Activation of a CrkL-stat5 signaling complex by type I interferons

Type I interferons (IFNalpha and IFNbeta) transduce signals by inducing tyrosine phosphorylation of Jaks and Stats, as well as the CrkL adapter, an SH2/SH3-containing protein which provides a link to downstream pathways that mediate growth inhibition. We report that Stat5 interacts constitutively with the IFN receptor-associated Tyk-2 kinase, and during IFNalpha stimulation its tyrosine-phosphorylated form acts as a docking site for the SH2 domain of CrkL. CrkL and Stat5 then form a complex that translocates to the nucleus. This IFN-inducible CrkL-Stat5 complex binds in vitro to the TTCTAGGAA palindromic element found in the promoters of a subset of IFN-stimulated genes. Thus, during activation of the Type I IFN receptor, CrkL functions as a nuclear adapter protein and, in association with Stat5, regulates gene transcription through DNA binding.

RANTES and MIP-1alpha activate stats in T cells

The chemokines RANTES (regulated on activation, normal T cell expressed and secreted) and MIP (macrophage inflammatory protein)-1alpha have been implicated in regulating T cell functions. RANTES-induced T cell activation is apparently mediated via two distinct signal transduction cascades: one linked to recruitment of pertussis toxin-sensitive G proteins and the other linked to protein-tyrosine kinase activation. In this report, we identified that the transcription factors Stat1 and Stat3 (for signal transducers and activators of transcription) are rapidly activated in T cells in response to RANTES and MIP-1alpha. Nuclear extracts from MOLT-4 and Jurkat T cells treated with RANTES or MIP-1alpha contain tyrosine-phosphorylated Stat1:1 and Stat1:3 dimers that exhibit DNA-binding activity. We demonstrated that RANTES and MIP-1alpha treatment of Jurkat cells resulted in transcriptional activation of a Stat-inducible gene, c-fos, with kinetics consistent with Stat activation by these chemokines. RANTES and MIP-1alpha mediate their effects via shared chemokine receptors (CCRs): CCR1, CCR4, and CCR5. Our data revealed a concordance between chemokine-induced Stat activation and c-fos induction and CCR4 and CCR5 expression. These findings indicate that chemokine-mediated activation of G-protein-coupled receptors leads to signal transduction that invokes intracellular phosphorylation intermediates used by other cytokine receptors.

The IRS-pathway operates distinctively from the Stat-pathway in hematopoietic cells and transduces common and distinct signals during engagement of the insulin or interferon-alpha receptors

Binding of interferon-alpha (IFN-alpha) to its receptor on hematopoietic cells activates the signal transducers and activators of transcription (Stat)- and insulin receptor substrate (IRS)-pathways, and regulates expression of antiproliferative and antiviral activities. However, it remains unknown whether these two pathways cooperate in the generation of IFN-alpha responses or function independently, and whether IRS-proteins transduce distinct downstream signals in response to IFNs or insulin/insulin-like growth factor (IGF)-1-mediated activation. Our data show that in response to IFN-alpha treatment, IRS-1 functions selectively as a docking protein for the SH2 domains of the p85 subunit of the PI 3'-kinase, but not the SH2 domain of Grb-2 which is engaged during insulin/IGF-1 signaling. In studies with THP-1 human myelomonocytic cells and 32D mouse myeloid cells, which are IRS-defective, we found that the IFN-alpha-regulated activation of Stat-1, Stat-2, and Stat-3 does not require the function of the IRS-system. Furthermore, THP-1 cells are responsive to the protective effect of IFN-alpha against vesicular stomatitis virus. Both 32D and THP-1 cells were resistant to the growth inhibitory effect of IFN-alpha, but this effect was not reversible by expression of IRS-1 or IRS-2 alone in 32D cells. Taken altogether these data show that: (1) The IRS-system transduces common and distinct signals in response to IFN-alpha or insulin/lGF-1 stimulation of hematopoietic cells. (2) The IRS-pathway operates separately from the Stat-pathway, and its function is not essential for the generation of the antiviral effect of IFN-alpha. (3) Neither the IRS- nor the Stat-pathways alone are sufficient to mediate the antiproliferative effects of IFN-alpha in hematopoietic cells, and additional signaling elements are required.

Interaction of p59fyn with interferon-activated Jak kinases

During IFN alpha stimulation, p59(fyn) associates with the Type I IFNR-associated Tyk-2 kinase in several human hematopoietic cell lines in vivo. This interaction is direct, and is mediated by the SH2 domain in p59(fyn), as shown by binding studies using glutathione-S-transferase fusion proteins and far western blots. Furthermore, in response to IFN alpha-treatment of cells, the SH2 domain of Fyn interacts with the Tyk-2-associated c-cbl proto-oncogene product. In a similar manner, during IFN gamma stimulation, p59(fyn) associates via its SH2 domain with the activated form of the IFN gamma-dependent Jak-2 kinase. These data suggest that p59(fyn) is a common element in IFN alpha and IFN gamma signaling, and is selectively engaged by the Type I or II IFN receptors via specific interactions with distinct Jak kinases.

