ku80. Besides Fbxl12, six other chromatin-binding F box proteins were identified in our screen of a subset of Xenopus F box proteins: β-TrCP, Fbh1, Fbxl19, Fbxo24, Fbxo28 and Kdm2b. Our study unveils a novel function for the SCF ubiquitin ligase in regulating the dynamic interaction between DNA repair machineries and DSBs.
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Affiliation(s)
- Lisa Postow
- Laboratory of Chromosome and Cell Biology, Rockefeller University, New York, NY, USA.
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Abstract
Developmentally programmed polyploidy occurs by at least four different mechanisms, two of which (endoreduplication and endomitosis) involve switching from mitotic cell cycles to endocycles by the selective loss of mitotic cyclin-dependent kinase (CDK) activity and bypassing many of the processes of mitosis. Here we review the mechanisms of endoreplication, focusing on recent results from Drosophila and mice.
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Affiliation(s)
- Norman Zielke
- Deutsches Krebsforschungszentrum (DKFZ)-Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH) Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany.
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125
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Chen L, Tweddle DA. p53, SKP2, and DKK3 as MYCN Target Genes and Their Potential Therapeutic Significance. Front Oncol 2012; 2:173. [PMID: 23226679 PMCID: PMC3508619 DOI: 10.3389/fonc.2012.00173] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 11/01/2012] [Indexed: 12/15/2022] Open
Abstract
Neuroblastoma is the most common extra-cranial solid tumor of childhood. Despite significant advances, it currently still remains one of the most difficult childhood cancers to cure, with less than 40% of patients with high-risk disease being long-term survivors. MYCN is a proto-oncogene implicated to be directly involved in neuroblastoma development. Amplification of MYCN is associated with rapid tumor progression and poor prognosis. Novel therapeutic strategies which can improve the survival rates whilst reducing the toxicity in these patients are therefore required. Here we discuss genes regulated by MYCN in neuroblastoma, with particular reference to p53, SKP2, and DKK3 and strategies that may be employed to target them.
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Affiliation(s)
- Lindi Chen
- Newcastle Cancer Centre, Northern Institute for Cancer Research, Newcastle University Newcastle, UK
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126
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Chen B, Zhao R, Su CH, Linan M, Tseng C, Phan L, Fang L, Yang HY, Yang H, Wang W, Xu X, Jiang N, Cai S, Jin F, Yeung SCJ, Lee MH. CDK inhibitor p57 (Kip2) is negatively regulated by COP9 signalosome subunit 6. Cell Cycle 2012. [PMID: 23187808 DOI: 10.4161/cc.22887] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Subunit 6 of the COP9 signalosome complex, CSN6, is known to be critical to the regulation of the MDM2-p53 axis for cell proliferation and anti-apoptosis, but its many targets remain unclear. Here we show that p57 (Kip2) is a target of CSN6, and that CSN6 is a negative regulator of p57 (Kip2) . CSN6 associates with p57 (Kip2) , and its overexpression can decrease the steady-state expression of p57 (Kip2) ; accordingly, CSN6 deficiency leads to p57 (Kip2) stabilization. Mechanistic studies show that CSN6 associates with p57 (Kip2) and Skp2, a component of the E3 ligase, which, in turn, facilitates Skp2-mediated protein ubiquitination of p57 (Kip2) . Loss of Skp2 compromised CSN6-mediated p57 (Kip2) destabilization, suggesting collaboration between Skp2 and CSN6 in degradation of p57 (Kip2) . CSN6's negative impact on p57 (Kip2) elevation translates into cell growth promotion, cell cycle deregulation and potentiated transformational activity. Significantly, univariate Kaplan-Meier analysis of tumor samples demonstrates that high CSN6 expression or low p57 expression is associated with poor overall survival. These data suggest that CSN6 is an important negative regulator of p57 (Kip2) , and that overexpression of CSN6 in many types of cancer could lead to decreased expression of p57 (Kip2) and result in promoted cancer cell growth.
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Affiliation(s)
- Bo Chen
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
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Yan L, Yun N, Xiu-Min D, Xu-Qi X. Oncogenic role of Skp2 and p27Kip1 in intraductal proliferative lesions of the breast. ACTA ACUST UNITED AC 2012; 27:161-6. [PMID: 23062638 DOI: 10.1016/s1001-9294(14)60049-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE To investigate whether the connection of p27(Kip1) to S-phase kinase-associated protein 2 (Skp2) plays an oncogenic role in intraductal proliferative lesions of the breast. METHODS Here we investigated the mechanism involved in association of Skp2’s degradation of p27(Kip1) with the breast carcinogenesis by immunohistochemical method through detection of Skp2 and p27(Kip1) protein levels in 120 paraffin-embedded tissues of intraductal proliferative lesions including usual ductal hyperplasia (UDH, n=30), atypical ductal hyperplasia (n=30), flat epithelial atypia (FEA, n=30), and ductal carcinoma in situ (DCIS, n=30). Moreover, the expression status of Skp2 and p27(Kip1) in 30 cases of the normal breast paraffin-embedded tissues were explored. RESULTS The DCIS group was with the highest Skp2 level and the lowest p27(Kip1) level, and the UDH group was with the lowest Skp2 level and the highest p27(Kip1) level.Both Skp2 and p27(Kip1) levels in the DCIS group were significantly different from those in the UDH group (all P<0.01).The levels of Skp2 and p27(Kip1) in the FEA group were significantly different from both the DCIS and UDH groups (all P<0.05).p27(Kip1) was negatively correlated with Skp2 in both the UDH group (r=-0.629, P=0.026) and DCIS group (r=-0.893, P=0.000). CONCLUSION Overexpression of Skp2 might be the mechanism underlying p27(Kip1) over degradation.
