Interleukin (IL)-1α and IL-1β are pivotal to the initiation and orchestration of inflammation. Unlike most cytokines, IL-1 does not have a signal peptide and therefore secretion requires 2 independent processes; an initial signal to induce the up-regulation of the inactive precursor (pro-IL-1) and a second signal to drive cleavage and subsequent secretion. Whereas many previous studies have focused on the mechanisms that drive IL-1 secretion, the aims of this thesis were to investigate the processes that regulate the intracellular precursors of IL-1 (pro-IL-1α and pro-IL-1β). The hypothesis here was that regulation of these precursors may serve to control the vigour of IL-1 secretion and, ultimately, may influence the potency of pro-inflammatory responses. Post-translational modifications were of particular interest in this thesis, as these modifications are becoming increasingly important to immune system function. Ubiquitination is an important post-translational modification whereby ubiquitin, an 8.5kDa protein, is covalently bound to lysine residues on substrate proteins. In chapter 2, evidence was provided to show that in murine DC, IL-1α and IL-1β are polyubiquitinated and that, in both DC and macrophages, this polyubiquitination drives the proteasomal degradation of IL-1. In addition, these data demonstrated that in the presence of a second signal, polyubiquitinated IL-1 is still available for secretion. Overall, these investigations highlight that the polyubiquitination and proteasomal degradation of IL-1 serves as an essential process in the regulation of IL-1 and, therefore, should be considered as an extra dimension to the current two-signal paradigm of IL-1 release. To support this work, an immortalized bone marrow derived murine macrophage cell line and a human monocyte cell line that both stably express fluorescent IL-1β were employed to measure the rate of IL-1β degradation. In these investigations, it was shown that fluorescence is a reliable readout for measuring IL-1β degradation in these cell lines. In addition, it was demonstrated that that TLR-stimulation leads to an inhibition in IL-1β ubiquitination and degradation. Together, the work presented herein highlights that ubiquitination actively regulates the vigour of IL-1β protein expression and thus may be an important regulator of inflammation. To complement this work, a broader approach was taken, whereby the interactome of pro-IL-1β was explored using a human protein microarray. In these investigations, a human proteome microarray containing 19,951 unique proteins was used to identify proteins that bind human recombinant pro-IL-1β. In these analyses, calmodulin was identified as a particularly strong hit, with a SNR of ~11. Using an ELISA-based protein-binding assay, the interaction of recombinant calmodulin with pro-IL-1β, but not mature IL-1β, 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-1β secretion in human monocytes. Collectively, the evidence presented in these investigations suggests that following calcium influx, pro-IL-1β interacts with intracellular calmodulin and that this interaction is central for IL-1β processing and release. In addition, a number of other potentially important pro-IL-1β-interacting proteins were also identified in this work, including IL22RA2 and PLCXD3. Overall, the work presented in this thesis serves to highlight that IL-1 is regulated by a broad range of potentially important intracellular processes. We postulate that these processes may be pivotal in the regulation of inflammation and thus the maintenance of homeostasis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:679977 |
| Date | January 2015 |
| Creators | Ainscough, Joseph |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/understanding-the-intracellular-regulation-of-interleukin1(40e6e798-11ed-4a07-a0fa-16189c0aa222).html |
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