Evidence for RANTES, monocyte chemotactic protein-1, and macrophage inflammatory protein-1 beta expression in Kawasaki disease

OBJECTIVE

Patients with Kawasaki disease mount an immune response directed to their abnormally stimulated vascular endothelium, that is associated with vascular inflammation and injury and a predisposition to arterial aneurysm formation. This suggests that specific pro-inflammatory cytokines may mediate these hyperreactive responses. The selective chemoattractant and activation effects of chemokines on lymphocytes identifies them as potential candidates in mediating selective inflammatory processes in Kawasaki disease. We examined peripheral blood from patients with Kawasaki disease for chemokine gene expression.

METHODS

Consecutive samples from 14 patients during the acute, subacute, and convalescent phases of their illness were collected and elaborated for RANTES, macrophage inflammatory protein-1 beta (MIP-1 beta) and monocyte chemotactic protein-1 (MCP-1) expression.

RESULTS

RANTES and MCP-1 gene expression levels were significantly elevated in 12 of the 14 patients, and MIP-1 beta gene expression was elevated in 13 of the 14 patients. There was no obvious correlation between clinical phase of the disease and chemokine expression level, yet elevated expression levels were detected in all phases, including the convalescent phase, when laboratory evidence of lymphocyte activation has been shown to return to normal. Serial samples showed persistence or increased expression of chemokine genes into the convalescent phase in patients with coronary artery lesions.

CONCLUSION

Chemokine mediated inflammatory events may persist in the convalescent phase of Kawasaki disease and may contribute to further risk of vascular endothelial cell injury, specifically coronary aneurysm formation.

Activation of the phosphatidylinositol 3-kinase serine kinase by IFN-alpha

During engagement of the type I IFN receptor, IRS-1 is phosphorylated on tyrosine and associates with the p85 regulatory subunit of the phosphatidylinositol (PI) 3'-kinase, which is a dual-specificity enzyme possessing both lipid and serine kinase activities. We sought to determine whether treatment of cells with IFN-alpha activates the PI 3'-kinase serine kinase. 32P-labeling experiments and phosphoaminoacid analysis of immunoprecipitated IRS-1 protein demonstrated that, in addition to tyrosine phosphorylation, IFN-alpha induces its phosphorylation on serine residues. In vitro kinase assays on alphaIRS-1 immunoprecipitates also demonstrated IFN-alpha-dependent serine phosphorylation of IRS-1, suggesting that the protein associates with an IFN-alpha-regulated serine kinase. Furthermore, IFN-alpha-dependent phosphorylation of IRS-1 was detected in in vitro kinase assays on alpha p85 immunoprecipitates, and was inhibited by pretreatment of cells with the specific PI 3'-kinase inhibitor wortmannin, consistent with a regulatory role of the PI 3'-kinase serine kinase on the phosphorylation of the protein. Treatment of cells with wortmannin also inhibited the phosphorylation of the p85 subunit of PI 3'-kinase and the type I IFN-regulated activation of the Map kinase, but had no inhibitory effect on the IFN-alpha-induced activation of Tyk-2 and Jak-1 kinases nor on the activation of Stat-1, Stat-2, and Stat-3. Taken all together, these data establish that the PI 3'-kinase serine kinase is activated by IFN-alpha and may play an important role in the transmission of type I IFN receptor-generated signals.

Activation of the phosphatidylinositol 3-kinase serine kinase by IFN-alpha

During engagement of the type I IFN receptor, IRS-1 is phosphorylated on tyrosine and associates with the p85 regulatory subunit of the phosphatidylinositol (PI) 3'-kinase, which is a dual-specificity enzyme possessing both lipid and serine kinase activities. We sought to determine whether treatment of cells with IFN-alpha activates the PI 3'-kinase serine kinase. 32P-labeling experiments and phosphoaminoacid analysis of immunoprecipitated IRS-1 protein demonstrated that, in addition to tyrosine phosphorylation, IFN-alpha induces its phosphorylation on serine residues. In vitro kinase assays on alphaIRS-1 immunoprecipitates also demonstrated IFN-alpha-dependent serine phosphorylation of IRS-1, suggesting that the protein associates with an IFN-alpha-regulated serine kinase. Furthermore, IFN-alpha-dependent phosphorylation of IRS-1 was detected in in vitro kinase assays on alpha p85 immunoprecipitates, and was inhibited by pretreatment of cells with the specific PI 3'-kinase inhibitor wortmannin, consistent with a regulatory role of the PI 3'-kinase serine kinase on the phosphorylation of the protein. Treatment of cells with wortmannin also inhibited the phosphorylation of the p85 subunit of PI 3'-kinase and the type I IFN-regulated activation of the Map kinase, but had no inhibitory effect on the IFN-alpha-induced activation of Tyk-2 and Jak-1 kinases nor on the activation of Stat-1, Stat-2, and Stat-3. Taken all together, these data establish that the PI 3'-kinase serine kinase is activated by IFN-alpha and may play an important role in the transmission of type I IFN receptor-generated signals.

