Stimulation of Gαq Promotes Stress Granule Formation

Abstract

During adverse environmental conditions, mammalian cells regulate protein production by sequestering the translation machinery in membraneless organelles (i.e. stress granules) whose formation is carefully regulated. In this study, we show a direct connection between G protein signaling and stress granule formation through phospholipase Cβ (PLCβ). In cells, PLCβ localizes to both the cytoplasm and plasma membrane. We find that a major population of cytosolic PLCβ binds to stress granule proteins; specifically, eIF5A and Ago2, whose RNA-induced silencing activity is halted under stress. PLCβ1 is activated by Gαq in response to hormones and neurotransmitters and we find that activation of Gαq shifts the cytosolic population of PLCβ1 to the plasma membrane, releasing stress granule proteins. This release is accompanied by the formation of intracellular particles containing stress granule markers, an increase in the size and number of particles, and a shift of cytosolic RNAs to larger sizes consistent with cessation of transcription. Arrest of protein synthesis is seen when the cytosolic level of PLCβ1 is lowered by siRNA or by osmotic stress, but not cold, heat or oxidative stress causes similar behavior. Our results fit a simple thermodynamic model in which eIF5a and its associated proteins partition into particles after release from PLCβ1 due to Gαq stimulation. Taken together, our studies show a link between Gαq-coupled signals and transcription through stress granule formation.