Janus kinase 3

Janus kinase 3
PDB rendering based on 1yvj.
Available structures PDB 1YVJ, 3LXK, 3LXL, 3PJC
Identifiers
Symbols	JAK3; JAK-3; JAK3_HUMAN; JAKL; L-JAK; LJAK
External IDs	OMIM: 600173 MGI: 99928 HomoloGene: 181 GeneCards: JAK3 Gene
EC number	2.7.10.2
Gene Ontology Molecular function • nucleotide binding • protein kinase activity • protein tyrosine kinase activity • protein tyrosine kinase activity • non-membrane spanning protein tyrosine kinase activity • protein binding • ATP binding Cellular component • cytoplasm • cytosol • cytoskeleton • endomembrane system • membrane Biological process • negative regulation of dendritic cell cytokine production • protein phosphorylation • enzyme linked receptor protein signaling pathway • elevation of cytosolic calcium ion concentration • intracellular protein kinase cascade • intracellular protein kinase cascade • tyrosine phosphorylation of STAT protein • STAT protein import into nucleus • peptidyl-tyrosine phosphorylation • cytokine-mediated signaling pathway • B cell differentiation • negative regulation of interleukin-10 production • negative regulation of interleukin-12 production • positive regulation of activated T cell proliferation • tyrosine phosphorylation of Stat5 protein • regulation of apoptotic process • T cell homeostasis • T cell homeostasis • innate immune response • negative regulation of FasL biosynthetic process • negative regulation of T-helper 1 cell differentiation • positive regulation of anti-apoptosis • positive regulation of transcription from RNA polymerase II promoter • protein autophosphorylation • positive regulation of immune response • negative regulation of T cell activation • positive regulation of calcium ion transport • JAK-STAT cascade involved in growth hormone signaling pathway • regulation of T cell apoptosis • negative regulation of thymocyte apoptosis • response to interleukin-2 • response to interleukin-4 • response to interleukin-15 • response to interleukin-9 Sources: Amigo / QuickGO
Orthologs
Species	Human	Mouse
Entrez	3718	16453
Ensembl	ENSG00000105639	ENSMUSG00000031805
UniProt	P52333	Q62137
RefSeq (mRNA)	NM_000215.3	NM_001190830.1
RefSeq (protein)	NP_000206.2	NP_001177759.1
Location (UCSC)	Chr 19: 17.94 – 17.96 Mb	Chr 8: 74.2 – 74.21 Mb
PubMed search	[1]	[2]

Tyrosine-protein kinase JAK3 is an enzyme that in humans is encoded by the JAK3 gene. Janus kinase 3 is a tyrosine kinase that belongs to the Janus family of kinases. Other members of the Janus family include JAK1, JAK2 and Tyk2. Janus kinases (JAKs) are relatively large kinases of approximately 1150 amino acids with apparent molecular weights of 120-130 kDa. They are cytosolic tyrosine kinases that are specifically associated with cytokine receptors. Since cytokine receptor proteins lack enzymatic activity, they are dependent upon JAKs to initiate signaling upon binding of their ligands (e.g. cytokines). The cytokine receptors can be divided into five major subgroups based on their different domains and activation motifs. JAK3 is required for signaling of the type I receptors that use the common gamma chain (γc).

Some cytokine receptors and their involvement with JAK kinases

Type	Subgroup	Cytokine Receptor	JAK Kinase
I	homodimeric	EPO, TPO, GH, G-CSF	JAK2
	uses common beta chain (CSF2RΒ)	IL-3, IL-5, GM-CSF	JAK2
	uses gp130 chain	IL-6, IL-11	JAK1, JAK2, Tyk2
	uses common gamma chain (γc)	IL-2, IL-4, IL-7, IL-9, IL-15, IL-21	JAK1, JAK3
II		IFN-α, IFN-β, IFN-γ	JAK1, JAK2, Tyk2

Function

In contrast to the relatively ubiquitous expression of JAK1, JAK2 and Tyk2, JAK3 is predominantly expressed in hematopoietic cells, such as NK cells, T cells and B cells. JAK3 functions in signal transduction and interacts with members of the STAT (signal transduction and activators of transcription) family. JAK3 is predominantly expressed in immune cells and transduces a signal in response to its activation via tyrosine phosphorylation by interleukin receptors. Mutations that abrogate Janus kinase 3 function cause an autosomal SCID (severe combined immunodeficiency disease).

