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Wei T, Grace M, Uberoi A, Romero-Masters JC, Lee D, Lambert PF, Munger K. The Mus musculus Papillomavirus Type 1 E7 Protein Binds to the Retinoblastoma Tumor Suppressor: Implications for Viral Pathogenesis. mBio 2021; 12:e0227721. [PMID: 34465025 PMCID: PMC8406179 DOI: 10.1128/mbio.02277-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 08/05/2021] [Indexed: 12/17/2022] Open
Abstract
The species specificity of papillomaviruses has been a significant roadblock for performing in vivo pathogenesis studies in common model organisms. The Mus musculus papillomavirus type 1 (MmuPV1) causes cutaneous papillomas that can progress to squamous cell carcinomas in laboratory mice. The papillomavirus E6 and E7 genes encode proteins that establish and maintain a cellular milieu that allows for viral genome synthesis and viral progeny synthesis in growth-arrested, terminally differentiated keratinocytes. The E6 and E7 proteins provide this activity by binding to and functionally reprogramming key cellular regulatory proteins. The MmuPV1 E7 protein lacks the canonical LXCXE motif that mediates the binding of multiple viral oncoproteins to the cellular retinoblastoma tumor suppressor protein, RB1. Our proteomic experiments, however, revealed that MmuPV1 E7 still interacts with RB1. We show that MmuPV1 E7 interacts through its C terminus with the C-terminal domain of RB1. Binding of MmuPV1 E7 to RB1 did not cause significant activation of E2F-regulated cellular genes. MmuPV1 E7 expression was shown to be essential for papilloma formation. Experimental infection of mice with MmuPV1 expressing an E7 mutant that is defective for binding to RB1 caused delayed onset, lower incidence, and smaller sizes of papillomas. Our results demonstrate that the MmuPV1 E7 gene is essential and that targeting noncanonical activities of RB1, which are independent of RB1's ability to modulate the expression of E2F-regulated genes, contribute to papillomavirus-mediated pathogenesis. IMPORTANCE Papillomavirus infections cause a variety of epithelial hyperplastic lesions, or warts. While most warts are benign, some papillomaviruses cause lesions that can progress to squamous cell carcinomas, and approximately 5% of all human cancers are caused by human papillomavirus (HPV) infections. The papillomavirus E6 and E7 proteins are thought to function to reprogram host epithelial cells to enable viral genome replication in terminally differentiated, normally growth-arrested cells. E6 and E7 lack enzymatic activities and function by interacting and functionally altering host cell regulatory proteins. Many cellular proteins that can interact with E6 and E7 have been identified, but the biological relevance of these interactions for viral pathogenesis has not been determined. This is because papillomaviruses are species specific and do not infect heterologous hosts. Here, we use a recently established mouse papillomavirus (MmuPV1) model to investigate the role of the E7 protein in viral pathogenesis. We show that MmuPV1 E7 is necessary for papilloma formation. The retinoblastoma tumor suppressor protein (RB1) is targeted by many papillomaviral E7 proteins, including cancer-associated HPVs. We show that MmuPV1 E7 can bind RB1 and that infection with a mutant MmuPV1 virus that expresses an RB1 binding-defective E7 mutant caused smaller and fewer papillomas that arise with delayed kinetics.
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Affiliation(s)
- Tao Wei
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Miranda Grace
- Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, USA
| | - Aayushi Uberoi
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - James C. Romero-Masters
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Denis Lee
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Paul F. Lambert
- McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Karl Munger
- Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, USA
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Retinoblastoma Tumor Suppressor Protein Roles in Epigenetic Regulation. Cancers (Basel) 2020; 12:cancers12102807. [PMID: 33003565 PMCID: PMC7600434 DOI: 10.3390/cancers12102807] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 09/19/2020] [Accepted: 09/27/2020] [Indexed: 12/14/2022] Open
Abstract
Simple Summary Loss of function of the retinoblastoma gene (RB1) is the rate-limiting step in the initiation of both the hereditary and sporadic forms of retinoblastoma tumor. Furthermore, loss of function of the retinoblastoma tumor suppressor protein (pRB) is frequently found in most human cancers. In retinoblastoma, tumor progression is driven by epigenetic changes following pRB loss. This review focuses on the diverse functions of pRB in epigenetic regulation. Abstract Mutations that result in the loss of function of pRB were first identified in retinoblastoma and since then have been associated with the propagation of various forms of cancer. pRB is best known for its key role as a transcriptional regulator during cell cycle exit. Beyond the ability of pRB to regulate transcription of cell cycle progression genes, pRB can remodel chromatin to exert several of its other biological roles. In this review, we discuss the diverse functions of pRB in epigenetic regulation including nucleosome mobilization, histone modifications, DNA methylation and non-coding RNAs.
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Parada CA, Osbun J, Kaur S, Yakkioui Y, Shi M, Pan C, Busald T, Karasozen Y, Gonzalez-Cuyar LF, Rostomily R, Zhang J, Ferreira M. Kinome and phosphoproteome of high-grade meningiomas reveal AKAP12 as a central regulator of aggressiveness and its possible role in progression. Sci Rep 2018; 8:2098. [PMID: 29391485 PMCID: PMC5794791 DOI: 10.1038/s41598-018-19308-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Accepted: 12/29/2017] [Indexed: 01/05/2023] Open
Abstract
There is a need to better understand meningioma oncogenesis for biomarker discovery and development of targeted therapies. Histological or genetic criteria do not accurately predict aggressiveness. Post-translational studies in meningioma progression are lacking. In the present work, we introduce a combination of mass spectrometry-based phosphoproteomics and peptide array kinomics to profile atypical and anaplastic (high-grade) meningiomas. In the discovery set of fresh-frozen tissue specimens (14), the A-kinase anchor protein 12 (AKAP12) protein was found downregulated across the grades. AKAP12 knockdown in benign meningioma cells SF4433 increases proliferation, cell cycle, migration, invasion, and confers an anaplastic profile. Differentially regulated pathways were characteristic of high-grade meningiomas. Low AKAP12 expression in a larger cohort of patients (75) characterized tumor invasiveness, recurrence, and progression, indicating its potential as a prognostic biomarker. These results demonstrate AKAP12 as a central regulator of meningioma aggressiveness with a possible role in progression.
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Affiliation(s)
- Carolina Angelica Parada
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA
| | - Joshua Osbun
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA
| | - Sumanpreet Kaur
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA
| | - Youssef Yakkioui
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA
| | - Min Shi
- Department of Pathology/University of Washington School of Medicine, Harborview Medical Center, Seattle/WA, 98104, USA
| | - Catherine Pan
- Department of Pathology/University of Washington School of Medicine, Harborview Medical Center, Seattle/WA, 98104, USA
| | - Tina Busald
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA
| | - Yigit Karasozen
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA
| | - Luis Francisco Gonzalez-Cuyar
- Department of Pathology/University of Washington School of Medicine, Harborview Medical Center, Seattle/WA, 98104, USA
| | - Robert Rostomily
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA
| | - Jing Zhang
- Department of Pathology/University of Washington School of Medicine, Harborview Medical Center, Seattle/WA, 98104, USA
| | - Manuel Ferreira
- Departments of Neurosurgery/University of Washington School of Medicine, University of Washington Medical Center, Seattle/WA, 98195, USA.
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de Oliveira GAP, Rangel LP, Costa DC, Silva JL. Misfolding, Aggregation, and Disordered Segments in c-Abl and p53 in Human Cancer. Front Oncol 2015; 5:97. [PMID: 25973395 PMCID: PMC4413674 DOI: 10.3389/fonc.2015.00097] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2015] [Accepted: 04/10/2015] [Indexed: 01/31/2023] Open
Abstract
The current understanding of the molecular mechanisms that lead to cancer is not sufficient to explain the loss or gain of function in proteins related to tumorigenic processes. Among them, more than 100 oncogenes, 20-30 tumor-suppressor genes, and hundreds of genes participating in DNA repair and replication have been found to play a role in the origins of cancer over the last 25 years. The phosphorylation of serine, threonine, or tyrosine residues is a critical step in cellular growth and development and is achieved through the tight regulation of protein kinases. Phosphorylation plays a major role in eukaryotic signaling as kinase domains are found in 2% of our genes. The deregulation of kinase control mechanisms has disastrous consequences, often leading to gains of function, cell transformation, and cancer. The c-Abl kinase protein is one of the most studied targets in the fight against cancer and is a hotspot for drug development because it participates in several solid tumors and is the hallmark of chronic myelogenous leukemia. Tumor suppressors have the opposite effects. Their fundamental role in the maintenance of genomic integrity has awarded them a role as the guardians of DNA. Among the tumor suppressors, p53 is the most studied. The p53 protein has been shown to be a transcription factor that recognizes and binds to specific DNA response elements and activates gene transcription. Stress triggered by ionizing radiation or other mutagenic events leads to p53 phosphorylation and cell-cycle arrest, senescence, or programed cell death. The p53 gene is the most frequently mutated gene in cancer. Mutations in the DNA-binding domain are classified as class I or class II depending on whether substitutions occur in the DNA contact sites or in the protein core, respectively. Tumor-associated p53 mutations often lead to the loss of protein function, but recent investigations have also indicated gain-of-function mutations. The prion-like aggregation of mutant p53 is associated with loss-of-function, dominant-negative, and gain-of-function effects. In the current review, we focused on the most recent insights into the protein structure and function of the c-Abl and p53 proteins that will provide us guidance to understand the loss and gain of function of these misfolded tumor-associated proteins.
