Autophagy and linear ubiquitination in the leukaemic bone marrow microenvironment

• Applicant: Professorin Dr. Daniela Krause
• Subject Area: Hematology, Oncology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456266326

The role of the diverse constituents of the bone marrow microenvironment (BMM) for the regulation of normal haematopoietic stem cells is being elucidated. But how the BMM interacts with and influences the course of a leukaemia is largely still unknown, although knowledge of this could lead to the development of novel therapies. Various signaling pathways are being investigated in an effort to eradicate cancer stem cells in the haematological malignancies, the cause of relapse and progression. Such pathways include autophagy, a natural, cellular ‘self-eating’ process, which leads to the breakdown of dysfunctional cellular components, or the linear ubiquitination pathway, which modifies proteins. However, understanding and, eventually, targeting these quality control pathways in cells of the BMM has not been attempted, although it is likely that these processes in niche cells influence leukaemia progression.Our preliminary data have shown that mice with deficiency of pleckstrin homology domain-containing family M member (PLEKHM) 1, a protein involved in the generation of lysosomes or vesicles, which carry various proteins and other cargo, have shortened survival when transplanted with B-cell acute lymphoblastic leukaemia (B-ALL) cells. Secondary transplantation of B-ALL cells from a PLEKHM 1-deficient BMM suggests that this BMM increases the number and/or function of leukaemic stem cells. Further, PLEKHM1-deficient mesenchymal stromal cells (MSC), components of the BMM, had altered autophagy and increased protein loading of their exosomes, i.e. small vesicles released from MSC. Exosomes from PLEKHM 1-deficient MSC carried higher amounts of syndecans, coreceptors for growth factor receptors, for instance on leukaemia cells. We showed that leukaemia cells likely take up transferred exosomes leading to an alteration of the leukaemia cells’ signal transduction towards a more ‘stem’-like phenotype, also by coculture with PLEKHM 1 KO MSC. Autophagy flux and vesicle distribution is also altered within PLEKHM 1 KO MSC. In addition, for linear ubiquitination, we have shown that mice with endothelial cell-specific deficiency of otulin, a deubiquitinase, have significantly accelerated disease course in three different types of acute myeloid leukaemia.Hypothesizing that autophagy and linear ubiquitination in bone marrow niche cells influence leukaemia progression, we will test a) the role of PLEKHM1-dependent autophagy and exosome generation, b) otulin-dependent linear ubiquitination in endothelial cells, as well as c) the possibility of therapeutic targeting of exosomes and linear ubiquitination in niche cells of the leukaemic BMM. This will be performed using in vivo leukaemia models, in vitro coculture assays, mass spectrometry and biochemical strategies with the overall goal of translating our findings on quality control in the BMM into clinical medicine and to, eventually, design clinical trials with novel agents.

• DFG Programme: Research Grants