Since JAK3 expression is restricted mostly to hematopoietic cells, its role in cytokine signaling is thought to be more restricted than other JAKs. It is most commonly expressed in T cells and NK cells, but has been induced in other leukocytes, including monocytes. JAK3 is involved in signal transduction by receptors that employ the common gamma chain (γc) of the type I cytokine receptor family (e.g. IL-2R, IL-4R, IL-7R, IL-9R, IL-15R, and IL-21R). Mutations of JAK3 result in severe combined immunodeficiency (SCID). Mice that do not express JAK3 have T-cells and B-cells that fail to respond to many cytokines.

In addition to its well-known roles in T cells and NK cells, JAK3 has recently been found to mediate IL-8 stimulation in human neutrophils. IL-8 primarily functions to induce chemotaxis in neutrophils and lymphocytes, and JAK3 silencing severely inhibits IL-8-mediated chemotaxis.

Interactions

Janus kinase 3 has been shown to interact with CD247, TIAF1 and IL2RG.

Signal Transduction Model

Activation of JAK3 by cytokine receptors that contain the common gamma chain (γc)

JAK3 is activated only by cytokines whose receptors contain the common gamma chain (γc) subunit: IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21. Cytokine binding induces the association of separate cytokine receptor subunits and the activation of the receptor-associated JAKs. In the absence of cytokine, JAKs lack protein tyrosine kinase activity. Once activated, the JAKs create docking sites for the STAT transcription factors by phosphorylation of specific tyrosine residues on the cytokine receptor subunits. STATs (signal transduction and activators of transcription) are members of a family of transcription factors, and they have src homology 2 (SH2) domains that allow them to bind to these phosphorylated tyrosine residues. After undergoing JAK-mediated phosphorylation, the STAT transcription factors dimerize, translocate to the nucleus, bind DNA at specific elements and induce expression of specific genes. Cytokine receptors selectively activate particular JAK-STAT pathways to induce transcription of different genes. IL-2 and IL-4 activate JAK1, JAK3 and STAT5.

Disease Relevance

Activating mutations in JAK1, JAK2, and JAK3 have been identified as causes of hematological cancers, while inactivating mutations of JAK3 are known causes of immune deficiency. Mutations in the common gamma chain (γc) result in X-linked severe combined immunodeficiency (X-SCID). Since γc specifically associates with JAK3, mutations in JAK3 also result in SCID. Deficiency of JAK3 blocks signaling of the following cytokines and their effects:

• IL-2 - T cell proliferation and maintenance of peripheral tolerance
• IL-4 - differentiation of Th2 cells
• IL-7 - thymocyte development in the thymus
• IL-9 - survival signal for various hematopoietic cells
• IL-15 - NK cell development
• IL-21 - regulation of immunoglobulin class switching in B cells

Overall, JAK3 deficiency results in the phenotype of SCID characterized by T⁻B⁺NK⁻, which indicates the absence of T cells and NK cells. Although B cells are present, they are non-functional due to defective B cell activation and impaired antibody class switching.

Since JAK3 is required for immune cell development, targeting JAK3 could be a useful strategy to generate a novel class of immunosuppressant drugs. Moreover, unlike other JAKs, JAK3 is primarily expressed in hematopoietic cells, so a highly specific JAK3 inhibitor should have precise effects on immune cells and minimal pleiotropic defects. The selectivity of a JAK3 inhibitor would also have advantages over the current widely used immunosuppressant drugs, which have abundant targets and diverse side effects. A JAK3 inhibitor could be useful for treating autoimmune diseases, especially those in which a particular cytokine receptor has a direct role on disease pathogenesis. For example, signaling through the IL-15 receptor is known to be important in the development rheumatoid arthritis, and the receptors for IL-4 and IL-9 play roles in the development of allergic responses.

A selective JAK3 inhibitor, designated CP-690550, has been developed and shown promise in clinical trials. This drug has nanomolar potency against JAK3 and was shown to be effective in preventing transplant rejection in a nonhuman primate renal transplant model. CP-690550 also demonstrated immunosuppressive activity in phase I and II clinical trials of rheumatoid arthritis, psoriasis and organ transplant rejection. CP-690550 (Tofacitinib) is currently being investigated in phase III clinical trials by Pfizer for the treatment of rheumatoid arthritis.

