STEROIDOGENIC FACTOR-I IS AN ESSENTIAL TRANSCRIPTIONAL ACTIVATOR FOR GONAD-SPECIFIC EXPRESSION OF PROMOTER-I OF THE RAT PROLACTIN RECEPTOR GENE

The expression of the prolactin receptor is under the control of two p utative tissue-specific (PI, gonads; PII, liver) and one common (PIII) promoters (Hu, Z. Z., Zhuang, L., and Dufau, M. L. (1996) J. Biol. Ch em, 271, 10242-10246). The three promoter regions were co-localized to the rat chromosomal locus 2q16, in the order 5'-PIII-PI-PII-3'. To in vestigate the mechanisms of gonad-specific utilization of PI, the prom oter domain, regulatory cis-elements, and trans-factors were identifie d in gonadal cells. The promoter domain localized to the 152-base pair 5' of the transcriptional start site at -549 is highly active in gona dal cells but has minimal. activity in hepatoma cells. It contains a s teroidogenic factor 1 (SF-1) element (-668) that binds the SF-1 protei n of nuclear extracts from gonadal cells and is essential for promoter activation. A CCAAT box (-623) contributes minimally to basal activit y in the absence of the SF-1 element, and two adjacent TATA-like seque nces act as inhibitory elements. Thus, PI belongs to a class of TATA-l ess/non-initiator gene promoters, These findings demonstrate an essent ial role for SF-1 in transcriptional activation of promoter I of the p rolactin receptor gene, which may explain the tissue-specific expressi on of PI in the gonads but not in the liver and the mammary gland.