Mammalian target of rapamycin (mTOR) regulates various fundamental cellular events including cell proliferation, protein synthesis, metabolism, apoptosis, and autophagy. Tumor suppressive miR-99b-5p has been implicated in regulating PI3K/AKT/mTOR signaling in a variety of types of cancer. Our previous study suggested the reciprocal miR-99b-5p/MTOR (downregulated/upregulated) pairing as a key microRNA-mRNA regulatory component involved in the prostate cancer (PCa) disparities. In this study, we further validated the expression profiles of mTOR and miR-99b-5p in the PCa, colon, breast, and lung cancer specimens and cell lines. The immunohistochemistry (IHC), immunofluorescence, Western blot, and RT-qPCR assays have confirmed that mTOR is upregulated while miR-99b-5p is downregulated in different patient cohorts and a panel of cancer cell lines. Intriguingly, elevated nuclear mTOR expression was observed in African American PCa and other advanced cancers. Transfection of the miR-99b-5p mimic resulted in a significant reduction in nuclear mTOR and androgen receptor (AR), while a slight/moderate to no decrease in cytoplasmic mTOR and AR in PCa and other cancer cells, suggesting that miR-99b-5p inhibits mTOR and AR expression and their nuclear translocation. Moreover, overexpression of miR-99b-5p targets/inhibits AR-mTOR axis, subsequently initiating cell apoptosis and sensitizing docetaxel-induced cytotoxicity in various cancers. In conclusion, our data suggest that reciprocal miR-99b-5p/nuclear mTOR pairing may be a more precise diagnostic/prognostic biomarker for aggressive PCa, than miR-99b-5p/MTOR pairing or mTOR alone. Targeting the AR-mTOR axis using miR-99b-5p has also been suggested as a novel therapeutic strategy to induce apoptosis and overcome chemoresistance in aggressive PCa.

African American (AA) men exhibit 1.6-fold higher prostate cancer (PCa) incidence and 2.4-fold higher mortality rates compared to European American (EA) men. In addition to socioeconomic factors, emerging evidence suggests that intrinsic biological differences may explain part of PCa disparities. In this study, we applied microRNA (miRNA)-driven bioinformatics to evaluate whether differential miRNA-mRNA regulatory networks play a role in promoting the AA PCa disparities. 10 differentially expressed miRNAs were imported to mirPath V.3 algorithm, leading to identification of 58 signaling pathways differentially regulated in AA PCa versus EA PCa. Among these pathways, we particularly focused on mTOR and VEGF signaling, where we identified 5 reciprocal miRNA-mRNA pairings: miR-34a-5p/HIF1A, miR-34a-5p/PIK3CB, miR-34a-5p/IGFBP2, miR-99b-5p/MTOR and miR-96-5p/MAPKAPK2 in AA PCa versus EA PCa. RT-qPCR validation confirmed that miR-34a-5p, miR-99b-5p and MAPKAPK2 were downregulated, while miR-96-5p, IGFBP2, HIF1A, PIK3CB and MTOR were upregulated in AA PCa versus EA PCa cells. Transfection of miRNA mimics/antagomir followed by RT-qPCR and Western blot analysis further verified that IGFBP2, HIF1A and PIK3CB are negatively regulated by miR-34a-5p, whereas MTOR and MAPKAPK2 are negatively regulated by miR-99b-5p and miR-96-5p, respectively, at mRNA and protein levels. Targeting reciprocal pairings by miR-34a-5p mimic, miR-99b-5p mimic or miR-96-5p antagomir downregulates HIF1α, PI3Kβ, mTOR, IGFBP2 but upregulates MAPKAPK2, subsequently reducing cell proliferation and sensitizing docetaxel-induced cytotoxicity in PCa cells. These results suggest that miRNA-mRNA regulatory network plays a critical role in AA PCa disparities, and targeting these core miRNA-mRNA pairings may reduce PCa aggressiveness and overcome the chemoresistance in AA patients.

Prostate cancer (PCa) is the most frequently diagnosed cancer and the second leading cause of cancer deaths among American men. Complex genetic and epigenetic mechanisms are involved in the development and progression of PCa. MicroRNAs (miRNAs) are short noncoding RNAs that regulate protein expression at the post-transcriptional level by targeting mRNAs for degradation or inhibiting protein translation. In the past two decades, the field of miRNA research has rapidly expanded, and emerging evidence has revealed miRNA dysfunction to be an important epigenetic mechanism underlying a wide range of diseases, including cancers. This review article focuses on understanding the functional roles and molecular mechanisms of deregulated miRNAs in PCa aggressiveness and drug resistance based on the existing literature. Specifically, the miRNAs differentially expressed (upregulated or downregulated) in PCa vs. normal tissues, advanced vs. low-grade PCa, and treatment-responsive vs. non-responsive PCa are discussed. In particular, the oncogenic and tumor-suppressive miRNAs involved in the regulation of (1) the synthesis of the androgen receptor (AR) and its AR-V7 splice variant, (2) PTEN expression and PTEN-mediated signaling, (3) RNA splicing mechanisms, (4) chemo- and hormone-therapy resistance, and (5) racial disparities in PCa are discussed and summarized. We further provide an overview of the current advances and challenges of miRNA-based biomarkers and therapeutics in clinical practice for PCa diagnosis/prognosis and treatment.

