72 kDa type IV collagenase also known as matrix metalloproteinase-2 (MMP-2) and gelatinase A is an enzyme that in humans is encoded by the MMP2 gene. [5] The MMP2 gene is located on chromosome 16 at position 12.2. [6]
72 kDa type IV collagenase also known as matrix metalloproteinase-2 (MMP-2) and gelatinase A is an enzyme that in humans is encoded by the MMP2 gene. [5] The MMP2 gene is located on chromosome 16 at position 12.2. [6]
Proteins of the matrix metalloproteinase (MMP) family are involved in the breakdown of extracellular matrix (ECM) in normal physiological processes, such as embryonic development, reproduction, and tissue remodeling, as well as in disease processes, such as arthritis and metastasis. Most MMP's are secreted as inactive proproteins which are activated when cleaved by extracellular proteinases. This gene encodes an enzyme which degrades type IV collagen, the major structural component of basement membranes. The enzyme plays a role in endometrial menstrual breakdown, regulation of vascularization and the inflammatory response. [7]
Activation of MMP-2 requires proteolytic processing. A complex of membrane type 1 MMP (MT1-MMP/MMP14) and tissue inhibitor of metalloproteinase 2 recruits pro-MMP 2 from the extracellular milieu to the cell surface. Activation then requires an active molecule of MT1-MMP and auto catalytic cleavage. Clustering of integrin chains promotes activation of MMP-2. Another factor that will support the activation of MMP-2 is cell-cell clustering. A wild-type activated leukocyte cell adhesion molecule (ALCAM) is also required to activate MMP-2.
Mutations in the MMP2 gene are associated with Torg-Winchester syndrome, multicentric osteolysis, arthritis syndrome, [8] [9] and possibly keloids.
Activity of MMP-2 relative to the other gelatinase (MMP-9) has been associated with severity of chronic airway diseases including Idiopathic interstitial pneumonia and Bronchiectasis. In idiopathic interstitial pneumonia, MMP-2 activity was elevated in patients with the less severe disease phenotype which is more responsive and reversible with corticosteroid therapy. [10] In non-cystic fibrosis bronchiectasis, MMP-2 concentration was elevated in patients with Haemophilus influenzae airway infection compared to Pseudomonas aeruginosa airway infection. [11] Bronchiectasis patients with P. aeruginosa infection have a more rapid decline in lung function. [12] Disease-causing mutations in the MMP2 gene cause a rare type of skeletal dysplasia Multicentric Osteolysis, Nodulosis, and Arthropathy syndrome. Abnormal mutations cause defective collagen remodelling. The disease manifestations include bone destruction especially of the wrists and tarsus, generalized osteoporosis and joint stiffness and eventually destruction. [13] [9]
Altered expression and activity levels of MMPs have been strongly implicated in the progression and metastasis of many forms of cancer. Increased MMP-2 activity has also been linked with a poor prognosis in multiple forms of cancer including colorectal, melanoma, breast, lung, ovarian, and prostate. [14] Furthermore, changes in MMP-2 activity can come from alterations in levels of transcription, MMP secretion, MMP activation, or MMP inhibition. MMP production in many cancers may be upregulated in surrounding stromal tissue rather than simply in the tumor lesion. For instance, Mook, et al. showed that MMP-2 mRNA levels are strikingly similar between metastatic and non-metastatic lesions in colorectal cancer, but metastatic cases are correlated with higher levels of MMP-2 mRNA in surrounding healthy tissue. [15] For this reason, it is difficult to fully understand the complex role of MMPs in cancer progression.
