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Johnston S, Syed B, Parks R, Ellis I, Green A, Keyomarsi K, Hunt K, Leung C. CYTOPLASMIC CYCLIN E: AN EXQUISITE MARKER OF TUMOR BIOLOGY IN OLDER WOMEN WITH PRIMARY BREAST CANCER. J Geriatr Oncol 2019. [DOI: 10.1016/s1879-4068(19)31151-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Kim JA, Dustin D, Gu G, Corona-Rodriguez A, Edwards D, Coarfa C, Keyomarsi K, Fuqua SA. Abstract PD7-11: Therapeutic strategy for ESR1 mutation driven-endocrine resistance in ER-positive breast cancers. Cancer Res 2019. [DOI: 10.1158/1538-7445.sabcs18-pd7-11] [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
Abstract
Background: Endocrine therapy is used in estrogen receptor (ER)-positive breast cancers, however, 25% of these patients are at risk of distant relapse and the development of acquired endocrine resistance. Recently mutations in the ER gene (ESR1) have been validated to be acquired during the development of endocrine resistance. The most frequent ESR1 mutation, Y537S, promotes ligand-independent ER activity and emerges subclonally during aromatase inhibitor treatment. In this study, we examined the effects of the Y537S ESR1 mutation on cell cycle signaling and therapeutic response to a novel checkpoint inhibitor.
Material and Methods: MCF-7 cells expressing the Y537S ESR1 mutation were generated by CRISPR-Cas9 knock-in techniques. Cells were incubated in steroid deprived conditions. Cell cycle analysis and apoptosis were examined by flow cytometry annnexin-V assays. Proliferation was analyzed by BrdU incorporation. Cell cycle checkpoint kinases were examined by western blot analysis. Cell growth was analyzed using soft agar and MTT assays. Replication stress was identified by RPA32 and gamma-H2AX foci formation assay. For in vivo studies, MCF-7 ESR1 Y537S mutant cells were injected into female athymic nude mice with 17β-estradiol (E2) supplemented water. When tumors reached 350 mm3, tamoxifen (20 mg/kg; s.c.; three times a week), fulvestrant (200 mg/kg; s.c; once a week) and/or PF477736 Chk1 inhibitor (7.5 mg/kg; i.p.; twice a day and twice a week) was treated without E2.
Results: ESR1 Y537S mutant cells accumulated approximately 5 fold in S phase and 1.7 fold in G2/M phase compared to control cells in estrogen-deprived (ED) conditions. BrdU incorporation also increased about 2.5-fold, however, apoptosis was decreased about 60 % compared with wild-type ER parental cells. ESR1 Y537S mutant cells induced significant replication stress, showing increased RPA32 foci together with increased gamma H2AX foci, a marker of DNA double-stranded breaks. ChIP-seq analysis revealed binding sites on ATR and CHEK1 genomic locations. ATR/Chk1-mediated checkpoint signaling was activated in ESR1 Y537S mutant cells, and was repressed with fulvestrant, tamoxifen, or ESR1 siRNA treatment. The Chk1 inhibitor, PF477736, sensitized MCF-7 expressing the ESR1 Y537S mutation to endocrine treatments such as fulvestrant, tamoxifen, and the ER degrader AZD9496 in cell proliferation assays. In MCF-7 ESR1 Y537S mutant xenograft and patient derived mouse models, tamoxifen treatment combined with the Chk1 inhibitor PF477736 repressed primary xenograft tumor doubling times (P=0.038, Wilcoxon test). Treatment of mutant tumors with PF477736 together with fulvestrant significantly inhibited the frequency of distant lung metastases by 80% (P=0.0031, t-test), suggesting that these combinations may be useful in second line treatment of metastatic breast cancer patients resistant to endocrine therapies.
Conclusion: These preclinical results suggest that ESR1 mutant tumors have a therapeutic vulnerability to combination endocrine therapy with cell cycle checkpoint kinase inhibitors. These data demonstrate that this new therapeutic approach may be useful to restore endocrine sensitivity in metastatic breast cancer patients with ESR1 mutation driven-endocrine resistance.
Citation Format: Kim J-A, Dustin D, Gu G, Corona-Rodriguez A, Edwards D, Coarfa C, Keyomarsi K, Fuqua SA. Therapeutic strategy for ESR1 mutation driven-endocrine resistance in ER-positive breast cancers [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD7-11.
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Keyomarsi K, Vijayaraghavan S, Karakas C, Doostan I, Chen X, Bui T, Hunt KK, Tripahty D. Abstract P5-04-03: Palbociclib synergizes with autophagy inhibitors to induce senescence in breast cancer. Cancer Res 2017. [DOI: 10.1158/1538-7445.sabcs16-p5-04-03] [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
Abstract
This abstract was withdrawn by the authors.
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Alexander A, Karakas C, Gong Y, Alvarez R, Ueno NT, Keyomarsi K. Abstract P6-12-09: Targeting deregulated cyclin E in inflammatory breast cancer via sequential combination therapy. Cancer Res 2013. [DOI: 10.1158/0008-5472.sabcs13-p6-12-09] [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
Abstract
Inflammatory breast cancer (IBC) is a rare, highly aggressive form of breast cancer, accounting for 2-5% of all breast cancers in the US and 10% of breast cancer deaths. Unfortunately, until recently this disease has not been studied extensively at the molecular/cellular level despite the compelling unmet need to develop more effective therapies. In spite of receiving aggressive multidisciplinary therapy (anthracycline-taxane-based neoadjuvant chemotherapy, modified-radical-mastectomy and adjuvant radiation therapy), only about 40% of IBC patients survive 5 years. The goal of this project is to identify new targets that can be exploited pharmacologically either in combination with current therapies or with other novel agents.
