Kinetic evidence for an activation step following binding of human interferon alpha 2 to the membrane receptors of Daudi cells

Epigenetic therapy overcomes treatment resistance in T cell prolymphocytic leukemia

T cell prolymphocytic leukemia (T-PLL) is a rare, mature T cell neoplasm with distinct features and an aggressive clinical course. Early relapse and short overall survival are commonplace. Use of the monoclonal anti-CD52 antibody alemtuzumab has improved the rate of complete remission and duration of response to more than 50% and between 6 and 12 months, respectively. Despite this advance, without an allogeneic transplant, resistant relapse is inevitable. We report seven complete and one partial remission in eight patients receiving alemtuzumab and cladribine with or without a histone deacetylase inhibitor. These data show that administration of epigenetic agents can overcome alemtuzumab resistance. We also report epigenetically induced expression of the surface receptor protein CD30 in T-PLL. Subsequent treatment with the anti-CD30 antibody-drug conjugate brentuximab vedotin overcame organ-specific (skin) resistance to alemtuzumab. Our findings demonstrate activity of combination epigenetic and immunotherapy in the incurable illness T-PLL, particularly in the setting of previous alemtuzumab therapy.

Transcription factor YY1 binds to the murine beta interferon promoter and regulates its transcriptional capacity with a dual activator/repressor role

The induction of the beta interferon (IFN-beta) gene constitutes one of the first responses of the cell to virus infection. Its regulation is achieved through an intricate combination of virus-induced binding of transcription factors and local chromatin remodeling. In this work, we demonstrate that transcription factor YY1, known to interact with histone deacetylases (HDAC) and histone acetyltransferases, has a dual activator/repressor role during the regulation of the IFN-beta promoter activity. We show that YY1 specifically binds in vitro and in vivo to the murine IFN-beta promoter at positions -90 and -122. Overexpression of YY1 strongly repressed the transcriptional capacity of a stably integrated IFN-beta promoter fused to a chloramphenicol acetyltransferase reporter gene as well as the endogenous IFN activity of murine L929 cells via an HDAC activity. Stably integrated IFN-beta promoters mutated at the -90 site were no longer repressed by YY1, could no longer be activated by trichostatin A, displayed a retarded postinduction turn off, and a reduced virus-induced activity. Introduction of a mutation at the -122 site did not affect YY1-induced repression, but promoters with this mutation displayed a reduced virus-induced activity. Stably integrated full-length promoters (from position -330 to +20) mutated at both YY1-binding sites displayed extremely reduced promoter activities. We conclude that YY1 has a dual activator/repressor role on IFN-beta promoter activity depending on its binding site and time after infection.

Inhibition of histone deacetylation induces constitutive derepression of the beta interferon promoter and confers antiviral activity

The induction of alpha/beta interferon (IFN-alpha/beta) genes constitutes one of the first responses of the cell to virus infection. The IFN-beta gene is constitutively repressed in uninfected cells and is transiently activated after virus infection. In this work we demonstrate that histone deacetylation regulates the silent state of the murine IFN-beta gene. Using chromatin immunoprecipitation (ChIP) assays, we show a direct in vivo correlation between the transcriptionally silent state and a state of hypoacetylation of histone H4 on the IFN-beta promoter region. Trichostatin A (TSA), a specific inhibitor of histone deacetylases, induced strong, constitutive derepression of the murine IFN-beta promoter stably integrated into a chromatin context, as well as the hyperacetylation of histone H4, without requiring de novo protein synthesis. We also show in this work that TSA treatment strongly enhances the endogenous IFN level and confers an antiviral state to murine fibroblastic L929 cells. Inhibition of histone deacetylation with TSA protected the cells against the lost of viability induced by vesicular stomatitis virus (VSV) and inhibited VSV multiplication. Using antibodies neutralizing IFN-alpha/beta, we show that the antiviral state induced by TSA is due to TSA-induced IFN production. The demonstration of the predominant role of histone deacetylation during the regulation of the constitutive repressed state of the IFN-beta promoter constitutes an interesting advance on the understanding of the negative regulation of this gene and opens up the possibility of new therapeutic perspectives.

The type I interferon receptor: structure, function, and evolution of a family business

Recent results indicate that coherent models of how multiple interferons (IFN) are recognized and signal selectively through a common receptor are now feasible. A proposal is made that the IFN receptor, with its subunits IFNAR-1 and IFNAR-2, presents two separate ligand binding sites, and this double structure is both necessary and sufficient to ensure that the different IFN are recognized and can act selectively. The key feature is the duplication of the extracellular domain of the IFNAR-1 subunit and the configurational geometry that this imposes on the intracellular domains of the receptor subunits and their associated tyrosine kinases.

