Downregulation of miR-99b-5p and Upregulation of Nuclear mTOR Cooperatively Promotes the Tumor Aggressiveness and Drug Resistance in African American Prostate Cancer

Abstract

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.

PI3K/AKT/mTOR Signaling Pathway in HPV-Driven Head and Neck Carcinogenesis: Therapeutic Implications

“…Indeed, a significant reduction in nuclear mTOR and androgen receptor (AR) has been detected, targeting the AR-mTOR axis using miR-99b-5p. This finding suggests that miR-99b-5p is a novel potential therapeutic target in this type of cancer [27]. Other cancers such as glioblastoma [28], lung [29], multiple myeloma [30] and lymphomas [31] are additionally characterized by PI3K/Akt/mTOR alterations.…”

Aberrant PI3Kδ splice isoform as a potential biomarker and novel therapeutic target for endocrine cancers

“…The protocol for IHC assay was adapted/modified from our previous studies ( 34 , 35 ). Briefly, TMA slides were first deparaffinized in xylene, followed by immersion in xylene/alcohol (1:1) solution and rehydrated through graded alcohols (100%, 95%, 70% and 50% of alcohol, respectively) to distilled water.…”

“…IHC images were captured using Pannormic Midi Digital Scanner (3DHISTECH Ltd., Budapest, Hungary) and visualized using CaseViewer program (3DHISTECH, Budapest, Hungary). The analysis and quantification of IHC images were performed using ImageJ software (NIH, Bethesda, MD, USA), as described in our previous study ( 34 ). The statistical analysis was performed using ANOVA with Tukey’s post-hoc test for the multiple comparisons.…”

Biomarkers for Early Detection of Cancer: Molecular Aspects

“…The issue of tumor resistance to drugs is further highlighted in a study by Gujrati et al [ 7 ], which was conducted in African American men with prostate cancer. The nuclear mammalian target of rapamycin (mTOR) is known to regulate cell proliferation, protein synthesis, metabolism, apoptosis, and autophagy [ 8 ], and was shown to be elevated in patients with prostate cancer as well as other advanced cancers (lung, breast, and colon).…”

“…The nuclear mammalian target of rapamycin (mTOR) is known to regulate cell proliferation, protein synthesis, metabolism, apoptosis, and autophagy [ 8 ], and was shown to be elevated in patients with prostate cancer as well as other advanced cancers (lung, breast, and colon). The dysregulation of microRNA, specifically microRNA-99b-5p, is known to be linked with prostate cancer [ 9 ], and in the study by Gujrati et al [ 7 ] it was found to be downregulated. These investigators went on to demonstrate, in vitro, that transfection with microRNA-99b-5p significantly reduced the expression levels of nuclear mTOR and androgen receptor (AR).…”