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Molecular and Cellular Biology, May 2000, p. 3331-3344, Vol. 20, No. 10
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Role of the Cyclic AMP Response Element Binding Complex and Activation of Mitogen-Activated Protein Kinases in Synergistic Activation of the Glycoprotein Hormone alpha  Subunit Gene by Epidermal Growth Factor and Forskolin

Mark S. Roberson,* Makiko Ban, Tong Zhang, and Jennifer M. Mulvaney

Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853

Received 25 October 1999/Returned for modification 10 December 1999/Accepted 17 February 2000

The aim of these studies was to elucidate a role for epidermal growth factor (EGF) signaling in the transcriptional regulation of the glycoprotein hormone alpha  subunit gene, a subunit of chorionic gonadotropin. Studies examined the effects of EGF and the adenylate cyclase activator forskolin on the expression of a transfected alpha  subunit reporter gene in a human choriocarcinoma cell line (JEG3). At maximal doses, administration of EGF resulted in a 50% increase in a subunit reporter activity; forskolin administration induced a fivefold activation; the combined actions of EGF and forskolin resulted in synergistic activation (greater than eightfold) of the alpha  subunit reporter. Mutagenesis studies revealed that the cyclic AMP response elements (CRE) were required and sufficient to mediate EGF-forskolin-induced synergistic activation. The combined actions of EGF and forskolin resulted in potentiated activation of extracellular signal-regulated kinase (ERK) enzyme activity compared with EGF alone. Specific blockade of ERK activation was sufficient to block EGF-forskolin-induced synergistic activation of the alpha  subunit reporter. Pretreatment of JEG3 cells with a p38 mitogen-activated protein kinase inhibitor did not influence activation of the alpha  reporter. However, overexpression of c-Jun N-terminal kinase (JNK)-interacting protein 1 as a dominant interfering molecule abolished the synergistic effects of EGF and forskolin on the alpha  subunit reporter. CRE binding studies suggested that the CRE complex consisted of CRE binding protein and EGF-ERK-dependent recruitment of c-Jun-c-Fos (AP-1) to the CRE. A dominant negative form of c-Fos (A-Fos) that specifically disrupts c-Jun-c-Fos DNA binding inhibited synergistic activation of the alpha  subunit. Thus, synergistic activation of the alpha  subunit gene induced by EGF-forskolin requires the ERK and JNK cascades and the recruitment of AP-1 to the CRE binding complex.

* Corresponding author. Mailing address: Department of Biomedical Sciences T6-008a VRT, Cornell University, Ithaca, NY 14853. Phone: (607) 253-3469. Fax: (607) 253-3851. E-mail: msr14{at}cornell.edu.

Molecular and Cellular Biology, May 2000, p. 3331-3344, Vol. 20, No. 10
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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