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

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. Overall design: RNA-sequencing of human leukemia cell line with induction of wildtype or mutant MEF2C.

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Brown FC, Still E, Koche RP, Yim CY, Takao S, Cifani P, Reed C, Gunasekera S, Ficarro SB, Romanienko P, Mark W, McCarthy C, de Stanchina E, Gonen M, Seshan V, Bhola P, O'Donnell C, Spitzer B, Stutzke C, Lavallée VP, Hébert J, Krivtsov AV, Melnick A, Paietta EM, Tallman MS, Letai A, Sauvageau G, Pouliot G, Levine R, Marto JA, Armstrong SA, Kentsis A