Interleukin-4 induces activation of mitogen-activated protein kinase and phosphorylation of shc in human keratinocytes

A Small-Molecule Inhibitor to the Cytokine Interleukin-4

Interleukin-4 (IL-4) is a multifunctional cytokine and an important regulator of inflammation. When deregulated, IL-4 activity is associated with asthma, allergic inflammation, and multiple types of cancer. While antibody-based inhibitors targeting the soluble cytokine have been evaluated clinically, they failed to achieve their end points in trials. Small-molecule inhibitors are an attractive alternative, but identifying effective chemotypes that inhibit the protein-protein interactions between cytokines and their receptors remains an active area of research. As a result, no small-molecule inhibitors to the soluble IL-4 cytokine have yet been reported. Here, we describe the first IL-4 small-molecule inhibitor identified and characterized through a combination of binding-based approaches and cell-based activity assays. The compound features a nicotinonitrile scaffold with micromolar affinity and potency for the cytokine and disrupts type II IL-4 signaling in cells. Small-molecule inhibitors of these important cell-signaling proteins have implications for numerous immune-related disorders and inform future drug discovery and design efforts for these challenging protein targets.

Fueling Cancer Immunotherapy With Common Gamma Chain Cytokines

Adoptive T cell transfer therapy (ACT) using tumor infiltrating lymphocytes or lymphocytes redirected with antigen receptors (CAR or TCR) has revolutionized the field of cancer immunotherapy. Although CAR T cell therapy mediates robust responses in patients with hematological malignancies, this approach has been less effective for treating patients with solid tumors. Additionally, toxicities post T cell infusion highlight the need for safer ACT protocols. Current protocols traditionally expand T lymphocytes isolated from patient tumors or from peripheral blood to large magnitudes in the presence of high dose IL-2 prior to infusion. Unfortunately, this expansion protocol differentiates T cells to a full effector or terminal phenotype in vitro, consequently reducing their long-term survival and antitumor effectiveness in vivo. Post-infusion, T cells face further obstacles limiting their persistence and function within the suppressive tumor microenvironment. Therapeutic manipulation of T cells with common γ chain cytokines, which are critical growth factors for T cells, may be the key to bypass such immunological hurdles. Herein, we discuss the primary functions of the common γ chain cytokines impacting T cell survival and memory and then elaborate on how these distinct cytokines have been used to augment T cell-based cancer immunotherapy.

Interleukin-4 Enhances the Sensitivity of Human Monocytes to Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand Through Upregulation of Death Receptor 4

Interleukin (IL)-4 is generally thought to promote tumor cell growth and inhibit apoptosis. However, its role in characteristics of monocytic leukemia cells was rarely reported. In this study, we assessed the role of IL-4 in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sensitivity of human monocytes. After incubation with IL-4 for 24 h, death receptor 4 (DR4) was significantly increased without downregulation of TRAIL decoy receptors and antiapoptotic proteins in THP-1 monocytes, and human primary monocytes and U-937 cells also exhibited increased TRAIL-induced apoptosis compared with control. Enhancement of TRAIL-mediated apoptosis by IL-4 was blocked by anti-DR4-neutralizing antibodies. Both upregulation of DR4 and enhancement of TRAIL-mediated apoptosis by IL-4 could be blocked by inhibitors of Janus kinase (JAK)/signal transducer and activator of transcription (STAT), phosphoinositol 3-kinase (PI3K)/Akt, and extracellular signal-regulated kinase to varying degrees. Thus, our data demonstrated a novel effect on TRAIL sensitivity on monocytes and monocytic leukemia cells of IL-4 and suggested that it may be necessary to reconsider the impact of current therapies against IL-4, JAK/STAT, and PI3K/Akt pathways with regard to TRAIL sensitivity.

The Use of In Vitro Systems for Evaluating Immunotoxicity: The Report and Recommendations of an ECVAM Workshop

This is the report of a workshop organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods that are of importance to the biosciences and which replace, reduce or refine the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures that would enable it to become well informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organization of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (Anonymous, 1994). The workshop on "The use of in vitro systems for evaluating Immunotoxicity" was held at ECVAM (Ispra), Italy, on 24th-26th November 2003. The participants represented academia, national organizations, international regulatory bodies and industry. The aim of the workshop was to review the state-of-the-art in the field of in vitro immunotoxicology, and to develop strategies towards the replacement of in vivo testing. At the end of this report are listed the recommendations that should be considered for prevalidation and validation of relevant and reliable procedures, that could replace the use of animals in chemical and cosmetics toxicity testing.

Prevention of TGF-beta-induced apoptosis by interlukin-4 through Akt activation and p70S6K survival signaling pathways

In this study, we demonstrate that interleukin-4 (IL-4) protects human hepatocellular carcinoma (HCC) cell line Hep3B from apoptosis induced by transforming growth factor-beta (TGF-beta). Further investigation of IL-4-transduced signaling pathways revealed that both insulin response substrate 1 and 2 (IRS-1/-2) and extracellular signal-regulated kinase (ERK) pathways were activated after IL-4 stimulation. The IRS-1/-2 activation was accompanied by the activation of phosphotidylinositol-3-kinase (PI3K), leading to Akt and p70 ribosomal protein S6 kinase (p70S6K). Interestingly, a protein kinase C (PKC) inhibitor, Gö6976, inhibited the phosphorylation of Akt, suggesting that the Akt activation was PKC-dependent. Using specific inhibitors for PI3K or ERK, we demonstrated that the PI3K pathway, but not the ERK pathway, was required for protection. The constitutively active form of PI3K almost completely rescued TGF-beta-induced apoptosis, further supporting the importance of the PI3K pathway in the protective effect of IL-4. Furthermore, a dominant negative Akt and/or Gö6976 only partially blocked the anti-apoptotic effect of IL-4. Similarly, rapamycin, which interrupted the activation of p70S6K, also only partially blocked the protective effect of IL-4. However, in the presence of both rapamycin and dominant negative Akt with or without Gö6976, IL-4 almost completely lost the anti-apoptotic effect, suggesting that both Akt and p70S6K pathways were required for the protective effect of IL-4 against TGF-beta-induced apoptosis.

