The α-subunit of the heterotrimeric G protein G13 activates a phospholipase D isozyme by a pathway requiring Rho family GTPases

G(13) belongs to the G(12) family of heterotrimeric G proteins, whose effecters are poorly defined. The present study was designed to test if phospholipase D (PLD) is regulated by G(13) and if Rho-type small GTPases are involved. Expression of the constitutively active Q226L mutant of the alpha-subunit of G(13) in COS-7 cells stimulated the activity of a rat brain phospholipase D isozyme (rPLD1) co-expressed in the cells. Wild type G alpha(13) was ineffective unless the cells were incubated with AlF4-. rPLD1 was previously shown to be activated by constitutively active V14RhoA in COS-7 cells (Park, S. K., Provost, J. J., Bae, C. D., Ho, W. T., and Exton, J. H. (1997) J. Biol. Chem. 272, 29263-29272). When the endogenous Rho proteins of the cells were inactivated by treatment with C3 exoenzyme from Clostridium botulinum, the ability of G alpha(13)Q226L to activate rPLD1 was greatly attenuated. Co-transfection of dominant negative N19RhoA and N17Rac-1, but not N17Cdc42Hs or N17Ras, also inhibited the activation. Expression of constitutively active G alpha(q) in COS-7 cells also activated rPLD1, but constitutively active forms of G alpha(i2) and G alpha(s) were without effect. These findings support an effector role for PLD in G(13) signaling and demonstrate a requirement for Rho GTPases in this response.