Lentivirus production

The apoptosis repressor with caspase recruitment domain (ARC) protein is a strong independent adverse prognostic marker in acute myeloid leukemia (AML). We previously reported that ARC regulates leukemia-microenvironment interactions through the NFkappaB/IL1beta signaling network. Malignant cells have been reported to release IL1beta, which induces PGE2 synthesis in mesenchymal stromal cells (MSC), in turn activating beta-catenin signaling and inducing the cancer stem cell phenotype. Although Cox-2 and its enzymatic product PGE2 play major roles in inflammation and cancer, the regulation and role of PGE2 in AML are largely unknown. Here, we report that AML-MSC cocultures greatly increase Cox-2 expression in MSC and PGE2 production in an ARC/IL1beta-dependent manner. PGE2 induced the expression of beta-catenin, which regulated ARC and augmented chemoresistance in AML cells; inhibition of beta-catenin decreased ARC and sensitized AML cells to chemotherapy. NOD/SCIDIL2RgammaNull-3/GM/SF mice transplanted with ARC-knockdown AML cells had significantly lower leukemia burden, lower serum levels of IL1beta/PGE2, and lower tissue human ARC and beta-catenin levels, prolonged survival, and increased sensitivity to chemotherapy than controls. Collectively, we present a new mechanism of action of antiapoptotic ARC by which ARC regulates PGE2 production in the tumor microenvironment and microenvironment-mediated chemoresistance in AML.Significance: The antiapoptotic protein ARC promotes AML aggressiveness by enabling detrimental cross-talk with bone marrow mesenchymal stromal cells.