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HGNC Approved Gene Symbol: CRLF2
Cytogenetic location: Xp22.33 Genomic coordinates (GRCh38) : X:1,190,490-1,212,649 (from NCBI)
Cytokine signals are mediated through specific receptor complexes, the components of which are mostly members of the type I cytokine receptor family. Type I cytokine receptors, such as CRLF2, share conserved structural features in their extracellular domain. Receptor complexes are typically heterodimeric, consisting of alpha chains, which provide ligand specificity, and beta (or gamma) chains, which are required for the formation of high-affinity binding sites and signal transduction. CRLF2 and IL7R-alpha (146661) form a heterodimeric receptor for TSLP (607003) (summary by Zhang et al. (2001) and Reche et al. (2001)).
By random sequencing of a dendritic cell (DC) cDNA library, Zhang et al. (2001) isolated a cDNA encoding CRLF2, which they termed CRL2. Sequence analysis predicted that the 371-amino acid type I transmembrane protein contains an N-terminal signal peptide, 4 potential N-linked glycosylation sites, 2 of 4 conserved cysteine residues, and a PSDWS sequence in place of the hallmark WSXWS motif. The protein also has a transmembrane domain and a 119-amino acid intracellular domain with a conserved membrane-proximal 'box 1' motif and a potential signal-transducing tyrosine residue. Northern blot analysis revealed expression of a 4.5-kb transcript in spleen, peripheral blood leukocytes, and promyelocytic leukemia cells but not in other tissues or cell lines tested. RT-PCR analysis detected expression in peripheral monocytes, monocyte-derived DCs, and other monocytic cell lines. Expression was upregulated in activated monocytes but not in T cells. Western blot analysis showed expression of a 48-kD FLAG-tagged protein, which is larger than the predicted molecular mass, suggesting that CRLF2 is indeed glycosylated.
Tonozuka et al. (2001) independently cloned the CRLF2 cDNA from a human T lymphocyte cDNA library. They found that the CRLF2 protein contains 2 fibronectin type III-like domains in the N-terminal extracellular region and box-1- and box-2-like motifs in the C-terminal intracellular region. CRLF2 shares 35% amino acid sequence identity with delta-1/TSLPR. Northern blot analysis detected CRLF2 transcripts of 1.6 kb and 0.9 kb in heart, skeletal muscle, kidney, and liver, as well as transcripts of 2.2 kb and 1.6 kb in fetal liver and of 0.9 kb in placenta and bone marrow.
Reche et al. (2001) cloned CRLF2, which they termed TSLPR, as well as its ligand, TSLP. They noted that there is a soluble splice variant of mouse Tslpr and suggested that an analogous human molecule could act as a TSLP inhibitor.
By database analysis, Wilson et al. (2013) found that mouse Tslp receptor was expressed in dorsal root ganglia (DRG). RT-PCR confirmed expression of TSLPR and its binding partner, IL7R-alpha, in human and mouse DRG. In situ hybridization of mouse DRG revealed localization of Tslpr and Il7r-alpha in a subset of small-diameter DRG neurons. Immunostaining of mouse skin also revealed Tslpr staining in cutaneous sensory nerve endings in close apposition to keratinocytes.
Reche et al. (2001) showed that expression of TSLPR and IL7R, together but not alone, induced a proliferative response to TSLP, but not to IL7 (146660), indicating that the functional TSLP receptor consists of these 2 subunits. PCR analysis of cDNA libraries suggested that DCs and monocytes coexpress IL7R and TSLPR. Incubation of DCs or monocytes with TSLP enhanced expression of CCL17 (601520), CCL18 (603757), CCL22 (602957), and CCL19 (602227). IL7, on the other hand, induced expression of CCL17, CCL22, and CCL19, but also CXCL8 (146930), CXCL7 (121010), CXCL5 (600324), CXCL1 (155730), CXCL2 (139110), and CXCL3 (139111). Functional analysis indicated that TSLP enhances the DC maturation process, as evidenced by upregulation of DC markers and costimulatory molecules and stronger T-cell proliferation.
Siracusa et al. (2011) demonstrated that TSLP promotes systemic basophilia, that disruption of TSLP-TSLPR interactions results in defective basophil responses, and that TSLPR-sufficient basophils can restore TH2-cell-dependent immunity in vivo. TSLP acted directly on bone marrow-resident progenitors to promote basophil responses selectively. Critically, TSLP could elicit basophil responses in both IL3 (147740)-IL3R (see 308385)-sufficient and -deficient environments, and genomewide transcriptional profiling and functional analyses identified heterogeneity between TSLP-elicited versus IL3-elicited basophils. Furthermore, activated human basophils expressed TSLPR, and basophils isolated from eosinophilic esophagitis (see 610247) patients were distinct from classical basophils. Siracusa et al. (2011) concluded that collectively, their studies identified previously unrecognized heterogeneity within the basophil cell lineage and indicated that expression of TSLP may influence susceptibility to multiple allergic diseases by regulating basophil hematopoiesis and eliciting a population of functionally distinct basophils that promote TH2 cytokine-mediated inflammation.
