Two rare disease-associated Tyk2 variants are catalytically impaired but signaling competent.
Tyk2 belongs to the Janus protein tyrosine kinase family and is involved in signaling of immunoregulatory cytokines (type I and III IFNs, IL-6, IL-10, and IL-12 families) via its interaction with shared receptor subunits. Depending on the receptor complex, Tyk2 is coactivated with either Jak1 or Jak2, but a detailed molecular characterization of the interplay between the two enzymes is missing. In human populations, the Tyk2 gene presents high levels of genetic diversity with >100 nonsynonymous variants being detected. In this study, we characterized two rare Tyk2 variants, I684S and P1104A, which have been associated with susceptibility to autoimmune disease. Specifically, we measured their in vitro catalytic activity and their ability to mediate Stat activation in fibroblasts and genotyped B cell lines. Both variants were found to be catalytically impaired but rescued signaling in response to IFN-α/β, IL-6, and IL-10. These data, coupled with functional study of an engineered Jak1 P1084A, support a model of nonhierarchical activation of Janus kinases in which one catalytically competent Jak is sufficient for signaling provided that its partner behaves as proper scaffold, even if inactive. Through the analysis of IFN-α and IFN-γ signaling in cells with different Jak1 P1084A levels, we also illustrate a context in which a hypomorphic Jak can hamper signaling in a cytokine-specific manner. Given the multitude of Tyk2-activating cytokines, the cell context-dependent requirement for Tyk2 and the catalytic defect of the two disease-associated variants studied in this paper, we predict that these alleles are functionally significant in complex immune disorders.
Unit of Cytokine Signaling, Institut Pasteur, Paris 75724, France.
Zhi
Z
Li
Milica
M
Gakovic
Josiane
J
Ragimbeau
Maija-Leena
ML
Eloranta
Lars
L
Rönnblom
Frédérique
F
Michel
Sandra
S
Pellegrini
D000483:Alleles; D000595:Amino Acid Sequence; D001327:Autoimmune Diseases / Q000201:enzymology / Q000235:genetics* / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D002461:Cell Line, Transformed; D015870:Gene Expression; D020022:Genetic Predisposition to Disease; D005822:Genetic Vectors; D004854:Herpesvirus 4, Human / Q000235:genetics; D006801:Humans; D007370:Interferon Type I / Q000276:immunology / Q000494:pharmacology; D016753:Interleukin-10 / Q000276:immunology / Q000494:pharmacology; D015850:Interleukin-6 / Q000276:immunology / Q000494:pharmacology; D053613:Janus Kinase 1 / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010957:Plasmids; D020641:Polymorphism, Single Nucleotide; D015398:Signal Transduction / Q000276:immunology*; D053634:TYK2 Kinase / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D014162:Transfection
C508609:IL10 protein, human; C508600:IL6 protein, human; D007370:Interferon Type I; D015850:Interleukin-6; D016753:Interleukin-10; C507904:JAK1 protein, human; D053613:Janus Kinase 1; D053634:TYK2 Kinase; C070139:TYK2 protein, human