FOLLITROPIN ACTION ON THE TRANSFERRIN GENE IN SERTOLI CELLS IS MEDIATED BY CAMP-RESPONSIVE-ELEMENT-BINDING-PROTEIN AND ANTAGONIZED BY CHICKEN OVALBUMIN-UPSTREAM-PROMOTER-TRANSCRIPTION FACTOR

The transcription of the transferrin (Tf) gene is induced by follitrop in via cAMP in rat Sertoli cells. We previously demonstrated that the cAMP-responsive-element-binding protein (CREB) interacts on the proxim al region II (PRII) of the human Tf promoter (Suire et al., 1995). The PRII region is identified as essential for cAMP inducibility of the T f promoter and contains a CCAAT box. This unexpected result led us to study the relation that exists between CREB and the PRII site. In the liver, CCAAT/enhancer-binding (C/EBP) proteins act at the PRII site. A lthough these factors are absent in Sertoli cells, their overexpressio n in Sertoli cells disturbs basal and induced transcription. C/EBP alp ha and delta were able to stimulate the basal transcription driven by the -100 to +39 region, placed upstream of the chloramphenicol acetylt ransferase (CAT) gene. However, only C/EBP alpha allowed the cAMP-indu cible expression. The K-a of CREB bZIP (254-327), a deleted form of CR EB, for the CRE site (3.92x10(8)M(-1)) and for the PRII site (1.38x10( 8)M(-1)) were determined using the surface plasmon resonance (SPR) met hod. The K-a values were similar, although the derived kinetics were d ifferent: higher k(a) and k(d) of CREB for the PRII site were found co mpared with the CRE site. Since we observed important dissociation kin etics, we hypothesized that the binding of CREB to the PRII site is st abilized by CREB-binding protein (CBP) or by chicken-ovalbumin-upstrea m-promoter transcription factor (COUP-TF) binding to PRI site near to PRII. However, we observed that the overexpression of CBP in Sertoli c ells did not potentiate the basal and cAMP-stimulated activity of CREB of the -100 to +39Tf-CAT construct. In basal and cAMP-stimulated cond itions, COUP-TF appeared to repress the transcription driven by the -1 00 to +39 region in a specific manner. These results demonstrate a dir ect action of CREB on hTf promoter, which is antagonized by COUP-TF an d may explain the transcriptional regulation of Tf by follitropin, via cAMP.