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Affiliation(s)
- Guilherme A. P. de Oliveira
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Luciana P. Rangel
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
- Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Danielly C. Costa
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Jerson L. Silva
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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Zaharieva MM, Kirilov M, Chai M, Berger SM, Konstantinov S, Berger MR. Reduced expression of the retinoblastoma protein shows that the related signaling pathway is essential for mediating the antineoplastic activity of erufosine. PLoS One 2014; 9:e100950. [PMID: 24987858 PMCID: PMC4079453 DOI: 10.1371/journal.pone.0100950] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Accepted: 06/02/2014] [Indexed: 01/13/2023] Open
Abstract
Erufosine is a new antineoplastic agent of the group of alkylphosphocholines, which interferes with signal transduction and induces apoptosis in various leukemic and tumor cell lines. The present study was designed to examine for the first time the mechanism of resistance to erufosine in malignant cells with permanently reduced expression of the retinoblastoma (Rb) protein. Bearing in mind the high number of malignancies with reduced level of this tumor-suppressor, this investigation was deemed important for using erufosine, alone or in combination, in patients with compromised RB1 gene expression. For this purpose, clones of the leukemic T-cell line SKW-3 were used, which had been engineered to constantly express differently low Rb levels. The alkylphosphocholine induced apoptosis, stimulated the expression of the cyclin dependent kinase inhibitor p27Kip1 and inhibited the synthesis of cyclin D3, thereby causing a G2 phase cell cycle arrest and death of cells with wild type Rb expression. In contrast, Rb-deficiency impeded the changes induced by eru-fosine in the expression of these proteins and abrogated the induction of G2 arrest, which was correlated with reduced antiproliferative and anticlonogenic activities of the compound. In conclusion, analysis of our results showed for the first time that the Rb signaling pathway is essential for mediating the antineoplastic activity of erufosine and its efficacy in patients with malignant diseases may be predicted by determining the Rb status.
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Affiliation(s)
- Maya M. Zaharieva
- Toxicology and Chemotherapy Unit, German Cancer Research Center, Heidelberg, Germany
| | - Milen Kirilov
- Department of Molecular Biology of the Cell I, German Cancer Research Center, Heidelberg, Germany
| | - Minquang Chai
- Department of Molecular Biology of the Cell I, German Cancer Research Center, Heidelberg, Germany
| | - Stefan M. Berger
- Department of Molecular Biology, Central Institute of Mental Health, Mannheim, Germany
| | - Spiro Konstantinov
- Laboratory for Molecular Pharmacology and Experimental Chemotherapy, Department for Pharmacology, Pharmacotherapy and Toxicology, Faculty of Pharmacy, Medical University of Sofia, Sofia, Bulgaria
| | - Martin R. Berger
- Toxicology and Chemotherapy Unit, German Cancer Research Center, Heidelberg, Germany
- * E-mail:
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Abstract
The mammalian ABL1 gene encodes the ubiquitously expressed nonreceptor tyrosine kinase ABL. In response to growth factors, cytokines, cell adhesion, DNA damage, oxidative stress, and other signals, ABL is activated to stimulate cell proliferation or differentiation, survival or death, retraction, or migration. ABL also regulates specialized functions such as antigen receptor signaling in lymphocytes, synapse formation in neurons, and bacterial adhesion to intestinal epithelial cells. Although discovered as the proto-oncogene from which the Abelson leukemia virus derived its Gag-v-Abl oncogene, recent results have linked ABL kinase activation to neuronal degeneration. This body of knowledge on ABL seems confusing because it does not fit the one-gene-one-function paradigm. Without question, ABL capabilities are encoded by its gene sequence and that molecular blueprint designs this kinase to be regulated by subcellular location-dependent interactions with inhibitors and substrate activators. Furthermore, ABL shuttles between the nucleus and the cytoplasm where it binds DNA and actin--two biopolymers with fundamental roles in almost all biological processes. Taken together, the cumulated results from analyses of ABL structure-function, ABL mutant mouse phenotypes, and ABL substrates suggest that this tyrosine kinase does not have its own agenda but that, instead, it has evolved to serve a variety of tissue-specific and context-dependent biological functions.
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7
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Lee TC, Gombos DS, Harbour JW, Mansfield NC, Murphree AL. Retinoblastoma. Retina 2013. [DOI: 10.1016/b978-1-4557-0737-9.00128-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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8
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Sahin F, Sladek TL. E2F-1 binding affinity for pRb is not the only determinant of the E2F-1 activity. Int J Biol Sci 2010; 6:382-95. [PMID: 20616879 PMCID: PMC2899456 DOI: 10.7150/ijbs.6.382] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2010] [Accepted: 07/02/2010] [Indexed: 11/07/2022] Open
Abstract
E2F-1 is the major cellular target of pRB and is regulated by pRB during cell proliferation. Interaction between pRB and E2F-1 is dependent on the phosphorylation status of pRB. Despite the fact that E2F-1 and pRB have antagonistic activities when they are overexpressed, the role of the E2F-1-pRB interaction in cell growth largely remains unknown. Ideally, it would be better to study the properties of a pRB mutant that fails to bind to E2F, but retains all other activities. To date, no pRB mutation has been characterized in sufficient detail to show that it specifically eliminates E2F binding but leaves other interactions intact. An alternative approach to this issue is to ask whether mutations that change E2F proteins binding affinity to pRB are sufficient to change cell growth in aspect of cell cycle and tumor formation. Therefore, we used the E2F-1 mutants including E2F-1/S332-7A, E2F-1/S375A, E2F-1/S403A, E2F-1/Y411A and E2F-1/L132Q that have different binding affinities for pRB to better understand the roles of the E2F-1 phosphorylation and E2F-1-pRB interaction in the cell cycle, as well as in transformation and gene expression. Data presented in this study suggests that in vivo phosphorylation at amino acids 332-337, 375 and 403 is important for the E2F-1 and pRB interaction in vivo. However, although E2F-1 mutants 332-7, 375 and 403 showed similar binding affinity to pRB, they showed different characteristics in transformation efficiency, G0 accumulation, and target gene experiments.
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Affiliation(s)
- Fikret Sahin
- Department of Microbiology and Immunology, Finch University of Health Sciences/Chicago Medical School (now Rosalind Franklin University), North Chicago, Illinois 60064-3095, USA.
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9
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Huang X, Masselli A, Frisch SM, Hunton IC, Jiang Y, Wang JYJ. Blockade of tumor necrosis factor-induced Bid cleavage by caspase-resistant Rb. J Biol Chem 2007; 282:29401-13. [PMID: 17686781 DOI: 10.1074/jbc.m702261200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tumor necrosis factor-alpha (TNF) activates caspase-8 to cleave effector caspases or Bid, resulting in type-1 or type-2 apoptosis, respectively. We show here that TNF also induces caspase-8-dependent C-terminal cleavage of the retinoblastoma protein (Rb). Interestingly, fibroblasts from Rb(MI/MI) mice, in which the C-terminal caspase cleavage site is mutated, exhibit a defect in Bid cleavage despite caspase-8 activation. Recent results suggest that TNF receptor endocytosis is required for the activation of caspase-8. Consistent with this notion, inhibition of V-ATPase, which plays an essential role in acidification and degradation of endosomes, specifically restores Bid cleavage in Rb(MI/MI) cells. Inhibition of V-ATPase sensitizes Rb(MI/MI) but not wild-type fibroblasts to TNF-induced apoptosis and stimulates inflammation-associated colonic apoptosis in Rb(MI/MI) but not wild-type mice. These results suggest that Rb cleavage is required for Bid cleavage in TNF-induced type-2 apoptosis, and this requirement can be supplanted by the inhibition of V-ATPase.
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Affiliation(s)
- XiaoDong Huang
- Division of Biological Sciences, Department of Medicine, University of California, San Diego, La Jolla, California 92093-0820, USA
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10
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Mishra S, Melino G, Murphy LJ. Transglutaminase 2 kinase activity facilitates protein kinase A-induced phosphorylation of retinoblastoma protein. J Biol Chem 2007; 282:18108-18115. [PMID: 17478427 DOI: 10.1074/jbc.m607413200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Transglutaminase 2 (TG2, tissue transglutaminase) is a multifunctional protein involved in cross-linking a variety of proteins, including retinoblastoma protein (Rb). Here we show that Rb is also a substrate for the recently identified serine/threonine kinase activity of TG2 and that TG2 phosphorylates Rb at the critically important Ser780 residue. Furthermore, phosphorylation of Rb by TG2 destabilizes the Rb.E2F1 complex. TG2 phosphorylation of Rb was abrogated by high Ca2+ concentrations, whereas TG2 transamidating activity was inhibited by ATP. TG2 was itself phosphorylated by protein kinase A (PKA). Phosphorylation of TG2 by PKA attenuated its transamidating activity and enhanced its kinase activity. Activation of PKA in mouse embryonic fibroblasts (MEF) with dibutyryl-cAMP enhanced phosphorylation of both TG2 and Rb by a process that was inhibited by the PKA inhibitor H89. Treatment with dibutyryl-cAMP enhanced Rb phosphorylation in MEFtg2+/+ cells but not in MEFtg2-/- cells. These data indicate that Rb is a substrate for TG2 kinase activity and suggest that phosphorylation of Rb, which results from activation of PKA in fibroblasts, is indirect and requires TG2 kinase activity.