Application of genomic DNA affinity chromatography identifies multiple interferon-alpha-regulated Stat2 complexes

Interferon-alpha (IFN-alpha)-induced signal transduction is mediated by the phosphorylation-activation of the signal transducer and activator of transcription (STAT) proteins Stat1, Stat2, and Stat3. Previous studies have shown that these activated STATs dimerize to form four distinct STAT complexes which translocate to the nucleus and activates transcription by binding to specific promoter elements. The interferon-stimulated gene factor-3 (ISGF3) consists of Stat2 and Stat1 heterodimers in association with a DNA-binding protein, p48, that binds to the interferon stimulated response element. Homo-and heterodimers of Stat1 and Stat3 bind to the palindromic interferon response element (pIRE). In this report we demonstrate the utility of a biochemical procedure that we have developed, based on genomic DNA affinity chromatography, for the identification of IFN-alpha-induced STAT complexes. Using this approach, we identified ISGF3-independent Stat2-containing STAT complexes. Results from the analysis of Stat2 complexes in the electrophoretic mobility shift assay were consistent with genomic DNA affinity chromatography results and identified a Stat2:1 complex that binds with low affinity to the pIRE of the interferon regulatory factor-1 gene. Immunoprecipitation studies of Stat2 revealed an IFN-alpha dependent co-precipitation of both Stat1 and Stat3. Taken together, our results suggest that IFN-alpha activates, in addition to ISGF3, other Stat2-containing STAT complexes, one of which binds to an element related to the interferon regulatory factor-1 pIRE.

Configuration of the interferon-alpha/beta receptor complex determines the context of the biological response

Constituents of the Type 1 interferon (IFN) receptor (IFNABR) identified to date include the alpha and beta transmembrane subunits and the associated intracellular kinases, Jak 1 and Tyk 2. In this report, we demonstrate that a human cell type that expresses both subunits of IFNABR, together with Jak 1 and Tyk 2, exhibits a limited binding capacity for and is only partially sensitive to the effects of IFN-alpha/beta, despite adequate levels of the cytoplasmic transcription factors Stat1, Stat2, and Stat3. Specifically, a low affinity interaction between IFN-alpha/beta and cell surface receptors results in ISGF3 (Stat1:2) activation and an antiviral response, yet no IFN-inducible growth inhibition. Using a panel of murine cells that are variably configured with respect to the human IFNABR-alpha/beta subunits, we provide evidence that an additional component(s) encoded on human chromosome 21 is required to confer high affinity binding and IFN-inducible growth inhibition to cells that express the alpha and beta subunits of the IFNABR. The data indicate that transcriptional activation that leads to an antiviral response is mediated by IFN-alpha/beta activation of IFNABR-alpha and IFNABR-beta in the context of a low affinity interaction, yet a high affinity interaction is necessary for signal transducing events that mediate growth inhibition. We provide evidence that the extent of ISGF3 activation correlates directly with the magnitude of an antiviral but not a growth inhibitory response.

Chemokine expression in rheumatoid arthritis (RA): evidence of RANTES and macrophage inflammatory protein (MIP)-1 beta production by synovial T cells

Earlier studies from this laboratory provided evidence for restricted cytokine expression in the T cell population in RA tissues. Specifically, IL-2, IL-4, IL-6 and interferon-gamma (IFN-gamma) gene expression levels were low. The selective chemoattractant and activation effects of chemokines on leucocytes identify them as potentially ideal candidates in mediating selective inflammatory processes in RA. Accordingly, we undertook studies to examine constitutive chemokine gene expression in RA tissues. RANTES, monocyte chemotactic protein-1 (MCP-1) and MIP-1 beta gene expression was examined in both the T and non-T cell populations in RA peripheral blood (PB), synovial fluid (SF) and synovial tissues (ST). Our results identified elevated levels of both RANTES and MIP-1 beta gene expression in circulating RA PB and SF T cells. By contrast, MCP-1 expression was virtually absent in RA PB, yet elevated MCP-1 mRNA levels were detected primarily in the non-T cell populations of the SF and ST samples. Histological examination of affected rheumatoid joints revealed extensive RANTES and MIP-1 beta expression in sites of lymphocyte infiltration and cell proliferation, namely the synovial lining and sublining layers. Fractionation or RA ST patient samples revealed that RANTES expression was restricted to the T cells, whereas MIP-1 beta expression was detected in both T and non-T fractions. These data suggest that MCP-1, MIP-1 beta and RANTES may have a central role in the trafficking of reactive molecules involved in immunoregulation and in the inflammatory processes in RA.

Interferon receptor recognition peptides enhance the biological potency of interferon alphas

Based on our earlier studies that defined three strategic regions in the Type 1 interferon (IFN) molecule associated with receptor interactions and biological activity, three IFN receptor recognition peptides (IRRP) were synthesized, with amino acid sequences CLKDRHD (IRRP1), ESLLEKFYTELYQQLND (IRRP2) and YFQRITLYLTEKKYSPCA (IRRP3) and examined for biological effectiveness. In cell surface receptor binding studies, the binding capacity of cells for IFN-alpha s was increased in the presence of the IRRPs. Increased receptor occupancy resulted in increased phosphorylation-activation of the transcription factor ISGF3 and enhanced antiviral activity. The potentiating effect on IFN-induced growth inhibition was less marked. These data suggest that the IRRPs may influence the biological potency of IFN-alpha by facilitating accessibility to cell surface receptor components. The IRRPs may function to increase the number of low affinity receptor-ligand interactions necessary to initiate receptor oligomerization, thereby catalysing the formation of high affinity IFN-receptor complexes.

