Abstract
In most androgen responsive cells or tissues, androgen regulates androgen receptor (AR) levels, a process termed autoregulation. Since the extent of biological response to androgen is correlated with AR concentration, AR autoregulation is a determinant of cellular sensitivity to androgen. AR mRNA and protein are up- or down-regulated by androgen in a tissue-specific manner. The AR promoter and upstream region of the AR gene are not sufficient to confer androgen regulation of AR mRNA levels. This observation motivated us to search for cis-acting elements responsible for AR autoregulation in exonic sequences of the AR gene. Both up- and down-regulation of AR mRNA can be reproduced in cells expressing a transfected AR cDNA. Sequences present in the AR cDNA, but not the heterologous promoter that drives expression of the cDNA, are responsible for this androgenic regulation of AR mRNA. AR mRNA is up-regulated by androgen in an androgen-independent human prostate cancer cell line, PC3, expressing a transfected AR cDNA. This androgen-inducible up-regulation of AR mRNA is due to androgen stimulation of AR mRNA transcription. I have identified a 350 bp androgen responsive region within the AR coding region that is responsible for this AR mRNA up-regulation. This 350 bp fragment contains two androgen response elements (AREs), ARE-1 and ARE-2, that are separated by 182 bp. ARE-1 (5$\sp\prime$-TGTCCT-3$\sp\prime$) and ARE-2 (5$\sp\prime$-AGTACTCC-3$\sp\prime$) function synergistically to mediate AR mRNA up-regulation. Both ARE-1 and ARE-2 mediate this AR mRNA up-regulation, since an AR cDNA bearing silent mutations of ARE-1 and ARE-2 is not up-regulated by androgen. DNase I footprinting analysis demonstrates AR binds to sequences that encompass ARE-1 and ARE-2 as well as a third region located between these AREs. ARE-1 and ARE-2 act synergistically with respect to binding to AR. Up-regulation of AR mRNA by androgen is accompanied by AR protein up-regulation in PC3 cells. These PC3 cells expressing AR fail to be desensitized by prolonged androgen exposure unlike other AR-containing cells. These results suggest that AR mRNA and protein up-regulation may influence cellular sensitivity to androgen.