The proposed studies focus on the potentially unique interaction of the protein kinase C (PKC), extracellular-regulated protein kinase (ERK) and p38 kinase signaling pathways during activation of the glycoprotein hormone alpha subunit gene by gonadotropin releasing hormone (GnRH). Luteinizing hormone (LH) and follicle- stimulating hormone (FSH) are heterodimeric glycoproteins which share a common alpha subunit. Secretion of GnRH mediates secretion and synthesis of LH and FSH. GnRH action on PKC is required for alpha subunit gene expression. Evidence in this proposal implicates ERK and p38 kinase activation in the """"""""GnRH signaling pathway."""""""" Effects of GnRH on ERK and p38 kinase depend up[on PKC. Combined activation of the PKC, ERK and p38 pathways represents a novel signaling strategy that may be essential to pituitary-specific gene regulation. A novel target of the GnRH pathway is a mitogen-activated protein kinase phosphatase (MKP) capable of ERK inactivation. Thus, GnRH functions to upregulate the ERK pathway and potentially attenuates ERK activity by increased amounts of MKP mRNA. The overall hypotheses are that; 1) GnRH activation of the alpha subunit promoter depends on PKC isoforms functioning as a Raf kinase-kinase; 2) the p38 pathway acts combinatorially with PKC and/or ERK's to mediate gene expression in the pituitary and: 3) MAPK phosphatases modulate the kinetics of ERK inactivation and alter GnRH-induced expression of the alpha subunit gene.
Specific aims to test these hypotheses are: 1. Examine the role of GnRH on integration of kinases upstream of ERK. 2. Further investigate the involvement of p38 kinase in the GnRH signaling pathway. 3. Examine the relationship between the GnRH pathway and MAPK phosphatases. Experimental approaches include use of phospho-specific antibodies, immune complex kinase assays, transient and stable transfection studies, mutagenesis, RNA blotting assays and antisense inhibition/rescue experiments. It is anticipated these studies will identify key mechanisms which regulate intracellular signaling linking GnRH receptor occupancy to specific intracellular events that alter pituitary-specific gene expression.
| White, B R; Duval, D L; Mulvaney, J M et al. (1999) Homologous regulation of the gonadotropin-releasing hormone receptor gene is partially mediated by protein kinase C activation of an activator protein-1 element. Mol Endocrinol 13:566-77 |
