NFAT5
Encyclopedia
Nuclear factor of activated T-cells 5, also known as NFAT5, is a human gene
that encodes a transcription factor
that regulates the expression of genes involved in the osmotic stress.
The product of this gene is a member of the nuclear factors of activated T cell
s (NFAT
) family of transcription factor
s. Proteins belonging to this family play a central role in inducible gene transcription during the immune response. This protein regulates gene expression induced by osmotic stress
in mammalian cells. Unlike monomeric members of this protein family, this protein exists as a homodimer and forms stable dimers with DNA elements. Multiple transcript variants encoding different isoforms have been found for this gene.
s, which are less toxic than excess ions but which also aid in water retention. Under conditions of hyperosmolarity, NFAT5 is synthesized and accumulates in the nucleus. NFAT5 stimulates the transcription of genes for aldose reductase
(AR), the sodium chloride-betaine cotransporter (SLC6A12) the sodium/myo-inositol cotransporter (SLC5A3
), the taurine transporter (SLC6A6
) and neuropathy target esterase
which are involved in the production and uptake of organic osmolytes. Additionally, NFAT5 induces heat shock proteins, Hsp70
, and osmotic stress proteins. NFAT5 is also implicated in cytokine production.
It has been shown that when NFAT5 is inhibited in renal and immune cells, these cells become significantly more susceptible to osmotic stress. NFAT5 deficient mice were found to suffer from massive cell loss in the renal medulla. Additionally, mice expressing a dominant-negative form of NFAT5 in their eyes exhibited decreased viability under hypertonic extracellular environment.
family consists of five different forms: NFAT1, NFAT2, NFAT3, NFAT4, and NFAT5 (this protein). The proteins in this family are expressed in nearly every tissue in the body and are known transcriptional regulators in cytokine
and immune cell expression. Among the different forms of NFAT, NFAT5 is an important component of the hyperosmolar stress response system.
cDNA of NFAT5 was first isolated from a human brain cDNA library. Subsequent analysis revealed that NFAT5 is a member of the Rel family, which also consists of NF-κB and NFATc
proteins. The largest Rel protein, it consists of nearly 1,500 amino acid residues. Like the other Rel proteins, NFAT5 contains the Rel homology domain
, a conserved DNA-binding domain
. Outside of the Rel homology domain
, no similarities exist between NFAT5 and NF-κB or NFATc. Among these differences is the absence of docking sites for calcineurin, which is necessary for NFATc nuclear import. Instead, NFAT5 is a constitutively nuclear protein whose activity and localization does not depend on calcineurin-mediated dephosphorylation. Increased NFAT5 transcription is correlated with p38 MAPK
-mediated phosphorylation.
, a guanine nucleotide exchange factor (GEF
) localized near the plasma membrane, is activated by osmotic stress through changes in the cytoskeleton structure. Alternatively, Brx may also be activated through changes in its interactions with possible osmosensor molecules at the cell membrane. Upon Brx activation, the GEF domain of Brx facilitates activation of Rho-type small G proteins
from its inactive GDP
state to active GTP
state. Additionally, activated Brx also recruits and physically interacts with JIP4, a p38 MAPK
-specific scaffold protein. JIP4 binds to downstream kinases, MKK3
and MKK6
. This complex then activates p38 mitogen-activated protein kinase (MAPK). Activation of p38 MAPK is regulated by Cdc42
and Rac1
. Activation of p38 MAPK is a necessary step for NFAT5 expression.
It has been found that NFAT5 expression, following hyperosmolarity, depends on p38 mitogen-activated protein kinase (MAPK). The addition of a p38 MAPK inhibitor was found to correlate with decreased NFAT5 expression, even in the presence of osmotic stress signals. However, the downstream transcription of the NFAT5 gene by p38 MAPK is currently not yet characterized. It is hypothesized that p38 MAPK phosphorylation activates c-Fos
and interferon regulatory factors (IRFs
), which bind to AP-1-binding sites and ISRES (Interferon Stimulated Response Element) respectively. Binding to these sites consequently activates the transcription of target genes.
