Genetic mutations pre-dispose to the development of hematologic cancers such as MPNs. A frequent event in the aging hematopoietic system are mutations of JAK2, a protein essential for the development of hematopoietic cells. Nonetheless, there is currently no treatment option available to directly target disease-maintaining Jak2-mutated clones and a detailed understanding of the underlying pathogenic molecular mechanisms is needed.

We have identified functionally relevant proteins responsible for maintenance of MPN cells and identified proteins involved in mRNA splicing and processing as a novel class of targets phosphorylated by mutant JAK2. We showed that phosphorylation of splicing factor Y-box Protein 1 (YBX1) by mutated JAK2 is a critical downstream event, essential for mRNA splicing of the ERK-signaling component Mitogen-activated Protein Kinase Interacting Serine/Threonine Kinase 1 (MKNK1). Inactivation of the splicing factor Ybx1 sensitized Jak2-mutated cells to JAK-inhibitor induced apoptosis through abrogation of persistent ERK-signaling. Overall, our findings introduced hijacking of the spliceosome machinery through post-translational modification by an oncogenic kinase, rather than mutation of the splicing factor itself, as a pathogenic mechanism.

Following our observation that inhibition of additional signaling pathways can sensitize cells to JAK-i-mediated apoptosis, we have focused our research on delineating cellular mechanisms that mediate clonal development and disease progression. Using JAK2- mutated human cell lines of blast-phase (BP-) MPN that represent the end stage of clonal progression, we have conducted and analyzed genome-wide CRISPR/Cas9-screens to identify molecules with specific functional relevance in JAK2-mutated BP-MPN versus other subtypes of AML and on dependencies that persist upon Jak-inhibitor therapy.

By this, we identified CER1, a member of the cysteine knot superfamily as an exclusive dependency in JAK2-mutated cell lines with increased, above average mRNA expression. In addition, by now, we can offer first evidence for a functional relevance of CER1 in maintenance and progression of JAK2-mutated cells as first transcriptional studies suggest its involvement in major cell signaling pathways such as JAK-STAT- and WNT-signaling, transcription factors (such as MYC) and differentiation related gene expression programs. Hence, we propose that interference with the CER1-signaling network may induce clonal regression and based on the hypothesis that CER1 is functionally relevant for disease persistence and progression, the project described here aims to answer the following core questions:

How does CER1 influence the transcriptional program and cellular signaling in JAK2-mutated MPNs?

 How is disease persistence and progression influenced by CER1?

Which secondary dependencies can be validated for translational development in primary human MPN clones?