One of the major implications of MMPs in cancer progression is their role in ECM degradation, which allows cancer cells to migrate out of the primary tumor to form metastases. More specifically, MMP-2 (along with MMP-9) is capable of degrading type IV collagen, the most abundant component of the basement membrane. The basement membrane is important for maintaining tissue organization, providing structural support for cells, and influencing cell signaling and polarity. Degradation of the basement membrane is an essential step for the metastatic progression of most cancers. [15]
Cancer cell invasion, ECM degradation, and metastasis are highly linked with the presence of invadopodia, protrusive and adhesive structures on cancer cells. Invadopodia have been shown to concentrate MMPs (including MT1-MMP, MMP-2, and MMP-9) for localized release and activation. [16] Furthermore, degradation products of MMP activity may further promote invadopodia formation and MMP activity. [17] Finally, MMP-2 and several other MMPs have been shown to proteolytically activate TGF-β, which has been shown to promote epithelial mesenchymal transition (EMT), a key process involved in cancer metastasis. [18]
MMP degradation of the ECM affects cellular behavior through changes in integrin-cell binding, by releasing growth factors harbored by the ECM, by generating ECM degradation products, and by revealing cryptic binding sites in ECM molecules. [19] For instance, MMP-2 degradation of collagen type I can reveal a previously inaccessible cryptic binding site that binds with the αvβ3 integrin expressed by human melanoma cells. Signaling through this integrin is necessary for melanoma cell viability and growth in a collagen matrix and can potentially rescue the cells from apoptosis. [20] As another example, cleavage of laminin-5, a component of the basement membrane, by MMP-2 has been shown to reveal a cryptic site inducing migration of breast epithelial cells. [21]
More generally, by degrading the ECM, MMPs release growth factors that were previously bound to the ECM, allowing them to bind with cell receptors and influence cell signaling. Furthermore, many MMPs also activate other proMMPs along with growth factors. [19] MMP-2 has also been shown to cleave other non-ECM substrates including growth factors such as TGF-β, FGF receptor-1, proTNF, IL-1β and various chemokines. [22] For instance, MMP-2 has been implicated, along with MMP-9 in cleaving latent TGF-β, which has complex interactions with cancer cells. TGF-β generally plays a role in maintaining tissue homeostasis and preventing tumor progression. However, genetically unstable cancer cells can often evade regulation by TGF-β by altering TGF-β receptors in downstream signaling processes. Furthermore, expression of TGF-β is also correlated with immune tolerance and may help shield cancer cells from immune regulation. [23]
MMP-2 also plays an important role in the formation of new blood vessels within tumors, a process known as angiogenesis. This process is essential for tumor progression, because as tumors grow they need increasing supplies of oxygen and nutrients. Localized MMP-2 activity plays an important role in endothelial cell migration, a key feature of angiogenesis. Additionally, MMP-9 and other MMPs have been suggested to also play a complex, indirect role in angiogenesis by promoting VEGF mobilization and generating antiangiogenic factors. [15]
For instance, when studying carcinogenesis of pancreatic islets in transgenic mice, Bergers et al. showed that MMP-2 and MMP-9 were upregulated in angiogenic lesions and that the upregulation of these MMPs triggered the release of bioactive VEGF, a potent stimulator of angiogenesis. Additionally, the group determined that MMP-2 knockout mice showed decreased rates of tumor growth relative to tumor growth rates in wild type mice. [24] Furthermore, increased expression and activity of MMP-2 has been tied to increased vascularization of lung carcinoma metastases in the central nervous system, which likely increases survival rate of these metastases. [25]
Finally, MMP-2 has been also shown to drive lymphangiogenesis, which is often excessive in tumor environments and can provide a route of metastasis for cancer cells. Detry, et al. showed that knocking down mmp2 in zebrafish prevented the formation of lymphatic vessels without altering angiogenesis, while MMP-2 inhibition slowed the migration of lymphatic endothelial cells and altered the morphology of new vessels. [15] These results suggest that MMP-2 may alter tumor viability and invasion by regulating lymphangiogenesis in addition to angiogenesis.
Clinical trials for cancer therapies using MMP inhibitors have yielded generally unsuccessful results. These poor results are likely due to the fact that MMPs play complex roles in tissue formation and cancer progression, and indeed many MMPs have both pro and anti-tumorogenic properties. Furthermore, most clinical studies involve advanced stages of cancer, where MMP inhibitors are not particularly effective. Finally, there are no reliable biomarkers available for assessing the efficacy of MMP inhibitors and MMPs are not directly cytotoxic (so they do not cause tumor shrinkage), so it is difficult for researchers to determine whether the inhibitors have successfully reached their targets. [14]
However, initial clinical trials using broad spectrum MMP inhibitors did show some positive results. Phase I clinical trials showed that MMP inhibitors are generally safe with minimal adverse side effects. Additionally, trials with marimastat did show a slight increase in survival of patients with gastric or pancreatic cancer. [14]
Various research groups have already suggested many strategies for improving the effectiveness of MMP inhibitors in cancer treatment. First, highly specific MMP inhibitors could be used to target the functions of specific MMPs, which should allow doctors to increase the treatment dosage while minimizing adverse side effects. MMP inhibitors could also be administered along with cytotoxic agents or other proteinase inhibitors. Finally, MMP inhibitors could be used during earlier stages of cancer to prevent invasion and metastasis. [14]
Additionally, the overexpression of MMPs in tumors can potentially be leveraged to direct the release of chemotherapeutic agents specifically to tumor sites. For example, cytotoxic agents or siRNA could be encapsulated in liposomes or viral vectors that become activated only upon proteolytic cleavage by a target MMP. Moreover, the tumor-targeting characteristics of MMP inhibitors provide a promising strategy for identifying small tumors. Researchers could link MMP inhibitors to imaging agents to facilitate the detection of tumors before they spread. Though initial trials yielded disappointing results, MMP inhibitors offer significant potential for improving cancer treatment by slowing the process of cancer cell invasion and metastasis. [14]
MMP2 has been shown to interact with:
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 belong to a larger family of proteases known as the metzincin superfamily.