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Affiliation(s)
- Lv Yan
- Department of Acupuncture and Moxibustion, Tianjin University of Traditional Chinese Medicine, Tianjin 300193, China.
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128
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Wei S, Chu PC, Chuang HC, Hung WC, Kulp SK, Chen CS. Targeting the oncogenic E3 ligase Skp2 in prostate and breast cancer cells with a novel energy restriction-mimetic agent. PLoS One 2012; 7:e47298. [PMID: 23071779 PMCID: PMC3470570 DOI: 10.1371/journal.pone.0047298] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Accepted: 09/12/2012] [Indexed: 11/18/2022] Open
Abstract
Substantial evidence supports the oncogenic role of the E3 ubiquitin ligase S-phase kinase-associated protein 2 (Skp2) in many types of cancers through its ability to target a broad range of signaling effectors for ubiquitination. Thus, this oncogenic E3 ligase represents an important target for cancer drug discovery. In this study, we report a novel mechanism by which CG-12, a novel energy restriction-mimetic agent (ERMA), down-regulates the expression of Skp2 in prostate cancer cells. Pursuant to our previous finding that upregulation of β-transducin repeat-containing protein (β-TrCP) expression represents a cellular response in cancer cells to ERMAs, including CG-12 and 2-deoxyglucose, we demonstrated that this β-TrCP accumulation resulted from decreased Skp2 expression. Evidence indicates that Skp2 targets β-TrCP for degradation via the cyclin-dependent kinase 2-facilitated recognition of the proline-directed phosphorylation motif 412SP. This Skp2 downregulation was attributable to Sirt1-dependent suppression of COP9 signalosome (Csn)5 expression in response to CG-12, leading to increased cullin 1 neddylation in the Skp1-cullin1-F-box protein complex and consequent Skp2 destabilization. Moreover, we determined that Skp2 and β-TrCP are mutually regulated, providing a feedback mechanism that amplifies the suppressive effect of ERMAs on Skp2. Specifically, cellular accumulation of β-TrCP reduced the expression of Sp1, a β-TrCP substrate, which, in turn, reduced Skp2 gene expression. This Skp2-β-TrCP-Sp1 feedback loop represents a novel crosstalk mechanism between these two important F-box proteins in cancer cells with aberrant Skp2 expression under energy restriction, which provides a proof-of-concept that the oncogenic Csn5/Skp2 signaling axis represents a “druggable” target for this novel ERMA.
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Affiliation(s)
- Shuo Wei
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, Columbus, Ohio, United States of America
| | - Po-Chen Chu
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, Columbus, Ohio, United States of America
| | - Hsiao-Ching Chuang
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, Columbus, Ohio, United States of America
| | - Wen-Chun Hung
- National Institute of Cancer Research, National Health Research Institute, Zhunan, Miaoli County, Taiwan
| | - Samuel K. Kulp
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, Columbus, Ohio, United States of America
| | - Ching-Shih Chen
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, Columbus, Ohio, United States of America
- Institute of Basic Medical Sciences, National Cheng-Kung University, Tainan, Taiwan
- * E-mail:
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129
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Tury A, Mairet-Coello G, DiCicco-Bloom E. The multiple roles of the cyclin-dependent kinase inhibitory protein p57(KIP2) in cerebral cortical neurogenesis. Dev Neurobiol 2012; 72:821-42. [PMID: 22076965 DOI: 10.1002/dneu.20999] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The members of the CIP/KIP family of cyclin-dependent kinase (CDK) inhibitory proteins (CKIs), including p57(KIP2), p27(KIP1), and p21(CIP1), block the progression of the cell cycle by binding and inhibiting cyclin/CDK complexes of the G1 phase. In addition to this well-characterized function, p57(KIP2) and p27(KIP1) have been shown to participate in an increasing number of other important cellular processes including cell fate and differentiation, cell motility and migration, and cell death/survival, both in peripheral and central nervous systems. Increasing evidence over the past few years has characterized the functions of the newest CIP/KIP member p57(KIP2) in orchestrating cell proliferation, differentiation, and migration during neurogenesis. Here, we focus our discussion on the multiple roles played by p57(KIP2) during cortical development, making comparisons to p27(KIP1) as well as the INK4 family of CKIs.
