Sertoli cell-specific expression of the human transferrin gene. Comparison with the liver-specific expression

We present a comparative study of the cis- and trans-acting elements governing the expression of the human transferrin (Tf) gene in two tissues, liver and testis, where Tf is expressed at various levels. We have previously identified the elements of the promoter, negative, and enhancer regions involved in the liver-specific expression of the gene. By transfection experiments of primary cultured rat Sertoli cells compared with hepatoma cells, DNase I footprinting, and gel retardation studies, we have analyzed 3.6 kilobase pairs of the Tf regulatory region. The far upstream enhancer functional in Hep3B cells is inactive in Sertoli cells; in the two cell types, different nuclear factors appear to bind to a DNA domain crucial for enhancer activity. Similar negative- and positive-acting elements are present in the distal promoter in both tissues. However different combinations of proximal promoter elements control tissue-specific expression. Liver-specific transcription is governed by the interaction of the Tf-LF1 protein and a C/EBP-related factor with the -125 to -45 region. In Sertoli cells, a -34 to -18 TATA box-binding factor is sufficient to initiate basal-level transcription. Efficient expression is achieved by the association of two factors binding either to the (-82, -1) or to the (-153, -52) region. The addition of a third adjacent element decreases the promoter activity, suggesting that the balance of three factors binding to the proximal sites regulates testis-specific expression.