MiR-21 in the Cancers of the Digestive System and Its Potential Role as a Diagnostic, Predictive, and Therapeutic Biomarker

SIMPLE SUMMARY: MicroRNAs are small, non-coding RNA molecules that can regulate the expression of various cancer-related genes and thereby contribute to tumorigenesis and progression of many cancer types. The biological functions and therapeutic potential of miR-21 have been comprehensively investigated. In the current study, we provide an inclusive review of the potential targets, and the current applications as a diagnostic and prognostic cancer biomarker of miR-21. We also summarize the scientific evidence that has highlighted miR-21 as a therapeutic agent as well as the challenges for its use as a therapeutic tool in different cancer types in the digestive system. ABSTRACT: MicroRNAs (miRNAs) are small non-coding RNAs. They can regulate the expression of their target genes, and thus, their dysregulation significantly contributes to the development of cancer. Growing evidence suggests that miRNAs could be used as cancer biomarkers. As an oncogenic miRNA, the roles of miR-21 as a diagnostic and prognostic biomarker, and its therapeutic applications have been extensively studied. In this review, the roles of miR-21 are first demonstrated via its different molecular networks. Then, a comprehensive review on the potential targets and the current applications as a diagnostic and prognostic cancer biomarker and the therapeutic roles of miR-21 in six different cancers in the digestive system is provided. Lastly, a brief discussion on the challenges for the use of miR-21 as a therapeutic tool for these cancers is added.