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Affiliation(s)
- Suresh Mishra
- Departments of Physiology and Internal Medicine, University of Manitoba, Winnipeg R3E 0W3, Canada.
| | - Gerry Melino
- Department of Biochemistry Laboratory, Instituto Dermapatico dell'Immaculata-Institute for Hospitalization, Care and Scientific Research, Department of Experimental Medicine and Biological Sciences, University of Rome, 00133 Tor Vergata, Italy
| | - Liam J Murphy
- Departments of Physiology and Internal Medicine, University of Manitoba, Winnipeg R3E 0W3, Canada
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Murphree AL, Samuel MA, Harbour JW, Mansfield NC. Retinoblastoma. Retina 2006. [DOI: 10.1016/b978-0-323-02598-0.50028-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Rodier G, Makris C, Coulombe P, Scime A, Nakayama K, Nakayama KI, Meloche S. p107 inhibits G1 to S phase progression by down-regulating expression of the F-box protein Skp2. ACTA ACUST UNITED AC 2005; 168:55-66. [PMID: 15631990 PMCID: PMC2171673 DOI: 10.1083/jcb.200404146] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Cell cycle progression is negatively regulated by the pocket proteins pRb, p107, and p130. However, the mechanisms responsible for this inhibition are not fully understood. Here, we show that overexpression of p107 in fibroblasts inhibits Cdk2 activation and delays S phase entry. The inhibition of Cdk2 activity is correlated with the accumulation of p27, consequent to a decreased degradation of the protein, with no change of Thr187 phosphorylation. Instead, we observed a marked decrease in the abundance of the F-box receptor Skp2 in p107-overexpressing cells. Reciprocally, Skp2 accumulates to higher levels in p107−/− embryonic fibroblasts. Ectopic expression of Skp2 restores p27 down-regulation and DNA synthesis to the levels observed in parental cells, whereas inactivation of Skp2 abrogates the inhibitory effect of p107 on S phase entry. We further show that the serum-dependent increase in Skp2 half-life observed during G1 progression is impaired in cells overexpressing p107. We propose that p107, in addition to its interaction with E2F, inhibits cell proliferation through the control of Skp2 expression and the resulting stabilization of p27.
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Affiliation(s)
- Geneviève Rodier
- Institut de recherche en immunovirologie et cancérologie, Université de Montréal, Montreal, Quebec H3C 3J7, Canada
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Keller SA, Ullah Z, Buckley MS, Henry RW, Arnosti DN. Distinct developmental expression of Drosophila retinoblastoma factors. Gene Expr Patterns 2005; 5:411-21. [PMID: 15661648 DOI: 10.1016/j.modgep.2004.09.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2003] [Revised: 09/07/2004] [Accepted: 09/08/2004] [Indexed: 11/20/2022]
Abstract
Retinoblastoma (RB) tumor suppressor proteins are important regulators of the cell cycle and are implicated in a wide variety of human tumors. Genetic analysis of RB mutations in humans and in model systems indicates that individual RB proteins also have distinct functions in development. Specific target genes or mechanisms of action of individual RB proteins in developmental contexts are not well understood, however. To better understand the developmental activities of the two RB family members in Drosophila, we have characterized endogenous expression patterns of Rbf1 and Rbf2 proteins and transcripts in embryos and imaginal discs. These gene products are coexpressed at several stages of development, however, spatial and temporal differences are evident, including partly complementary patterns of expression in the embryonic central nervous system.
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Affiliation(s)
- Scott A Keller
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824-1319, USA
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Hirsch HA, Jawdekar GW, Lee KA, Gu L, Henry RW. Distinct mechanisms for repression of RNA polymerase III transcription by the retinoblastoma tumor suppressor protein. Mol Cell Biol 2004; 24:5989-99. [PMID: 15199152 PMCID: PMC480882 DOI: 10.1128/mcb.24.13.5989-5999.2004] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The retinoblastoma (RB) protein represses global RNA polymerase III transcription of genes that encode nontranslated RNAs, potentially to control cell growth. However, RNA polymerase III-transcribed genes exhibit diverse promoter structures and factor requirements for transcription, and a universal mechanism explaining global repression is uncertain. We show that RB represses different classes of RNA polymerase III-transcribed genes via distinct mechanisms. Repression of human U6 snRNA (class 3) gene transcription occurs through stable promoter occupancy by RB, whereas repression of adenovirus VAI (class 2) gene transcription occurs in the absence of detectable RB-promoter association. Endogenous RB binds to a human U6 snRNA gene in both normal and cancer cells that maintain functional RB but not in HeLa cells whose RB function is disrupted by the papillomavirus E7 protein. Both U6 promoter association and transcriptional repression require the A/B pocket domain and C region of RB. These regions of RB contribute to U6 promoter targeting through numerous interactions with components of the U6 general transcription machinery, including SNAP(C) and TFIIIB. Importantly, RB also concurrently occupies a U6 promoter with RNA polymerase III during repression. These observations suggest a novel mechanism for RB function wherein RB can repress U6 transcription at critical steps subsequent to RNA polymerase III recruitment.
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Affiliation(s)
- Heather A Hirsch
- Program in Cell and Molecular Biology, Michigan State University, East Lansing 48824, USA
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Garnovskaya MN, Mukhin YV, Vlasova TM, Grewal JS, Ullian ME, Tholanikunnel BG, Raymond JR. Mitogen-induced Rapid Phosphorylation of Serine 795 of the Retinoblastoma Gene Product in Vascular Smooth Muscle Cells Involves ERK Activation. J Biol Chem 2004; 279:24899-905. [PMID: 15069084 DOI: 10.1074/jbc.m311622200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
We examined the relationship between mitogen-activated MEK (mitogen and extracellular signal-regulated protein kinase kinase) and phosphorylation of the gene product encoded by retinoblastoma (hereafter referred to as Rb) in vascular smooth muscle cells. Brief treatment of the cells with 100 nm angiotensin II or 1 microm serotonin resulted in serine phosphorylation of Rb that was equal in magnitude to that induced by treating cells for 20 h with 10% fetal bovine serum ( approximately 3 x basal). There was no detectable rapid phosphorylation of two close cousins of Rb, p107 and p130. Phosphorylation state-specific antisera demonstrated that the rapid phosphorylation occurred on Ser(795), but not on Ser(249), Thr(252), Thr(373), Ser(780), Ser(807), or Ser(811). Phosphorylation of Rb Ser(795) peaked at 10 min, lagging behind phosphorylation of MEK and ERK (extracellular signal-regulated protein kinase). Rb Ser(795) phosphorylation could be blocked by PD98059, a MEK inhibitor, and greatly attenuated by apigenin, an inhibitor of the Ras --> Raf --> MEK --> ERK pathway. The effect also appears to be mediated by CDK4. Immunoprecipitation/immunoblot studies revealed that serotonin and angiotensin II induced complex formation between CDK4, cyclin D1, and phosphorylated ERK. These studies show a rapid, novel, and selective phosphorylation of Rb Ser(795) by mitogens and demonstrate an unexpected rapid linkage between the actions of the Ras --> Raf --> MEK --> ERK pathway and the phosphorylation state of Rb.
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Affiliation(s)
- Maria N Garnovskaya
- Medical and Research Services of the Ralph H. Johnson Veterans Affairs Medical Center and Department of Medicine (Nephrology Division) of the Medical University of South Carolina, Charleston, South Carolina 29425, USA.
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16
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Chau BN, Chen TT, Wan YY, DeGregori J, Wang JYJ. Tumor necrosis factor alpha-induced apoptosis requires p73 and c-ABL activation downstream of RB degradation. Mol Cell Biol 2004; 24:4438-47. [PMID: 15121862 PMCID: PMC400462 DOI: 10.1128/mcb.24.10.4438-4447.2004] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2003] [Revised: 11/21/2003] [Accepted: 02/21/2004] [Indexed: 11/20/2022] Open
Abstract
The retinoblastoma protein (RB) suppresses cell proliferation and apoptosis. We have previously shown that RB degradation is required for tumor necrosis factor alpha (TNF-alpha) to induce apoptosis. We show here the identification of two apoptotic effectors, i.e., c-ABL tyrosine kinase and p73, which are activated by TNF-alpha following RB degradation. In cells expressing a degradation-resistant RB protein (RB-MI), TNF-alpha does not activate c-ABL. RB-MI also inhibits TNF-alpha-mediated activation of p73. Genetic deletion and pharmacological inhibition of c-ABL or p73 diminish the apoptotic response to TNF-alpha in human cell lines and mouse fibroblasts. Thymocytes isolated from Rb(MI/MI), Abl(-/-), or p73(-/-) mice are resistant to TNF-alpha-induced apoptosis compared to their wild-type counterparts. This is in contrast to p53(-/-) thymocytes, which exhibit a wild-type level of apoptosis in response to TNF-alpha. Thus, c-ABL and p73 contribute to apoptosis induced by TNF-alpha, in addition to their role in promoting DNA damage-associated cell death.