Previous work has identified tumor-specific low molecular weight forms of cyclin E, termed LMW-E, that are preferentially found in triple negative breast cancers (TNBC) and serve as a poor prognostic biomarker. As a result of cleavage, LMW-E preferentially accumulates in the cytoplasm where it exerts its pleiotropic oncogenic functions including deregulating the cell cycle. Furthermore, we have shown that TNBC cells harboring LMW-E are sensitive to CDK inhibitors.
To establish the clinical relevance of targeting the cyclin E/CDK2 axis in IBC, a pilot study was performed to determine the incidence of LMW-E. We performed IHC on 11 post-chemotherapy surgical specimens from MDACC. All tumors expressed cyclin E, 8 of which had predominantly cytoplasmic staining, indicative of LMW-E expression. These results are now being validated in a larger cohort of samples. These promising preliminary results led us to perform in vitro experiments to determine sensitivity to CDK2 inhibitors and characterize cell cycle profiles.
Similar to non-IBC breast cancers, IBC tumors can be ER-positive, TNBC or HER2-overexpressing; however, there are only TN-IBC or HER2+ cell lines. We utilized 2 cell lines for these studies, one of which is TN-IBC, the other of which is ER-negative and HER2-overexpressing. These cell lines were treated with a panel of CDK inhibitors to evaluate their sensitivity in both short-term and long-term assays. The long-term assay we developed called the high-throughput survival assay was used to examine combinations of agents for potential synergies using isobologram analysis. We have demonstrated chemotherapy-specific synergistic cell death when cells are first treated with CDK inhibitor in IBC and non-IBC cell lines.
Using flow cytometry, we have demonstrated that CDK inhibitors induce a G2/M arrest, which is further increased by sequential treatment with chemotherapy. Furthermore, combination treatment leads to cell death, as measured by sub-G1 DNA content.
Taken together, these studies provide solid evidence that targeting CDK2 is a promising strategy in treating IBC tumors that express cyclin E. Beyond these early pre-clinical advances, however, we demonstrated clear sequence-specificity for certain pairs of drugs, implying that future clinical studies should be designed taking into account the mechanism of action of cell cycle targeting drugs.
Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-12-09.
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Valero V, Wingate H, Chada S, Liu Y, Palalon F, Mills G, Keyomarsi K, Hunt KK. MDA-7 results in downregulation of AKT concomitant with apoptosis and cell cycle arrest in breast cancer cells. Cancer Gene Ther 2011; 18:510-9. [PMID: 21546925 DOI: 10.1038/cgt.2011.20] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The melanoma differentiation-associated gene-7 (mda-7) is a known mediator of apoptosis in cancer cells but not in normal cells. We hypothesized that MDA-7 interferes with the prosurvival signaling pathways that are commonly altered in cancer cells to induce growth arrest and apoptosis. We also identified the cell signaling pathways that are antagonized by MDA-7 leading to apoptosis. Using an adenoviral expression system, mda-7 was introduced into the breast cancer cell lines SKBr3, MCF-7 and MDA-MB-468, each with a different estrogen receptor (ER) and HER-2 receptor status. Downstream targets of MDA-7 were assessed by reverse phase protein array analysis, western blot analysis and immunofluorescence confocal microscopy. Our results show that MDA-7-induced apoptosis was mediated by caspases in all cell lines tested. However, MDA-7 modulates additional pathways in SKBr3 (HER-2 positive) and MCF-7 (ER positive) cells including downregulation of AKT-GSK3β and upregulation of cyclin-dependent kinase inhibitors in the nucleus. This leads to cell cycle arrest in addition to apoptosis. In conclusion, MDA-7 abrogates tumor-promoting pathways including the activation of caspase-dependent signaling pathways ultimately leading to apoptosis. In addition, depending on the phenotype of the breast cancer cell, MDA-7 modulates cell cycle regulating pathways to mediate cell cycle arrest.
