title: Ca2+/calmodulin-dependent protein kinase II regulates Tiam1 by reversible protein phosphorylation.
abstract: A number of guanine nucleotide exchange factors have been identified that activate Rho family GTPases, by promoting the binding of GTP to these proteins. We have recently demonstrated that lysophosphatidic acid and several other agonists stimulate phosphorylation of the Rac1-specific exchange factor Tiam1 in Swiss 3T3 fibroblasts, and that protein kinase C is involved in Tiam1 phosphorylation (Fleming, I. N., Elliott, C. M., Collard, J. G., and Exton, J. H. (1997) J. Biol. Chem. 272, 33105-33110). We now show, through manipulation of intracellular [Ca2+] and the use of protein kinase inhibitors, that both protein kinase Calpha and Ca2+/calmodulin-dependent protein kinase II are involved in the phosphorylation of Tiam1 in vivo. Furthermore, we show that Ca2+/calmodulin-dependent protein kinase II phosphorylates Tiam1 in vitro, producing an electrophoretic retardation on SDS-polyacrylamide gel electrophoresis. Significantly, phosphorylation of Tiam1 by Ca2+/calmodulin-dependent protein kinase II, but not by protein kinase C, enhanced its nucleotide exchange activity toward Rac1, by approximately 2-fold. Furthermore, Tiam1 was preferentially dephosphorylated by protein phosphatase 1 in vitro, and treatment with this phosphatase abolished the Ca2+/calmodulin-dependent protein kinase II activation of Tiam1. These data demonstrate that protein kinase Calpha and Ca2+/calmodulin-dependent protein kinase II phosphorylate Tiam1 in vivo, and that the latter kinase plays a key role in regulating the activity of this exchange factor in vitro.
authors.affiliation: Howard Hughes Medical Institute and the Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0295, USA.
authors.forename: I N
authors.initials: IN
authors.lastname: Fleming
authors.forename: C M
authors.initials: CM
authors.lastname: Elliott
authors.forename: F G
authors.initials: FG
authors.lastname: Buchanan
authors.forename: C P
authors.initials: CP
authors.lastname: Downes
authors.forename: J H
authors.initials: JH
authors.lastname: Exton
mesh_terms: D016475:3T3 Cells; D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D054645:Protein Phosphatase 1; D011506:Proteins / Q000378:metabolism*; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D007527:Isoenzymes; D011506:Proteins; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513260:Tiam1 protein, mouse; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D011493:Protein Kinase C; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1