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Affiliation(s)
- B Nelson Chau
- Division of Biological Sciences and Cancer Center, University of California, San Diego, La Jolla, California 92093-0322, USA
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17
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Abstract
The pRb and p53 proteins have tumour suppressor functions and both are regulators of transcription. Their mechanisms of transcriptional regulation are unrelated in many ways--in contrast, it would appear, to their biological functions. This review highlights their biological connections in the light of recent advances in understanding the mechanisms of pRb and p53 function.
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Affiliation(s)
- T Kouzarides
- Wellcome/CRC Institute and the Dept of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QR, UK
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18
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Goodrich DW. How the other half lives, the amino-terminal domain of the retinoblastoma tumor suppressor protein. J Cell Physiol 2003; 197:169-80. [PMID: 14502556 DOI: 10.1002/jcp.10358] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The retinoblastoma tumor suppressor gene (RB1) is currently the only known gene whose mutation is necessary and sufficient for the development of a human cancer. Mutation or deregulation of RB1 is observed so frequently in other tumor types that compromising RB1 function may be a prerequisite for malignant transformation. Identifying the molecular mechanisms that provide the basis for RB1-mediated tumor suppression has become an important goal in the quest to understand and treat cancer. The lion's share of research on these mechanisms has focused on the carboxy-terminal half of the RB1 encoded protein (pRB). This focus is with good reason since this part of the protein, now called the "large pocket," is required for most of its known activities identified in vitro and in vivo. Large pocket mediated mechanisms alone, however, cannot account for all observed properties of pRB. The thesis presented here is that the relatively uncharacterized amino-terminal half of the protein makes important contributions to pRB-mediated tumor suppression. The goals of this review are to summarize evidence indicating that an amino-terminal structural domain is important for pRB function and to suggest a general hypothesis as to how this domain can be integrated with current models of pRB function.
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Affiliation(s)
- David W Goodrich
- Department of Pharmacology & Therapeutics, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, New York 14263, USA.
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19
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Vella V, Zhu J, Frasca F, Li CY, Vigneri P, Vigneri R, Wang JYJ. Exclusion of c-Abl from the nucleus restrains the p73 tumor suppression function. J Biol Chem 2003; 278:25151-7. [PMID: 12716888 DOI: 10.1074/jbc.m301962200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The p73alpha protein is a functional homolog of the p53 tumor suppressor. Although the TP53 gene is frequently mutated in human cancers, the TP73 gene is rarely inactivated. We have found that p73alpha is highly expressed in a significant fraction of anaplastic thyroid cancer, whereas it is not detectable in normal thyroid epithelial cells or in papillary and follicular thyroid cancer cells. Interestingly, the tumor suppression function of p73alpha is actively restrained in anaplastic thyroid cancer cells. We have also found that c-Abl tyrosine kinase, an activator of p73, is excluded from the nucleus of p73alpha-positive thyroid cancer cells; whereas c-Abl undergoes nuclear-cytoplasmic shuttling in normal thyroid and p73-negative thyroid cancer cells. We constructed an AblNuk-FK506-binding protein (FKBP) fusion protein to enforce the nuclear accumulation of an inducible Abl kinase. Activation of this nuclear AblNuk-FKBP by dimerization with AP20187 in anaplastic thyroid cancer cells increased the levels of p73alpha and p21Cip1 and caused p73-dependent apoptosis. These results suggest subcellular segregation of c-Abl from p73 to be a strategy for disrupting the tumor suppression function of p73alpha.
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Affiliation(s)
- Veronica Vella
- Division of Biological Sciences and the Cancer Center, University of California, San Diego, La Jolla 92093-0322, USA
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20
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Chung J, Cho J, Baek W, Suh S, Kwon TK, Park J, Suh M. Expression of RB C pocket fragments in HSF induces delayed cell cycle progression and sensitizes to apoptosis upon cellular stresses. Cell Prolif 2002; 35:247-56. [PMID: 12153616 PMCID: PMC6496431 DOI: 10.1046/j.1365-2184.2002.00245.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The retinoblastoma protein (RB) plays an important role in growth suppression through the formation of multiple protein complexes with its target proteins using A/B and C pockets. Even though the A/B and C pockets co-operate for growth suppression, the function of RB in growth arrest is inhibited by the coexpression of RB C fragments with full length RB in the absence of p53, which implies that C pocket fragments are likely to act as a dominant-negative inhibitor of RB function. In contrast, the loss of the RB functions in the presence of p53 triggers a cell cycle arrest or apoptosis by p53-dependent pathways. Thus, it still remains to be elucidated whether the expression of RB C pocket fragments in the presence of p53 induces delayed cell cycle progression and sensitizes cells to apoptosis through p53-dependent pathways. Our results show that the expression of RB C pocket fragments not only induces delayed cell cycle progression, which is mediated by the down-regulation of cyclin A, cyclin E, and E2F-1, but also sensitizes cells to apoptosis through p53-dependent pathways.
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Affiliation(s)
- Junah Chung
- Department of Microbiology, School of Medicine, Keimyung University, Taegu
| | - Jae‐We Cho
- Department of Microbiology, College of Medicine, Seonam University, Namwon, Chunpook
| | - Won‐Ki Baek
- Department of Microbiology, School of Medicine, Keimyung University, Taegu
| | - Seong‐Il Suh
- Department of Microbiology, School of Medicine, Keimyung University, Taegu
| | - Taeg Kyu Kwon
- Department of Immunology, School of Medicine, Keimyung University, Taegu, Republic of Korea
| | - Jong‐Wook Park
- Department of Immunology, School of Medicine, Keimyung University, Taegu, Republic of Korea
| | - Min‐Ho Suh
- Department of Microbiology, School of Medicine, Keimyung University, Taegu
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21
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Farkas T, Hansen K, Holm K, Lukas J, Bartek J. Distinct phosphorylation events regulate p130- and p107-mediated repression of E2F-4. J Biol Chem 2002; 277:26741-52. [PMID: 12006580 DOI: 10.1074/jbc.m200381200] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The "pocket proteins" pRb (retinoblastoma tumor suppressor protein), p107, and p130 regulate cell proliferation via phosphorylation-sensitive interactions with E2F transcription factors and other proteins. We previously identified 22 in vivo phosphorylation sites in human p130, including three sites selectively targeted by cyclin D-Cdk4(6) kinases. Here we assessed the effects of alanine substitution at the individual or combined Cdk4(6)-specific sites in p130, compared with homologous sites in p107 (Thr(369)/Ser(650)/Ser(964)). In U-2-OS cells, the triple p107(DeltaCdk4)* mutant strongly inhibited E2F-4 activity and imposed a G(1) arrest resistant to cyclin D1 coexpression. In contrast, the p130(DeltaCdk4) mutant still responded to cyclin D1, suggesting the existence of additional phosphorylation sites critical for E2F-4 regulation. Extensive mutagenesis, sensitive E2F reporter assays, and cell cycle analyses allowed the identification of six such residues (serines 413, 639, 662, 1044, 1080, and 1112) that, in addition to the Cdk4-specific sites, are necessary and sufficient for the regulation of E2F-4 and the cell cycle by p130. Surprisingly, 12 of the in vivo phosphorylation sites seem dispensable for E2F regulation and probably modulate other functions of p130. These results further elucidate the complex regulation of p130 and provide a molecular mechanism to explain the differential control of p107 and p130 by cyclin-dependent kinases.
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Affiliation(s)
- Thomas Farkas
- Danish Cancer Society, Institute of Cancer Biology, Strandboulevarden 49, Copenhagen DK-2100, Denmark
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22
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Abstract
Studies of the retinoblastoma gene (Rb) have shown that its protein product (pRb) acts to restrict cell proliferation, inhibit apoptosis, and promote cell differentiation. The frequent mutation of the Rb gene, and the functional inactivation of pRb in tumor cells, have spurred interest in the mechanism of pRb action. Recently, much attention has focused on pRb's role in the regulation of the E2F transcription factor. However, biochemical studies have suggested that E2F is only one of many pRb-targets and, to date, at least 110 cellular proteins have been reported to associate with pRb. The plethora of pRb-binding proteins raises several important questions. How many functions does pRb possess, which of these functions are important for development, and which contribute to tumor suppression? The goal of this review is to summarize the current literature of pRb-associated proteins.
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Affiliation(s)
- E J Morris
- Laboratory of Molecular Oncology, Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129, USA
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23
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Adams PD. Regulation of the retinoblastoma tumor suppressor protein by cyclin/cdks. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1471:M123-33. [PMID: 11250068 DOI: 10.1016/s0304-419x(01)00019-1] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The retinoblastoma tumor suppressor protein (pRB) is a paradigm for understanding cell cycle- and proliferation-dependent transcription and how deregulation of this process contributes to the neoplastic process in humans. The ability of pRB to regulate transcription, and consequently cell proliferation and differentiation, is regulated by the activity of cyclin/cdks. In general, phosphorylation of pRB by cyclin/cdks inactivates pRB-mediated transcriptional inhibition and growth suppression. However, it is apparent that pRB is a multi-functional protein that can inhibit transcription through various mechanisms. This review focuses on recent data to suggest that different pRB functions are progressively and cooperatively inactivated by multiple cyclin/cdk complexes during G1- and S-phase. The implications of such a model for pRB-mediated tumor suppression are discussed.
