C-Jun represses transcription of the human chorionic gonadotropin alpha and beta genes through distinct types of CREs.

Abstract

Chorionic gonadotropin (CG) is a heterodimeric placental hormone encoded by separate alpha and beta subunit genes that is essential for the maintenance of pregnancy. The production of CG is stimulated by DNA synthesis inhibitors and by cAMP. The present study demonstrates that the proto-oncogene c-jun represses transcription of the human CG alpha and CG beta promoters. c-Jun repressed the CG alpha promoter through a canonical cAMP response element (CRE) that is known to bind c-Jun and other members of the B-Zip transcription factor family. In the CG beta promoter, two adjacent sites, CRE1 (-299 to -289) and CRE2 (-240 to -219), conveyed cAMP responsiveness via sequences that are distinct from the canonical element, TGACGTCA. Mutations within CG beta CRE1 or CRE2 reduced or abolished, respectively, c-Jun-mediated repression. Although the CG beta CREs do not contain consensus sequences previously described to bind c-Jun, CRE2 bound c-Jun and c-Fos in electrophoretic mobility shift assays. Supershift assays, using anti-JUN antibody, demonstrated that Jun formed part of the native complex that binds the CRE2 in JEG-3 cells. A series of c-Jun mutants were used to analyze the transcription factor domains required for repression of the CG subunit promoters. The DNA binding and leucine zipper domains of c-Jun as well as the amino terminus, were required for repression of both subunit promoters. Thus, both the CG alpha and CG beta genes are repressed by c-Jun through promoter regions that convey cAMP-induced transcription, although these DNA sequences are unrelated.