Poster Presentation 35th Lorne Cancer Conference 2023

Distinct assemblies of heterodimeric cytokine receptors govern stemness programs in leukaemia (#273)

Winnie L Kan 1 , Urmi Dhagat 2 , Kerstin B Kaufmann 3 , Timothy R Hercus 1 , Tracy L Nero 2 , Andy GX Zeng 3 , John Toubia 1 , Karen Steffi Cheung Tung Shing 2 , Kaylene J Simpson 4 , Daniel Thomas 5 , Paul G Ekert 6 , Denis Tvorogov 1 , Richard J D'Andrea 1 , John E Dick 3 , Michael W Parker 2 , Angel F Lopez 7
  1. The Centre for Cancer Biology, SA Pathology and the University of South Australia, Adelaide, South Australia, Australia
  2. Department of Biochemistry and Pharmacology and the ACRF Facility for Innovative Cancer Drug Discovery, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
  3. Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada
  4. Victorian Centre for Functional Genomics, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
  5. Department of Medicine, University of Adelaide, Adelaide, South Australia, Australia
  6. Translational Tumour Biology Group, Children's Cancer Institute, Lowy Cancer Centre, University of New South Wales, Randwick, New South Wales, Australia
  7. Human Immunology, SA Pathology, Adelaide, South Australia, Australia

Leukemia stem cells (LSC) possess distinct self-renewal and arrested differentiation properties that are responsible for disease emergence, therapy failure and recurrence in acute myeloid leukemia (AML). AML displays extensive biological and clinical heterogeneity, with a rare common denominator being the over expression of the interleukin-3 (IL-3) receptor in LSC, a feature that has puzzled cancer experts and haematologists since its first description in 2000. IL-3 is a pleiotropic cytokine that stimulates survival, proliferation and differentiation of haematopoietic stem and progenitor cells and acts by binding a heterodimeric receptor (IL-3R) composed of a cytokine-specific IL3Rα subunit and a βc signaling subunit. Since the IL-3R, unlike several overexpressed receptors in other cancers, is a heterodimer and lacks intrinsic tyrosine kinase activity, how this can possibly influence the pathogenesis of AML has remained a mystery. Here, we show that the IL-3 receptor stoichiometry varies across the individual cells that make up the AML hierarchy. The highest IL3Rα to βc ratios are found on primitive LSCs and is clinically associated with poor patient survival and relapse. Using crystallographic, super resolution single cell FLIM-FRET analyses, signalling and transcriptomic approaches, and multiple in vitro and in vivo stem cell and biological cell systems, we show that stem cell fate is controlled through the assembly of the IL-3R into hexamer and dodecamer configurations through a unique interface. The stoichiometry of IL3Rα to βc subunits directly regulates receptor assembly with higher IL3Rα/βc ratios biasing hexamer formation and lower ratios biasing dodecamer formation. The hexamer activates distinct signalling and transcriptional programs to induce stemness whereas the dodecameric assembly mediates differentiation. Importantly, the higher IL3Rα/βc ratios in LSCs drive hexamer-mediated stemness programs and promote LSC function. Our study establishes a new paradigm where alternative cytokine receptor stoichiometries activate unique signalling to instruct cell fate and to govern cell state plasticity in the AML hierarchy, which likely work in synergy with existing mutations to promote stem cell transformation and leukaemogenesis. This concept may also transcend to other cancers that are driven by stem cell hierarchies and be harnessed for therapeutic purposes through engineering of cytokines to target cytokine receptor assemblies.