Achieving resistance specificity in prostate cancer

Androgen deprivation restores ARHGEF2 to promote neuroendocrine differentiation of prostate cancer

Androgen receptor (AR) plays an important role in the progression of prostate cancer and has been targeted by castration or AR-antagonists. The emergence of castration-resistant prostate cancer (CRPC) after androgen deprivation therapy (ADT) is inevitable. However, it is not entirely clear how ADT fails or how it causes resistance. Through analysis of RNA-seq data, we nominate ARHGEF2 as a pivotal androgen-repressed gene. We show that ARHGEF2 is directly suppressed by androgen/AR. AR occupies the enhancer and communicates with the promoter region of ARHGEF2. Functionally, ARHGEF2 is important for the growth, lethal phenotype, and survival of CRPC cells and tumor xenografts. Correspondingly, AR inhibition or AR antagonist treatment can restore ARHGEF2 expression, thereby allowing prostate cancer cells to induce treatment resistance and tolerance. Overall, our findings provide an explanation for the contradictory clinical results that ADT resistance may be caused by the up-regulation of ARHGEF2 and provide a novel target.

Co-downregulation of GRP78 and GRP94 Induces Apoptosis and Inhibits Migration in Prostate Cancer Cells

Background

Both glucose-regulated protein 78 kDa (GRP78) and glucose-regulated protein 94 kDa (GRP94) are important molecular chaperones that play critical roles in maintaining tumor survival and progression. This study investigated the effects in prostate cancer cells following the downregulation of GRP78 and GRP94.

Methods

RNA interference was used to downregulate GRP78 and GRP94 expression in the prostate cancer cell line, PC-3. The effects on apoptosis and cell migration was examined along with expression of these related proteins.

Results

Small interfering RNAs targeting GRP78 and GRP94 successfully down-regulated their expression. This resulted in the induction of apoptosis and inhibition of cell migration. Preliminary mechanistic studies indicated that caspase-9 (cleaved) and Bax expression levels were upregulated while Bcl-2 and vimentin expression levels were downregulated.

Conclusion

Co-downregulation of GRP78 and GRP94 expression induces apoptosis and inhibits migration in prostate cancer cells.

MicroRNA-4719 and microRNA-6756-5p Correlate with Castration-Resistant Prostate Cancer Progression through Interleukin-24 Regulation

Prostate cancer (PCa) is the second leading cause of cancer death in the United States. The five-year survival rate for men diagnosed with localized PCa is nearly 100%, yet for those diagnosed with aggressive PCa, it is less than 30%. The pleiotropic cytokine Interleukin-24 (IL-24) has been shown to specifically kill PCa cells compared to normal cells when overexpressed in both in vitro and in vivo studies. Despite this, the mechanisms regulating IL-24 in PCa are not well understood. Since specific microRNAs (miRNAs) are dysregulated in PCa, we used miRNA target prediction algorithm tools to identify miR-4719 and miR-6556-5p as putative regulators of IL-24. This study elucidates the expression profile and role of miR-4719 and miR-6756-5p as regulators of IL-24 in PCa. qRT-PCR analysis shows miR-4719 and miR-6756-5p overexpression significantly decreases the expression of IL-24 in PCa cells compared to the negative control. Compared to the indolent PCa and normal prostate epithelial cells, miR-4719 and miR-6756-5p are significantly overexpressed in castration-resistant prostate cancer (CRPC) cell lines, indicating that their gain may be an early event in PCa progression. Moreover, miR-4719 and miR-6756-5p are significantly overexpressed in the CRPC cell line of African-American males (E006AA-hT) compared to CRPC cell lines of Caucasian males (PC-3 and DU-145), indicating that miR-4719 and miR-6756-5p may also play a role in racial disparity. Lastly, the inhibition of expression of miR-4719 and miR-6756-5p significantly increases IL-24 expression and inhibits proliferation and migration of CRPC cell lines. Our findings indicate that miR-4719 and miR-6756-5p may regulate CRPC progression through the targeting of IL-24 expression and may be biomarkers that differentiate between indolent and CRPC. Strategies to inhibit miR-4719 and miR-6756-5p expression to increase IL-24 in PCa may have therapeutic efficacy in aggressive PCa.

Up regulation of the steroid hormone synthesis regulator HSD3B2 is linked to early PSA recurrence in prostate cancer

HSD3B2 plays a crucial role in steroid hormone biosynthesis and is thus of particular interest in hormone dependent tumors such as prostate cancer. To clarify the clinical relevance of HSD3B2 expression in prostate cancer, we analyzed HSD3B2 protein expression by immunohistochemistry on our preexisting tissue microarray with 12.247 annotated cancers. Compared with normal tissue cytoplasmic HSD3B2 staining was stronger in prostate cancers. In 9371 interpretable cancers, HSD3B2 expression was found in 95.5% of cancers and was considered weak in 29.9%, moderate in 40.7% and strong in 24.9%. HSD3B2 up regulation was linked to advanced pathological tumor stage (pT), high Gleason grade, elevated preoperative PSA levels (p < 0.0001 each), lymph node metastasis (p = 0.0019), accelerated cell proliferation (p < 0.0001), androgen receptor (AR) expression (p < 0.0001), and early biochemical recurrence (p < 0.0001). HSD3B2 up regulation was only marginally more frequent in ERG positive (98%) than in ERG negative cancers (94%; p < 0.0001) and was strongly linked to deletions of 5q and 6q (p < 0.0001 each). Multivariate analyses showed that the prognostic impact of HSD3B2 expression was independent of established preoperative, but not of postoperative prognostic parameters. In summary, the results of our study demonstrate that HSD3B2 is strongly up regulated in a fraction of prostate cancers that are characterized by increased AR signaling, adverse tumor phenotype and early biochemical recurrence.