A novel role for Gβγ in mitotic Golgi fragmentation

Abstract

Heterotrimeric G proteins (αβγ) function at the cytoplasmic surface of cell's plasma membrane and act as molecular switches to transduce extracellular signals and generate cellular responses. However, recent studies point out to evidence that G proteins play non-canonical roles at unique intracellular locations. Previous work in our lab and others has established that Gβγ regulates a signaling pathway on the cytoplasmic surface of Golgi membranes that controls the Golgi exit, i.e., generation, of transport vesicles of select protein cargo destined for the plasma membrane. This study is focused on understanding intracellular G protein signaling by identifying a role for Gβγ in Golgi fragmentation and identifying mechanisms and subcellular sites of regulation. We used siRNA-mediated knockdown to deplete Gβγ in cells, and established that Gβγ is required for mitotic fragmentation of the Golgi. We demonstrate that Gβγ acts upstream of protein kinase D in the signaling pathway and regulates the phosphorylation of Golgi structural protein Grasp55 to regulate Golgi fragmentation occurring during mitosis. Our results show that knockdown of Gβγ results in delayed entry to mitosis and also delayed mitotic progression. These results implicate a novel role for Gβγ in regulating mitotic Golgi fragmentation and cell cycle progression.