Nonproteolytic functions of matrix metalloproteinases in pathology and insights for the development of novel therapeutic inhibitors

Figures & data

Figure 1 Schematic drawing depicting the domain structure of MMPs.

Notes: The signal peptide guides the MMP through the rough endoplasmic reticulum during synthesis and is cleaved off during secretion by the docking enzyme; the SH propeptide domain maintains the enzyme inactive by blocking the catalytic site, and it is removed or unfolded for MMP activation; the catalytic domain contains the active site of the enzyme and the Zn2+-binding segment. This basic structure is contained in MMP-7 and MMP-26 (matrilysins). MMP-2 and MMP-9 contain three fibronectin-like type II repeats between the active site and the Zn2+-binding segment, and these are responsible for the gelatin-binding property. MMP-9 contains an additional O-glycosylated region, which confers flexibility to the molecule. Except for MMP-7 and MMP-26, all other MMPs contain a carboxy-terminal hemopexin domain, which confers specificity and interacts with many ligands and receptors. The hemopexin and catalytic domains are connected by a small hinge region. MT-MMPs have an additional transmembrane domain and a short cytoplasmic tail or a GPI linkage, which anchor MT-MMPs to the cell membrane.
Abbreviations: MMP, matrix metalloproteinase; SH, sulfhydryl-containing; GPI, glycosylphosphatidylinositol; MT, membrane-type.

Table 1 Molecular interactions and biological effects involving noncatalytic MMP domains

MMP	Receptor/ligand	Cell type	Biological effect	References
MMP-1	α2β 1 integrin	Neural cells, monocytes	Release of MMP-9, Akt dephosphorylation	44,45
MMP-2	αVβ3 integrin	Lung adenocarcinoma	Increased VEGF expression and angiogenesis	46
MMP-3	HSP90β	Mammary gland epithelial cells	Cell invasion, branching morphogenesis wnt5 inactivation, hyperbranching phenotype	47,48
	Wnt5b
MMP-9	LRP-1	Schwann cells, COS-1	ERKI/2 and Akt activation, cell migration, catabolism	31
	LRP-2/megalin	Yolk sac sarcoma cells (BNI6)	MMP-9 endocytosis and catabolism
	IGF-1, EGFR, PDGFR	Schwann cells	Ras/Raf/MEK-ERK regulation, phenotypic remodeling	50
	α4β 1 integrin, CD44v	Chronic lymphocytic leukemia	MMP-9 cell surface localization, activation of the Lyn/STAT3/Mcl-I pathway, cell migration/arrest, cell survival	54,55,57
	CD44	Breast carcinoma	EGFR activation, cell migration	51
		Melanoma	Actomyosin contractility, rounded amoeboid, cell invasion proMMP-9/CSPG complex formation, prevention of TIMP-1 binding to proMMP-9, weaker binding to gelatin	58
	CSPG	Monocytic cells		32
	Ku protein	Monocytes	MMP-9 internalization, cell invasion	33
MMP-14	TIMP-2	Breast carcinoma, fibrosarcoma	ERKI/2 activation, cell proliferation, and migration	6I,62
	HIF-1α	Macrophages	Stimulation of glycolysis and ATP production	64
		Myeloid cells	RacI activation, lamellipodia activity Cell motility, cell fusion	65
	β1 integrin	Mammary epithelial cells	ERK activation, branching morphogenesis	66

Abbreviations: MMP, matrix metalloproteinase; VEGF, vascular endothelial growth factor; LRP, lipoprotein receptor-related protein; ERK, extracellular signal-regulated kinase; IGF, insulin-like growth factor; PDGFR, platelet-derived growth factor receptors; EGFR, epidermal growth factor receptor; CSPG, chondroitin sulfate proteoglycans; TIMP, tissue inhibitor of metalloproteinase; ATP, adenosine triphosphate; HIF, hypoxia-inducible factor; MEK, mitogen-activated protein kinase kinase; STAT3, signal transducer and activator of transcription 3; Mcl-1, myeloid cell leukemia-1.

Figure 2 Ribbon diagram of the monomeric hemopexin domain of MMP-9 (PEX9) showing the location of drug target sites.

Notes: (A) PEX9, similar to other PEX domains of MMPs, is composed of four structural blades surrounding a central cavity. (B) Spatial location of the P3 and P6 amino acid sequences within PEX9 (research originally published in The Journal of Biological Chemistry. Ugarte-Berzal E, Bailón E, Amigo-Jiménez I, Albar JP, García-Marco JA, García-Pardo A. A novel CD44-binding peptide from the pro-matrix metalloproteinase-9 hemopexin domain impairs adhesion and migration of chronic lymphocytic leukemia (CLL) cells. The Journal of Biological Chemistry. 2014; 289(22):15340–15349. © the American Society for Biochemistry and Molecular Biology.⁷⁹). P3 is located in blade 4 and interacts with α4β1 integrin; P6 is located in blade 1 and binds to CD44.⁷⁹ P3 and P6 act synergistically to inhibit MMP-9-induced CLL cell adhesion and migration, thus serving as therapeutic peptides and simultaneously pointing to “druggable” targets in PEX9. An additional CD44-binding sequence located in the outermost strand of blade 1 has also been reported. (C) Diagram showing the binding sites within PEX9 of small MW compounds mapped by in silico docking (adapted from Cancer Research, Copyright 2011;71(14):4977–4988. Dufour A, Sampson NS, Li J, et al. Small-molecule anticancer compounds selectively target the hemopexin domain of matrix metalloproteinase-9, with permission from AACR⁸²). As observed, both the small compounds and the P3 and P6 sequences are located in close proximity within the central cavity of PEX9. Targeting this region may therefore be a useful approach to control the pathogenic functions of MMP-9, particularly in cancer and inflammation.
Abbreviations: MW, molecular weight; MMP, matrix metalloproteinase; PEX, hemopexin domain; CLL, chronic lymphocytic leukemia.

Ugarte-Berzal E, Bailón E, Amigo-Jiménez I, Albar JP, García-Marco JA, García-Pardo A. A novel CD44-binding peptide from the pro-matrix metalloproteinase-9 hemopexin domain impairs adhesion and migration of chronic lymphocytic leukemia (CLL) cells. J Biol Chem. 2014;289(22):15340–15349.

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Dufour A, Sampson NS, Li J, et al. Small-molecule anticancer compounds selectively target the hemopexin domain of matrix metalloproteinase-9. Cancer Res. 2011;71(14):4977–4988.

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