Interleukin receptor activates a MYD88-ARNO-ARF6 cascade to disrupt vascular stability

The innate immune response is essential for combating infectious disease. Macrophages and other cells respond to infection by releasing cytokines such as interleukin-1β (IL-1β), which in turn activate a well-described myeloid differentiation factor 88 (MYD88) -mediated, nuclear factor-κB (NF-κB) -dependent transcriptional pathway that results in inflammatory cell activation and recruitment(1–4). Endothelial cells, which usually serve as a barrier to the movement of inflammatory cells out of the blood and into tissue, are also critical mediators of the inflammatory response(5,6). Paradoxically, the same cytokines vital to a successful immune defense also have disruptive effects on endothelial cell-cell interactions and can trigger degradation of barrier function and dissociation of tissue architecture(7–9). The mechanism of this barrier dissolution and its relationship to the canonical NF-κB pathway remains ill defined. Here we show that the direct, immediate, and disruptive effects of IL-1β on endothelial stability are NF-κB independent and are instead the result of signaling via the small GTPase, ADP-ribosylation factor 6 (ARF6), and its activator, ARF nucleotide binding site opener (ARNO). Moreover, we show that ARNO binds directly to the adaptor protein MYD88, and thus propose MYD88-ARNO-ARF6 as a proximal IL-1β signaling pathway distinct from that mediated by NF-κB (Supplementary Fig. 1). Finally, we show that SecinH3, an inhibitor of ARF guanine nucleotide-exchange factors (GEFs) such as ARNO, enhances vascular stability and significantly improves outcomes in animal models of inflammatory arthritis and acute inflammation.