| TRPV2 | |||||||||||||||||||||||||||||||||||||||||||||||||||
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| Aliases | TRPV2, VRL, VRL-1, VRL1, transient receptor potential cation channel subfamily V member 2 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| External IDs | OMIM:606676;MGI:1341836;HomoloGene:7993;GeneCards:TRPV2;OMA:TRPV2 - orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Transient receptor potential cation channel subfamily V member 2 is aprotein that in humans is encoded by theTRPV2gene.[5][6] TRPV2 is a nonspecific cation channel that is a part of the TRP channel family. This channel allows the cell to communicate with its extracellular environment through the transfer of ions, and responds to noxious temperatures greater than 52 °C. It has a structure similar to that ofpotassium channels, and has similar functions throughout multiple species; recent research has also shown multiple interactions in the human body.
The vanilloid TRP subfamily (TRPV) named after the vanilloid receptor 1 consist of six members, four of them (TRPV1-TRPV4) have been related to thermal sensation. TRPV2 shares 50% of its homology with TRPV1. Compared to TRPV1 channels, TRPV2 channels do not open in response to vanilloids likecapsaicin or thermal stimuli around 43 °C.[7] This may be due to the composition of the ankyrin repeat domains in TRPV2, which are different than those in TRPV1. However, TRPV2 channels can open by noxious temperatures greater than 52 °C.[7] TRPV2 initially was characterized as a noxious heat sensor channel, but more evidence suggest its importance in various osmosensory and mechanosensory mechanisms. The channel can open in response to a variety of stimuli includinghormones,growth factors, mechanical stretching,heat, osmotic swelling, lysophospholipids, andcannabinoids. These channels are expressed in medium to large diameter neurons,motor neurons, and other non-neuronal tissues like theheart andlungs, which indicates its versatile function. The channel has an important role for basic cell function including contraction,cell proliferation, andcell death. The same channel can have different functions depending on the type of tissue. Other roles of TRPV2 continue to be explored in an attempt to define the role of translocation of TRPV2 by growth factors.SET2 is a TRPV2 selective antagonist.[8]
TRPV2 was independently discovered by two research groups and described in 1999. It was identified in the lab ofDavid Julius as a close homolog of TRPV1, known as the first identified thermosensitive ion channel.[5] Itaru Kojima from Gunma University was looking for a protein which is responsible for the entry of calcium into cells in response toinsulin-like growth factor-1 (IGF-1). Upon stimulation of cells with IGF-1, it was discovered that TRPV2 translocates towards and integrates into the cell membrane and increases intracellular calcium concentrations.
TRPV2 channel has a similar structure topotassium channels, which are the largestion channel family. This channel is composed of six transmembrane spanning regions (S1-S6) with a pore forming loop between S5 and S6.[9] The pore forming loop also defines the selectivity filter, which determines the ions that are able to enter the channel. The S1-S4 region, as well as the N and C terminals of the protein, is important in reference to the gating of the channel. Although TRPV2 is a nonspecific cation channel, it is more permeable to calcium ions; calcium is an intracellular messenger and plays a very important role in a variety of different cellular processes. At rest, the pore channel is closed; in the activated state, the channel opens, allowing the influx of sodium and calcium ions that initiates anaction potential.
The TRPV subfamily of channels of 1 through 4 have unique functions. One important variation is that these channels trigger cellular signaling pathways via non-selective cation flux, making them unique. Specifically, the TRPV2 channel has structural similarities amongst the other members of the TRPV family. For instance, the channel consists of sixtransmembrane domains and a pore forming loop between S5 and S6.[9] Within the human genome, putative homologs can be found. This suggests that theamino acids andproteins coded come from a common ancestor where their structures are conserved in function.
Among the subfamily, TRPV2 and TRPV1 share 50% of their sequence identity not only in humans, but in rats as well. The rat TRPV2 can be comparable to that of humans because they exhibit similar surface localization among one another. Each channel possessesATP binding regions and the 50% sequence identity between TRPV1 and TRPV2 suggests that both channel'sAnkyrin repeat domain (ARD) bind to different regulatory ligands as well.[9] The channels structure can be observed as similar to that ofpotassium channels. In knockout mice, the physiological thermal responses show similar activation to wild-type mice. On top of that, humans, rats, and mice are consideredorthologues.
