The IL-3 receptor α subunit N-terminal domain: role in receptor assembly and signalling — ASN Events
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  2. Poster Session 1
  3. The IL-3 receptor α subunit N-terminal domain: role in receptor assembly and signalling

The IL-3 receptor α subunit N-terminal domain: role in receptor assembly and signalling (#276)

Winnie L Kan 1 , Timothy R Hercus 1 , Sophie E Broughton 2 , Tracy L Nero 2 , Mara Dottore 1 , Frank C Stomski 1 , Emma F Barry 1 , Barbara J McClure 1 , Urmi Dhagat 2 , Matthew P Hardy 3 , Nicholas J Wilson 3 , Michael W Parker 2 , Angel F Lopez 1
  1. Centre for Cancer Biology, SA Pathology and University of South Australia, Adelaide, SA, Australia
  2. ACRF Rational Drug Discovery Centre, St Vincent's Institute of Medical Research, Fitzroy, VIC, Australia
  3. CSL Limited, Parkville, VIC, Australia

Interleukin (IL)-3, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-5 are responsible for the survival, proliferation, differentiation and activation of hematopoietic cells. IL-3 signals through a receptor consisting of a ligand-specific α subunit (IL3Rα) and a β subunit (βc), which is shared with the GM-CSF and IL-5 receptors. IL-3Rα is overexpressed on the surface of leukaemic stem cells in patients with acute myelogenous leukaemia, allowing the targeting of leukaemic stem cells with specific antibodies1. Our previous studies demonstrated that the GM-CSF receptor assembles into a hexamer consisting of 2 GM-CSF molecules, 2 αsubunits and a βc homodimer, which subsequently forms a higher-order dodecamer complex upon cytokine binding that is required for Jak2 transphosphorylation and full activation2. We have recently solved the structure of IL3Rα, which contains the N-terminal domain (NTD) and domains 2 and 3 and demonstrated that IL-3 can bind IL-3Rα through “open” and “closed” conformations of the receptor3. What remains unknown is how the NTD contributes to receptor signalling and its functional significance.

The aim of the present study is to determine the role of the NTD of IL-3Rα in IL-3 binding, higher-order receptor assembly and cell signalling. We generated several mutants that disrupt the conformation of the NTD, which were tested in signalling and functional studies. The results showed that the binding affinity of IL-3 to the mutant receptors and proliferative activity in immortalized mouse fetal liver cells expressing the mutants were reduced and similar to that observed for IL-3Rα that lacks the NTD. We will present further biochemical data that suggests that the mutants follow different pathways to the formation of the receptor dodecameric complex. Although the IL-3Rα NTD is not essential for ligand binding, its conformation once ligand-bound plays a crucial role in initiating and directing the assembly of a functional higher order complex.

  1. Jin, L et al. (2009). Monoclonal antibody-mediated targeting of CD123, IL-3 receptor alpha chain, eliminates human acute myeloid leukemic stem cells. Cell Stem Cell 5, 31-42.
  2. Hansen G et al. (2008). The structure of the GM-CSF receptor complex reveals a distinct mode of receptor activation. Cell 134, 496-507.
  3. Broughton, SE et al. (2014). Dual Mechanism of interleukin-3 receptor blockade by an anti-cancer antibody. Cell Reports 8, 410-419.