A murine IL-4 receptor antagonist that inhibits IL-4- and IL-13-induced responses prevents antigen-induced airway eosinophilia and airway hyperresponsiveness.

The closely related Th2 cytokines, IL-4 and IL-13, share many biological functions that are considered important in the development of allergic airway inflammation and airway hyperresponsiveness (AHR). The overlap of their functions results from the IL-4R alpha-chain forming an important functional signaling component of both the IL-4 and IL-13 receptors. Mutations in the C terminus region of the IL-4 protein produce IL-4 mutants that bind to the IL-4R alpha-chain with high affinity, but do not induce cellular responses. A murine IL-4 mutant (C118 deletion) protein (IL-4R antagonist) inhibited IL-4- and IL-13-induced STAT6 phosphorylation as well as IL-4- and IL-13-induced IgE production in vitro. Administration of murine IL-4R antagonist during allergen (OVA) challenge inhibited the development of allergic airway eosinophilia and AHR in mice previously sensitized with OVA. The inhibitory effect on airway eosinophilia and AHR was associated with reduced levels of IL-4, IL-5, and IL-13 in the bronchoalveolar lavage fluid as well as reduced serum levels of OVA-IGE: These observations demonstrate the therapeutic potential of IL-4 mutant protein receptor antagonists that inhibit both IL-4 and IL-13 in the treatment of allergic asthma.

Role of MEKK2-MEK5 in the regulation of TNF-alpha gene expression and MEKK2-MKK7 in the activation of c-Jun N-terminal kinase in mast cells.

Cross-linking of the high-affinity IgE receptor (FcepsilonRI) on mast cells with IgE and multivalent antigen triggers mitogen-activated protein (MAP) kinase activation and cytokine gene expression. We report here that MAP kinase kinase 4 (MKK4) gene disruption does not affect either MAP kinase activation or cytokine gene expression in response to cross-linking of FcepsilonRI in embryonic stem cell-derived mast cells. MKK7 is activated in response to cross-linking of FcepsilonRI, and this activation is inhibited by MAP/ERK kinase (MEK) kinase 2 (MEKK2) gene disruption. In addition, expression of kinase-inactive MKK7 in the murine mast cell line MC/9 inhibits c-Jun NH(2)-terminal kinase (JNK) activation in response to cross-linking of FcepsilonRI, whereas expression of kinase-inactive MKK4 does not affect JNK activation by this stimulus. However, FcepsilonRI-induced activation of the tumor necrosis factor-alpha (TNF-alpha) gene promoter is not affected by expression of kinase-inactive MKK7. We describe an alternative pathway by which MEKK2 activates MEK5 and big MAP kinase1/extracellular signal-regulated kinase 5 in addition to MKK7 and JNK, and interruption of this pathway inhibits TNF-alpha promoter activation. These findings suggest that JNK activation by antigen cross-linking is dependent on the MEKK2-MKK7 pathway, and cytokine production in mast cells is regulated in part by the signaling complex MEKK2-MEK5-ERK5.

Inactivation of NF-kappaB by EBV BZLF-1-encoded ZEBRA protein in human T cells.

We have previously shown that the EBV ZEBRA protein (also denoted EB1, Z, or Zta) encoded by the BZLF open reading frame is expressed in primary human thymocytes and in human T lymphoblastoid cell lines infected by EBV. Expression of EBV-encoded gene products in T lymphocytes could contribute to viral pathogenesis during acute EBV infection as well as in individuals coinfected with EBV and HIV. HPB-ALL and Jurkat T lymphoblastoid cell lines transiently and stably expressing ZEBRA were characterized in this work. Expression of ZEBRA protein in human T lymphoblastoid cells was associated with decreased expression of an NF-kappaB reporter gene, altered expression of the NF-kappaB p50 protein subunit, and decreased DNA binding by components of NF-kappaB. These observations suggest that inactivation of NF-kappaB transcription by ZEBRA in EBV-infected T cells may be a novel mechanism of viral pathogenesis analogous in part to over-expression of the endogenous cytoplasmic inhibitor of NF-kappaB, IkappaBalpha.

Requirement for Shc in TCR-mediated activation of a T cell hybridoma.

