p53 Gene status and expression of p53, mdm2, and p21Waf1/Cip1 proteins in colorectal cancer

Abstract 

Abrogation of the normal p53 pathway is the most common molecular alteration in human cancer. p53 Gene status can be potentially assessed through the expression of proteins known to be activated by the wild-type p53 (wt p53) system, such as mdm2 and p21Waf1/Cip1. In this study, the frequency of mdm2, p21Waf1/Cip1, and p53 protein expression was investigated using immunohistochemistry (IHC) in 88 colorectal carcinomas (CRCs). The relationship between these expressions and p53 status was examined. p53 status and the immunophenotypes characterizing these tumors were correlated with standard prognostic variables. Mutation of p53 was detected using single-strand conformational polymorphism (SSCP) analysis and sequencing. Concordance between p53 gene status and p53 immunoreactivity was seen in 62 of 88 (70.45%) carcinomas. Mdm2 expression was found in 22 of 45 (48.88%) and 5 of 43 (11.62%) of the tumors with wt p53 and mutated p53 (P<0.0001), respectively. Predominantly, higher p21Waf1/Cip1 expression was associated with wt p53 (P<0.001). All wt p53 cases that expressed mdm2 also expressed p21Waf1/Cip1. These results suggest that there is a subgroup of CRCs in which p53 is functionally active, inducing transcription of mdm2 and Waf1/Cip1. Their combined evaluation may provide important clues for planning adjuvant systemic therapy and gene therapy based on the restitution of p53 function. However, no significant association was found between the immunophenotypes and the standard prognostic variables investigated.