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Affiliation(s)
- P D Adams
- Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111, USA.
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24
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Abstract
Genome instability has been implicated in the generation of multiple somatic mutations that underlie cancer. Germline mutation in the retinoblastoma (RB) gene leads to tumor formation in both human and experimental animal models, and reintroduction of wild-type RB is able to suppress neoplastic phenotypes. Rb governs the passage of cells through the G1 phase-restriction point and this control is lost in most cancer cells. Rb has also been shown to promote terminal differentiation and prevent cell cycle reentry. Recent studies implicate Rb in mitotic progression, faithful chromosome segregation, checkpoint control, and chromatin remodeling, suggesting that Rb may function in the maintenance of genome integrity. It is likely that Rb suppresses tumor formation by virtue of its multiple biological activities. A single protein capable of performing multiple antioncogenic functions may be a common characteristic of other tumor suppressors including p53 and BRCA1/2.
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Affiliation(s)
- L Zheng
- Department of Molecular Medicine/Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, Texas 78245, USA
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25
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Miyake S, Sellers WR, Safran M, Li X, Zhao W, Grossman SR, Gan J, DeCaprio JA, Adams PD, Kaelin WG. Cells degrade a novel inhibitor of differentiation with E1A-like properties upon exiting the cell cycle. Mol Cell Biol 2000; 20:8889-902. [PMID: 11073989 PMCID: PMC86544 DOI: 10.1128/mcb.20.23.8889-8902.2000] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Control of proliferation and differentiation by the retinoblastoma tumor suppressor protein (pRB) and related family members depends upon their interactions with key cellular substrates. Efforts to identify such cellular targets led to the isolation of a novel protein, EID-1 (for E1A-like inhibitor of differentiation 1). Here, we show that EID-1 is a potent inhibitor of differentiation and link this activity to its ability to inhibit p300 (and the highly related molecule, CREB-binding protein, or CBP) histone acetylation activity. EID-1 is rapidly degraded by the proteasome as cells exit the cell cycle. Ubiquitination of EID-1 requires an intact C-terminal region that is also necessary for stable binding to p300 and pRB, two proteins that bind to the ubiquitin ligase MDM2. A pRB variant that can bind to EID1, but not MDM2, stabilizes EID-1 in cells. Thus, EID-1 may act at a nodal point that couples cell cycle exit to the transcriptional activation of genes required for differentiation.
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Affiliation(s)
- S Miyake
- Department of Adult Oncology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA
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26
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Hirsch HA, Gu L, Henry RW. The retinoblastoma tumor suppressor protein targets distinct general transcription factors to regulate RNA polymerase III gene expression. Mol Cell Biol 2000; 20:9182-91. [PMID: 11094070 PMCID: PMC102176 DOI: 10.1128/mcb.20.24.9182-9191.2000] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The retinoblastoma protein (RB) represses RNA polymerase III transcription effectively both in vivo and in vitro. Here we demonstrate that the general transcription factors snRNA-activating protein complex (SNAP(c)) and TATA binding protein (TBP) are important for RB repression of human U6 snRNA gene transcription by RNA polymerase III. RB is associated with SNAP(c) as detected by both coimmunoprecipitation of endogenous RB with SNAP(c) and cofractionation of RB and SNAP(c) during chromatographic purification. RB also interacts with two SNAP(c) subunits, SNAP43 and SNAP50. TBP or a combination of TBP and SNAP(c) restores efficient U6 transcription from RB-treated extracts, indicating that TBP is also involved in RB regulation. In contrast, the TBP-containing complex TFIIIB restores adenovirus VAI but not human U6 transcription in RB-treated extracts, suggesting that TFIIIB is important for RB regulation of tRNA-like genes. These results suggest that different classes of RNA polymerase III-transcribed genes have distinct general transcription factor requirements for repression by RB.
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MESH Headings
- Adenoviruses, Human
- Autoradiography
- Cell Extracts
- Cell Nucleus/metabolism
- Chromatography
- Cloning, Molecular
- Electrophoresis, Polyacrylamide Gel
- HeLa Cells
- Humans
- Models, Genetic
- Precipitin Tests
- Promoter Regions, Genetic/genetics
- RNA Polymerase III/genetics
- RNA Polymerase III/metabolism
- RNA, Viral/genetics
- RNA, Viral/metabolism
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Retinoblastoma Protein/genetics
- Retinoblastoma Protein/metabolism
- Ribonucleoprotein, U4-U6 Small Nuclear/genetics
- Ribonucleoprotein, U4-U6 Small Nuclear/metabolism
- TATA Box
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Transcription, Genetic/genetics
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Affiliation(s)
- H A Hirsch
- Cell and Molecular Biology Program, Michigan State University, East Lansing, Michigan 48824, USA
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27
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Affiliation(s)
- J W Harbour
- Division of Molecular Oncology, Washington University, St. Louis, Missouri 63110, USA
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28
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Tamrakar S, Ludlow JW. The carboxyl-terminal region of the retinoblastoma protein binds non-competitively to protein phosphatase type 1alpha and inhibits catalytic activity. J Biol Chem 2000; 275:27784-9. [PMID: 10889204 DOI: 10.1074/jbc.m004542200] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
pRB, a negative-growth regulatory protein, is a demonstrated substrate for type 1 serine/threonine protein phosphatases (PP1). In a recent report from this laboratory, we demonstrated that select forms of phosphorylated as well as hypophosphorylated pRB can be found complexed with the alpha-isotype of PP1 (PP1alpha). This complex can also be observed when PP1 is rendered catalytically dead by toxin inhibition. These data suggested to us that pRB may bind to PP1 at one or more sites other than the catalytically active one on the enzyme and that such binding may play a role other than bringing the substrate into contact with the enzyme to facilitate catalysis. To address this possibility we utilized a series of pRB deletion mutants and coprecipitation studies to map the pRB domain involved in binding to PP1. Together with competition assays using in vivo expression of SV40 T-antigen, we show here that the carboxyl-terminal region of pRB is both necessary and sufficient for physical interaction with PP1. Subsequent biochemical analyses demonstrated inhibition of PP1 catalytic activity toward the standard substrate phosphorylase a when this enzyme is bound to pRB containing this region. K(m) and V(max) calculations revealed that pRB binds to PP1 in a non-competitive manner. These data support the notion that pRB, in addition to being a substrate for PP1, also functions as a PP1 inhibitor. The significance of this finding with respect to the functional importance of this interaction is discussed.
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Affiliation(s)
- S Tamrakar
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry and University of Rochester Cancer Center, Rochester, New York 14642, USA
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29
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Chen TT, Wang JY. Establishment of irreversible growth arrest in myogenic differentiation requires the RB LXCXE-binding function. Mol Cell Biol 2000; 20:5571-80. [PMID: 10891495 PMCID: PMC86015 DOI: 10.1128/mcb.20.15.5571-5580.2000] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The crystal structure of the A-B domain of RB has defined the binding pocket for the LXCXE peptide motif. Using the crystal structure as a guide, we have inactivated the LXCXE-binding pocket by replacing N757 with Phe [to obtain RB(N757F)]. RB(N757F) does not bind to viral oncoproteins but retains the ability to bind and inhibit E2F. RB(N757F) is less effective than the wild-type RB [RB(WT)] in repressing E2F-regulated transcription, and its repression activity is not affected by trichostatin A, an inhibitor of histone deacetylases. However, RB(N757F) is as effective as RB(WT) in suppressing cell growth. Interestingly, RB(N757F) cannot establish an irreversible growth arrest in differentiated myocytes. Differentiated myocytes with RB(WT) become refractory to serum. By contrast, differentiated myocytes with RB(N757F) undergo DNA synthesis and phosphorylate RB(N757F) in response to serum, despite a high level of p21Cip1 expression. Mutation of the phosphorylation sites in RB(N757F) rescued its defect and allowed myocytes to permanently withdraw from the cell cycle. These results demonstrate that it is possible to inactivate the LXCXE-binding pocket without compromising the overall integrity of RB. Moreover, the LXCXE-binding pocket is dispensable for the intrinsic growth suppression function of RB. However, the LXCXE-binding function is essential for RB to establish the serum-refractory state in differentiated myocytes.
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Affiliation(s)
- T T Chen
- Department of Biology and the Cancer Center, University of California, San Diego, La Jolla, California 92093-0322, USA
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30
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Fajas L, Paul C, Zugasti O, Le Cam L, Polanowska J, Fabbrizio E, Medema R, Vignais ML, Sardet C. pRB binds to and modulates the transrepressing activity of the E1A-regulated transcription factor p120E4F. Proc Natl Acad Sci U S A 2000; 97:7738-43. [PMID: 10869426 PMCID: PMC16614 DOI: 10.1073/pnas.130198397] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The retinoblastoma protein pRB is involved in the transcriptional control of genes essential for cell cycle progression and differentiation. pRB interacts with different transcription factors and thereby modulates their activity by sequestration, corepression, or activation. We report that pRB, but not p107 and p130, binds to and facilitates repression by p120(E4F), a ubiquitously expressed GLI-Kruppel-related protein identified as a cellular target of E1A. The interaction involves two distinct regions of p120(E4F) and the C-terminal part of pRB. In vivo pRB-p120(E4F) complexes can only be detected in growth-arrested cells, and accordingly contain the hypophosphorylated form of pRB. Repression of an E4F-responsive promoter is strongly increased by combined expression of p120(E4F) and pRB, which correlates with pRB-dependent enhancement of p120(E4F) binding activity. Elevated levels of p120(E4F) have been shown to block growth of mouse fibroblasts in G(1). We find this requires pRB, because RB(-/-) fibroblasts are significantly less sensitive to excess p120(E4F).