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Bedrosian I, Shaye A, Sahin A, Hao Q, Hunt K, Keyomarsi K. QS295. Cyclin E Deregulation Is an Early Event in the Development of Breast Cancer. J Surg Res 2009. [DOI: 10.1016/j.jss.2008.11.601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Akli S, Van Pelt CS, Bui TN, Keyomarsi K. CDK2 is required for LMW-cyclin E mediated murine mammary tumorigenesis. Cancer Res 2009. [DOI: 10.1158/0008-5472.sabcs-2007] [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
Abstract
Abstract #2007
Cyclin E is a regulatory protein with multiple functions that activates CDK2, controls centrosome duplication, and regulates histone gene transcription. Our previous studies have shown that the presence of Low-molecular-weight (LMW) forms of cyclin E correlates strongly with decreased survival in patients with breast cancer. Transgenic mice overexpressing LMW cyclin E had increased incidence of mammary tumors and distant metastasis when compared to full length cyclin E. The critical role of LMW cyclin E in mammary tumorigenesis may be the result of the ability of LMW cyclin E to bind and activate the cyclin-dependent kinase 2 (CDK2). To specifically test the importance of LMW cyclin E-associated CDK2 kinase activity in mammary tumorigenesis, we generated double and triple transgenic mice LMW cyclin E-T1;CDK2-/-, and LMW cyclin E-T1;p53+/-;CDK2-/-. We found that: (i) The development of the mammary glands proceeds relatively normally in these animals demonstrating that CDK2 kinase activity is largely dispensable for mammary gland development; (ii) These mice were resistant to breast cancers initiated by LMW cyclin E overexpression. Whereas LMW-cyclin E-T1 mice in CDK2+/- or CDK2+/+ background succumb to mammary tumors with mean latencies of 16 and 19.5 months respectively, their LMW cyclin E-T1; CDK2-/- littermates do not form mammary tumors up to 24 months (P=0.05 CDK2+/+ versus CDK2-/-; P=0.0252 CDK2+/- versus CDK2-/-; P=0.1457 CDK2+/+ versus CDK2+/-, Log rank test). Similarly, while MMTV-LMW cyclin E-T1/p53+/- transgenic mice in CDK2+/- or CDK2+/+ background succumb to mammary gland tumors between 7 and 13 months with 100% penetrance, their MMTV-LMW cyclin E-T1;p53+/-; CDK2-/- littermates are resistant to tumor formation (P<0.01 CDK2+/+ versus CDK2-/-; P=0.011 CDK2+/- versus CDK2-/-, P=0.5072 CDK2+/+ versus CDK2+/-, Log rank Test). In fact none of the CDK2-/- mice developed mammary tumors when crossed with cyclin E LMW transgenic mice. However, 2 out of the 12 MMTV-LMW cyclin E; p53+/-; CDK2-/- mice generated salivary gland tumors. Hence, these LMW cyclin E; p53+/-; CDK2-/- are susceptible to LMW cyclin E induced salivary tumors in the absence of CDK2. We concluded that CDK2 is critically required for LMW cyclin E induced mammary tumorigenesis and consequently, the loss of CDK2 renders CDK2-/- mice resistant to breast cancer induced by LMW cyclin E expression. In clear contrast to mammary epithelial cells, we found that in salivary gland cells LMW cyclin E continued to elicit malignant transformation even in the absence of CDK2. Our work suggests that due to the requirement of CDK2 for LMW-cyclin E mediated mammary tumorigeneis, these tumors are prime candidates for anti-CDK2 therapy.
Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2007.
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Bagheri-Yarmand R, Keyomarsi K. Overexpression of LMW cyclin E results in faster M phase progression via Cdc25C interaction leading to chromosome missegragation in breast cancer cells. Cancer Res 2009. [DOI: 10.1158/0008-5472.sabcs-5032] [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
Abstract
Abstract #5032
Cyclin E is a G (1) cyclin essential for S-phase entry and has a profound role in oncogenesis. Cyclin E is overexpressed and present in low-molecular-weight (LMW) isoforms in breast cancer cells and tumor tissues compared to normal cells and tissues. Such alteration of cyclin E is linked to poor patient outcome. We have previously shown that ectopic expression of low molecular weight of Cyclin E (LMW-E) in breast cancer cell lines induces genomic instability by promoting aneuploidy and the formation of structural chromosomal lesion. To determine the mechanism of induction of genomic instability by ectopic expression of LMW-E, we generated the MCF-7 cells inducibly expressing either the full length (EL) or low molecular weight (LMW-E) form of cyclin E. We observed 5.5 fold higher number of cells with centrosome defects in LMW-E induced versus EL induced cells. Notably, elevated levels of LMW-E led to a significant increase in fragmented nuclei and multinucleated cells. Immunofluorescence analysis also showed a 4-5 fold increase in the number of cells containing lagging chromosomes and anaphase bridges. Karyotype analysis for gross chromosomal aberrations metaphase preparation of the uninduced and EL and LMW induced cells showed a significantly higher percentage of chromosomal defects including dicentric chromosome and chromosomal breaks associated with LMW-E overexpression. We also show that while overexpression of EL leads to accumulation of cells in S and G2/M phases of the cell cycle, the overexpression of LMW of cyclin E causes a faster M phase progression. As a consequence, LMW-cyclin E overexpressing cells are resistant to nocodazole-induced M phase arrest. Using biochemical assays, we show that EL and LMW-E interact with the phosphatase Cdc25C and when either EL or LMW are in complex with CDK2 that they phosphorylate Cdc25C. Such association of LMW-E with Cdc25C results premature inactivation of cyclin B/CDK1 upon treatment of these cells with nocodazole. Additionally, continued induction of LMW-E results in premature inactivation of PLK1 in mitotic cells and deregulated localization of PLK1 such that it is no longer associated to central spindles during anaphase and telophase. Collectively, these results suggest that overexpression of LMW-E interferes with the activation of CDK1 during mitosis. The relatively low activity of CDK1 during the passage through prophase, prometaphase, and metaphase interferes with the regulation of the spindle checkpoint and facilitates the premature transition of dividing cells from metaphase to anaphase resulting in chromosomal instability and aneuploidy. This is the first observation of how mechanistically the overexpression of a proto-oncogene can lead to genomic instability in breast cancer.
Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5032.