Interleukin-4 downregulates TNFalpha-induced IL-8 production in keratinocytes

Interleukin (IL)-8 is a CXC chemokine induced by pro-inflammatory cytokines such as TNFalpha, IL-1beta and IL-6 in different cell types including keratinocytes. IL-4 regulation of TNFalpha-induced IL-8 expression is cell-type specific. In this study, we show that in the keratinocyte cell line HaCaT, IL-4 decreases TNFalpha-induced IL-8 mRNA expression. We then investigated the mechanism of IL-4 effect and showed that IL-4 downregulates TNFalpha-induced IL-8 promoter activity in luciferase reporter assays. Moreover, overexpression of either the endogenous JAK inhibitor SOCS-1 or a dominant negative form of the STAT6 transcription factor (STAT6DeltaC) interferes with the IL-4 inhibitory effect on IL-8 promoter. Finally we demonstrate, using a NF-kappaB-dependent promoter luciferase construct that IL-4 interferes, at least in part, with NF-kappaB transcriptional activity. Overall our results suggest that IL-4 regulates TNFalpha-induced IL-8 expression at a transcriptional level and this mechanism involves STAT6 and NF-kappaB transcription factors.

IL-4-induced priming of human intestinal mast cells for enhanced survival and Th2 cytokine generation is reversible and associated with increased activity of ERK1/2 and c-Fos

In synergy with stem cell factor (SCF), IL-4 strongly enhances mast cell proliferation and shifts IgE-dependent cytokine production in mature human mast cells toward an increased release of Th2 cytokines such as IL-3, IL-5, and IL-13 and a decreased IL-6 expression. In this study we analyzed the kinetics and the mechanisms of these IL-4 effects on mast cells purified from intestinal tissue. If the cells were first cultured with IL-4 for 14 days and then without IL-4 for another 14 days, mast cells lost the capacity of producing higher amounts of Th2 cytokines and regained the capacity of producing IL-6. The IL-4-induced up-regulation of mast cell proliferation and FcepsilonRI expression was also reversible if IL-4 was withdrawn for 14 days. Interestingly, in contrast to IL-4, proliferation and phenotype of human intestinal mast cells were not affected by IL-13 although both cytokines were capable of inducing STAT6 activation. Instead, IL-4 treatment (but not IL-13 treatment) was associated with an increased activity of ERK1/2 and c-Fos, the downstream target of ERK1/2 and component of the transcription factor AP-1. Consistently, mast cell proliferation and cytokine expression in response to IL-4 was blocked by the MEK inhibitor PD98059. In summary, our data show that the IL-4 effects on human intestinal mast cell functions are reversible and accompanied by an increased activity of ERK1/2 and c-Fos.

Molecular biology of the 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase gene family

The 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3beta-HSD) isoenzymes are responsible for the oxidation and isomerization of Delta(5)-3beta-hydroxysteroid precursors into Delta(4)-ketosteroids, thus catalyzing an essential step in the formation of all classes of active steroid hormones. In humans, expression of the type I isoenzyme accounts for the 3beta-HSD activity found in placenta and peripheral tissues, whereas the type II 3beta-HSD isoenzyme is predominantly expressed in the adrenal gland, ovary, and testis, and its deficiency is responsible for a rare form of congenital adrenal hyperplasia. Phylogeny analyses of the 3beta-HSD gene family strongly suggest that the need for different 3beta-HSD genes occurred very late in mammals, with subsequent evolution in a similar manner in other lineages. Therefore, to a large extent, the 3beta-HSD gene family should have evolved to facilitate differential patterns of tissue- and cell-specific expression and regulation involving multiple signal transduction pathways, which are activated by several growth factors, steroids, and cytokines. Recent studies indicate that HSD3B2 gene regulation involves the orphan nuclear receptors steroidogenic factor-1 and dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome gene 1 (DAX-1). Other findings suggest a potential regulatory role for STAT5 and STAT6 in transcriptional activation of HSD3B2 promoter. It was shown that epidermal growth factor (EGF) requires intact STAT5; on the other hand IL-4 induces HSD3B1 gene expression, along with IL-13, through STAT 6 activation. However, evidence suggests that multiple signal transduction pathways are involved in IL-4 mediated HSD3B1 gene expression. Indeed, a better understanding of the transcriptional factors responsible for the fine control of 3beta-HSD gene expression may provide insight into mechanisms involved in the functional cooperation between STATs and nuclear receptors as well as their potential interaction with other signaling transduction pathways such as GATA proteins. Finally, the elucidation of the molecular basis of 3beta-HSD deficiency has highlighted the fact that mutations in the HSD3B2 gene can result in a wide spectrum of molecular repercussions, which are associated with the different phenotypic manifestations of classical 3beta-HSD deficiency and also provide valuable information concerning the structure-function relationships of the 3beta-HSD superfamily. Furthermore, several recent studies using type I and type II purified enzymes have elegantly further characterized structure-function relationships responsible for kinetic differences and coenzyme specificity.

Downregulation of IL-4-induced signalling in hippocampus contributes to deficits in LTP in the aged rat

Ageing is characterized by deficits in learning and memory and by a deficit in long-term potentiation (LTP) in hippocampus. Several age-related changes, including dysfunction of calcium homeostatic mechanisms and upregulation of inflammatory processes are likely to contribute to these deficits. Here we exploited the fact that aged rats fall into a subgroup which fail to sustain LTP in perforant path granule cell synapses as a result of tetanic stimulation, and a subgroup which sustains LTP in a manner indistinguishable from young rats, in an effort to identify differential changes in the two subgroups. The age-related increase in IL-1beta concentration and IL-1beta-induced signalling was more profound in aged rats which failed to sustain LTP. We demonstrate that functional IL-4 receptors are expressed in rat hippocampus and that age is associated with a decrease in IL-4 concentration accompanied by a decrease in phosphorylation of JAK-1 and STAT-6. We propose that the imbalance between pro-inflammatory and anti-inflammatory cytokines in the aged brain significantly contributes to age-related deficits in synaptic function.

Interleukin-4 receptor signaling pathways in asthma pathogenesis

Asthma is a chronic allergic inflammatory disease, the initiation and progression of which is dependent on the cytokines interleukin (IL)-4 and IL-13 acting through related receptor complexes. Disease pathogenesis is effected by intracellular signaling pathways that couple primarily to specific motifs within the intracellular domain of the IL-4 receptor alpha chain (IL-4Ralpha), a subunit that is common to the IL-4 and IL-13 receptor complexes. Recent studies using genetic approaches have identified distinct functions for the respective IL-4Ralpha-coupled signaling pathways in regulating both early and chronic stages of asthma. Polymorphisms in components of the IL-4 and IL-13 cytokine-receptor axes are associated with allergy and asthma, suggesting that variations among individuals in the activity of this pathway contribute to disease susceptibility and manifestations.

