Dynamic Desensitization of Ga q Signaling and Ga q -dependent GPCR Crosstalk by GRKs.

G protein-coupled receptor (GPCR) signaling is subject to many regulatory mechanisms that occur over a range of time scales. Compared to analysis of slow, trafficking-based mechanisms relatively little attention has been paid to rapid mechanisms that take place on the seconds time scale. In our study, we utilized live cell calcium imaging to investigate the acute effects of a subfamily of GRKs, GRK2 and 3 on both Gq signaling and Gi/s-Gq crosstalk. We first focused on group 1 metabotropic glutamate receptors (mGluRs) and found that overexpression of GRK2 and 3 drives an acute desensitization of Gq-dependent signaling. This desensitization effect occurs on the seconds time scale, is rapidly reversible, and depends on direct interaction between GRK and Gq but is independent of its kinase activity. We find that this mode of rapid desensitization is generalizable across Gq-coupled GPCRs and is insensitive to the widely used GRK2/3 kinase inhibitor CMPD101. Finally, we studied whether the extent and timing of crosstalk between Gi and Gs-coupled receptors with Gq-coupled receptors is also regulated by GRK2. We find that GRK2 dramatically reduces the level of functional crosstalk and accelerated the timing of desensitization of calcium responses to Gi or Gs-coupled receptor activation. This regulatory effect of GRK on crosstalk is dependent on its interaction with both Gq and G beta gamma, but is independent of its kinase activity as well. Together this work reveals potent forms of GPCR signaling regulation with major implications across physiological contexts.