MMP7
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Matrilysin also known as matrix metalloproteinase-7 (MMP-7), pump-1 protease (PUMP-1), or uterine metalloproteinase is an
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
in humans that is encoded by the ''MMP7''
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
. The enzyme () has also been known as ''matrin'', ''putative (or punctuated) metalloproteinase-1'', ''matrix metalloproteinase pump 1'', ''PUMP-1 proteinase'', ''PUMP'', ''metalloproteinase pump-1'', ''putative metalloproteinase'', ''MMP''). Human MMP-7 has a molecular weight around 30 kDa. Matrilysin was discovered by Sellers and Woessner in the uterus of the rat in 1988. The complementary DNA (cDNA) of human MMP7 was isolated in 1988 by Muller et al. MMP7 is a member of the
matrix metalloproteinase Matrix metalloproteinases (MMPs), also known as matrix metallopeptidases or matrixins, are metalloproteinases that are calcium-dependent zinc-containing endopeptidases; other family members are adamalysins, serralysins, and astacins. The MMPs b ...
(MMP) family consisting of structural-related zinc-dependent
endopeptidase Endopeptidase or endoproteinase are proteolytic peptidases that break peptide bonds of nonterminal amino acids (i.e. within the molecule), in contrast to exopeptidases, which break peptide bonds from end-pieces of terminal amino acids. For this re ...
s. The primary role of cleaved/activated MMP7 is to break down
extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...
by degrading macromolecules including casein, type I, II, IV, and V
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
s,
fibronectin Fibronectin is a high- molecular weight (~500-~600 kDa) glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. Fibronectin also binds to other extracellular matrix proteins such as collage ...
, and
proteoglycan Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to whic ...
.


Gene, regulation, and expression

The human MMP7 is located on chromosome 11 q22.3. ''MMP'' genes are clustered in q region of human Chromosome 11 including ''matrilysin, collagenase-1, stromelysin1, stromelysin-2, and metalloelastase'' genes. It consists of 267 amino acids. The cDNA of MMP7 is 49% homologous to stromelysin-1. Comparing to other members of MMP family, MMP7 does not have a C-terminal protein domain. The promoter of the human MMP7 contains a TATA box, an activator protein 1 (AP-1) site, and two inverted polyomavirus enhancer A-binding proteins 2 (PEA-3). The AP-1/PEA-3 binding motif is required and essential for MMP7 to be responsive to growth factors, oncogenes and phorbol ester. Also, the PEA and AP-1 are required for Matrilysin/CAT reporter constructs induced by tumor promoter 12-O-tetradecanoulphorbol-13-acetate (TPA) and epidermal growth factor (EGF). In addition, the high level expression of AP-1 and its binding proteins were found to be associated with mutant Ki-Ras suggesting the high expression of matrilysin in Ras activated cells is AP-1 dependent. The expression of MMP7 is regulated by the Wnt/ β catenin signaling pathway, and mediated by transformation growth factor β (TGF-β).TGF-β stimulates ECM and suppresses the steady-state level of MMP7, stromelysin mRNAs, and secretion of zymogens. The isoforms of TGF-β inhibit MMP7 mRNA and protein in the human endometrium via progesterone mediated pathway. However, the opposite effects of TGF-β on MMP7 were observed among transformed cells. In human glioma cell lines and human squamous cell carcinoma cell line II-4, TGF-β stimulates the expression of MMP7 mRNA and proteins, and facilities the invasive behavior of cells. The promoter region of the human MMP7 gene contains two or more sites that are homologous to the NR-IL6 binding sequences indicating MMP7 can bind to IL-1 and IL-6. In addition, the level of MMP7 mRNA is elevated followed the treatment of tumor necrosis factor α (TNF- α) and IL-1 β in human mesangial cells. MMP7 are commonly expressed in epithelial cells including ductal epithelium of exocrine glands in skin, salivary glands, pancreas, glandular epithelium of intestine and reproductive organ, liver, and breast. In addition, MMP7 is highly expressed in the luminal surface of dysplastic glands in human colorectal cancers.