Shared receptor components but distinct complexes for alpha and beta interferons

The type I interferon family includes 13 alpha, one omega and one beta subtypes recognized by a complex containing the receptor subunits ifnar1 and ifnar2 and their associated Janus tyrosine kinases, Tyk2 and Jak1. To investigate the reported differences in the way that alpha and beta interferons signal through the receptor, we introduced alanine-substitutions in the ifnar2 extracellular domain, and expressed the mutants in U5A cells, lacking endogenous ifnar2. A selection, designed to recover mutants that responded preferentially to alpha or beta interferon yielded three groups: I, neutral; II, sensitive to alpha interferon, partially resistant to beta interferon; III, resistant to alpha interferon, partially sensitive to beta interferon. A mutant clone, TMK, fully resistant to alpha interferon with good sensitivity to beta interferon, was characterized in detail and compared with U5A cells complemented with wild-type ifnar2 and also with Tyk2-deficient 11.1 cells, which exhibit a similar alpha-unresponsive phenotype with a partial beta interferon response. Using anti-receptor antibodies and mutant forms of beta interferon, three distinct modes of ligand interaction could be discerned: (i) alpha interferon with ifnar1 and ifnar2; (ii) beta interferon with ifnar1 and ifnar2; (iii) beta interferon with ifnar2 alone. We conclude that alpha and beta interferons signal differently through their receptors because the two ligand subtypes interact with the receptor subunits ifnar 1 and ifnar2 in entirely different ways.

Prolonged STAT1 Activation Related to the Growth Arrest of Malignant Lymphoma Cells by Interferon-α

Multiple biologic effects of interferon-α (IFN-α), including cell growth inhibition and antiviral protection, are initiated by tyrosine phosphorylation of STAT proteins. Although this signal pathway has been intensively investigated, the relevance of STAT signal persistence has received scant attention. Using paired isogenic lymphoma cells (Daudi), which either are sensitive or resistant to growth inhibition by IFN-α, we found comparable initial tyrosine phosphorylation of multiple STAT proteins; however, the phosphorylation durations and associated DNA-binding activities diverged. Phosphorylation and DNA-binding capacity of STAT1 decreased after 4 to 8 hours in resistant cells, as compared with 24 to 32 hours in sensitive cells, whereas phosphorylation of STAT3 and STAT5b was briefer in both lines. Functional significance of the prolonged STAT1 signal, therefore, was explored by experimental interruption of tyrosine phosphorylation, either by premature withdrawal of the IFN-α or deferred addition of pharmacologically diverse antagonists: staurosporine (protein kinase inhibitor), phorbol 12-myristate 13-acetate (growth promoter), or aurintricarboxylic acid (ligand competitor). Results indicated that an approximately 18-hour period of continued STAT1 phosphorylation was associated with growth arrest, but that antiviral protection developed earlier. These differences provide novel evidence of a temporal dimension to IFN-α signal specificity and show that duration of STAT1 activation may be a critical variable in malignant cell responsiveness to antiproliferative therapy.

Characterization of a domain of a human type I interferon receptor protein involved in ligand binding

Two monoclonal antibodies that recognize different epitopes of the extracellular domain of one of the proteins that constitute the type I interferon receptor were used to delineate the interferon binding site. Antibody 64G12 both inhibits the binding of radiolabeled interferon-alpha 2 and IFN-alpha 8 to their cell surface receptors and neutralizes the antiviral and antiproliferative actions of all the type I interferons tested, including IFN-beta, IFN-omega, and human leukocyte IFN, a mixture of different interferon-alpha isotypes. Antibody 34F10 recognizes the type I interferon receptor with an affinity similar to that of the MAb 64G12 but does not inhibit either the binding or the biologic activity of any of the type I interferons tested. Both antibodies recognize a protein of 105 +/- 5 kD from either Daudi or Ly28 cells. Immunoprecipitation following surface iodination demonstrated that the neutralizing MAb recognizes a protein of 105 kD and the nonneutralizing MAb a protein of 110 kD in extracts of Daudi cells. A second less intense band was also detected by both antibodies. Cross-linking of IFN-alpha 2 to its receptor before immunoprecipitation prevented the neutralizing antibody from immunoprecipitating the receptor protein, but the nonneutralizing MAb was still able to recognize a 140 kD protein corresponding to the cross-linked interferon-receptor protein complex. Thus, an interferon binding domain appears to be localized in a region between amino acids 23 and 229 of the extracellular domain of a transmembrane protein that forms part of the type I interferon receptor complex containing the epitopes recognized by each antibody.

Distinct domains of the protein tyrosine kinase tyk2 required for binding of interferon-alpha/beta and for signal transduction

tyk2 belongs to the JAK family of nonreceptor protein tyrosine kinases recently found implicated in signaling through a large number of cytokine receptors. These proteins are characterized by a large amino-terminal region and two tandemly arranged kinase domains, a kinase-like and a tyrosine kinase domain. Genetic and biochemical evidence supports the requirement for tyk2 in interferon-alpha/beta binding and signaling. To study the role of the distinct domains of tyk2, constructs lacking one or both kinase domains were stably transfected in recipient cells lacking the endogenous protein. Removal of either or both kinase domains resulted in loss of the in vitro kinase activity. The mutant form truncated of the tyrosine kinase domain was found to reconstitute binding of interferon-alpha 8 and partial signaling. While no contribution of this protein toward interferon-beta binding was evident, increased signaling could be measured. The mutant form lacking both kinase domains did not exhibit any detectable activity. Altogether, these results show that a sequential deletion of domains engenders a sequential loss of function and that the different domains of tyk2 have distinct functions, all essential for full interferon-alpha and -beta binding and signaling.

