HDAC Inhibition Induces MicroRNA-182, which Targets RAD51 and Impairs HR Repair to Sensitize Cells to Sapacitabine in Acute Myelogenous Leukemia

Abstract

Purpose The double strand breaks elicited by sapacitabine, a clinically active nucleoside analog prodrug are repaired by Rad51 and the homologous recombination repair (HR) pathway which could potentially limit its toxicity. We investigated the mechanism by which HDAC inhibitors targeted Rad51 and HR to sensitize AML cells to sapacitabine. Experimental Design Chromatin immunoprecipitation identified the role of HDACs in silencing microRNA-182 in AML. Immunoblotting, gene expression, overexpression or inhibition of miR-182 and luciferase assays established that miR-182 directly targeted Rad51. HR reporter assays, apoptotic assays and colony forming assays established that the miR-182, as well as the HDAC inhibition-mediated decreases in Rad51 inhibited HR repair and sensitized cells to sapacitabine. Results The gene repressors, HDAC1 and HDAC2, became recruited to the promoter of miR-182 to silence its expression in AML. HDAC inhibition induced miR-182 in AML cell lines and primary AML blasts. miR-182 targeted Rad51 protein both in luciferase assays and in AML cells. Overexpression of miR-182, as well as HDAC inhibition-mediated induction of miR-182 were linked to time- and dose-dependent decreases in the levels of Rad51, an inhibition of HR, increased levels of residual damage and decreased survival after exposure to double strand damage inducing agents. Conclusions Our findings define the mechanism by which HDAC inhibition induces miR-182 to target Rad51 and highlights a novel pharmacological strategy that compromises the ability of AML cells to conduct HR, thereby sensitizing AML cells to DNA damaging agents that activate HR as a repair and potential resistance mechanism.

Dysregulation and functional roles of miR-183-96-182 cluster in cancer cell proliferation, invasion and metastasis

“…In addition, miR-96 is known to down-regulate RAD51 (a DNA repair protein) and REV1 (a DNA polymerase) to promote cellular sensitivity to cisplatin, which binds to and cause crosslinking of DNA to ultimately trigger apoptosis [36]. Similar results were also found for miR-182 in acute myelogenous leukemia [21]. Thus, the over-expression of miR-96/miR-182 appears to dramatically promote drug sensitization in cancer cells [36].…”

Genetic variants in microRNA‐binding sites of DNA repair genes as predictors of recurrence in patients with squamous cell carcinoma of the oropharynx

“…This study suggested that the binding of miR-197 to RAD51 rs7180135 might alter miR-197-mRNA-binding and might predict sensitivity of tumors to radiotherapy, thus affecting outcomes in bladder cancer 13 . Several other miRNAs have previously been shown to target RAD51 and inhibit its role in homologous recombination repair, including miRNA-182, miR-155, miR-103, and miR-107 in several types of human cancer 37-39 . In addition, miR-182 can impede DNA repair and may increase the susceptibility of breast cancer to radiotherapy and chemotherapy through downregulation of BRCA1 40 .…”

The Potential of Targeting DNA Repair Deficiency in Acute Myeloid Leukemia

“…The recombinase pro- As the HR repair pathway is so important in cell survival and correct replication, it has become a therapeutic target in cancer cells which already contain a DNA repair defects. Molecules which inhibit HR activity, such as Mirin, are in the early phases of development [18]. Mirin inhibits the nuclease activity of Mre11 within the MRN complex, thereby inhibiting the initiation of HR.…”

“…These small molecule inhibitors, and others similar (such as RAD51 inhibitors), are still in early phase trials. These molecules target HR through various avenues [18]. Targeting cABL and HSP90 are also being investigated in HRR deficient cells [16].…”