Targeted inactivation of the IL-4 receptor alpha chain I4R motif promotes allergic airway inflammation

The insulin/interleukin-4 (IL-4) receptor (I4R) motif mediates the association of insulin receptor substrate (IRS)-2 with the interleukin-4 (IL-4)Ralpha chain and transduces mitogenic signals in response to IL-4. Its physiological functions were analyzed in mice with a germline point mutation that changed the motif's effector tyrosine residue into phenylalanine (Y500F). The Y500F mutation abrogated IRS-2 phosphorylation and impaired IL-4-induced CD4+ T lymphocyte proliferation but left unperturbed Stat6 activation, up-regulation of IL-4-responsive gene products, and Th cell differentiation under Th2 polarizing conditions. However, in vivo the Y500F mutation was associated with increased allergen-induced IgE production, airway responsiveness, tissue eosinophilia, and mucus production. These results define an important role for the I4R motif in regulating allergic inflammation.

Development of colitis in signal transducers and activators of transcription 6-deficient T-cell receptor alpha-deficient mice: a potential role of signal transducers and activators of transcription 6-independent interleukin-4 signaling for the generation of Th2-biased pathological CD4+ betabetaT cells

Forbidden CD4(+)betabeta T cells, which produce interleukin (IL)-4 predominantly, are a pathological subset in the development of colitis in T-cell receptor alpha chain (TCRalpha)-deficient mice. Stimulation of naive CD4(+) T cells with IL-4 induces Th2 development via the activation of signal transducers and activators of transcription (STAT) 6. In the present study, we had found that IL-4 enhanced the expression of STAT6 in CD4(+)betabeta T cells isolated from TCRalpha(-/-) mice with colitis, suggesting that the IL-4 signal in the CD4(+)betabeta T cells is mediated by STAT6. To further investigate the role of STAT6 in the development of colitis induced by TCRalpha deficiency, we generated double-deficient mice by crossing TCRalpha(-/-) mice and STAT6(-/-) mice. Surprisingly, STAT6 deficiency did not result in decreased severity of colitis in TCRalpha(-/-) mice. STAT6-deficient CD4(+)betabeta T cells produced IL-4 and intraperitoneal injection of anti-IL-4 monoclonal antibody in the nondiseased TCRalpha(-/-) and STAT6 double-deficient mice prevented the colitis formation, thus indicating that the cells differentiated into the Th2 phenotype have the ability to mediate the development of the colitis in the absence of STAT6.

IL-4 and IL-12 regulate proteoglycan-induced arthritis through Stat-dependent mechanisms

IL-4, a well-recognized modulator of macrophage activation, is perceived as an anti-inflammatory cytokine; however, under certain circumstances IL-4 may function as a proinflammatory cytokine. We have previously demonstrated that IL-4 treatment of mice with proteoglycan-induced arthritis (PGIA) inhibited the development of disease. To determine whether the capacity of IL-4 to inhibit disease is dependent on IL-4-mediated regulation of IL-12, we assessed the requirement for IL-4 in modulating development of PGIA. Immunization of mice, lacking IL-4 and Stat6, with proteoglycan results in a significant increase in arthritis severity in comparison to wild-type controls, suggesting that arthritis severity is regulated by IL-4 through a Stat6-dependent mechanism. Concomitant with exacerbated disease in IL-4(-/-) mice, there is a significant increase in the systemic production of proinflammatory cytokines IL-12, TNF-alpha, and IFN-gamma and in levels of mRNA transcripts for proinflammatory cytokines and chemokines in joints. Disease is suppressed in Stat4(-/-) mice indicating that elevated levels of IL-12 contribute to exacerbation of arthritis and that suppression is accompanied by reduced levels of IFN-gamma production. In support of this, IFN-gamma(-/-) mice are protected from PGIA and the degree of inflammation is similar to Stat4(-/-) mice. The decrease in disease severity in IFN-gamma(-/-) and Stat4(-/-) mice correlates with diminished TNF-alpha levels but there is no switch to a Th2-type response. Taken together, these results suggest that IL-4 regulates the severity of disease in PGIA by controlling IL-12 production, which in turn regulates the magnitude of IFN-gamma expression through a Stat4-dependent pathway.

Keratinocytes and cytokines

The skin has long been recognized as a major producer of cytokines, but the keratinocyte as principal epidermal cell has received less attention as potential source and target of cytokines. Nevertheless, keratinocytes produce a plethora of cytokines including interleukin (IL)-1, -6, -7, -8, -10, -12, -15, -18, and -20, and tumor necrosis factor alpha (TNF). The production by keratinocytes of pro-inflammatory (IL)-1, -6, -8, and TNF was recognized early and is well studied. Keratinocyte-derived IL-7 and -15 are considered to be significant in T-cell trafficking, possibly even in the pathogenesis of cutaneous T-cell lymphoma. Immunomodulatory IL-10 and -12 originating from keratinocytes are considered to be responsible for systemic effects, and IL-18 perhaps has a similar action. Keratinocytes were fairly recently recognized as being source or target of other IL-10 family members like IL-20 and IL-24 and the role of these cytokines in specific diseases is under investigation. In addition, a variety of cytokine receptors are present on keratinocytes like those for IL-4, -13, and -17 and to lesser degree IL-2. The ability to study the expression of cytokines by keratinocytes in vivo and in vitro using primary cells, immortalized cells or even organotypic culture systems offers many possibilities to further investigate the role of cytokine production in keratinocyte biology and disease.