Evidence for glycosphingolipid modification of the type 1 IFN receptor

P1-determinant glycolipids that include two membrane glycosphingolipids, globotriaosylceramide (Gal alpha 1-4Gal beta 1-4Glc-ceramide, Gb3) and galabiosylceramide (Gal alpha 1-4Gal-ceramide, Gb2) are receptors for an Escherichia coli-derived subunit toxin, verotoxin (VT-1). Studies with Daudi cells and glycosphingolipid-deficient Daudi mutants and U937 cells identified that the presence of Gb2/Gb3 correlates with IFN-alpha sensitivity. Comparison of amino acid sequences between VT-1 and the extracellular region of the 63-kDa IFN-alpha beta receptor (IFNAR) peptide reveals regions of identity, specifically in those domains in the VT-1 B subunit, that have been implicated as Gb2/Gb3 binding sites. In direct ligand binding studies, we show that membrane Gb2/Gb3 content affects the binding capacity of cells for IFN-alpha, although IFNAR cell surface expression is unaffected. Binding of IFN-alpha to the receptor leads to kinase-associated phosphorylation of the latent transcription factor, ISGF3, which activates transcription by binding to IFN-stimulated regulatory elements in IFN-sensitive genes. Electrophoretic mobility band shift assays indicated that U-937 and Daudi mutant cells, deficient in Gb2 and Gb3, exhibited reduced nuclear factor binding to the human 2-5A synthetase IFN-stimulated regulatory element when compared with wild-type Daudi cells, after exposure to IFN-alpha. Moreover, when Daudi cells were treated with a ceramide analogue, 1-phenyl-2-(decanoylamino)-3-morpholino-1-propanol, Gb2 and Gb3 synthesis was inhibited and a concomitant reduction in IFN-induced ISGF3 activation was noted. IFNAR cell surface expression was unaffected by 1-phenyl-2-(decanoylamino)-3-morpholino-1-propanol treatment. By using a fusion protein of the extracellular domain of IFNAR linked at the carboxyl terminus to the Fc portion of IgG1, we demonstrate that IFNAR is able to bind preferentially to Gb2. These results suggest that an association of IFNAR with membrane Gal alpha 1-4Gal containing glycolipids facilitates receptor-mediated signaling.

Evidence for glycosphingolipid modification of the type 1 IFN receptor

P1-determinant glycolipids that include two membrane glycosphingolipids, globotriaosylceramide (Gal alpha 1-4Gal beta 1-4Glc-ceramide, Gb3) and galabiosylceramide (Gal alpha 1-4Gal-ceramide, Gb2) are receptors for an Escherichia coli-derived subunit toxin, verotoxin (VT-1). Studies with Daudi cells and glycosphingolipid-deficient Daudi mutants and U937 cells identified that the presence of Gb2/Gb3 correlates with IFN-alpha sensitivity. Comparison of amino acid sequences between VT-1 and the extracellular region of the 63-kDa IFN-alpha beta receptor (IFNAR) peptide reveals regions of identity, specifically in those domains in the VT-1 B subunit, that have been implicated as Gb2/Gb3 binding sites. In direct ligand binding studies, we show that membrane Gb2/Gb3 content affects the binding capacity of cells for IFN-alpha, although IFNAR cell surface expression is unaffected. Binding of IFN-alpha to the receptor leads to kinase-associated phosphorylation of the latent transcription factor, ISGF3, which activates transcription by binding to IFN-stimulated regulatory elements in IFN-sensitive genes. Electrophoretic mobility band shift assays indicated that U-937 and Daudi mutant cells, deficient in Gb2 and Gb3, exhibited reduced nuclear factor binding to the human 2-5A synthetase IFN-stimulated regulatory element when compared with wild-type Daudi cells, after exposure to IFN-alpha. Moreover, when Daudi cells were treated with a ceramide analogue, 1-phenyl-2-(decanoylamino)-3-morpholino-1-propanol, Gb2 and Gb3 synthesis was inhibited and a concomitant reduction in IFN-induced ISGF3 activation was noted. IFNAR cell surface expression was unaffected by 1-phenyl-2-(decanoylamino)-3-morpholino-1-propanol treatment. By using a fusion protein of the extracellular domain of IFNAR linked at the carboxyl terminus to the Fc portion of IgG1, we demonstrate that IFNAR is able to bind preferentially to Gb2. These results suggest that an association of IFNAR with membrane Gal alpha 1-4Gal containing glycolipids facilitates receptor-mediated signaling.

