1. VEGF family proteins
Vascular Endothelial Growth Factor (VEGF) is a key factor in the formation of new blood vessels. VEGF can induce the regeneration of existing blood vessels (angiogenesis) or the formation of new blood vessels (angiogenesis), and is therefore key to embryonic development and vascular repair. VEGF can also be used by solid tumors to promote their growth. VEGF plays a critical role in tumorigenesis and progression, making it a key target for cancer treatments. Studies have shown that single nucleotide polymorphisms (SNPs) in the VEGF gene are predictive and prognostic markers for major solid tumors, including breast cancer, non-small cell lung cancer, colorectal cancer, and prostate cancer. VEGF family proteins include VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E, VEGF-F, PIGF, and EG-VEGF. VEGF-A is by far the most effective angiogenesis inducer, while VEGF-E is more targeted to induce localized lesions of angiogenesis.
2. VEGF family protein receptors
VEGF mainly regulates angiogenesis and activates intracellular signaling pathways by binding to its receptors (VEGFR1, VEGFR2 and VEGFR3); after VEGFR and VEGF proteins bind, the tyrosine in their intracellular signal transduction regions is phosphorylated, thereby activating intracellular signaling pathways, ultimately leading to the growth, proliferation and maturation of vascular endothelial cells and the formation of new blood vessels.
Figure 1. Different members of the VEGF family bind to different types of VEGF receptors [1]
The biological activity of the VEGF family is mediated by binding to two types of receptors: receptors with tyrosine kinase activity and receptors without tyrosine kinase activity. The first type of receptor consists of three structurally related receptors, characterized by the presence of seven immunoglobulin like domains in the extracellular domain, one transmembrane region, and an intracellular consensus tyrosine kinase sequence interrupted by a kinase insertion domain. On the other hand, receptors without kinase activity are neurofilament protein-1 (NRP-1) and neurofilament protein-2 (NRP-2), which are also receptors for signaling proteins.
2.1 Tyrosine kinase receptor
Tyrosine kinase receptors (VEGFRs) are divided into VEGFR-1, VEGFR-2, and VEGFR-3. They function in the form of dimers. When VEGF binds to tyrosine kinase receptors, the conformation of the intracellular kinase region changes, producing kinase activity to catalyze substrate protein phosphorylation, ultimately leading to a series of biological effects through cascade reactions of signaling molecules. The binding strength between VEGF and VEGFR-1 is 10 times stronger than that of VEGFR-2, but R1 activity is weaker and is considered to have a negative regulatory function on VEGFR-2. Therefore, VEGFR-2 is the main receptor that produces physiological effects. VEGFR-1 and VEGFR-2 are mainly distributed on the surface of tumor vascular endothelium, regulating tumor angiogenesis, and are also overexpressed in macrophages and tumor cells; VEGFR-3 is mainly distributed on the surface of lymphatic endothelium, regulating the generation of tumor lymphatic vessels. In addition, the VEGFR family can bind not only to VEGF protein but also to other proteins such as neurotrophins, integrins, and cadherin.
2.2 Neurociliary protein receptor
Neuropilins (NRPs) are divided into NRP-1 and NRP-2. NRPs are single transmembrane glycoproteins that contain three extracellular domains. Domain B is the VEGF binding region, and domain A promotes the binding of domain B to VEGF. Domain C binds to VEGFR-2 to form a heteropolymer. NRPs have no tyrosine kinase activity and mainly assist in the binding of VEGF and VEGFR-2. NRP-1 mainly participates in the regulation of arterial endothelial function, while NRP-2 mainly participates in the regulation of venous and lymphatic endothelial function.
3. The function of VEGF family proteins
VEGFs are highly specific vascular endothelial growth factors that play important physiological functions in angiogenesis, maintenance, and generation. They can induce endothelial cell survival, proliferation, migration, vascular proliferation, and increase vascular permeability.