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Affiliation(s)
- L Fajas
- Institut de Génétique Moléculaire, Unité Mixte de Recherche 5535, IFR 24, Centre National de la Recherche Scientifique, 1919 Route de Mende, 34293, Montpellier cedex 5, France
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31
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Gill RM, Hamel PA. Subcellular compartmentalization of E2F family members is required for maintenance of the postmitotic state in terminally differentiated muscle. J Cell Biol 2000; 148:1187-201. [PMID: 10725332 PMCID: PMC2174298 DOI: 10.1083/jcb.148.6.1187] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Maintenance of cells in a quiescent state after terminal differentiation occurs through a number of mechanisms that regulate the activity of the E2F family of transcription factors. We report here that changes in the subcellular compartmentalization of the E2F family proteins are required to prevent nuclei in terminally differentiated skeletal muscle from reentering S phase. In terminally differentiated L6 myotubes, E2F-1, E2F-3, and E2F-5 were primarily cytoplasmic, E2F-2 was nuclear, whereas E2F-4 became partitioned between both compartments. In these same cells, pRB family members, pRB, p107, and p130 were also nuclear. This compartmentalization of the E2F-1 and E2F-4 in differentiated muscle cells grown in vitro reflected their observed subcellular location in situ. We determined further that exogenous E2F-1 or E2F-4 expressed in myotubes at levels fourfold greater than endogenous proteins compartmentalized identically to their endogenous counterparts. Only when overexpressed at higher levels was inappropriate subcellular location for these proteins observed. At these levels, induction of the E2F-regulated genes, cyclins A and E, and suppression of factors associated with myogenesis, myogenin, and p21(Cip1) was observed. Only at these levels of E2F expression did nuclei in these terminally differentiated cells enter S phase. These data demonstrate that regulation of the subcellular compartmentalization of E2F-family members is required to maintain nuclei in a quiescent state in terminally differentiated cells.
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Affiliation(s)
- R. Montgomery Gill
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Paul A. Hamel
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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32
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Cucinotta FA, Dicello JF. On the development of biophysical models for space radiation risk assessment. ADVANCES IN SPACE RESEARCH : THE OFFICIAL JOURNAL OF THE COMMITTEE ON SPACE RESEARCH (COSPAR) 2000; 25:2131-2140. [PMID: 11542866 DOI: 10.1016/s0273-1177(99)01065-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Experimental techniques in molecular biology are being applied to study biological risks from space radiation. The use of molecular assays presents a challenge to biophysical models which in the past have relied on descriptions of energy deposition and phenomenological treatments of repair. We describe a biochemical kinetics model of cell cycle control and DNA damage response proteins in order to model cellular responses to radiation exposures. Using models of cyclin-cdk, pRB, E2F's, p53, and G1 inhibitors we show that simulations of cell cycle populations and G1 arrest can be described by our biochemical approach. We consider radiation damaged DNA as a substrate for signal transduction processes and consider a dose and dose-rate reduction effectiveness factor (DDREF) for protein expression.
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Affiliation(s)
- F A Cucinotta
- NASA, Johnson Space Center, Houston, TX 77058-0001, USA
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33
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Abstract
The c-Abl tyrosine kinase and its transforming variants have been implicated in tumorigenesis and in many important cellular processes. c-Abl is localized in the nucleus and the cytoplasm, where it plays distinct roles. The effects of c-Abl are mediated by multiple protein-protein and protein-DNA interactions and its tyrosine kinase domain. At the biochemical level, the mechanism of c-Abl kinase activation and the identification of its target proteins and cellular machineries have in part been solved. However, the phenotypic outcomes of these molecular events remained in large elusive. c-Abl has been shown to regulate the cell cycle and to induce under certain conditions cell growth arrest and apoptosis. In this respect the interaction of c-Abl with p53 and p73 has attracted particular attention. Recent findings have implicated c-Abl in an ionizing irradiation signaling pathway that elicits apoptosis. In this pathway p73 is an important immediate downstream effector. Here I review the current knowledge about these nuclear processes in which c-Abl is engaged and discuss some of their possible implications on cell physiology. Cell Death and Differentiation (2000) 7, 10 - 16.
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Affiliation(s)
- Y Shaul
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
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34
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Bonetto F, Fanciulli M, Battista T, De Luca A, Russo P, Bruno T, De Angelis R, Di Padova M, Giordano A, Felsani A, Paggi MG. Interaction between the pRb2/p130 C-terminal domain and the N-terminal portion of cyclin D3. J Cell Biochem 1999; 75:698-709. [PMID: 10572252 DOI: 10.1002/(sici)1097-4644(19991215)75:4<698::aid-jcb15>3.0.co;2-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
An association between cyclin D3 and the C-terminal domain of pRb2/p130 was demonstrated using the yeast two-hybrid system. Further analysis restricted the epitope responsible for the binding within the 74 N-terminal amino acids of cyclin D3, independent of the LXCXE amino acid motif present in the D-type cyclin N-terminal region. In a coprecipitation assay in T98G cells, a human glioblastoma cell line, the C-terminal domain of pRb2/p130 was able to interact solely with cyclin D3, while the corresponding portion of pRb interacted with either cyclin D3 or cyclin D1. In T98G cells, endogenous cyclin D3-associated kinase activity showed a clear predisposition to phosphorylate preferentially the C-terminal domain of pRb2/p130, rather than that of pRb. This propensity was also confirmed in LAN-5 human neuroblastoma cells, where phosphorylation of the pRb2/p130 C-terminal domain and expression of cyclin D3 also decreased remarkably in the late neural differentiation stages.
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Affiliation(s)
- F Bonetto
- Laboratory for Cell Metabolism and Pharmacokinetics, Center for Experimental Research, Regina Elena Cancer Institute, 00158 Rome, Italy
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35
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Abstract
The inactivation of the p53 and Rb pathways would account for the majority of human tumours. There are many levels of cross talk between p53 and Rb that have been identified. However, the identification of the mdm2-Rb interaction established a closer link between the two most well studied tumour suppressors, p53 and Rb. Recent studies of the novel trimeric complex Rb-mdm2-p53 provided us with a functional insight of how the two tumour suppressors can act together in regulating p53 induced apoptosis. Beginning with the properties of the Rb-mdm2-p53 trimeric complex, we shall review the propounding evidence suggesting that the apoptotic function of p53 is linked to its transrepression function. The uncoupling of the apoptotic function and transactivation function of p53 will also be discussed.
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Affiliation(s)
- D B Yap
- Ludwig Institute for Cancer Research, Imperial College School of Medicine, St. Mary's campus, Norfolk Place, London, W2 1PG, UK
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36
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Abstract
The retinoblastoma protein (pRB) can both positively and negatively regulate transcription. The former correlates with its ability to promote differentiation and the latter with its ability to regulate entry into S-phase. pRB negatively regulates transcription by forming complexes with members of the E2F transcription factor family. These complexes, when bound to E2F sites within certain target genes, actively repress transcription through a variety of mechanisms including physical interaction with adjacent transcriptional activation domains and recruitment of proteins that directly, or indirectly, lead to histone deacetylation. pRB function is, in turn, modulated by phosphorylation mediated by cyclin-dependent kinases. Emerging data suggest that combinatorial control of pRB function may be achieved through the use of different phosphoacceptor sites, different cyclin/cdk docking sites, and different cyclin/cdk complexes. The untimely activation of E2F responsive genes can induce apoptosis. This comes about at least partly through the induction of ARF, which leads to the stabilization and activation of p53. BioEssays 1999;21:950-958.
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Affiliation(s)
- W G Kaelin
- Department of Adult Oncology and Howard Hughes Medical Institute, Dana-Farber Cancer Institute, and Harvard Medical School, Boston, Massachusetts, USA.
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37
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Jensen DE, Rauscher FJ. Defining biochemical functions for the BRCA1 tumor suppressor protein: analysis of the BRCA1 binding protein BAP1. Cancer Lett 1999; 143 Suppl 1:S13-7. [PMID: 10546591 DOI: 10.1016/s0304-3835(99)90004-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- D E Jensen
- Wistar Institute, Philadelphia, PA 19104, USA
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38
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Kohn KW. Molecular interaction map of the mammalian cell cycle control and DNA repair systems. Mol Biol Cell 1999; 10:2703-34. [PMID: 10436023 PMCID: PMC25504 DOI: 10.1091/mbc.10.8.2703] [Citation(s) in RCA: 280] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Eventually to understand the integrated function of the cell cycle regulatory network, we must organize the known interactions in the form of a diagram, map, and/or database. A diagram convention was designed capable of unambiguous representation of networks containing multiprotein complexes, protein modifications, and enzymes that are substrates of other enzymes. To facilitate linkage to a database, each molecular species is symbolically represented only once in each diagram. Molecular species can be located on the map by means of indexed grid coordinates. Each interaction is referenced to an annotation list where pertinent information and references can be found. Parts of the network are grouped into functional subsystems. The map shows how multiprotein complexes could assemble and function at gene promoter sites and at sites of DNA damage. It also portrays the richness of connections between the p53-Mdm2 subsystem and other parts of the network.