Acetylation by histone acetyltransferase CREB-binding protein/p300 of STAT6 is required for transcriptional activation of the 15-lipoxygenase-1 gene

Interleukin-4 (IL-4) induces expression of reticulocyte-type 15-lipoxygenase-1 (15-LOX-1) in various mammalian cells via the Janus kinase/signal transducer and activator of transcription 6 (STAT6) signaling system. We studied the mechanism of 15-LOX-1 induction in A549 lung epithelial cells and found that genistein, a potent tyrosine kinase inhibitor, prevented phopsphorylation of STAT6, its binding to the 15-LOX-1 promoter, and the expression of catalytically active enzyme. In contrast, cycloheximide did not prevent 15-LOX-1 induction. Surprisingly, we found that IL-4 up-regulated the histone acetyltransferase activity of CREB-binding protein (CBP)/p300, which is responsible for acetylation of nuclear histones and STAT6. The acetylation of both proteins appears to be essential for the IL-4-induced signal transduction cascade, because inhibition of CBP/p300 by the viral wild-type E1A oncoprotein abrogated acetylation of both histones and STAT6 and strongly suppressed transcriptional activation of the 15-LOX-1 gene. Moreover, we found that the inhibition by sodium butyrate of histone deacetylases, which apparently suppress 15-LOX-1 gene transcription, synergistically enhanced the IL-4-stimulated 15-LOX-1 expression. These data suggest that both phosphorylation and acetylation of STAT6 as well as acetylation of nuclear histones are involved in transcriptional activation of the 15-LOX-1 gene, although these reactions follow differential kinetics. STAT6 phosphorylation proceeds within the first hour of IL-4 stimulation. In contrast, CBP/p300-mediated acetylation requires 9-11 h, and similar kinetics were observed for the expression of the active enzyme. Thus, our results suggest that in the absence of IL-4, nuclear histones may be bound to regulatory elements of the 15-LOX-1 gene, preventing its transcription. IL-4 stimulation causes rapid phosphorylation of STAT6, but its binding to the promoter appears to be prevented by nonacetylated histones. After 9-11 h, when histones become acetylated, STAT6 binding sites may be demasked so that the phosphorylated and acetylated transcription factor can bind to activate gene transcription.

Novel anti-inflammatory effects of the inhaled corticosteroid fluticasone propionate during lung myofibroblastic differentiation

Asthma is characterized by an irreversible subepithelial fibrosis with the appearance of myofibroblasts, which can be now considered important early participants in inflammatory responses as well as potential targets for anti-inflammatory drugs. In this study, we show that fluticasone propionate (FP), a powerful inhaled corticosteroid (ICS), displays novel anti-inflammatory effects on human lung fibroblasts during their myofibroblastic differentiation. Indeed, FP inhibits in lung myofibroblasts, at a very early stage of differentiation, the activation of Janus kinase/STAT pathways induced by IL-13 (tyrosine kinase 2, STAT1, STAT3, STAT6, mitogen-activated protein kinase). Contrarily, in mildly or fully differentiated myofibroblastic cultures, FP still displays a potential anti-inflammatory activity even if it only inhibits tyrosine kinase 2 phosphorylation. Moreover, FP inhibits constitutive and TGF-beta-induced expression of alpha-smooth muscle actin, the main marker of myofibroblastic differentiation, both in very early and in mild differentiated myofibroblasts. Finally, FP displays an additional powerful anti-inflammatory effect, decreasing nuclear translocation of NF-kappaB independent of the degree of myofibroblastic differentiation. These data 1) suggest that myofibroblasts are priority targets for ICS, which is able to revert them to a normal phenotype even if they appear to be already engaged in their differentiation, and 2) may help to explain why asthma is improved by an early ICS treatment, whereas advanced asthma is more resistant to these drugs.

Direct effects of interleukin-13 on signaling pathways for physiological responses in cultured human airway smooth muscle cells

Numerous studies have suggested an important role for the Th2 cytokines interleukin (IL)-13 and IL-4 in the development of allergic asthma. We tested the hypothesis that IL-13 and IL-4 have direct effects on cultured airway smooth muscle cells (HASM). Using RT-PCR, we showed that HASM cells express transcripts for IL-4alpha, IL-13RalphaI, and IL-13RalphaII, but not for the common IL-2Rgamma chain. We then analyzed the capacity of the two cytokines to activate signaling pathways in HASM cells. Both IL-13 and IL-4 caused STAT-6 phosphorylation, but the time course was different between the two cytokines, with peak effects occurring 15 min after addition of IL-4 and 1 h after addition of IL-13. Effects on signaling were observed at cytokine concentrations as low as 0.3 ng/ml. IL-4 and IL-13 also caused phosphorylation of ERK MAP kinase. As suggested by the signaling studies, the biological responses of the two cytokines were also different. We used magnetic twisting cytometry to measure cell stiffness of HASM cells and tested the capacity of IL-4 and IL-13 to interfere with the reductions in cell stiffness induced by the beta-agonist isoproterenol (ISO). IL-13 (50 ng/ml for 24 h), but not IL-4, significantly reduced beta-adrenergic responsiveness of HASM cells, and the MEK inhibitor U0126 significantly reduced the effects of IL-13 on ISO-induced changes in cell stiffness. We propose that these direct effect of IL-13 on HASM cells may contribute at least in part to the airway narrowing observed in patients with asthma.

Stat6 is necessary and sufficient for IL-4's role in Th2 differentiation and cell expansion

IL-4 plays a critical role in the differentiation of TCR-stimulated naive CD4 T cells to the Th2 phenotype. In response to IL-4, the IL-4R activates a set of phosphotyrosine binding domain-containing proteins, including insulin receptor substrate 1/2, Shc, and IL-4R interacting protein, as well as Stat6. Stat6 has been shown to be required for Th2 differentiation. To determine the roles of the phosphotyrosine binding adaptors in Th2 differentiation, we prepared a retrovirus containing a mutant of the human (h)IL-4R alpha-chain, Y497F, which is unable to recruit these adaptors. The mutant hIL-4Ralpha, as well as the wild-type (WT) hIL-4Ralpha, was introduced into naive CD4 T cells. Upon hIL-4 stimulation, Y497F worked as well as the WT hIL-4Ralpha in driving Th2 differentiation, as measured by Gata3 up-regulation and IL-4 production. Furthermore, IL-4-driven cell expansion was also normal in the cells infected with Y497F, although cells infected with Y497F were not capable of phosphorylating insulin receptor substrate 2. These results suggest that the signal pathway mediated by Y497 is dispensable for both IL-4-driven Th2 differentiation and cell expansion. Both WT and Y497F hIL-4Ralpha lose the ability to drive Th2 differentiation and cell expansion in Stat6-knockout CD4 T cells. A constitutively activated form of Stat6 introduced into CD4 T cells resulted in both Th2 differentiation and enhanced cell expansion. Thus, activated Stat6 is necessary and sufficient to mediate both IL-4-driven Th2 differentiation and cell expansion in CD4 T cells.

IL-4 and IL-13 induce myofibroblastic phenotype of human lung fibroblasts through c-Jun NH2-terminal kinase-dependent pathway

BACKGROUND

Myofibroblasts play a role in the airway remodeling response of bronchial asthma. IL-4 and IL-13 are possibly involved in the airway remodeling response by inducing extracellular matrix production by fibroblasts. However, the roles of these cytokines in inducing the phenotypic modulation of human lung fibroblasts (HLFs) to myofibroblasts and the intracellular signal have not been determined.

