G3BP1 is a SWI/SNF-bound regulator of transcription that modulates activation of STATs.

RAS GTPase-activating protein-binding protein 1 (G3BP1) is a component of the RAS signaling pathway and a phosphorylation-dependent RNA/DNA endoribonuclease that links signal transduction and RNA metabolism. We identified G3BP1 as a nuclear interactor of platelet-derived growth factor receptor-β, forming a complex with BAF155, a component of the SWI/SNF chromatin remodeling complex, as well as with the transcription factor STAT3. Depletion of G3BP1 in human primary fibroblasts AG1523 reduced PDGF-BB-induced activation of STAT3 while increasing mRNA levels of FOS, MYC, and CCND1, which encode proteins involved in growth stimulation. Both STAT1 and cyclin D1 mRNA and protein levels were elevated upon G3BP1 knockdown, identifying G3BP1 as a negative regulator of STAT1 and cyclin D1 expression. G3BP1 depletion did not abolish PDGF-BB-induced proliferation of human primary fibroblasts. Thus, G3BP1 interacts with the SWI/SNF chromatin remodeling complex in the nucleus and regulates cell growth pathways by modulating STAT signaling and transcription of growth-associated genes.