DNA-BINDING PROTEINS THAT INTERACT WITH THE 19-BASE PAIR (CRE-LIKE) ELEMENT FROM THE HCMV MAJOR IMMEDIATE-EARLY PROMOTER IN DIFFERENTIATINGHUMAN EMBRYONAL CARCINOMA-CELLS

The pluripotent human embryonal carcinoma (EC) cell line NTERA-2 provi des a useful tool for investigating cell differentiation in a way that is pertinent to the development of the early human embryo. The major immediate early (MIE) gene of human cytomegalovirus (HCMV), which is n ot transcribed in undifferentiated NTERA-2 EC cells but is transcribed in their differentiated derivatives, offers a model with which to stu dy the developmental regulation of gene activity during the differenti ation of these cells. We have investigated the regulatory activity of the cAMP response elements (CRE) and the activation protein (AP1) site found within several repeated 19-base-pair (bp) elements from the HCM V MIE promoter, and the developmental regulation of nuclear DNA-bindin g factors that interact with these sites. The 19-bp CRE but not the AP 1 site is responsive to cAMP in undifferentiated NTERA-2 EC and its ac tivity is enhanced upon differentiation. Nuclear proteins of the CREB, Fos, and Jun families bind to these sites, but, surprisingly, their l evels only show limited regulation during NTERA-2 differentiation. Thi s contrasts with results obtained with murine EC cells. However, addit ional and apparently novel proteins with molecular weights between 800 00 and 90000, and binding specificities for both CRE and AP1 sites, we re detected in undifferentiated EC cells. The activity of these protei ns decreased markedly after differentiation, indicating their involvem ent in negative regulation of the CRE/AP1-like site in undifferentiate d EC cells. This suggests novel members able to interact via leucine z ippers with other members of the Jun-Fos-CREB family of DNA binding pr oteins that are also involved in this regulation.