Although the Brx-mediated activation of NFAT5 has only been examined in lymphocyte response to osmotic stress, it is hypothesized that this mechanism is a common one in other cell types.
Additionally, NFAT5 plays a role in integrin-induced cell migration. Cancer cells that undergo metastasis often express NFAT5. Inhibition of NFAT5 in these migrating cells was found to deter cell migration, while overexpression of NFAT5 enhanced movement.
NFAT5 is also involved in cellular proliferation. NFAT5 mRNA expression is particularly high in proliferating cells. Inhibition of NFAT5 in embryonic fibroblasts resulted in cell cycle arrest
.
Although NFAT5 has been found to be important in other biological processes besides hyperosmotic stress response, the mechanism by which NFAT5 acts in these other processes are currently not well known.
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
that encodes a transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
that regulates the expression of genes involved in the osmotic stress.
The product of this gene is a member of the nuclear factors of activated T cell
T cell
T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...
s (NFAT
NFAT
Nuclear factor of activated T-cells is a general name applied to a family of transcription factors shown to be important in immune response. One or more members of the NFAT family is expressed in most cells of the immune system...
) family of transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
s. Proteins belonging to this family play a central role in inducible gene transcription during the immune response. This protein regulates gene expression induced by osmotic stress
Osmotic shock
Osmotic shock or osmotic stress is a sudden change in the solute concentration around a cell, causing a rapid change in the movement of water across its cell membrane. Under conditions of high concentrations of either salts, substrates or any solute in the supernatant, water is drawn out of the...
in mammalian cells. Unlike monomeric members of this protein family, this protein exists as a homodimer and forms stable dimers with DNA elements. Multiple transcript variants encoding different isoforms have been found for this gene.
Osmotic stress
Tissues that comprise the kidneys, skin, and eyes are often subjected to osmotic stresses. When the extracellular environment is hypertonic, cells lose water and consequently, shrink. To counteract this, cells increase their sodium uptake in order to lose less water. However, an increase in intracellular ionic concentration is harmful to the cell. Cells can alternatively synthesize enzymes and transporters that increase intracellular concentration of organic osmolyteOsmolyte
Osmolytes are compounds affecting osmosis. They are soluble in the solution within a cell, or in the surrounding fluid, e.g. as plasma osmolytes. They play a role in maintaining cell volume and fluid balance. For example, when a cell swells due to external osmotic pressure, membrane channels open...
s, which are less toxic than excess ions but which also aid in water retention. Under conditions of hyperosmolarity, NFAT5 is synthesized and accumulates in the nucleus. NFAT5 stimulates the transcription of genes for aldose reductase
Aldose reductase
Aldose reductase is an NADPH-dependent oxidoreductase that catalyzes the reduction of a variety of aldehydes and carbonyls, including monosaccharides...
(AR), the sodium chloride-betaine cotransporter (SLC6A12) the sodium/myo-inositol cotransporter (SLC5A3
SLC5A3
Sodium/myo-inositol cotransporter is a protein that in humans is encoded by the SLC5A3 gene.Expression of the myo-inositol transport protein is regulated by osmotic stress.-Further reading:...
), the taurine transporter (SLC6A6
SLC6A6
Sodium- and chloride-dependent taurine transporter is a protein that in humans is encoded by the SLC6A6 gene.-Further reading:...
) and neuropathy target esterase
Neuropathy target esterase
Neuropathy target esterase also known as patatin-like phospholipase domain-containing protein 6 is a neuropathy target esterase enzyme that in humans is encoded by the PNPLA6 gene....
which are involved in the production and uptake of organic osmolytes. Additionally, NFAT5 induces heat shock proteins, Hsp70
Hsp70
The 70 kilodalton heat shock proteins are a family of ubiquitously expressed heat shock proteins. Proteins with similar structure exist in virtually all living organisms...
, and osmotic stress proteins. NFAT5 is also implicated in cytokine production.
