Résumé
Multiple Myeloma (MM) is a still lethal disease in 2013 characterized by the accumulation in the bone marrow of a clone of malignant plasma cells.
Recent studies have shown that epigenetic modifications play a role by silencing various cancer-related genes in MM. We initiated a microarray-based genome-wide screen for genes responding to DNMT inhibition in MM cells and built a “DNA methylation gene score” that makes it possible identification of myeloma patients that will be sensitive to DNMT inhibitors. Among the genes regulated by DNMT inhibitor and associated with the worst prognostic value in patients, RECQ1 was identified. RECQ helicase are DNA unwinding enzymes involved in the maintenance of chromosome stability. RECQ1 is highly expressed in various types of solid tumors. RECQ1 silencing in cancer cells results in mitotic catastrophe and prevents tumor growth in murine models. In glioblastoma cells, depletion of RECQ1 induces reduction in cellular proliferation, spontaneous γ-H2AX foci formation and hypersensitivity to drugs. Furthermore, it was described that RECQ1 protein could interact with MSH proteins, RAD51 and PARP1 involved in DNA repair pathways.
RECQ1 protein is expressed in human myeloma cell lines (HMCLs) and primary myeloma cells of patients. In four HMCLs (XG2, XG7, XG19 and LP1), RECQ1 was downregulated by conditional shRNA expression through lentiviral delivery. RECQ1 knock down inhibits growth of myeloma cells, induces 53BP1 foci formation and apoptosis. RECQ1 depletion sensitizes myeloma cells to DNA alkylating agent (melphalan) but not to corticosteroid (dexamethasone) or proteasome inhibitor (bortezomib). Using immunoprecipitation of myeloma cell nuclear proteins with anti-RECQ1 antibody, RECQ1 was shown to interact with PARP1 but not RAD51 or MSH2. An increased association of the two proteins was found upon DNA damages induced by melphalan. In agreement, RECQ1 depletion sensitizes myeloma cell lines to the PJ34 hydrochloride hydrate PARP inhibitor.
In conclusion, RECQ1 could represent a biomarker of drug resistance in MM, which is targeted by DNMT inhibitor. This suggests association of alkylating agents and/or PARP inhibitors with DNMT inhibitor may represent a promising therapeutic approach.