Tumstatin
Encyclopedia
Tumstatin is a protein fragment cleaved from collagen
that serves as both an antiangiogenic and proapoptotic agent. It has similar function to canstatin, endostatin
, restin, and arresten, which also affect angiogenesis
. Angiogenesis
is the growth of new blood vessels from pre-existing blood vessels, and is important in tumor growth and metastasis. Angiogenesis is stimulated by many growth factors, the most prevalent of which is vascular endothelial growth factor
(VEGF).
, which is cleaved from collagen XVIII. The two proteins share 14% amino acid
homology, making them very similar in structure. It has been proven to inhibit many types of cells, including bovine endothelial cells, HeLa
cells, endothelial cells, and Human umbilical vein endothelial cells (HUVEC) cells.
at the alpha chain on the collagen strand. Tumstatin interacts with the αvβ3 integrin found in the apoptosis
pathway. There are two activation sites on the tumstatin fragment. One is at the N-terminus and is responsible for inhibiting angiogenesis. The other is at the C-terminus end and is primarily responsible for the proapoptotic action. Tumstatin inhibits the activation of FAK (Focal Adhesion Kinase), Phosphoinositide 3-kinase
(PI3-kinase), protein kinase B (PKB/Akt
), and mammalian target of rapamycin (mTOR). In addition to affecting these pathways, it also prevents the dissociation of eukaryotic initiation factor 4E protein (eIF4E) from 4Ebinding protein 1. These pathways are involved in cell proliferation
, so tumstatin reacting with them results in changes in the amount of cell division that occurs.
and the second is to increase the amount of cellular apoptosis
, or programmed cell death. Both of these have implications for cancer. In cancerous tumors, there is always increased angiogenesis as the tumor needs an increased blood supply in order to survive and thrive. Tumors are able to create and sustain their own blood vessel growth, allowing them to grow independently of the surrounding tissue. This is one of The Hallmarks of Cancer
. Another hallmark is the tumor’s ability to avoid apoptosis. Apoptosis is greatly involved in ensuring that damaged cells are not replicated, and this pathway is often avoided in cancerous cells. This means that the tumor cells are able to stay alive and keep proliferating even though they have been damaged. Tumstatin affects both angiogenesis and apoptosis, and treatment using this protein can have positive implications in tumor reduction.
of the tumor and is thus able to affect tumor growth. By affecting the apoptotic pathway, tumstatin inhibits the proliferation of endothelial cells... Tumstatin is a cell-specific inhibitor for protein synthesis and therefore affects angiogenesis, which occurs at the protein synthesis level. It has been shown that the efficacy of tumstatin in reducing angiogenesis in tumors increases with tumor size (tumors larger than 500 mm³).
In addition to limiting the proliferation of endothelial cells, tumstatin also limits angiogenesis in melanoma
cells. The 54-132 amino acid
sequence of the tumstatin fragment binds both endothelial and melanoma cells but only inhibits endothelial cell proliferation which the 185-203 amino acid sequence also binds both and inhibits only melanoma proliferation. This is important in discovering the correct binding sites for different cells types and could help to make cancer therapies more cell-type specific.
One study showed that mice with a genetic deletion of the αvβ3 integrin showed accelerated tumor growth and that when tumstatin was replaced into the system, the tumor growth was disrupted and the tumor shrunk. It has also been shown that tumstatin has antiangiogenic properties in prostate cancer
cells (PCa). PCa was introduced onto a Matrigel and treated with tumstatin, and the formation of new blood vessels as seen in the control did not occur with tumstatin. These studies suggest that tumstatin may be a viable treatment for many types of cancer, including but not limited to melanoma and prostate cancer.
Combination treatments involving tumstatin paired with another cancer-fighting drug could be extremely beneficial. One study combined treatments of tumstatin with bevacizumab
, or Avastin. This was very successful in downregulating the proliferation of renal carcinoma cells in xenografts.
cells.
