High expression of RARα2 induces drug-resistance in myeloma cells. (A) The clonogenic capacity was compared between RARα2 OE and EV cells of OCI-MY5 and ARP1 lines treated with bortezomib, doxorubicin, and etoposide (magnification ×40). (B) Cell apoptosis was compared between RARΑ2 OE and EV cells of OCI-MY5 and ARP1 lines treated with bortezomib, doxorubicin, and etoposide by flow cytometry. (C) Flow cytometry shows the activity of drug efflux pump between RARα2 OE and EV cells in OCI-MY5 and ARP1 lines. (D-E) Western blots show the expression of ABCC3 in RARα2-OE OCI-MY5 and ARP1 cells (D) as well as in RARα2-shRNA KMS11 and ARK cells (E).