Activation of protein kinase D by signaling through Rho and the α subunit of the heterotrimeric G protein G13

Protein kinase D (PKD/PKC mu) immunoprecipitated from COS-7 cells transiently transfected with either a constitutively active mutant of Rho (RhoQ63L) or the Rho-specific guanine nucleotide exchange factor pOnco-Lbc (Lbc) exhibited a marked increase in basal activity. Addition of aluminum fluoride to cells co-transfected with PKD and wild type Gal, also induced PKD activation. Co-transfection of Clostridium botulinum C3 toxin blocked activation of PKD by RhoQ63L, Lbc, or aluminum fluoride-stimulated G alpha (13). Treatment with the protein kinase C inhibitors GF I or Ro 31-8220 prevented the increase in PKD activity induced by RhoQ63L, Lbc, or aluminum fluoride-stimulated G alpha (13). PKD activation in response to G alpha (13) signaling was also completely prevented by mutation of Ser-744 and Ser-748 to Ala in the kinase activation loop of PKD. Co-expression of C. botulinum C3 toxin and a COOH-terminal fragment of G alpha (q) that acts in a dominant-negative fashion blocked PKD activation in response to agonist stimulation of bombesin receptor. Expression of the COON-terminal region of G alpha (13) also attenuated PKD activation in response to bombesin receptor stimulation. Our results show that G alpha (13) contributes to PKD activation through a Rho- and protein kinase C-dependent signaling pathway and indicate that PKD activation is mediated by both G alpha (q) and G alpha (13) in response to bombesin receptor stimulation.