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Prostate cancer is the most common cancer in men. The molecular mechanisms leading to its development are poorly understood. Maspin is a tumor-suppressing serpin expressed in normal breast and prostate epithelium. We have found that expression of maspin in normal and carcinoma-derived prostate epithelial cells is differentially regulated at the transcriptional level. We have identified two different kinds of cis elements, Ets and hormonal responsive element (HRE), in the maspin promoter. The Ets element is active in regulating maspin expression in normal prostate epithelial cells but inactive in tumor cells. The HRE site is a negative element that is active in both cell types. This negative DNA sequence can repress a heterologous promoter recognized by the androgen receptor. We conclude that expression of maspin is under the influence of both a positive Ets and a negative HRE element. Loss of maspin expression during tumor progression apparently results from both the absence of transactivation through the Ets element and the presence of transcription repression through the negative HRE element recognized by androgen receptor.
Zhang et al. (Tue,) studied this question.