BIOCHEMICAL ROLE OF THE P53 GENE PRODUCT IN HUMAN CANCER

p53肿瘤抑制基因产物的突变失活是最重要的

Mutational inactivation of the p53 tumor suppressor gene product is the most common genetic aberration identified in human cancer to date. Understanding the biochemical role of p53 in negative growth control could potentially lead to the identification of new biomarkers for early detection of human cancer as well as of the development of novel drug therapy. A majority (greater than 95%) of the missense point mutations identified in the p53 gene are clustered within a conserved region of p53 located between amino acids 115 and 300 that is designated the conformational domain. Mutations within this domain could conceivably disrupt the normal binding of proteins that mediate and/or regulate the tumor suppressor activity of p53. In support of this hypothesis, the SV40 DNA tumor virus transforming protein, large T-antigen, binds to the conformational domain of p53 and induces a conformational change that stabilizes the protein. The conformational change also results in loss of binding of T-antigen to p53. Missense mutations in the conformational domain also result in a similar conformational change and stabilization of p53. The interaction of p53 with a cellular homologue or homologue(s) of SV40 large T-antigen within the conformational domain thus may be disrupted by missense mutations. The putative protein or proteins that interact within the conformational domain of p53 must be identified to begin to elucidate its biochemical function. Using excess quantities of a p53 chimeric protein (p53[115-300]) to probe lung cancer cell lysates, we have been able to isolate several proteins that specifically bind to the wild-type p53 sequence between amino acids 115 to 300. Two mutant p53 chimeric proteins exhibited significantly reduced binding to these proteins. The specific aims of this proposal are directed toward the goal of characterizing, identifying, and determining the relevance of these proteins with respect to p53 function both in vitro and in vivo. It is anticipated that such studies will provide further insight into the biochemical mechanism and regulation of the tumor suppressor function of p53. In addition, other genetic alterations affecting expression of regulatory proteins that interact within the conformational domain of p53 might play a role in the pathogenesis of the other approximately 50% of human tumors that express normal p53.