Specific antiviral activities of the human alpha interferons are determined at the level of receptor (IFNAR) structure

Differences in activity among the family of human IFNs alpha are much reduced if these ligands are assayed on bovine cells. In particular, the activity of IFN alpha D is much higher on bovine than on human cells. To examine these differences, the bovine counterpart of the human IFNAR has been cloned and expressed in a human cell line. The transfected cell line now recognizes the human IFN alpha D as a high-specific-activity IFN subtype, indicating that the differences in sensitivity between the bovine and human cells to the human IFN alpha lie in the structure of the IFNAR chain rather than in the other components of the functional receptor.

Behavior of a cloned murine interferon alpha/beta receptor expressed in homospecific or heterospecific background

A murine interferon (IFN) alpha/beta receptor was cloned from the IFN-sensitive L1210 cell line on the basis of its homology with the human receptor. A combination of methods that includes the screening of random-primed and oligo(dT)-primed cDNA libraries and polymerase chain reactions with a single-side specificity was used. At the amino acid level, the murine IFN-alpha/beta shows 46% identity with its human counterpart. Both human WISH cells presenting a low sensitivity to mouse IFN and a murine L1210 mutant subline that does not express the receptor have been stably transfected with the murine IFN-alpha/beta receptor. Whereas transfected human cells became sensitive to a limited number of mouse IFN-alpha/beta subtypes, the transfected murine L1210 mutant was found to be fully complemented and became sensitive to all mouse IFN-alpha/beta subtypes tested, including those that were not active on transfected human cells. These results strongly suggest that the receptor described here is implicated in the mediation of the activities of all murine IFN-alpha/beta subtypes.

Transmembrane signalling by interferon-alpha

Human leukocyte interferon (IFN-alpha) binds to discrete cell surface receptors on target cells, and thereby alters gene expression. Transmembrane signaling by IFN-alpha involves the production of DAG without an increased intracellular free calcium concentration, and the subsequent activation of calcium-independent isoforms of PKC (beta and epsilon). Selective PKC inhibitors (H-7 and staurosporine) can block the ability of IFN-alpha to activate the transcription of a distinct set of genes, called the IFN-stimulated genes (ISG), and to protect cells against viral infection. IFN-alpha also induces the rapid changes in protein phosphorylation, which may include latent transcription factors for ISGs.

DNA protein interactions at the interferon-responsive promoter elements: potential for an H-DNA conformation

The regions of several genes (IFI-56K, HLA-A3, HLA-DR and 6-16) containing the (putative) ISRE (Interferon Stimulatable Response Element) were tested for their ability to be recognized by HeLa cells nuclear extract proteins. In a band shift assay, all probes yielded two B1 and B2 DNA-protein complexes of similar mobilities. Unexpectedly the titration of the B1 complex with a synthetic ISRE core (OL1), promoted the formation of B2. Both the probe and OL1 were recovered in B2. For each probe, the possibility of the part of the sequence involved in B1 complex to form a H-DNA structure with the part of the sequence involved in B2 exists. Such a structure was favored by the colinearity of the pairing regions and requires ATP. Although probes seemed to have a secondary structure, the formal existence of a H-DNA structure has not been demonstrated. Such a model could be extended to other interferon inducible gene promoters and may account for their binding properties and differential inducibility after 5' deletion or point mutations.

Murine tumor cells expressing the gene for the human interferon alpha beta receptor elicit antibodies in syngeneic mice to the active form of the receptor

The cellular receptor for the human alpha and beta interferons (IFN) was expressed, by gene transfer, in a murine hepatoma-derived cell line, BTG 9A. Injected subcutaneously into the syngeneic mouse (C57BL/6), the parental and the transfected cells grew and formed tumors which later regressed. More than half the mice bearing tumors derived from cells expressing the receptor, developed IgG antibodies capable of blocking the activity, on human cells, of human recombinant IFN-alpha B, -alpha A, -alpha D and of natural human IFN-beta, but not of recombinant IFN-gamma. Cross-reactivity of human IFN-alpha on murine and bovine cells was unaffected by these antibodies. The binding of human IFN-alpha to solubilized receptors from human lymphoid cell lines was also blocked and complexes of radiolabeled recombinant IFN-alpha A or IFN-alpha B, chemically cross-linked to their human receptor could be immunoprecipitated by the antisera. IFN alpha beta receptor protein, purified by electrophoresis in sodium dodecylsulfate, was not recognized. We conclude that the antibodies are directed against the forms of the IFN alpha beta receptor actually expressed on the membrane.

