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)

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Abstract
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. 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. 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). 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.