Molecular genetics of the retinoblastoma suppressor gene.

The retinoblastoma gene (RB) is the prototype of a class of genes, called tumor suppressor genes, for which loss-of-function mutations are oncogenic. Such genes would then normally function to suppress or prevent tumor formation. Classical genetic and cytogenetic studies of retinoblastoma, a rare childhood eye cancer, laid a fundamental groundwork for the molecular cloning of this gene. Surprisingly, mutations of RB are found not only in retinoblastomas but also in some osteosarcomas, soft-tissue sarcomas, and carcinomas of breast, lung, prostate or bladder, suggesting a broad role for RB in human oncogenesis. In support of this hypothesis, a wild-type copy of RB is able to suppress the neoplastic properties of several types of tumor cells with mutated endogenous RB alleles. The RB gene product, pp110RB, is a nuclear phosphoprotein with DNA binding activity. RB protein is cyclically phosphorylated and dephosphorylated during the cell division cycle, and may play a significant role in its regulation.