African Americans (AAs) have among the highest incidence of prostate cancer (PCa) and mortality attributable to this disease, and AA PCa disparities remains a clinical challenge. Specifically, AAs are 1.6 times more likely to develop PCa, and 2.4 times more likely to die from this disease compared to European Americans (EAs). A number of studies have shown that higher mortality and recurrence rates of PCa in AA men were observed even after adjustment for socioeconomic factors, suggesting that intrinsic biological difference may account for part of the PCa disparities. Our recent genomic study has identified global splicing events as critical drivers for promoting AA and EA PCa disparities. In this study, we utilized population-specific cell lines as in-vitro AA and EA PCa models to evaluate the molecular functions of the aberrant splice variants involved in cancer aggressiveness and drug resistance. Comprehensive functional assays (such as MTT, apoptosis, invasion, kinase activity assays, and western blotting analysis in PCa cells treated with vehicle or small molecule drugs, etc.) were employed to elucidate the functional roles of an oncogenic splice variant, PIK3CD-S, in AA and EA PCa cells in response to drug treatments. Immunohistochemistry and RNAScope assays were performed to examine the expression profile of PIK3CD-L (full length) and PIK3CD-S variants in an independent PCa cohort derived from AA and EA patients. Higher PIK3CD-S/PIK3CD-L expression ratios were detected in AA PCa cell lines and patient specimens. In addition, the functional validations have indicated that the higher PIK3CD-S/PIK3CD-L expression ratio in AA PCa cells potentially contributes to the higher cell proliferative and invasive capacities. By targeting splicing mechanism and/or PI3K isoforms using specific small molecule inhibitors in AA and EA cell models, we further explored the functional mechanisms of these oncogenic splice variants underlying the drug resistance. In conclusion, our molecular mapping/validation and functional analysis suggest that high PIK3CD-S/PIK3CD-L expression profile may contribute to the PCa aggressiveness and treatment resistance in AA PCa, potentially serving as a precision prognostic biomarker and novel drug target in advanced PCa Citation Format: Siyoung Ha, Himali Gujrati, Bi-Dar Wang. Aberrant mRNA splice variants as novel prognostic biomarkers for tumor aggressiveness and treatment resistance in African American prostate cancer [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr C043.

Prostate cancer (PCa) is the most frequently diagnosed cancer and second leading cause of cancer death among American men. Notably, African American (AA) men exhibit 1.6-fold higher incidence rate and 2.4-fold higher mortality rate when compared to European American (EA) men. Besides socioeconomic factors, accumulating genomic data suggest that intrinsic genetic risk elements also play critical roles in promoting PCa disparities. MicroRNAs (miRNAs) are involved in epigenetic mechanisms regulating mRNA expression in various human diseases, including cancers. In this study, we have applied a systems biology approach (by integrating mRNA and miRNA profiling data, target prediction, and pathway analysis) to identify critical signaling networks differentially regulated between AA and EA PCa. Using miRNA-drive algorithm mirPath V.3 coupled with mRNA mapping, and global test algorithm coupled with miRNA mapping, we identified several cancer pathways, such as ERBB, mTOR, HIF, and VEGF signaling, that are significantly regulated by AA-depleted/enriched miRNAs and mRNAs. Specifically, reciprocal miRNA-mRNA pairs miR-34a-5p/HIF1A, miR-34a-5p/PIK3CB, miR-34a-5p/IGFBP2, and miR-99b-5p/MTOR (downregulated/upregulated in AA vs. EA PCa), and miR-96-5p/MAPKAPK2 (upregulated/downregulated in AA vs. EA PCa) were identified as core miRNA/mRNA regulators in activation of mTOR and VEGF signaling in AA PCa. RT-qPCR, Western blotting, and immunohistochemistry assays in AA and EA PCa cell lines and patient samples have confirmed that these miRNAs and mRNAs are differentially expressed in AA and EA PCa. Furthermore, molecular targeting miRNA/mRNA pairings using miR-34a-5p, miR-99b-5p mimics and/or miR-96-5p antagomir consequently reduced cell proliferation and enhanced docetaxel-induced cytotoxicity in AA PCa cells. In summary, these results suggest that deregulated miRNA/mRNA reciprocal pairs play critical roles in promoting cancer aggressiveness and chemoresistance in AA PCa. Further development of these miRNA/mRNA pairings as precision diagnostic/prognostic biomarkers and novel therapeutic targets may pave a new path for PCa diagnosis and treatment. Citation Format: Himali Gujrati, Siyoung Ha, Bi-Dar Wang. Deregulated microRNA-mRNA reciprocal pairs as novel precision biomarkers and therapeutic targets for African American prostate cancer [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr C058.