Multidimensional degradomics identifies systemic autoantigens and intracellular matrix proteins as novel gelatinase B/MMP-9 substrates

Abstract

The action radius of matrix metalloproteinases or MMPs is not restricted to massive extracellular matrix (ECM) degradation, it extends to the proteolysis of numerous secreted and membrane-bound proteins. Although many instances exist in which cells disintegrate, often in conjunction with induction of MMPs, the intracellular MMP substrate repertoire or degradome remains relatively unexplored. We started an unbiased exploration of the proteolytic modification of intracellular proteins by MMPs, using gelatinase B/MMP-9 as a model enzyme. To this end, multidimensional degradomics technology was developed by the integration of broadly available biotechniques. In this way, 100-200 MMP-9 candidate substrates were isolated, of which 69 were identified. Integration of these results with the known biological functions of the substrates revealed many novel MMP-9 substrates from the intracellular matrix (ICM), such as actin, tubulin, gelsolin, moesin, ezrin, Arp2/3 complex subunits, filamin B and stathmin. About 2/3 of the identified candidates were autoantigens described in multiple autoimmune conditions and in cancer (e.g. annexin I, nucleolin, citrate synthase, HMGB1, alpha-enolase, histidyl-tRNA synthetase, HSP27, HSC70, HSP90, snRNP D3). These findings led to the insight that MMPs and other proteases may have novel (immuno)regulatory properties by the clearance of toxic and immunogenic burdens of abundant ICM proteins released after extensive necrosis. In line with the extracellular processing of organ-specific autoantigens, proteolysis might also assist in the generation of immunodominant 'neo-epitopes' from systemic autoantigens. The study of proteolysis of ICM molecules, autoantigens, alarmins and other crucial intracellular molecules may result in the discovery of novel roles for proteolytic modification.

Association between matrix metalloproteinase 9 promoter polymorphisms and Behçet's disease

“…Furthermore, MMP-9 is able to generate a remnant epitope of autoantigen, which induces or sustains an autoimmune response [36]. It has been reported that antiendothelial cell antibody-positive serum showed reactivity to alpha-enolase in patients with BD and that alpha-enolase is a substrate for MMP-9 [37,38]. Interestingly, BD has been considered a type 1 helper T cell (T h 1)-driven disease, and T h 1 lymphocyte was reported to produce greater MMP-9 secretion than T h 2 cells [39].…”

Human matrix metalloproteinases: An ubiquitarian class of enzymes involved in several pathological processes

“…Two evidences, reported by the same authors, illustrate the MMP-9 pathogenic activity (Cauwe et al, 2009(Cauwe et al, , 2011. The first one is the identification of several intra-cellular novel substrates, which enlarge the enzyme degradome and could be involved in the development of such a pathology.…”

Angiogenic neutrophils: a novel subpopulation paradigm

“…1 Recently, the combination of imatinib and anti-CTLA-4 was reported to induce tumor clearance in a spontaneous model of GIST. 4 Agonist anti-OX40 has been reported to increase immunity through both neutralization of Treg function and increased resistance of T effectors to suppression 7 and is currently under clinical development. 8 Although OX40 engagement leads to T-cell expansion, Treg numbers also increased in the present study.…”

“…6 This latter function may be achieved by MMP-9 degrading intracellular matrix (ICM) proteins released from dead/damaged cells. 7 Finally, a cell type must then come in and help with revascularization and healing. Whether only inflammatory neutrophils enter infectious sites while both inflammatory and angiogenic neutrophils enter sterile injury to help with progression of inflammation and restitution remains unclear, but the current study may support such a scenario.…”