OBJECTIVE

We examined the effect of IL-4 and IL-13 on inducing the phenotypic modulation of HLFs to myofibroblasts characterized by alpha-smooth muscle actin and examined the role of the mitogen-activated protein (MAP) kinase superfamily in inducing the myofibroblastic phenotype of the HLF to clarify these issues.

METHODS

Phosphorylation and activities of c-Jun NH(2)-terminal kinase (JNK), p38 MAP kinase, and extracellular signal-regulated kinase (Erk) were examined by using Western blotting and in vitro kinase assay. Expression of alpha-smooth muscle actin in IL-4- and IL-13-stimulated HLFs was analyzed by means of Western blotting.

RESULTS

The results showed that (1) IL-4 and IL-13 increased alpha-smooth muscle actin expression in a dose- and time-dependent manner; (2) IL-4 and IL-13 induced increases in JNK and Erk phosphorylation and activity but not p38 MAP kinase activity; (3) CEP-1347 and PD 98059 attenuated IL-4- and IL13-induced JNK and Erk activity, respectively; and (4) CEP-1347, but not PD 98059, attenuated IL-4- and IL-13-induced alpha-smooth muscle actin expression.

CONCLUSION

These results indicate that IL-4 and IL-13 are capable of inducing the phenotypic modulation of HLFs to myofibroblasts, and JNK, but not p38 MAP kinase and Erk, regulates IL-4- and IL-13-induced phenotypic modulation of HLFs to myofibroblasts.

Epidermal growth factor regulates astrocyte expression of the interleukin-4 receptor via a MAPK-independent pathway

Human astrocytes express the interleukin (IL)-4 receptor alpha chain (IL-4R alpha) in vitro and in vivo but mechanisms governing astrocyte IL-4R alpha expression have not been established. We hypothesized that epidermal growth factor (EGF) and IL-4, agents that profoundly affect astrocyte proliferation, might also alter IL-4R alpha expression. Exposure to EGF for 24 h enhanced IL-4R alpha mRNA levels; in contrast, IL-4 yielded no increase. Immunoblotting demonstrated that EGF but not IL-4 increased astrocyte IL-4R alpha protein after 2--4 days of exposure. Similarly, EGF but not IL-4 strongly activated phosphorylation of p42/p44 extracellular regulated kinase isoforms, a reaction blocked by the mitogen-activated protein kinase (MAPK) inhibitor, PD98059. PD98059 also blocked EGF-stimulated DNA synthesis but not IL-4R alpha mRNA levels, while antibody to the EGF receptor (erbB1) blocked both EGF effects. Data suggest that astrocyte IL-4R alpha expression is upregulated by EGF but not by IL-4 in an EGF-receptor-dependent manner and that mechanisms are independent of MAPK activation.

Multiple signal transduction pathways mediate interleukin-4-induced 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase in normal and tumoral target tissues

The 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (3beta-HSD) isoenzymes catalyze an essential step in the formation of all classes of active steroid hormones. We have recently shown that 3beta-HSD type 1 gene expression is specifically induced by interleukin (IL)-4 and IL-13 in several human cancer cell lines and in normal human mammary and prostatic epithelial cells in primary culture. There is evidence that IL-4 stimulates bifurcating signaling pathways in which the Stat6-signal pathway is involved in differentiation and gene regulation, whereas insulin receptor substrate (IRS) proteins mediate the mitogenic action of IL-4. As a matter of fact, we have shown that IL-4-activated Stat6 in all cell lines studied, where IL-4 induced 3beta-HSD type 1 expression but not in those cell lines that failed to respond to IL-4. The mechanism of the induction of 3beta-HSD type 1 gene expression was further characterized in ZR-75-1 human breast cancer cells. We have also found that IL-4 rapidly induced IRS-1 and IRS-2 phosphorylation in these cell lines. Moreover, insulin-like growth factor (IGF)-1 and insulin, which are well known to cause IRS-1 and IRS-2 phosphorylation, increased the stimulatory effect of IL-4 on 3beta-HSD activity. IRS-1 and IRS-2 are adapter molecules that provide docking sites for different SH2 domain-containing proteins, leading to the activation of multiple pathways, such as the phosphatidylinositol (PI) 3-kinase and the mitogen-activated protein (MAP) pathways. The inhibition of IL-4-induced 3beta-HSD expression by PI 3-kinase inhibitors (wortmannin and LY294002) as well as an inhibitor of MAP kinase activation (PD98059), indicates the involvement of those pathways in this response to IL-4. Wortmannin also blocked MAP kinase activation by IL-4, insulin and IGF-1 suggesting that the MAP kinase cascade acts as a downstream effector of PI 3-kinases. Furthermore, we showed that the PKC activator phorbol-12-myristate-13-acetate (PMA) also potentiated the IL-4-induced 3beta-HSD activity, thus suggesting that one signaling molecule that is involved in the signal transduction of the IL-4 action on 3beta-HSD type 1 expression is also a substrate for PKC. Taken together, these findings suggest the existence of a novel mechanism of gene regulation by IL-4. This mechanism would involve in the phosphorylation of IRS-1 and IRS-2, which transduce the IL-4 signal through a PI 3-kinase- and MAP kinase-dependent signaling pathway. However, the inability of IGF-1, insulin and PMA to stimulate 3beta-HSD type 1 expression by themselves in the absence of IL-4 indicates that the multiple pathways downstream of IRS-1 and IRS-2 must act in cooperation with an IL-4-specific signaling molecule, such as the transcription factor Stat6. It is also of interest to note that there also appear to be differences between the regulation of the 3beta-HSD type 1 and type 2 promoters.