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Mittendorf E, McKenzie-Johnson T, Liu Y, Keyomarsi K, Hunt K. 102. J Surg Res 2007. [DOI: 10.1016/j.jss.2006.12.115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Keyomarsi K, Akli S. Targeting the cell cycle for prognosis and therapy of breast cancer. Breast Cancer Res 2005. [PMCID: PMC4233488 DOI: 10.1186/bcr1067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Koepp DM, Schaefer LK, Ye X, Keyomarsi K, Chu C, Harper JW, Elledge SJ. Phosphorylation-dependent ubiquitination of cyclin E by the SCFFbw7 ubiquitin ligase. Science 2001; 294:173-7. [PMID: 11533444 DOI: 10.1126/science.1065203] [Citation(s) in RCA: 620] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Cyclin E binds and activates the cyclin-dependent kinase Cdk2 and catalyzes the transition from the G1 phase to the S phase of the cell cycle. The amount of cyclin E protein present in the cell is tightly controlled by ubiquitin-mediated proteolysis. Here we identify the ubiquitin ligase responsible for cyclin E ubiquitination as SCFFbw7 and demonstrate that it is functionally conserved in yeast, flies, and mammals. Fbw7 associates specifically with phosphorylated cyclin E, and SCFFbw7 catalyzes cyclin E ubiquitination in vitro. Depletion of Fbw7 leads to accumulation and stabilization of cyclin E in vivo in human and Drosophila melanogaster cells. Multiple F-box proteins contribute to cyclin E stability in yeast, suggesting an overlap in SCF E3 ligase specificity that allows combinatorial control of cyclin E degradation.
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Porter DC, Zhang N, Danes C, McGahren MJ, Harwell RM, Faruki S, Keyomarsi K. Tumor-specific proteolytic processing of cyclin E generates hyperactive lower-molecular-weight forms. Mol Cell Biol 2001; 21:6254-69. [PMID: 11509668 PMCID: PMC87349 DOI: 10.1128/mcb.21.18.6254-6269.2001] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cyclin E is a G(1) cyclin essential for S-phase entry and has a profound role in oncogenesis. Previously this laboratory found that cyclin E is overexpressed and present in lower-molecular-weight (LMW) isoforms in breast cancer cells and tumor tissues compared to normal cells and tissues. Such alteration of cyclin E is linked to poor patient outcome. Here we report that the LMW forms of cyclin E are hyperactive biochemically and they can more readily induce G(1)-to-S progression in transfected normal cells than the full-length form of the protein can. Through biochemical and mutational analyses we have identified two proteolytically sensitive sites in the amino terminus of human cyclin E that are cleaved to generate the LMW isoforms found in tumor cells. Not only are the LMW forms of cyclin E functional, as they phosphorylate substrates such as histone H1 and GST-Rb, but also their activities are higher than the full-length cyclin E. These nuclear localized LMW forms of cyclin E are also biologically functional, as their overexpression in normal cells increases the ability of these cells to enter S and G(2)/M. Lastly, we show that cyclin E is selectively cleaved in vitro by the elastase class of serine proteases to generate LMW forms similar to those observed in tumor cells. These studies suggest that the defective entry into and exit from S phase by tumor cells is in part due to the proteolytic processing of cyclin E, which generates hyperactive LMW isoforms whose activities have been modified from that of the full-length protein.
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Bacus SS, Gudkov AV, Lowe M, Lyass L, Yung Y, Komarov AP, Keyomarsi K, Yarden Y, Seger R. Taxol-induced apoptosis depends on MAP kinase pathways (ERK and p38) and is independent of p53. Oncogene 2001; 20:147-55. [PMID: 11313944 DOI: 10.1038/sj.onc.1204062] [Citation(s) in RCA: 297] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2000] [Revised: 10/24/2000] [Accepted: 10/26/2000] [Indexed: 01/13/2023]
Abstract
The anti-cancer agent paclitaxel (Taxol) stabilizes microtubules leading to G2/M cell cycle arrest and apoptotic cell death. In order to analyse the molecular mechanisms of Taxol-induced cytotoxicity, we studied the involvement of mitogen-activated protein kinases (MAPK) ERK and p38 as well as the p53 pathways in Taxol-induced apoptosis. The human breast carcinoma cell line MCF7 and its derivatives, MCF7/HER-2 and MDD2, were used in the study. We found that Taxol treatment strongly activated ERK, p38 MAP kinase and p53 in MAP kinase MCF7 cells prior to apoptosis. PD98059 or SB203580, specific inhibitors of ERK and p38 kinase activities, significantly decreased apoptosis, leaving the surviving cells arrested in G2/M. These inhibitors did not significantly affect Taxol-induced alterations in the cell cycle regulatory proteins Rb, p53, p21/Waf1 and Cdk-2. In addition, inactivation of p53 did not affect cellular sensitivity to Taxol killing. However, cells with inactivated p53, unlike cells harboring wild type p53, failed to arrest in G2/M after treatment with Taxol and continued to divide or go into apoptosis. Our data show that both ERK and p38 MAP kinase cascades are essential for apoptotic response to Taxol-induced cellular killing and are independent of p53 activity. However, p53 may serve as a survival factor in breast carcinoma cells treated with Taxol by blocking cells in G2/M phase of the cell cycle.
