LARGE FRAGMENT OF THE PROBASIN PROMOTER TARGETS HIGH-LEVELS OF TRANSGENE EXPRESSION TO THE PROSTATE OF TRANSGENIC MICE

BACKGROUND. Androgen regulation and prostate-specific expression of ta rgeted genes in transgenic mice can be controlled by a small DNA fragm ent of the probasin (PB) promoter (-426 to +28 base pairs, bp). Althou gh the small PB fragment was sufficient to direct prostate-specific ex pression, the low levels of transgene expression suggested that import ant upstream regulatory sequences were missing. METHODS. To enhance tr ansgene expression, a large fragment of the PB promoter (LPB, -11,500 to +28 bp) was isolated, linked to the bacterial chloramphenicol acety l transferase (CAT) gene, and microinjected into CD1 mouse oocytes to generate transgenic mouse lines. RESULTS. As shown by the immunohistoc hemical studies, CAT gene expression was restricted to the prostatic e pithelial cells in a tissue-specific manner. High levels of CAT gene e xpression were observed in two of the six LPB-CAT transgenic Lines. In Line I, developmental regulation of LPB-CAT was detected early, from 1 to 4 weeks of age, with the activity of CAT increasing from 3 to 40, 936 dpm/min/mg protein. Upon sexual maturation and elevated serum andr ogen levels (7 weeks of age), a further 18-fold rise in CAT activity o ccurred. Hormone ablation by castration in mature mice dramatically re duced transgene expression, whereas treatment with androgens returned LPB-CAT expression to precastration levels. In contrast, treatment wit h glucocorticoids had no significant effect on CAT gene expression. Zi nc treatment of the castrated animals also increased LPB-CAT expressio n three- to four-fold in two prostatic lobes. CONCLUSIONS. This study demonstrates that important regulatory DNA sequences located in the LP B fragment contribute to tissue-specific expression and greatly increa se levels of transgene expression induced by androgens and zinc. (C) 1 997 Wiley-Liss, Inc.