It has been shown that when NFAT5 is inhibited in renal and immune cells, these cells become significantly more susceptible to osmotic stress. NFAT5 deficient mice were found to suffer from massive cell loss in the renal medulla. Additionally, mice expressing a dominant-negative form of NFAT5 in their eyes exhibited decreased viability under hypertonic extracellular environment.
Structure
The NFATNFAT
Nuclear factor of activated T-cells is a general name applied to a family of transcription factors shown to be important in immune response. One or more members of the NFAT family is expressed in most cells of the immune system...
family consists of five different forms: NFAT1, NFAT2, NFAT3, NFAT4, and NFAT5 (this protein). The proteins in this family are expressed in nearly every tissue in the body and are known transcriptional regulators in cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
and immune cell expression. Among the different forms of NFAT, NFAT5 is an important component of the hyperosmolar stress response system.
cDNA of NFAT5 was first isolated from a human brain cDNA library. Subsequent analysis revealed that NFAT5 is a member of the Rel family, which also consists of NF-κB and NFATc
NFATC1
Nuclear factor of activated T-cells, cytoplasmic 1 is a protein that in humans is encoded by the NFATC1 gene.-Further reading:- External links :...
proteins. The largest Rel protein, it consists of nearly 1,500 amino acid residues. Like the other Rel proteins, NFAT5 contains the Rel homology domain
Rel homology domain
The Rel homology domain is a protein domain found in a family of eukaryotic transcription factors, which includes NF-κB, NFAT, among others. Some of these transcription factors appear to form multi-protein DNA-bound complexes...
, a conserved DNA-binding domain
DNA-binding domain
A DNA-binding domain is an independently folded protein domain that contains at least one motif that recognizes double- or single-stranded DNA. A DBD can recognize a specific DNA sequence or have a general affinity to DNA...
. Outside of the Rel homology domain
Rel homology domain
The Rel homology domain is a protein domain found in a family of eukaryotic transcription factors, which includes NF-κB, NFAT, among others. Some of these transcription factors appear to form multi-protein DNA-bound complexes...
, no similarities exist between NFAT5 and NF-κB or NFATc. Among these differences is the absence of docking sites for calcineurin, which is necessary for NFATc nuclear import. Instead, NFAT5 is a constitutively nuclear protein whose activity and localization does not depend on calcineurin-mediated dephosphorylation. Increased NFAT5 transcription is correlated with p38 MAPK
P38 mitogen-activated protein kinases
P38 mitogen-activated protein kinases are a class of mitogen-activated protein kinases that are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock, and are involved in cell differentiation and apoptosis....
-mediated phosphorylation.
Mechanism of Activation
Although the precise mechanism by which osmotic stress is sensed by the cell is unclear, it has been suggested that BrxAKAP13
A-kinase anchor protein 13 is an enzyme that in humans is encoded by the AKAP13 gene.-Interactions:AKAP13 has been shown to interact with Estrogen receptor alpha, CTNNAL1 and PRKAR2A.-Further reading:...
, a guanine nucleotide exchange factor (GEF
Guanine nucleotide exchange factor
Guanine nucleotide exchange factors activate monomeric GTPases by stimulating the release of guanosine diphosphate to allow binding of guanosine triphosphate . A variety of unrelated structural domains have been shown to exhibit guanine nucleotide exchange activity...
) localized near the plasma membrane, is activated by osmotic stress through changes in the cytoskeleton structure. Alternatively, Brx may also be activated through changes in its interactions with possible osmosensor molecules at the cell membrane. Upon Brx activation, the GEF domain of Brx facilitates activation of Rho-type small G proteins
Rho family of GTPases
The Rho family of GTPases is a family of small signaling G protein , and is a subfamily of the Ras superfamily. The members of the Rho GTPase family have been shown to regulate many aspects of intracellular actin dynamics, and are found in all eukaryotic organisms including yeasts and some plants...
from its inactive GDP
Guanosine diphosphate
Guanosine diphosphate, abbreviated GDP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside guanosine. GDP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase guanine....
state to active GTP
Guanosine triphosphate
Guanosine-5'-triphosphate is a purine nucleoside triphosphate. It can act as a substrate for the synthesis of RNA during the transcription process...
state. Additionally, activated Brx also recruits and physically interacts with JIP4, a p38 MAPK
P38 mitogen-activated protein kinases
P38 mitogen-activated protein kinases are a class of mitogen-activated protein kinases that are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock, and are involved in cell differentiation and apoptosis....
