PTPN22 Deficiency Cooperates with the CD45 E613R Allele to Break Tolerance on a Non-Autoimmune Background

University of California, San Francisco, 94143, USA.
The Journal of Immunology (Impact Factor: 4.92). 05/2009; 182(7):4093-106. DOI: 10.4049/jimmunol.0803317
Source: PubMed


Pep and CD45 are tyrosine phosphatases whose targets include the Src-family kinases, critical mediators of Ag receptor signaling. A polymorphism in PTPN22, the gene that encodes the human Pep orthologue Lyp, confers susceptibility to multiple human autoimmune diseases in the context of complex genetic backgrounds. However, the functional significance of the R620W risk allele is not clear. We report that misexpression of wild-type or R620W Pep/Lyp in Jurkat cells, in the context of its binding partner Csk, unmasks the risk allele as a hypomorph. It has been shown previously that although Pep-deficient mice on the B6 background have hyperresponsive memory T cells, autoimmunity does not develop. Mice containing a point mutation in the CD45 juxtamembrane wedge domain (E613R) develop a B cell-driven, lupus-like disease on the mixed 129/B6 background, but not on the B6 background. We studied the ability of Pep deficiency to act as a genetic modifier of the CD45 E613R mutation on the nonautoimmune B6 background to understand how complex susceptibility loci might interact in autoimmunity. In this study we report that double mutant mice develop a lupus-like disease as well as lymphadenopathy, polyclonal lymphocyte activation, and accelerated memory T cell formation. Following Ag receptor stimulation, peripheral B cells in the double mutant mice phenocopy hyperresponsive CD45 E613R B cells, whereas peripheral T cells respond like Pep(-/-) T cells. These studies suggest that Pep(-/-) T cells in the context of a susceptible microenvironment can drive hyperresponsive CD45 E613R B cells to break tolerance.

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Available from: Arthur Weiss, Jun 30, 2014
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    • "Accordingly, an initial hypothesis as to how the R620W variation might promote autoimmunity was that variant LYP augments inhibition of thymocyte TCR signaling and allows the escape of higher numbers of auto-reactive T cells or of T cells exhibiting a higher functional avidity (higher strength of self-pMHC and TCR interaction) [12], [49]. Since formulation of the hypothesis, additional data variably supporting a “gain-of-function”[13], [15]–[18], “loss-of-function” [20], [21], [50] or “altered-function” [23], [24] phenotype of LYP-W620 in TCR signaling have been published. "
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    ABSTRACT: A C1858T (R620W) variation in the PTPN22 gene encoding the tyrosine phosphatase LYP is a major risk factor for human autoimmunity. LYP is a known negative regulator of signaling through the T cell receptor (TCR), and murine Ptpn22 plays a role in thymic selection. However, the mechanism of action of the R620W variant in autoimmunity remains unclear. One model holds that LYP-W620 is a gain-of-function phosphatase that causes alterations in thymic negative selection and/or thymic output of regulatory T cells (Treg) through inhibition of thymic TCR signaling. To test this model, we generated mice in which the human LYP-W620 variant or its phosphatase-inactive mutant are expressed in developing thymocytes under control of the proximal Lck promoter. We found that LYP-W620 expression results in diminished thymocyte TCR signaling, thus modeling a "gain-of-function" of LYP at the signaling level. However, LYP-W620 transgenic mice display no alterations of thymic negative selection and no anomalies in thymic output of CD4(+)Foxp3(+) Treg were detected in these mice. Lck promoter-directed expression of the human transgene also causes no alteration in thymic repertoire or increase in disease severity in a model of rheumatoid arthritis, which depends on skewed thymic selection of CD4(+) T cells. Our data suggest that a gain-of-function of LYP is unlikely to increase risk of autoimmunity through alterations of thymic selection and that LYP likely acts in the periphery perhaps selectively in regulatory T cells or in another cell type to increase risk of autoimmunity.
    Full-text · Article · Feb 2014 · PLoS ONE
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    • "In murine systems, mutations conferring BCR hyperresponsiveness , such as those involving negative signaling molecules such as SHP-1 (Zouali & Sarmay, 2004), CD22 (O'Keefe et al., 1999), or FCγRIIb (Fukuyama et al., 2005), are associated with a SLE-like disease. On the other hand, mutations involving positive regulators such as CD45 can disrupt immune tolerance via constitutive activation of Src kinases, leading to autoantibody production (Zikherman et al., 2009). Given the central role of SYK and BTK in transmission of antigen receptor signals that are critical for autoantibody production and the various innate immune effector functions discussed above (Table 2), pharmacological inhibition of the catalytic function of these enzymes is expected to have pleiotropic anti-inflammatory effects and impact multiple steps in the pathogenesis of autoimmune disorders. "
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    ABSTRACT: Spleen Tyrosine Kinase (SYK) and Bruton's Tyrosine Kinase (BTK) are non-receptor cytoplasmic tyrosine kinases that are primarily expressed in cells of hematopoietic lineage. Both are key mediators in coupling activated immunoreceptors to downstream signaling events that affect diverse biological functions, from cellular proliferation, differentiation and adhesion to innate and adaptive immune responses. As such, pharmacological inhibitors of SYK or BTK are being actively pursued as potential immunomodulatory agents for the treatment of autoimmune and inflammatory disorders. Deregulation of SYK or BTK activity has also been implicated in certain hematological malignancies. To date, from a clinical perspective, pharmacological inhibition of SYK activity has demonstrated encouraging efficacy in patients with rheumatoid arthritis (RA), while patients with relapsed or refractory chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) have benefited from covalent inhibitors of BTK in early clinical studies. Here, we review and discuss recent insights into the emerging role of the SYK-BTK axis in innate immune cell function as well as in the maintenance of survival and homing signals for tumor cell progression. The current progress on the clinical development of SYK and BTK inhibitors is also highlighted.
    Full-text · Article · Feb 2013 · Pharmacology [?] Therapeutics
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    • "A recent work has proposed that a reduced interaction with CSK leads to a lower tyrosine phosphorylation of LYP in a negative regulatory site, responsible for the increase in the activity of LYP [14]. Although the gain-of-function phenotype has received support from several studies, there is no agreement on this point; and recent reports have claimed that LYPW is a loss of function variant [15], [16]. Furthermore, knockout mice deficient in Pep phosphatase did not develop any autoimmune disease [17], despite augmented LCK activity in re-stimulated T-lymphocytes and an increase in the number of germinal centers. "
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    ABSTRACT: The protein tyrosine phosphatase LYP, a key regulator of TCR signaling, presents a single nucleotide polymorphism, C1858T, associated with several autoimmune diseases such as type I diabetes, rheumatoid arthritis, and lupus. This polymorphism changes an R by a W in the P1 Pro rich motif of LYP, which binds to CSK SH3 domain, another negative regulator of TCR signaling. Based on the analysis of the mouse homologue, Pep, it was proposed that LYP and CSK bind constitutively to inhibit LCK and subsequently TCR signaling. The detailed study of LYP/CSK interaction, here presented, showed that LYP/CSK interaction was inducible upon TCR stimulation, and involved LYP P1 and P2 motifs, and CSK SH3 and SH2 domains. Abrogating LYP/CSK interaction did not preclude the regulation of TCR signaling by these proteins.
    Full-text · Article · Jan 2013 · PLoS ONE
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