Desensitization of signaling by oncostatin M in human vascular cells involves cytoplasmic Tyr residue 759 in gp130 but is not mediated by either Src homology 2 domain-containing tyrosine phosphatase 2 or suppressor of cytokine signaling 3

Human Cytomegalovirus Immediate-Early 1 Protein Rewires Upstream STAT3 to Downstream STAT1 Signaling Switching an IL6-Type to an IFNγ-Like Response

The human cytomegalovirus (hCMV) major immediate-early 1 protein (IE1) is best known for activating transcription to facilitate viral replication. Here we present transcriptome data indicating that IE1 is as significant a repressor as it is an activator of host gene expression. Human cells induced to express IE1 exhibit global repression of IL6- and oncostatin M-responsive STAT3 target genes. This repression is followed by STAT1 phosphorylation and activation of STAT1 target genes normally induced by IFNγ. The observed repression and subsequent activation are both mediated through the same region (amino acids 410 to 445) in the C-terminal domain of IE1, and this region serves as a binding site for STAT3. Depletion of STAT3 phenocopies the STAT1-dependent IFNγ-like response to IE1. In contrast, depletion of the IL6 receptor (IL6ST) or the STAT kinase JAK1 prevents this response. Accordingly, treatment with IL6 leads to prolonged STAT1 instead of STAT3 activation in wild-type IE1 expressing cells, but not in cells expressing a mutant protein (IE1dl410-420) deficient for STAT3 binding. A very similar STAT1-directed response to IL6 is also present in cells infected with a wild-type or revertant hCMV, but not an IE1dl410-420 mutant virus, and this response results in restricted viral replication. We conclude that IE1 is sufficient and necessary to rewire upstream IL6-type to downstream IFNγ-like signaling, two pathways linked to opposing actions, resulting in repressed STAT3- and activated STAT1-responsive genes. These findings relate transcriptional repressor and activator functions of IE1 and suggest unexpected outcomes relevant to viral pathogenesis in response to cytokines or growth factors that signal through the IL6ST-JAK1-STAT3 axis in hCMV-infected cells. Our results also reveal that IE1, a protein considered to be a key activator of the hCMV productive cycle, has an unanticipated role in tempering viral replication.

Our previous work has shown that the human cytomegalovirus (hCMV) major immediate-early 1 protein (IE1) modulates host cell signaling pathways involving proteins of the signal transducer and activator of transcription (STAT) family. IE1 has also long been known to facilitate viral replication by activating transcription. In this report we demonstrate that IE1 is as significant a repressor as it is an activator of host gene expression. Many genes repressed by IE1 are normally induced via STAT3 signaling triggered by interleukin 6 (IL6) or related cytokines, whereas many genes activated by IE1 are normally induced via STAT1 signaling triggered by interferon gamma (IFNγ). Our results suggest that the repression of STAT3- and the activation of STAT1-responsive genes by IE1 are coupled. By targeting STAT3, IE1 rewires upstream STAT3 to downstream STAT1 signaling. Consequently, genes normally induced by IL6 are repressed while genes normally induced by IFNγ become responsive to IL6 in the presence of IE1. We also demonstrate that, by switching an IL6 to an IFNγ-like response, IE1 tempers viral replication. These results suggest an unanticipated dual role for IE1 in either promoting or limiting hCMV propagation and demonstrate how a key viral regulatory protein merges two central cellular signaling pathways to divert cytokine responses relevant to hCMV pathogenesis.

The inflammatory mediator oncostatin M induces angiopoietin 2 expression in endothelial cells in vitro and in vivo

OBJECTIVES

Members of the glycoprotein 130 (gp130) receptor-gp130 ligand family play a role in angiogenesis in different tissues. We tested the effect of this cytokine family on the angiopoietin (Ang)-Tie system, which is involved in blood vessel maturation, stabilization, and regression.

RESULTS

Oncostatin M (OSM) increased Ang2 expression in human umbilical vein endothelial cells via Janus kinase/signal transducer and activator of transcription (JAK/STAT) and mitogen-activated protein (MAP) kinase activation. Furthermore, OSM induced Ang2 expression in macrovascular endothelial cells isolated from the human aorta and in microvascular endothelial cells isolated from human heart. Our in vivo experiments revealed that mRNA expression of Ang2 in hearts of mice injected with OSM increased significantly, and levels of OSM mRNA significantly correlated with mRNA levels of Ang2 in human hearts. In addition, OSM increased the expression of its own receptors, gp130 and OSM receptor, in endothelial cells in vitro and in mice in vivo, and levels of OSM mRNA significantly correlated with mRNA levels of gp130 and OSM receptor in human hearts.

