Regulation of the human chorionic gonadotropin alpha- and beta-subunit promoters by AP-2

J Biol Chem. 1997 Jun 13;272(24):15405-12. doi: 10.1074/jbc.272.24.15405.

Abstract

Production of the placental hormone, chorionic gonadotropin (CG), increases dramatically as cytotrophoblasts fuse to form syncytiotrophoblasts. The CG alpha- and beta-promoters are both responsive to cAMP, although the kinetics of cAMP stimulation are different. In an effort to understand the mechanisms of coordinate induction of these genes, AP-2 binding sites were identified in the promoter regions of the alpha and CGbeta genes. AP-2 bound to the upstream regulatory element (-186 to -156 base pairs (bp)) in the alpha-promoter and to several different regions of the CGbeta promoter, including footprints 2 and 4B (FP2, -311 to -279 bp; FP4B, 221 to -200 bp). AP-2 antibodies induced supershifts of these complexes, confirming the identity of the protein-DNA complex. In JEG-3 cells, which contain abundant AP-2, mutations in these CGbeta AP-2 sites reduced basal activity and decreased cAMP stimulation. In AP-2-deficient Hep-G2 cells, co-transfection of AP-2 stimulated expression of the CGbeta promoter 10-20-fold, and the alpha-promoter was induced by 3-6-fold. Mutations that eliminate AP-2 binding to CGbeta FP4B reduced AP-2 stimulation by more than 80%, whereas mutations in FP2 reduced AP-2 stimulation by less than 50%. Analyses of AP-2 mutants revealed a requirement for the DNA binding/dimerization domain and the amino-terminal proline-rich and acid-rich transactivation domains for stimulation of the CGbeta promoter. Primary cultures of placental cytotrophoblasts were differentiated into syncytiotrophoblasts in vitro to examine AP-2 expression by reverse transcriptase-polymerase chain reaction. AP-2 mRNA levels increased by day 2 and continued to rise in parallel with a marked increase in alpha and CGbeta gene expression. We conclude that both the alpha and CGbeta promoters contain binding sites for AP-2 and suggest that this transcription factor provides a mechanism for coordinating the induction of these genes during placental cell differentiation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cell Nucleus / metabolism
  • Chorionic Gonadotropin, beta Subunit, Human / genetics*
  • Chorionic Gonadotropin, beta Subunit, Human / metabolism
  • DNA-Binding Proteins / metabolism*
  • Glycoprotein Hormones, alpha Subunit / genetics*
  • Glycoprotein Hormones, alpha Subunit / metabolism
  • Humans
  • Placenta / metabolism
  • Promoter Regions, Genetic*
  • Protein Binding
  • Transcription Factor AP-2
  • Transcription Factors / metabolism*

Substances

  • Chorionic Gonadotropin, beta Subunit, Human
  • DNA-Binding Proteins
  • Glycoprotein Hormones, alpha Subunit
  • Transcription Factor AP-2
  • Transcription Factors