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MEF2C phosphorylation is required for chemotherapy resistance in acute myeloid leukemia [mutant MEF2C]

ABSTRACT: In acute myeloid leukemia, chemotherapy resistance remains prevalent and poorly understood. Using functional proteomics of patient AML specimens, we identified MEF2C S222 phosphorylation as a specific marker of primary chemoresistance. We found that transgenic Mef2cS222A/S222A mice engineered to block MEF2C phosphorylation exhibited normal hematopoiesis, but were resistant to leukemogenesis induced by MLL-AF9. MEF2C phosphorylation was required for leukemia stem cell maintenance, induced by MARK kinases in cells, and blocked by selective MARK inhibitor MRT199665, which caused apoptosis of MEF2C-activated human AML cell lines and primary patient specimens, but not those lacking MEF2C. These findings identify signaling-dependent dysregulation of transcription factor control as a determinant of therapy response in AML, with immediate potential for improved diagnosis and therapy for this disease.

ORGANISM(S): Homo sapiens

PROVIDER: GSE94453 | GEO | 2018/07/23

REPOSITORIES: GEO

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Project description:Acute myelogenous leukemia (AML) is driven by leukemic stem cells (LSC) generated by mutations that confer (or maintain) self-renewal potential coupled to an aberrant differentiation program. Using retroviral mutagenesis, we identified genes that generate LSC in collaboration with genetic disruption of the gene encoding interferon response factor 8 (Irf8), which induces a myeloproliferation in vivo. Amongst the targeted genes, we identified Mef2c, encoding a MADS transcription factor, and confirmed that over-expression induced a myelomonocytic leukemia in cooperation with Irf8 deficiency. Strikingly, several of the genes identified in our screen have been reported to be upregulated in the mixed-lineage leukemia (MLL) subtype. High MEF2C expression levels were confirmed in AML patient samples with MLL gene disruptions, prompting an investigation of the causal interplay. Using a conditional mouse strain, we demonstrated that Mef2c deficiency does not impair the establishment nor maintenance of LSC generated in vitro by MLL/ENL fusion proteins â?? however, its loss led to compromised homing and invasiveness of the tumor cells. Mef2c-dependent targets included several genes encoding matrix metalloproteinases and chemokine ligands and receptors, providing a mechanistic link to increased homing and motility. Thus an early event in LSC generation may be responsible for the aggressive nature of this leukemia subtype. Experiment Overall Design: For gene expression profiling of M/E cells, RNA was isolated from M/E-Mef2c del/- cells infected with MYs-iPAC (empty vector) or MYs-pMef2cASR after puromycin selection at three different time points, pooled, and hybridized against the Agilent Whole Mouse Genome Microarray 4x44K using the one-color service of Miltenyi. Transcript levels were verified by real-time RT-PCR using the SYBRGreen Reaction Mix (Roche Mannheim) in a Roche Light-Cycler. cDNA levels were normalized against Hprt transcript levels. Primers and amplification conditions are available upon request.

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MEF2C phosphorylation is required for chemotherapy resistance in acute myeloid leukemia [mutant MEF2C]

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