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Chen X, Lowe M, Herliczek T, Hall MJ, Danes C, Lawrence DA, Keyomarsi K. Protection of normal proliferating cells against chemotherapy by staurosporine-mediated, selective, and reversible G(1) arrest. J Natl Cancer Inst 2000; 92:1999-2008. [PMID: 11121462 DOI: 10.1093/jnci/92.24.1999] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND A major limiting factor in human cancer chemotherapy is toxicity in normal tissues. Our goal was to determine whether normal proliferating cells could be protected from chemotherapeutic agents by taking advantage of the differential drug sensitivity of cell cycle G(1) checkpoint in normal and cancer cells. METHODS Normal mammary epithelial cells and mammary cancer cells were initially treated with staurosporine at a cytostatic (i.e., nonlethal) concentration, which preferentially arrests normal cells in the G(0)/G(1) phase of the cell cycle without affecting the proliferation of tumor cells. After the selective arrest of normal cells in G(0)/G(1), both normal and tumor cells were treated with doxorubicin or camptothecin, two cytotoxic (i.e., lethal) chemotherapeutic agents. Cells were then allowed to recover in drug-free medium for 12 days. RESULTS After pretreatment of both normal and tumor cells with staurosporine followed by treatment with doxorubicin or camptothecin, tumor cells were selectively killed by chemotherapeutic agents, whereas normal cells resumed proliferation after the drugs were removed. Pretreatment with staurosporine also protected normal circulating lymphocytes that had been induced to proliferate in vitro with phytohemagglutinin from chemotherapeutic agents. Staurosporine-induced arrest of normal cells in G(0)/G(1) phase was reversible, and arrested cells tolerated doses of camptothecin that were more than 100-fold higher than necessary to eradicate all tumor cells in culture. Staurosporine-mediated G(0)/G(1) arrest targets the retinoblastoma protein (pRb) pathway and was accompanied by a rapid decrease in cyclin-dependent kinase (CDK) 4 protein levels, increased binding of CDK inhibitors p21 and p27 to CDK2, and inhibition of CDK2 activity in normal cells. CONCLUSIONS Breast cancer cells with defective checkpoints regulated by the pRb pathway can be targeted specifically with chemotherapeutic agents, following staurosporine-mediated, selective and reversible G(0)/G(1) arrest in normal cells.
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Porter DC, Keyomarsi K. Novel splice variants of cyclin E with altered substrate specificity. Nucleic Acids Res 2000; 28:E101. [PMID: 11095697 PMCID: PMC115185 DOI: 10.1093/nar/28.23.e101] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2000] [Revised: 09/20/2000] [Accepted: 10/01/2000] [Indexed: 11/14/2022] Open
Abstract
Cyclin E, a G(1) cyclin, is overexpressed and present in low molecular weight (LMW) isoforms in breast cancer cells and tumor tissues. In this study we have examined the possibility that the shortened mRNA splice variants could give rise to tumor-specific cyclin E LMW proteins. We used the Splice Capture method to identify, enumerate and isolate known spliced mRNAs and to look for previously undetected mRNA forms of cyclin E that might be translated into the LMW proteins. We show that a new splice variant of cyclin E found in tumor cells isolated by the Splice Capture strategy, named Delta48, activates CDK2 more robustly than full-length cyclin E when assayed from transiently transfected cells with the natural substrate GST-Rb. We also found the Splice Capture method to be superior to the conventional RNase protection assay in analyzing the cyclin E mRNA present in normal and tumor cells. Splice Capture enumerated the relative abundance of known forms of cyclin E mRNA and easily discovered new splice variants in both normal and tumor cells. We conclude that the abundance of cyclin E splice variants in cells may represent a novel form of regulation of cyclin E, and if translated they show altered substrate specificity compared to the full length form of cyclin E.
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Chen X, Danes C, Lowe M, Herliczek TW, Keyomarsi K. Activation of the estrogen-signaling pathway by p21(WAF1/CIP1) in estrogen receptor-negative breast cancer cells. J Natl Cancer Inst 2000; 92:1403-13. [PMID: 10974076 DOI: 10.1093/jnci/92.17.1403] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND Estrogen stimulates the proliferation of cells in normal mammary glands and most estrogen receptor (ER)-positive mammary carcinomas by binding to the ER and promoting the transcription of ER-responsive genes. In cells with functional ERs, estrogen mediates the transition of cells from the G(1) to S phase of the cell cycle. Several cell cycle regulatory proteins have been implicated in the ER-signaling pathway involved in estrogen-mediated growth stimulation and antiestrogen-mediated growth arrest. We sought to determine whether p21, a cyclin-dependent kinase inhibitor, is a component of this pathway and, if so, whether it can mediate estrogen's action in ER-negative breast cancer cells. METHODS We overexpressed p21 with a tetracycline-inducible system in ER-negative, p21-negative breast cancer cells. Activity of the ER-signaling pathway was monitored in transient transfection assays by using constructs in which the ER promoter or the estrogen-response element (ERE) controls Luciferase expression. The growth-modulating effects of estradiol and antiestrogens on p21-overexpressing clones were assessed. All P: values are from two-sided tests. RESULTS A strong positive association was found between the expression of p21 and ER in nine breast cancer cell lines and in tumor samples from 60 patients with breast cancer (P:<. 001). Overexpression of p21 in a p21-negative, ER-negative cell line induced both the ER and ERE promoters in an estrogen-responsive manner. Last, stable p21 clones that also lack the expression of wild-type ER were responsive to the growth-inhibitory effects of ICI 182,780, a potent antiestrogen, and the growth-stimulatory effects of 17beta-estradiol. CONCLUSION The ability of p21 to mediate the activation of the estrogen-signaling pathway in ER-negative tumor cells suggests that p21 plays a novel role in this pathway, a finding that also has important clinical implications.