Structure

A MMP7 protein is bounded by four metal ions including a catalytic zinc ion, a structural zinc ion, and two calcium ions. The catalytic zinc ion binds to three His residues in the HEXGHXXGXXH region in tetracoordination. The calcium ion binding play important role in stabilizing the secondary structure. MMP7 has a shallow hydrophobic substrate-binding pocket. In contrast to MMP9 which has the longest hinge, MMP7 lacks hemopexin and does not have a hinge. Instead, MMP7 contains a variable C-terminal hemopexin-like domain facilitates substrate specificity. The protein of MMP7 is secreted as zymogen. The prodoamin of MMP7 contains an approximately 9 kD highly conserved “cysteine switch” PRCGXPD sequence near the C-terminal containing cysteine residues. Cysteine residues bind to the catalytic zinc keeping the protein latent. The dissociation of cysteine –Zinc coordination starts from the cleavage of the first 30 amino acids of the prodomain, which leads to a conformation change, and further results in autoproteolysis and the cleavage of the whole prodomain at Glu-Tyr site. According to Woessner et al., the Mr of MMP7 is 28,000 for the latent form and 19,000 Mr for the active form after the cleavage of its prodomain.


Interactions

Promatrilysin (Pro-MMP7) is converted from the latent form to the active form by endoproteinases, and plasmin. Plasmin cleaves at the site recognizable to trypsin, is considered as the most possible physiological activator. In vitro, plasmin can activate pro-MMP7 to 50% of its full activity. Also, researchers used activated recombinant pro-MMP7 and purified substrates to investigate the proteolytic activity of MMp7 in vitro, and found that MMP7 cleaves many protein substrates mainly including ECM components, proMMPs, and nonmatrix proteins. MMP7 cleaves the glycoprotein entactin that links laminin and collagen IV at about 100-600 times faster than collagenase-1. In addition, MMP7 can activate other MMPs. Activated MMP7 and APMA can increase the activity of collagenase-1, and MMP7 can also convert the latent progelatinase A to its active form.


Function

Proteins of the
matrix metalloproteinase Matrix metalloproteinases (MMPs), also known as matrix metallopeptidases or matrixins, are metalloproteinases that are calcium-dependent zinc-containing endopeptidases; other family members are adamalysins, serralysins, and astacins. The MMPs b ...
(MMP) family are involved in the breakdown of
extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...
in normal physiological processes, such as
embryonic development An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
,
reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...
, and tissue remodeling, as well as in disease processes, such as
arthritis Arthritis is a term often used to mean any disorder that affects joints. Symptoms generally include joint pain and stiffness. Other symptoms may include redness, warmth, swelling, and decreased range of motion of the affected joints. In som ...
and
metastasis Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...
. Most MMP's are secreted as inactive
proprotein A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein (or peptide) that can be turned into an active form by post-translational modification, such as breaking off a piece of the molecule or adding on another molecule ...
s which are activated when cleaved by extracellular
proteinase A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...
s. The
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
encoded by this gene degrades
proteoglycan Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to whic ...
s,
fibronectin Fibronectin is a high- molecular weight (~500-~600 kDa) glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. Fibronectin also binds to other extracellular matrix proteins such as collage ...
,
elastin Elastin is a protein that in humans is encoded by the ''ELN'' gene. Elastin is a key component of the extracellular matrix in gnathostomes (jawed vertebrates). It is highly elastic and present in connective tissue allowing many tissues in the bod ...
and
casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins (CSN1S1, αS1, aS2, CSN2, β, K-casein, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of ...
and differs from most MMP family members in that it lacks a conserved
C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...
protein domain. The enzyme is involved in
wound healing Wound healing refers to a living organism's replacement of destroyed or damaged tissue by newly produced tissue. In undamaged skin, the epidermis (surface, epithelial layer) and dermis (deeper, connective layer) form a protective barrier again ...
, and studies in mice suggest that it regulates the activity of
defensin Defensins are small cysteine-rich cationic proteins across cellular life, including vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, ...
s in
intestinal mucosa The gastrointestinal wall of the gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut (the lumen) outwards, these are: # Mucosa # Submucosa # Muscular layer # Serosa or adventitia The mucosa is ...
. MMP7 was initially characterized by Woessner et al. It digests components of the extracellular matrix, cleaves the α 2 (I) chain of gelatin more rapidly, and digests the B chain of insulin at Ala14-Leu and Tyr16-Leu, and has no action on
collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
types I, II, IV, V. The optimal pH of MMP7 is at 7 and the pI is at 5.9. MMP4 is inhibited by α 2-macroglobulin and TIMP. The inhibition of MMP7 activity commonly relies on metal-chelating agents including EDTA and 1,10-phenanthroline, especially zinc chelation. Therefore, the selectivity of MMP7 inhibition is challenging since almost all members of MMPs family contain catalytic domains with zinc binding sites. TIMP-1 and 2 noncovalently bound to active MMP7 at the catalytic site inhibiting MMP7 activity. The activated MMP7 can also cleave the propeptides of proMMP2 and proMMP9 to facilitate tumor invasion.


