MEF2B C-terminal mutations enhance transcriptional activity and stability to drive B cell lymphomagenesis
Chuanjiang Yu, Qiong Shen, Antony B. Holmes, Tongwei Mo, Anna Tosato, Rajesh Soni, Clarissa Corinaldesi, Sanjay Koul, Laura Pasqualucci, Shafinaz Hussein, F. Forouhar, Riccardo Dalla‐Favera, Katia Basso
Abstract
The myocyte enhancer factor 2B (MEF2B) transcription factor is frequently mutated in germinal center (GC)-derived B-cell lymphomas. Its ammino (N)-terminal mutations drive lymphomagenesis by escaping interaction with transcriptional repressors, while the function of carboxy (C)-terminal mutations remains to be elucidated. Here, we show that MEF2B C-tail is physiologically phosphorylated at specific residues and phosphorylation at serine (S)324 is impaired by lymphoma-associated mutations. Lack of phosphorylation at S324 enhances the interaction of MEF2B with the SWI/SNF chromatin remodeling complex, leading to higher transcriptional activity. In addition, these mutants show an increased protein stability due to impaired interaction with the CUL3/KLHL12 ubiquitin complex. Mice expressing a phosphorylation-deficient lymphoma-associated MEF2B mutant display GC enlargement and develop GC-derived lymphomas, when crossed with Bcl2 transgenic mice. These results unveil converging mechanisms of action for a diverse spectrum of MEF2B mutations, all leading to its dysregulation and GC B-cell lymphomagenesis. N-terminal mutations in the transcription factor Myocyte Enhancer Factor 2B (MEF2B) are reported to drive lymphomagenesis. Here, the authors show that lymphoma-associated C-terminal mutations in MEF2B impair its phosphorylation, leading to increased stability and transcriptional activity to promote B-cell lymphomagenesis.