[Show abstract][Hide abstract]ABSTRACT: The autoinflammatory syndromes are systemic disorders characterized by apparently unprovoked inflammation in the absence of high-titer autoantibodies or antigen-specific T lymphocytes. One such illness, TNF-receptor-associated periodic syndrome (TRAPS), presents with prolonged attacks of fever and severe localized inflammation. TRAPS is caused by dominantly inherited mutations in TNFRSF1A (formerly termed TNFR1), the gene encoding the 55 kDa TNF receptor. All known mutations affect the first two cysteine-rich extracellular subdomains of the receptor, and several mutations are substitutions directly disrupting conserved disulfide bonds. One likely mechanism of inflammation in TRAPS is the impaired cleavage of TNFRSF1A ectodomain upon cellular activation, with diminished shedding of the potentially antagonistic soluble receptor. Preliminary experience with recombinant p75 TNFR–Fc fusion protein in the treatment of TRAPS has been favorable.
Full-text · Article · Sep 2000 · Current Opinion in Immunology
[Show abstract][Hide abstract]ABSTRACT: The immune system is an important target for the cytokine TGF-β1, whose actions on lymphocytes are largely inhibitory. TGF-β has been reported to inhibit IL-12- and IL-2-induced cell proliferation and IFN-γ production by T cells and NK cells; however, the mechanisms of inhibition have not been clearly defined. It has been suggested by some studies that TGF-β blocks cytokine-induced Janus kinase (JAK) and STAT activation, as in the case of IL-2. In contrast, other studies with cytokines like IFN-γ have not found such an inhibition. The effect of TGF-β on the IL-12-signaling pathway has not been addressed. We examined this and found that TGF-β1 did not have any effect on IL-12-induced phosphorylation of JAK2, TYK2, and STAT4 although TGF-β1 inhibited IL-2- and IL-12-induced IFN-γ production. Similarly, but in contrast to previous reports, we found that TGF-β1 did not inhibit IL-2-induced phosphorylation of JAK1, JAK3, and STAT5A. Furthermore, gel shift analysis showed that TGF-β1 did not prevent activated STAT4 and STAT5A from binding to DNA. Our results demonstrate that the inhibitory effects of TGF-β on IL-2- and IL-12-induced biological activities are not attributable to inhibition of activation of JAKs and STATs. Rather, our data suggest the existence of alternative mechanisms of inhibition by TGF-β.
Full-text · Article · Mar 1999 · The Journal of Immunology
[Show abstract][Hide abstract]ABSTRACT: Cytokines are critically important for the growth and development of a variety of cells. Janus kinases (JAKs) associate with
cytokine receptors and are essential for transmitting downstream cytokine signals. However, the regulation of the enzymatic
activity of the JAKs is not well understood. Here, we investigated the role of tyrosine phosphorylation of JAK3 in regulating
its kinase activity by analyzing mutations of tyrosine residues within the putative activation loop of the kinase domain.
Specifically, tyrosine residues 980 and 981 of JAK3 were mutated to phenylalanine individually or doubly. We found that JAK3
is autophosphorylated on multiple sites including Y980 and Y981. Compared with the activity of wild-type (WT) JAK3, mutant
Y980F demonstrated markedly decreased kinase activity, and optimal phosphorylation of JAK3 on other sites was dependent on
Y980 phosphorylation. The mutant Y980F also exhibited reduced phosphorylation of its substrates, γc and STAT5A. In contrast,
mutant Y981F had greatly increased kinase activity, whereas the double mutant, YY980/981FF, had intermediate activity. These
results indicate that Y980 positively regulates JAK3 kinase activity whereas Y981 negatively regulates JAK3 kinase activity.
These observations in JAK3 are similar to the findings in the kinase that is closely related to the JAK family, ZAP-70; mutations
of tyrosine residues within the putative activation loop of ZAP-70 also have opposing actions. Thus, it will be important
to determine whether this feature of regulation is unique to JAK3 or if it is also a feature of other JAKs. Given the importance
of JAKs and particularly JAK3, it will be critical to fully dissect the positive and negative regulatory function of these
and other tyrosine residues in the control of kinase activity and hence cytokine signaling.
Full-text · Article · Dec 1997 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract]ABSTRACT: JAK3 is a protein tyrosine kinase that specifically associates with the common γ chain (γc), a shared subunit of receptors for interleukin (IL) 2, 4, 7, 9, and 15. Patients deficient in either JAK3 or γc presented with virtually identical forms of severe combined immunodeficiency (SCID), underscoring the importance of the JAK3–γc interaction. Despite the key roles of JAK3 and γc in lymphocytic development and function, the molecular basis of this interaction remains poorly understood. In this study,
we have characterized the regions of JAK3 involved in γc association. By developing a number of chimeric JAK3–JAK2 constructs, we show that the binding specificity to γc can be conferred to JAK2 by transferring the N-terminal domains of JAK3. Moreover, those JAK3–JAK2 chimeras capable of binding
γc were also capable of reconstituting IL-2 signaling as measured by inducible phosphorylation of the chimeric JAK3–JAK2 protein,
JAK1, the IL-2 receptor β chain, and signal transducer and activator of transcription 5A. Subsequent deletion analyses of
JAK3 have identified the N-terminal JH7-6 domains as a minimal region sufficient for γc association. Furthermore, expression of the mutant containing only the JH7-6 domains effectively competed with full-length
JAK3 for binding to γc. We conclude that the JH7-6 domains of JAK3 are necessary and sufficient for γc association. These studies offer clues toward a broader understanding of JAK-mediated cytokine signaling and may provide
a target for the development of novel therapeutic modalities in immunologically mediated diseases.
Full-text · Article · Jun 1997 · Proceedings of the National Academy of Sciences