The small ubiquitin-like modifier SUMO-3 acts as a neutrophil chemoattractant via the chemokine receptors CXCR1 and CXCR2

Introduction: Small ubiquitin-like modifiers (SUMOs) are small peptides conjugated to proteins during post-translational modification which have been reported to modulate several aspects of the immune system, notably in auto-immune disorders. Methods: We used a SUMO-based bacterial expression system to create a recombinant protein putatively expressed by Toxocara canis, which we hypothesised might antagonise responses via the chemokine receptor CXCR1. Results: Although our recombinant Toxocara canis protein was devoid of antagonist activity, we serendipitously observed that recombinant SUMO-3 protein had chemotactic activity for CXCR1 transfectants. Further study found that SUMO-3 acted as a full agonist of CXCR1 and the closely related receptor CXCR2, the latter responses ablated by a CXCR2 antagonist. SUMO-3 showed similar efficacy at both receptors but reduced potency when compared to CXCL8, with chemotaxis observed at high nanomolar to micromolar concentrations. In receptor endocytosis assays, SUMO-3 induced internalisation of CXCR1 and CXCR2, with inferior potency and efficacy to CXCL8. Translating our findings to primary cells, a broad range of SUMO-3 concentration gradients were shown to induce the chemotaxis of human neutrophils. Finally, SUMO-3 was found to be released by necrotic cells into the extracellular milieu. Conclusions: Collectively, our findings suggest that SUMO-3 can induce the chemotaxis of neutrophils via CXCR1 and CXCR2. We postulate that in vivo, release of SUMO-3 from necrotic cells may serve to recruit neutrophils, contributing to tissue homeostasis and the resolution of inflammation.