Targeted knockdown of DJ-1 induces multiple myeloma cell death via KLF6 upregulation

Multiple myeloma (MM) is an incurable plasma B cell malignancy. Despite recent advancements in anti-MM therapies, development of drug resistance remains a major clinical hurdle. DJ-1, a Parkinson's disease-associated protein, is upregulated in many cancers and its knockdown suppresses tumor growth and overcomes chemoresistance. However, the role of DJ-1 in MM remains unknown. Using gene expression databases we found increased DJ-1 expression in MM patient cells, which correlated with shorter overall survival and poor prognosis in MM patients. Targeted DJ-1 knockdown using siRNAs induced necroptosis in myeloma cells. We found that Krüppel-like factor 6 (KLF6) is expressed at lower levels in myeloma cells compared to PBMCs, and DJ-1 knockdown increased KLF6 expression in myeloma cells. Targeted knockdown of KLF6 expression in DJ-1 knockdown myeloma cells rescued these cells from undergoing cell death. Higher DJ-1 levels were observed in bortezomib-resistant myeloma cells compared to parent cells, and siRNA-mediated DJ-1 knockdown reversed bortezomib resistance. DJ-1 knockdown increased KLF6 expression in bortezomib-resistant myeloma cells, and subsequent siRNA-mediated KLF6 knockdown rescued bortezomib-resistant myeloma cells from undergoing cell death. We also demonstrated that specific siRNA-mediated DJ-1 knockdown reduced myeloma cell growth under a hypoxic microenvironment. DJ-1 knockdown reduced the expression of HIF-1α and its target genes in hypoxic-myeloma cells, and overcame hypoxia-induced bortezomib resistance. Our findings demonstrate that elevated DJ-1 levels correlate with myeloma cell survival and acquisition of bortezomib resistance. Thus, we propose that inhibiting DJ-1 may be an effective therapeutic strategy to treat newly diagnosed as well as relapsed/refractory MM patients.