Shedding of NG2 by MMP-13 Attenuates Anoikis

Abstract

Disruption of cell-matrix interactions can lead to anoikis-apoptosis due to loss of matrix contacts. We previously showed that Nerve/glial antigen 2 (NG2) is a novel anoikis receptor. Specifically, overexpression of NG2 leads to anoikis propagation, whereas its suppression leads to anoikis attenuation. Interestingly, NG2 expression decreases in late anoikis, suggesting that NG2 reduction is also critical to this process. Thus, we hypothesized that NG2 undergoes cleavage to curtail anoikis propagation. Further, since matrix metalloproteinases (MMPs) cleave cell surface receptors, play a major role in modulating apoptosis, and are associated with death receptor cleavage during apoptosis, we further hypothesized that cleavage of NG2 could be mediated by MMPs to regulate anoikis. Indeed, anoikis conditions triggered release of the NG2 extracellular domain into condition media during late apoptosis, and this coincided with increased MMP-13 expression. Treatment with an MMP-13 inhibitor and MMP-13 siRNA increased anoikis, since these treatments blocked NG2 release. Further, NG2-positive cells exhibited increased anoikis upon MMP-13 inhibition, whereas MMP-13 inhibition did not increase anoikis in NG2-null cells, corroborating that retention of NG2 on the cell membrane is critical for sustaining anoikis, and its cleavage for mediating anoikis attenuation. Similarly, NG2 suppression with siRNA inhibited NG2 release and anoikis. In contrast, MMP-13 overexpression or exogenous MMP-13 reduced anoikis by more effectively shedding NG2. In conclusion, maintenance of NG2 on the cell surface promotes anoikis propagation, whereas its shedding by MMP-13 actions attenuates anoikis. Given that these findings are derived in the context of periodontal ligament fibroblasts, these data have implications for periodontal inflammation and periodontal disease pathogenesis.

Functional roles of CSPG4/NG2 in chondrosarcoma

“…In contrast to ADAMTS4 and MMP3, the expression of MMP13 increased with CSGP4/ NG2 knock-down. The reasons for this difference are not clear, but a recent study has highlighted a relationship between NG2 and MMP13 and the regulation of anoikis (Joo et al 2014) raising the possibility of a feedback loop between cell surface or extracellular CSPG4/NG2 levels and MMP13 production which has been lost in the B3 chondrosarcoma (NG2/CSPG4 knock-down) cells.…”

Apoptosis, autophagy, necroptosis, and cancer metastasis

“… MMPs Prominent family of proteinases MMPs played roles in the regulation of ECM turnover, cancer cell migration, cell growth, inflammation, and angiogenesis [ 62 ]. They also interfered with the induction of apoptosis in malignant cells via the cleavage of ligands or receptors in the apoptotic pathways [ 63 - 65 ]. Note: NSCLC, non-small-cell lung cancer; Apaf-1, apoptotic protease-activating factor; IAPs, cellular inhibitors of apoptosis proteins; XIAP, X-linked inhibitor of apoptosis; DAPK, death-associated protein kinase; FADD, Fas-associated death domain-containing protein; sFas, soluble Fas; DcR3, decoy receptor 3; TRAIL, TNF-related apoptosis-inducing ligand; DcR1, decoy receptor 1, also referred to as TRAIL-R3; DcR2, decoy receptor 2, also referred to as TRAIL-R4; OPG, osteoprotegerin; DR4, death receptor 4; TβR I/II, TGF-β receptor I/II; MMPs, matrix metalloproteinases; JNK, c-Jun N-terminal kinases.…”

“…For instance, MMP-7 was reported to cleave membrane-bound FasL on doxorubicin-treated cancer cells, thereby attenuating apoptosis and increasing the resistance of these cells to chemotherapy [ 63 , 64 ]. MMP-13 was shown to be involved in the shedding of nerve/glial antigen 2 (NG2), a novel anoikis receptor, thereby contributing to the attenuation of anoikis [ 65 ].…”

Structural deciphering of the NG2/CSPG4 proteoglycan multifunctionality

“…However, on macrophages and OPCs, the NG2/CSPG4 ectodomain may also be dislodged from the cell surface by MT1-MMP/MMP14, which finds its preferential cleavage site within the upper portion of the N-terminal D1 subdomain [i.e., within residues 490-500 (64)]. The preventive effect on surface shedding observed with a spectrum of MMP inhibitors, along with in vitro digestion and colocalization studies, also implicates MMP9 and MMP13 in the proteolytic processing of NG2/CSPG4 (69)(70)(71).…”