Transcription factors induced by interferons alpha and gamma

Factors induced by interferons (IFNs) bind to the IFN-stimulated response elements (ISREs) of many genes. In human cells treated with type I (alpha, beta) IFN, factor E is induced in about 1 min and factor M after about 1 hr. Factor G is induced after about 1 hr in cells treated with type II (gamma) IFN. G and M have very similar positions in bandshift assays, sensitivities to cycloheximide, footprints on an ISRE and relative affinities for different ISREs. Four different patterns of expression were observed in different cell lines: E,M and G strongly induced; M and G strongly but E weakly; only E and M induced; only E induced. Transcription in response to IFN alpha is initiated by E and probably maintained by M since, in fibroblasts, M is present maximally when transcription is most active and declines together with transcription. In Bristol-8 cells, where induction of M is not detected, transcription is still induced by IFN alpha and still declines in its continued presence, suggesting that M is not essential for either process. A variant ISRE with two G-to-C mutations binds E especially weakly but M and G strongly. The mutations don't change the response of a reporter gene to IFN gamma but do abolish its response to IFN alpha, suggesting that the binding of M is not sufficient for the latter. G probably acts positively, since its appearance correlates well with induction of transcription by IFN gamma. A 39-bp ISRE from the 9-27 gene binds E much better than M or G. Conversely, a 39-bp ISRE from the 6-16 gene binds M and G much better than E. Different patterns of expression of E, M, and G and different affinities of these factors for alternative ISREs may play a part in modulating the relative responses of genes to type I and type II IFNs in vivo.

DNA-protein interactions at the interferon-responsive promoter: evidences for an involvement of phosphorylation

Several alpha beta and gamma interferons (IFN) induced genes are regulated transcriptionally via a 29 bp cis acting regulatory element (ICS, Interferon Consensus Sequence). The ICS binding capacity of HeLa cell nuclear extracts was strictly dependent on the presence of nucleoside triphosphate and Mg2+. It increased upon alpha beta or gamma IFN treatment of the cells. Three 50 mer synthetic oligonucleotides containing the ICS or putative ISRE (Interferon Stimulatable Response Element), representing portions of genes inducible by alpha beta IFN (HLA-A3 and IFI-56K) or by gamma (HLA-DR) were used as probes to titrate nuclear factors interacting with the ICS. All three probes were retarded in a mobility shift assay in two bands. Phosphorylation conditions were crucial for demonstrating their existence and/or their relative amounts. A factor whose activity and/or amount was modulated upon IFN treatment, appeared to be involved in phosphorylation dependent post-translational modification(s) of the ISRE binding proteins responsible for altered binding properties.

Genetic transfer of a functional human interferon alpha receptor into mouse cells: cloning and expression of its cDNA

A cDNA coding for the human interferon alpha receptor has been cloned using a gene transfer approach. This consists of transferring human DNA to mouse cells and selecting for cells sensitive to human interferon alpha. The transfected cells expressed the human interferon alpha receptor, and a 5 kb human DNA was isolated from a secondary transfectant. This DNA defects an mRNA present in human cells and was used to clone a 2.7 kb cDNA from a library constructed from human Daudi cells. The sequence of the cDNA is presented. It codes for a glycoprotein of 557 amino acids with an N-terminal hydrophobic region and a single transmembrane-spanning segment. Mouse cells expressing the cDNA become sensitive to the antiviral activity of and express binding sites for human interferon alpha, demonstrating that the cloned cDNA encodes a functional human interferon alpha receptor.

Drug-induced alterations of tumor necrosis factor-mediated cytotoxicity: discrimination of early versus late stage action

The killing of L-M cells by murine tumor necrosis factor (mTNF) was investigated by a combination of drug, antiserum neutralization, and kinetic studies. Kinetic studies with 125I-mTNF showed that the bulk of association of ligand with L-M cells peaked within 2 hr and the ligand was not degraded. Cell surface receptors were depleted (down regulated) by 6 hr when death commenced. The off-rates of acid-dissociable (surface bound) and acid-indissociable (internalized) compartments were found to be 9 min and 35 hr, respectively. Nevertheless, complete cell killing required the persistent presence of mTNF for up to 20 hr. This requirement was ablated by the concomitant addition of cycloheximide. Antiserum completely inhibited cytotoxicity when it was applied up to 4 hr after mTNF, but antiserum added 1 hr after mTNF was not neutralizing in the presence of cycloheximide. Thus, the inclusion of cycloheximide temporally dissociated early events (internalization and signal transduction) from lysis. Other drugs with and without cycloheximide were found to preferentially affect either early or later aspects of cell death. Phorbol myristate acetate and the ionophore A23187 were potent inhibitors of cytotoxicity, and staurosporine was a potent enhancer. These agents were more effective when added 1 hr before mTNF and cycloheximide than when added 1 hr after and likely affected early events in the cytolytic program. In contrast, chloroquine and cAMP likely affect more terminal aspects of cytotoxicity. Dibutyrylcyclic AMP, cholera, and pertussis toxins enhanced cytotoxicity. They were equipotent when added either before or after mTNF regardless of the presence of cycloheximide. Likewise, chloroquine was an equipotent inhibitor when added either before or after mTNF regardless of the presence of cycloheximide. Agents that primarily affect association events may be more likely to impinge on other TNF-mediated activities than agents that primarily affect lysis.

