Subcellular Localization and Oligomerization of R7 RGS Proteins: a Potential Mechanism of Regulating GPCR Signaling

Abstract

Regulators of G‐protein signaling (RGS proteins) accelerate the GTPase activity of Gi/o family heterotrimeric G‐proteins. Our work is focused on R7 family RGS proteins, which include RGS6, 7, 9 and 11. These proteins exist as obligatory dimers with the atypical Gβ subunit, Gβ5 and are involved in regulation of sensory transduction, addiction, memory and learning, and metabolism. We previously showed that RGS7 localizes not only to the plasma membrane but also to distinct cytoplasmic puncta, both in primary neurons and transfected cells. Here we show that cytoplasmic RGS7 colocalizes with vesicles containing neurotrophic factors such as BDNF. We also used chemical crosslinking, immunoprecipiatation and mass spectrometry to identify binding partners of vesicular RGS7. This approach identified a few candidate proteins. However, our results unexpectedly showed that RGS7 exist as an oligomer ((Gβ5‐RGS7)n , where n=2 or 3) in the vesicles. When R7 binding protein (R7BP) recruits RGS7 to the plasma membrane, it causes the departure of RGS7 complex from the vesicles and dissociation of the oligomeric form. The DEP (but not RGS or DHEX) domain of RGS7 is required for oligomerization. Gβ5 is essential for RGS7 stability but not for oligomerization. We also found that RGS7 hetero‐oligomerize with RGS6 and 11 but not with RGS9. Our on‐going studies are aimed on understanding the role oligomerization and vesicular localization play in signal transduction.