Physical Poster + E-Poster Presentation 34th Lorne Cancer Conference 2022

Surprisingly, pro-survival MCL-1 is not essential for haematopoietic development (#237)

Kerstin Brinkmann 1 , Annli Tee 1 , Gemma Kelly 1 , Andreas Strasser 1
  1. Walter and Eliza Hall Institute of Medical Research, Carlton, VIC, Australia

Apoptosis is vital for embryonic development and tissue homeostasis in adults. Defects in apoptosis can emerge from the overexpression of pro-survival BCL-2 protein family members, and this can give rise to diseases including cancer and autoimmune disorders1. BH3-mimetic drugs that inhibit select pro-survival BCL-2 proteins have been developed for cancer therapy. However, whereas the BCL-2 inhibitor Venetoclax is well tolerated in patients, the use of other BH3-mimetics that inhibit related proteins MCL-1 or BCL-XL is more challenging due to on-target toxicity to non-malignant cells, including haematopoietic cells2. Pro-survival BCL-2 proteins play critical roles in haematopoiesis. MCL-1 is essential for the survival of haematopoietic stem and progenitor cells (HSPCs) as well as many immature and mature blood cell populations3. In contrast, the essential roles for BCL-2 and BCL-XL during haematopoiesis is restricted to specific haematopoietic subpopulations. We aim to determine the unique roles of MCL-1 compared to the other pro-survival BCL-2 family members and to understand why Mcl-1 knockout mice die at embryonic day E3.5. We used CRISPR to produce “gene-swap” mice in which the MCL-1 coding region was replaced with the coding region for BCL-2 (Bcl-2>Mcl-1). Excitingly, homozygous Bcl-2>Mcl-1KI/KI embryos developed until E12.5 and some even beyond, however, these embryos had major abnormalities. To examine the impact of replacement of MCL-1 by BCL-2 on haematopoiesis, lethally irradiated mice were reconstituted with Bcl-2>Mcl-1KI/KI HSPCs from E12.5 embryos. The expression of BCL-2 in place of MCL-1 in the haematopoietic system allowed the generation of all blood cell types. However, the reconstituted mice had massive abnormal increases (~7-fold) in white blood cells. Bcl-2>Mcl-1+/Ki mice also showed substantial accumulations of antibody-secreting plasma cells and immature B cells in their spleen and bone marrow. This suggests that the Bcl-2>Mcl-1 gene-swap mice may develop SLE-like autoimmune disease similar to vav-bcl-2 mice that overexpress BCL-2. Our work demonstrates that BCL-2 can replace MCL-1 in haematopoiesis, but this replacement causes abnormal accumulation of lymphoid cells.

  1. Adams, J. M. & Cory, S. The BCL-2 arbiters of apoptosis and their growing role as cancer targets. Cell death and differentiation 25, 27-36, doi:10.1038/cdd.2017.161 (2018). 
  2. Kelly, G. L. & Strasser, A. Toward Targeting Antiapoptotic MCL-1 for Cancer Therapy. Annual Review of Cancer Biology 4, 299-313, doi:10.1146/annurev-cancerbio-030419-033510 (2020). 
  3. Opferman, J.T., Letai, A., Beard, C., Sorcinelli, M.D., Ong, C.C. and Korsmeyer, S.J., 2003. Development and maintenance of B and T lymphocytes requires antiapoptotic MCL-1. Nature, 426(6967), pp.671-676. 
  4. Ogilvy, S., Metcalf, D., Bath, M.L., Harris, A.W. and Adams, J.M., 1999. Constitutive Bcl-2 expression throughout the hematopoietic compartment affects multiple lineages and enhances progenitor cell survival. Proceedings of the National Academy of Sciences, 96(26), pp.14943-14948.