title: Functional relevance of microRNAs miR-141 and miR-375 in prostate cancer development and mechanistic analyses of androgen receptor dimerization
Creators: name: Guzman Galvan, Juan Luis
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2024

description: Prostate cancer (PCa) is the second most common cancer in men worldwide. The causes of this disease are mostly unknown, however, besides the patient's age a genetic predisposition as well as factors like ethnicity, nutrition and family history also seem to play a role. While use of prostatic-specific antigen (PSA) levels in the routine has facilitated that most of cancers are detected while they are organ confined and hence potentially chances for a curative treatment, progressive prostate cancer is still a therapeutic challenge. Therefore, there is an urgent need for molecularly targeted therapies. This requires the identification and understanding of novel molecular factors that are relevant in prostate cancer progression and therapy response. MicroRNAs (miRNAs) are small regulatory non-coding RNAs of 19-22 nucleotides length. To date more than 2000 miRNAs have been identified in the human genome with every miRNA being able to regulate a large number of genes which are functionally related to physiologic and pathologic processes like cell differentiation, cell cycle control, proliferation, apoptosis and via these biological processes, miRNAs play an important role in cancer development. Based on previous studies on the potential roles of miR-141 and miR-375 as oncogenic miRNAs involved in the pro-tumorigenic Pl3K-AKT signaling pathway regulating tumor suppressors PTEN and PHLPP1/2, the first aim of this study was to determine molecular effects and functional consequences of miR-141/miR-375-mediated regulation on the Pl3K-AKT signaling pathway and thus on progression of prostate cancer. Moreover, the impact of miR-141/miR-375 inhibition with anti-miRs on PCa cell lines was examined in vitro. Direct inhibition of miR-141 and miR-375 displayed up-regulation of phosphatases PHLPP1 and PHLPP2 leading to down-regulation of the Pl3K-AKT pathway. In addition, down-regulation of miR-141 and miR-375 led to changes in proliferation and apoptosis in PCa cell lines. We also investigated one specific resistance mechanism that has gained increasing attention, the generation of androgen receptor (AR) splice variants. More specifically, androgen receptor splice variant-7 (AR-V7) has been described to mediate resistance to the newer drugs targeting the AR pathway (Enzalutamide and Abiraterone). The goal was to mechanistically precise the interaction between AR and AR-V7 in null-AR HEK-293 cells using the NanoLuc Binary Technology (NanoBiT) structural complementation assay under androgen stimulation and -deprivation conditions. We described an androgen-regulated interaction between AR and AR-V7 forming heterodimers in the nucleus, whereas AR-V7 was found to dimerize in the absence of androgens with a constitutively active nuclear localization. By doing so, androgen splice variants may control the degree of response of AR to androgen and to androgen-directed therapies. The findings described in this work underline the promising role of miRNAs as novel treatment in prostate cancer and underscore a critical need to develop effective means to target both AR and AR-V7 to achieve complete AR blockade to more effectively combat of these clinically challenging tumors.