Normal tissue development

Quondamatteo et al. immunohistochemically stained MMP7, and localized MMP7 in early human liver development. They reported that MMP7 was presented in some hepatocytes and endothelial cells in the 6th gestational week, and only hematopoietic cells remained after that time.


Tissue remodeling

In order for MMPs to escape TIMP inhibition, active MMP7s are recruited to the plasma membrane of
epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
inducing membrane-associated growth factors processing for epithelial repair and proliferation. In human endometrium, the expression of MMP7 mRNA increases at menstruation and remains high during the proliferative phase. Also, MMP-7 binds to the plasma membrane of epithelium containing cholesterol-rich domain. The bounded MMP7 is active and resistant to TIMP inhibition. It promotes the activity of the epithelial plasma membrane and associated substrates including E-cadherin, β4-integrin, TNF-alpha, RAS, heparin-binding EGF, IGF binding proteins and plasminogen. Further, this process promotes epithelial cell migration, proliferation and apoptosis. For menstruation, it promotes the endometrium regeneration after menstrual breakdown. Huang et al. reported that the proteolytic activity of MMP7 plays major role in tissue remodeling in biliary atresia-associated liver fibrosis.


Clinical significance

MMP7 cleaves collagen III/IV/V/IX/X/XI and proteoglycan indicating that MMP inhibitors can potentially be used in therapies that are involved in inhibition of tissue degradation, remodeling, anti-angiogenesis and inhibition of tumor invasion.


Role in Cancer

MMP7 is found to potentially be involved in tumor metastasis and inflammatory processes. The upregulation of MMP7 is associated with many malignant tumors including esophagus, stomach, colon, liver, pancreas, and renal cell carcinomas. High MMP7 expression facilitates cancer invasion and angiogenesis by degrading extracellular matrix macromolecules and connective tissues. These degradations are associated with many mechanisms including embryogenesis, postpartum uterine involution, tissue repair, angiogenesis, bone remodeling, arthritis, decubitus ulcer, and tumor metastasis/invasion. Activated MMP7 activates MMP2 and MMP9 zymogens, and mediates the proteolytic process of the precursors of tumor necrosis factors and urokinase plasminogen activators.


Colon cancer and MMP7 expression

MMP7 cleaves cell surface proteins, promotes adhesion of cancer cells, and increases the potential of tumor metastasis. Higashi et al. reported that the binding of MMP7 to cholesterol sulfate on the cell surface plays a critical role in the cell membrane-related proteolytic action. Also, the internal Ile 29, Arg33, Arg51, and Trp 55 and 171-173 residues at MMP7 C-terminal located on the opposite side of the catalytic site of MMP7 are required for cholesterol sulfate binding. Wild type MMP7 can digest fibronectin, but mutant MMP7 fails to induce the aggregation of colon cancer cells. In addition, Qasim et al. reported that MMP7 is highly expressed in advanced colorectal adenomatous polys with severe dysplasia. Further, MMP7 is involved in converting colorectal adenomas into malignant state and facilitating the growth.


References


Further reading

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External links

* * The
MEROPS MEROPS is an online database for peptidases (also known as proteases, proteinases and proteolytic enzymes) and their inhibitors. The classification scheme for peptidases was published by Rawlings & Barrett in 1993, and that for protein inhibitor ...
online database for peptidases and their inhibitors
M10.008
{{Portal bar, Biology, border=no Matrix metalloproteinases EC 3.4.24