Gelatinases are enzymes capable of degrading gelatin through hydrolysis, playing a major role in degradation of extracellular matrix and tissue remodeling. Gelatinases are a type of matrix metalloproteinase (MMP), a family of enzymes that depend on zinc as a cofactor and can break down parts of the extracellular matrix. MMPs have multiple subgroups, including gelatinase A and gelatinase B. Gelatinases are assigned a variety of Enzyme Commission numbers: gelatinase A uses 3.4.24.24, and gelatinase B uses 3.4.24.35, in which the first three numbers are same. The first digit, 3, is the class. Class 3 enzymes are hydrolases, enzymes that catalyze hydrolysis reactions, that is, they cleave bonds in presence of water. The next digit represents sub-class 4, or proteases, which are enzymes who hydrolyze peptide bonds in proteins. The next number is the sub-subclass of 24, which consists of metalloendopeptidases which contain metal ions in their active sites, in this case zinc, which help in cleaving peptide bonds. The last part of the EC number is the serial number, identifying specific enzymes within a sub-subclass. 24 represents gelatinase A, which is a metalloproteinase that breaks down gelatin and collagen, while 35 represents gelatinase B, which hydrolyzes peptide bonds.
Tissue inhibitors of metalloproteinases (TIMPs) are specific endogenous protease inhibitors to the matrix metalloproteinases. There are four TIMPs; TIMP1, TIMP2, TIMP3 and TIMP4. TIMP3 has been observed progressively downregulated in Human papillomavirus-positive neoplastic keratinocytes derived from uterine cervical preneoplastic lesions at different levels of malignancy. For this reason, TIMP3 is likely to be associated with tumorigenesis and may be a potential prognostic marker for uterine cervical preneoplastic lesions progression.
Matrix metalloproteinase-9 (MMP-9), also known as 92 kDa type IV collagenase, 92 kDa gelatinase or gelatinase B (GELB), is a matrixin, a class of enzymes that belong to the zinc-metalloproteinases family involved in the degradation of the extracellular matrix. In humans the MMP9 gene encodes for a signal peptide, a propeptide, a catalytic domain with inserted three repeats of fibronectin type II domain followed by a C-terminal hemopexin-like domain.
Matrix metalloproteinase-14 is an enzyme that in humans is encoded by the MMP14 gene.
Tissue inhibitor of metalloproteinases 2 (TIMP2) is a gene and a corresponding protein. The gene is a member of the TIMP gene family. The protein is thought to be a metastasis suppressor.
Matrilysin also known as matrix metalloproteinase-7 (MMP-7), pump-1 protease (PUMP-1), or uterine metalloproteinase is an enzyme in humans that is encoded by the MMP7 gene. The enzyme has also been known as matrin, putative 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.
TIMP metallopeptidase inhibitor 1, also known as TIMP1, a tissue inhibitor of metalloproteinases, is a glycoprotein with a molecular weight of 28 kDa. TIMP1 is expressed from several tissues of organisms.
Collagenase 3 is an enzyme that in humans is encoded by the MMP13 gene. It is a member of the matrix metalloproteinase (MMP) family. Like most MMPs, it is secreted as an inactive pro-form. MMP-13 has a predicted molecular weight around 54 kDa. It is activated once the pro-domain is cleaved, leaving an active enzyme composed of the catalytic domain and the hemopexin-like domain PDB: 1PEX. Although the actual mechanism has not been described, the hemopexin domain participates in collagen degradation, the catalytic domain alone being particularly inefficient in collagen degradation. During embryonic development, MMP-13 is expressed in the skeleton as required for restructuring the collagen matrix for bone mineralization. In pathological situations it is highly overexpressed; this occurs in human carcinomas, rheumatoid arthritis and osteoarthritis.