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Fasco MJ, Keyomarsi K, Arcaro KF, Gierthy JF. Expression of an estrogen receptor alpha variant protein in cell lines and tumors. Mol Cell Endocrinol 2000; 166:156-69. [PMID: 11203301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
Human estrogen receptor alpha (ER) mRNA is a mixture of wild type and alternatively spliced variants. Many studies have examined the potential of ER mRNA profiles to serve as diagnostic/prognostic cancer biomarkers, but only a few have attempted to correlate ER mRNA profiles with protein expression. Representative ER mRNA pools were reproduced from the cDNAs of MCF-7 cells, a human breast tumor and human uterus and translated in a protease-free environment by reticulocyte lysates to determine relative translation efficiencies between the various ER mRNA transcripts and to facilitate identification of translated proteins. Cell line and tumor extracts were then examined for expression of the ER variant proteins identified in reticulocyte lysate translations. Each of the ER mRNA pools were translated by reticulocyte lysates into two ER proteins with molecular weights of approximately 60 and 52 kD. Western immunoblotting with various C- and N-terminal-directed, anti-ER antibodies and comparison with expressed ER protein standards established that the 52 kD protein (ERDelta7P) was translated from the predominant splice variant mRNA in each pool, which is missing exon 7. The 60 kD protein contained wild type ER sequence minus 61 C-terminal amino acids lost due to an intentional run off truncation. ERDelta7P expression was subsequently demonstrated in MCF-7 cells by Western immunoblotting with the site-directed antibodies. A protein corresponding to ERDelta7P was also detected in other ER positive breast tumor cell lines, and extracts of ER positive breast and uterine tumors. This widespread expression of ERDelta7P in vivo suggests that it may have some biological function. ERDelta7P may also affect immunohistochemical evaluation of ER positivity in tumors depending upon the level of its expression and the antibody used.
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MESH Headings
- Alternative Splicing
- Base Sequence
- Breast Neoplasms/genetics
- Breast Neoplasms/metabolism
- DNA Primers/genetics
- Estrogen Receptor alpha
- Female
- Gene Expression
- Genetic Variation
- Humans
- In Vitro Techniques
- Neoplasms, Hormone-Dependent/genetics
- Neoplasms, Hormone-Dependent/metabolism
- Protein Biosynthesis
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Neoplasm/genetics
- RNA, Neoplasm/metabolism
- Receptors, Estrogen/chemistry
- Receptors, Estrogen/genetics
- Receptors, Estrogen/metabolism
- Reticulocytes/metabolism
- Tumor Cells, Cultured
- Uterine Neoplasms/genetics
- Uterine Neoplasms/metabolism
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18
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Robertson KD, Keyomarsi K, Gonzales FA, Velicescu M, Jones PA. Differential mRNA expression of the human DNA methyltransferases (DNMTs) 1, 3a and 3b during the G(0)/G(1) to S phase transition in normal and tumor cells. Nucleic Acids Res 2000; 28:2108-13. [PMID: 10773079 PMCID: PMC105379 DOI: 10.1093/nar/28.10.2108] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2000] [Revised: 03/24/2000] [Accepted: 03/24/2000] [Indexed: 01/12/2023] Open
Abstract
DNA methylation is essential for mammalian development, X-chromosome inactivation, and imprinting yet aberrant methylation patterns are one of the most common features of transformed cells. One of the proposed causes for these defects in the methylation machinery is overexpression of one or more of the three known catalytically active DNA methyltransferases (DNMTs) 1, 3a and 3b, yet there are clearly examples in which overexpression is minimal or non-existent but global methylation anomalies persist. An alternative mechanism which could give rise to global methylation errors is the improper expression of one or more of the DNMTs during the cell cycle. To begin to study the latter possibility we examined the expression of the mRNAs for DNMT1, 3a and 3b during the cell cycle of normal and transformed cells. We found that DNMT1 and 3b levels were significantly downregulated in G(0)/G(1)while DNMT3a mRNA levels were less sensitive to cell cycle alterations and were maintained at a slightly higher level in tumor lines compared to normal cell strains. Enzymatic activity assays revealed a similar decrease in the overall methylation capacity of the cells during G(0)/G(1)arrest and again revealed that a tumor cell line maintained a higher methylation capacity during arrest than a normal cell strain. These results reveal a new level of control exerted over the cellular DNA methylation machinery, the loss of which provides an alternative mechanism for the genesis of the aberrant methylation patterns observed in tumor cells.
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19
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Fasco MJ, Keyomarsi K, Arcaro KF, Gierthy JF. Expression of an estrogen receptor alpha variant protein in cell lines and tumors. Mol Cell Endocrinol 2000; 162:167-80. [PMID: 10854710 DOI: 10.1016/s0303-7207(00)00194-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Human estrogen receptor alpha (ER) mRNA is a mixture of wild type and alternatively spliced variants. Many studies have examined the potential of ER mRNA profiles to serve as diagnostic/prognostic cancer biomarkers, but only a few have attempted to correlate ER mRNA profiles with protein expression. Representative ER mRNA pools were reproduced from the cDNAs of MCF-7 cells, a human breast tumor and human uterus and translated in a protease-free environment by reticulocyte lysates to determine relative translation efficiencies between the various ER mRNA transcripts and to facilitate identification of translated proteins. Cell line and tumor extracts were then examined for expression of the ER variant proteins identified in reticulocyte lysate translations. Each of the ER mRNA pools were translated by reticulocyte lysates into two ER proteins with molecular weights of approximately 60 and 52 kD. Western immunoblotting with various C- and N-terminal-directed, anti-ER antibodies and comparison with expressed ER protein standards established that the 52 kD protein (ERDelta7P) was translated from the predominant splice variant mRNA in each pool, which is missing exon 7. The 60 kD protein contained wild type ER sequence minus 61 C-terminal amino acids lost due to an intentional run off truncation. ERDelta7P expression was subsequently demonstrated in MCF-7 cells by Western immunoblotting with the site-directed antibodies. A protein corresponding to ERDelta7P was also detected in other ER positive breast tumor cell lines, and extracts of ER positive breast and uterine tumors. This widespread expression of ERDelta7P in vivo suggests that it may have some biological function. ERDelta7P may also affect immunohistochemical evaluation of ER positivity in tumors depending upon the level of its expression and the antibody used.