CONCLUSION

Our data, showing the effects of OSM on the Ang-Tie system in endothelial cells, in hearts of mice, and in human heart tissue, provide yet another link between inflammation and angiogenesis.

Regulation of arterial-venous differences in tumor necrosis factor responsiveness of endothelial cells by anatomic context

We analyzed tumor necrosis factor (TNF) responses of human umbilical artery and vein endothelial cells (HUAECs and HUVECs) in organ and cell culture. In organ culture, TNF induced expression of E-selectin, VCAM-1, and ICAM-1 on HUVECs but only ICAM-1 on HUAECs. Activation of nuclear factor-kappaB, c-jun, and ATF2 by TNF was comparable in HUAECs and HUVECs, whereas binding of transcription factors and p300 co-activator to the E-selectin enhancer was lower in HUAECs compared to HUVECs. In cell culture, HUAECs rapidly acquired inducible E-selectin and VCAM-1 whereas ICAM-1 inducibility decreased. Culture of HUVECs rapidly decreased TNF responses of all three genes. By 72 hours in cell culture, TNF-treated HUVECs and HUAECs showed comparable adhesion molecule induction and transcription factor binding to the E-selectin enhancer. Freshly isolated HUAECs expressed higher levels of Kruppel-like factor 2 (KLF2) than HUVECs, consistent with greater KLF2 induction by arterial levels of shear stress in vitro. KLF2 expression decreased rapidly in both cell types during culture. Transduction of HUVECs with KLF2 reduced TNF-mediated induction of E-selectin and VCAM-1 while increasing ICAM-1 induction and reduced transcription factor/co-activator binding to the E-selectin enhancer. In conclusion, the differential responses of HUAECs and HUVECs to TNF in organ culture correlate with transcription factor/co-activator binding to DNA and converge during cell culture. Flow-induced expression of KLF2 contributes to the in situ responses of HUAECs but not of HUVECs.

Signal transducer and activator of transcription 3 involvement in the development of renal interstitial fibrosis after unilateral ureteral obstruction

BACKGROUND

In vitro studies suggest that the signal transducer and activator of transcription (STAT) plays a critical role in renal fibrosis. However, the process of STAT activation in vivo remains unclear. This study in rats aimed to localize STAT3 activation within the kidney and examine the in vivo relationship between STAT3 activation and renal fibrosis.

METHODS

Unilateral ureteral obstruction (UUO) was induced in the rats and the kidneys examined 3 or 7 days after obstruction. Activation of STAT3 in western blot and immunohistochemical analyses was identified by the phosphorylated form of STAT3 (pSTAT3).

RESULTS

Myofibroblasts were identified by alpha-smooth muscle actin expression and were upregulated in obstructed kidneys. pSTAT3 was localized mainly in tubular epithelial cells of collecting ducts in normal and obstructed kidneys and interstitial cells in obstructed kidneys. After UUO, western blotting showed a fourfold increase in pSTAT3, with a peak at day 7. Immunostaining showed a sixfold increase in pSTAT3 at day 7 in tubular epithelial cells and a 2500-fold increase at day 7 in interstitial cells.

CONCLUSION

STAT3 was activated in rat tubular epithelial cells and myofibroblasts after UUO, suggesting that STAT3 may contribute to the progression of interstitial fibrosis.