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Affiliation(s)
- Anna Tury
- Department of Neuroscience and Cell Biology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey, USA
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130
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Depamphilis ML, de Renty CM, Ullah Z, Lee CY. "The Octet": Eight Protein Kinases that Control Mammalian DNA Replication. Front Physiol 2012; 3:368. [PMID: 23055977 PMCID: PMC3458233 DOI: 10.3389/fphys.2012.00368] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2012] [Accepted: 08/27/2012] [Indexed: 01/12/2023] Open
Abstract
Development of a fertilized human egg into an average sized adult requires about 29 trillion cell divisions, thereby producing enough DNA to stretch to the Sun and back 200 times (DePamphilis and Bell, 2011)! Even more amazing is the fact that throughout these mitotic cell cycles, the human genome is duplicated once and only once each time a cell divides. If a cell accidentally begins to re-replicate its nuclear DNA prior to cell division, checkpoint pathways trigger apoptosis. And yet, some cells are developmentally programmed to respond to environmental cues by switching from mitotic cell cycles to endocycles, a process in which multiple S phases occur in the absence of either mitosis or cytokinesis. Endocycles allow production of viable, differentiated, polyploid cells that no longer proliferate. What is surprising is that among the 516 (Manning et al., 2002) to 557 (BioMart web site) protein kinases encoded by the human genome, only eight regulate nuclear DNA replication directly. These are Cdk1, Cdk2, Cdk4, Cdk6, Cdk7, Cdc7, Checkpoint kinase-1 (Chk1), and Checkpoint kinase-2. Even more remarkable is the fact that only four of these enzymes (Cdk1, Cdk7, Cdc7, and Chk1) are essential for mammalian development. Here we describe how these protein kinases determine when DNA replication occurs during mitotic cell cycles, how mammalian cells switch from mitotic cell cycles to endocycles, and how cancer cells can be selectively targeted for destruction by inducing them to begin a second S phase before mitosis is complete.
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Affiliation(s)
- Melvin L Depamphilis
- Program in Genomics of Differentiation, National Institute of Child Health and Human Development, National Institutes of Health Bethesda, MD, USA
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131
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Han C, Jin L, Mei Y, Wu M. Endoplasmic reticulum stress inhibits cell cycle progression via induction of p27 in melanoma cells. Cell Signal 2012; 25:144-9. [PMID: 23010535 DOI: 10.1016/j.cellsig.2012.09.023] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2012] [Revised: 09/10/2012] [Accepted: 09/16/2012] [Indexed: 11/16/2022]
Abstract
The accumulation of unfolded proteins in the endoplasmic reticulum (ER) triggers the unfolded protein response (UPR), a stress signaling pathway. The UPR coordinates the induction of ER chaperones with decreased protein synthesis and growth arrest in G1 phase of the cell cycle. However, the molecular mechanism underlying UPR-induced G1 cell cycle arrest remains largely unknown. Here we report that activation of the UPR response by tunicamycin (TM), an ER stress inducer, leads to accumulation of p27 and G1 cell cycle arrest in melanoma cells. This accumulation of p27 is due to the inhibition on its polyubiquitination and subsequent degradation upon TM treatment. Correlated with p27 stabilization, the levels of Skp2, an E3 ligase for p27, are decreased in response to TM treatment. More importantly, knockdown of p27 greatly reduces TM-induced G1 cell cycle arrest. Taken together, these data implicate p27 as a critical mediator of ER stress-induced growth arrest.
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Affiliation(s)
- Chuanchun Han
- Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, PR China
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133
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Inhibition of S-phase kinase-associated protein 2 (Skp2) reprograms and converts diabetogenic T cells to Foxp3+ regulatory T cells. Proc Natl Acad Sci U S A 2012; 109:9493-8. [PMID: 22645357 DOI: 10.1073/pnas.1207293109] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Autoreactive pathogenic T cells (Tpaths) and regulatory T cells (Tregs) express a distinct gene profiles; however, the genes and associated genetic/signaling pathways responsible for the functional determination of Tpaths vs. Tregs remain unknown. Here we show that Skp2, an E3 ubiquitin ligase that affects cell cycle control and death, plays a critical role in the function of diabetogenic Tpaths and Tregs. Down-regulation of Skp2 in diabetogenic Tpaths converts them into Foxp3-expressing Tregs. The suppressive function of the Tpath-converted Tregs is dependent on increased production of TGF-β/IL-10, and these Tregs are able to inhibit spontaneous diabetes in NOD mice. Like naturally arising Foxp3(+) nTregs, the converted Tregs are anergic cells with decreased proliferation and activation-induced cell death. Skp2 down-regulation leads to Tpath-Treg conversion due at least in part to up-regulation of several genes involved in cell cycle control and genes in the Foxo family. Down-regulation of the cyclin-dependent kinase inhibitor p27 alone significantly attenuates the effect of Skp2 on Tpaths and reduces the suppressive function of converted Tregs; its effect is further improved with concomitant down-regulation of p21, Foxo1, and Foxo3. In comparison, Skp2 overexpression does not change Tpath function, but significantly decreases Foxp3 expression and abrogates the suppressive function of nTregs. These findings support the critical role of Skp2 in functional specification of Tpaths and Tregs, and demonstrate an important molecular mechanism mediating Skp2 function in balancing immune tolerance during autoimmune disease development.