One study has been done to determine the exact pathway used by tumstatin to induce apoptosis. This revealed that the pathway occurs within the mitochondria. The study used HepG2 human liver carcinoma cells to test this, and found that tumstatin upregulated the expression of Caspase-9
, Fas
, Bax
, Bid
, and p53
while downregulating Bcl-2
. The addition of tumstatin induced the release of cytochrome c
by decreasing the mitochondrial membrane potential. These results show that the proapoptotic activation pathway for tumstatin occurs through mitochondrial regulation, and can aid in determining appropriate cancer treatments.
and apoptosis
has potential to treat other diseases affected by these pathways as well.
as a result of diabetes mellitus
is a result of persistent high blood sugar, and is characterized by a lessened globular filtration rate. The mechanism behind diabetic nephropathy is similar to that of angiogenesis, and for this reason, tumstatin may have implications in treating the disease. It was found that VEGF is one of the mediators of glomerular hypertrophy, which causes nephropathy. Since tumstatin inhibits the binding of VEGF, it inhibits diabetic nephropathy as well as resulting in decreased glomerular hypertrophy and hyperfiltration.
These findings suggest that tumstatin might be used as a treatment for diabetes by regulating the angiogenesis pathways.
, treatment with tumstatin may be beneficial. Type-IV collagen
is present in the basement membrane within normal lungs, and this is reduced in asthmatic patients. There are also increased levels of MMP
in the lungs of asthmatics. Since tumstatin is cleaved by MMP from the collagen in the basement membrane, it has been found that there are much lower levels of tumstatin in the airways of asthmatics than in normal patients. This could account for the increased angiogenesis and hyperresponsiveness of the airways. Increasing the levels of tumstatin in the airways would lead to decreased angiogenesis and therefore eased breathing.
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
that serves as both an antiangiogenic and proapoptotic agent. It has similar function to canstatin, endostatin
Endostatin
]Endostatin is a naturally-occurring 20-kDa C-terminal fragment derived from type XVIII collagen. It is reported to serve as an anti-angiogenic agent, similar to angiostatin and thrombospondin....
, restin, and arresten, which also affect angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
. Angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
is the growth of new blood vessels from pre-existing blood vessels, and is important in tumor growth and metastasis. Angiogenesis is stimulated by many growth factors, the most prevalent of which is vascular endothelial growth factor
Vascular endothelial growth factor
Vascular endothelial growth factor is a signal protein produced by cells that stimulates vasculogenesis and angiogenesis. It is part of the system that restores the oxygen supply to tissues when blood circulation is inadequate....
(VEGF).
Structure and Function
Tumstatin is a 28 kDa fragment cleaved from collagen type IV There are two subsegments of the peptide that are active; T3 peptide and T7 peptide. The structure is very similar to that of endostatinEndostatin
]Endostatin is a naturally-occurring 20-kDa C-terminal fragment derived from type XVIII collagen. It is reported to serve as an anti-angiogenic agent, similar to angiostatin and thrombospondin....
, which is cleaved from collagen XVIII. The two proteins share 14% amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
homology, making them very similar in structure. It has been proven to inhibit many types of cells, including bovine endothelial cells, HeLa
HeLa
A HeLa cell is a cell type in an immortal cell line used in scientific research. It is the oldest and most commonly used human cell line. The line was derived from cervical cancer cells taken on February 8, 1951 from Henrietta Lacks, a patient who eventually died of her cancer on October 4, 1951...
cells, endothelial cells, and Human umbilical vein endothelial cells (HUVEC) cells.
Mechanism of action
The tumstatin fragment is cleaved by matrix metalloproteinase-9 (MMP)Matrix metalloproteinase
Matrix metalloproteinases are zinc-dependent endopeptidases; other family members are adamalysins, serralysins, and astacins. The MMPs belong to a larger family of proteases known as the metzincin superfamily....
at the alpha chain on the collagen strand. Tumstatin interacts with the αvβ3 integrin found in the apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
pathway. There are two activation sites on the tumstatin fragment. One is at the N-terminus and is responsible for inhibiting angiogenesis. The other is at the C-terminus end and is primarily responsible for the proapoptotic action. Tumstatin inhibits the activation of FAK (Focal Adhesion Kinase), Phosphoinositide 3-kinase
Phosphoinositide 3-kinase
Phosphatidylinositol 3-kinases are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which in turn are involved in cancer. In response to lipopolysaccharide, PI3K phosphorylates p65, inducing...
(PI3-kinase), protein kinase B (PKB/Akt
AKT
Akt, also known as Protein Kinase B , is a serine/threonine protein kinase that plays a key role in multiple cellular processes such as glucose metabolism, cell proliferation, apoptosis, transcription and cell migration.-Family members:...
), and mammalian target of rapamycin (mTOR). In addition to affecting these pathways, it also prevents the dissociation of eukaryotic initiation factor 4E protein (eIF4E) from 4Ebinding protein 1. These pathways are involved in cell proliferation
Cell growth
The term cell growth is used in the contexts of cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells"...
