The effects ofRB2/p130 on tumorigenesis

The retinoblastoma family of proteins, pRb/p105, p107 and pRb2/p130, are defined by their structural and functional homology to the patriarch of the family, Rb/p105, the prototypic tumor suppressor gene. Precise characterization of the proteins has revealed that even though the proteins may be able to functionally complement each another, they are not fully functionally redundant. The focus of the research presented herein has been the functional characterization of the putative tumor suppressor gene pRb2/p130 and its possible link to human cancer. Immunohistochemical studies were performed which demonstrated that lack of pRb2/p130 expression was an independent prognostic indicator that inversely correlated with the aggressiveness of human lung and endometrial cancers and could be used to identify patients at a five fold increased risk of dying from the disease. pRb2/p130 has been shown to be the target of several DNA tumor viruses that functionally inactivate the entire Rb-family to elicit neoplastic transformation. Evidence supporting the application of such a scenario to the development and/or progression of human cancer has been shown for mesothelioma. Furthermore, mutations have been detected in the RB2/p130 gene by southern blot analysis, SSCP and direct sequencing in human tumor cell lines and primary tumors. The cell cycle regulatory role and growth suppressive function of pRb2/p130 on tumor growth has been demonstrated in vitro and in vivo by development of an inducible expression system and by viral-mediated gene transfer. Additionally, the molecular mechanisms involved in the biological activity of pRb2/p130 have been examined. In conclusion, the putative tumor suppressor gene pRb2/p130 fulfills the definition of a tumor suppressor gene in that its expression is growth suppressive to tumor formation and the gene is found mutated in primary tumors. The direct role of pRb2/p130 in regulating the functional activity of the cell cycle machinery provides an additional link between neoplastic transformation and disruptions in the cell cycle machinery