Background:Despite recent advancements, metastatic castration-resistant prostate cancer (CRPC) is not considered curative. Novel approaches for identification of therapeutic targets of CRPC are needed.Methods:Next-generation sequencing revealed 945–1248 miRNAs from each lethal mCRPC sample. We constructed miRNA expression signatures of CRPC by comparing the expression of miRNAs between CRPC and normal prostate tissue or hormone-sensitive prostate cancer (HSPC). Genome-wide gene expression studies and in silico analyses were carried out to predict miRNA regulation and investigate the functional significance and clinical utility of the novel oncogenic pathways regulated by these miRNAs in prostate cancer (PCa).Results:Based on the novel miRNA expression signature of CRPC, miR-145-5p and miR-145-3p were downregulated in CRPC. By focusing on miR-145-3p, which is a passenger strand and has not been well studied in previous reports, we showed that miR-145-3p targeted 4 key molecules, i.e., MELK, NCAPG, BUB1, and CDK1, in CPRC. These 4 genes significantly predicted survival in patients with PCa.Conclusions:Small RNA sequencing for lethal CRPC and in silico analyses provided novel therapeutic targets for CRPC.

Background:Our present study of the microRNA (miRNA) expression signature in castration-resistant prostate cancer (CRPC) revealed that the clustered miRNAs microRNA-221 (miR-221) and microRNA-222 (miR-222) are significantly downregulated in cancer tissues. The aim of this study was to investigate the functional roles of miR-221 and miR-222 in prostate cancer (PCa) cells.Methods:A CRPC miRNA signature was constructed by PCR-based array methods. Functional studies of differentially expressed miRNAs were analysed using PCa cells. The association between miRNA expression and overall survival was estimated by the Kaplan–Meier method. In silico database and genome-wide gene expression analyses were performed to identify molecular targets regulated by the miR-221/222 cluster.Results:miR-221 and miR-222 were significantly downregulated in PCa and CRPC specimens. Kaplan–Meier survival curves showed that low expression of miR-222 predicted a short duration of progression to CRPC. Restoration of miR-221 or miR-222 in cancer cells revealed that both miRNAs significantly inhibited cancer cell migration and invasion. Ecm29 was directly regulated by the miR-221/222 cluster in PCa cells.Conclusions:Loss of the tumour-suppressive miR-221/222 cluster enhanced migration and invasion in PCa cells. Our data describing targets regulated by the tumour-suppressive miR-221/222 cluster provide insights into the mechanisms of PCa and CRPC progression.

For patients with head and neck squamous cell carcinoma (HNSCC), survival rates have not improved due to local recurrence and distant metastasis. Current targeted molecular therapies do not substantially benefit HNSCC patients. Therefore, it is necessary to use advanced genomic approaches to elucidate the molecular mechanisms underlying the aggressiveness of HNSCC cells. Analysis of our microRNA (miRNA) expression signature by RNA sequencing showed that the miR‐199 family (miR‐199a‐5p, miR‐199a‐3p, miR‐199b‐5p and miR‐199b‐3p) was significantly reduced in cancer tissues. Ectopic expression of mature miRNA demonstrated that all members of the miR‐199 family inhibited cancer cell migration and invasion by HNSCC cell lines (SAS and HSC3). These findings suggested that both passenger strands and guide strands of miRNA are involved in cancer pathogenesis. In silico database and genome‐wide gene expression analyses revealed that the gene coding for integrin α3 (ITGA3) was regulated by all members of the miR‐199 family in HNSCC cells. Knockdown of ITGA3 significantly inhibited cancer cell migration and invasion by HNSCC cells. Moreover, overexpression of ITGA3 was confirmed in HNSCC specimens, and high expression of ITGA3 predicted poorer survival of the patients (P = 0.0048). Our data revealed that both strands of pre‐miR‐199a (miR‐199a‐5p and miR‐199a‐3p) and pre‐miR‐199b (miR‐199b‐5p and miR‐199b‐3p) acted as anti‐tumor miRNA in HNSCC cells. Importantly, the involvement of passenger strand miRNA in the regulation of cellular processes is a novel concept in RNA research. Novel miRNA‐based approaches for HNSCC can be used to identify potential targets for the development of new therapeutic strategies.

Analysis of microRNA (miRNA) expression signatures in prostate cancer (PCa) and castration‐resistant PCa has revealed that miRNA‐223 is significantly downregulated in cancer tissues, suggesting that miR‐223 acts as a tumor‐suppressive miRNA by targeting oncogenes. The aim of this study was to investigate the functional roles of miR‐223 and identify downstream oncogenic targets regulated by miR‐223 in PCa cells. Functional studies of miR‐223 were carried out to investigate cell proliferation, migration, and invasion using PC3 and PC3M PCa cell lines. Restoration of miR‐223 significantly inhibited cancer cell migration and invasion in PCa cells. In silico database and genome‐wide gene expression analyses revealed that ITGA3 and ITGB1 were direct targets of miR‐223 regulation. Knockdown of ITGA3 and ITGB1 significantly inhibited cancer cell migration and invasion in PCa cells by regulating downstream signaling. Moreover, overexpression of ITGA3 and ITGB1 was observed in PCa clinical specimens. Thus, our data indicated that downregulation of miR‐223 enhanced ITGA3/ITGB1 signaling and contributed to cancer cell migration and invasion in PCa cells. Elucidation of the molecular pathways modulated by tumor‐suppressive miRNAs provides insights into the mechanisms of PCa progression and metastasis.

microRNAs, a class of small non-coding RNAs, regulate protein-coding gene expression by repressing translation or cleaving RNA transcripts in a sequence-specific manner. A growing body of evidence suggests that microRNAs contribute to prostate cancer development, progression and metastasis. Based on reports describing microRNA expression signatures, several differentially expressed microRNAs have been discovered. In the present review, eight genome-wide microRNA expression signatures were used to select aberrantly expressed microRNAs (i.e. upregulated and downregulated microRNAs) in prostate cancer clinical specimens. Also, we mapped these selected microRNAs in the human genome. Interestingly, some clustered microRNAs, such as miR-221/222, miR-143/ 145, miR-23b/27b/24-1 and miR-1/133a, are frequently downregulated in cancer tissues, and recent studies have shown that these clustered microRNAs function as tumor suppressors. We also discuss the functional significance of the differentially expressed microRNAs and the molecular pathways/targets regulated by these microRNAs. These recent findings of microRNAs in prostate cancer will facilitate the development of effective strategies for microRNA-based therapeutics for the treatment of prostate cancer.