Mechanisms of Androgen-Mediated Repression of the Maspin Tumor Suppressor Gene in Prostate Cancer

Abstract

It is estimated that one in six men in North America will be diagnosed with prostate cancer (PCa) during his lifetime. Localized PCa is often treated using surgery and radiation. Advanced and metastatic PCa can be treated by blocking the production or action of androgens, the male sex hormones. This androgen depletion therapy is only temporarily successful because PCa frequently returns in an androgen-refractory form that is resistant to hormonal manipulations and capable of growing in an androgen-depleted environment. Androgen receptor (AR) is a nuclear receptor transcription factor necessary for normal prostate cell growth and function as well as for growth of PCa. Androgens activate the AR, which translocates to the nucleus where it transcriptionally activates or represses target genes. One such gene is the Maspin tumor suppressor. Maspin is a proteinase inhibitor that serves to prevent proteinase degradation of the extracellular matrix, which is prerequisite to tumor invasion and metastasis. Androgens transcriptionally repress Maspin, but the mechanisms have not yet been fully characterized. To investigate the mechanisms of Maspin repression, a plasmid containing the luciferase reporter gene under the control of the Maspin promoter was constructed and transfected into VCaP and LNCaP PCa cell lines. Transfected cells were treated with dihydrotestosterone (a natural androgen) or mibolerone (a synthetic androgen) for 24 hours. Luciferase activity was subsequently measured by dual luciferase assay. These experiments have indicated that the AR may not directly repress Maspin transcription. Ongoing research will utilize real time PCR to determine whether AR inhibits Maspin transcription via a direct or indirect mechanism.