Phosphorylation of the cyclic AMP response element binding protein mediates transforming growth factor beta-induced downregulation of cyclin A in vascular smooth muscle cells.
Transforming growth factor beta (TGFbeta), a multifunctional cytokine associated with vascular injury, is a potent inhibitor of cell proliferation. The current results demonstrate that the TGFbeta-induced growth arrest of vascular smooth muscle cells (VSMCs) is associated with cyclin A downregulation. TGFbeta represses the cyclin A gene through a cyclic AMP (cAMP) response element, which complexes with the cAMP response element binding protein (CREB). The CREB-cyclin A promoter interaction is hindered by TGFbeta, preceded by a TGFbeta receptor-dependent CREB phosphorylation. Induction of CREB phosphorylation with forskolin or 6bnz-cAMP mimics TGFbeta's inhibitory effect on cyclin A expression. Conversely, inhibition of CREB phosphorylation with a CREB mutant in which the phosphorylation site at serine 133 was changed to alanine (CREB-S133A) upregulated cyclin A gene expression. Furthermore, the CREB-S133A mutant abolished TGFbeta-induced CREB phosphorylation, cyclin A downregulation, and growth inhibition. Since we have previously shown that the novel PKC isoform protein kinase C delta (PKCdelta) is activated by TGFbeta in VSMCs, we tested the role of this kinase in CREB phosphorylation and cyclin A downregulation. Inhibition of PKCdelta by a dominant-negative mutant or by targeted gene deletion blocked TGFbeta-induced CREB phosphorylation and cyclin A downregulation. Taken together, our data indicate that phosphorylation of CREB stimulated by TGFbeta is a critical step leading to the inhibition of cyclin A expression and, thus, VSMC proliferation.
Kamiya
Kentaro
K
Department of Surgery, Weill Cornell Medical College of Cornell University, New York, NY 1002, USA.
Sakakibara
Kenji
K
Ryer
Evan J
EJ
Hom
Raymond P
RP
Leof
Edward B
EB
Kent
K Craig
KC
Liu
Bo
B
D000818:Animals; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D019925:Cyclin A / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects*; D051379:Mice; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D051745:Protein Kinase C-delta / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020218:Response Elements; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D017362:Cyclic AMP Response Element-Binding Protein; D019925:Cyclin A; D016212:Transforming Growth Factor beta; D051745:Protein Kinase C-delta