Engagement of the TCR determines the fate of T cells to activate their functional programs, proliferate, or undergo apoptosis. The intracellular signal transduction pathways that dictate the specific outcome of receptor engagement have only been partially elucidated. The adapter protein, Shc, is involved in cytokine production, mitogenesis, transformation, and apoptosis in different cell systems. We found that Shc becomes phosphorylated on tyrosine residues upon stimulation of the TCR in DO11.10 hybridoma T cells; therefore, we investigated the role of Shc in activation-induced cell death in these cells by creating a series of stably transfected cell lines. Expression of Shc-SH2 (the SH2 domain of Shc) or Shc-Y239/240F (full-length Shc in which tyrosines 239 and 240 have been mutated to phenylalanine) resulted in the inhibition of activation-induced cell death and Fas ligand up-regulation after TCR cross-linking. Expression of wild-type Shc or Shc-Y317F had no significant effect. In addition, we found that Shc-SH2 and Shc-Y239/240F, but not Shc-Y317F, inhibited phosphorylation of extracellular signal-regulated protein kinase and production of IL-2 after TCR cross-linking. These results indicate an important role for Shc in the early signaling events that lead to activation-induced cell death and IL-2 production after TCR activation.

The extracellular signal-regulated kinase pathway is required for activation-induced cell death of T cells.

T cells can undergo activation-induced cell death (AICD) upon stimulation of the T cell receptor-CD3 complex. We found that the extracellular signal-regulated kinase (ERK) pathway is activated during AICD. Transient transfection of a dominant interfering mutant of mitogen-activated/extracellular signal-regulated receptor protein kinase kinase (MEK1) demonstrated that down-regulation of the ERK pathway inhibited FasL expression during AICD, whereas activation of the ERK pathway with a constitutively active MEK1 resulted in increased expression of FasL. We also found that pretreatment with the specific MEK1 inhibitor PD98059 prevented the induction of FasL expression during AICD and inhibited AICD. However, PD98059 had no effect on other apoptotic stimuli. We found only very weak ERK activity during Fas-mediated apoptosis (induced by Fas cross-linking). Furthermore, preincubation with the MEK1 inhibitor did not inhibit Fas-mediated apoptosis. Finally, we also demonstrated that pretreatment with the MEK1 inhibitor could delay and decrease the expression of the orphan nuclear steroid receptor Nur77, which has been shown to be essential for AICD. In conclusion, this study demonstrates that the ERK pathway is required for AICD of T cells and appears to regulate the induction of Nur77 and FasL expression during AICD.

Cloning of p97/Gab2, the major SHP2-binding protein in hematopoietic cells, reveals a novel pathway for cytokine-induced gene activation.

Several components in cytokine signaling remain unidentified. We report the cloning and initial characterization of one such component, p97, a widely expressed scaffolding protein distantly related to Drosophila DOS and mammalian Gab1. Upon cytokine, growth factor, or antigen receptor stimulation, p97 becomes tyrosyl phosphorylated and associates with several SH2 domain-containing proteins, including SHP2. Expression of p97 mutants unable to bind SHP2 blocks cytokine-induced c-fos promoter activation, inhibiting Elk1-mediated and STAT5-mediated transactivation. Surprisingly, such mutants do not inhibit MAPK activation. Our results identify p97 as an important regulator of receptor signaling that controls a novel pathway to immediate-early gene activation and suggest multiple functions for SHP2 in cytokine receptor signaling.

Tyrosine-phosphorylated Cbl binds to Crk after T cell activation.

Crk is a Src homology 2 (SH2)/Src homology 3 (SH3)-containing adapter protein that has been implicated in intracellular signaling in fibroblasts and PC12 pheochromocytoma cells. Crk has been shown to bind to a tyrosine-phosphorylated protein of 116 kDa after TCR-mediated T cell activation. Here we demonstrate that the Crk-associated p116 phosphoprotein is not the Crk-associated substrate (Cas) but, rather, is a protein product of the c-cbl proto-oncogene. Whereas Cas was not tyrosine-phosphorylated after T cell activation, Cbl became highly phosphorylated. Crk immunoprecipitates from activated T cell lysates contain tyrosine-phosphorylated Cbl. This association is mediated by the SH2 domain of Crk, as evidenced by the interaction between Cbl and the fusion protein product of a glutathione S-transferase (GST) expression construct encoding the Crk-SH2 domain in vitro. Furthermore, phosphopeptide-binding studies revealed that the GST-Crk SH2 domain binds to a tyrosine-phosphorylated peptide corresponding to amino acids 770-781 of Cbl with high affinity. Cbl is a protein tyrosine kinase (PTK) substrate that becomes phosphorylated after engagement of numerous cell surface receptors including the TCR. Data revealed by genetic studies in the nematode, Caenorhabditis elegans, implicates a Cbl-like molecule, Sli-1, as a negative regulator of the Let-23-signaling pathway. Because the signal from the Let-23 pathway affects the activation status of the Let-60 (Ras homologue in C. elegans) pathway, the activation-dependent association between Crk and Cbl may represent another TCR-generated signal leading to Ras-related pathways.

