circCRKL, a circRNA derived from CRKL, regulates BCR-ABL via sponging miR-877-5p to promote chronic myeloid leukemia cell proliferation

Background: The Bcr-Abl fusion protein is the key factor that results in the occurrence of chronic myeloid leukemia (CML). Imatinib (IM) is a targeted inhibitor of Bcr-Abl to achieve complete remission. However, remission failure occurs due to acquired resistance caused by secondary Bcr-Abl mutations, underlining the need for novel BCR-ABL-targeting strategies. Circular RNAs (circRNAs) derived from tumor-related genes have been revealed as possible therapeutic targets for relevant cancers in recent investigations. In CML, the roles of this kind of circRNA are yet obscure.

Methods: Firstly, RT-qPCR was used for determining circCRKL expression level in cell lines and clinical samples, RNase R and Actinomycin D were employed to verify the stability of circCRKL. Then shRNAs were designed to specifically knockdown circCRKL. The function of circCRKL in vitro was investigated using CCK-8, colony formation assay, and flow cytometry, while a CML mouse model was constructed to explore the function in vivo. Finally, a dual-luciferase reporter assay, RNA pull-down, RNA immunoprecipitation, and rescue experiments were conducted to investigate the mechanism of circCRKL functioning.

Results: Here, we determined circCRKL, which derives from CML-relevant gene CRKL, is over-expressed in Bcr-Abl⁺ cells. Then we noticed knocking down circCRKL using shRNA lentivirus dampens the proliferation of Bcr-Abl⁺ cells both in vitro and in vivo, and augments susceptibility of resistant cells to IM. Intriguingly, we observed that circCRKL has a considerable impact on the expression level of Bcr-Abl. Mechanistically, circCRKL could behave like a decoy for miR-877-5p to enhance the Bcr-Abl level, allowing Bcr-Abl⁺ cells to maintain viability.

Conclusions: Overall, the current study uncovers that circCRKL is specifically expressed and regulates Bcr-Abl expression level via decoying miR-877-5p in Bcr-Abl⁺ cells, highlighting that targeting circCRKL along with imatinib treatment could be utilized as a potential therapeutic strategy for CML patients.