Interferon-induced early changes in nuclear protein interactions with the interferon consensus sequence

A number of genes are transcriptionally regulated by interferons via a cis acting regulatory element (interferon consensus sequence). After incubation with HeLa cell nuclear extracts, a synthetic 29 mers probe representing the consensus was retarded as a single band whose amount increased after the addition of IFN to the cells. DNase I footprinting showed that a region of the non coding strand was protected differentially upon interferon treatment. After nuclear protein blotting and probing with the oligonucleotide, two proteins (114 and 50 kDa) of the desired specificity were revealed. Their absolute and relative amounts do not appear to be dependent of the IFN treatment.

Complex binding of the embryonic interferon, ovine trophoblast protein-1, to endometrial receptors

Ovine embryos produce an interferon (IFN)-alpha II in significant quantities during early pregnancy. This IFN, previously termed ovine trophoblast protein-1 (oTP-1), is a 172-amino-acid polypeptide which has been suggested to be the causal agent in maternal recognition of pregnancy in the ewe. Here we report the binding of oTP-1 and a recombinant bovine IFN-alpha I1 (rBoIFN-alpha I1; 165-166 amino acids long) to membrane preparations from ovine uterine endometrium. Both oTP-1 and rBoIFN-alpha I1 competed with each other for receptor binding. Based on Scatchard analysis, [125I]oTP-1 binding was determined to be complex and resolvable into a high-affinity (Kd = 3.8 x 10(-11) M, 30 fmoles/mg protein) and a low affinity (Kd = 1.7 x 10(-10) M; 96 fmoles/mg protein) component. Conversely [125I]rBoIFN-alpha I1 bound to only a single high-affinity receptor (Kd = 6.1 x 10(-11) M; 174 fmoles/mg protein). Cross-linking experiments using disuccinimidyl suberate revealed that [125I]oTP-1 associated with membrane polypeptides of two molecular weight classes (Mr 100,000 and 70,000), and could be displaced from both with rBoIFN-alpha I1. In contrast, [125I]rBoIFN-alpha I1 cross-linked to only the 100,000 Mr membrane polypeptide. These data provide evidence that the binding parameters of oTP-1 and rBoIFN-alpha I1 to endometrial receptors are different.

Interferon removes its own receptors as it blocks the division of Daudi cells

The Burkitt-derived line, Daudi, whose proliferation is inhibited by human alpha-interferon (IFN-alpha), was treated with 125I-labelled recombinant human IFN-alpha A. After separation from unbound ligand, cell-bound IFN was extracted with the detergent digitonin yielding soluble and insoluble complexes of IFN and receptor, together with a certain amount of uncomplexed IFN. 1. Soluble complexes were stable enough to be separated from uncomplexed IFN by permeation chromatography. Treatment of soluble complexes with the bifunctional reagent, disuccinimidyl suberate, yielded a radioactive product separating with an Mr of 130,000 on electrophoresis in sodium dodecyl sulphate. Similar complexes could be recovered with sodium dodecyl sulphate from the digitonin-insoluble residue, treated with the bi-functional reagent. 2. The total (soluble and insoluble) of complexed IFN obtained after digitonin extraction was a constant fraction (0.62) of the total cell-bound radioactivity, being independent of the concentration of IFN added to the cells (less than pM to greater than nM), and of the time of incubation (1 min to 20 h). However, between 30 min and 3 h of incubation, the insoluble complex increased, at the expense of the soluble complex, and there appeared a cellular pool of degraded ligand. From 3 h to 20 h the distribution of ligand-derived radioactivity remained constant while the total amount decreased to less than 10% of its value at 30 min. This decrease in binding was matched by the appearance of an equivalent quantity of radiolabelled fragments in the culture medium. 3. The inhibition of cellular division due to IFN was shown to be coincident with the disappearance of cellular binding and with the cell-mediated degradation of receptor-complexed IFN. We propose that IFN removes its own receptor and, in doing so, blocks a linked function necessary for the stimulated growth of Daudi cells.

Electrostatic interactions in the cellular dynamics of the interferon-receptor complex

Using membrane preparations of the interferon receptor, prepared from cells of the Burkitt line, Daudi, we have examined the binding of three human recombinant alpha-interferons. 1. We discovered a binding titration of the interferons IFN-alpha A and IFN-alpha D in the pH range 6-9. Receptor binding, negligible at pH 6, rises to a maximum close to pH 9. We have shown that binding of IFN-alpha A at basic pH is to the same receptors as at neutrality and that IFN-receptor complexes extracted with digitonin are more stable at basic pH than they are at neutrality. 2. The recombinant interferon, IFN-alpha B, shows little change of binding in the pH range 6-9. At its basic optimum the binding of IFN-alpha A approaches that of IFN-alpha B, while at neutral pH the binding of IFN-alpha A is 3-4 times less. This difference at neutral pH is seen on intact cells as well as on membrane preparations. The specific activity of IFN-alpha B is close to that of IFN-alpha A, both of which are 10-20 times more active than IFN-alpha D; and the binding titration is, therefore, independent of the initial binding affinities. 3. Using hybrid IFNs constructed from the DNA sequences of alpha D and alpha B, we have isolated the sequence responsible for the binding titration to the segment comprising amino acids 61-92. Examination of these sequences reveals that Lys-84 is present in all the IFN-alpha except IFN-alpha B where it is replaced by Glu; and Tyr-90, present in most of the common IFN-alpha including alpha A and alpha D, is replaced by Asp in IFN-alpha B. Lys and Tyr would normally titrate in the pH range 6-9. We conclude that the binding titration is due to an electrostatic interaction and we propose that the interaction is between IFN-receptor complexes. The role of the interaction in the binding losses that accompany the antiproliferative effects of IFN is discussed.

