HNRNPA2B1 as a trigger of RNA switch modulates the miRNA-mediated regulation of CDK6

The functional inactivation of tumor suppressor microRNA (miRNA) is closely related to the tumorigenesis of cancer. There are instances where the miRNA and the corresponding target both exist in a cell, but the target gene silencing do not occur as expected. Herein, we found that both miR-506 and its target CDK6 are highly co-expressed in lung cancer cells. Sequence analyses suggested that a miR-506 binding site (1648-1654) and a cis-element (1785-1795) for binding by heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1) are evolutionarily conserved and forms a stem structure in the 3' untranslated region (3'UTR) of CDK6. Furthermore, HNRNPA2B1 can bind to the stem structure to denature it and recruit the RNA helicase DExH-box helicase 9 (DHX9) to the 3'UTR, which ultimately facilitates miRNAs-mediated CDK6 silencing. These results indicate that the cis-element of the 3'UTR of CDK6, where HNRNPA2B1 binds, serves as an RNA switch to regulate miRNAs' function in cancer cells.