PECAM-1 modulates thrombin-induced tissue factor expression on endothelial cells

Platelet endothelial cell adhesion molecule-1 (PECAM-1) (CD31) is known to inhibit platelet function and thrombus formation. The mechanisms involved in PECAM-1's roles as a modulator of hemostasis are still not completely understood. We examined the role of PECAM-1 as a regulator of tissue factor (TF) expression, a known important inducer of thrombosis. Wildtype and CD31KO mice underwent transient (30 min) renal ischemia followed by 24 h re-perfusion and their kidneys assessed for apoptosis, fibrin formation, and tissue factor expression. CD31KO mice exhibited increased tubular epithelial and endothelial apoptosis, increased fibrin deposition, and tissue factor expression. Human umbilical vein endothelial cells (HUVEC) transfected with antisense (AS) PECAM-1 oligonucleotides to downregulate PECAM-1 expression, exhibited greater induction of TF mRNA and protein expression as well as increased expression and nuclear localization of the transcription factor Egr-1 compared to scrambled AS PECAM-1 (Scr)-treated HUVEC following thrombin stimulation. TF induction was found to be mediated through thrombin receptor PAR-1 and the Galphai/o subunit of G-protein, confirmed by PAR-1 antagonist and pertussis toxin inhibition respectively. Thrombin-mediated TF induction was dependent on Rho Kinase activity, phosphorylation of p38(MAPK) and p85 & Akt dephosphorylation. The inverse correlation of PI3K-Akt phosphorylation with p38 (MAPK) phosphorylation was confirmed by pharmacological inhibition. These studies suggest that PECAM-1 is involved in regulating a signaling pathway, affecting PI3K and Akt activation, p38 (MAPK) phosphorylation, which in turn, affects Egr-1 expression and nuclear translocation, ultimately affecting TF expression. These findings provide new insights into the action of PECAM-1 as a modulator of thrombosis.

Exchange protein activated by cyclic AMP (Epac)-mediated induction of suppressor of cytokine signaling 3 (SOCS-3) in vascular endothelial cells

Here, we demonstrate that elevation of intracellular cyclic AMP (cAMP) in vascular endothelial cells (ECs) by either a direct activator of adenylyl cyclase or endogenous cAMP-mobilizing G protein-coupled receptors inhibited the tyrosine phosphorylation of STAT proteins by an interleukin 6 (IL-6) receptor trans-signaling complex (soluble IL-6Ralpha/IL-6). This was associated with the induction of suppressor of cytokine signaling 3 (SOCS-3), a bona fide inhibitor in vivo of gp130, the signal-transducing component of the IL-6 receptor complex. Attenuation of SOCS-3 induction in either ECs or SOCS-3-null murine embryonic fibroblasts abolished the inhibitory effect of cAMP, whereas inhibition of SHP-2, another negative regulator of gp130, was without effect. Interestingly, the inhibition of STAT phosphorylation and SOCS-3 induction did not require cAMP-dependent protein kinase activity but could be recapitulated upon selective activation of the alternative cAMP sensor Epac, a guanine nucleotide exchange factor for Rap1. Consistent with this hypothesis, small interfering RNA-mediated knockdown of Epac1 was sufficient to attenuate both cAMP-mediated SOCS-3 induction and inhibition of STAT phosphorylation, suggesting that Epac activation is both necessary and sufficient to observe these effects. Together, these data argue for the existence of a novel cAMP/Epac/Rap1/SOCS-3 pathway for limiting IL-6 receptor signaling in ECs and illuminate a new mechanism by which cAMP may mediate its potent anti-inflammatory effects.

Oncostatin M receptor-mediated signal transduction is negatively regulated by SOCS3 through a receptor tyrosine-independent mechanism

Down-regulation of interleukin (IL)-6-type cytokine signaling has been shown to occur, among other mechanisms, via induction of the feedback inhibitor SOCS3 (suppressor of cytokine signaling 3). Binding of SOCS3 to the phosphorylated Tyr(759) in the cytoplasmic region of gp130, the common signal transducing receptor chain of all IL-6-type cytokines, is necessary for inhibition of Janus kinase-mediated signaling. In the present study, we analyzed the effect of SOCS3 on signal transduction by the proinflammatory cytokine oncostatin M (OSM), which signals through a receptor complex of gp130 and the OSM receptor (OSMR). OSM leads to a much stronger and prolonged induction of SOCS3 in HepG2 hepatoma cells and murine embryonal fibroblasts (MEF) compared with IL-6. A negative effect of SOCS3 on OSM signaling was confirmed using MEF cells lacking SOCS3. We can show that the OSMR-mediated signaling is inhibited by SOCS3 to a similar extent as previously described for gp130. However, the inhibition occurs independent of tyrosine motifs within the OSMR. Instead, SOCS3 interacts directly with JAK1 in a stimulation-dependent manner, a mechanism so far only known for SOCS1.