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Affiliation(s)
- K W Kohn
- Laboratory of Molecular Pharmacology, Division of Basic Sciences, National Cancer Institute, Bethesda, Maryland 20892, USA.
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39
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Wang S, Ghosh RN, Chellappan SP. Raf-1 physically interacts with Rb and regulates its function: a link between mitogenic signaling and cell cycle regulation. Mol Cell Biol 1998; 18:7487-98. [PMID: 9819434 PMCID: PMC109329 DOI: 10.1128/mcb.18.12.7487] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/1998] [Accepted: 08/26/1998] [Indexed: 01/02/2023] Open
Abstract
Cells initiate proliferation in response to growth factor stimulation, but the biochemical mechanisms linking signals received at the cell surface receptors to the cell cycle regulatory molecules are not yet clear. In this study, we show that the signaling molecule Raf-1 can physically interact with Rb and p130 proteins in vitro and in vivo and that this interaction can be detected in mammalian cells without overexpressing any component. The binding of Raf-1 to Rb occurs subsequent to mitogen stimulation, and this interaction can be detected only in proliferating cells. Raf-1 can inactivate Rb function and can reverse Rb-mediated repression of E2F1 transcription and cell proliferation efficiently. The region of Raf-1 involved in Rb binding spanned residues 1 to 28 at the N terminus, and functional inactivation of Rb required a direct interaction. Serum stimulation of quiescent human fibroblast HSF8 cells led to a partial translocation of Raf-1 into the nucleus, where it colocalized with Rb. Further, Raf-1 was able to phosphorylate Rb in vitro quite efficiently. We believe that the physical interaction of Raf-1 with Rb is a vital step in the growth factor-mediated induction of cell proliferation and that Raf-1 acts as a direct link between cell surface signaling cascades and the cell cycle machinery.
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Affiliation(s)
- S Wang
- Department of Pathology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA
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40
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Jiang Y, Hossain A, Winkler MT, Holt T, Doster A, Jones C. A protein encoded by the latency-related gene of bovine herpesvirus 1 is expressed in trigeminal ganglionic neurons of latently infected cattle and interacts with cyclin-dependent kinase 2 during productive infection. J Virol 1998; 72:8133-42. [PMID: 9733854 PMCID: PMC110151 DOI: 10.1128/jvi.72.10.8133-8142.1998] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/1998] [Accepted: 06/23/1998] [Indexed: 11/20/2022] Open
Abstract
Despite productive viral gene expression in the peripheral nervous system during acute infection, the bovine herpesvirus 1 (BHV-1) infection cycle is blocked in sensory ganglionic neurons and consequently latency is established. The only abundant viral transcript expressed during latency is the latency-related (LR) RNA. LR gene products inhibit S-phase entry, and binding of the LR protein (LRP) to cyclin A was hypothesized to block cell cycle progression. This study demonstrates LRP is a nuclear protein which is expressed in neurons of latently infected cattle. Affinity chromatography indicated that LRP interacts with cyclin-dependent kinase 2 (cdk2)-cyclin complexes or cdc2-cyclin complexes in transfected human cells or infected bovine cells. After partial purification using three different columns (DEAE-Sepharose, Econo S, and heparin-agarose), LRP was primarily associated with cdk2-cyclin E complexes, an enzyme which is necessary for G1-to-S-phase cell cycle progression. During acute infection of trigeminal ganglia or following dexamethasone-induced reactivation, BHV-1 induces expression of cyclin A in neurons (L. M. Schang, A. Hossain, and C. Jones, J. Virol. 70:3807-3814, 1996). Expression of S-phase regulatory proteins (cyclin A, for example) leads to neuronal apoptosis. Consequently, we hypothesize that interactions between LRP and cell cycle regulatory proteins promote survival of postmitotic neurons during acute infection and/or reactivation.
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Affiliation(s)
- Y Jiang
- Department of Veterinary and Biomedical Sciences, Center for Biotechnology, University of Nebraska, Lincoln, Lincoln, Nebraska 68583-0905, USA
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41
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Ciacci-Zanella JR, Merrill AH, Wang E, Jones C. Characterization of cell-cycle arrest by fumonisin B1 in CV-1 cells. Food Chem Toxicol 1998; 36:791-804. [PMID: 9737426 DOI: 10.1016/s0278-6915(98)00034-9] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Fusarium moniliforme is a widespread fungal pathogen which primarily infects corn, but can also infect rice or wheat. Fusarium moniliforme produce several mycotoxins, the most prominent of which is called fumonisin B1 (FB1). Epidemiological studies have indicated that ingestion of fumonisins correlates with a higher incidence of oesophageal cancer in Africa and China. Fumonisins also cause a neurodegenerative disease in horses, induce hepatic cancer in rats, are nephrotoxic in rats, or cause pulmonary oedema in swine. Structurally, fumonisins resemble sphingolipids and can alter sphingolipid biosynthesis. suggesting that sphingolipid alterations play a role in disease and carcinogenesis. Previous studies determined that FB1 blocked cell-cycle progression in CV-1 cells but not COS-7 cells. Herein, we have examined the effects that FB1 treatment has on cell-cycle regulatory proteins. Our studies established that FB1 treatment of CV-1 cells, but not COS-7 cells, leads to dephosphorylation of the retinoblastoma (Rb) protein. Cyclin dependent kinase 2 (CDK2) activity was repressed five- to 10-fold and cyclin E protein levels were lower in CV-1 cells after fumonisin treatment. Two CDK inhibitors, Kip1 and Kip2, were induced within 3 hours after fumonisin treatment of CV-1 cells, suggesting these two proteins mediate cell-cycle arrest induced by FB1. This mycotoxin caused large increases in sphinganine within 3 hours after addition of FB1. As sphingoid bases are known to induce Rb phosphorylation, this increase in sphinganinie might be the stimulus for the suppression of cyclin dependent kinase activities via Kip1 and Kip2. The ability of FB1 to accumulate sphingosine or sphinganine and arrest the cell cycle in some cells but not others may play an important role in carcinogenesis or disease.
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Affiliation(s)
- J R Ciacci-Zanella
- Center for Biotechnology, Department of Veterinary and Biomedical Sciences, University of Nebraska, Lincoln 68583, USA
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42
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Affiliation(s)
- N Dyson
- Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129 USA.
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43
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Batsché E, Muchardt C, Behrens J, Hurst HC, Crémisi C. RB and c-Myc activate expression of the E-cadherin gene in epithelial cells through interaction with transcription factor AP-2. Mol Cell Biol 1998; 18:3647-58. [PMID: 9632747 PMCID: PMC108947 DOI: 10.1128/mcb.18.7.3647] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
E-cadherin plays a pivotal role in the biogenesis of the first epithelium during development, and its down-regulation is associated with metastasis of carcinomas. We recently reported that inactivation of RB family proteins by simian virus 40 large T antigen (LT) in MDCK epithelial cells results in a mesenchymal conversion associated with invasiveness and a down-regulation of c-Myc. Reexpression of RB or c-Myc in such cells allows the reexpression of epithelial markers including E-cadherin. Here we show that both RB and c-Myc specifically activate transcription of the E-cadherin promoter in epithelial cells but not in NIH 3T3 mesenchymal cells. This transcriptional activity is mediated in both cases by the transcription factor AP-2. In vitro AP-2 and RB interaction involves the N-terminal domain of AP-2 and the oncoprotein binding domain and C-terminal domain of RB. In vivo physical interaction between RB and AP-2 was demonstrated in MDCK and HaCat cells. In LT-transformed MDCK cells, LT, RB, and AP-2 were all coimmunoprecipitated by each of the corresponding antibodies, and a mutation of the RB binding domain of the oncoprotein inhibited its binding to both RB and AP-2. Taken together, our results suggest that there is a tripartite complex between LT, RB, and AP-2 and that the physical and functional interactions between LT and AP-2 are mediated by RB. Moreover, they define RB and c-Myc as coactivators of AP-2 in epithelial cells and shed new light on the significance of the LT-RB complex, linking it to the dedifferentiation processes occurring during tumor progression. These data confirm the important role for RB and c-Myc in the maintenance of the epithelial phenotype and reveal a novel mechanism of gene activation by c-Myc.
