The analysis of oncogenic variants of negative JAK/STAT regulators: Mechanisms and Significance

• Applicant: Professor Dr. Ralf Marienfeld, since 5/2023
• Subject Area: Pathology
• Term: since 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257217594

Cytokine-induced and receptor tyrosine kinase (RTK) -mediated activation of Janus Kinase (JAK) / Signal Transducer and Activator of Transcription (STAT) signaling pathways control cell growth and survival. Solid and lymphoid tumors, especially B-cell lymphomas, such as classic Hodgkin lymphoma (cHL), diffuse large-cell B-cell lymphoma (DLBCL) and primarily mediastinal B-cell lymphoma (PMBL)) often show a dysregulated JAK / STAT activation, partly due to inactivating mutations in negative JAK / STAT regulators such as PTPN1, PTPN2 and SOCS1. The importance of protein tyrosine phosphatase 1B (PTP1B / gene: PTPN1) for cHL was the focus of the first funding period. The starting point was shortened PTPN1 mRNA variants, which we identified in cHL cell lines and in Hodgkin / Reed-Sternberg cells. One of these PTPN1 variants, which lacked the catalytic center with exon 6, significantly increased JAK / STAT activity and JAK / STAT-dependent gene expression. As a result, there was increased cell growth and increased chemotherapy resistance after PTP1BΔ6 expression in L-428 cHL cells, which was based in part on an induced PTP1BWT proteolysis. While PTPN1Δ6 is a splice variant, another PTPN1 variant, PTPN1Δ2-4, is based on a PTPN1 mutation. But PTPN1Δ2-4 also increased JAK / STAT activity and gene expression, cell growth and resistance to chemotherapy drugs, without changing the stability of PTP1BWT. The aim of this follow-up application is to deepen this knowledge about the importance of the PTPN1 variants and to expand the focus on SOCS1, because we have observed a similar positive effect of a selected SOCS1 mutant in preliminary work. For an in-depth analysis, the interactome of the PTP1B variants is to be determined by means of coupled affinity chromatography mass spectrometry and the new interactions are to be characterized biochemically and functionally in order to obtain knowledge about additional, affected signaling pathways. Planned analyzes of the phospho-proteomes and transcriptomes modified by PTP1B variants have the same goal. To analyze the SOCS1 mutants, we want to characterize different SOCS1 mutants (SNPS, small DelIns, as well as nonsense and frame shift mutants) biochemically and functionally. To this end, their influence on the JAK / STAT system and on the survival and apoptosis of a suitable B-cell lymphoma cell line is examined. Interestingly, transcription factors and signaling pathways, which are important for B cell development, are also involved in B cell lymphomagenesis, like Pax5 and BCL6. As the expression of these transcription factors (TFs) and cofactors (coTFs) are controlled by canonical NF-kB as well as by JAK/STAT signaling, we will determine the impact of SOCS1, PTP1B or their oncogenic variants on the TFs and coTFs. With the program presented here, we hope to obtain not only in-depth knowledge of cHL pathogenesis, but also implications for the regulation of the JAK / STAT signaling pathways in other tumor entities.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Peter Möller
• Ehemalige Antragstellerin: Dr. Malena Zahn, until 4/2023