A Long Noncoding RNA, GAS5 Can Be a Biomarker for Docetaxel Response in Castration Resistant Prostate Cancer

While functional studies of long noncoding RNAs (lncRNAs) have mostly focused on how they influence disease diagnosis and prognosis, the pharmacogenomic relevance of lncRNAs remains largely unknown. Here, we test the hypothesis that the expression of a lncRNA, grow arrest-specific 5 (GAS5) can be a biomarker for docetaxel response in castration resistant prostate cancer (CRPC) using both prostate cancer (PCa) cell lines and CRPC patient datasets. Our results suggest that lower GAS5 expression is associated with docetaxel resistance in both PCa cell lines and CRPC patients. Further experiments also suggest that GAS5 is downregulated in docetaxel resistant CRPC cell lines, which reinforces its potential as a biomarker for docetaxel response. To examine the underlying biological mechanisms, we transiently knockdown GAS5 expression in PCa cell lines and then subject the cells to docetaxel treatment overtime. We did not observe a decrease in docetaxel induced growth inhibition or apoptosis in the siRNA treated cells. The findings suggest that there is no direct causal relationship between change in GAS5 expression and docetaxel response. Subsequently, we explored the indirect regulation among GAS5, ATP binding cassette subfamily B member 1 (ABCB1), and docetaxel sensitivity. We showed that transient knockdown GAS5 did not lead to significant changes in ABCB1 expression. Therefore, we rule out the hypothesis that GAS5 directly down regulate ABCB1 that lead to docetaxel sensitivity. In conclusion, our work suggests that GAS5 can serve as a predictive biomarker for docetaxel response in CRPC; however, the exact mechanism behind the observed correlation remain to be elucidated.

Targeting TR4 nuclear receptor with antagonist bexarotene increases docetaxel sensitivity to better suppress the metastatic castration-resistant prostate cancer progression

Prostate cancer (PCa) is the second leading cause of cancer death in men in America, and there are no curative options for metastatic castration-resistant prostate cancer (mCRPC). Docetaxel (DTX) has been used as a standard chemotherapy for the mCRPC. However, resistance to DTX is a significant clinical problem as half of patients fail to respond to therapy. The TR4 nuclear receptor has been reported to play an important role in PCa progression, however, its linkage to the DTX resistance remains unclear. Here we found that TR4 was upregulated after DTX chemotherapy in the mCRPC cells and patients, and TR4 expression is correlated with DTX sensitivity with a higher level conferring chemo-resistance. Targeting TR4 with an antagonist bexarotene (Bex, a derivative of retinoid) suppressed the TR4 transactivation with increased DTX chemo-sensitivity. Mechanism dissection studies revealed that TR4 might alter the DTX chemo-sensitivity via modulating the TR4/lincRNA-p21/HIF-1α/VEGF-A signaling. Together, these results suggest that targeting this newly identified TR4/lincRNA-p21/HIF-1α/VEGF-A signaling with Bex, an FDA-approved drug, may increase the DTX chemo-sensitivity to better suppress the mCRPC progression.

Eya2 Is Overexpressed in Human Prostate Cancer and Regulates Docetaxel Sensitivity and Mitochondrial Membrane Potential through AKT/Bcl-2 Signaling

The aberrant expression of Eya2 has been observed in a wide range of cancer types. However, the clinical significance and biological effects of EYA2 in human prostate cancer remain unknown. In this study, we showed that increased levels of Eya2 protein correlated with advanced TNM stage, T stage, and a higher Gleason score. Data from the Cancer Genome Atlas (TCGA) prostate cohort consistently revealed that Eya2 mRNA was positively correlated with a higher Gleason score, higher T stage, and positive nodal metastasis in prostate cancer. Furthermore, data from the Oncomine database showed increased levels of EYA2 mRNA expression in prostate cancer tissues compared with normal tissues. Eya2 protein expression was also higher in prostate cancer cell lines compared with a normal RWPE-1 cell line. We selected LNCaP and PC-3 cell lines for plasmid overexpression and shRNA knockdown. CCK-8, colony formation, and Matrigel invasion assays demonstrated that the overexpression of Eya2 promoted proliferation, colony number, and invasion while Eya2 shRNA inhibited proliferation rate, colony formation, and invasion ability. CCK-8 and Annexin V assays showed that Eya2 reduced sensitivity to docetaxel and docetaxel-induced apoptosis while Eya2 shRNA showed the opposite effects. The overexpression of Eya2 also downregulated the cleavage of caspase3 and PARP while Eya2 depletion upregulated caspase3 and PARP cleavage. Notably, JC-1 staining demonstrated that Eya2 upregulated mitochondrial membrane potential. We further revealed that the overexpression of Eya2 upregulated Bcl-2, matrix metalloproteinase 7 (MMP7), and AKT phosphorylation. Accordingly, data from the TCGA prostate cohort indicated that EYA2 mRNA was positively correlated with the expression of Bcl-2 and MMP7. The inhibition of AKT attenuated EYA2-induced Bcl-2 upregulation. In conclusion, our data demonstrated that Eya2 was upregulated in prostate cancers. EYA2 promotes cell proliferation and invasion as well as cancer progression by regulating docetaxel sensitivity and mitochondrial membrane potential, possibly via the AKT/Bcl-2 axis.

Propofol Reversed Hypoxia-Induced Docetaxel Resistance in Prostate Cancer Cells by Preventing Epithelial–Mesenchymal Transition by Inhibiting Hypoxia-Inducible Factor 1α

Prostate cancer is the second most frequently diagnosed cancer worldwide. Hypoxia-induced epithelial–mesenchymal transition (EMT), driven by hypoxia-inducible factor 1α (HIF-1α), is involved in cancer progression and metastasis. The present study was designed to explore the role of propofol in hypoxia-induced resistance of prostate cancer cells to docetaxel. We used the Cell Counting Kit-8 and 5-ethynyl-2′-deoxyuridine incorporation assay to measure cell viability and cell proliferation, respectively, in prostate cancer cell lines. Then, we detected HIF-1α, E-cadherin, and vimentin expression using western blotting. Propofol reversed the hypoxia-induced docetaxel resistance in the prostate cancer cell lines. Propofol not only decreased hypoxia-induced HIF-1α expression, but also reversed hypoxia-induced EMT by suppressing HIF-1α. Furthermore, small interfering RNA–mediated silencing of HIF-1α reversed the hypoxia-induced docetaxel resistance, although there was little change in docetaxel sensitivity between the hypoxia group and propofol group. The induction of hypoxia did not affect E-cadherin and vimentin expression, and under the siRNA knockdown conditions, the effects of propofol were obviated. These data support a role for propofol in regulating EMT in prostate cancer cells. Taken together, our findings demonstrate that propofol plays an important role in hypoxia-induced docetaxel sensitivity and EMT in prostate cancer cells and that it is a potential drug for overcoming drug resistance in prostate cancer cells via HIF-1α suppression.