Synergistic antiproliferative effects of glucocorticoids and interferon-alpha on some lymphoid cell lines

The Daudi B lymphoblastoid cell line was previously demonstrated to be highly sensitive to the antiproliferative effect of recombinant interferon-alpha A (rIFN-alpha A). In the present study, glucocorticoid hormones were shown to act synergistically with rIFN-alpha A to further increase the sensitivity of Daudi cells to rIFN-alpha A. At 10(-6) M, dexamethasone, prednisolone, or hydrocortisone alone had little effect on Daudi cell growth, but they greatly potentiated the antiproliferative activity of rIFN-alpha A. The synergy between rIFN-alpha A and glucocorticoids on Daudi cells was not related to the inhibitory effects of glucocorticoids on prostaglandin or leukotriene synthesis, since no synergy was observed between rIFN-alpha A and indomethacin or nordihydroguaiaretic acid. Glucocorticoids and rIFN-alpha A also had appreciable synergistic antiproliferative effects on two out of five other IFN-sensitive lymphoid cell lines. When Raji B lymphoblastoid cells, which were quite resistant to the antiproliferative effect of rIFN-alpha A, were treated with the combination of glucocorticoids and rIFN-alpha A, no significant synergistic effects were observed. The synergistic antiproliferative effects of glucocorticoids and rIFN-alpha A observed with some IFN-sensitive lymphoid cell lines in this in vitro study may have clinical relevance in the treatment of certain lymphoid malignancies that are sensitive to rIFN-alpha A therapy.

Regulation of cell growth by interferon

Interferons can regulate growth and differentiation in a wide range of cell types. These mechanisms are currently being examined. Interferons inhibit the growth of tumour cells and are thus potential anti-cancer agents. They can also inhibit normal cell growth in vitro, and stimulate tumour cell growth in vitro. They may also be involved in some autoimmune diseases. This review examines the effect of interferons on cell proliferation, function, and growth, focusing primarily on in vitro cell systems.

Lanthanide ion enhancement of interferon binding to cells

Pretreatment of purified [125I]-labeled human and mouse beta interferons (IFN) with lanthanum chloride (LaCl3) enhanced 20-30 fold the binding of the [125I]-IFNs to human A549 and mouse L cells at 0 degree C and also enhanced antiviral activity in homologous cells. Although lanthanides enhanced cross-species binding of both human and mouse [125I]-IFNs, there was no increase in cross-species antiviral activity. Unlabeled IFN not treated with LaCl3 did not compete with [125I]-IFN treated with LaCl3 for cellular receptors. However, unlabeled IFN treated with LaCl3 did compete with LaCl3-treated [125I]-IFN. These results suggest that lanthanide treated IFNs do not bind to the same receptors as native IFNs.

Differential human interferon alpha receptor expression on proliferating and non-proliferating cells

The expression of interferon-alpha (IFN-alpha) receptors was studied on a variety of human cells, using monoiodinated IFN-alpha 2 probes. Steady-state binding at 4 degrees C revealed a single class of non-interacting IFN receptor on peripheral blood lymphocytes, and tonsillar B lymphocytes, which are both known to be G0/G1 resting cell populations. The binding affinity of this class of receptor was found to be on the order of 5 X 10(-10) M, expressed as an apparent dissociation constant (Kd). However, cells proliferating either in culture or in vivo were found to express a heterogeneity in IFN-alpha 2 binding. Such binding could be objectively resolved (by a version of the LIGAND program of P. Munson) into a two-site receptor model. Hill plots of binding to proliferating cells indicated a negative cooperativity in the interaction of IFN and receptor. The high-affinity component, expressed on proliferating cells, typically exhibits a Kd of (1-10) X 10(-11) M, while the lower-affinity component indicates a Kd of (1-10) X 10(-9) M. Furthermore, the low-affinity component is apparently expressed on the order of 10-200 times the copy number, per cell, of the high-affinity site. Affinity-labeling experiments revealed that, in addition to the 140-160-kDa IFN-binding complex reported by others, both the proliferating and non-proliferating cell populations possess a novel IFN-binding component of 60 kDa.

