TRANS-ACTING FACTORS DICTATE THE SPECIES-SPECIFIC PLACENTAL EXPRESSION OF CORTICOTROPIN-RELEASING FACTOR GENES IN CHORIOCARCINOMA CELL-LINES

CRF, in addition to its role in the hypothalamus, demonstrates species -specific expression in the placentas of higher primates, but not rode nts. Transient transfections of BeWo and JEG-3 choriocarcinoma cells, as models for human trophoblasts, demonstrate regulated expression of human (h) CRF-luciferase reporter genes, whereas little or no expressi on is detected in other lines, including CV-1 cells. The rodent chorio carcinoma cell line, Rcho-1, a model for rodent trophoblasts, is defec tive in the expression of transfected hCRF genes. The mouse CRF promot er behaves similarly to the corresponding hCRF construct. It is active in BeWo and inactive in Rcho-1 cells. The transcriptional response to cAMP contributes to the specific expression of CRF. Analyses of delet ed or mutated hCRF promoters identify a key role for protein kinase A- dependent pathways. A major part, but not all, of this effect is media ted by the canonical cAMP response element conserved in mouse, rat, an d human CRF promoters. Additional deletions of the human CRF promoter identify control regions that also contribute to the observed species- specific expression pattern, and each identified region binds factors in nuclear extracts derived from the appropriate cell line. These stud ies using human and rodent choriocarcinoma cell lines as models of pla cental trophoblasts demonstrate dominant effects of cellular trans-act ing factors, rather than DNA sequence differences, in dictating the sp ecies-specific placental expression of CRF.