, so tumstatin reacting with them results in changes in the amount of cell division that occurs.
Role in cancer
Because tumstatin interacts with the αvβ3 integrin in two separate locations, it has two distinct functions. The first is to inhibit angiogenesisAngiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
and the second is to increase the amount of cellular apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
, or programmed cell death. Both of these have implications for cancer. In cancerous tumors, there is always increased angiogenesis as the tumor needs an increased blood supply in order to survive and thrive. Tumors are able to create and sustain their own blood vessel growth, allowing them to grow independently of the surrounding tissue. This is one of The Hallmarks of Cancer
The Hallmarks of Cancer
"The Hallmarks of Cancer" is a seminal peer-reviewed article published in the journal Cell in January 2000 by US cancer researchers Douglas Hanahan and Robert Weinberg....
. Another hallmark is the tumor’s ability to avoid apoptosis. Apoptosis is greatly involved in ensuring that damaged cells are not replicated, and this pathway is often avoided in cancerous cells. This means that the tumor cells are able to stay alive and keep proliferating even though they have been damaged. Tumstatin affects both angiogenesis and apoptosis, and treatment using this protein can have positive implications in tumor reduction.
Antiangiogenesis actions
Since tumstatin has been shown to reduce angiogenesis in tumors, there is great potential to use this knowledge as treatment for cancer. Tumstatin binds to the endotheliumEndothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...
of the tumor and is thus able to affect tumor growth. By affecting the apoptotic pathway, tumstatin inhibits the proliferation of endothelial cells... Tumstatin is a cell-specific inhibitor for protein synthesis and therefore affects angiogenesis, which occurs at the protein synthesis level. It has been shown that the efficacy of tumstatin in reducing angiogenesis in tumors increases with tumor size (tumors larger than 500 mm³).
In addition to limiting the proliferation of endothelial cells, tumstatin also limits angiogenesis in melanoma
Melanoma
Melanoma is a malignant tumor of melanocytes. Melanocytes are cells that produce the dark pigment, melanin, which is responsible for the color of skin. They predominantly occur in skin, but are also found in other parts of the body, including the bowel and the eye...
cells. The 54-132 amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
sequence of the tumstatin fragment binds both endothelial and melanoma cells but only inhibits endothelial cell proliferation which the 185-203 amino acid sequence also binds both and inhibits only melanoma proliferation. This is important in discovering the correct binding sites for different cells types and could help to make cancer therapies more cell-type specific.
One study showed that mice with a genetic deletion of the αvβ3 integrin showed accelerated tumor growth and that when tumstatin was replaced into the system, the tumor growth was disrupted and the tumor shrunk. It has also been shown that tumstatin has antiangiogenic properties in prostate cancer
Prostate cancer
Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. Most prostate cancers are slow growing; however, there are cases of aggressive prostate cancers. The cancer cells may metastasize from the prostate to other parts of the body, particularly...
cells (PCa). PCa was introduced onto a Matrigel and treated with tumstatin, and the formation of new blood vessels as seen in the control did not occur with tumstatin. These studies suggest that tumstatin may be a viable treatment for many types of cancer, including but not limited to melanoma and prostate cancer.
Combination treatments involving tumstatin paired with another cancer-fighting drug could be extremely beneficial. One study combined treatments of tumstatin with bevacizumab
Bevacizumab
Bevacizumab is a drug that blocks angiogenesis, the growth of new blood vessels. It is commonly used to treat various cancers, including colorectal, lung, breast, kidney, and glioblastomas....
, or Avastin. This was very successful in downregulating the proliferation of renal carcinoma cells in xenografts.
Proapoptotic actions
The second mechanism of action for tumstatin in combating cancer cells is to induce apoptosis. Apoptosis is induced through the same receptor as the antiangiogenic receptor, αvβ3.. It has been shown to increase apoptosis in HUVEC cells as well as HeLaHeLa
A HeLa cell is a cell type in an immortal cell line used in scientific research. It is the oldest and most commonly used human cell line. The line was derived from cervical cancer cells taken on February 8, 1951 from Henrietta Lacks, a patient who eventually died of her cancer on October 4, 1951...
cells.