IL-4-activated STAT-6 inhibits IFN-gamma-induced CD40 gene expression in macrophages/microglia

The antagonism between the cytokines IFN-gamma and IL-4 is well documented, but the mechanism by which IL-4 inhibits IFN-gamma-induced gene expression is not clearly understood. CD40 is a type I transmembrane protein that is critical for proper functioning of the immune system. We have previously shown that IFN-gamma is the most potent inducer of CD40 expression by macrophages and microglia. In this report, we describe the molecular mechanisms by which IL-4 inhibits IFN-gamma-induced CD40 expression. IL-4 suppresses IFN-gamma-induced CD40 gene expression in both macrophages and microglia, and such inhibition is dependent on the activation of STAT-6. Nuclear run-on and transfection studies indicate that IL-4-mediated repression is at the transcriptional level. Furthermore, IL-4 inhibition of IFN-gamma-induced CD40 expression is specific, since IL-4 does not inhibit IFN-gamma-induced IFN-responsive factor-1 gene expression. Site-directed mutagenesis studies demonstrate that two STAT binding sites, named proximal and distal IFN-gamma-activated sequences, in the human CD40 promoter are important for IL-4 inhibition of IFN-gamma-induced CD40 promoter activity. Moreover, EMSAs indicate that IL-4-activated STAT-6 binds to these two STAT binding sites. These results suggest that IL-4 inhibition of IFN-gamma-induced CD40 gene expression is mediated by direct STAT-6 binding to the CD40 promoter.

Unusual interleukin-4 and -13 signaling in human normal and tumor lung fibroblasts

IL-4 and IL-13 act on human lung fibroblasts through specific receptors differing in their composition. Indeed, the gammac chain is constitutively expressed in tumor lung myofibroblast but not in normal cells. Here, we have analysed the signal transduction induced by IL-4 and IL-13 in both cell types, in order to better understand the molecular mechanisms underlying tumor stromal development. The IL-4Ralpha chain is constitutively phosphorylated and pre-associated with the JAK1 protein in both cell types. In normal cells, we detected the activation of the classic IRS-2 or JAK1/STAT6 pathways, the phosphorylation of JAK2, while Tyk2 was constitutively phosphorylated and not modified by both cytokines. In addition to these pathways, in lung tumor myofibroblasts, IL-4 and IL-13 induced the phosphorylation of JAK3 and increased the phosphorylation of Tyk2. Interestingly, in both cell types IL-4 and IL-13 triggered an unusual pattern of STAT1 and STAT3 activation. These events probably correspond to a tissue-specific signaling important for the immunoregulatory functions of airways fibroblasts. Indeed, the inflammatory-like pattern of STATs signaling triggered by IL-4 and IL-13 in these cells may favor the homing of inflammatory and/or metastatic cells. In lung myofibroblasts, these properties could be modified through the different pattern of JAK activation.

Transient inhibition of interleukin 4 signaling by T cell receptor ligation

Interleukin (IL)-4 and IL-12 together with T cell receptor (TCR) engagement are crucial for the differentiation of CD4(+) T cells into T helper (Th)2 or Th1 cells, respectively. Although IL-4 receptors (IL-4Rs) but not IL-12Rs are expressed on naive CD4(+) T cells, IL-4 has no apparent advantage over IL-12 in driving naive T cell differentiation when the cells are primed with both IL-4 and IL-12 in vitro. It was found that IL-4-induced phosphorylation of Janus kinases 1 and 3, IL-4R alpha, signal transducer and activator of transcription 6, and insulin receptor substrate 2 was strikingly but transiently inhibited by TCR ligation both in conventional and TCR transgenic T cells. TCR engagement also blocked the expression of an IL-4-inducible gene. Signals induced by other cytokines, including IL-2, IL-6, and interferon alpha, but not by insulin-like growth factor 1, were also blocked by TCR engagement. The capacity of various inhibitors to reverse TCR-mediated inhibition of IL-4 signaling suggested that activation of the Ras-mitogen-activated protein kinase pathway and of the calcineurin pathway contribute to desensitizing IL-4R. IL-4 responsiveness returned at about the time ( approximately 12 h) that IL-12-mediated signaling was first observed. Thus, through different mechanisms, neither IL-4R nor IL-12R has any clear advantage in polarizing cells; rather, the availability of cytokine is probably the limiting factor in this process.

IL-4-dependent induction of BCL-2 and BCL-X(L)IN activated T lymphocytes through a STAT6- and pi 3-kinase-independent pathway

Both B and T lymphocytes require ongoing signals to maintain their viability. The pleiotropic cytokine interleukin (IL-) 4 plays an important role in the maintenance of activated T cells, perhaps reflecting induction of the anti-apoptotic genes Bcl-2 and Bcl-X(L). However, it is not known which of the signalling pathways known to link the IL-4 receptor with transcription regulation are required, or if the levels of Bcl-2/X induction under such physiologic conditions are sufficient to account for the anti-apoptotic effects of IL-4. We report here that although blockade of pathways (PI 3-kinase and pp70 S6 kinase) recruited by the IRS-1/2 adaptor proteins inhibited the anti-apoptotic function of IL-4, Bcl-2/X induction were normal. These findings were recapitulated in primary and culture-adapted T cells whose Stat6 signalling pathway also was defective. These results demonstrate that both the Stat6 and PI 3-kinase pathways can be dispensable for Bcl-2/X induction by IL-4, thus suggesting the involvement of an additional signal transduction pathway. Moreover, the preservation of Bcl-2/X induction despite inhibition of the anti-apoptotic function of IL-4 indicates that this cytokine activates additional protective mechanisms.

IL-4 regulation of IL-6 production involves Rac/Cdc42- and p38 MAPK-dependent pathways in keratinocytes

The stress-activated pathways leading to activation of p38 MAP kinase (p38 MAPK) and c-jun N-terminal kinases (JNK) have been shown to be activated by pro-inflammatory cytokines, physical and chemical stresses as well as a variety of hematopoietic growth factors. One exception is interleukin (IL)-4, which does not activate this pathway in hematopoietic cell. We report here that in A431, a keratinocytic cell line, IL-4 activates Rac and Cdc42 and their downstream effector p21-activated kinase (PAK). Rac and Cdc42 appear to regulate a protein kinase cascade initiated at the level of PAK and leading to activation of p38 MAPK, since IL-4 stimulates tyrosine phosphorylation of p38 MAPK and increases its catalytic activity. As A431 cells are able to produce IL-6 in response to IL-4 stimulation, we assessed the involvement of p38 MAPK in IL-6 gene expression. A pyrimidazole compound, SB203580, a specific inhibitor of p38 MAPK, inhibits production and gene expression of IL-6. SB203580 reduced significantly the stability of IL-6 mRNA. Here we provide evidence that p38 MAPK is activated in response to IL-4 and is involved in IL-6 synthesis by stabilizing IL-6 mRNA.

