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NCI CANCERLIT^® Search: Retinoblastoma Gene (RB) - July 2002

Imprima English

National Cancer Institute^®
Ultima Vez Modificado: 1 de julio del 2002

Altered expression of the cell cycle regulatory molecules pRb, p53 and MDM2 exert a synergetic effect on tumor growth and chromosomal
Sequential extension of proliferative lifespan in human fibroblasts induced by over-expression of CDK4 or 6 and loss of p53 function.

Table of Contents

1
UI - 10965496
AU - Gorgoulis VG; Zacharatos P; Kotsinas A; Mariatos G; Liloglou T; Vogiatzi
TI - T; Foukas P; Rassidakis G; Garinis G; Ioannides T; Zoumpourlis V; Bramis J; Michail PO; Asimacopoulos PJ; Field JK; Kittas C Altered expression of the cell cycle regulatory molecules pRb, p53 and MDM2 exert a synergetic effect on tumor growth and chromosomal instability in non-small cell lung carcinomas (NSCLCs).
SO - Mol Med 2000 Mar;6(3):208-37
AD - Department of Histology and Embryology, Medical School, University of Athens, Greece.
BACKGROUND: Recent in vitro studies provide evidence that the cell cycle molecules pRb, p53 and MDM2 form a tightly regulated protein network. In this study, we examined the relationship of this protein network in a series of non-small cell lung carcinomas (NSCLCs), with the kinetic parameters, including proliferative activity or proliferation index (PI) and apoptotic index (AI), and ploidy status of the tumors. MATERIAL AND METHODS: A total of 87 NSCLCs were examined using immunohistochemical and molecular methods in order to estimate the status of the pRb-p53-MDM2 network. The kinetic parameters and the ploidy status of the tumors were assessed by in situ assays. The possible associations between alterations of the network, kinetic parameters and ploidy status of the carcinomas were assessed with a series of statistical methods. RESULTS: Aberrant expression of pRb (Ab) and overexpression of p53 (P) and MDM2 (P) proteins were observed in 39%, 57%, and 68% of the carcinomas, respectively. The comprehensive analysis revealed that concurrent alterations in all three cell cycle regulatory molecules were the most frequent pattern, pRb(Ab)/p53(P)/MDM2(P); this "full abnormal" phenotype represented approximately 27% of the cases. This immunoprofile obtained the highest PI/AI value; whereas, the "normal" phenotype was the lowest one (p = 0.004). Furthermore, the pattern pRb(Ab)/p53(P)/MDM2(P) acquired the highest PI (p < 0.001) and lowest AI (p < 0.001) scores. Interestingly, the groups of carcinomas with impaired expression of one or two molecules attained PI/AI ratio values clustered in a narrow range placed in the middle of the scores exhibited by the "normal" and "full abnormal" phenotypes. These tumors had significantly lower AI, but similar PI values, compared with those noticed in the normal pattern. In addition, it was observed that the pRb(Ab)/p53(P)/MDM2(P) phenotype was also significantly associated with aneuploidy (p = 0.002) and a tendency was observed when the expression of two components was altered (p = 0.055). CONCLUSIONS: Our findings suggest that simultaneous deregulation of all members of the pRb-p53-MDM2 network confers an additive effect on tumor growth. The apoptotic pathway seems to be more susceptible to its defects than the cell proliferation machinery. The findings of the ploidy analysis, which are in parallel with those regarding the proliferative activity and the apoptotic rate study, further support the concept that these molecules constitute a tightly regulated network participating in cell cycle control and chromosomal stability.

2
UI - 12082615
AU - Morris M; Hepburn P; Wynford-Thomas D
TI - Sequential extension of proliferative lifespan in human fibroblasts induced by over-expression of CDK4 or 6 and loss of p53 function.
SO - Oncogene 2002 Jun 20;21(27):4277-88
AD - Cancer Research Campaign Laboratories, Department of Pathology, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XN, UK.
Replicative senescence is thought to be a significant barrier to human tumorigenesis, which in human fibroblasts, and many other cell types, can be overcome experimentally by combined loss of function of p53 and Rb 'pathways'. To avoid the confounding pleiotropic effects of HPVE7 frequently used in such studies, here we have employed retroviral vectors over-expressing CDK4 or CDK6 as a more representative model of naturally-occurring mutations targeting the Rb pathway. We show that these can extend fibroblast lifespan by approximately 10 population doublings, ending in a viable senescence-like state which contrasts with the apoptotic end-stage seen with E7. Compared with 'normal' senescence, this growth arrest was, in most cases, not accompanied by any further increase in p21(Waf1) levels but with up to a 19-fold increase in p16(Ink4a). Surprisingly however, this could not explain arrest, since expression of mutant CDK4 and/or CDK6, incapable of binding p16(Ink4a), did not confer any greater lifespan extension than the wild-type CDKs. Subsequent abrogation of p53 function by a second vector, encoding HPVE6, downregulated p21(Waf1) and conferred a second lifespan extension, ending in a crisis-like state, consistent with full escape from senescence. These data: (i) point to a back-up 'senescence' mechanism distinct from induction of p21(Waf1) or p16(Ink4a); and (ii) provide an in vitro model of clonal evolution through successive dysfunction of Rb and p53 pathways in a relevant human cell context.

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