Evidence for a physical association between the Shc-PTB domain and the beta c chain of the granulocyte-macrophage colony-stimulating factor receptor.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) regulates the growth and function of several myeloid cell types at different stages of maturation. The effects of GM-CSF are mediated through a high affinity receptor that is composed of two chains: a unique, ligand-specific alpha chain and a beta common chain (beta c) that is also a component of the receptors for interleukin 3 (IL-3) and IL-5. Beta c plays an essential role in the transduction of extra cellular signals to the nucleus through its recruitment of secondary messengers. Several downstream signaling events induced by GM-CSF stimulation have been described, including activation of tyrosine kinases and tyrosine phosphorylation of cellular proteins (including beta c) and activation of the Ras/mitogen-activated protein kinase and the JAK/STAT pathways. A region within the beta c cytoplasmic tail (amino acids 517-763) has been reported to be necessary for tyrosine phosphorylation of the adapter protein, Shc, and for the subsequent GM-CSF-induced activation of Ras. In this paper, we describe a physical association between the tyrosine phosphorylated GM-CSF receptor (GMR)-beta c chain and Shc in vivo. Using a series of cytoplasmic truncation mutants of beta c and various mutant Shc proteins, we demonstrate that the N-terminal phosphotyrosine-binding (PTB) domain of Shc binds to a short region of beta c (amino acids 549-656) that contains Tyr577. Addition of a specific phosphopeptide encoding amino acids surrounding this tyrosine inhibited the interaction between beta c and shc. Moreover, mutation of a key residue within the phosphotyrosine binding pocket of the Shc-PTB domain abrogated its association with beta c. These observations provide an explanation for the previously described requirement for Tyr577 of beta c for GM-CSF-induced tyrosine phosphorylation of Shc and have implications for Ras activation through the GM-CSF, IL-3, and IL-5 receptors.

Diminished tyrosine protein kinase activity in T cells unresponsive to TCR stimulation.

Tyrosine phosphorylation is thought to be one of the earliest steps in antigenic activation of T cells. Three nonreceptor tyrosine kinases, p56lck, p60fyn, and ZAP-70, are known to be involved in T cell receptor (TCR) signaling, albeit their functional roles appear to be different. Whereas p60fyn and ZAP-70 are functionally associated with the T cell antigen receptor, p56lck is essential for TCR signaling without being directly coupled to the TCR. We have studied a mutant variant of the Jurkat T cell line (J32-3.2), in which basal activities of p56lck and p60fyn are 2- to 2.5-fold reduced relative to those in its parental line (J32) while basal activity of ZAP-70 remains unchanged, and compared responses of J32-3.2 and J32 to TCR stimulation. We have demonstrated that tyrosine phosphorylation following CD3 cross-linking in J32-3.2 cells was extremely short-lived and thus insufficient for the induction of subsequent physiological responses. This was at least partially due to the diminished tyrosine kinase activity in these cells. A decrease in the activity of src-related kinases was caused primarily by their lower expression, whereas expression of ZAP-70 was unchanged but its response to CD3 cross-linking was diminished, correlating with the deficient tyrosine phosphorylation of the CD3 zeta-chain, recently observed in J32-3.2. These data are consistent with the idea that src-related kinases phosphorylate the zeta-chain, which in turn recruits ZAP-70 required to sustain the signal.

Identification of a novel functional 85-kD glycoprotein restricted to long-term dividing human lymphocytic lines.

Lymphocyte activation induces or increases the expression of several surface structures, some of which are directly involved in cell growth such as receptors for IL2 or transferrin. To identify new structures characteristic of activated lymphocytes, we developed a series of mAbs against functionally defined human T-cell clones or the NK-mediating cell line YT2C2. In this study, we report the isolation of an mAb termed AY19 recognizing, at the cell surface, an 85-kD glycoprotein whose expression is restricted to T-lymphocyte clones, leukemic T-cell lines, and T-ALL peripheral blood cells. Biochemical studies, as well as phenotypic analysis, revealed that this structure is different from all previously identified molecules on the cell surface of lymphocytes. Furthermore, functional studies showed that triggering of this 85-kD structure on cloned T-lymphocytes through the AY19 epitope led to an inhibition of CD3-induced proliferation. These findings suggest that the AY19 mAb defines a T-cell antigen expressed mainly on long-term dividing lymphocytes and, therefore, its putative ligand might play a role in the regulation of T-lymphocyte growth induced by CD3-TcR stimulation.