Identification of a DNA-binding site for the transcription factor GC2 in the promoter region of the p12 gene and repression of its positive activity by upstream negative regulatory elements.

Mouse secretory protease inhibitor p12 is significantly transcribed by the cells from the seminal vesicle, the coagulating gland, the ventral prostate, and to a lesser level by the pancreas. It is otherwise undetectable in every other tissue examined. To study the molecular mechanisms involved in this model of cell-specific control of gene expression, we cloned fragments containing various lengths of the p12 promoter upstream of the CAT reporter gene. We demonstrated that p12 sequences from +34 to -108 relative to the CAP site can confer a constitutive level of CAT expression following transient transfection in non-prostatic CV1 and GH4C1 cells. We identified within this minimal p12 promoter the cis-acting sequences needed to direct such a significant level of CAT expression. A DNA-binding site (p12.A) highly homologous to the rat growth hormone (rGH) sequence recognized by the trans-acting factor GC2 was identified between the TATA- and the double CAAT-box sequences from the p12 promoter. Using competition and mutation analysis, we provide evidence that the positively acting p12.A-binding protein is likely to be the rGH GC2 transcription factor, suggesting that the same, or a very similar factor, regulates expression of both rGH and p12 genes. By further analysis of the p12 5'-flanking sequences, we demonstrated that plasmids including sequences from -109 to -843 can strongly repress the level of transcription directed by this minimal p12 promoter, providing evidence for the presence of cis-acting negative regulatory elements critical for the establishment of p12 gene extinction in non-prostatic cells.