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134
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Joaquin M, Gubern A, González-Nuñez D, Josué Ruiz E, Ferreiro I, de Nadal E, Nebreda AR, Posas F. The p57 CDKi integrates stress signals into cell-cycle progression to promote cell survival upon stress. EMBO J 2012; 31:2952-64. [PMID: 22569127 PMCID: PMC3395087 DOI: 10.1038/emboj.2012.122] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2011] [Accepted: 04/04/2012] [Indexed: 11/16/2022] Open
Abstract
The stress-activated protein kinase p38 phosphorylates p57/Kip2, resulting in enhanced CDK2 inhibition and a cell-cycle delay that helps cells to survive under stress. The p57Kip2 cyclin-dependent kinase inhibitor (CDKi) has been implicated in embryogenesis, stem-cell senescence and pathologies, but little is known of its role in cell cycle control. Here, we show that p57Kip2 is targeted by the p38 stress-activated protein kinase (SAPK). Phosphorylation of p57Kip2 at T143 by p38 enhances its association with and inhibition of Cdk2, which results in cell-cycle delay upon stress. Genetic inactivation of the SAPK or the CDKi abolishes cell-cycle delay upon osmostress and results in decreased cell viability. Oxidative stress and ionomycin also induce p38-mediated phosphorylation of p57 and cells lacking p38 or p57 display reduced viability to these stresses. Therefore, cell survival to various stresses depends on p57 phosphorylation by p38 that inhibits CDK activity. Together, these findings provide a novel molecular mechanism by which cells can delay cell cycle progression to maximize cell survival upon stress.
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Affiliation(s)
- Manel Joaquin
- Departament de Ciències Experimentals i de la Salut, Cell Signaling Research Group, Univeristat Pompeu Fabra, Barcelona, Spain.
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135
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Yumimoto K, Matsumoto M, Oyamada K, Moroishi T, Nakayama KI. Comprehensive identification of substrates for F-box proteins by differential proteomics analysis. J Proteome Res 2012; 11:3175-85. [PMID: 22524983 DOI: 10.1021/pr201216u] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Although elucidation of enzyme-substrate relations is fundamental to the advancement of biology, universal approaches to the identification of substrates for a given enzyme have not been established. It is especially difficult to identify substrates for ubiquitin ligases, given that most such substrates are immediately ubiquitylated and degraded as a result of their association with the enzyme. We here describe the development of a new approach, DiPIUS (differential proteomics-based identification of ubiquitylation substrates), to the discovery of substrates for ubiquitin ligases. We applied DiPIUS to Fbxw7α, Skp2, and Fbxl5, three of the most well-characterized F-box proteins, and identified candidate substrates including previously known targets. DiPIUS is thus a powerful tool for unbiased and comprehensive screening for substrates of ubiquitin ligases.
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Affiliation(s)
- Kanae Yumimoto
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University , 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan
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136
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Suzuki S, Fukasawa H, Misaki T, Togawa A, Ohashi N, Kitagawa K, Kotake Y, Liu N, Niida H, Nakayama K, Nakayama KI, Yamamoto T, Kitagawa M. The amelioration of renal damage in Skp2-deficient mice canceled by p27 Kip1 deficiency in Skp2-/- p27-/- mice. PLoS One 2012; 7:e36249. [PMID: 22558406 PMCID: PMC3338689 DOI: 10.1371/journal.pone.0036249] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Accepted: 03/29/2012] [Indexed: 12/02/2022] Open
Abstract
SCF-Skp2 E3 ubiquitin ligase (Skp2 hereafter) targets several cell cycle regulatory proteins for degradation via the ubiquitin-dependent pathway. However, the target-specific physiological functions of Skp2 have not been fully elucidated in kidney diseases. We previously reported an increase in Skp2 in progressive nephropathy and amelioration of unilateral ureteral obstruction (UUO) renal injury associated with renal accumulation of p27 in Skp2(-/-) mice. However, it remains unclear whether the amelioration of renal injury in Skp2(-/-) mice is solely caused by p27 accumulation, since Skp2 targets several other proteins. Using Skp2(-/-)p27(-/-) mice, we investigated whether Skp2 specifically targets p27 in the progressive nephropathy mediated by UUO. In contrast to the marked suppression of UUO renal injury in Skp2(-/-) mice, progression of tubular dilatation associated with tubular epithelial cell proliferation and tubulointerstitial fibrosis with increased expression of collagen and α-smooth muscle actin were observed in the obstructed kidneys in Skp2(-/-)p27(-/-) mice. No significant increases in other Skp2 target proteins including p57, p130, TOB1, cyclin A and cyclin D1 were noted in the UUO kidney in Skp2(-/-) mice, while p21, c-Myc, b-Myb and cyclin E were slightly increased. Contrary to the ameliorated UUO renal injure by Skp2-deficiency, the amelioration was canceled by the additional p27-deficiency in Skp2(-/-)p27(-/-) mice. These findings suggest a pathogenic role of the reduction in p27 targeted by Skp2 in the progression of nephropathy in UUO mice.
