COORDINATE CONTROL OF THE ALPHA-SUBUNIT AND BETA-SUBUNIT GENES OF HUMAN CHORIONIC-GONADOTROPIN BY TROPHOBLAST SPECIFIC ELEMENT-BINDING PROTEIN

The alpha- and beta-subunit genes of hCG are coordinately regulated in the trophectoderm of the early embryo and placenta. Placenta-specific expression of the alpha-subunit gene is determined by a composite enh ancer made of three clustered components: cAMP-responsive elements, a GATA site, and the trophoblast-specific element (TSE). We have investi gated the basis of placenta-specific expression of the major hCG beta- subunit gene, hCG beta 5. Enhancement of expression localizes to the r egion from -305 to -279, whereas full cAMP regulation requires the reg ion from -305 to -249. Four DNAse-I footprints are present, three of w hich can be competed by the TSE element from the alpha-subunit gene. M ethylation interference establishes that binding to the element locate d in the key region for expression, from -301 to -275, requires contac ts with a CCNNNGGG core sequence that matches the alpha-subunit gene T SE. Sequence-specific DNA affinity chromatography using the alpha-subu nit gene TSE allows purification of TSE-binding protein. This purified protein binds specifically to the key element, -301 to -275, and to a t least two additional TSE elements clustered in the regulatory region of the hCG beta 5 gene. We conclude that both the alpha- and beta-sub unit genes of hCG require the placenta-specific factor TSE-binding pro tein for expression, providing a mechanism for their coordinate regula tion in placental cells.