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Affiliation(s)
- E Batsché
- CJF INSERM 94-02, Université René Descartes, 75270 Paris cedex 06, France
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44
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Whitaker LL, Su H, Baskaran R, Knudsen ES, Wang JY. Growth suppression by an E2F-binding-defective retinoblastoma protein (RB): contribution from the RB C pocket. Mol Cell Biol 1998; 18:4032-42. [PMID: 9632788 PMCID: PMC108988 DOI: 10.1128/mcb.18.7.4032] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/1998] [Accepted: 04/22/1998] [Indexed: 02/07/2023] Open
Abstract
Growth suppression by the retinoblastoma protein (RB) is dependent on its ability to form complexes with transcription regulators. At least three distinct protein-binding activities have been identified in RB: the large A/B pocket binds E2F, the A/B pocket binds the LXCXE peptide motif, and the C pocket binds the nuclear c-Abl tyrosine kinase. Substitution of Trp for Arg 661 in the B region of RB (mutant 661) inactivates both E2F and LXCXE binding. The tumor suppression function of mutant 661 is not abolished, because this allele predisposes its carriers to retinoblastoma development with a low penetrance. In cell-based assays, 661 is shown to inhibit G1/S progression. This low-penetrance mutant also induces terminal growth arrest with reduced but detectable activity. We have constructed mutations that disrupt C pocket activity. When overproduced, the RB C-terminal fragment did not induce terminal growth arrest but could inhibit G1/S progression, and this activity was abolished by the C-pocket mutations. In full-length RB, the C-pocket mutations reduced but did not abolish RB function. Interestingly, combination of the C-pocket and 661 mutations completely abolished RB's ability to cause an increase in the percentage of cells in G1 and to induce terminal growth arrest. These results suggest that the A/B or C region can induce a prolongation of G1 through mechanisms that are independent of each other. In contrast, long-term growth arrest requires combined activities from both regions of RB. In addition, E2F and LXCXE binding are not the only mechanisms through which RB inhibits cell growth. The C pocket also contributes to RB-mediated growth suppression.
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Affiliation(s)
- L L Whitaker
- Department of Biology, Center for Molecular Genetics, and Cancer Center, University of California, San Diego, La Jolla, California 92093-0322, USA
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45
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Taagepera S, McDonald D, Loeb JE, Whitaker LL, McElroy AK, Wang JY, Hope TJ. Nuclear-cytoplasmic shuttling of C-ABL tyrosine kinase. Proc Natl Acad Sci U S A 1998; 95:7457-62. [PMID: 9636171 PMCID: PMC22649 DOI: 10.1073/pnas.95.13.7457] [Citation(s) in RCA: 244] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The ubiquitously expressed nonreceptor tyrosine kinase c-Abl contains three nuclear localization signals, however, it is found in both the nucleus and the cytoplasm of proliferating fibroblasts. A rapid and transient loss of c-Abl from the nucleus is observed upon the initial adhesion of fibroblasts onto a fibronectin matrix, suggesting the possibility of nuclear export [Lewis, J., Baskaran, R. , Taagepera, S., Schwartz, M. & Wang, J. (1996) Proc. Natl. Acad. Sci. USA 93, 15174-15179]. Here we show that the C terminus of c-Abl does indeed contain a functional nuclear export signal (NES) with the characteristic leucine-rich motif. The c-Abl NES can functionally complement an NES-defective HIV Rev protein (RevDelta3NI) and can mediate the nuclear export of glutathione-S-transferase. The c-Abl NES function is sensitive to the nuclear export inhibitor leptomycin B. Mutation of a single leucine (L1064A) in the c-Abl NES abrogates export function. The NES-mutated c-Abl, termed c-Abl NES(-), is localized exclusively to the nucleus. Treatment of cells with leptomycin B also leads to the nuclear accumulation of wild-type c-Abl protein. The c-Abl NES(-) is not lost from the nucleus when detached fibroblasts are replated onto fibronectin matrix. Taken together, these results demonstrate that c-Abl shuttles continuously between the nucleus and the cytoplasm and that the rate of nuclear import and export can be modulated by the adherence status of fibroblastic cells.
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Affiliation(s)
- S Taagepera
- Department of Biology, Center for Molecular Genetics and the Cancer Center, University of California at San Diego, La Jolla CA 92093-0322, USA
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46
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Smith KJ, Barrett TL, Smith WF, Skelton HM. A review of tumor suppressor genes in cutaneous neoplasms with emphasis on cell cycle regulators. Am J Dermatopathol 1998; 20:302-13. [PMID: 9650707 DOI: 10.1097/00000372-199806000-00015] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cells normally have five options. These include renewal or proliferation, terminal differentiation, quiescence, senescence, and apoptosis. Many factors interact with cell cycle regulators to direct the cells toward these different options. Tumor suppressor genes play a pivotal role in this process. Alterations in these genes may limit the options that cells have and thus play a significant role in the multistep process of carcinogenesis. We will focus on tumor suppressor genes and especially tumor suppressor genes that interact directly with the cell cycle proteins.
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Affiliation(s)
- K J Smith
- National Naval Medical Center, Bethesda, Maryland, USA
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47
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Watanabe G, Albanese C, Lee RJ, Reutens A, Vairo G, Henglein B, Pestell RG. Inhibition of cyclin D1 kinase activity is associated with E2F-mediated inhibition of cyclin D1 promoter activity through E2F and Sp1. Mol Cell Biol 1998; 18:3212-22. [PMID: 9584162 PMCID: PMC108903 DOI: 10.1128/mcb.18.6.3212] [Citation(s) in RCA: 133] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/1997] [Accepted: 03/06/1998] [Indexed: 02/07/2023] Open
Abstract
Coordinated interactions between cyclin-dependent kinases (Cdks), their target "pocket proteins" (the retinoblastoma protein [pRB], p107, and p130), the pocket protein binding E2F-DP complexes, and the Cdk inhibitors regulate orderly cell cycle progression. The cyclin D1 gene encodes a regulatory subunit of the Cdk holoenzymes, which phosphorylate the tumor suppressor pRB, leading to the release of free E2F-1. Overexpression of E2F-1 can induce apoptosis and may either promote or inhibit cellular proliferation, depending upon the cell type. In these studies overexpression of E2F-1 inhibited cyclin D1-dependent kinase activity, cyclin D1 protein levels, and promoter activity. The DNA binding domain, the pRB pocket binding region, and the amino-terminal Sp1 binding domain of E2F-1 were required for full repression of cyclin D1. Overexpression of pRB activated the cyclin D1 promoter, and a dominant interfering pRB mutant was defective in cyclin D1 promoter activation. Two regions of the cyclin D1 promoter were required for full E2F-1-dependent repression. The region proximal to the transcription initiation site at -127 bound Sp1, Sp3, and Sp4, and the distal region at -143 bound E2F-4-DP-1-p107. In contrast with E2F-1, E2F-4 induced cyclin D1 promoter activity. Differential regulation of the cyclin D1 promoter by E2F-1 and E2F-4 suggests that E2Fs may serve distinguishable functions during cell cycle progression. Inhibition of cyclin D1 abundance by E2F-1 may contribute to an autoregulatory feedback loop to reduce pRB phosphorylation and E2F-1 levels in the cell.
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Affiliation(s)
- G Watanabe
- Albert Einstein Cancer Center, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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48
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Abstract
Cyclin-dependent kinases play a key role in promoting and regulating the transition from G1 to S phase in all eukaryotic organisms. The kinase activities involved are distinguished from those participating in other cell cycle phase transitions in that they are driven by a class of specialised G1-specific cyclins. Although the G1 regulatory components have diverged structurally in the course of evolution, the regulatory mechanisms and principles remain highly conserved from yeast to vertebrates. An important issue that remains is that of identifying the principal targets phosphorylated by G1 cyclin-dependent kinases.
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Affiliation(s)
- S I Reed
- Department of Molecular Biology, Scripps Research Institute, La Jolla, CA 92037, USA
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49
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Raitano AB, Whang YE, Sawyers CL. Signal transduction by wild-type and leukemogenic Abl proteins. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1333:F201-16. [PMID: 9426204 DOI: 10.1016/s0304-419x(97)00023-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- A B Raitano
- Hematology-Oncology, Department of Medicine, UCLA School of Medicine, Los Angeles, CA 90095-1678, USA
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50
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Fortunato EA, Sommer MH, Yoder K, Spector DH. Identification of domains within the human cytomegalovirus major immediate-early 86-kilodalton protein and the retinoblastoma protein required for physical and functional interaction with each other. J Virol 1997; 71:8176-85. [PMID: 9343168 PMCID: PMC192274 DOI: 10.1128/jvi.71.11.8176-8185.1997] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The human cytomegalovirus major immediate-early 86-kDa protein (IE2 86) plays an important role in the trans activation and regulation of HCMV gene expression. Previously, we demonstrated that IE2 86 contains three regions (amino acids [aa] 86 to 135, 136 to 290, and 291 to 364) that can independently bind to in vitro-translated Rb when IE2 86 is produced as a glutathione S-transferase fusion protein (M. H. Sommer, A. L. Scully, and D. H. Spector, J. Virol. 68:6223-6231, 1994). In this report, we have elucidated the regions of Rb involved in binding to IE2 86 and have further analyzed the functional nature of the interaction between these two proteins. We find that two domains on Rb, the A/B pocket and the carboxy terminus, can each independently form a complex with IE2 86. In functional assays, we demonstrate that IE2 86 and another IE protein, IE1 72, can counter the enlarged flat cell phenotype, but not the G1/S block, which results from expression of wild-type Rb in the human osteosarcoma cell line Saos-2. Mutational analysis reveals that there are two domains on IE2 86 that can independently affect Rb function. One region (aa 241 to 369) includes the major Rb-binding domain, while the second maps to the amino-terminal region (aa 1 to 85) common to both IE2 86 and IE1 72. These data show that Rb and IE2 86 physically and functionally interact with each other via at least two separate domains and provide further support for the hypothesis that IE2 86 may exert its pleiotropic effects through the formation of multimeric protein complexes.
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Affiliation(s)
- E A Fortunato
- Department of Biology, University of California, San Diego, La Jolla 92093-0357, USA
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