PT  - JOURNAL ARTICLE
AU  - Fiona C. Brown
AU  - Eric Still
AU  - Paolo Cifani
AU  - Sumiko Takao
AU  - Casie Reed
AU  - Scott B. Ficarro
AU  - Richard P. Koche
AU  - Peter Romanienko
AU  - Willie Mark
AU  - Conor O’Donnell
AU  - Barbara Spitzer
AU  - Crystal Stutzke
AU  - Andrei V. Krivtsov
AU  - Gayle Pouliot
AU  - Nathanael Gray
AU  - Jarrod A. Marto
AU  - Scott Armstrong
AU  - Alex Kentsis
TI  - MEF2C phosphorylation is required for chemotherapy resistance in acute myeloid leukemia
AID  - 10.1101/107201
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 107201
4099  - http://biorxiv.org/content/early/2017/02/09/107201.short
4100  - http://biorxiv.org/content/early/2017/02/09/107201.full
AB  - HIGHLIGHTSMEF2C S222 phosphorylation is a specific marker of chemotherapy resistance in diagnostic AML patient specimens.MEF2C S222 phosphorylation is dispensable for normal hematopoiesis in mice, as established using genome editing in vivo, but is required for MLL-AF9 induced leukemogenesis.MARK kinases specifically phosphorylate MEF2C S222, potentiating its transcriptional activity.Chemical inhibition of MARK-induced MEF2C phosphorylation overcomes chemotherapy resistance of and exhibits selectivity toxicity against MEF2C-activated human AML cells.SUMMARY 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 Mef2cS222A/S222A knock-in mutant 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, and induced by MARK kinases in cells. Treatment with the selective MARK inhibitor MRT199665 caused apoptosis of MEF2C-activated human AML cell lines and primary patient specimens, but not those lacking MEF2C phosphorylation. These findings identify kinase-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.