HUMAN STEM-CELL FACTOR PROMOTER DEOXYRIBONUCLEIC-ACID SEQUENCE AND REGULATION BY CYCLIC 3',5'-ADENOSINE-MONOPHOSPHATE IN A SERTOLI-CELL LINE

Stem cell factor (SCF) gene expression is regulated by FSH in testicul ar Sertoli cells. Many functions of FSH are mediated through the secon d messenger cAMP. We show that cAMP activates transcription of the hum an SCF promoter in a Sertoli cell line. The human SCF promoter was clo ned in cosmid vector pWE15, and its DNA sequence was determined for th e promoter region extending 2.3 kilobase pairs upstream from the trans lation start site at +184 bp. The in vivo messenger RNA (mRNA) start s ite, by primer-extension studies, was located in exon 1 at +109 bp in human testis mRNA, and at +99 bp in mouse SF7 Sertoli cell line or GC1 germ cell line mRNA. To test which regions of the SCF promoter are ne cessary for regulation by cAMP, a series of 5'-end deletions of this r egion were cloned onto the luciferase reporter gene in plasmid pXP1. T he SCF promoter region was fused to luciferase downstream (at +120) fr om its +109 mRNA start site, extending upstream a variable distance to BstXI (-162), BamHI (-313), Bgl2 (-853), or XbaI (-2185). The shortes t of these fragments extending only to -162 bp, contains possible SP1 and AP-2 elements. When mouse Sertoli SF7 or human JEG.3 cell lines we re transfected with these plasmids, all of the mutants were regulated by 8Br-cAMP or forskolin, as expected for the SCF gene, whereas FSH an d TPA had no effect. In the shortest promoter deletion -162, luciferas e expression from SF7 cells in serum-free media was at a moderate basa l level, but it was induced in six h about a-fold by 8Br-cAMP, and ove r 7-fold by forskolin (an adenylate cyclase activator) to high levels, similar to the SV40 positive control promoter. In SCF-luc plasmids ex tending to -853 or -2185, luciferase expression was still inducible by 8Br-cAMP and forskolin to high levels, but basal promoter activity wa s repressed to levels over 15-fold lower, in both the absence or prese nce of testosterone in the media for SF7 cells. The distal portion of the human SCF promoter (between -313 and -853, and also -853 and -2185 ) inhibits the basal level of transcription, while the proximal region (5' of -162) can mediate activation by cAMP.