Possible involvement of Shc in IL-4-induced germline epsilon transcription in a human B cell line

The IL-4Ralpha contains the I4R motif which binds to the phosphotyrosine binding domain of several adaptor proteins, including IRS-1/2 and Shc. Although the involvement of IRS-1/2 in IL-4-induced PI3-kinase activation is known, there is little information on the role of Shc in IL-4 signaling. In this study, we found the preferential utilization of Shc by the IL-4Ralpha in a human Burkitt's B lymphoma cell line, DND39. IL-4 induced the association of tyrosine-phosphorylated Shc with the IL-4Ralpha, whereas no detectable tyrosine phosphorylation of IRS-1 or IRS-2 was induced. IL-4-induced germline epsilon promoter activation was enhanced by overexpression of Shc and was inhibited by truncated Shc lacking the collagen-homologous domain. We further found the association of Shc with PLCgamma1. Although direct tyrosine phosphorylation of PLCgamma1 was not detectable, the amount of PLCgamma1 coprecipitable with anti-phosphotyrosine was increased after IL-4 stimulation. These results suggest that Shc can function as an adaptor protein of the IL-4Ralpha and mediate the germline epsilon transcription.

Biologic functions and signaling of the interleukin-4 receptor complexes

IL-4 is a pleiotropic cytokine which plays a pivotal role in shaping immune responses. The effects of IL-4 are mediated after binding to high affinity receptor complexes present on hematopoietic as well as non-hematopoietic cells. This review will summarize the current knowledge on the molecular structure of the different types of IL-4 receptor (IL-4R) complexes as well as the signal transduction mechanisms induced by IL-4 leading to cellular proliferation and / or gene activation. IL-4 effects are modulated by soluble forms of the respective receptor molecules which are produced by several immune cells in a regulated manner. The biological impact of recently described IL-4R allotypes of mice and humans as well as the results of studies with IL-4R knockout mice will be particularly emphasized.

Binding of IL-4 to the IL-13Ralpha(1)/IL-4Ralpha receptor complex leads to STAT3 phosphorylation but not to its nuclear translocation

Interleukin-4 (IL-4) is a pleiotropic cytokine, which acts on both hematopoietic and non-hematopoietic cells, through different types of receptor complexes. In this study, we report that in human B cells, IL-4 caused rapid phosphorylation of Janus kinase (JAK) 1 and JAK3 tyrosine kinases. In keratinocytes, the hematopoietic-specific receptor common gamma(c) chain is not expressed and the IL-13 receptor alpha(1) (IL-13Ralpha(1)) participates in IL-4 signal transduction. In keratinocytes, IL-4 induced JAK1 and JAK2 phosphorylation but, unlike in immune cells, IL-4 did not involve JAK3 activation for its signaling. In both cell types, IL-4 induced phosphorylation and DNA binding activation of the signal transducer and activator of transcription (STAT) 6 protein. Furthermore, IL-4 stimulation of keratinocytes also induced tyrosine phosphorylation of STAT3 which was found to bind to the phosphorylated IL-13Ralpha(1). STAT3 however did not significantly translocate to the nucleus, nor did it bind with high affinity to target DNA sequences.

The IL-4 receptor: signaling mechanisms and biologic functions

Interleukin-4 is a multifunctional cytokine that plays a critical role in the regulation of immune responses. Its effects depend upon binding to and signaling through a receptor complex consisting of the IL-4R alpha chain and the common gamma chain (gamma c), resulting in a series of phosphorylation events mediated by receptor-associated kinases. In turn, these cause the recruitment of mediators of cell growth, of resistance to apoptosis, and of gene activation and differentiation. Here we describe our current understanding of the organization of the IL-4 receptor, of the signaling pathways that are induced as a result of receptor occupancy, and of the various mechanisms through which receptor function is modulated. We particularly emphasize the modular nature of the receptor and the specialization of different receptor regions for distinct functions, most notably the independent regulation of cell growth and gene activation.

Insulin-like growth factor I synergizes with interleukin 4 for hematopoietic cell proliferation independent of insulin receptor substrate expression

In the present study, we investigated the potential role of insulin-like growth factor I (IGF-I) receptor (IGF-IR) in cell proliferation by overexpressing it in 32D myeloid progenitor cells. The overexpression of IGF-IR caused the transfectants to proliferate in response to IGF-I in the absence of insulin receptor substrate (IRS) expression. The activation of overexpressed wild-type IGF-IR, but not that of an ATP-binding mutant of IGF-IR, resulted in the increased tyrosine phosphorylation of several intracellular proteins, including SHC, Src homology 2-containing inositol-5-phosphatase, protein kinase C-delta, and Erk2. Grb2 association with SHC and mitogen-activated protein kinase (MAPK) activity was also enhanced in response to IGF-I stimulation. Interestingly, the stimulation of the IGF-IR transfectants with interleukin 4 (IL-4) also resulted in strong mitogenesis independent of IRS expression. Moreover, IGF-I and/or IL-4 induced long-term cell growth of the IGF-IR transfectants. IL-4 was able to synergize with IGF-I for DNA synthesis, even in the parental 32D cells and a pro-B-cell line, Baf3, indicating the physiological importance of the two growth factors in hematopoietic cell proliferation. IL-4 stimulation of the IGF-IR transfectants resulted in enhanced tyrosine phosphorylation of SHC, Erk2, and signal transducer and activator of transcription 6 (STAT6) proteins. Both IL-4 and IGF-I were able to induce c-myc early response gene expression, and this expression was maximal in the presence of both factors. Finally, we demonstrated that a MAPK kinase inhibitor was able to suppress mitogenesis of the IGF-IR transfectants in response to IGF-I and/or IL-4. Together, our results suggest that IL-4 synergizes with IGF-I for hematopoietic cell proliferation, likely through cross talk between SHC/Grb2/MAPK and STAT6 pathways and through c-myc gene up-regulation.

