Involvement of protein tyrosine phosphatases in activation of the trimeric G protein Gq/11

Abstract

A variety of receptors coupled to the heterotrimeric guanine nucleotide-binding protein G q/11 stimulate intracellular Ca 2+ release through inositol (1,4,5)-trisphosphate (IP 3 ) formation. We previously reported that tyrosine phosphorylation of the a subunit of the G q/11 protein by protein tyrosine kinases (PTKs) regulates the activation of G q/11 protein. Here we show that protein tyrosine phosphatases (PTPs) are also essential for G q/11 protein activation. We ®nd that G q/11 protein-coupled receptor-mediated formation of IP 3 is blocked by PTP inhibitors as well as PTK inhibitors. These inhibitors act prior to G q/11 protein activation. Tyrosine phosphorylation of the a subunit of G q/11 appears to inhibit its interaction with receptors. Thus, PTP is required for controlling the level of tyrosine phosphorylation of the a subunit of G q/11 to promote its interaction with receptors. Therefore, we conclude that PTKs and PTPs co-operate to proceed activation cycle of the G q/11 protein through tyrosine phosphorylation and de-phosphorylation of the a subunit of G q/11 .

Pasteurella multocida Toxin Facilitates Inositol Phosphate Formation by Bombesin through Tyrosine Phosphorylation of Gαq

“…C1165S to promote tyrosine phosphorylation of G␣ q without leading to its activation conflicts with the model proposed by Umemori et al (13) suggesting that tyrosine phosphorylation occurred downstream of GTP binding. We decided to investigate whether phosphorylation of G␣ q was required for activation of phospholipase C. Cultures of Swiss 3T3 cells were treated with the broad spectrum tyrosine kinase inhibitor genistein to block phosphorylation of G␣ q .…”

“…Several neuropeptides that regulate cell growth and differentiation induce tyrosine phosphorylation of G␣ q . Recent studies have indicated that G␣ q phosphorylation forms part of a novel cycle in which tyrosine kinases and phosphatases regulate G q activation (11)(12)(13). The aim of the present study was to further investigate the role of phosphorylation using PMT.…”

“…Subsequent studies by Umemori et al (12,13) have further investigated the role of G q tyrosine phosphorylation in regulating G protein activity. These authors demonstrated that G q was phosphorylated upon ligand activation.…”

“…Src family kinases (subsequently referred to as Src kinases) have been postulated to be possible regulators of this process (11)(12)(13). To clarify the role of Src kinases, we utilized the recently described Src/Yes/Fyn-deficient (SYF Ϫ/Ϫ ) cell line (23).…”

“…Interestingly, phosphorylation of G␣ q increased its ability to activate phospholipase C␤ in an in vitro model, suggesting that phosphorylation may modulate the activity of the G protein in vivo (11). Modulation of G␣ q phosphorylation using chemical inhibitors of tyrosine kinases or tyrosine phosphatases had a profound effect on the production of inositol trisphosphates (IP 3 ) in vivo (12,13). Furthermore, transient expression of a dominant active mutant of the Fyn tyrosine kinase elevated the phosphorylation of G␣ q but blocked receptor-stimulated IP 3 production (12).…”