Transformation of human bronchial epithelial cells alters responsiveness to inflammatory cytokines

BACKGROUND

Inflammation is commonly associated with lung tumors. Since inflammatory mediators, including members of the interleukin-6 (IL-6) cytokine family, suppress proliferation of normal epithelial cells, we hypothesized that epithelial cells must develop mechanisms to evade this inhibition during the tumorigenesis. This study compared the cytokine responses of normal epithelial cells to that of premalignant cells.

METHODS

Short-term primary cultures of epithelial cells were established from bronchial brushings. Paired sets of brushings were obtained from areas of normal bronchial epithelium and from areas of metaplastic or dysplastic epithelium, or areas of frank endobronchial carcinoma. In 43 paired cultures, the signalling through the signal transducer and activator of transcription (STAT) and extracellular regulated kinase (ERK) pathways and growth regulation by IL-6, leukemia inhibitory factor (LIF), oncostatin M (OSM), interferon-gamma (IFNgamma) or epidermal growth factor (EGF) were determined. Inducible expression and function of the leukemia inhibitory factor receptor was assessed by treatment with the histone deacetylase inhibitor depsipeptide.

RESULTS

Normal epithelial cells respond strongly to OSM, IFNgamma and EGF, and respond moderately to IL-6, and do not exhibit a detectable response to LIF. In preneoplastic cells, the aberrant signaling that was detected most frequently was an elevated activation of ERK, a reduced or increased IL-6 and EGF response, and an increased LIF response. Some of these changes in preneoplastic cell signaling approach those observed in established lung cancer cell lines. Epigenetic control of LIF receptor expression by histone acetylation can account for the gain of LIF responsiveness. OSM and macrophage-derived cytokines suppressed proliferation of normal epithelial cells, but reduced inhibition or even stimulated proliferation was noted for preneoplastic cells. These alterations likely contribute to the supporting effects that inflammation has on lung tumor progression.

CONCLUSION

This study indicates that during the earliest stage of premalignant transformation, a modified response to cytokines and EGF is evident. Some of the altered cytokine responses in primary premalignant cells are comparable to those seen in established lung cancer cell lines.

Induction of suppressor of cytokine signaling-3 by herpes simplex virus type 1 confers efficient viral replication

We showed previously that infection of herpes simplex virus type 1 (HSV-1) rapidly induced the suppressor of cytokine signaling-3 (SOCS3), a host negative regulator of the JAK/STAT pathway, in the amnion cell line FL. Thus, HSV-1 suppresses the interferon (IFN) signaling pathway at the step of IFN-induced phosphorylation of janus kinases during an early infection stage. In the present study, we examined SOCS3 induction by HSV-1 infection in several types of human cell lines. FL cells and the T-cell line CCRF-CEM strongly induced SOCS3 during HSV-1 infection. The virus rapidly propagated in both cell lines and produced a lytic infection. On the other hand, the monocytic cell lines U937 and THP-1, and the B-cell line AKATA showed neither SOCS3 induction nor suppression of IFN-induced STAT1 phosphorylation during HSV-1 infection. These cell lines resulted in a persistent or prolonged infection, which continuously produced a low titer of infectious virus. The induction of SOCS3 by HSV-1 should occur via STAT3 activation immediately after HSV-1 infection. SOCS3 induction was inhibited by the addition of a Jak3 inhibitor WHI-P131. Treatment with WHI-P131 or transfection of antisense oligonucleotides specific for SOCS3 dramatically suppressed replication of HSV-1 in FL cells. The suppression of viral replication by WHI-P131 was released in the presence of neutralizing anti-IFN-alpha and anti-IFN-beta antibodies. In conclusion, suppression of IFN signaling by HSV-1-induced SOCS3 is required for efficient replication and lytic infection of HSV-1. The SOCS3 induction varied among cell lines, indicating that it is an important factor determining the cell type specificity of efficient HSV-1 replication.