One study has been done to determine the exact pathway used by tumstatin to induce apoptosis. This revealed that the pathway occurs within the mitochondria. The study used HepG2 human liver carcinoma cells to test this, and found that tumstatin upregulated the expression of Caspase-9
Caspase-9
Caspase-9 is an initiator caspase, encoded by the CASP9 gene.CASP9 orthologs have been identified in all mammals for which complete genome data are available. Unique orthologs are also present in lizards, lissamphibians, and teleosts....
, Fas
Fas receptor
The FAS receptor also known as apoptosis antigen 1 , cluster of differentiation 95 or tumor necrosis factor receptor superfamily member 6 is a protein that in humans is encoded by the TNFRSF6 gene....
, Bax
Bcl-2-associated X protein
The Bcl-2–associated X protein, or Bax is a protein of the Bcl-2 gene family. It promotes apoptosis by competing with Bcl-2 proper.The BAX gene was the first identified pro-apoptotic member of the Bcl-2 protein family....
, Bid
BH3 interacting domain death agonist
The BH3 interacting-domain death agonist, or BID, gene is a pro-apoptotic member of the Bcl-2 protein family. Bcl-2 family members share one or more of the four characteristic domains of homology entitled the Bcl-2 homology domains , and can form hetero- or homodimers...
, and p53
P53
p53 , is a tumor suppressor protein that in humans is encoded by the TP53 gene. p53 is crucial in multicellular organisms, where it regulates the cell cycle and, thus, functions as a tumor suppressor that is involved in preventing cancer...
while downregulating Bcl-2
Bcl-2
Bcl-2 is the founding member of the Bcl-2 family of apoptosis regulator proteins encoded by the BCL2 gene. Bcl-2 derives its name from B-cell lymphoma 2, as it is the second member of a range of proteins initially described in chromosomal translocations involving chromosomes 14 and 18 in...
. The addition of tumstatin induced the release of cytochrome c
Cytochrome c
The Cytochrome complex, or cyt c is a small heme protein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins. Cytochrome c is a highly soluble protein, unlike other cytochromes, with a solubility of about 100 g/L and is an...
by decreasing the mitochondrial membrane potential. These results show that the proapoptotic activation pathway for tumstatin occurs through mitochondrial regulation, and can aid in determining appropriate cancer treatments.
Role in other diseases
Since the mechanisms of both of these pathways are not unique to cancer, tumstatin’s regulation of angiogenesisAngiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
and apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
has potential to treat other diseases affected by these pathways as well.
Diabetes
Diabetic nephropathyDiabetic nephropathy
Diabetic nephropathy , also known as Kimmelstiel-Wilson syndrome, or nodular diabetic glomerulosclerosis and intercapillary glomerulonephritis, is a progressive kidney disease caused by angiopathy of capillaries in the kidney glomeruli. It is characterized by nephrotic syndrome and diffuse...
as a result of diabetes mellitus
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
is a result of persistent high blood sugar, and is characterized by a lessened globular filtration rate. The mechanism behind diabetic nephropathy is similar to that of angiogenesis, and for this reason, tumstatin may have implications in treating the disease. It was found that VEGF is one of the mediators of glomerular hypertrophy, which causes nephropathy. Since tumstatin inhibits the binding of VEGF, it inhibits diabetic nephropathy as well as resulting in decreased glomerular hypertrophy and hyperfiltration.
These findings suggest that tumstatin might be used as a treatment for diabetes by regulating the angiogenesis pathways.
Asthma
In patients with asthmaAsthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, treatment with tumstatin may be beneficial. Type-IV collagen
Type-IV collagen
Type-IV collagen is a type of collagen found primarily in the basal lamina. The type IV collagen C4 domain at the C-terminus is not removed in post-translational processing, and the fibers link head-to-head, rather than in parallel. Also, type-IV lacks the regular glycine in every third residue...
is present in the basement membrane within normal lungs, and this is reduced in asthmatic patients. There are also increased levels of MMP
Matrix metalloproteinase
Matrix metalloproteinases are zinc-dependent endopeptidases; other family members are adamalysins, serralysins, and astacins. The MMPs belong to a larger family of proteases known as the metzincin superfamily....
in the lungs of asthmatics. Since tumstatin is cleaved by MMP from the collagen in the basement membrane, it has been found that there are much lower levels of tumstatin in the airways of asthmatics than in normal patients. This could account for the increased angiogenesis and hyperresponsiveness of the airways. Increasing the levels of tumstatin in the airways would lead to decreased angiogenesis and therefore eased breathing.