Oncomir

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An oncomir (also called oncomiR) is a small RNA molecule that is linked to cancer. MicroRNAs (miRNAs) are about 22 nucleotides long and usually act to turn off specific messenger RNAs, stopping the production of certain proteins. When oncomirs are not regulated properly, they can help cancer grow, spread, or become more aggressive.

What oncomirs do
- They can act as oncogenes, meaning that too much of them helps cancer form.
- Some oncomirs act like loss‑of-function tumor suppressors, so when they are too low, cancer can develop.
- They usually kill or calm down cells by blocking the production of target genes, or by making target mRNAs less stable.
- The levels of oncomirs can be higher or lower in tumors.

Viruses and oncomirs
Some viruses carry miRNAs that mimic human miRNAs and can influence cancer development. For example, the Epstein–Barr virus (EBV) is linked to several cancers through such mechanisms.

A key moment in research
Researchers first linked miRNAs to cancer in 2002, when miR-15a and miR-16-1 were found to be reduced in a type of leukemia. The term oncomiR was coined in 2006 to describe miRNAs that promote cancer, especially the well-studied OncomiR-1 (also called miR-17-92), a cluster that makes several miRNAs from one transcript.

OncomiR-1 and cancer
- The OncomiR-1 cluster produces miR-17, miR-18, miR-19a, miR-19b, miR-20, and miR-92.
- These miRNAs help cancer cells avoid death and keep growing by interfering with important genes such as E2F1.
- Each miRNA from this cluster can have hundreds of target mRNAs, so there are many ways it can influence cancer.

MiRNAs as cancer markers
Because miRNAs are Stable and specific to tissues, they can serve as cancer markers. Differences in miRNA patterns have been found in various cancers, including pancreatic cancer and liver cancer. miRNAs can also be detected in blood, as extracellular RNAs (exRNAs), offering a noninvasive way to help diagnose or monitor cancer.

Examples of well-studied oncomirs
- miR-17: part of OncomiR-1; can affect cell growth by targeting E2F1.
- miR-19: downregulates PTEN, boosting the PI3K-Akt survival pathway.
- miR-21: elevated in many cancers; lowers PDCD4, helping invasion and metastasis.
- miR-155: often overexpressed; can reduce SOCS1 and may be a target in breast cancer.
- miR-569: linked to 3q26.2 amplification; promotes growth and metastasis by inhibiting TP53INP1.

Anti-oncomirs
Some miRNAs protect against cancer by suppressing oncogenes. Let-7 is a famous anti-oncomir that helps keep cell growth in check. Other anti-oncomirs like miR-143 and miR-145 can slow cancer cell growth, and researchers are exploring ways to use modified versions of these miRNAs as therapies to improve stability and effectiveness.

In short, oncomirs are tiny RNA molecules that can drive or restrain cancer. Studying them helps us understand cancer biology, find new biomarkers, and develop potential RNA‑based therapies.