Dual-specificity phosphatase 6 (DUSP6) mRNA and protein abundance is regulated by fibroblast growth factor 2 in sheep granulosa cells and inhibits c-Jun N-terminal kinase (MAPK8) phosphorylation

Abstract

Growth factors regulate ovarian follicle development and they signal through intracellular pathways including mitogen-activated protein kinase (MAPK) phosphorylation, which is negatively regulated by a subfamily of 23 dual-specificity phosphatases (DUSP). Using sheep granulosa cells as a model, we detected mRNA encoding 16 DUSPs in vivo and in vitro. Stimulation of cells in vitro with FGF2 increased (p < 0.05) abundance of DUSP1, DUSP2, DUSP5 and DUSP6 mRNA, and abundance of DUSP1 and DUSP6 proteins (p < 0.05). In contrast, neither FGF8b nor FGF18 had any major effect on DUSP mRNA abundance. Inhibition of DUSP6 action with the inhibitor BCI significantly increased (p < 0.05) MAPK8 (JNK) phosphorylation but not phosphoMAPK14 (p38) or MAPK3/1 (ERK1/2) abundance. This study suggests that FGFs stimulate DUSP protein abundance, that DUSP6 regulates MAPK8 phosphorylation in granulosa cells, and DUSPs are involved in the differential MAPK signaling of individual FGF ligands.

Keywords: DUSPs; FGF regulation; Granulosa cells; MAPK pathway; Ovarian folliculogenesis; Ruminants.