Further reading

• Notarangelo LD, Mella P, Jones A et al (2002). "Mutations in severe combined immune deficiency (SCID) due to JAK3 deficiency". Hum. Mutat. 18 (4): 255–63. doi:10.1002/humu.1188. PMID 11668610. 
• Russell SM, Tayebi N, Nakajima H et al (1995). "Mutation of Jak3 in a patient with SCID: essential role of Jak3 in lymphoid development". Science 270 (5237): 797–800. doi:10.1126/science.270.5237.797. PMID 7481768. 
• Johnston JA, Wang LM, Hanson EP et al (1996). "Interleukins 2, 4, 7, and 15 stimulate tyrosine phosphorylation of insulin receptor substrates 1 and 2 in T cells. Potential role of JAK kinases". J. Biol. Chem. 270 (48): 28527–30. doi:10.1074/jbc.270.48.28527. PMID 7499365. 
• Musso T, Johnston JA, Linnekin D et al (1995). "Regulation of JAK3 expression in human monocytes: phosphorylation in response to interleukins 2, 4, and 7". J. Exp. Med. 181 (4): 1425–31. doi:10.1084/jem.181.4.1425. PMC 2191962. PMID 7535338. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2191962. 
• Rolling C, Treton D, Beckmann P et al (1995). "JAK3 associates with the human interleukin 4 receptor and is tyrosine phosphorylated following receptor triggering". Oncogene 10 (9): 1757–61. PMID 7538655. 
• Lai KS, Jin Y, Graham DK et al (1995). "A kinase-deficient splice variant of the human JAK3 is expressed in hematopoietic and epithelial cancer cells". J. Biol. Chem. 270 (42): 25028–36. doi:10.1074/jbc.270.42.25028. PMID 7559633. 
• Macchi P, Villa A, Giliani S et al (1995). "Mutations of Jak-3 gene in patients with autosomal severe combined immune deficiency (SCID)". Nature 377 (6544): 65–8. doi:10.1038/377065a0. PMID 7659163. 
• Russell SM, Johnston JA, Noguchi M et al (1994). "Interaction of IL-2R beta and gamma c chains with Jak1 and Jak3: implications for XSCID and XCID". Science 266 (5187): 1042–5. doi:10.1126/science.7973658. PMID 7973658. 
• Miyazaki T, Kawahara A, Fujii H et al (1994). "Functional activation of Jak1 and Jak3 by selective association with IL-2 receptor subunits". Science 266 (5187): 1045–7. doi:10.1126/science.7973659. PMID 7973659. 
• Johnston JA, Kawamura M, Kirken RA et al (1994). "Phosphorylation and activation of the Jak-3 Janus kinase in response to interleukin-2". Nature 370 (6485): 151–3. doi:10.1038/370151a0. PMID 8022485. 
• Witthuhn BA, Silvennoinen O, Miura O et al (1994). "Involvement of the Jak-3 Janus kinase in signalling by interleukins 2 and 4 in lymphoid and myeloid cells". Nature 370 (6485): 153–7. doi:10.1038/370153a0. PMID 8022486. 
• Kawamura M, McVicar DW, Johnston JA et al (1994). "Molecular cloning of L-JAK, a Janus family protein-tyrosine kinase expressed in natural killer cells and activated leukocytes". Proc. Natl. Acad. Sci. U.S.A. 91 (14): 6374–8. doi:10.1073/pnas.91.14.6374. PMC 44204. PMID 8022790. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=44204. 
• Verbsky JW, Bach EA, Fang YF et al (1996). "Expression of Janus kinase 3 in human endothelial and other non-lymphoid and non-myeloid cells". J. Biol. Chem. 271 (24): 13976–80. doi:10.1074/jbc.271.24.13976. PMID 8662778. 
• Fusaki N, Iwamatsu A, Iwashima M, Fujisawa J (1997). "Interaction between Sam68 and Src family tyrosine kinases, Fyn and Lck, in T cell receptor signaling". J. Biol. Chem. 272 (10): 6214–9. doi:10.1074/jbc.272.10.6214. PMID 9045636. 
• Fujitani Y, Hibi M, Fukada T et al (1997). "An alternative pathway for STAT activation that is mediated by the direct interaction between JAK and STAT". Oncogene 14 (7): 751–61. doi:10.1038/sj.onc.1200907. PMID 9047382. 
• Safford MG, Levenstein M, Tsifrina E et al (1997). "JAK3: expression and mapping to chromosome 19p12-13.1". Exp. Hematol. 25 (5): 374–86. PMID 9168059. 
• Sharfe N, Dadi HK, O'Shea JJ, Roifman CM (1997). "Jak3 activation in human lymphocyte precursor cells". Clin. Exp. Immunol. 108 (3): 552–6. doi:10.1046/j.1365-2249.1997.4001304.x. PMC 1904698. PMID 9182906. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1904698. 
• Candotti F, Oakes SA, Johnston JA et al (1997). "Structural and functional basis for JAK3-deficient severe combined immunodeficiency". Blood 90 (10): 3996–4003. PMID 9354668. 

External links

• MeSH Janus+Kinase+3