Functional analysis of regulatory mechanism of G protein signal network

点击翻译按钮获取中文摘要

G proteins are composed of a, p, and y subunits, and transmit a variety of signals from G protein-coupled receptors (GPCRs) to intracellular effectors by acting as molecular switch. We demonstrated that the GPCR signaling through Gq and JNK negatively regulates the neural progenitor cell migration. Moreover, we found that Ric-8 and flotillins are a new type of Gq-binding regulatory proteins. Ric-8A promoted the guanine nucleotide exchange of Gαq, and amplified the Gq-mediated cellular responses, such as intracellular Ca mobilization and JNK activation. It was revealed that Ric-8A translocates from cytosol to membrane upon receptor stimulation. The knockdown of flotillins, which are known to be lipid raft maker proteins, by siRNA attenuated the GPCR-induced p38 MAPK activation and tyrosine phosphorylation. Treatment with Src tyrosine kinase inhibitors and cholesterol depleting agent methyl-beta-cyclodextrin also inhibited the GPCR-induced p38 MAPK activation and tyrosine phosphorylation. These lines of evidence suggested that a Gq-coupled receptor activates p38 MAPK through lipid rafts and Src, in which flotillins positively regulates the Gq signaling. Previously, we demonstrated that FRG, a novel RhoGEF for Cdc42, is activated downstream of Gq-coupled receptor. In this research, we found that FRG functions in the signaling pathway downstream CD47 and Src and is involved in the development of axons and dendrites in hippocampal neurons. Another RhoGEF P-Rex1 is activated by G protein βγ subunit and essential for reactive oxygen species (ROS) production in neutrophils. We found that intramolecular domain interaction of P-Rex1 is critical for Gβγ-induced activation and PKA-induced inhibition.