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Affiliation(s)
- Sayuri Suzuki
- Department of Molecular Biology, Hamamatsu University School of Medicine, Hamamatsu, Japan
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Cks1 promotion of S phase entry and proliferation is independent of p27Kip1 suppression. Mol Cell Biol 2012; 32:2416-27. [PMID: 22508990 DOI: 10.1128/mcb.06771-11] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cks1 is an activator of the SCF(Skp2) ubiquitin ligase complex that targets the cell cycle inhibitor p27(Kip1) for degradation. The loss of Cks1 results in p27(Kip1) accumulation and decreased proliferation and inhibits tumorigenesis. We identify here a function of Cks1 in mammalian cell cycle regulation that is independent of p27(Kip1). Specifically, Cks1(-/-); p27(Kip1-/-) mouse embryonic fibroblasts retain defects in the G(1)-S phase transition that are coupled with decreased Cdk2-associated kinase activity and defects in proliferation that are associated with Cks1 loss. Furthermore, concomitant loss of Cks1 does not rescue the tumor suppressor function of p27(Kip1) that is manifest in various organs of p27(Kip1-/-) mice. In contrast, defects in mitotic entry and premature senescence manifest in Cks1(-/-) cells are p27(Kip1) dependent. Collectively, these findings establish p27(Kip1)-independent functions of Cks1 in regulating the G(1)-S transition.
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138
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Jiang J, Pan Y, Regan KM, Wu C, Zhang X, Tindall DJ, Huang H. Androgens repress expression of the F-box protein Skp2 via p107 dependent and independent mechanisms in LNCaP prostate cancer cells. Prostate 2012; 72:225-32. [PMID: 21630295 PMCID: PMC4413901 DOI: 10.1002/pros.21430] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Accepted: 05/04/2011] [Indexed: 01/14/2023]
Abstract
BACKGROUND Androgens control homeostasis of the normal prostate and growth of prostate cancer (PCa) through the androgen receptor (AR) by regulating gene networks involving in cell proliferation, differentiation, and survival. We demonstrated previously that expression of Skp2, a key protein regulating cell entry into the S phase, is inhibited by androgens in an AR-dependent manner (Oncogene, 2004; 23(12): 2161-2176). However, the underlying mechanism of this regulation is unknown. METHODS Using the LNCaP PCa cell line as a working model, the effect of androgens on the expression of Skp2 was examined by Western and Northern blot analyses. Cell cycle was measured by fluorescence-activated cell sorting (FACS). Gene transfection was performed by electroporation to manipulate the expression levels of proteins studied. RESULTS At physiological levels androgens markedly repressed Skp2 expression but slightly induced Skp2 expression at subphysiological levels. Androgens modestly decreased the stability of the Skp2 protein. Androgenic repression of Skp2 expression was completely abolished by E1A-mediated inactivation of pocket proteins including RB, p130, and p107. Moreover, ectopic expression of p107 inhibited Skp2 expression, and silencing of p107 partially blocked androgenic repression of Skp2. CONCLUSIONS Our data indicate that androgens repress Skp2 expression via p107-dependent and -independent pathways in PCa cells. These regulatory mechanisms may be targeted for the development of new therapeutics of androgen-refractory PCa.
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Affiliation(s)
- Jingting Jiang
- Third Affiliated Hospital, Soochow University, Changzhou 213003, China
- Key Laboratory of Stem Cell of Jiangsu Province, Institute of Biotechnology, Key Laboratory of Clinical Immunology of Jiangsu Province, Soochow University, Suzhou 215007, China
| | - Yunqian Pan
- Masonic Cancer Center and Department of Laboratory Medicine and Pathology, University of Minnesota, MN 55455, USA
- Department of Pathology, Stony Brook University Medical Center, Stony Brook, NY 11794, USA
| | - Kevin M. Regan
- Departments of Urology and Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
| | - Changping Wu
- Third Affiliated Hospital, Soochow University, Changzhou 213003, China
| | - Xueguang Zhang
- Key Laboratory of Stem Cell of Jiangsu Province, Institute of Biotechnology, Key Laboratory of Clinical Immunology of Jiangsu Province, Soochow University, Suzhou 215007, China
- To whom correspondence should be addressed to: ; ; or
| | - Donald J. Tindall
- Departments of Urology and Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
- To whom correspondence should be addressed to: ; ; or
| | - Haojie Huang
- Masonic Cancer Center and Department of Laboratory Medicine and Pathology, University of Minnesota, MN 55455, USA
- Department of Pathology, Stony Brook University Medical Center, Stony Brook, NY 11794, USA
- To whom correspondence should be addressed to: ; ; or
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139
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Wang Z, Fukushima H, Inuzuka H, Wan L, Liu P, Gao D, Sarkar FH, Wei W. Skp2 is a promising therapeutic target in breast cancer. Front Oncol 2012; 1. [PMID: 22279619 PMCID: PMC3263529 DOI: 10.3389/fonc.2011.00057] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Breast cancer is the most common type of cancer among American women, and remains the second leading cause of cancer-related death for female in the United States. It has been known that several signaling pathways and various factors play critical roles in the development and progression of breast cancer, such as estrogen receptor, Notch, PTEN, human epidermal growth factor receptor 2, PI3K/Akt, BRCA1, and BRCA2. Emerging evidence has shown that the F-box protein S-phase kinase associated protein 2 (Skp2) also plays an important role in the pathogenesis of breast cancer. Therefore, in this brief review, we summarize the novel functions of Skp2 in the pathogenesis of breast cancer. Moreover, we provide further evidence regarding the state of our knowledge toward the development of novel Skp2 inhibitors especially natural "chemopreventive agents" as targeted approach for the prevention and/or treatment of breast cancer.