Wilson et al. (2013) found that Tslp was secreted by keratinocytes and that it activated DRG sensory neurons to evoke an itch response in mice. Tslp-evoked itch did not require lymphocytes, mast cells, or cytokines. Use of chemical inhibitors and knockout mice revealed that secretion of Tslp by keratinocytes required Nfat (see 600489) activation-dependent Tslp expression, followed by calcium signaling via Par2 (F2RL1; 600933), Orai1 (610277), and Stim1 (605921). The itch response via DRG neuronal activation required Tslp receptor, the ion channel Trpa1 (604775), and phospholipase C (see 172420) signaling. Application of Tslp directly increased intracellular calcium in DRG neurons via Trpa1 channels. Pharmacologic activation of store-operated calcium channels caused robust TSLP expression and secretion by human cutaneous and airway epithelial cells.
CRLF2/P2RY8 FUSION GENE
Mullighan et al. (2009) reported a recurring interstitial deletion of pseudoautosomal region 1 of chromosomes X and Y in B-progenitor ALL (613035) that juxtaposes the first, noncoding exon of P2RY8 (300525) with the coding region of CRLF2. They identified the P2RY8/CRLF2 fusion in 7% of individuals with B-progenitor ALL and 53% of individuals with ALL associated with Down syndrome. CRLF2 alteration was associated with activating JAK mutations, and expression of human P2RY8/CRLF2 together with mutated mouse Jak2 (147796) resulted in constitutive JAK-STAT activation and cytokine-independent growth of Ba/F3 cells overexpressing IL7R-alpha. Mullighan et al. (2009) concluded that rearrangement of CRLF2 and JAK mutation together contribute to leukemogenesis in B-progenitor ALL.
By FISH, Tonozuka et al. (2001) mapped the CRLF2 gene to the pseudoautosomal region, Xp22.3 and Yp11.3 (CRLF2Y; 400023).
Using a mouse model of allergic skin inflammation elicited by repeated epicutaneous (EC) sensitization with ovalbumin (OVA) to tape-stripped skin, which mimics the scratching-inflicted injury associated with atopic dermatitis (see 603165), He et al. (2008) found that Tslpr -/- mice had reduced inflammation, with fewer eosinophils and local Th2 cytokine expression, but unchanged splenocyte secretion of these cytokines. Addition of Tslp significantly enhanced Th2 cytokine secretion in vitro by targeting Tslpr on antigen-specific T cells. Intradermal injection of anti-Tslp blocked the development of allergic skin inflammation after EC antigen challenge of OVA-immunized wildtype mice. He et al. (2008) proposed that TSLP is essential for antigen-driven Th2 cytokine secretion by skin-infiltrating effector T cells.
He, R., Oyoshi, M. K., Garibyan, L., Kumar, L., Ziegler, S. F., Geha, R. S. TSLP acts on infiltrating effector T cells to drive allergic skin inflammation. Proc. Nat. Acad. Sci. 105: 11875-11880, 2008. [PubMed: 18711124] [Full Text: https://doi.org/10.1073/pnas.0801532105]
Mullighan, C. G., Collins-Underwood, J. R., Phillips, L. A. A., Loudin, M. G., Liu, W., Zhang, J., Ma, J., Coustan-Smith, E., Harvey, R. C., Willman, C. L., Mikhail, F. M., Meyer, J., and 12 others. Rearrangement of CRLF2 in B-progenitor- and Down syndrome-associated acute lymphoblastic leukemia. Nature Genet. 41: 1243-1246, 2009. [PubMed: 19838194] [Full Text: https://doi.org/10.1038/ng.469]
Reche, P. A., Soumelis, V., Gorman, D. M., Clifford, T., Liu, M., Travis, M., Zurawski, S. M., Johnston, J., Liu, Y.-J., Spits, H., de Waal Malefyt, R., Kastelein, R. A., Bazan, J. F. Human thymic stromal lymphopoietin preferentially stimulates myeloid cells. J. Immun. 167: 336-343, 2001. [PubMed: 11418668] [Full Text: https://doi.org/10.4049/jimmunol.167.1.336]
Siracusa, M. C., Saenz, S. A., Hill, D. A., Kim, B. S., Headley, M. B., Doering, T. A., Wherry, E. J., Jessup, H. K., Siegel, L. A., Kambayashi, T., Dudek, E. C., Kubo, M., Cianferoni, A., Spergel, J. M., Ziegler, S. F., Comeau, M. R., Artis, D. TSLP promotes interleukin-3-independent basophil haematopoiesis and type 2 inflammation. Nature 477: 229-233, 2011. [PubMed: 21841801] [Full Text: https://doi.org/10.1038/nature10329]
Tonozuka, Y., Fujio, K., Sugiyama, T., Nosaka, T., Hirai, M., Kitamura, T. Molecular cloning of a human novel type I cytokine receptor related to delta-1/TSLPR. Cytogenet. Cell Genet. 93: 23-25, 2001. [PubMed: 11474172] [Full Text: https://doi.org/10.1159/000056941]
Wilson, S. R., The, L., Batia, L. M., Beattie, K., Katibah, G. E., McClain, S. P., Pellegrino, M., Estandian, D. M., Bautista, D. M. The epithelial cell-derived atopic dermatitis cytokine TSLP activates neurons to induce itch. Cell 155: 285-295, 2013. [PubMed: 24094650] [Full Text: https://doi.org/10.1016/j.cell.2013.08.057]
Zhang, W., Wang, J., Wang, Q., Chen, G., Zhang, J., Chen, T., Wan, T., Zhang, Y., Cao, X. Identification of a novel type I cytokine receptor CRL2 preferentially expressed by human dendritic cells and activated monocytes. Biochem. Biophys. Res. Commun. 281: 878-883, 2001. [PubMed: 11237741] [Full Text: https://doi.org/10.1006/bbrc.2001.4432]