3.1. The functions of different subtypes of VEGF
VEGF-A can be divided into VEGF121、VEGF145、VEGF165、VEGF183、VEGF189和VEGF206. Currently, VEGF-A is the most effective vascular growth inducing factor to date. VEGF165 and VEGF121 can be expressed in most tissues, while VEGF206 is almost not expressed in normal tissues. VEGF-A is a glycosylated mitogen that specifically acts on endothelial cells and has multiple functions, including mediating increased vascular permeability, inducing angiogenesis, angiogenesis and endothelial cell growth, promoting cell migration, and inhibiting cell apoptosis. VEGF-A mediates the growth of new blood vessels from existing ones (angiogenesis) by binding to cell surface receptors VEGFR1 and VEGFR2. These two receptors act through different pathways, promoting endothelial cell proliferation and migration, as well as the formation of tubular structures.
VEGF-B is expressed in most tissues, especially in the heart, skeletal muscle, and pancreas. VEGF-B binds to VEGF receptor 1 (VEGF R1), but not to VEGF R2 or VEGF R3. The connection between VEGF-B and VEGF R1 on endothelial cells has been shown to regulate the expression and activity of urokinase type plasminogen activator and plasminogen activator inhibitor 1. The hydrolyzed form of VEGF-B protein also binds to neuroplasmin-1 (NP-1), which is a ligand involved in neuronal guidance. Besides VEGF-B, NP-1 has been shown to bind to PLGF-2, VEGF165, and VEGF R1. VEGF-B plays an important role in several types of neurons. It is very important for protecting retinal and cortical neurons during stroke, as well as motor neurons during motor neuron diseases such as amyotrophic lateral sclerosis.
The main function of VEGF-C is lymphangiogenesis, which mainly acts on lymphatic endothelial cells through its receptor VEGFR-3, promoting their survival, growth, and migration. It is a specific growth factor for lymphatic vessels in various models. VEGF-C also induces physiological and tumor angiogenesis and angiogenesis through interaction with VEGF R2.
VEGF-D is a secreted glycoprotein of the VEGF/PDGF family. VEGF regulates angiogenesis and lymphangiogenesis during development and tumor growth, which is characterized by the formation of cystine node structure by eight conserved cysteine residues. The amino acid (aa) sequence identity between VEGF-C and VEGF-D is 23%. Mouse and human VEGF-D are ligands for VEGFR3, which are active between species and exhibit enhanced affinity during processing. The processed human VEGF-D protein is also a ligand for VEGF R2. VEGF R3 is strongly expressed in lymphatic endothelial cells and is crucial for regulating the growth and differentiation of lymphatic endothelial cells. Both VEGF-C and VEGF-D promote tumor lymphangiogenesis. Consistent with their activity on VEGF receptors, the binding of VEGF-C and VEGF-D to neuropiliproteins contributes to VEGF R3 signaling in lymphangiogenesis. It has been confirmed that VEGF-D is overexpressed in tumor tissues and patient serum samples of several human cancers.
PGF (placental growth factor) and PlGF bind and signal through VEGF R1/Flt-1 instead of VEGF R2/Flk-1/KDR, while VEGF binds to VEGF R1/Flt-1 but only signals through the angiogenic receptor VEGF R2. Therefore, PlGF and VEGF compete for binding to VEGF R1, and high PlGF can prevent VEGF/VEGF R1 binding and promote VEGF/VEGF R2 mediated angiogenesis. However, PlGF (especially PlGF-1) and certain forms of VEGF can form dimers, thereby reducing the angiogenic effect of VEGF on VEGF R2. PlGF induces monocyte activation, migration, and production of inflammatory cytokines and VEGF. These activities promote wound, fracture and heart repair, but also lead to inflammation in active sickle cell disease and atherosclerosis. PGF plays a role in the growth and differentiation of trophoblast cells. Trophoblast cells, especially extra trophoblast cells, are responsible for invading the maternal artery. The normal development of placental blood vessels is crucial for the normal development of embryos. Under normal physiological conditions, PGF is also expressed at low levels in other organs such as the heart, lungs, thyroid, and skeletal muscles.
