Activation of mitogen-activated protein kinases by gonadotropins and cyclic adenosine 5'-monophosphates in porcine granulosa cells

Abstract

A variety of growth factors and guanosine triphosphate (GTP) binding protein-linked receptors are known to activate mitogen activated protein kinases (MAPK); however, no evidence exists demonstrating activation of the MAPK pathway by glycoprotein hormones. Using porcine granulosa cells (PGC), we show that physiological concentrations of LH and FSH increase enzymatic activity 1) of p44MAPK extracellular regulated kinase 1 (ERK1) but not that of p42MAPK (ERK2) in the cytosol and 2) of both ERK1 and ERK2 in the nucleus. Cytosolic ERK1 was activated by LH more rapidly than by FSH. Cyclic AMP increased kinase activities of both ERK1 and ERK2 in the cytoplasm as well as in the nucleus. Activation of ERK1 by gonadotropins and cAMP was accompanied by increased tyrosine phosphorylation of the kinase. Immunohistochemical studies demonstrated predominantly cytoplasmic staining for MAPK in untreated PGC cultures whereas treatment with gonadotropins led to increased nuclear immunoreactivity indicating translocation of MAPK to the nucleus. The translocation as well as increase in nuclear ERK1 and ERK2 was delayed and coincided with a decrease in cytosolic ERK1 activity. Epidermal growth factor (EGF) increased ERK1 and ERK2-associated kinase activity 7-8-fold in the cytoplasm of PGC, while kinase activity of cytoplasmic ERK1 was enhanced 3-4-fold by LH, FSH, or cAMP. In summary, we have for the first time demonstrated that gonadotropins (and cAMP) can activate MAPK in appropriate target cells.