cAMP EXERTS A FINE CONTROL OF MAP KINASE PHOSPHATASE-1 LEVELS: IMPLICATIONS ON GENE TRANSCRIPTION

BRION L, GOROSTIZAGA A, SUÁREZ G, MORI SEQUEIROS GARCÍA M, PODEROSO C, CORNEJO MACIEL F, PODESTÁ EJ, PAZ C.

Mar del Plata, Argentina

Congreso; XLIII Reunión Anual de SAIB; 2007

SAIB

MAP kinase phosphatase-1 (MKP-1) controls nuclear MAP kinase activity with important consequences for gene transcription. In adrenal and Leydig cells, trophic hormones trigger ERK1/2 activation, a key step in Steroidogenic Acute Regulatory (StAR) protein induction and steroidogenesis. In addition, we have reported a hormone/cAMP-dependent transcriptional increase of MKP-1 in those cells. In this study we analyzed the post translational regulation of MKP-1 and its functional role on gene transcription. Western blot analysis showed that 8Br-cAMPstimulation (0-3 h) up regulates MKP-1 in MA-10 Leydig cells transiently overexpressing the protein in a magnitude higher than that observed in mock transfected cells, an effect that was reduced by blocking ERK1/2 activation. Since proteasome inhibitors also produced MKP-1 accumulation, our study suggests that PKA/ERK1/2mediated phosphorylation of the enzyme impairs its proteasomal degradation. We also tested the role of MKP-1 on cAMP-stimulated StAR promoter activity using a reporter (luciferase) system. 8Br-cAMP stimulation (6 h) enhanced promoter activity (Control=0.36±0.03 vs 8Br=0.99±0.10, P<0.01) and MKP-1 overexpression reduced the effect (8Br/MKP1=0.46±0.09, P<0.01 vs 8Br). We conclude that cAMP exerts a fine control of MKP-1 levels that sets a temporal limit to the regulation ofMAPkinase-induced gene transcription.