ERN1 and plasma cell myeloma: PLK2 is hyper-expressed in multiple myeloma (MM) patients; PLK2 further inhibits C/EBP homologous protein (CHOP) and enhances inositol-requiring enzyme 1α (IRE1α) by inhibiting KIRA8 (kinase-inhibiting RNase attenuator 8), which in turn affects ER stress and facilitates cell survival; Meanwhile, KIRA8/IRE1α could reversely regulate PLK2 expression; KIRA8 and PLK2 inhibitors exert anti-MM effects by inducing apoptosis and regulating cell proliferation (81).