Cross-talk among gp130 cytokines in adipocytes

The interleukin-6 (IL-6) family of cytokines is a family of structurally and functionally related proteins, including IL-6, IL-11, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1). These proteins are also known as gp130 cytokines because they all share gp130 as a common transducer protein within their functional receptor complexes. Several of these cytokines (LIF, OSM, CNTF, and CT-1) also utilize the LIF receptor (LIFR) as a component of their receptor complex. We have shown that all of these cytokines are capable of activating both the JAK/STAT and p42/44 mitogen-activated protein kinase signaling pathways in 3T3-L1 adipocytes. By performing a variety of preincubation studies and examining the ability of these cytokines to activate STATs, ERKs, and induce transcription of SOCS-3 mRNA, we have also examined the ability of gp130 cytokines to modulate the action of their family members. Our results indicate that a subset of gp130 cytokines, in particular CT-1, LIF, and OSM, has the ability to impair subsequent signaling activity initiated by gp130 cytokines. However, IL-6 and CNTF do not exhibit this cross-talk ability. Moreover, our results indicate that the cross-talk among gp130 cytokines is mediated by the ability of these cytokines to induce ligand-dependent degradation of the LIFR, in a proteasome-independent manner, which coincides with decreased levels of LIFR at the plasma membrane. In summary, our results demonstrate that an inhibitory cross-talk among specific gp130 cytokines in 3T3-L1 adipocytes occurs as a result of specific degradation of LIFR via a lysosome-mediated pathway.

Oncostatin M: a pleiotropic cytokine in the central nervous system

Oncostatin M (OSM), a member of the interleukin-6 (IL-6) cytokine family, has yet to be well studied, especially in the context of the central nervous system (CNS). The biological functions of OSM are complex and variable, depending on the cellular microenvironment. Inflammatory responses and tumor development are among two of the major events that OSM is involved in. Although OSM levels remain low in the normal CNS, elevated expression occurs in pathological conditions. Therefore, it is crucial to understand the regulation of OSM to control its expression and/or its effects. Accumulating data demonstrate that OSM binds to specific receptor complexes, then activates two major signaling pathways: Janus Kinase-Signal Transducers and Activators of Transcription (JAK-STAT) and Mitogen-Activated Protein Kinase (MAPK), to regulate downstream events. In this review, we focus on the biological functions of OSM, the signaling pathways of OSM in the CNS, and OSM involvement in CNS diseases.

Human endothelial cells enhance human immunodeficiency virus type 1 replication in CD4+ T cells in a Nef-dependent manner in vitro and in vivo

Infected CD4+ T cells are the primary sites of human immunodeficiency virus type 1 (HIV-1) replication in vivo. However, signals from professional antigen-presenting cells (APCs), such as dendritic cells and macrophages, greatly enhance HIV-1 replication in T cells. Here, we report that in cocultures, vascular endothelial cells (ECs), which in humans can also serve as APCs, can enhance HIV-1 production of both CCR5- and CXCR4-utilizing strains approximately 50,000-fold. The observed HIV-1 replication enhancement conferred by ECs occurred only in memory CD4+ T cells, required expression of major histocompatibility complex class II (MHC-II) molecules by the ECs, and could not be conferred by fixed ECs, all of which are consistent with a requirement for EC-mediated T-cell activation via T-cell receptor (TCR) signaling. Deletion of nef (Nef-) decreased HIV-1 production by approximately 100-fold in T cells cocultured with ECs but had no effect on virus production in T cells cocultured with professional APCs or fibroblasts induced to express MHC-II. Human ECs do not express B7 costimulators, but Nef- replication in CD4(+)-T-cell and EC cocultures could not be rescued by anti-CD28 antibody. ECs act in trans to enhance wild-type but not Nef- replication and facilitate enhanced wild-type replication in naive T cells when added to T-cell or B-lymphoblastoid cell cocultures, suggesting that ECs also provide a TCR-independent signal to infected T cells. Consistent with these in vitro observations, wild-type HIV-1 replicated 30- to 50-fold more than Nef- in human T cells infiltrating allogeneic human skin grafts on human huPBL-SCID/bg mice, an in vivo model of T-cell activation by ECs. Our studies suggest that ECs, which line the entire cardiovascular system and are, per force, in frequent contact with memory CD4+ T cells, provide signals to HIV-1-infected CD4+ T cells to greatly enhance HIV-1 production in a Nef-dependent manner, a mechanism that could contribute to the development of AIDS.

