THE MOUSE ANDROGEN RECEPTOR IS SUPPRESSED BY THE 5'-UNTRANSLATED REGION OF THE GENE

The androgen receptor (AR) mediates the biological functions of androg ens and is essential for normal growth and differentiation of urogenit al organs as well as initiation and maintenance of spermatogenesis. Wi thdrawal of androgens by castration or other methods has been shown to cause a marked, although often temporary, regression of many prostate cancers. In order to gain a better understanding of the transcription al regulation of the AR, a series of truncation mutants derived from t he 5'-region of the mouse AR (mAR) were inserted into the promoter-les s plasmid pBLCAT3 and transiently expressed in the mouse (alpha T3-1 a nd GT1-7 cell lines. The results of these experiments indicate the pre sence of a negative regulatory element in the 5'-untranslated region o f the gene, which is able to reduce chloramphenicol acetyltransferase (CAT) activity by 77-89%. We have named this element the mAR suppresso r (mARS). DNase-I protection assays of the 5'-untranslated region disc losed a protected domain. Gel mobility-assays using the mARS revealed the presence of three protein-DNA complexes that could specifically bi nd to this protected domain. Insertion of the mARS into the thymidine kinase promoter containing pBLCAT2 vector resulted in a 2- to 10-fold decrease in CAT activity, but only if the insert was 3' to the start o f transcription initiation. Finally, point mutations within the mARS w ere able to increase transcription of the AR promoter by 2.3-fold. The results of these experiments indicate that the mAR 5'-untranslated re gion contains a suppressor element. The suppressor is in a region that is bound by one or more proteins and is capable of suppressing the th ymidine kinase promoter in a position-specific manner. Characterizatio n of this suppressor may provide insight into the physiological means by which the AR is regulated in normal development and/or pathogenesis of androgen target tissues.