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 autoimmune 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 T. 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.