-specific scaffold protein. JIP4 binds to downstream kinases, MKK3
MAP2K3
Dual specificity mitogen-activated protein kinase kinase 3 is an enzyme that in humans is encoded by the MAP2K3 gene.-Interactions:MAP2K3 has been shown to interact with TAOK2 and PLCB2.-Further reading:...
and MKK6
MAP2K6
Dual specificity mitogen-activated protein kinase kinase 6 also known as MAP kinase kinase 6 or MAPK/ERK kinase 6 is an enzyme that in humans is encoded by the MAP2K6 gene, on chromosome 17.- Function :...
. This complex then activates p38 mitogen-activated protein kinase (MAPK). Activation of p38 MAPK is regulated by Cdc42
CDC42
Cell division control protein 42 homolog also known as CDC42 is a protein involved in regulation of the cell cycle. In humans, CDC42 is encoded by the CDC42 gene.- Function :...
and Rac1
RAC1
Ras-related C3 botulinum toxin substrate 1 also known as Rac1 is a protein that in humans is encoded by the RAC1 gene. Several alternatively spliced transcript variants of this gene have been described, but the full-length nature of some of these variants has not been determined.- Function :Rac1 is...
. Activation of p38 MAPK is a necessary step for NFAT5 expression.
It has been found that NFAT5 expression, following hyperosmolarity, depends on p38 mitogen-activated protein kinase (MAPK). The addition of a p38 MAPK inhibitor was found to correlate with decreased NFAT5 expression, even in the presence of osmotic stress signals. However, the downstream transcription of the NFAT5 gene by p38 MAPK is currently not yet characterized. It is hypothesized that p38 MAPK phosphorylation activates c-Fos
C-Fos
In the field of molecular biology and Genetics, c-Fos is a protein encoded by the FOS gene.-Structure and function:c-Fos is a cellular proto-oncogene belonging to the immediate early gene family of transcription factors. c-Fos has a leucine-zipper DNA binding domain, and a transactivation domain at...
and interferon regulatory factors (IRFs
Interferon regulatory factors
Interferon regulatory factors are proteins which regulate transcription of interferons .They are used in the JAK-STAT signaling pathway....
), which bind to AP-1-binding sites and ISRES (Interferon Stimulated Response Element) respectively. Binding to these sites consequently activates the transcription of target genes.
Although the Brx-mediated activation of NFAT5 has only been examined in lymphocyte response to osmotic stress, it is hypothesized that this mechanism is a common one in other cell types.
Additional Roles
NFAT5 has also been implicated in other biological roles, such as in embryonic development. Mice in the embryonic stages with non-function NFAT5 exhibited reduced survivorship.Additionally, NFAT5 plays a role in integrin-induced cell migration. Cancer cells that undergo metastasis often express NFAT5. Inhibition of NFAT5 in these migrating cells was found to deter cell migration, while overexpression of NFAT5 enhanced movement.
NFAT5 is also involved in cellular proliferation. NFAT5 mRNA expression is particularly high in proliferating cells. Inhibition of NFAT5 in embryonic fibroblasts resulted in cell cycle arrest
Cell cycle checkpoint
Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division in eukaryotic cells. These checkpoints verify whether the processes at each phase of the cell cycle have been accurately completed before progression into the next phase...
.
Although NFAT5 has been found to be important in other biological processes besides hyperosmotic stress response, the mechanism by which NFAT5 acts in these other processes are currently not well known.