Three-dimensional model of a human interferon-alpha consensus sequence

A computer-built, three-dimensional, atomic-level model for human interferon-alpha (IFN-alpha) was constructed. This model was prepared using the primary amino acid sequence of consensus IFN-alpha (IFN-alpha Con1) and the alpha-carbon Cartesian coordinates of murine IFN-beta as a homolog guide to the model building. In agreement with an earlier report from this laboratory, the two domains 29-35 and 123-140 are in close spatial proximity in this model, and may constitute a receptor recognition domain, whereas the region bounded by residues 78-95 is somewhat removed from this region on the molecule and may constitute an alternative active site. Extrapolating from the model, we propose that, of the stretch 123-140, the residues that are exposed are 123, 125, 126, 128-130, and 132-139; and of the stretch 29-35, all are accessible. Additionally, we propose that there may be sufficient complexity in the Type 1 IFN receptor to account for the differential sensitivities between IFN-alpha s and IFN-beta that may be associated with residue differences in the region 78-95, specifically at residues 84, 86, and 87. This model conforms with experimental data that identify specific amino acid residues in human IFN-alpha that either do, or do not, affect the active conformation and biological activities of the molecule.

Inhibitory effects of alpha-interferon on epidermal growth factor-mediated receptor-dependent events

To examine the mechanisms by which alpha-interferon (IFN-alpha) inhibits growth factor-mediated proliferative responses, we examined specific ligand-activated, receptor-dependent events. In direct ligand binding studies, we showed that IFN-alpha treatment of cells leads to a reduction in epidermal growth factor (EGF) receptor recognition at the cell surface, coupled with an alteration in the binding characteristics of EGF for its specific receptors. Specifically, the heterogeneity of binding exhibited by EGF was affected, and there was loss of the high affinity binding component. EGF-induced autophosphorylation of the EGF receptor was unaffected by IFN treatment. The trafficking of EGF-receptor complexes was followed using three-dimensional confocal microscopy. Confocal imaging revealed that the rapid internalization of EGF-receptor complexes was significantly reduced when cells were exposed to IFN. Accompanying the IFN-induced changes in receptor binding characteristics, we identified an alteration in EGF receptor gene expression; when cells were treated with IFN-alpha, elevated RNA levels specific for the EGF receptor were detected. Overall, IFN-alpha treatment inhibited EGF-induced cell proliferation. Our results imply that EGF-bound receptors that are unable to internalize are not fully competent with respect to signal regulation of both gene expression and growth. The data suggest that the signaling potential of the bound growth factor-receptor complex is apparently increased by an unspecified, species-specific, high affinity binding component. We propose that IFN treatment of responsive cell prevents the interaction of EGF-bound receptor with this component.

Restricted cytokine expression in rheumatoid arthritis

OBJECTIVE

To determine the cytokine profile of the phenotypically activated T cell in rheumatoid arthritis (RA) synovium.

METHODS

Interleukin-2 (IL-2), IL-2 receptor (IL-2R), IL-6, IL-4, and interferon-gamma (IFN gamma) gene expression was examined in T cells from freshly isolated synovial fluids (SF) and synovial tissues (ST) from patients with RA. Estimates of baseline expression were determined using unstimulated peripheral blood (PB) T cells from healthy individuals. The corresponding positive controls were phytohemagglutinin-activated tonsil T cells.

RESULTS

In studies of paired PB and SF T cell samples from 17 RA patients, IL-2 messenger RNA (mRNA) levels in only 1 PB and 3 SF samples were more than 2 standard deviations above the mean of levels in unstimulated PB from healthy donors. Similarly, only 5 PB and 7 SF samples exhibited elevated IL-2R mRNA levels. IFN gamma gene expression was not detected in any of the paired RA PB or SF samples. Fractionated T cells from 12 RA ST were screened with similar results: Only 1 of 12 samples exhibited IL-2 mRNA levels more than 2 standard deviations above levels in baseline controls. IL-2R mRNA levels were low or not detected, and IFN gamma mRNA was absent. Subsequent studies showed that IL-4 and IL-6 gene expression levels were also low in RA tissues compared with tonsil T cell-positive controls.

CONCLUSION

These data provide evidence for restricted cytokine expression in the T cell population in RA tissues.

Definition of receptor binding domains in interferon-alpha

Earlier studies from this laboratory had identified three regions in interferon-alpha (IFN-alpha) that influence the active conformation of the molecule. These domains are associated with the amino acid residues 10-35, 78-107, and 123-166. In this report, we define these domains more accurately by identifying their critical clusters of amino acids. Using a panel of IFN-alpha 2a variants in antiviral, growth inhibitory, and receptor binding studies, we are able to show that these three domains, defined by residues 29-35, 78-95, and 123-140, are likely located on the surface of the molecule, with domains 29-35 and 123-140 in close spatial proximity. We conclude that the 29-35 and 123-140 domains are responsible for IFN-alpha receptor binding interactions and constitute receptor recognition sites in IFN-alpha. Extrapolating from our biological activity data, in the context of a number of predictive algorithms that provide insights into the hydrophobicity/hydrophilicity, surface probability, and flexibility of amino acid clusters, we infer that the residues 29-35 influence the active configuration of IFN-alpha most significantly. This region likely represents a loop structure that is relatively rigid in configuration. The carboxy-terminally located strategic domain, 123-140, is comprised of two clusters of amino acid residues, one that forms part of a rigid alpha-helix, the other a more flexible loop structure. Similarly, the 78-95 domain comprises a portion of an alpha-helical structure that is followed by a loop structure. Close examination of the amino acid sequences in all three regions among the different species of IFN-alpha s and human IFN-beta indicate that the 29-35 and 123-140 domains are most highly conserved, yet some variance is apparent in the 78-95 domain. We propose that the 78-95 region influences species specificity among the murine and human IFN-alpha s and determines the differential specificity of action between human IFN-alpha and human IFN-beta.