EG-VEGF，Endocrine gland derived vascular endothelial growth factor, also known as motor protein 1 (PK1), is a member of the motor protein family, which secretes proteins with a common structural motif containing ten conserved cysteine residues that can form five pairs of disulfide bonds. EG-VVEGF has been proven to effectively stimulate smooth muscle contraction in the gastrointestinal tract. In addition, EG-VVEGF is a tissue-specific angiogenic factor that exhibits biological activity similar to VEGF on specific cells. EG-VVEGF induces proliferation and migration of endothelial cells derived from endocrine glands in culture. EG-VGF binds to and activates two closely related G protein coupled receptors, namely EG-VGF/PK1-R1 and EG-VGF/PK2-R2. The activation of receptors stimulates phosphoinositol turnover and activates the p44/p42 MAP kinase signaling pathway.
3.2 The expression sites of different subtypes of VEGF
Table 1. Locations of VEGF expression in different subtypes
|
Subtypes of VEGF family proteins |
Expression site |
|
VEGF-A |
All vascularized tissues |
|
VEGF-B |
Early embryo, heart, skeletal muscle, vascular smooth muscle, pancreas and other tissues |
|
VEGF-C |
Early embryos, heart, kidney, lung, and vascular smooth muscle cells, etc |
|
VEGF-D |
Early embryos, heart, lungs, skeletal muscles, small intestine, and vascular smooth muscle cells, etc |
|
VEGF-E |
virus |
|
VEGF-F |
snake venom |
|
PIGF |
Placenta and other tissues |
|
EG-VEGF |
Endocrine gland sources (placenta, testes, ovaries, adrenal glands, and other tissues) |
3.3 The role of VEGF in diseases
VEGF and Cancer
At present, there are clear research results on the role of VEGF in promoting tumor angiogenesis and its relationship with the pathogenesis of human cancer.
High expression of VEGF and its mRNA can be observed in most malignant tumors, especially in areas with abundant vascular proliferation in tumor tissue. VEGF secreted by tumor cells and surrounding matrix stimulates endothelial cell proliferation and survival, leading to the formation of new blood vessels. New blood vessels may have structural abnormalities and leakage, and are associated with invasiveness, vascular density, metastasis, recurrence, and prognosis. Therefore, targeting VEGF is a potential approach for cancer treatment;
VEGF is also a broad-spectrum tumor biomarker that can cover almost all tumors, including non solid tumors such as leukemia. Due to its involvement in bone marrow hematopoietic mechanisms, the disease itself promotes the production of VEGF, and changes in VEGF concentration have reference value for clinical diagnosis. This is not possible with other tumor markers. VEGF begins to be produced in large quantities during the transformation of tumor cell clusters into solid tumors, often in the tumor Tis and T1 phases. This is the optimal period for tumor screening and can be diagnosed through existing clinical methods. However, other tumor markers are mostly produced in stages III and IV of the tumor, and have little significance for early screening.
VEGF and ophthalmic diseases
Many neovascular eye diseases in clinical practice are caused by overexpression of VEGF in the eye, which leads to the growth of new blood vessels, resulting in severe complications such as massive bleeding, fiber proliferation, tractional retinal detachment, and neovascular glaucoma. Competitive inhibition of VEGF-R2 can effectively inhibit angiogenesis and promote the regression of existing neovascularization, alleviate exudation, edema, and inflammatory reactions caused by vascular leakage, thereby slowing down the progression of retinal neovascularization. In ophthalmology, the use of VEGF inhibiting drugs can effectively block the growth of diseased neovascularization, thereby treating ophthalmic diseases.
In addition, the VEGF family is also associated with lymphangiogenesis, inflammatory response, hematopoietic function, and neuroprotective effects.
