Why is the COVID-19 virus deadly, while many other coronaviruses are fairly innocuous and just cause colds? A team of University of Alabama at Birmingham and Polish researchers propose an answer—the COVID-19 virus acts as a microRNA "sponge." This action modulates host microRNA levels in ways that aid viral replication and stymies the host immune response.

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This testable hypothesis results from analysis of current literature and a bioinformatic study of the COVID-19 virus and six other coronaviruses. It is published as a perspective in the American Journal of Physiology-Lung Cellular and Molecular Physiology.

Human microRNAs, or miRNAs, are short, non-coding RNAs with about 22 bases. They act to regulate gene expression by their complementary pairing with specific messenger RNAs of the cell. That pairing silences the messenger RNA, preventing it from being translated into a protein. Thus, miRNAs are a fine-tuned controller of cell metabolism or the cell's response to stress and adverse challenges, like infection by a virus.