Regulated expression of anti- and pro-apoptotic Bcl-2 proteins is required for proper development and functioning of the hematopoietic system, and deregulation of apoptosis can contribute to many diseases of the hematopoietic system. Two major subgroups can be defined: i) diseases with excessive apoptosis and ii) diseases with inadequate induction of apoptosis. While the former are characterized by cytopenia and, in the worst case, bone marrow failure, the latter are characterized by lympho- and myeloproliferation, autoimmunity and eventually leukemia. For most hematological diseases, the contribution of Bcl-2 proteins and their upstream regulators have not been characterized in detail. Also, the relevance of individual Bcl-2 proteins for maintenance of the healthy human hematopoietic system, both under homeostatic and stress conditions, has not yet been defined in full detail while it has been investigated in-depth in mice. Finally, cancer therapies interfere with the equilibrium of pro- and anti-apoptotic Bcl-2 proteins thereby inducing apoptosis. This effect is desired in malignant cells (i.e. leukemic cells), but represents an unwanted side effect on healthy bone marrow cells resulting in myelosuppression.
In the current funding period we are investigating, which pro-survival Bcl-2 proteins are required to maintain the human hematopoietic stem and progenitor cell (HSPC) pool, both in steady state and under stress. By doing so, we aim at defining the “minimal requirements” for stem cell survival and blood formation in humans. In addition, we are exploring signals, which potentially protect human HSPCs from stress, and interrogate their impact on the equilibrium of Bcl-2 proteins. Hence, it is our aim to identify molecules that increase resistance of HSPCs and improve blood formation under conditions of stress.
In the follow-up project of FOR2036, we will investigate how composition and regulation of Bcl-2 proteins is changed in pre-malignant and malignant hematopoietic cells. It can be assumed that cell death-resistant cells are selected during transformation and that this occurs in a multistep process. As model system, we will use cells with a constitutively activated RAS signaling cascade. Somatic mutations positively affecting this pathway (e.g. in KRAS, NRAS, PTPN11, NF1, CBL, BRAF etc.) are frequently found in human cancer, including juvenile myelomonocytic leukemia (JMML). In addition, these genes are mutated in the germline of patients with so-called RASopathies, which constitute a new set of cancer predisposition syndromes. Patients with RASopathies frequently suffer from transient myeloproliferation and/or JMML. RASopathies with myeloproliferation or JMML, and sporadic JMML are relevant diseases in pediatric oncology but at the same time valuable models for basic research by representing different steps of malignant transformation in a relatively simple cellular system that involves only few genes that are found to be mutated additionally. Our project will be based on the analysis of the Bcl-2 protein network in different mouse model systems, patient-derived cells and a xenograft model, together representing the multistep process of malignant transformation.
The specific aims of the project are:
Characterization of the Bcl-2 proteins that are deregulated in different stages of RAS-driven leukemic transformation
Identification of Bcl-2 proteins that are required for survival of MPD and JMML cells
Delineation of the pro-apoptotic effects of azacitidine on JMML cells
Evaluation of the therapeutic efficacy of BH3-mimetics on JMML, both alone or in combination with azacitidine
Miriam Erlacher (PI)
Sheila Bohler (PhD Student)
Sehar Afreen (PhD Student)
Ying Wu (MD PhD Student)
Cooperation within FOR2036
Georg Häcker, Alexander Egle, Philipp Jost, Markus Morrison (Rehm), Andreas Villunger