The cAMP response element-binding protein (CREB) has been shown to mediate transcriptional activation of genes in response to both cAMP and calcium influx signal transduction pathways. The roles of two multifunctional calcium/calmodulin-dependent protein kinases, CaMKIV and CaMKII, were examined in transient transfection studies that utilized either the full-length or the constitutively active forms of these kinases. The results indicate that CaMKIV is much more potent than CaMKII in activating CREB in three different cell lines.

Gonadotropin-releasing hormone (GnRH) interacts with a G protein-coupled receptor and increases the transcription of the glycoprotein hormone alpha-subunit gene. We have explored the possibility that mitogen-activated protein kinase (MAPK) plays a role in mediating GnRH effects on transcription. Activation of the MAPK cascade by an expression vector for a constitutively active form of the Raf-1 kinase led to stimulation of the alpha-subunit promoter in a concentration-dependent manner. GnRH treatment was found to increase the phosphorylation of tyrosine residues of MAPK and to increase MAPK activity, as determined by an immune complex kinase assay. A reporter gene assay using the MAPK-responsive, carboxy-terminal domain of the Elk1 transcription factor was also consistent with GnRH-induced activation of MAPK. Interference with the MAPK pathway by expression vectors for kinase-defective MAPKs or vectors encoding MAPK phosphatases reduced the transcription-stimulating effects of GnRH. The DNA sequences which are required for responses to GnRH include an Ets factor-binding site. An expression vector for a dominant negative form of Ets-2 was able to reduce GnRH effects on expression of the alpha-subunit gene. These findings provide evidence that GnRH treatment leads to activation of the MAPK cascade in gonadotropes and that activation of MAPK contributes to stimulation of the alpha-subunit promoter. It is likely that an Ets factor serves as a downstream transcriptional effector of MAPK in this system.

Recently, a pituitary-specific enhancer was identified within the 5' flanking region of The glycoprotein hormones are a family of heterodimeric proteins which consist of a common a subunit noncovalently associated with a hormone-specific 13 subunit (37). The glycoprotein hormones include the pituitary hormones, luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone. In addition, some species also synthesize a chorionic gonadotropin within the placenta. Within a species, the glycoprotein hormones all share a common a subunit, while the unique ,B subunits specify the biological activity of the heterodimer. In the pituitary gland, luteinizing hormone and follicle-stimulating hormone are synthesized within cells which are designated gonadotropes, while thyroid-stimulating hormone is synthesized in thyrotropes. Thus, the glycoprotein hormone a-subunit gene is expressed within two different cell types in the pituitary and in some species within the placenta. The mechanisms mediating the tissue-specific expression of the a-subunit gene have been the focus of a large number of studies. While a number of DNA elements which are important for at-subunit expression in the placenta have been identified (3,4,11,12,25,28,34,46), much less is known concerning requirements for expression in the pituitary. It has been demonstrated that reporter genes containing various * Corresponding author. Mailing address:

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