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UBC Theses and Dissertations

An investigation of cholesterol pathways in castration-resistant prostate cancer : the role of scavenger receptor class B type I (SR-BI) Twiddy, Alexis


Background. Scavenger Receptor Class B Type I (SR-BI) facilitates influx of cholesterol to the cell from lipoproteins in the circulation. This influx of cholesterol is important for many cellular functions, including synthesis of androgens. Castration-resistant prostate cancer tumors are able to synthesize androgens de novo in order to supplement the loss of exogenous sources often as a result of androgen deprivation therapy. By removing a source of cholesterol, silencing of SR-BI may impact the ability of prostate cancer cells, particularly those of castration-resistant state, to maintain the intracellular supply of androgens. Methods. SR-BI expression was knocked down in LNCaP (androgen-dependent) and C4-2 (castration-resistant) cells using small interfering RNA. The effect of down-regulation of SR-BI on cell toxicity, cell viability, and expression of various proteins was examined using a LDH assay, a MTS assay and western blotting in both cell types. In addition, cholesterol synthesis activity was measured using the radiolabeled precursor, ¹⁴C-acetate and cellular cholesterol, testosterone and PSA concentrations were assessed using fluorometric and colorometric assays. Results. Basal SR-BI and HSL protein expression was higher in C4-2 cells than LNCaP cells. Silencing of SR-BI expression by greater than 85% reduced PSA secretion in LNCaP and C4-2 SRBI-KD cells by 55% and 58% compared to negative control cells, respectively. SR-BI-KD C4-2 cells demonstrated significantly reduced cell viability (>25%) compared the NC cells as well as an increased cholesterol synthesis 6 days post-transfection. Conclusions. The down-regulation of SR-BI significantly impacted PSA production of both prostate cancer cell lines, as well as the viability of C4-2 cells in the presence and absence of HDL. Although corresponding changes in cholesterol and testosterone concentrations were not observed, the data suggest that silencing SR-BI and thereby reducing cholesterol influx impacts cholesterol pathways, as evidenced by a compensatory up-regulation of de novo cholesterol synthesis. This may affect substrate availability to the androgen synthesis pathway or may implicate a separate role of SR-BI in prostate cancer cells.

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