Interleukin-1beta Processing Is Dependent on a Calcium-mediated Interaction with Calmodulin*

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Interleukin-1 Processing Is Dependent on a Calcium-mediated Interaction with Calmodulin*

 

Joseph S. Ainscough‡1, G. Frank Gerberick§, Ian Kimber‡, and Rebecca J. Dearman‡
From the ‡ Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom and the § Procter & Gamble Co. , Cincinnati, Ohio 45253

 

The secretion of IL-1 is a central event in the initiation of inflammation. Unlike most other cytokines, the secretion of IL-1 requires two signals: one signal to induce the intracellular up-regulation of pro-IL-1 and a second signal to drive secretion of the bioactive molecule. The release of pro-IL-1is a complex process involving proteolytic cleavage by caspase-1. However, the exact mechanism of secretion is poorly understood. Here we sought to identify novel proteins involved in IL-1 secretion and intracellular processing to gain further insights into the mechanism of IL-1 release. A human proteome microarray containing 19,951 unique proteins was used to identify proteins that bind human recombinant pro-IL-1. Probes with a signal-to-noise ratio of >3 were defined as biologically relevant. In these analyses, calmodulin was identified as a particularly strong hit, with a signal-to-noise ratio of 11. Using an ELISA-based protein-binding assay, the interaction of recombinant calmodulin with pro-IL-1, but not mature IL-1, was confirmed and shown to be calcium-dependent. Finally, using small molecule inhibitors, it was demonstrated that both calcium and calmodulin were required for nigericin-induced IL-1 secretion in THP-1 cells and primary human monocytes. Together, these data suggest that, following calcium influx into the cell, pro-IL-1 interacts with calmodulin and that this interaction is important for IL-1 processing and release.

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