Characterization of a polyethylene glycol conjugate of recombinant human interferon-gamma

Recombinant human interferon-gamma was conjugated with polyethylene glycol (PEG) using succinimidyl coupling of amino groups in the protein. The PEG conjugated material showed antiviral, growth inhibitory and macrophage activation activities indistinguishable from those of the unmodified protein. The PEG conjugation reduced the receptor binding affinity slightly, but increased the half-life of the protein when measured in rats. Almost no clearance was observed within 6 hr after injection for the PEG conjugated protein, whereas a rapid clearance was seen for the unmodified interferon-gamma. Two possible sites of PEG attachment were identified in the protein: the N-terminal amino group and either lysine 129 or 131.

The effect of C-terminal processing on the activity of human interferon-gamma

Homogeneous recombinant human interferon-gamma (IFN-gamma) obtained from Escherichia coli (E. coli) was treated with a protease-containing fraction prepared from mechanically lysed E. coli cells. Polyacrylamide gel electrophoresis of the resulting product revealed two major components of molecular weight less than that of intact IFN-gamma. These were purified by ion exchange chromatography in the presence of 7 M urea and shown to have intact IFN-gamma N-terminal sequences, suggesting that they resulted via C-terminal cleavages of IFN-gamma. Amino acid analysis indicated that 4 C-terminal residues of IFN-gamma were lacking in one, and 15 in the other. The species lacking 4 C-terminal residues had activities virtually indistinguishable from those of IFN-gamma in antiviral and growth inhibitory assays using Encepharomyocarditis-treated HeLa or T98G cells and in a macrophage activation assay using macrophage-like U937 cells. The species lacking 15 C-terminal residues had markedly decreased activities in each of these assays, and had decreased binding affinity for IFN-gamma cell surface receptors. These observations define the C-terminal residues important for IFN-gamma's biological activity--information which should be useful in designing analogs of IFN-gamma with enhanced or altered biological activities.

The role of three domains in the biological activity of human interferon-alpha

Earlier studies showed that minor differences in primary structure among the interferon-alpha (IFN-alpha) protein family are reflected in their potency in selected biological assays. These studies have been extended and results from assays of antiviral, growth inhibitory and 2',5'-oligoadenylate (2-5A) synthetase activities indicate that the various novel hybrid and analog species are differentially biologically active. Overall these observations suggest a correlation between predicted secondary structure characteristics, receptor binding affinity, and 2-5A synthetase, antiviral and growth inhibitory activities. Studies with a consensus IFN-alpha analog particularly implicated the region around residues 78 and 79 as influencing antiviral activity. Neutralization experiments with a monoclonal antibody directed against a conserved region from residues 113 to 149 indicated that although this region of the IFN-alpha molecule may be important for antiviral activity, altering residues at sites removed from this region may reduce the effectiveness of the neutralizing antibody. Receptor binding experiments suggested that no single site at either the amino or carboxyl terminus of IFN-alpha alone determines receptor affinity or biological activity: apparently three distinct domains along IFN-alpha are involved (10-35, 78-107, 123-166). Overall, the data indicate that the three sites contribute toward the active configuration of human IFN-alpha.

The interaction of interferon-alpha and -gamma: regulation of (2-5)A synthetase activity

The interaction of IFN-alpha and IFN-gamma on the induction of antiviral, growth inhibitory, and (2-5)A synthetase activities was investigated in T98G and A549 cells. Synergistic or inhibitory effects which were host-cell dependent were seen with both simultaneous and sequential IFN treatments. Interestingly, IFN-gamma 1 pretreatment affected the levels of IFN-alpha-induced (2-5)A synthetase activity differently in the two cell types. In T98G cells, sequential treatment resulted in an overall decrease in induction of enzyme activity that was not observed in A549 cells. Receptor binding assays and measurements of steady-state mRNA levels indicated that this effect of IFN-gamma pretreatment does not occur at the level of either receptor expression or induction of transcription of the low-molecular-weight form of (2-5)A synthetase.

