Phosphorylation of beta-catenin by PKA promotes ATP-induced proliferation of vascular smooth muscle cells.
Extracellular ATP stimulates proliferation of vascular smooth muscle cells (VSMC) through activation of G protein-coupled P2Y purinergic receptors. We have previously shown that ATP stimulates a transient activation of protein kinase A (PKA), which, together with the established mitogenic signaling of purinergic receptors, promotes proliferation of VSMC (Hogarth DK, Sandbo N, Taurin S, Kolenko V, Miano JM, Dulin NO. Am J Physiol Cell Physiol 287: C449-C456, 2004). We also have shown that PKA can phosphorylate beta-catenin at two novel sites (Ser552 and Ser675) in vitro and in overexpression cell models (Taurin S, Sandbo N, Qin Y, Browning D, Dulin NO. J Biol Chem 281: 9971-9976, 2006). beta-Catenin promotes cell proliferation by activation of a family of T-cell factor (TCF) transcription factors, which drive the transcription of genes implicated in cell cycle progression including cyclin D1. In the present study, using the phosphospecific antibodies against phospho-Ser552 or phospho-Ser675 sites of beta-catenin, we show that ATP can stimulate PKA-dependent phosphorylation of endogenous beta-catenin at both of these sites without affecting its expression levels in VSMC. This translates to a PKA-dependent stimulation of TCF transcriptional activity through an increased association of phosphorylated (by PKA) beta-catenin with TCF-4. Using the PKA inhibitor PKI or dominant negative TCF-4 mutant, we show that ATP-induced cyclin D1 promoter activation, cyclin D1 protein expression, and proliferation of VSMC are all dependent on PKA and TCF activities. In conclusion, we show a novel mode of regulation of endogenous beta-catenin through its phosphorylation by PKA, and we demonstrate the importance of this mechanism for ATP-induced proliferation of VSMC.
Taurin
Sebastien
S
Department of Medicine, University of Chicago, Chicago, IL 60637, USA.
Sandbo
Nathan
N
Yau
Douglas M
DM
Sethakorn
Nan
N
Dulin
Nickolai O
NO
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001011:Aorta; D002455:Cell Division / Q000187:drug effects*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D010766:Phosphorylation; D051381:Rats; D011921:Rats, Inbred WKY; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
D018076:DNA, Complementary; D051176:beta Catenin; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases