Regulation of PKD1-mediated Golgi to cell surface trafficking by Gαq subunits

Background Information Heterotrimeric GTP‐binding proteins play a key role in cell trafficking regulation. Above all, specific Gβγ subunits have been shown to be a major component of a signal transduction pathway, which also involves phospholipases C (PLC), protein kinases C (PKC) and D (PKD), whose main function is to regulate transport between Golgi and plasma membrane. It was the involvement of PLC which led us to study the role of the other member of this G protein family, the α subunits, in the regulation of membrane fission at the Golgi apparatus. Results Among constitutive active (QL) variants of different G protein α subunit sub‐families, only GαqQL subunits were able to induce Golgi fragmentation, a phenotype that mainly reflects a membrane fission increase at this organelle. This phenotype was not observed with a GαqQL palmitoylation mutant, showing the need for a membrane‐bounded subunit. Besides, GαqQL‐dependent Golgi fission was blocked by specific PLC and PKC inhibitors, and in the presence of a PKD1‐kinase dead variant. In addition, GαqQL was the only α subunit capable of inducing PKD1 phosphorylation. Finally, Vesicular Stomatitis Virus thermosensitive mutant glycoprotein (VSVG tsO45) transport assays have demonstrated that GαqQL acts directly on Golgi membranes to regulate trafficking between this organelle and plasma membrane. Conclusions All these results indicate Gαq subunits for the first time as a regulator of PKD‐mediated intracellular trafficking between Golgi apparatus and plasma membrane, opening new perspectives in the understanding of internal trafficking regulation by external signals through G protein‐coupled receptors. Research article This manuscript describes for the first time the role of a specific Gαq subunit as an activator of a PKD1‐mediated signalling pathway that regulates vesicle transport between Golgi apparatus and plasma membrane. These observations are meant to be of great significance for the scientific community, since they would help to narrow the quest for the G‐protein‐coupled receptors involved in the regulation of PKD1‐dependent Golgi to plasma membrane vesicle trafficking.