The interferon receptors

Early studies on the mode of action of interferons have indicated that a receptor system on the cell surface is involved in its action. The first direct evidence to a high-affinity binding site was found only after pure interferon was available. Two different receptors, one specific for interferons-alpha and beta, and the other for interferon-gamma were recognized. A correlation between affinity to the receptor and specific activity was established. Cross-linked complexes of labeled interferons with their receptors were visualized on gel electrophoresis and even partially purified. Internalization of interferons after binding to the receptor was reported. The role of gangliosides as helpers of interferon binding was recently investigated. Fragments of interferons which still retained binding capacity were described and helped in elucidating the binding site on the interferon molecule.

Antiviral and antiproliferative effects of interferons in quiescent fibroblasts are dissociable

Quiescent mouse Swiss 3T3 cells or human fibroblasts treated with interferon for only 2 hr before the addition of serum are effectively protected against virus infection for up to 24 hr after the addition of serum and the removal of interferon. In sharp contrast, exposure of quiescent fibroblasts to interferon only before addition of serum or the peptides epidermal growth factor and insulin, has no inhibitory effect on cell proliferation. Further, even when interferon is added after the addition of growth factors, an exposure of several hours is required to inhibit stimulation of DNA synthesis. These findings strongly suggest that the antiviral action of interferons is dissociable from their ability to inhibit cell proliferation. The implications of these findings for elucidating the molecular events leading to the biological responses elicited by interferon are discussed.

Sensitivity to alpha/beta-interferon is independent of N-linked complex-type oligosaccharides on cell-surface-membrane glycoproteins

The extent of involvement of carbohydrate structures in the mechanism of action of alpha and beta-interferon (IFN-alpha, IFN-beta) is undefined. In this report we examine the role of complex-type N-linked oligosaccharides in the response to these interferons. The response of mouse leukemia L 1210S cells, grown in the presence of swainsonine, an inhibitor of Golgi mannosidase II [Tulsiani, D. R. P., Harris, T. M. and Touster, O. (1982) J. Biol. Chem. 257, 7936-7939; Elbein A. D., Solf, R., Dorling, P. R. and Vosbeck, K. (1981) Proc. Natl Acad. Sci. USA 78, 7393-7397], to mouse IFN-alpha/beta, both with respect to antiviral and antigrowth effects, remains intact in spite of the total absence of complex-type N-linked oligosaccharides. Also, there is no difference in the response to human IFN-beta of a parental Chinese hamster ovary cell line and a mutant lacking beta-N-acetylglucosaminyltransferase I and therefore unable to synthesize complex-type N-linked oligosaccharides [Stanley, P., Callibot, V. and Siminovitch, L. (1975) Cell 6, 121-128]. These results are significant in permitting the conclusion that the carbohydrate-specific binding of IFN-alpha and IFN-beta to gangliosides cannot be due to a similarity of the ganglioside carbohydrate to that of a glycoprotein containing a complex-type N-liked oligosaccharide.

Single high affinity binding of interferon alpha 2 to receptors on human lymphoblastoid cells: internalization and inactivation of receptors

The interaction of human recombinant interferon (rIFN) alpha 2 with its receptor on lymphoblastoid cells was studied using competitive displacement binding. The data were analysed with the LIGAND program, which tests their fit to one-site or multiple binding site models. The binding at 4 degrees and 37 degrees C fits a one-site model, with a similar KD for both IFN-sensitive and resistant cells. Binding at 37 degrees C to Daudi cells at high density fits artifactually a two-site model only when the receptor concentration is close to that of the KD. The binding of IFN to its receptor, therefore, follows a simple bimolecular interaction. Furthermore, IFN-sensitive and resistant cells internalize IFN at similar rates. We have examined whether IFN receptors are also internalized and whether they subsequently recycle to the cell surface. By measuring cell surface and total receptors, we have observed that after 2 h treatment with IFN total receptors remain constant whereas cell surface receptors decrease. After prolonged treatment with IFN, however, there is a loss of total receptors. By inactivating cell surface receptors with proteinase K, we have shown that a fraction of cell surface receptors becomes resistant to inactivation and is apparently internalized. Moreover, experiments which measure IFN receptors either during incubation in the presence of IFN or after IFN has been removed from the medium, show that receptors do not recycle to the cell surface after internalization. The addition of monensin, a drug which has been shown to inhibit receptor recycling, has no effect on the loss of IFN receptors.

Binding of 125I-labeled recombinant beta interferon (IFN-beta Ser17) to human cells

We investigated the binding of 125I-labeled beta interferon (IFN-beta Ser17), a nonglycosylated recombinant human fibroblast interferon in which cysteine at position 17 is replaced by serine by site-specific mutagenesis. An optimized chloramine T radiolabeling method produced a highly labeled, fully active 125I-IFN suitable for these studies. Unlike the case with the chloramine T method, incorporation of a single mole of Bolton-Hunter reagent into a mole of IFN-beta Ser17 led to nearly complete loss of biological activity. 125I-IFN-beta Ser17, prepared by the chloramine T method, bound specifically to human lymphoblastoid cells (Daudi) with a dissociation constant of 0.24 nM. The number of binding sites per cell was 4,000. In competition assays, unlabeled beta interferons (native, recombinant IFN-beta Cys17, and various preparations of IFN-beta Ser17) equally displaced labeled IFN-beta Ser17 on Daudi cells. Recombinant IFN-alpha-1 displaced 125I-IFN-beta binding to Daudi cells less efficiently than did unlabeled native or recombinant beta interferon. However, at the concentrations tested, native gamma interferon showed no competition with 125I-IFN. Our results indicate that IFN-beta Ser17 and native IFN-beta posses similar binding properties.

