Heterotrimeric G proteins regulate diverse physiological processes by modulating the activities of intracellular effectors. Members of the Gα
q family link activation of G protein-coupled receptors (GPCRs) to the stimulation of phospholipase Cβ (PLCβ) and calcium mobilization. However, they differ markedly in biochemical properties as well as tissue distribution. Recent findings also showed that some of the cellular activities of Gα
q family members are independent of PLCβ activation. Novel binding partners of Gα
q subunits have also been reported. However, little is known about proteins that interact with other members of the Gα
q family, such as the hematopoietic specific Gα
16. The research aim of this study is to identify Gα
16-interacting proteins and the roles of protein complexes in Gα...[
Read more ]
Heterotrimeric G proteins regulate diverse physiological processes by modulating the activities of intracellular effectors. Members of the Gα
q family link activation of G protein-coupled receptors (GPCRs) to the stimulation of phospholipase Cβ (PLCβ) and calcium mobilization. However, they differ markedly in biochemical properties as well as tissue distribution. Recent findings also showed that some of the cellular activities of Gα
q family members are independent of PLCβ activation. Novel binding partners of Gα
q subunits have also been reported. However, little is known about proteins that interact with other members of the Gα
q family, such as the hematopoietic specific Gα
16. The research aim of this study is to identify Gα
16-interacting proteins and the roles of protein complexes in Gα
16-mediated signaling. A guanine nucleotide exchange factor, p63RhoGEF, has been shown to interact with Gα
q/11 proteins and thus provides linkage to RhoA activation. In the present study, we employed co-immunoprecipitation studies in HEK293 cells to demonstrate that p63RhoGEF can form a stable complex with the constitutively active mutant of Gα
16 (Gα
16QL). Interestingly, overexpression of p63RhoGEF inhibited Gα
16QL-induced IP
3 production in a concentration-dependent manner. The binding of PLCβ
2 to Gα
16QL could be displaced by p63RhoGEF. Similarly, p63RhoGEF inhibited the binding of tetratricopeptide repeat 1 to Gα
16QL, leading to a suppression of Gα
16QL-induced Ras activation. In the presence of p63RhoGEF, Gα
16QL-induced STAT3 phosphorylation was significantly reduced and Gα
16QL-mediated SRE transcriptional activation was attenuated. In addition, it was found that multiple regions of Gα
16 are responsible for binding with p63RhoGEF. Taken together, these results suggest that p63RhoGEF binds to activated Gα
16 and inhibits its signaling pathways. Apart from p63RhoGEF, our co-immunoprecipitation assay also suggested that Gα
16 could interact with class IA PI3Ks but not class IB PI3K. In contrast to the observation in Gα
16/p63RhoGEF complex; both Gα
16 and Gα
16QL can effectively form signaling complexes with class IA PI3Ks. Differential characteristics between Gα
16 and Gα
q were observed in terms of the selectivity of PI3K isoforms. Gα
16 bound to both p110α and p110β but not p110δ. Signaling complexes of Gα
16/p110α could be found in hematopoietic cells which endogenously express Gα
16. It was also found that overexpression of class IA PI3Ks did not affect Gα
16QL-mediated PLC activation. In addition, the immunoprecipitation assay showed that overexpression of p85/p110α or p85/p110β did not interfere with the binding with Gα
16 and PLCβ
2. Furthermore, Gα
16QL attenuated PI3K-induced Akt phosphorylation and PIP
3 level. Collectively, the present study provides evidence that Gα
16 interacts with signaling molecules other than PLCβ and modulates different signaling pathways.
Post a Comment