IL-3 and IL-4 Activate Cyclic Nucleotide Phosphodiesterases 3 (PDE3) and 4 (PDE4) by Different Mechanisms in FDCP2 Myeloid Cells

In FDCP2 myeloid cells, IL-4 activated cyclic nucleotide phosphodiesterases PDE3 and PDE4, whereas IL-3, granulocyte-macrophage CSF (GM-CSF), and phorbol ester (PMA) selectively activated PDE4. IL-4 (not IL-3 or GM-CSF) induced tyrosine phosphorylation of insulin-receptor substrate-2 (IRS-2) and its association with phosphatidylinositol 3-kinase (PI3-K). TNF-α, AG-490 (Janus kinase inhibitor), and wortmannin (PI3-K inhibitor) inhibited activation of PDE3 and PDE4 by IL-4. TNF-α also blocked IL-4-induced tyrosine phosphorylation of IRS-2, but not of STAT6. AG-490 and wortmannin, not TNF-α, inhibited activation of PDE4 by IL-3. These results suggested that IL-4-induced activation of PDE3 and PDE4 was downstream of IRS-2/PI3-K, not STAT6, and that inhibition of tyrosine phosphorylation of IRS molecules might be one mechnism whereby TNF-α could selectively regulate activities of cytokines that utilized IRS proteins as signal transducers. RO31-7549 (protein kinase C (PKC) inhibitor) inhibited activation of PDE4 by PMA. IL-4, IL-3, and GM-CSF activated mitogen-activated protein (MAP) kinase and protein kinase B via PI3-K signals; PMA activated only MAP kinase via PKC signals. The MAP kinase kinase (MEK-1) inhibitor PD98059 inhibited IL-4-, IL-3-, and PMA-induced activation of MAP kinase and PDE4, but not IL-4-induced activation of PDE3. In FDCP2 cells transfected with constitutively activated MEK, MAP kinase and PDE4, not PDE3, were activated. Thus, in FDCP2 cells, PDE4 can be activated by overlapping MAP kinase-dependent pathways involving PI3-K (IL-4, IL-3, GM-CSF) or PKC (PMA), but selective activation of PDE3 by IL-4 is MAP kinase independent (but perhaps IRS-2/PI3-K dependent).

Signal transduction through cytokine receptors

Receptors for interleukins, colony stimulating factors, and hormones have a homology in their extracellular regions, characterized by the conserved cysteine residues and the tryptophan-serine-x-tryptophan-serine motif, thus, they are classified to the type 1 cytokine receptor superfamily. Janus tyrosine kinase (JAKs) have been found to be involved in the signal transduction through type I cytokine receptors. JAKs associate with the membrane proximal region in the cytoplasmic domain having box1 and box2, which are conserved among the family, and upon the stimulation JAKs can be aggregated following the receptor dimerization and activated probably by transphosphorylation. JAKs then phosphorylate the receptor and various signal transducing molecules, including STATs (signal transducer and activator of transcriptions) and other SH2-containing adapter molecules. STATs were initially identified as transcription factors containing a SH2 domain and regulating interferons-inducible genes. STATs can be tyrosine phosphorylated by JAKs and form dimer (either hetero- or homo-dimers) to enter the nucleus, resulting in the expression of a set of genes. On the other hand, adapter molecules such as Shc, GRB2, and SHP-2 have been shown to link the cytokine receptors to Ras, followed by the activation of the Raf-MEK-MAP kinase pathway, leading to the activation of various transcription factors in the nucleus. These two signals are generated by different ways upon the stimulation of the receptors and they elicit a variety of biological functions in various cell types. In this review, we will discuss the mechanism by which cytokines activate JAKs, STATs, and a variety of adapter molecules. We further discuss the roles of each signal transduction pathways in the expression of biological activities of cytokines.

Molecular cloning and characterization of the human p44 mitogen-activated protein kinase gene

The complete genomic structure of the human p44(mapk) gene (HMGW-approved symbol PRKM3) has been determined. The gene covers 9 kb and is composed of nine exons and eight introns. This structure is identical to the previously reported mouse p44(mapk) gene, indicating a high degree of evolutionary conservation. A sequence differing by one nucleotide from the consensus TATA box is present 132 positions upstream of the main transcription initiation point. This point has been located 415 nucleotides upstream of the translation initiation codon ATG and perfectly meets the consensus criteria for an initiator element (Inr). Multiple consensus sequences for factors that regulate either basal transcription or gene expression during cell differentiation and proliferation can be found in the putative promoter region. Some of them, such as several G/C boxes located downstream from the transcription initiation point, are also present in the homologous mouse gene, where they were shown to be functional.

Genistein analogues: effects on epidermal growth factor receptor tyrosine kinase and on stress-activated pathways

Two genistein analogues (MD831 and MD833) have been synthesized and analyzed for their biological properties and their mechanism of action im comparison to genistein either in vitro or in intact cells. We showed that, in vitro, one of these compounds (MD831) inhibits the tyrosine kinase activity associated with the epidermal growth factor receptor (EGFR) as efficiently as genistein. However, treatment of A431 cells with these compounds did not result in any significant modification of EGFR tyrosine phosphorylation. Extracellular-signal regulated kinase (ERK) phosphorylation in cells stimulated by EGF was enhanced in the presence of MD831, whereas the other compounds, genistein and MD833, were able to activate the c-jun N-terminal kinase (JNK). This study showed that two structurally related compounds could elicit markedly different pharmacological effects on two signalling pathways, one involved in the mitogenic response and the other in the stress response. Such compounds may be useful to characterize signalling events involved in cell response to physiological stimuli.

Comparison of the transactivation domains of Stat5 and Stat6 in lymphoid cells and mammary epithelial cells

Stat (signal transducers and activators of transcription) and Jak (Janus kinases) proteins are central components in the signal transduction events in hematopoietic and epithelial cells. They are rapidly activated by various cytokines, hormones, and growth factors. Upon ligand binding and cytokine receptor dimerization, Stat proteins are phosphorylated on tyrosine residues by Jak kinases. Activated Stat proteins form homo- or heterodimers, translocate to the nucleus, and induce transcription from responsive genes. Stat5 and Stat6 are transcription factors active in mammary epithelial cells and immune cells. Prolactin activates Stat5, and interleukin-4 (IL-4) activates Stat6. Both cytokines are able to stimulate cell proliferation, differentiation, and survival. We investigated the transactivation potential of Stat6 and found that it is not restricted to lymphocytes. IL-4-dependent activation of Stat6 was also observed in HC11 mammary epithelial cells. In these cells, Stat6 activation led to the induction of the beta-casein gene promoter. The induction of this promoter was confirmed in COS7 cells. The glucocorticoid receptor was able to further enhance IL-4-induced gene transcription through the action of Stat6. Deletion analysis of the carboxyl-terminal region of Stat6 and recombination of this region with a heterologous DNA binding domain allowed the delimitation and characterization of the transactivation domain of Stat6. The potencies of the transactivation domains of Stat5, Stat6, and viral protein VP16 were compared. Stat6 had a transactivation domain which was about 10-fold stronger than that of Stat5. In pre-B cells (Ba/F3), the transactivation domain of Stat6 was IL-4 regulated, independently from its DNA binding function.