Receptor dynamics of closely related ligands: "fast' and "slow' interferons

Two related human alpha interferons with 83% homology in their primary sequences show a similar specific activity on nonhuman cells, but a striking difference on human cells, on which alpha-1 shows 1-5% of the specific molar activity displayed by alpha-2. Both interferons were labelled with 125I, and their binding kinetics followed on growing cultures of the human Burkitt line Daudi. Binding of alpha-1 showed slower rates of association and faster rates of dissociation implying that differences in apparent binding affinity were responsible for the differences in specific molar activity. However, binding was shown to reach steady-state rather than an equilibrium, so differences in the dynamics of the ligand-receptor complexes may represent amplification of differences in the initial binding constant. alpha-2, but not alpha-1, induces a marked loss of binding sites leading to a high affinity steady-state binding. Inhibition of cell multiplication by both interferons depends on a continued stimulation by free ligands at steady-state. It is proposed that the differences in specific molar activity are, in the main, kinetic and cause alpha-1 and alpha-2 to behave respectively as "slow' and "fast' interferons.

Binding of 125I-labeled recombinant beta interferon (IFN-beta Ser17) to human cells

We investigated the binding of 125I-labeled beta interferon (IFN-beta Ser17), a nonglycosylated recombinant human fibroblast interferon in which cysteine at position 17 is replaced by serine by site-specific mutagenesis. An optimized chloramine T radiolabeling method produced a highly labeled, fully active 125I-IFN suitable for these studies. Unlike the case with the chloramine T method, incorporation of a single mole of Bolton-Hunter reagent into a mole of IFN-beta Ser17 led to nearly complete loss of biological activity. 125I-IFN-beta Ser17, prepared by the chloramine T method, bound specifically to human lymphoblastoid cells (Daudi) with a dissociation constant of 0.24 nM. The number of binding sites per cell was 4,000. In competition assays, unlabeled beta interferons (native, recombinant IFN-beta Cys17, and various preparations of IFN-beta Ser17) equally displaced labeled IFN-beta Ser17 on Daudi cells. Recombinant IFN-alpha-1 displaced 125I-IFN-beta binding to Daudi cells less efficiently than did unlabeled native or recombinant beta interferon. However, at the concentrations tested, native gamma interferon showed no competition with 125I-IFN. Our results indicate that IFN-beta Ser17 and native IFN-beta posses similar binding properties.

Regulation of protein synthesis in lymphoblastoid cells during inhibition of cell proliferation by human interferons

Treatment of human lymphoblastoid (Daudi) cells with interferons inhibits cell proliferation in culture within 24 h. The failure of cell growth has been shown to be associated with impaired processing and decreased stability of newly replicated DNA. Because there is a close relationship between DNA replication and protein synthesis we have measured protein synthesis in intact Daudi cells. Protein synthesis declined steadily between 24 and 96 h after interferon treatment to a value which is only 20-30% of the rate in control cells. The enzyme 2',5'-oligo(A) synthetase is induced but our data do not support a role for the 2',5'-oligo(A)-activated ribonuclease in the control of translation in this system.

Receptor mediated pathways for interferon action: in vivo implications

High affinity receptors for human interferon (IFN) are a common surface component of human nucleated cells. A model culture system has been used to mark the activation of surface receptors by IFN as the first step in several, possibly separate, pathways of action, some of which depend on the continued presence of IFN. Two types of equilibrium binding can be seen: an initial one of short duration corresponding to receptor activation and a second of longer duration corresponding to activation of a second site by IFN. Various different responses to IFN are seen to be determined by one or other of these equilibria. In vivo, implications are discussed in terms of the pharmacokinetic distribution of IFN, with particular reference to intravenous injection. Desensitization of target cells with respect to late equilibrium effects is seen as a possible consequence of receptor activation against the background of changing IFN concentration in vivo. A modulating effect of combined IFN species is proposed.

Complex kinetics of binding of human alpha-2 interferon to human, but not bovine cells

Human alpha-2 interferon (HuIFN-alpha 2) is an effective antiviral agent for bovine cells, but does not inhibit the proliferation of these heterologous cells. A comparison of the kinetics of binding of 125I-HuIFN-alpha 2 at 4 degrees C to several bovine and human cells, shows that the kinetics of the initial receptor interactions are very different in the two species. Binding of HuIFN-alpha 2 to bovine cells follows the simple kinetics predicted for one species of ligand interacting with one type of high-affinity receptor. The kinetics of binding to human cells showing a range of sensitivities to the antigrowth effect are complex and indicate that receptor occupancy increases the rate of association of ligand. It is suggested that dimers of HuIFN-alpha 2 may be formed on the human, but not the bovine receptor, and where these occur between receptors, their formation may relate to the inhibition of cell growth.