Stimulation of phospholipase Cβ1 by Gαq promotes the assembly of stress granule proteins

During adverse conditions, mammalian cells regulate protein production by sequestering the translational machinery in membrane-less organelles known as stress granules. Here, we found that activation of the G protein subunit Gαq promoted the formation of particles that contained stress granule proteins through a mechanism linked to the presence of phospholipase Cβ1 (PLCβ1) in the cytosol. In experiments with PC12 and A10 cells, we showed that under basal conditions, cytosolic PLCβ1 bound to stress granule associated proteins, including PABPC1, eIF5A, and Ago2. Knockdown of cytosolic PLCβ1 with siRNA or promoting its relocalization to the plasma membrane by activating Gαq resulted in the formation of particles containing the stress granule markers, PABPC1, G3BP1, and Ago2. Our studies showed that the composition of these particles resemble those formed under osmotic stress and are distinct from those formed by other stresses. Our results fit a simple thermodynamic model in which cytosolic PLCβ1 solubilizes stress granule proteins such that its movement to activated Gαq releases these particles to enable the formation of stress granules. Together, our data are suggestive of a link between Gαq-coupled signals and protein translation through stress granule formation.