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Affiliation(s)
- Zhiwei Wang
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
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140
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Follis AV, Galea CA, Kriwacki RW. Intrinsic Protein Flexibility in Regulation of Cell Proliferation: Advantages for Signaling and Opportunities for Novel Therapeutics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 725:27-49. [DOI: 10.1007/978-1-4614-0659-4_3] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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141
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Wang G, Chan CH, Gao Y, Lin HK. Novel roles of Skp2 E3 ligase in cellular senescence, cancer progression, and metastasis. CHINESE JOURNAL OF CANCER 2011; 31:169-77. [PMID: 22200179 PMCID: PMC3777478 DOI: 10.5732/cjc.011.10319] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
S-phase kinase-associated protein 2 (Skp2) belongs to the F-box protein family. It is a component of the SCF E3 ubiquitin ligase complex. Skp2 has been shown to regulate cellular proliferation by targeting several cell cycle-regulated proteins for ubiquitination and degradation, including cyclin-dependent kinase inhibitor p27. Skp2 has also been demonstrated to display an oncogenic function since its overexpression has been observed in many human cancers. This review discusses the recent discoveries on the novel roles of Skp2 in regulating cellular senescence, cancer progression, and metastasis, as well as the therapeutic potential of targeting Skp2 for human cancer treatment.
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Affiliation(s)
- Guocan Wang
- Belfer Institute for Applied Cancer Science, Dana-Farber Cancer Institute, Boston, MA 02115, USA
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142
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De Veylder L, Larkin JC, Schnittger A. Molecular control and function of endoreplication in development and physiology. TRENDS IN PLANT SCIENCE 2011; 16:624-34. [PMID: 21889902 DOI: 10.1016/j.tplants.2011.07.001] [Citation(s) in RCA: 202] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 07/19/2011] [Accepted: 07/21/2011] [Indexed: 05/03/2023]
Abstract
Endoreplication, also called endoreduplication, is a cell cycle variant of multicellular eukaryotes in which mitosis is skipped and cells repeatedly replicate their DNA, resulting in cellular polyploidy. In recent years, research results have shed light on the molecular mechanism of endoreplication control, but the function of this cell-cycle variant has remained elusive. However, new evidence is at last providing insight into the biological relevance of cellular polyploidy, demonstrating that endoreplication is essential for developmental processes, such as cell fate maintenance, and is a prominent response to physiological conditions, such as pathogen attack or DNA damage. Thus, endoreplication is being revealed as an important module in plant growth that contributes to the robustness of plant life.
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143
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Sistrunk C, Macias E, Nakayama K, Kim Y, Rodriguez-Puebla ML. Skp2 is necessary for Myc-induced keratinocyte proliferation but dispensable for Myc oncogenic activity in the oral epithelium. THE AMERICAN JOURNAL OF PATHOLOGY 2011; 178:2470-7. [PMID: 21641375 DOI: 10.1016/j.ajpath.2011.02.034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Revised: 02/08/2011] [Accepted: 02/17/2011] [Indexed: 12/27/2022]
Abstract
The proto-oncogene c-Myc encodes a transcription factor that is implicated in the regulation of cellular proliferation, differentiation, and apoptosis. Myc accelerates the rate of cell proliferation, at least in part, through its ability to down-regulate the expression of the cell cycle inhibitor p27(Kip1). Moreover, p27(Kip1) protein levels are regulated by ubiquitin-mediated turnover, leading to destruction by the E3 ubiquitin ligase SCF(Skp2). Therefore, we hypothesize that a lack of Skp2 expression should lead to increased p27(Kip1) levels and further inhibition of Myc-mediated proliferation and tumorigenesis. Myc expression in epithelial tissues of transgenic mice (K5-Myc) led to increased keratinocyte proliferation and the development of spontaneous tumors within the oral cavity. We generated K5-Myc-transgenic mice in an Skp2-null background. Consistent with our hypothesis, we found that Myc-mediated keratinocyte hyperproliferation was abolished by the loss of Skp2. However, Skp2 ablation did not affect Myc-driven tumorigenesis because the incidence, latency, and degree of differentiation of oral tumors were identical between K5-Myc/Skp2(+/+) and K5-Myc/Skp2(-/-) mice. Altogether, these findings suggest that Skp2 and p27(Kip1) are critical for Myc-driven keratinocyte proliferation; however, Myc-mediated tumorigenesis in the oral epithelium is independent of the Skp2-p27(Kip1) axis.
