Identification of a Functional Androgen-Response Element in the Exon 1-Coding Sequence of the Cystatin-Related Protein Gene crp2
Abstract Two hormone-responsive segments, one in the region of the promoter and one in intron 1, are identified in two homologous androgen-regulated and differentially expressed rat genes encoding the cystatin-related proteins (CRPs). Footprint analysis with the androgen receptor (AR) DNA-binding domain on the promoter-containing fragments reveals an AR-binding site downstream of the transcription start point in the crp2 gene (ARBSd/crp2,+ 40/+63). It displays an androgen response element-like sequence motif 5′-AGAAGAaaaTGTACA-3′ and overlaps with the ATG translation start codon. A double-stranded oligonucleotide containing this sequence forms a DNA-protein complex with the full-length AR synthesized by vaccinia, as seen in band shift assays. Additional AR-binding sites, ARBSu/crp1 and ARBSu/crp2, occur 5′ upstream of the transcription start point and are located at an identical position (−142/−120) in crp1 and crp2. The AR affinity for these two slightly different sequence motifs is relatively weak. The biological function of all three AR-binding sites as transcription control elements has been studied. The ARBSd/crp2 element clearly shows androgen-response element characteristics. The contribution of the common upstream element to the androgen-dependent control of reporter gene transcription is less clear. The transcription of a reporter gene construct containing the crp2 footprint fragment crp2F (−273/+88) is hormonally regulated as determined by transfection into the human breast cancer cell line T-47D. Androgens, but also glucocorticoids, efficiently stimulate steroid-dependent transcription of the chloramphenicol acetyltransferase gene. Mutation of the 5′-TGTACA-3′ sequence in ARBSd/crp2 destroys the AR binding and abolishes the androgen-dependent synthesis of chloramphenicol acetyltransferase. A large fragment derived from intron 1 of the crp1 and crp2 gene can also provide the androgen-dependent transcription of chimeric constructs in T-47D cells. However, the induction measured is less than the one observed with crp2F (−273/+88), and this activity seems to reside in several subfragments that each display a low but consistent androgen responsiveness.