Gα12 is targeted to the mitochondria and affects mitochondrial morphology and motility

G alpha 12 constitutes, along with G alpha 13, one of the four families of alpha subunits of heterotrimeric G proteins. We found that the N terminus of G alpha 12, but not those of other G alpha subunits, contains a predicted mitochondrial targeting sequence. Using confocal microscopy and cell fractionation, we demonstrated that up to 40% of endogenous G alpha 12 in human umbilical vein endothelial cells colocalize with mitochondrial markers. N-terminal sequence of G alpha 12 fused to GFP efficiently targeted the fusion protein to mitochondria. G alpha 12 with mutated mitochondrial targeting sequence was still located in mitochondria, suggesting the existence of additional mechanisms for mitochondrial localization. Lysophosphatidic acid, one of the known stimuli transduced by G alpha 12/13, inhibited mitochondrial motility, while depletion of endogenous G alpha 12 increased mitochondrial motility. G alpha 12Q229L variants uncoupled from RhoGEFs (but not fully functional activated G alpha 12Q229L) induced transformation of the mitochondrial network into punctate mitochondria and resulted in a loss of mitochondrial membrane potential. All examined G alpha 12Q229L variants reduced phosphorylation of Bcl-2 at Ser-70, while only mutants unable to bind RhoGEFs also decreased cellular levels of Bcl-2. These G alpha 12 mutants were also more efficient Hsp90 interactors. These findings are the first demonstration of a heterotrimeric G protein alpha subunit specifically targeted to mitochondria and involved in the control of mitochondrial morphology and dynamics.