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20
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Harwell RM, Porter DC, Danes C, Keyomarsi K. Processing of cyclin E differs between normal and tumor breast cells. Cancer Res 2000; 60:481-9. [PMID: 10667604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Cyclin E is a G1 cyclin essential for G1 to S-phase transition of the cell cycle with a profound role in oncogenesis. In tumor cells and tissues, cyclin E is overexpressed and present in its lower molecular weight (LMW) isoforms, and it can be used as a prognosticator for poor patient outcome. In this study, we have examined differences in the processing of cyclin E between normal mammary epithelial and breast cancer cell lines. Five NH2-terminally deleted epitope-tagged (FLAG) cyclin E vectors were constructed spanning the range of LMW forms observed in tumor cells. These constructs were transfected into normal and tumor cells and analyzed for the production of cyclin E-FLAG protein products by Western blot analysis with FLAG and cyclin E antibodies. Our results show that only tumor cells had the machinery to process these cyclin E-FLAG constructs to their LMW forms, whereas normal cells mainly expressed the full-length unprocessed form of each protein. Tumor and normal cells always process the cyclin E-FLAG protein in the same way as endogenously expressed cyclin E. This phenomenon is consistent with all of the cell lines used, regardless of transfection efficiency, time of processing posttransfection, or method of transfection. Furthermore, measurement of FLAG-associated kinase activity in the transfectants revealed that the protein products of the cyclin E-FLAG constructs are 10 times more active in tumor cells than in normal cells. These studies suggest that the LMW forms of cyclin E detected at a much higher level in tumor cells arise from posttranslational action of a protease.
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21
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Rao S, Gray-Bablin J, Herliczek TW, Keyomarsi K. The biphasic induction of p21 and p27 in breast cancer cells by modulators of cAMP is posttranscriptionally regulated and independent of the PKA pathway. Exp Cell Res 1999; 252:211-23. [PMID: 10502413 DOI: 10.1006/excr.1999.4620] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cyclic AMP (cAMP) elevation affects growth arrest and differentiation in a wide variety of breast cell lines; however, the mechanisms associated with this process are poorly understood. Previous studies linked cAMP-mediated growth arrest in breast tumor cells to increased levels of cyclin kinase inhibitor (CKI), p21. In the present study we examined the role of cAMP-dependent protein kinase (PKA) on p21 and p27 induction in the breast cancer cell line, MDA-MB-157. The induction of the CKIs by modulators of cAMP such as cholera toxin (CT) + 1-isobutyl-3-methylxanthine (IBMX) and lovastatin fluctuates with biphasic kinetics (although the kinetics of CKI induction with CT + IBMX treatment are different from that of lovastatin) and is depicted by the periodic accumulation of lower molecular weight forms of p21 and p27 which also correlate with fluctuations in CDK2 activity. Using three different approaches we show that the cAMP-mediated induction of CKIs is independent of PKA activity. In the first approach we treated MDA-MB-157 cells with a variety of cAMP modulators such as CT + IBMX, and forskolin in the presence or absence of H-89, a potent PKA inhibitor. This analysis revealed that the cAMP activators were capable of inducing p21 even though PKA activity was completely eliminated. In the second approach PKA dominant negative stable clones of MDA-MB-157 treated with CT + IBMX or forskolin also resulted in p21 induction, in the absence of any PKA activity. Last, treatment of MDA-MB-157 cells with lovastatin, another known cAMP modulator which also causes growth arrest, resulted in the induction of p21 and p27 without any increase in PKA activity. Collectively, the above results suggest that the induction of p21 by cAMP is through a novel pathway, independent of PKA activity.
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Chen X, Lowe M, Keyomarsi K. UCN-01-mediated G1 arrest in normal but not tumor breast cells is pRb-dependent and p53-independent. Oncogene 1999; 18:5691-702. [PMID: 10577141 DOI: 10.1038/sj.onc.1202948] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
In this study we investigated the growth inhibitory effects of UCN-01 in several normal and tumor-derived human breast epithelial cells. We found that while normal mammary epithelial cells w were very sensitive to UCN-01 with an IC(50) of 10nM tumor cells displayed little to no inhibition of growth with any measurable IC(50) at low UCN-01 concentrations (i.e. 0-80 nM). The UCN-01 treated normal cells arrested in G1 phase and displayed decreased expression of most key cell cycle regulators examined, resulting in inhibition of CDK2 activity due to increased binding of p27 to CDK2. Tumor cells on the other hand displayed no change in any cell cycle distribution or expression of cell cycle regulators. Examination of E6- and E7-derived strains of normal cells revealed that pRb and not p53 function is essential for UCN-01-mediated G1 arrest. Lastly, treatment of normal and tumor cells with high doses of UCN-01 (i.e. 300 nM) revealed a necessary role for a functional G1 checkpoint in mediating growth arrest. Normal cells, which have a functional G1 checkpoint, always arrest in G1 even at very high concentrations of UCN-01. Tumor cells on the other hand have a defective G1 checkpoint and only arrest in S phase with high concentrations of UCN-01. The effect of UCN-01 on the cell cycle is thus quite different from staurosporine, a structural analogue of UCN-01, which arrests normal cells in both G1 and G2, while tumor cells arrest only in the G2 phase of the cell cycle. Our results show the different sensitivity to UCN-01 of normal compared to tumor cells is dependent on a functional pRb and a regulated G1 checkpoint.