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Affiliation(s)
- Christopher Sistrunk
- Center for Comparative Medicine and Translational Research, North Carolina State University, Raleigh, North Carolina, USA
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144
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Wang Z, Gao D, Fukushima H, Inuzuka H, Liu P, Wan L, Sarkar FH, Wei W. Skp2: a novel potential therapeutic target for prostate cancer. Biochim Biophys Acta Rev Cancer 2011; 1825:11-7. [PMID: 21963805 DOI: 10.1016/j.bbcan.2011.09.002] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Revised: 09/12/2011] [Accepted: 09/13/2011] [Indexed: 12/29/2022]
Abstract
Prostate cancer is the most frequently diagnosed tumor in men and the second most common cause of cancer-related death for males in the United States. It has been shown that multiple signaling pathways are involved in the pathogenesis of prostate cancer, such as androgen receptor (AR), Akt, Wnt, Hedgehog (Hh) and Notch. Recently, burgeoning amounts of evidence have implicated that the F-box protein Skp2 (S-phase kinase associated protein 2), a well-characterized oncoprotein, also plays a critical role in the development and progression of prostate cancer. Therefore, this review discusses the recent literature regarding the function and regulation of Skp2 in the pathogenesis of prostate cancer. Furthermore, we highlight that Skp2 may represent an attractive therapeutic target, thus warrants further development of agents to target Skp2, which could have significant therapeutic impact on prostate cancer.
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Affiliation(s)
- Zhiwei Wang
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02115, USA
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145
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Borriello A, Caldarelli I, Bencivenga D, Criscuolo M, Cucciolla V, Tramontano A, Oliva A, Perrotta S, Della Ragione F. p57(Kip2) and cancer: time for a critical appraisal. Mol Cancer Res 2011; 9:1269-84. [PMID: 21816904 DOI: 10.1158/1541-7786.mcr-11-0220] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
p57(Kip2) is a cyclin-dependent kinase inhibitor belonging to the Cip/Kip family, which also includes p21(Cip1) and p27(Kip1). So far, p57(Kip2) is the least-studied Cip/Kip protein, and for a long time its relevance has been related mainly to its unique role in embryogenesis. Moreover, genetic and molecular studies on animal models and patients with Beckwith-Wiedemann syndrome have shown that alterations in CDKN1C (the p57(Kip2) encoding gene) have functional relevance in the pathogenesis of this disease. Recently, a number of investigations have identified and characterized heretofore unexpected roles for p57(Kip2). The protein appears to be critically involved in initial steps of cell and tissue differentiation, and particularly in neuronal development and erythropoiesis. Intriguingly, p27(Kip1), the Cip/Kip member that is most homologous to p57(Kip2), is primarily involved in the process of cell cycle exit. p57(Kip2) also plays a critical role in controlling cytoskeletal organization and cell migration through its interaction with LIMK-1. Furthermore, p57(Kip2) appears to modulate genome expression. Finally, accumulating evidence indicates that p57(Kip2) protein is frequently downregulated in different types of human epithelial and nonepithelial cancers as a consequence of genetic and epigenetic events. In summary, the emerging picture is that several aspects of p57(Kip2)'s functions are only poorly clarified. This review represents an appraisal of the data available on the p57(Kip2) gene and protein structure, and its role in human physiology and pathology. We particularly focus our attention on p57(Kip2) changes in cancers and pharmacological approaches for modulating p57(Kip2) levels.
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Affiliation(s)
- Adriana Borriello
- Department of Biochemistry and Biophysics, Second University of Naples, Naples, Italy
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146
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Checkpoint kinase 1 prevents cell cycle exit linked to terminal cell differentiation. Mol Cell Biol 2011; 31:4129-43. [PMID: 21791608 DOI: 10.1128/mcb.05723-11] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Trophoblast stem (TS) cells proliferate in the presence of fibroblast growth factor 4, but in its absence, they differentiate into polyploid trophoblast giant (TG) cells that remain viable but nonproliferative. Differentiation is coincident with expression of the cyclin-dependent kinase (CDK)-specific inhibitors p21 and p57, of which p57 is essential for switching from mitotic cell cycles to endocycles. Here, we show that, in the absence of induced DNA damage, checkpoint kinase-1 (CHK1), an enzyme essential for preventing mitosis in response to DNA damage, functions as a mitogen-dependent protein kinase that prevents premature differentiation of TS cells into TG cells by suppressing expression of p21 and p57, but not p27, the CDK inhibitor that regulates mitotic cell cycles. CHK1 phosphorylates p21 and p57 proteins at specific sites, thereby targeting them for degradation by the 26S proteasome. TG cells lack CHK1, and restoring CHK1 activity in TG cells suppresses expression of p57 and restores mitosis. Thus, CHK1 is part of a "G2 restriction point" that prevents premature cell cycle exit in cells programmed for terminal differentiation, a role that CHK2 cannot play.
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147
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Lee SB, Kim JJ, Chung JS, Lee MS, Lee KH, Kim BS, Tansey WP, Do Yoo Y. Romo1 is a negative-feedback regulator of Myc. J Cell Sci 2011; 124:1911-24. [PMID: 21558421 DOI: 10.1242/jcs.079996] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Degradation of Myc protein is mediated by E3 ubiquitin ligases, including SCF(Fbw7) and SCF(Skp2), but much remains unknown about the mechanism of S-phase kinase-associated protein (Skp2)-mediated Myc degradation. In the present study, we show that upregulated Myc protein, which triggers the G1-S phase progression in response to growth-stimulatory signals, induces reactive oxygen species modulator 1 (Romo1) expression. Romo1 subsequently triggers Skp2-mediated ubiquitylation and degradation of Myc by a mechanism not previously reported in normal lung fibroblasts. We also show that reactive oxygen species (ROS) derived from steady-state Romo1 expression are necessary for cell cycle entry of quiescent cells. From this study, we suggest that the generation of ROS mediated by pre-existing Romo1 protein is required for Myc induction. Meanwhile, Romo1 expression induced by Myc during G1 phase stimulates Skp2-mediated Myc degradation in a negative-feedback mechanism.
