Post translational modifications (PTM) of C/EBPß and functional implications

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A comprehensive and post-translational modification (PTM) dependent interactome of the pioneer transcription factor C/EBPbeta was disclosed using two complementary screening methods (APS and PRISMA) that returned approximately 650 and 1500 proteomic interactions, respectively. Experimentally induced lymphoid - myeloid trans-differen¬tiation revealed that decoration of C/EBPbeta with PTMs determines its reprogramming potential into myeloid sub-lineages and suggested an epigenetic PTM indexing-code on C/EBPbeta. Mixed lineage marker expression is a salient feature of lymphoma entities that express high C/EBPbeta levels, including Hodgkin-, anaplastic large cell-, Mantel cell lymphoma (HL, ALCL, MCL) and multiple myeloma (MM). We consider lineage switching in tumorigenesis in connection with cellular trans-differentiation events and a selective proliferative advantage. To determine the core functions of C/EBPbeta in transformation and lympho-myeloid reprogramming, we will employ state-of-the-art mass spectrometric analysis of the C/EBPbeta PTM index and its interactome in lymphoma cell lines and primary cells, in combination with a CRISPR/Cas9 based functional genomic complementation system of C/EBPbeta mutants in an ALCL cell line. Finally, SUMOylation was identified as a dynamic PTM and bottleneck for additional C/EBPbeta modifications. SUMOylation deficient C/EBPalpha,beta knock in mouse strains have been constructed and will be examined to explore how signaling events are coupled to C/EBPbeta modifications and epigenetic functions.