Impact of immunoproteasome function on transcriptional homeostasis in KMT2A-r AML

• Applicant: Professor Dr. Florian Heidel
• Subject Area: Hematology, Oncology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449291356

Chromosomal translocations found in acute myelogenous leukemia (AML) can generate oncogenic fusions with aberrant epigenetic and transcriptional functions. Fusion-oncogene driven leukemias remain a therapeutic challenge. While targeted therapies have improved the therapeutic landscape of AML, direct targeting of oncogenic fusions has not been successful so far. Specific subtypes such as leukemias harboring rearrangements of the KMT2A-gene (KMT2A-r) have a particularly poor prognosis due to residual disease persistence and a high relapse rate. Pharmacologic targeting of chromatin-associated protein complexes has shown significant responses in KMT2A-r AML but resistance frequently develops to single agents. This points to a need for therapeutic combinations that target multiple mechanisms. In the first funding period, we have used a proteomic approach to identify the catalytic immunoproteasome (IP) subunit PSMB8 as a specific vulnerability to enhance our understanding of functional dependencies in KMT2A-r AML. Genetic and pharmacologic inactivation of PSMB8 results in impaired proliferation of murine and human leukemic cells while normal hematopoietic cells remain unaffected. Disruption of IP function drives an increase in transcription factor BASP1 which in turn represses KMT2A-fusion protein target genes. Pharmacologic targeting of PSMB8 improves efficacy of Menin-inhibitors, synergistically reduces leukemia in human xenografts and shows preserved activity against Menin-inhibitor resistance mutations. This identifies and validates a cell-intrinsic mechanism whereby selective disruption of proteostasis results in altered transcription factor abundance and repression of oncogene-specific transcriptional networks. These data demonstrate that the IP is a relevant therapeutic target in AML and that targeting the IP in combination with Menin-inhibition could be a novel approach for treatment of KMT2A-r AML. In the second funding period we aim to (i) analyze the impact of PSMB8 on UPS function by proteome analysis and functional validation using CIRPSR/Cas9 mediated inactivation of UPS molecules, (ii) investigate the regulation of BASP1 transcription factor-complex in KMT2A-r AML by interactome analyses and chromatin-immunoprecipitation studies and (iii) assess for the effect of (immuno-)proteasome function on regulation of post-translational modifications (PTMs) through global and functional cell signaling studies. The aims defined here will determine how (mechanistically) disruption of transcription factor homeostasis and perturbation of the ubiquitin-proteasome-system (UPS) contribute to this functional dependency.

• DFG Programme: Research Grants