Interferon α but Not Interleukin 12 Activates STAT4 Signaling in Human Vascular Endothelial Cells

STAT4 signaling, activated by either interleukin 12 (IL12) or interferon alpha (IFNalpha), promotes T(H)1 responses in CD4(+) T cells. Vascular endothelial cells (EC) may also become polarized in response to various cytokines, favoring recruitment and activation of T(H)1 or T(H)2 effector cells. Here we have investigated the role of the STAT4 pathway in EC. Cultured human umbilical vein EC (HUVEC) express low levels of STAT4, which may be tyrosine-phosphorylated by treatment with IFNalpha but not IL12. This is because HUVEC lack both subunits of the IL12 receptor (IL12Rbeta1 and IL12Rbeta2), even following treatment with various cytokines. IL12 phosphorylation of STAT4 can be observed in HUVEC that have been transduced to express the IL12R. To identify STAT4-induced genes we pursued three approaches: analysis by DNA microarray and quantitative RT-PCR (Q-PCR) of the IL12 responses in IL12R-transduced EC; analysis by Q-PCR of IFNalpha responses in STAT4-overexpressing EC; and analysis of IFNalpha responses in U3A neuroblastoma cell lines that express either STAT1 or STAT4, but not both. In all three instances we observe STAT4-mediated induction of the chemokine monocyte chemoattractant protein 1 (MCP1) and suppressor of cytokine signaling 3 (SOCS3) mRNA, and we confirm the production of each protein in both IL12R-transduced EC and STAT4-transduced U3A cells. These observations reveal that there is a STAT4 response of EC, activated by IFNalpha but not IL12, and that it may modulate the pro-inflammatory behavior of EC.

The role of the inhibitors of interleukin-6 signal transduction SHP2 and SOCS3 for desensitization of interleukin-6 signalling

The immediate early response of cells treated with IL-6 (interleukin-6) is the activation of the signal transducer and activator of transcription (STAT)3. The Src homology domain 2 (SH2)-containing protein tyrosine phosphatase SHP2 and the feedback inhibitor SOCS3 (suppressor of cytokine signalling) are potent inhibitors of IL-6 signal transduction. Impaired function of SOCS3 or SHP2 leads to enhanced and prolonged IL-6 signalling. The inhibitory function of both proteins depends on their recruitment to the tyrosine motif 759 within glycoprotein gp130. In contrast to inactivation, desensitization of signal transduction is regarded as impaired responsiveness due to prestimulation. Usually, after activation the sensing receptor becomes inactivated by modifications such as phosphorylation, internalization or degradation. We designed an experimental approach which allows discrimination between desensitization and inactivation of IL-6 signal transduction. We observed that pre-stimulation with IL-6 renders cells less sensitive to further stimulation with IL-6. After several hours, the cells become sensitive again. We show that not only signal transduction through previously activated receptors is affected by desensitization but signalling through receptors which were not targeted by the first stimulation was also attenuated ( trans -desensitization). Interestingly, in contrast to inhibition, desensitization does not depend on the presence of functional SHP2. Furthermore, cells lacking SOCS3 show constitutive STAT3 activation which is not affected by pre-stimulation with IL-6. All these observations suggest that desensitization and inhibition of signalling are mechanistically distinct.

IL-11 protects human microvascular endothelium from alloinjury in vivo by induction of survivin expression

IL-11 can reduce tissue injury in animal models of inflammation but the mechanism(s) is unknown. When C.B-17 SCID/beige mice bearing human skin grafts are injected i.p. with human PBMC allogeneic to the donor skin, infiltrating T cells destroy human microvessels by day 21. Intradermal injection of human IL-11 (500 ng/day) delays the time course of graft microvessel loss without reducing the extent of T cell infiltration. Protective actions of IL-11 are most pronounced on day 15. IL-11 has no effect on T cell activation marker, effector molecule, cytokine expression, or endothelial ICAM-1 expression. IL-11 up-regulates the expression of survivin, a cytoprotective protein, in graft keratinocytes and endothelial cells. Topical application of survivin antisense oligonucleotide down-regulates survivin expression in both cell types and largely abrogates the protective effect of IL-11. We conclude that in this human transplant model, IL-11 exerts a cytoprotective rather than anti-inflammatory or immunomodulatory effect mediated through induction of survivin.