Cholesterol and phytosterols differentially regulate the expression of caveolin 1 and a downstream prostate cell growth-suppressor gene

Abstract

Background: The purpose of our study was to show the distinction between the apoptotic and anti-proliferative signaling of phytosterols and cholesterol-enrichment in prostate cancer cell lines, mediated by the differential transcription of caveolin-1, and N- myc downstream- regulated gene 1 ( NDRG1), a pro-apoptotic androgen-regulated tumor suppressor. Methods: PC-3 and DU145 cells were treated with sterols (cholesterol and phytosterols) for 72 h, followed by trypan blue dye-exclusion measurement of necrosis and cell growth measured with a Coulter counter. Sterol induction of cell growth-suppressor gene expression was evaluated by mRNA transcription using RT-PCR, while cell cycle analysis was performed by FACS analysis. Altered expression of Ndrg1 protein was confirmed by Western blot analysis. Apoptosis was evaluated by real time RT-PCR amplification of P53, Bcl- 2 gene and its related pro- and anti-apoptotic family members. Results: Physiological doses (16 μM) of cholesterol and phytosterols were not cytotoxic in these cells. Cholesterol-enrichment promoted cell growth ( P < 0.05), while phytosterols significantly induced growth-suppression ( P < 0.05) and apoptosis. Cell cycle analysis showed that contrary to cholesterol, phytosterols decreased mitotic subpopulations. We demonstrated for the first time that cholesterols concertedly attenuated the expression of caveolin- 1 ( cav- 1) and NDRG1 genes in both prostate cancer cell lines. Phytosterols had the opposite effect by inducing overexpression of cav- 1, a known mediator of androgen-dependent signals that presumably control cell growth or apoptosis. Conclusions: Cholesterol and phytosterol treatment differentially regulated the growth of prostate cancer cells and the expression of p53 and cav- 1, a gene that regulates androgen-regulated signals. These sterols also differentially regulated cell cycle arrest, downstream pro-apoptotic androgen-regulated tumor suppressor, NDRG1 suggesting that cav- 1 may mediate pro-apoptotic NDRG1 signals. Elucidation of the mechanism for sterol modulation of growth and apoptosis signaling may reveal potential targets for cancer prevention and/or chemotherapeutic intervention. Sterol regulation of NDRG1 transcription suggests its potential as biomarker for prediction of neoplasms that would be responsive to chemoprevention by phytosterols.