Circular RNA circ-CCT3 promotes bortezomib resistance in multiple myeloma via modulating miR-223-3p/BRD4 axis

Multiple myeloma is a frequent hematologic malignancy. Bortezomib is the first-line drug for multiple myeloma chemotherapy. The present study aimed to investigate the potential role and mechanism of circular RNA chaperonin containing TCP1 subunit 3 (circ-CCT3) in bortezomib resistance of multiple myeloma. The levels of circ-CCT3, microRNA-223-3p (miR-223-3p), and bromodomain-containing 4 (BRD4) were detected by quantitative real-time PCR or western blot. Cell Counting Kit-8 (CCK-8) method was used to measure the half-inhibitory concentration of bortezomib and cell viability. Cell cycle distribution, apoptosis, proliferation and migration were determined by flow cytometry, 5-ethynyl-2'-deoxyuridine, and wound healing assay. The levels of relevant proteins were checked via western blot. The binding association between miR-223-3p and circ-CCT3/BRD4 was validated via a dual-luciferase reporter assay. Circ-CCT3 and BRD4 were upregulated, while miR-223-3p was downregulated in bortezomib-resistant multiple myeloma patients and cells. Silencing of circ-CCT3 enhanced the sensitivity of bortezomib-resistant multiple myeloma cells to bortezomib. Circ-CCT3 knockdown weakened bortezomib resistance via modulating miR-223-3p. Moreover, miR-223-3p increased bortezomib sensitivity by inhibiting BRD4. Downregulation of circ-CCT3 attenuated bortezomib resistance of multiple myeloma via regulating miR-223-3p/BRD4 pathway, which provided a new potential target for multiple myeloma chemoresistance.