Regulation of Constitutive Cargo Transport from the trans-Golgi Network to Plasma Membrane by Golgi-localized G Protein βγ Subunits

Observations of Golgi fragmentation upon introduction of G protein beta gamma (G beta gamma) subunits into cells have implicated G beta gamma in a pathway controlling the fission at the trans-Golgi network (TGN) of plasma membrane (PM)-destined transport carriers. However, the subcellular location where G beta gamma acts to provoke Golgi fragmentation is not known. Additionally, a role for G beta gamma in regulating TGN-to-PM transport has not been demonstrated. Here we report that constitutive or inducible targeting of G beta gamma to the Golgi, but not other subcellular locations, causes phospholipase C- and protein kinase D-dependent vesiculation of the Golgi in HeLa cells; Golgi-targeted beta(1)gamma(2) also activates protein kinase D. Moreover, the novel G beta gamma inhibitor, gallein, and the G beta gamma-sequestering protein, GRK2ct, reveal that G beta gamma is required for the constitutive PM transport of two model cargo proteins, VSV-G and ss-HRP. Importantly, Golgi-targeted GRK2ct, but not a PM-targeted GRK2ct, also blocks protein transport to the PM. To further support a role for Golgi-localized G beta gamma, endogenous G beta was detected at the Golgi in HeLa cells. These results are the first to establish a role for Golgi-localized G beta gamma in regulating protein transport from the TGN to the cell surface.