CircFLNB upregulated by chemotherapy via alternative splicing suppresses the progression of colorectal cancer.

Alternative splicing (AS) is a tightly regulated process that gives rise to proteins with distinct or even opposing functions. But cancer-specific alternative splicing of circRNA formation is less likely to be identified. We identified circFLNB by a circRNA microarray and validated it by quantitative reverse transcription PCR. The role of circFLNB in CRC progression was assessed both in vitro and in vivo, and its downstream target genes were identified and validated in CRC cells by bioinformatics analysis and confirmed by luciferase reporter assays. The dysregulated alternative splicing events and splicing factors in chemotherapy-induced CRC tissues were identified using RNA-seq and rMATS analysis. The clinical implications of circFLNB were assessed in CRC tissue using the nomogram algorithm. We found that circFLNB was weakly expressed in colorectal cancer tissues and cells and its expression was increased by chemotherapy. Functionally, circFLNB repressed the proliferation and invasion of CRC cells in vitro, as well as inhibited the growth of CRC xenografts in mice in vivo. Mechanistically, circFLNB inhibited the proliferation of CRC in vivo and in vitro by targeting the miR-3127-3p/MOB1B/Hippo pathway. Furthermore, our investigation indicated that splicing factors QKI and CELF4 are essential and sufficient for the circFLNB biogenesis through chemotherapy-regulated alternative splicing. A patient prognosis model based on circFLNB expression levels can effectively predict the prognosis of CRC patients. Our research demonstrated that QKI- and CELF4- dependent alternative splicing induced by chemotherapy promotes circFLNB biogenesis, which inhibits CRC tumorigenesis via binding with miR-3127-3p to regulate the MOB1B/Hippo pathway.