Protein kinase C phosphorylates G12 alpha and inhibits its interaction with G beta gamma.
Of nine G protein alpha subunits examined, only alpha 12 and alpha z served as substrates for phosphorylation by various isoforms of protein kinase C in vitro. A close homolog of alpha 12, alpha 12 was not phosphorylated. Exposure of NIH 3T3 cells that stably express alpha 12 to phorbol 12-myristate 13-acetate also resulted in phosphorylation of the protein. Phosphorylation in vitro occurred near the amino terminus (probably Ser38), and approximately 1 mol of phosphate was incorporated per mol of alpha 12. Although G protein heterotrimers containing either alpha 12 or a z were poor substrates for phosphorylation, the isolated alpha subunits were phosphorylated equally well in their GDP- or GTP gamma S-bound forms. The guanine nucleotide binding properties of purified alpha 12 and alpha z were unaltered by phosphorylation, as was the capacity of alpha z to inhibit type V adenylyl cyclase. However, phosphorylation of either protein greatly reduced its affinity for G protein beta gamma subunits, consistent with the newly determined crystal structure of a G protein heterotrimer. We suggest that protein kinase C regulates alpha 12- and alpha z-mediated signaling pathways by preventing their association with beta gamma.
Kozasa
T
T
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235, USA.
Gilman
A G
AG
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D018411:Spodoptera; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate