Mechanisms governing subcellular localization and function of human RGS2

RGS proteins negatively regulate heterotrimeric G proteins at the plasma me mbrane. RGS2-GFP localizes to the nucleus, plasma membrane, and cytoplasm o f HEK293 cells. Expression of activated G(q) increased RGS2 association wit h the plasma membrane and de creased accumulation in the nucleus, suggestin g that signal-induced redistribution may regulate RGS2 function. Thus, we i dentified and characterized a conserved N-terminal domain in RGS2 that is n ecessary and sufficient for plasma membrane localization. Mutational and bi ophysical analyses indicated that this domain is an amphipathic Lu-helix th at binds vesicles containing acidic phospholipids. However, the plasma memb rane targeting function of the amphipathic helical domain did not appear to be essential for RGS2 to attenuate signaling by activated G(q). Neverthele ss, truncation mutants indicated that the N terminus is essential, potentia lly serving as a scaffold that binds receptors, signaling proteins, or nucl ear components. Indeed, the RGS2 N terminus directs nuclear accumulation of GFP. Although RGS2 possesses a nuclear targeting motif, it lacks a nuclear import signal and enters the nucleus by passive diffusion. Nuclear accumul ation of RGS2 does not limit its ability to attenuate G(q) signaling, becau se excluding RGS2 from the nucleus was without effect. RGS2 may nonetheless regulate signaling or other processes in the nucleus.