Structure/function studies on recombinant human gamma interferon

Structure/function relationships for human gamma interferon (IFN-gamma) were investigated using recombinant DNA-derived homologues produced in E. coli. The various biological effects examined were antiviral, growth inhibitory and 2-5A synthetase activities, as well as receptor binding characteristics. Specific structural changes led to IFN-gamma homologues with defined alterations in biological activities. Amino acid residue changes at the hydrophobic core of the molecule resulted in two homologues exhibiting loss of affinity for the IFN-gamma receptor and dramatically reduced biological activities. These diminished activities probably relate to the inability of the homologues to form appropriately folded structures. Residue changes at two sites associated with beta-turns on the surface of IFN-gamma likewise resulted in homologues with reduced biological activities. In these cases, the reduced biological activities were not associated with reduced receptor binding. Addition of cysteine-tyrosine-cysteine to the amino-terminus of IFN-gamma, known to perturb the protein conformation, slightly reduced the affinity of the so-derived homologue for the IFN-gamma receptor on T98G cells, and there was concommitant reduction in biological activities. Experiments with a monoclonal antibody that binds to the carboxy-terminus of IFN-gamma indicated that this region of the molecule may not influence antiviral or antiproliferative activities. Overall our data imply that several sites along the IFN-gamma polypeptide contribute to biological activity, and that receptor binding and effector sites are distinct.

Antiviral and antitumor effects of a human interferon analog, IFN-alpha Con 1, assessed in hamsters

An analog of human alpha-and beta-interferons (IFN-alpha and -beta) (generally consisting of the most frequently observed amino acid residue at each position in the molecule) has pronounced antiviral and antiproliferative activity in human and hamster cells. Intraperitoneal administration of this analog (designated IFN-alpha Con 1) to hamsters at 10(6) to 10(8) U/kg resulted in proportional increases in plasma concentrations through 6 h of monitoring. IFN-alpha Con 1 at these doses effectively limited encephalomyocarditis virus (EMCV) infections of hamsters. A natural human IFN-alpha preparation was also active against virus infections in hamsters. The antitumor activity of IFN-alpha Con 1 and natural human IFN-alpha was assessed in hamsters inoculated with lethal TBD932 lymphosarcoma. Various IFN treatment schedules resulted in prolonged survival following tumor challenge. IFN-alpha Con 1 administered at 10(5) to 10(6) U/hamster daily for 9-12 days following tumor challenge was effective in delaying tumor development, as was a natural human IFN-alpha preparation. The efficacies of combined IFN and cyclophosphamide therapies were determined. Unlike the natural human subtype IFN-alpha A, IFN-alpha Con 1 did not diminish the efficacy of cyclophosphamide (2.5 mg/hamster for 3 days) against the lymphosarcoma. However, an ineffective dose of cyclophosphamide (0.05 mg/hamster for 3 days) when combined with IFN-alpha Con 1 treatment showed enhanced antitumor activity. Combinations of cimetidine (16 mg/hamster for 4 days) and IFN-alpha Con 1 treatment did not prolong survival in this model system.

Antiherpetic effects of a human alpha interferon analog, IFN-alpha Con1, in hamsters

The efficacy of a novel consensus form of human alpha interferon designated IFN-alpha Con1 was evaluated against herpesvirus infections in vitro and in vivo. At comparable antiviral concentrations, natural lymphoblastoid IFN, IFN-alpha Con1, the molecular subtype IFN-alpha, and the hybrid IFN-alpha AD(Bgl) obtained by recombinant DNA methods conferred similar protection against herpes simplex virus type 1 and type 2 (HSV-2) infections of human cells in vitro. Whereas 7 X 10(5) U of IFN-alpha AD(Bgl) administered in 7 intraperitoneal (i.p.) doses between -4 and 96 h relative to infection protected 90% of mice from a lethal HSV-2 infection, a similar treatment regimen with IFN-alpha Con1 conferred no protection. Systemic HSV-2 infection of hamsters was rapidly lethal, but a single i.p. treatment with 10(6) U of either IFN-alpha Con1 or IFN-alpha AD(Bgl) was highly effective and protected 90 and 75% of animals, respectively, when given 6 h before infection; treatment with IFN-alpha Con1 protected 45% of animals when administered 10 h after infection. In addition, IFN-alpha Con1 was highly protective against acute cervicovaginal HSV-2 infection of hamsters when administered either in a single i.p. dose of 10(6) U at -6 or 10 h relative to infection or in multiple i.p. doses of 10(6) U between -6 and 120 h relative to infection. Protection was manifested by a delay in the onset of and a reduction in duration of infection, a reduction in the number of positive cervicovaginal infections, and an increase in the survival rate.

Modulation of human interferon-alpha receptor expression by human interferon-gamma

The human neuroblastoma cell line T98G is sensitive to the antiproliferative activity of both alpha- and gamma-interferons (IFNs). Specific binding of a homogeneous 125I-IFN-alpha 2 probe to high-affinity membrane receptors (apparent Kd = 6.2 X 10(-10) M) can be decreased by pretreatment of these cells with human IFN-gamma (HuIFN-gamma, derived by recombinant DNA techniques). The regulation of HuIFN-alpha 2 binding by such pretreatment is reflected by subsequent inhibition of both the antiviral and antiproliferative activities of HuIFN-alpha 2 on T98G cells. Thus, binding of HuIFN-gamma to its distinct cell-surface receptor can modify expression of the separate IFN-alpha receptor, presumably through an indirect effect on the apparent Kd of the IFN-alpha 2 receptor-ligand interaction.

