A-to-I RNA editing of BLCAP promotes cell proliferation by losing the inhibitory of Rb1 in colorectal cancer

The bladder cancer-associated protein (BLCAP) gene is a tumor-suppressor gene as its encoded protein can inhibit cell proliferation by stimulating apoptosis in many malignant tumors. It is also a novel site of adenosineto-inosine (A-to-I) RNA editing by ADAR (adenosine deaminase acting on RNA). In this study, we found by exome and transcriptome sequencing that there was an abnormal RNA editing event of the BLCAP gene in colorectal cancer (CRC) tissues compared to adjacent normal tissues. The editing of BLCAP transcripts promoted the degradation of BLCAP by ubiquitination, so BLCAP could not maintain its function as a tumor suppressor gene in CRC. Moreover, our further studies revealed that BLCAP could interact with Rb1 and inhibit its phosphorylation, while the loss of repressive effect due to reduced BLCAP protein levels caused by A-to-I RNA editing facilitates the transition from G1 to S phase of the cell cycle, leading to increased cell proliferation and reduced apoptosis. Thus, A-to-I RNA editing events tend to play an essential role in CRC carcinogenesis.