MALE-SPECIFIC TRANSCRIPTION INITIATION OF THE C4-SLP GENE IN MOUSE-LIVER FOLLOWS ACTIVATION OF STAT5

The mouse genes encoding the constitutively expressed complement compo nent C4 and its closely related isoform C4-Slp (sex-limited protein), which is expressed only in male animals of several strains, provide a unique model to study sequence elements and trans-acting factors respo nsible for androgen responsiveness. Our previous studies have shown th at hormonal induction of C4-Slp is mediated by a sex-specific pattern of growth hormone secretion. Promoter analyses in vitro have led to co ntradictory conclusions concerning the significance of C4-Slp-specific sequences in the 5' flanking region. Mutant mice carrying the H-2(aw1 8) haplotype, which is characterized by a large deletion in the S regi on covering the C4 and 21-OHase A genes, permit the direct in vivo ana lysis of C4-Slp transcription, unhindered by the presence of C4. Run-o n analysis of transcription in liver nuclei of males and females of th is strain demonstrated a 100-fold higher transcriptional activity in m ales, essentially determined at the transcription initiation level. Th e androgen dependence of transcription initiation was confirmed by run -on analysis of testosterone-treated females, where transcriptional ac tivity started after 6 days of androgen treatment and reached male lev els after 20 days. Conversely, the growth hormone-regulated activity o f transcription factor STAT5 was already detected in liver nuclei afte r 48 hr of androgen treatment. Furthermore, we demonstrate that activa ted STAT5 recognizes in vitro two upstream gamma interferon-activated sequence (GAS) elements of the C4-Slp gene, centered at positions -196 9 and -1831. We postulate that binding of STAT5 to these C4-Slp-specif ic GAS elements plays a crucial role in the chromatin remodelings that lead to transcriptional competence of the C4-Slp gene in the liver.