Identification of novel interacting proteins, structural features and signaling activities of human RGS6

Mammalian RGS proteins comprise a newly discovered protein family encoded by more than 20 genes, and each characterized by a hallmark RGS domain. Biochemical studies indicate that RGS proteins possess GAP activities towards certain Galpha subunits, thereby negatively regulate heterotrimeric G protein signaling. However little is known about the in vivo functions of RGS proteins in mammalian systems.; Human RGS6 is a member of a subfamily of RGS proteins that possess a DEP and a GGL domain. We have identified 36 distinct transcripts of RGS6 that arise by unusually complex processing of the RGS6 gene.; We revealed that RGS6 variants with complete GGL domains interacted with Gbeta5, while those lacking a complete GGL domain did not. Ectopic expression of certain RGS6 variant in cancer cells promoted cell death in caspase-dependent and -independent pathways. RGS6 expression in U2OS cells induced cell cycle arrest followed by apoptosis.; We identified two proteins interacting with RGS6, SCG10 and DMAP1. SCG10 is a neuronal growth-associated protein. Expression of SCG10-interacting forms of RGS6 with SCG10 resulted in co-localization of both proteins. RGS6 potentiated the ability of SCG10 to disrupt microtubule organization. Furthermore, expression of SCG10 and RGS6 each enhanced NGF-induced PC12 cell differentiation, and co-expression of SCG10 with RGS6 produced synergistic effects on NGF-induced PC12 differentiation. These effects of RGS6 on microtubules and neuronal differentiation were observed only with RGS6 proteins with complete GGL domains.; DMAP1 is a component of the Dnmt1 complex involved in repression of newly replicated genes. The domains of DMAP1:RGS6 interaction were mapped to the N-terminal region of the GGL domain of RGS6 and the C-terminal domain of DMAP1. RGS6L and RGS6S, but not a RGS6L deletion mutant lacking a DMAP1 binding module, co-immunoprecipitate DMAP1 and Dnmt1, the latter in a DMAP1-dependent manner. A recombinant GGL domain of RGS6 precipitated endogenous DMAP1 and Dnmt1. Co-expression of DMAP1 with RGS6L promoted nuclear migration of RGS6L and its co-localization with DMAP1. RGS6 inhibited the transcriptional repressor activity of DMAP1. RGS6 is the first member of the RGS protein family shown to interact with proteins involved in transcriptional regulation.