A potential role for cell cycle control proteins in regulation of the cyclic adenosine 5'-monophosphate-responsive glycoprotein hormone α subunit gene

The production of chorionic gonadotropin is coupled to the differentiation of the placenta. Expression of the subunit of chorionic gonadotropin [glycoprotein hormone α (GPH-α)] is also known to be stimulated by treatment of placental cells with either cAMP or DNA synthesis inhibitors. Given these features, we used adenovirus E1A as a molecular probe to investigate a potential role for cell cycle regulatory proteins and kinases in the regulation of GPH-α expression. The E1A protein contains well-characterized domains that interact with a variety of cell cycle regulatory proteins. The E1A conserved regions 1 and 2 bind proteins that regulate cell cycle progression, including pRB, p107, and p130. The amino- terminal region of E1A binds several high molecular weight proteins and inhibits the transcriptional coactivator function of p300 and the homologous cAMP response element (CRE)-binding protein. We found that coexpression of E1A13S activated the GPH-α promoter, whereas E1A12S caused marked repression. Deletion mutants and point mutations revealed that repression by E1A12S required the CRE of the GPH-α promoter. Several distinct domains in E1A12S were necessary for maximal repression. A mutation of the E1A amino terminus (RG2), which inhibits binding of p300 and related high molecular weight proteins, reduced 12S repression by 40%. Mutation of the pocket protein-binding domains reduced repression by 20%, and mutations of both domains reduced repression by 80%. Overexpression of p300 or the pocket proteins (pRB, p130, and p107) induced GPH-α promoter activity 2-4-fold. Because the E1A amino terminus and pocket protein-binding domains together induce p34(cdc2) kinase activity, the effect of p34(cdc2) kinase expression on GPH-α activity was also assessed. Coexpression of p34(cdc2) kinase or the activating p34(cdc2) kinase mutant (T14AY15F) inhibited GPH-α promoter activity and acted through the CRE. We conclude that the GPH-α gene CRE is subject to regulation by cell cycle regulatory kinases and proteins.