Autoregulation of the androgen receptor at the translational level:: Testosterone induces accumulation of androgen receptor mrna in the rat ventral prostate polyribosomes

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Several studies have documented that androgens have the ability to autoregulate their own receptor levels; however, the mechanism of such autoregulation remains poorly understood. Along these lines, our laboratory has shown that testosterone increased androgen receptor (AR) protein levels and binding in the castrated rat ventral prostate within 1 h. Ongoing protein synthesis was required for the testosterone effect, as the protein synthesis inhibitor cycloheximide blocked this effect. Testosterone and/or actinomycin D, an mRNA synthesis inhibitor, did not affect the steady-state AR mRNA levels. Therefore, we suggest that the early events induced by testosterone are posttranscriptional and that protein synthesis is required for the maintenance of AR protein and AR mRNA levels. In addition, we hypothesize that the testosterone posttranscriptional effect is primarily through the sequestering of AR mRNA in the prostate polyribosomes. To test this hypothesis, total RNA was isolated from prostate polyribosomes of controls and testosterone-treated rats and AR mRNA levels were quantitated by competitive reverse transcription–polymerase chain reaction. Polyribosomes profiles on linear sucrose gradients showed no difference in the sedimentation characteristics of ribosomal particles from the vehicle-treated control or testosterone-treated animals. Furthermore, because both polyribosomal preparations can direct protein synthesis to the same extent in a cell-free system, testosterone does not increase the efficiency of translation. However, competitive reverse transcription–polymerase chain reaction revealed that testosterone increases AR mRNA associated with polyribosomes by threefold after 1 h of treatment compared with control. These data suggest a rapid testosterone-mediated posttranscriptional mechanism, in which testosterone regulates the stability of the AR mRNA by sequestering it in polyribosomes, and consequently increasing its translation.