Adenosine Signaling Mediates SUMO-1 Modification of IκBα during Hypoxia and Reoxygenation

Small ubiquitin-like modifier 1 (SUMO-1) modification of I kappa B alpha has been described to actively participate in NF kappa B regulation. Following proteosomal degradation of I kappa B alpha, an auto-regulatory loop consisting of transcriptional activation of I kappa B alpha gene and SUMO-1 modification of newly synthesized I kappa B alpha proceeds. The SUMOylated I kappa B alpha form is resistant to signal-induced degradation, consequently halting NF kappa B activation. We describe a mechanistic model by which adenosine (Ado) signaling results in significant accumulation of SUMO-1 modified I kappa B alpha with subsequent attenuation of NF kappa B activation. Using models of hypoxia followed by reoxygenation (H/R), we have documented an H/R cycle-dependent increase in extracellular Ado correlating with increases in the cytoplasmic pool of I kappa B alpha/SUMO-1. We demonstrate a dose-dependent increase in I kappa B alpha/SUMO in cells treated with the general Ado receptor agonist NECA and abolished by Ado receptor antagonists. Experiments in cells exposed to cycles of H/R followed by hypoxia demonstrated differential patterns of SUMOylation and phosphorylation of I kappa B alpha, greatly impacting its proteosomal degradation by the 26 S proteasome. Assays targeting knockdown and overexpression of SUMO-1 demonstrated significant regulation of NF kappa B activation and NF kappa B-mediated gene transcription (interleukin-6). These results were confirmed in vivo using wild type and cd73 null mouse lung tissue. In summary, we present an endogenous mechanism by which cells and tissues acquire anti-inflammatory properties by recruiting a nondegradable form of I kappa B alpha, a major control point for NF kappa B activation via Ado signaling.