AP-2 family members regulate basal and cAMP-induced expression of human chorionic gonadotropin.
The AP-2 family of transcriptional regulator proteins has three members, alpha, beta and gamma. AP-2alpha and gamma are expressed in placenta and in the human trophoblast cell line JEG-3. AP-2 has been shown to regulate expression of the placental human chorionic gonado-tropin (hCG) alpha- and beta-subunit genes, however, previous work did not distinguish between the family members. Tryptic peptides of the AP-2 protein complexes purified from JEG-3 cells by oligo-affinity chromatography using the hCGalpha AP-2 site match the amino acid sequence of AP-2gamma. The fact that AP-2gamma is present at significant levels and binds the hCGalpha trophoblast-specific element suggests that AP-2gamma is at least part of the binding complex in vivo and plays a role in regulating hCG expression. We show that mutation of each of four AP-2 binding sites within the hCGbeta promoter decreases expression in transfection assays, demonstrating that all four sites are required for maximal expression in JEG-3 cells. Furthermore, we find differences in regulation of the family members: AP-2alpha mRNA levels increase in response to cAMP while AP-2gamma mRNA levels do not. The demonstrated importance of the AP-2 sites in controlling hCGalpha and beta expression and the likely involvement of more than one family member suggest that a balance in AP-2 proteins is involved in coordinate regulation of these genes. Moreover, many placenta-restricted genes are regulated by AP-2 proteins, thus members of this family may play an important overall role in placenta-specific expression.
LiCalsi
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The Departments of Reproductive Medicine and Neurosciences and the Center for the Study of Reproductive Biology and Disease, University of California at San Diego, La Jolla, CA 92093-0674, USA.
Christophe
S
S
Steger
D J
DJ
Buescher
M
M
Fischer
W
W
Mellon
P L
PL
D001483:Base Sequence; D006063:Chorionic Gonadotropin / Q000235:genetics*; D000242:Cyclic AMP / Q000502:physiology*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010920:Placenta / Q000378:metabolism; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*; D014407:Tumor Cells, Cultured
D006063:Chorionic Gonadotropin; D017931:DNA Primers; D004268:DNA-Binding Proteins; C493673:TFAP2A protein, human; C493679:TFAP2C protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D000242:Cyclic AMP