Antiviral activities of cloned human leukocyte interferons against herpes simplex virus type 2 infections of mice

Human alpha-interferons (IFN-alpha s) made in bacteria were examined for antiviral activity against herpes simplex virus type 2 (HSV-2) infections of mouse L-cells in vitro, and acute cervicovaginal and lethal systemic HSV-2 infections of BALB/c mice. The recombinant DNA-derived hybrid interferon IFN-alpha AD(Bgl) showed pronounced antiviral activity in vitro, exceeding the activity of either of the parental subtypes IFN-alpha A and IFN-alpha D and that of the other hybrids IFN-alpha AD(Pvu) and IFN-alpha DA(Bgl). A combination of topical and systemic treatments with IFN-alpha A and IFN-alpha AD(Bgl) failed to protect mice from subsequent challenge with an acute cervicovaginal infection of HSV-2. Protection from lethal systemic HSV-2 infection in mice was observed when IFN-alpha AD(Bgl) and IFN-alpha AD(Pvu) were administered systemically, whereas IFN-alpha A failed to confer protection. These results suggest that for protection against infection with HSV-2, the routes of introduction of the virus and of the interferon influence the host response to interferon therapy.

Human leukocyte interferon subtypes have different antiproliferative and antiviral activities on human cells

The antigrowth effects of 5 different cloned human leukocyte IFN subtypes (IFN-alpha A, B, C, D, F) and 2 molecular hybrids between them (IFN-alpha AD(Bg1II) and IFN-alpha DA(Bg1II)) were examined on 6 different human cell lines. The results indicate that the interferons sort into two distinct groups: IFN-alpha B, C and F showed comparable antiproliferative activity which was greater than that of IFN-alpha A, D, AD(Bg1II) and DA(Bg1II). The interferons could also be assigned to one of two groups on the basis of their antiviral activity. IFN-alpha A, D and AD(Bg1II) were observed to be more protective than IFN-alpha B, C and F against HSV-2 and EMCV infections, i.e. the relative antiviral efficacies of the cloned IFN subtypes were the reverse of their antiproliferative activities.

Differential binding of human interferon-alpha subtypes to receptors on lymphoblastoid cells

Highly purified human interferon-alpha subtype A (HuIFN alpha A) was iodinated for use in direct ligand binding studies on human lymphoblastoid (Daudi) cells. Unlabelled preparations of HuIFN alpha subtypes A, C, D, and hybrid molecules AD (Bgl II), AD (Pvu II), and DA (Bgl II) showed different responses in competition experiments with labelled alpha A probe. Specifically, IFNs alpha D and alpha DA were unable to displace the probe, whereas IFNS alpha A, alpha C, and the hybrid alpha ADs showed similar competition curves. These results support a two-idiotope model of IFN recognition by its receptor. IFN effects on [3H]-thymidine incorporation and cell growth (long term effects) did not reflect the apparent affinities of HuIFN alpha subtypes for cell surface receptor.

Relation of HVH-II to carcinoma of the cervix

An animal model is described that demonstrates the development of varying degrees of basal cell hyperplasia, metaplasia, and dysplasia following cervicovaginal herpesvirus hominis type II (HVH-II) infection. Although the study spanned a period of 30 months, the equivalent of 60 human years, there was no evidence of anaplasia. These results are considered in relation to the role of HVH-II as an initiator in the multistep process leading to cervical carcinoma.

Organ culture model for the study of HVH-II infections in carcinoma of the cervix

An experimental model is described whereby human and monkey cervical tissues may be maintained as organ cultures for 21 and 40 days, respectively. Inclusion of sodium carboxymethyl cellulose in the culture medium prolongs the survival time of tissues considerably. The sequential cytologic changes associated with herpesvirus hominis type II (HVH-II) infection are reported. These changes are considered in relation to the possible causal role of HVH-II infection in cervical carcinogenesis.

Ascending infection following cervicovaginal exposure to herpesvirus hominis type II

An animal model is presented that demonstrates that following cervicovaginal inoculation, infective doses of herpesvirus hominis type II induce a form of herpetic encephalitis. Immunofluorescent results indicate that there is both neural and hematogenous spread of the herpes infection. The possible role of a latent viral infection in the genesis of an acute disease of the central nervous system is investigated in this experimental system.

Relation of herpesvirus hominis type II to carcinoma of the cervix. An animal model for the induction of long-term latency of herpesvirus hominis type II

Proof of latency of herpesvirus hominis type II (HVH-II) following acute vaginocervical infection must be validated if it is to be considered an etiologic factor in carcinoma of the cervix. An animal model is presented which demonstrates acute HVH-II vaginocervical infection. Following the primary acute infection, animals maintained for an equivalent of 60 human years display persistance of the herpesvirus in the pelvic sensory ganglia. Evidence of the specificity of HVH-II as the infectious agent is presented.