Functional Interactions between the hBRM/hBRG1 Transcriptional Activators and the pRB Family of Proteins

Abstract

hBRG1 and hBRM are mammalian homologs of the SNF2/SWI2 yeast transcriptional activator. These proteins exist in a large multisubunit complex that likely serves to remodel chromatin and, in so doing, facilitates the function of specific transcription factors. The retinoblastoma protein (pRB) inhibits cell cycle progression by repressing transcription of specific growth-related genes. Using the yeast two-hybrid system, we demonstrate that the members of the hBRG1/hBRM family of proteins interact with the pRB family of proteins, which includes pRB, p107, and p130. Interaction between the hBRG1/hBRM family with the pRB family likely influences cellular proliferation, as both hBRG1 and hBRM, but not mutants of these proteins unable to bind to pRB family members, inhibit the formation of drug-resistant colonies when transfected into the SW13 human adenocarcinoma cell line, which lacks endogenous hBRG1 or hBRM. Further, hBRM and two isoforms of hBRG1 induce the formation of flat, growth-arrested cells in a pRB family-dependent manner when introduced into SW13 cells. This flat-cell-inducing activity is severely reduced by cotransfection of the wild-type E1A protein and variably reduced by the cotransfection of mutants of E1A that lack the ability to bind to some or all members of the pRB family.