MicroRNA-99b (miR-99b)

MicroRNA-99b is a small, non-coding RNA molecule belonging to the miR-99 family, composed of 20–25 nucleotides, that regulates gene expression at the post-transcriptional level by interacting with complementary mRNAs to inhibit translation or promote mRNA degradation. MiR-99b is implicated in key cellular processes—including cell proliferation, cell cycle regulation, apoptosis, and differentiation—with broad relevance in human disease. It acts predominantly as a tumor suppressor in several cancers (e.g., lung, gastric, prostate, some breast cancers) through direct inhibition of mTOR, FGFR3, IGF1R, and other oncogenes, but can also promote tumorigenesis and chemoresistance in certain contexts, such as leukemia and subtypes of breast cancer. Its altered expression is associated with cancer progression, neurodegenerative diseases like Alzheimer’s disease, and muscle wasting, making it a potential biomarker and therapeutic candidate, though context-dependent activity and off-target effects present challenges for clinical applications.

Other names

miR-99bmicroRNA-99b-5pmiR-99b-5pmiR-99 family (includes miR-99a, miR-99b, miR-100)

MicroRNA-99b primarily acts by RNA interference, leading to the inhibition of target mRNA translation or its degradation. Key molecular mechanisms include the suppression of mammalian target of rapamycin (mTOR) signaling, which contributes to tumor suppression and inhibition of protein synthesis. It also mediates the downregulation of fibroblast growth factor receptor 3 (FGFR3) and insulin-like growth factor 1 receptor (IGF1R). Furthermore, miR-99b is involved in the regulation of proteins such as TNF receptor-associated factor 2 (TRAF2), cyclin D1, CDK4/6, Bcl-2, and Bax.