INVESTIGATION OF THE TUMOUR NECROSIS FACTOR-STIMULATED GENE-6 (TSG-6) INTERACTOME; USE AND DEVELOPMENT OF SURFACE SENSITIVE TECHNIQUES

UoM administered thesis: Unknown

  • Authors:
  • Holly Birchenough

Abstract

Tumour necrosis factor-stimulated gene-6 (TSG-6) is a protein expressed in a wide range of cell types and tissues, predominantly in response to inflammatory stimuli. The expression of TSG-6 is believed to be associated with the protection of tissues from the damaging effects of inflammation. In animal models treatment with TSG-6 protein has been found to reduce inflammatory damage in myocardial infarction, corneal injury and arthritis. Endogenous TSG-6 production has been suggested to play a protective role in inflammatory arthritis and has been implicated in bone homeostasis. The expression of TSG-6 is also essential in the process of cumulus matrix formation that occurs around the oocyte in the periovulatory period and is necessary for successful ovulation and fertilisation. In many cases the mechanism underlying a particular TSG-6 function is not fully understood. TSG-6 has numerous binding partners including the serum glycoprotein inter-alpha-inhibitor (IalphaI), the growth factor bone morphogenetic protein-2 (BMP-2) and the extracellular matrix protein fibronectin, as well as glycosaminoglycans (GAGs) such as hyaluronan and heparan sulphate (HS). The TSG-6 protein is mostly composed of contiguous Link and CUB domains, with the majority of ligand binding sites identified within the Link module. The CUB domain of TSG-6 has been less extensively studied. Here biophysical techniques have been used to investigate the TSG-6 interactome including both the Link module and CUB domain. Intrinsic fluorescence spectroscopy was used to establish the metal-ion binding properties of the CUB domain, which was established to have a high affinity Ca2+-binding site. Using surface plasmon resonance (SPR), a novel metal-ion dependent interaction was found for the CUB domain of TSG-6 and the heavy chains (HCs) of IalphaI. Investigation using mutants of both the CUB domain of TSG-6 and HC of IalphaI established that the metal-ion binding sites within each protein are involved in the interaction. SPR analysis was also used to define the affinities and binding sites for TSG-6 interactions with fibronectin and BMP-2. High affinity interactions between TSG-6 ligands were also revealed (e.g. BMP-2 and HC, fibronectin and HC) and their binding sites defined. The discovery of the novel interactions between these TSG-6 ligands suggests crosstalk within the TSG-6 interactome, with the potential for ternary complex formation or indeed hierarchical orders of binding. Thus work was undertaken to develop a passivated lipid bilayer platform for use with surface sensitive techniques. This platform was used to investigate the hierarchy of protein and GAG interactions using quartz crystal microbalance with dissipation monitoring (QCM-D) and dual polarisation interferometry (DPI). The investigation revealed a novel role for the Link module of TSG-6 in heparin condensation, potentially via protein dimerisation and/or oligomerisation which could affect heparin/HS functions within the extracellular matrix (ECM). Thus the biophysical analysis of TSG-6 presented here has identified novel interactions and functions of TSG-6 which may provide mechanisms for the protective functioning of TSG-6 in inflammation and its ECM structuring role in ovulation.

Details

Original languageEnglish
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Award date31 Dec 2014