Inhomo sapiens, there is broad expression of TRPV2 in thelymph nodes,spleen,lung,appendix, andplacenta; it is mostly expressed in the lungs.[10] TRPV2 is majorly in a sub population of medium to largesensory neurons, as well as being distributed in thebrain andspinal cord.[11] The mRNA expression of TRPV2 is also found in human pulmonary and umbilical veinendothelial cells.[11] Based onmRNA expression of TRPV2 in mice, it is also speculated that it is expressed in arterial muscle cells, which can then be influenced by blood pressure; though it was evident that TRPV2 expression was localized in the intracellular area, some growth factors localized it to the plasmacell membrane.[11] In circulatory organs, studies and data suggest that TRPV2 may be a mechanosensor, meaning that it can sense changes in external stimuli; the mechanisms involved in opening TRPV2 by membrane stretching or hypoosmotic cell swelling have not yet been determined.[11]
Inmus musculus (house mouse), TRPV2 functions as a protein coding gene. There is broad expression of TRPV2 in thethymus,placenta,cerebellum, andspleen; it is most commonly expressed in the thymus.[12] Thethymus is a lymphoid organ involved in the function of the immune system, whereT cells mature. T cells are an important component to the adaptive immune system, because it is where the body adapts to foreign substances; this demonstrates TRPV2's importance in the immune system. TRPV2 in mus musculus is also activated by hypo-osmolarity and cell stretching, indicating that TRPV2 plays a role inmechanotransduction in mice as well.[12] In experiments with knockout mice (TRPV2KO mice), it was found that TRPV2 is expressed in brownadipocytes and inbrown adipose tissue (BAT). It can be concluded that TRPV2 plays a role in BATthermogenesis in mice, since it was found that a lack of TRPV2 impairs this thermogenesis in BAT; given these results, this could be a target for human obesity therapy.[13]
Inrattus norvegicus (Norway rat), there is broad expression of TRPV2 in theadrenal glands and the lungs, being most present in the adrenal glands. TRPV2 is also present in thethymus andspleen, but not in high amounts. Without using any external growth factors, TRPV2 is highly specific to the plasmacell membrane in rat adult dorsal root ganglions,cerebral cortex, and arterial muscle cells.[11]
TRPV2 plays a role in negative homeostatic control of excess cell proliferation by inducingapoptosis (programmed cell death).[9] This is accomplished predominantly through theFas pathway, also known as the death-inducing signaling complex. Activation of TRPV2 by growth factors and hormones induces the receptor to translocate from intracellular compartments to the plasma membrane, which initiates the development of death signals.[14] An example of the role of TRPV2 in apoptosis is its expression in the bladder cancer t24 cell line. TRPV2 in bladder cancer leads to apoptosis through the influx of calcium ions through the TPRV2 channel. In some tumors, the over-expression of TRPV2 can lead to abnormal signaling pathways that drives unchecked cell proliferation and resistance to apoptotic stimuli. The over-expression of TRPV2 has been linked to several cancer types and cell lines.[15][16] TRPV2 is expressed in humanHepG2 cells, a cell line containing human liver carcinogenic cells. Heat allows for calcium entry into these cells through TRPV2 channels, which aid in the maintenance of these cells.[17] TRPV2 also negatively affects patients withgliomas. TRPV2 in carcinogenicglial cells leads to resistance toapoptotic cell death, leading to harmful, carcinogenic cell survival.[18]
TRPV2 is expressed in the spleen,lymphocytes, andmyeloid cells includinggranulocytes,macrophages andmast cells. Among these cell types, TRPV2 mediates cytokine release,phagocytosis,endocytosis,podosome assembly, and inflammation.[19] The influx of calcium seems to play an important role in these functions.Mast cells areleukocytes (white blood cells) rich in histamine which are able to respond to a variety of stimuli, often initiating inflammatory and/or allergic responses. The responses generated by mast cells rely on the calcium influx in the plasma membrane with the help of channels. Surface localization of the TRPV2 protein along with coupling of the protein to calcium and proinflammatorydegranulation have been found in mast cells. The activation of TRPV2 in high temperatures permits calcium ion influx, inducing the release of proinflammatory factors. Therefore, TRPV2 is essential in mast cell degranulation as a result of its response to heat.[20]Immune cells are also able to kill pathogens by binding to them and engulfing them in a process known asphagocytosis. In macrophages TRPV2 recruitment toward the phagosome is regulated byPI3k signaling,protein kinase C, akt kinase, andSrc kinases.[9] They are able to locate these microbes throughchemotaxis which is TRPV2 mediated. When the pathogen is endocytosed it is degraded then presented on the membrane of antigen presenting cells (i.e. macrophages). Macrophages present these antigens to T cells via amajor histocompatibility complex (MHC). The region between the MHC-peptide and the T cell receptor is known as theimmunosynapse. TRPV2 channels are highly concentrated in this region. When these two cells interact, it allows calcium to diffuse through the TRPV2 channel. TRPV2mRNA has been detected inCD4+ andCD8+ T cells as well as in human B lymphocytes. TRPV2 is one type of ion channel that directs T cell activation, proliferation, and defense mechanisms. If the TRPV2 channel were absent or not functioning properly in T cells, T cell receptor signaling would not be optimal. TRPV2 also acts as a transmembrane protein on the surface of B cells, negatively controlling B cell activation.[20] Abnormal TRPV2 expression has been reported inhematological diseases includingmultiple myeloma,myelodysplastic syndrome,Burkitt lymphoma, andacute myeloid leukemia.[19]
TRPV2 seems to be essential in glucosehomeostasis. It is highly expressed in MIN6 cells, which is aβ-cell. These cell types are known for releasinginsulin, a molecule that functions to keep glucose levels low. Under unstimulated conditions, TRPV2 is localized in thecytoplasm. Activation causes the channel to translocate to theplasma membrane. This triggers the influx ofcalcium resulting in insulin secretion.[7]
TRPV2 is very important in the structure and function ofcardiomyocytes (heart cells). Compared to skeletal muscles, TRPV2 is expressed 10 times as high in cardiomyocytes[21] and is important in current conduction. TRPV2 has been shown to be involved in stretch-dependent responses in heart cells. TRPV2 expression is concentrated inintercalated discs which allows the synchronous contraction of cardiomyocytes. Abnormal expression of TRPV2 results in reduced shortening length, shortening rate, and lengthening rate which ultimately compromise cardiac contractile function.
Agonists include:[22]
This article incorporates text from theUnited States National Library of Medicine, which is in thepublic domain.
