A bioinformatics-based functional analysis shows that the specifically androgen-regulated gene SARG contains an active direct repeat androgen response element in the first intron

Abstract

We characterized the specifically androgen-regulated gene (SARG), which is expressed in the androgen receptor (AR) and glucocorticoid receptor (GR) positive cell line lymph node carcinoma of the prostate-1F5 (LNCaP-1F5). SARG mRNA expression can be up-regulated by androgens, but not by glucocorticoids. SARG mRNA expression is high in prostate tissue. SARG is composed of four exons and spans a region of 14.5 kbp on chromosome 1q32.2. Transcripts of 5.5, 3.3 and 2.3 kb are the result of alternative polyadenylation. SARG mRNA splice variants lack exon 2 and vary in length of exon 1. The SARG protein has a length of 601 amino acids and is located in the cytoplasm. By screening the 18 kbp genomic sequence flanking the transcription start site we identified the imperfect direct repeat 5'-TGTGCTaacTGTTCT-3'in intron 1 as an active androgen response element (ARE-SARG+4.6). A 569 bp genomic DNA fragment containing this element functioned as an androgen-specific enhancer in transiently transfected LNCaP-1F5 cells. ARE-SARG+4.6 cooperated with flanking sequences for optimal activity. Inactivation of ARE-SARG+4.6 completely abolished the androgen response of the enhancer. Chromatin immunoprecipitation (ChIP) experiments showed chromatin structural changes of the enhancer in the presence of R1881. ARE-SARG+4.6 was able to bind to the androgen receptor, but not to the glucocorticoid receptor, correlating with its androgen-specific activity in transfections.