Identification of tumor-suppressive miRNAs that target amino acid transporter LAT1 and exhibit anti-proliferative effects on cholangiocarcinoma cells

Amino acid transporter LAT1 is highly upregulated in various cancer types, including cholangiocarcinoma (CHOL), and contributes to the rapid proliferation of cancer cells and disease progression. However, the molecular mechanisms underlying the pathological upregulation of LAT1 remain largely unknown. This study pursued the possibility of miRNA-mediated regulation of the LAT1 expression in CHOL cells. Using online target prediction methods, we extracted five candidate miRNAs commonly predicted to regulate the LAT1 expression. Three of them, miR-194-5p, miR-122-5p, and miR-126-3p, were significantly downregulated in CHOL cancer compared to normal tissues. Correlation analysis revealed weak-to-moderate negative correlations between the expression of these miRNAs and LAT1 mRNA in CHOL cancer tissues. We selected miR-194-5p and miR-122-5p for further analyses and found that both miRNAs functionally target 3'UTR of LAT1 mRNA by a luciferase-based reporter assay. Transfection of the miRNA mimics significantly suppressed the LAT1 expression at mRNA and protein levels and inhibited the proliferation of CHOL cells, with a trend of affecting intracellular amino acids and amino acid-related signaling pathways. This study indicates that the decreased expression of these LAT1-targeting tumor-suppressive miRNAs contributes to the upregulation of LAT1 and the proliferation of CHOL cells, highlighting their potential for developing novel cancer therapeutics and diagnostics.

The microRNA-424/503 cluster: A master regulator of tumorigenesis and tumor progression with paradoxical roles in cancer

MicroRNAs (miRNAs) are a group of non-coding RNAs that play a crucial role in post-transcriptional gene regulation and act as indispensable mediators in several critical biological processes, including tumorigenesis, tissue homeostasis, and regeneration. MiR-424 and miR-503 are intragenic miRNAs that are clustered on human chromosome Xq26.3. Previous studies have reported that both miRNAs are dysregulated and play crucial but paradoxical roles in tumor initiation and progression, involving different target genes and molecular pathways. Moreover, these two miRNAs are concomitantly expressed in several cancer cells, indicating a coordinating function as a cluster. In this review, the roles and regulatory mechanisms of miR-424, miR-503, and miR-424/503 cluster are summarized in different types of cancers.

MicroRNA-4651 targets bromodomain-containing protein 4 to inhibit non-small cell lung cancer cell progression

Bromodomain-containing protein 4 (BRD4) overexpression in non-small cell lung cancer (NSCLC) promotes cancer progression. Here, we show that miR-4651 selectively targets and negatively regulates BRD4 in A549 and primary human NSCLC cells. RNA pull-down experiments confirmed that miR-4651 directly binds to BRD4 mRNA. Further, ectopic overexpression of miR-4651 in A549 cells and primary NSCLC cells decreased BRD4 3'-UTR luciferase reporter activity and its expression, whereas miR-4651 inhibition elevated both. Functional studies demonstrated that NSCLC cell growth, proliferation, and migration were suppressed with ectopic miR-4651 overexpression but enhanced with miR-4651 inhibition. BRD4 re-expression using a 3'-UTR mutant BRD4 reversed A549 cell inhibition induced by miR-4651 overexpression. Further, miR-4651 overexpression or inhibition failed to alter the functions of BRD4-KO A549 cells. In vivo, miR-4651-overexpressing A549 xenografts grew slowly than control A549 xenografts in severe combined immunodeficient mice. Finally, miR-4651 was downregulated in human NSCLC tissues, correlating with BRD4 elevation. Together, miR-4651 targets BRD4 to inhibit NSCLC cell growth in vitro and in vivo.