4. How to choose VEGF family proteins correctly?
4.1. Recombinant human VEGF165 and recombinant human VEGF121
Human VEGF165 and Human VEGF121 are the most abundantly expressed subtypes of VEGF-A. VEGF165 is a potent angiogenic factor that can stimulate endothelial cell proliferation, survival, promote angiogenesis, and increase vascular permeability. VEGF121 and VEGF165 have similar functions, but the difference is that VEGF121 does not bind to cell surface heparan sulfate glycoproteins (HSPGs) and mainly exists in its soluble form. And VEGF165 has the ability to bind to NRP-1 and NRP-2, so VEGF165 can also play a role in regulating angiogenesis, regulating the function of endothelial cells in veins and lymphatic vessels. Both VEGF165 and VEGF121 can stimulate endothelial cell proliferation and promote increased vascular endothelial cell permeability. However, after binding to receptors, VEGF165 primarily activates the MEK and ERK pathways to promote endothelial cell proliferation, while VEGF121 has a much stronger effect on vascular permeability than VEGF165.
4.2. The difference between recombinant human VEGF-C and recombinant human VEGF-D
VEGF-D functions similarly to VEGF-C, regulating angiogenesis and lymphangiogenesis during development and tumor growth. The amino acid (aa) sequence identity between VEGF-C and VEGF-D is 23%. Although VEGF-C is a key ligand for VEGF R3 during embryonic lymphatic development, VEGF-D is most plays a crucial role in the maturation of lymphatic vessels during neonatal development and bone growth. Both promote tumor lymphangiogenesis. Their activity on VEGF receptors is consistent. The binding of VEGF-C and VEGF-D to neuropiliproteins facilitates VEGF R3 signaling in lymphangiogenesis, while the binding to integrin α 9 β 1 mediates endothelial cell adhesion and migration. Overexpression of VEGF-C in tumor cells can induce tumor lymphangiogenesis, leading to increased lymphatic flow and metastasis to regional lymph nodes. It also induces physiological and intratumoral neovascularization and angiogenesis by interacting with VEGFR2.
Table 2. Differences in VEGF Family Protein Subtypes
|
Product Name |
Cat |
Receptor |
Role |
|
Human VEGF165 |
VEGFR-1、VEGFR-2、NRP-1、NRP-2、HSPGs |
Stimulate endothelial cell proliferation (priority), survival, promote angiogenesis, and increase vascular permeability. |
|
|
Human VEGF121 |
VEGFR-1、VEGFR-2 |
Stimulate endothelial cell proliferation, survival, promote angiogenesis, and increase vascular permeability (priority). |
|
|
Human VEGF-C |
VEGFR-2、VEGFR-3 NRP-1、NRP-2 |
Inducing lymphatic vessel formation, associated with tumor metastasis |
|
|
Human VEGF-D |
VEGFR-2、VEGFR-3、 NRP-2 |
Inducing lymphatic vessel formation, associated with tumor metastasis |
|
|
Human EG-VEGF |
PROKR1 |
Promote the proliferation and migration of endocrine gland endothelial cells. |
5. References
[1]. Silvia Silva-Hucha,Angel M. Pastor,Sara Morcuende.Neuroprotective Effect of Vascular Endothelial Growth Factor on Motoneurons of the Oculomotor System.Int. J. Mol. Sci. 2021, 22(2), 814.
6. Related products
|
Product Name |
Cat |
Specifications |
|
Human VEGF165 |
10μg/100μg/500μg |
|
|
Human VEGF121 |
10μg/100μg/500μg |
|
|
Human VEGF-C |
25μg/100μg/500μg |
|
|
Human VEGF-D |
25μg/100μg/500μg |
|
|
Human EG-VEGF |
5μg/100μg/500μg |
|
|
Human VEGFR2/KDR ,mFc Tag |
25μg/100μg/500μg |
|
|
Human VEGFR2/KDR Protein, His tag |
25μg/100μg/500μg |