RT Journal Article
SR Electronic
T1 Protein Kinase A and B-Raf Mediate Extracellular Signal-Regulated Kinase Activation by Thyrotropin
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 1123
OP 1129
DO 10.1124/mol.109.060129
VO 76
IS 5
A1 Vuchak, Lisa A.
A1 Tsygankova, Oxana M.
A1 Prendergast, Gregory V.
A1 Meinkoth, Judy L.
YR 2009
UL http://molpharm.aspetjournals.org/content/76/5/1123.abstract
AB Thyrotropin (TSH) regulates thyroid cell proliferation and function through cAMP-mediated signaling pathways that activate protein kinase A (PKA) and Epac/Rap1. The respective roles of PKA versus Epac/Rap1 in TSH signaling remain unclear. We set out to determine whether PKA and/or Rap1 mediate extracellular signal-regulated kinase (ERK) activation by TSH. Neither blocking Rap1 activity nor silencing the expression of Rap1 impaired TSH or forskolin-induced ERK activation in Wistar rat thyroid cells. Direct activation of Epac1 failed to stimulate ERK activity in starved cells, suggesting that Epac-induced Rap1 activity is not coupled to ERK activation in rat thyroid cells. By contrast, PKA activity was required for cAMP-stimulated ERK phosphorylation and was sufficient to increase ERK phosphorylation in starved cells. Expression of dominant-negative Ras inhibited ERK activation by TSH, forskolin, and N6-monobutyryl (6MB)-cAMP, a selective activator of PKA. Silencing the expression of B-Raf also inhibited ERK activation by TSH, forskolin, and 6MB-cAMP, but not that stimulated by insulin or serum. Depletion of B-Raf impaired TSH-induced DNA synthesis, indicating a functional role for B-Raf in TSH-regulated proliferation. Collectively, these results position PKA, Ras, and B-Raf as upstream regulators of ERK activation and identify B-Raf as a selective target of cAMP-elevating agents in thyroid cells. These data provide the first evidence for a functional role for B-Raf in TSH signaling. © 2009 The American Society for Pharmacology and Experimental Therapeutics