Effects of mutations in pleckstrin homology domain on beta-adrenergic receptor kinase activity in intact cells

Pleckstrin homology domain of G protein-coupled receptor kinase-2 binds to PKC and affects the activity of PKC kinase

AIM: To study the detail mechanism of interaction between PKC and GRK₂ and the effect of GRK₂ on activity of PKC.

METHODS: The cDNA of pleckstrin homology (PH) domain located in GRK₂ residue 548 to 660 was amplified by PCR with the mRNA of human GRK₂ (β1-adrenergic receptor kinase) as template isolated from human fresh placenta, the expression vector pGEX-PH inserted with the aboved cDNA sequence for GRK₂ PH domain protein and the expression vectors for GST (glutathion-s-transferase) -GRK₂ PH domain fusion protein, BTK (Bruton’s tyrosine kinase) PH domain and GST protein were constructed. The expression of GRK₂ in culture mammalian cells (6 cell lines: PC-3, MDCK, SGC7901, Jurkat cell etc.) was determined by SDS-PAGE and Co-immunoprecipitation. The binding of GRK₂ PH domain, GST-GRK₂ PH domain fusion protein and BTK PH domain to PKC in vitro were detected by SDS-PAGE and Western blot, upon prolonged stimulation of epinephrine, the binding of GRK₂ to PKC was also detected by western blot and Co-immunoprecipitation.

RESULTS: The binding of GRK₂ PH domain to PKC in vitro was confirmed by western blot, as were the binding upon prolonged stimulation of epinephrine and the binding of BTK PH domain to PKC. In the present study, GRK₂ PH domain was associated with PKC and down-regulated PKC activity, but Btk PH domain up-regulated PKC activity as compared with GRK₂ PH domain.

CONCLUSION: GRK₂ can bind with PKC and down-regulated PKC activity.

New thoughts on the role of the beta-gamma subunit in G-protein signal transduction

Heterotrimeric G proteins are involved in numerous biological processes, where they mediate signal transduction from agonist-bound G-protein-coupled receptors to a variety of intracellular effector molecules and ion channels. G proteins consist of two signaling moieties: a GTP-bound alpha subunit and a beta-gamma heterodimer. The beta-gamma dimer, recently credited as a significant modulator of G-protein-mediated cellular responses, is postulated to be a major determinant of signaling fidelity between G-protein-coupled receptors and downstream effectors. In this review we have focused on the role of beta-gamma signaling and have included examples to demonstrate the heterogeneity in the heterodimer composition and its implications in signaling fidelity. We also present an overview of some of the effectors regulated by beta-gamma and draw attention to the fact that, although G proteins and their associated receptors play an instrumental role in development, there is rather limited information on beta-gamma signaling in embryogenesis.