TGF-BETA SIGNALING IN MURINE EMBRYONIC PALATE CELLS INVOLVES PHOSPHORYLATION OF THE CREB TRANSCRIPTION FACTOR

number of studies over the last several years have demonstrated a cruc ial role for TGF-beta in epithelial and mesenchymal differentiation du ring development of the embryonic palate. Molecular mechanism(s) of si gnal transduction responsible for eliciting these responses remain unr esolved. Since cAMP signaling also modulates the same tissue different iation in the developing palate and palate-derived cells, we hypothesi zed that TGF-beta activity may be mediated through cAMP-inducible path ways. We thus examined the effects of TGF-beta on activation of the cA MP regulatory element binding protein CREB, a nuclear transcription fa ctor which mediates transcription of genes containing CRE recognition sequences in their promoters. We examined the ability of TGF-beta-trea ted murine embryonic palate mesenchymal (MEPM) cells to phosphorylate CREB on the amino acid residue serine 133, phosphorylation of which is indispensable for transcriptional activation. TGF-beta treatment led to increased phosphorylation of CREB ser-133 in a time- and dose-depen dent manner. Inhibition of serine-threonine phosphatases by okadaic ac id enhanced but did not prolong this response. TGF-beta failed to indu ce the activity of protein kinase A (PKA), a known CREB kinase. Inhibi tion of either PKA or calcium/calmodulin kinase II (CaMK II) did not a brogate phosphorylation of CREB by TGF-beta. TGF-beta treatment also d id not induce phosphorylation of mitogen-activated protein kinases, er k-1 and erk-2, on tyrosine 185, suggesting that these kinases do not m ediate CREB phosphorylation by TGF-beta. Additionally, TGF-beta had no effect on CREB binding to known CREB DNA consensus recognition sequen ces, CRE and TRE. Together, these data suggest an alternative or novel CREB kinase in MEPM cells through which TGF-beta acts to induce CREB ser-133 phosphorylation and subsequent activation of CRE-containing ge nes. (C) 1997 Academic Press.