RT Journal Article
SR Electronic
T1 Thyrotropin Activates Mitogen-Activated Protein Kinase Pathway in FRTL-5 by a cAMP-Dependent Protein Kinase A-Independent Mechanism
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 924
OP 933
DO 10.1124/mol.60.5.924
VO 60
IS 5
A1 Luisa Iacovelli
A1 Loredana Capobianco
A1 Lorena Salvatore
A1 Michele Sallese
A1 Gabriel Maximo D'Ancona
A1 Antonio De Blasi
YR 2001
UL http://molpharm.aspetjournals.org/content/60/5/924.abstract
AB The involvement of mitogen-activated protein (MAP) kinases in the mitogenic effect of thyrotropin (TSH) is not fully elucidated. In FRTL-5 cells, we found that the MAP kinase kinase (MEK) inhibitors UO126 and PD98059 substantially decreased TSH-induced DNA synthesis, indicating that MAP kinases are involved in the TSH-stimulated proliferative response. Accordingly, TSH, forskolin (FSK) and 8-bromo-cAMP induced a rapid (3 min) and transient activation of ERK1/2, as assessed by phosphorylation of myelin basic protein and ERK1/2. This effect was cAMP-dependent and protein kinase A (PKA)-independent. The activation of Rap1 and B-Raf was involved in the mechanism of MAP kinase stimulation by TSH. TSH induced rapid (3 min) GDP/GTP exchange and activation of Rap1. After a 3-min exposure to FSK, B-Raf was recruited to a vesicular compartment, where it colocalized with Rap1. Both activation of Rap1 and translocation of B-Raf were PKA-independent. The Rap1 dominant negative Rap1N17 significantly reduced TSH-stimulated but not insulin-like growth factor 1-stimulated ERK1/2 phosphorylation, whereas the Ras dominant negative RasN17 inhibited the effect of both agonists. In conclusion, our results document that TSH increases intracellular cAMP, which rapidly stimulates MAP kinase cascade independent of PKA. This novel mechanism could integrate other pathways involved in TSH-stimulated proliferative response.