Identification of ATRA-induced signals in RARα2⁺ MM cells. (A) Western blots examined pSTAT3 and pERK1/2 in RARα2 (R2)–overexpressing ARP.1, OCI-MY5 (OCI), and XG-1 cells with (+) or without (−) ATRA treatment. (B) Western blot analysis of caspase-3 and caspase-9 in R2-overexpressing ARP.1, OCI, and XG-1 cells with (+) or without (−) ATRA treatment. β-actin was used as loading control. Shown are the representative results of 3 independent experiments.