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23
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Rao S, Porter DC, Chen X, Herliczek T, Lowe M, Keyomarsi K. Lovastatin-mediated G1 arrest is through inhibition of the proteasome, independent of hydroxymethyl glutaryl-CoA reductase. Proc Natl Acad Sci U S A 1999; 96:7797-802. [PMID: 10393901 PMCID: PMC22141 DOI: 10.1073/pnas.96.14.7797] [Citation(s) in RCA: 287] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In this paper we present the finding that lovastatin arrests cells by inhibiting the proteasome, which results in the accumulation of p21 and p27, leading to G1 arrest. Lovastatin is an inhibitor of hydroxymethyl glutaryl (HMG)-CoA reductase, the rate-limiting enzyme in cholesterol synthesis. Previously, we reported that lovastatin can be used to arrest cultured cells in the G1 phase of the cell cycle, resulting in the stabilization of the cyclin-dependent kinase inhibitors (CKIs) p21 and p27. In this report we show that this stabilization of p21 and p27 may be the result of a previously unknown function of the pro-drug, beta-lactone ring form of lovastatin to inhibit the proteasome degradation of these CKIs. The lovastatin mixture used in this study is 80% open-ring form and 20% pro-drug, beta-lactone form. We show that while the lovastatin open-ring form and pravastatin (a lovastatin analogue, 100% open ring) inhibit the HMG-CoA reductase enzyme, lovastatin pro-drug inhibits the proteasome but does not inhibit HMG-CoA reductase. In addition, many of the properties of proteasome inhibition by the pro-drug are the same as the specific proteasome inhibitor lactacystin. Lastly, mevalonate (used to rescue cells from lovastatin arrest) unexpectedly abrogates the lactacystin and lovastatin pro-drug inhibition of the proteasome. Mevalonate increases the activity of the proteasome, which results in degradation of the CKIs, allowing lovastatin- and lactacystin-arrested cells to resume cell division. The lovastatin-mediated inhibition of the proteasome suggests a unique mechanism for the chemopreventative effects of this agent seen in human cancer.
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Rao S, Lowe M, Herliczek TW, Keyomarsi K. Lovastatin mediated G1 arrest in normal and tumor breast cells is through inhibition of CDK2 activity and redistribution of p21 and p27, independent of p53. Oncogene 1998; 17:2393-402. [PMID: 9811471 DOI: 10.1038/sj.onc.1202322] [Citation(s) in RCA: 144] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Previously, we reported that lovastatin, a potent inhibitor of the enzyme HMG CoA reductase also acts as an antimitogenic agent by arresting cells in the G1 phase of the cell cycle resulting in cell cycle-independent alteration of cyclin dependent kinase inhibitors (CKIs). In the present study we have investigated the nature of the CKIs (p21 and p27) alterations resulting in G1 arrest in both normal and tumor breast cell lines by lovastatin. We show that even though lovastatin treatment causes G1 arrest in a wide variety of normal and tumor breast cells irrespective of their p53 or pRb status, the p21 and p27 protein levels are not increased in all cell lines treated suggesting that the increase in p21 and p27 protein expression per se is not necessary for lovastatin mediated G1 arrest. However, the binding of p21 and p27 to CDK2 increases significantly following treatment of cells with lovastatin leading to inhibition of CDK2 activity and a subsequent arrest of cells in G1. The increased CKI binding to CDK2 is achieved by the redistribution of both p21 and p27 from CDK4 to CDK2 complexes subsequent to decreases in CDK4 and cyclin D3 expression following lovastatin treatment. Lastly, we show that lovastatin treatment of 76N-E6 breast cell line with an altered p53 pathway also results in G1 arrest and similar redistribution of CKIs from CDK4 to CDK2 as observed in other breast cell lines examined. These observations suggest that lovastatin induced G1 arrest of breast cell lines is through a p53 independent pathway and is mediated by decreased CDK2 activity through redistribution of CKIs from CDK4 to CDK2.
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Keyomarsi K, Herliczek TW. The role of cyclin E in cell proliferation, development and cancer. PROGRESS IN CELL CYCLE RESEARCH 1998; 3:171-91. [PMID: 9552414 DOI: 10.1007/978-1-4615-5371-7_14] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Normal cell proliferation is under strict regulation governed by checkpoints located at distinct points in the cell cycle. The deregulation of these checkpoint events and the molecules associated with them may transform a normal cell into a cancer cell. One of these checkpoints whose deregulation results in transformation occurs at the Restriction point, near the G1/S boundary. The periodic appearance of one of the recently identified regulatory cyclins, cyclin E, coincides precisely with the timing of the Restriction point. The deregulation in the expression and activity of cyclin E has been associated with a number of cancers and is thought to be involved in the process of oncogenesis. In this chapter, we summarise the current knowledge on the regulation and apparent function of cyclin E in normal proliferating cells and in developing tissue and alterations of these processes in cancer.
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