Activation of G alpha q sequesters specific transcripts into Ago2 particles

The G alpha q/phospholipase C beta 1 (PLC beta 1) signaling system mediates calcium responses from hormones and neurotransmitters. While PLC beta 1 functions on the plasma membrane, there is an atypical cytosolic population that binds Argonaute 2 (Ago2) and other proteins associated with stress granules preventing their aggregation. Activation of G alpha q relocalizes cytosolic PLC beta 1 to the membrane, releasing bound proteins, promoting the formation of stress granules. Here, we have characterized Ago2 stress granules associated with G alpha q activation in differentiated PC12 cells, which have a robust G alpha q/PLC beta 1 signaling system. Characterization of Ago2-associated stress granules shows shifts in protein composition when cells are stimulated with a G alpha q agonist, or subjected to heat shock or osmotic stress, consistent with the idea that different stresses result in unique stress granules. Purified Ago2 stress granules from control cells do not contain RNA, while those from heat shock contain many different mRNAs and miRs. Surprisingly, Ago2 particles from cells where G alpha q was stimulated show only two transcripts, chromogranin B, which is involved in secretory function, and ATP synthase 5f1b, which is required for ATP synthesis. RT-PCR, western blotting and other studies support the idea that G alpha q-activation protects these transcripts. Taken together, these studies show a novel pathway where G alpha q/PLC beta regulates the translation of specific proteins.