G protein βγ translocation to the Golgi activates the mitogen‐activated protein kinases via phosphoinositide 3‐kinase γ

The activation of G protein‐coupled receptors (GPCRs) induces the translocation of G protein βγ complex from the plasma membrane (PM). However, its functions are not well known. Here we demonstrated that among the entire twelve Gγ family members, Gγ9 is the most translocatable Gγ subunit. More than 80% of Gγ9, in complex with Gβ1, relocated from the PM to the Golgi in response to CXCR4 activation by stromal cell‐derived factor 1α (SDF1α) and the half time of the translocation was about 5 seconds. To study the function of Gβγ translocation to the Golgi, we focused on the activation of the mitogen‐activated protein kinases (MAPK) ERK1/2. CRISPR‐Cas9‐mediated knockout of Gγ9 abolished ERK1/2 activation by SDF1α, whereas knockout of the least‐translocatable Gγ3 had no effect. To investigate if Gβγ‐mediated ERK1/2 activation indeed occurred on the Golgi, we employed an inducible system to specifically express Gβγ onto the Golgi. Interestingly, the targeted expression of Gγ2, Gγ3 and Gγ9, in complex with Gβ1, onto the Golgi each induced remarkable ERK1/2 activation. Such constitutive ERK1/2 activation was blocked by the expression of Gα subunits, the targeted expression of the Gβγ blocker GRK2ct at the Golgi, and chemical treatments to disrupt the Golgi structure. By contrast, the expression of individual Gγ subunits at the PM did not activate ERK1/2. To define the downstream effectors of Gβγ, we determined the effect of selective pharmacological inhibition of phosphoinositide 3‐kinase (PI3K), phospholipase C, PKC and PKD on ERK1/2 activation. This strategy identified PI3Kγ and PI3Kδ to be essential for Gβγ‐mediated ERK1/2 activation. Indeed, knockout of PI3Kγ by CRISPR‐Cas9 almost abolished ERK1/2 activation induced by both SDF1α and Gγ9 targeting to the Golgi. Similar to CXCR4, α 2 ‐adrenergic receptor‐mediated ERK1/2 activation was also dramatically inhibited by Gγ9 and PI3Kγ knockout. We further showed that knockout of Gγ9 and PI3Kγ markedly suppressed the migration and invasion of prostate cancer PC3 cells in response to SDF1α stimulation in vitro. Gγ9 and PI3Kγ knockout also significantly reduced the bone metastasis of PC3 tumors following intra‐cardiac injection of PC3‐Luc cells in athymic nude mice. Overall, our data demonstrate a novel function for Gβγ translocation to the Golgi to spatiotemporally control the activation of the MAPK pathway by GPCRs and tumor progression. Support or Funding Information NIH R01 GM118915