Matrix metalloproteinase-26 also known as matrilysin-2 and endometase is an enzyme that in humans is encoded by the MMP26 gene.
Stromelysin-3 (SL-3) also known as matrix metalloproteinase-11 (MMP-11) is an enzyme that in humans is encoded by the MMP11 gene.
Metalloproteinase inhibitor 4 is an enzyme that in humans is encoded by the TIMP4 gene.
Reversion-inducing-cysteine-rich protein with kazal motifs, also known as RECK, is a human gene, thought to be a metastasis suppressor.
Matrix metalloproteinase-25 is an enzyme that in humans is encoded by the MMP25 gene.
Neutrophil collagenase, also known as matrix metalloproteinase-8 (MMP-8) or PMNL collagenase (MNL-CL), is a collagen cleaving enzyme which is present in the connective tissue of most mammals. In humans, the MMP-8 protein is encoded by the MMP8 gene. The gene is part of a cluster of MMP genes which localize to chromosome 11q22.3. Most MMP's are secreted as inactive proproteins which are activated when cleaved by extracellular proteinases. However, the enzyme encoded by this gene is stored in secondary granules within neutrophils and is activated by autolytic cleavage.
Metalloprotease inhibitors are cellular inhibitors of the Matrix metalloproteinases (MMPs). MMPs belong to a family of zinc-dependent neutral endopeptidases. These enzymes have the ability to break down connective tissue. The expression of MMPs is increased in various pathological conditions like inflammatory conditions, metabolic bone disease, to cancer invasion, metastasis and angiogenesis. Examples of diseases are periodontitis, hepatitis, glomerulonephritis, atherosclerosis, emphysema, asthma, autoimmune disorders of skin and dermal photoaging, rheumatoid arthritis, osteoarthritis, multiple sclerosis, Alzheimer's disease, chronic ulcerations, uterine involution, corneal epithelial defects, bone resorption and tumor progression and metastasis. Due to the role of MMPs in pathological conditions, inhibitors of MMPs may have therapeutic potential. Several other proteins have similar inhibitory effects, however none as effective. They might have other biological activities which have yet been fully characterised.
Invadopodia are actin-rich protrusions of the plasma membrane that are associated with degradation of the extracellular matrix in cancer invasiveness and metastasis. Very similar to podosomes, invadopodia are found in invasive cancer cells and are important for their ability to invade through the extracellular matrix, especially in cancer cell extravasation. Invadopodia are generally visualized by the holes they create in ECM -coated plates, in combination with immunohistochemistry for the invadopodia localizing proteins such as cortactin, actin, Tks5 etc. Invadopodia can also be used as a marker to quantify the invasiveness of cancer cell lines in vitro using a hyaluronic acid hydrogel assay.
In medicine, desmoplasia is the growth of fibrous connective tissue. It is also called a desmoplastic reaction to emphasize that it is secondary to an insult. Desmoplasia may occur around a neoplasm, causing dense fibrosis around the tumor, or scar tissue (adhesions) within the abdomen after abdominal surgery.
Angiogenesis is the process of forming new blood vessels from existing blood vessels, formed in vasculogenesis. It is a highly complex process involving extensive interplay between cells, soluble factors, and the extracellular matrix (ECM). Angiogenesis is critical during normal physiological development, but it also occurs in adults during inflammation, wound healing, ischemia, and in pathological conditions such as rheumatoid arthritis, hemangioma, and tumor growth. Proteolysis has been indicated as one of the first and most sustained activities involved in the formation of new blood vessels. Numerous proteases including matrix metalloproteinases (MMPs), a disintegrin and metalloproteinase domain (ADAM), a disintegrin and metalloproteinase domain with throbospondin motifs (ADAMTS), and cysteine and serine proteases are involved in angiogenesis. This article focuses on the important and diverse roles that these proteases play in the regulation of angiogenesis.
Metastatic breast cancer, also referred to as metastases, advanced breast cancer, secondary tumors, secondaries or stage IV breast cancer, is a stage of breast cancer where the breast cancer cells have spread to distant sites beyond the axillary lymph nodes. There is no cure for metastatic breast cancer; there is no stage after IV.
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