EXPRESSION AND HORMONE REGULATION OF PROLACTIN RECEPTORS IN RAT DORSAL AND LATERAL PROSTATE

We have studied the receptors that presumably mediate the biological e ffects of PRL in rat dorsal (DP) and lateral (LP) prostate. The PRL re ceptor proteins mere localized to the glandular secretory epithelium o f prostatic tis sue by immunohistochemistry. Both the short and the lo ng PRL receptor proteins were detected in DP and LP by Western blot an alysis and cross-linking of [I-125]human PRL to membrane preparations of DP and LP. Three messenger RNAs (mRNAs) for the long [1.3-1.7, 2.5, and 9.5-10 kilobases (kb)] and short (0.6-0.7, 3.0-4.6, and 10-12 kb) PRL receptors were expressed in dorsal and lateral lobes of rat prost ate. Testosterone (T), estrogen (E), and PRL regulation of PRL recepto r expression in rat DP and LP was studied in organ culture, which has been shown to be a suitable model to study hormone responses of prosta tic tissue in vitro. The mRNAs of the short and long PRL receptors wer e differentially regulated in rat dorsolateral prostate. T, E, and PRL regulated the level of the long PRL receptor mRNAs in a tissue-specif ic manner, whereas hormone regulation of the short PRL receptor mRNAs was only modest. Furthermore, the hormonal responses of the different mRNA splicing variants of the long PRL receptor were not all similar; T, E, and PRL each increased the expression of 1.3- to 1.7-kb and 9.5- to 10-kb transcripts in DP, but only T did so in LP, whereas no clear regulation for the 2.5-kb mRNA could be observed in either tissue. Th is suggests that the hormonal regulation occurs at least at the posttr anscriptional level. The effects of T and E were counteracted by the a ntihormones cyproterone and toremifene, respectively, indicating a spe cific receptor-mediated manner of steroid action.