GnRH activates ERK1/2 leading to the induction of c-fos and LHbeta protein expression in LbetaT2 cells

Abstract

GnRH acts on pituitary gonadotropes to stimulate the synthesis and release of LH and FSH. However, the signaling pathways downstream of the GnRH receptor that mediate these effects are not fully understood. In this paper, we demonstrate that GnRH activates ERK, c-Jun N-terminal kinase, and p38MAPK in the LbetaT2 gonadotrope cell line. Phosphorylation of both ERK and p38MAPK are stimulated rapidly, 30- to 50-fold in 5 min, but activation of c-Jun N-terminal kinase has slower kinetics, reaching only 10-fold after 30 min. Activation of ERK by GnRH is blocked by inhibition of MAPK kinase (MEK) and partially blocked by inhibition of PKC and calcium, but not PI3K or p38MAPK signaling. We demonstrate that phosphorylated ERK accumulates in the nucleus in a PKC-dependent manner. We also show that GnRH induces c-fos and LHbeta subunit protein expression in LbetaT2 cells via MEK. Experiments with EGTA or calcium channel antagonists indicated that calcium influx is important for the induction of both genes by GnRH. In conclusion, these results show that GnRH activates all three MAPK subfamilies in LbetaT2 cells and induces c-fos and LHbeta protein expression through calcium and MEK-dependent mechanisms. These results also demonstrate that the nuclear translocation of ERK by GnRH requires PKC signaling.