We study how signals regulate the function of C/EBP and how C/EBPs “talk” to other proteins of the gene regulatory and epigenetic machinery. Both, C/EBPα,β specify cell fates by altering the structure of chromatin and modifying gene expression. Expression of C/EBPα,β in B cells induces their trans-differentiation to myeloid cells, suggesting “pioneering” and “master switch” transcription factor functions. Cell lineage switching, mostly from the lymphoid lineage to myeloid cells, occurs in relapsing leukemia and is accompanied by unfavorable clinical prognosis. We have developed an assay to monitor the trans-differentiation capacity of C/EBPs in great detail. The assay is based on primary v-abl transformed B cells that can be grown to large quantities and are therefore amenable to genetic manipulation and analysis by molecular genetics and biochemistry. By inserting C/EBPα,β or mutants thereof into v-abl B cells and by genetic manipulation at the B cell stage, we can disclose how C/EBPs precisely determine cell fate choice during lymphoid-myeloid lineage switching.
We found that C/EBPα,β are decorated with a multitude of signal dependent post-translational modifications (PTM). Experimental manipulation of distinct PTM sites alters the interactome, and concomitantly, the trans-differentiation capacity of C/EBPs. Accordingly, we presume that a “PTM-Indexing Code” predefines the C/EBP interactome and the resulting epigenetic functions. Using proteomic techniques (in collaboration with Phillip Mertins, MDC Proteomics Core Unit, and Gunnar Dittmar, Proteome & Genome Research Unit, ILH, Luxembourg) we have disclosed hundreds of interaction partners with C/EBPα,β, many of which depend on PTMs. We currently explore how the PTM-dependent C/EBP-interactors participate in directing cell fate, using our lymphoid-myeloid lineage-switch assay in combination with recombinant genetics and mass spectrometry.
Dittmar, G., Perez-Hernandez, D., Kowenz-Leutz, E., Kirchner, M., Kahlert, G., Wesolowski, R., Baum, K., Knoblich, M., Muller, A., Wolf, J., Reimer, U., Leutz, A., Protein Interaction Screen on Peptide Matrix (PRISMA) reveals interaction footprints and the PTM-dependent interactome of intrinsically disordered C/EBPβ.
Cirovic, B., Schönheit, J., Kowenz-Leutz, E., Ivanovska, J., Klement, C., Pronina, N., Begay, V., Leutz, A., C/EBP-Induced Transdifferentiation Reveals Granulocyte-Macrophage Precursor-like Plasticity of B Cells. Stem Cell Reports, 8: 346-359; 10.1016/j.stemcr.2016.12.015, (2017)