Long non-coding RNAs are key players in Prostate cancer tumorigenesis and drug resistance (2020)

Long non-coding RNAs (lncRNAs) have been characterized as key players in several cancer-associated processes such as tumorigenesis and drug resistance. Emerging evidence indicates that lncRNAs affect initiation and progression of several cancers, including prostate cancer (PCa) and its advanced forms, such as metastatic castration resistant prostate cancer (mCRPC).
Among others, H19 is one of the most studied oncogenic lncRNAs in cancer and has been associated with cancer tumorigenesis and progression, via mediating several pathways an acting in different mechanisms of action, including epigenetic and miRNA regulation.
We have investigated lncRNA roles in PCa tumorigenesis by analysing the E006AA cell model. Emerging evidence has shown that parental E006AA are not tumorigenic in nude mice, while its derived E006AA-ht, is highly tumorigenic. Via high-throughput RNA sequencing we have shown that E006AA-ht overexpress different lncRNAs compared to E006AA. Interestingly, we found a high upregulation of H19 in E006AA-ht vs the parental cell line. Our in vitro validation has confirmed the sequencing data and further research could unravel a crucial role of H19 in PCa tumorigenesis, opening a new challenging chapter of lncRNAs research. We hypothesize that H19 could be involved in in vivo immunity suppression and our further studies aim at investigating H19 in this molecular and clinical context.
Furthermore, we have studied lncRNAs as key players in cancer aggressiveness by using cellular models of mCRPC. From our studies, HORAS5 (i.e. linc00161) emerged as the most consistently upregulated lncRNA in CRPC patient-derived xenografts. This lncRNAs was previously associated with cancer drug-response in osteosarcoma, ovarian cancer and hepatocellular carcinoma. Our study has shown for the first time that HORAS5 promotes drug resistance in CRPC. After a preliminary drug screen, we have selected the chemotherapeutics cabazitaxel for further investigation. Via lentiviral-mediated overexpression and siRNA-based silencing we have regulated HORAS5 expression and analysed cell count and apoptosis of CRPC cells exposed to clinically achievable concentrations of cabazitaxel.
The overexpression of HORAS5 increases cabazitaxel resistance, while HORAS5 silencing has an opposite effect, via inhibition of apoptosis. RNA sequencing and RT-qPCR revealed that BCL2A1 is the most upregulated transcript in HORAS5 overexpressing cells exposed to cabazitaxel, and that BCL2A1 silencing decreases cell count and increases caspase activity. Our data suggest that BCL2A1 expression is induced by HORAS5, thereby enhancing CRPC cells resistance to cabazitaxel. Transfection of CRPC cells with HORAS5-targeting ASOs can effectively silence this lncRNA and determine a decrease of cabazitaxel resistance. We have also shown that both HORAS5 and BCL2A1 upregulation results in decreased survival in PCa patients and samples from mCRPC patients treated with taxanes have upregulation of HORAS5.
Overall, our studies bring novel insights into crucial roles of lncRNAs in PCa progression and aggressiveness making them emerging targets for cancer treatment at different stages.