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Affiliation(s)
- Seung Baek Lee
- Laboratory of Molecular Cell Biology, Graduate School of Medicine, Korea University College of Medicine, Korea University, Seoul 136-705, Republic of Korea
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148
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Abstract
Exit from quiescence and reentry into cell cycle is essential for HSC self-renewal and regeneration. Skp2 is the F-box unit of the SCF E3-ligase that targets the CDK inhibitors (CKIs) p21(Cip1), p27(Kip1), p57(Kip2), and p130 for degradation. These CKIs inhibit the G(1) to S-phase transition of the cell cycle, and their deletion results in increased cell proliferation and decreased stem cell self-renewal. Skp2 deletion leads to CKIs stabilization inducing cell-cycle delay or arrest, and conversely, increased Skp2 expression is often found in cancers. Here, we show that SKP2 expression is increased in HSC and progenitors in response to hematopoietic stress from myelosuppression or after transplantation. At steady state, SKP2 deletion decreased the mitotic activity of HSC and progenitors resulting in enhanced HSC quiescence, increased HSC pool size, and maintenance. However, the inability to rapidly enter cell cycle greatly impaired the short-term repopulating potential of SKP2 null HSC and their ability to regenerate after myeloablative stress. Mechanistically, deletion of SKP2 in HSC and progenitors stabilized CKIs in vivo, particularly p27(Kip1), p57(Kip2), and p130. Our results demonstrate a previously unrecognized role for SKP2 in regulating HSC and progenitor expansion and hematopoietic regeneration after stress.
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149
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The hallmarks of CDKN1C (p57, KIP2) in cancer. Biochim Biophys Acta Rev Cancer 2011; 1816:50-6. [PMID: 21447370 DOI: 10.1016/j.bbcan.2011.03.002] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Revised: 03/18/2011] [Accepted: 03/22/2011] [Indexed: 12/18/2022]
Abstract
Cyclin-dependent kinase inhibitor 1C CDKN1C (p57(KIP2)) regulates several hallmarks of cancer, including apoptosis, cell invasion and metastasis, tumor differentiation and angiogenesis. p57(KIP2) is generally not mutated in cancer, but its expression is downregulated through epigenetic changes such as DNA methylation and repressive histone marks at the promoter. This opens up possibilities for therapeutic intervention through reactivation of p57(KIP2) gene expression. Furthermore, p57(KIP2) has been tested as a prognostic factor for many types of cancer, even differentiating between early and late stage cancer. In this review, the multifunctional tumor suppressor capabilities of p57(KIP2), the mechanisms of p57(KIP2) transcriptional repression in cancer, and the therapeutic potential of reactivation of p57(KIP2) protein expression will be discussed.
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150
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Wen H, Kim N, Fuentes EJ, Mallinger A, Gonzalez-Alegre P, Glenn KA. FBG1 is a promiscuous ubiquitin ligase that sequesters APC2 and causes S-phase arrest. Cell Cycle 2011; 9:4506-17. [PMID: 21135578 DOI: 10.4161/cc.9.22.13743] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
During cell proliferation, protein degradation is strictly regulated by the cell cycle and involves two complementary ubiquitin ligase complexes, the SCF (Skp, Cullin, F-box) and APC/C (Anaphase Promoting Complex/Cyclosome) ubiquitin ligases. SCF ligases are constitutively active and generally target only proteins after they have been selected for degradation, usually by phosphorylation. In contrast, APC/C complexes are themselves activated by phosphorylation and their substrates contain a targeting signal known as degron, a consensus amino acid sequence such as a D-Box. SCF complexes degrade proteins during the G1 phase. However, as DNA synthesis begins, the SCF complexes are degraded and APC/C complexes are activated. APC-2, a protein crucial to cell division, initiates anaphase by triggering the degradation of multiple proteins. This study explores an unexpected interaction between APC-2 and SCFFBG1. We found that FBG1 is a promiscuous ubiquitin ligase with many partners. Immunoprecipitation experiments demonstrate that FBG1 and APC2 interact directly. Mutagenesis-based experiments show that this interaction requires a D-Box found within the FBG1 F-box domain. Unexpectedly, we demonstrate that co-expression with FBG1 increases total APC2 levels. However, free APC2 is decreased, inhibiting cell proliferation. Finally, FACS analysis of cell populations expressing different forms of FBG1 demonstrate that this ubiquitin ligase induces S-phase arrest, illustrating the functional consequences of the interaction described. In summary, we have discovered a novel APC2 inhibitory activity of FBG1 independent from its function as ubiquitin ligase, providing the basis for future studies of FBG1 in aging and cancer.
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Affiliation(s)
- Hsiang Wen
- Department of Internal Medicine, Roy and Lucille A. Carver College of Medicine, Iowa City, USA
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