Activation of the luteinizing hormone beta promoter by gonadotropin-releasing hormone requires c-Jun NH2-terminal protein kinase

Regulation of the mitogen-activated protein kinase (MAPK) family by gonadot ropin-releasing hormone (GnRH) in the gonadotrope cell line L beta T2 was i nvestigated. Treatment with gonadotropin-releasing hormone agonist (GnRHa) activates extracellular signal-regulated kinase (ERK) and c-Jun NH2-termina l kinase (JNK), Activation of ERK by GnRHa occurred within 5 min, and decli ned thereafter, whereas activation of JNK by GnRHa occurred with a differen t time frame, i.e. it was detectable at 5 min, reached a plateau at 30 min, and declined thereafter. GnRHa-induced ERK activation was dependent on pro tein kinase C or extracellular and intracellular Ca2+, whereas GnRHa-induce d JNK activation was not dependent on protein kinase C or on extracellular or intracellular Ca2+. To determine whether a mitogen-activated protein kin ase family cascade regulates rat luteinizing hormone beta (LH beta) promote r activity, we transfected the rat LH beta (-156 to +7)luciferase construct into L beta T2 cells. GnRH activated the rat LH beta promoter activity in a time-dependent manner. Neither treatment with a mitogen-activated protein kinase/ERK kinase (MEK) inhibitor, PD98059, nor cotransfection with a cata lytically inactive form of a mitogen-activated protein kinase construct inh ibited the induction of the rat LH beta promoter by GnRH, Furthermore, cotr ansfection with a dominant negative Ets had no effect on the response of th e rat LH beta promoter to GnRH. On the other hand, cotransfection with eith er dominant negative JNK or dominant negative c-Jun significantly inhibited the induction of the rat LH beta promoter by GnRH. In addition, GnRH did n ot induce either the rat LH beta promoter activity in L beta T2 cells trans fected stably with dominant negative c-Jun, These results suggest that GnRH a differentially activates ERK and JNK, and a JNK cascade is necessary to e licit the rat LH beta promoter activity in a c-Jun-dependent mechanism in L beta T2 cells.