Faculty Bibliography

Genes containing the interferon-stimulated response element (ISRE) enhancer have been characterized as transcriptionally responsive primarily to type I interferons (IFN alpha/beta). Induction is due to activation of a multimeric transcription factor, interferon-stimulated gene factor 3 (ISGF3), which is activated by IFN alpha/beta but not by IFN gamma. We found that ISRE-containing genes were induced by IFN gamma as well as by IFN alpha in Vero cells. The IFN gamma response was dependent on the ISRE and was accentuated by preexposure of cells to IFN alpha, a treatment that increases the abundance of ISGF3 components. Overexpression of ISGF3 polypeptides showed that the IFN gamma response depended on the DNA-binding protein ISGF3 gamma (p48) as well as on the 91-kDa protein STAT91 (Stat1 alpha). The transcriptional response to IFN alpha required the 113-kDa protein STAT113 (Stat2) in addition to STAT91 and p48. Mutant fibrosarcoma cells deficient in each component of ISGF3 were used to confirm that IFN gamma induction of an ISRE reporter required p48 and STAT91, but not STAT113. A complex containing p48 and phosphorylated STAT91 but lacking STAT113 bound the ISRE in vitro. IFN gamma-induced activation of this complex, preferentially formed at high concentrations of p48 and STAT91, may explain some of the overlapping responses to IFN alpha and IFN gamma

IFN alpha and IFN gamma induce rapid activation of gene expression following binding to cell surface receptors on target cells. Gene transcription depends on latent transcription factors that become activated in response to IFN treatment. These proteins, termed Stats for signal transducers and activators of transcription, serve as intrinsic elements of the signaling pathway. In untreated cells, they are sequestered in the cytoplasm. Upon treatment of cells with IFN, they become tyrosine phophorylated by receptor-bound protein tyrosine Kinases of the Jak family, assemble into multimeric complexes, and localise to the cell nucleus. Differential activation and combinatorial association of these transcription factors produce the biological responses characteristic of each IFN

The molecular components which mediate cytokine signaling from the cell membrane to the nucleus were studied. Upon the interaction of cytokines with their receptors, members of the janus kinase (Jak) family of cytoplasmic protein tyrosine kinases and of the signal transducers and activators of transcription (Stat) family of transcription factors are activated through tyrosine phosphorylation. It has been suggested that the Stat proteins are substrates of the Jak protein tyrosine kinases. MGF-Stat5 is a member of the Stat family which has been found to confer the prolactin response. MGF-Stat5 can be phosphorylated and activated in its DNA binding activity by Jak2. The activation of MGF-Stat5 is not restricted to prolactin. Erythropoietin (EPO) and growth hormone (GH) stimulate the DNA binding activity of MGF-Stat5 in COS cells transfected with vectors encoding EPO receptor and MGF-Stat5 or vectors encoding GH receptor and MGF-Stat5. The activation of DNA binding by prolactin, EPO and GH requires the phosphorylation of tyrosine residue 694 of MGF-Stat5. The transcriptional induction of a beta-casein promoter luciferase construct in transiently transfected COS cells is specific for the prolactin activation of MGF-Stat5; it is not observed in EPO- and GH-treated cells. In the UT7 human hematopoietic cell line, EPO and granulocyte-macrophage colony stimulating factor activate the DNA binding activity of a factor closely related to MGF-Stat5 with respect to its immunological reactivity, DNA binding specificity and molecular weight. These results suggest that MGF-Stat5 regulates physiological processes in mammary epithelial cells, as well as in hematopoietic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The species specificity of interferons (IFNs) depends on restricted recognition of these ligands by multisubunit cell surface receptors. Expression of the human receptor subunit IFNAR in mouse cells conferred sensitivity only to one subtype of human IFN, IFN-alpha B. Other genes on human chromosome 21 were required for responses to other subtypes of type I IFN. In contrast, IFNAR expression in hamster cells did not confer sensitivity to any human IFN tested, including IFN-alpha B. Using human-hamster somatic cell hybrids, we mapped the Ifnabr gene, encoding a ligand-binding subunit of the IFN-alpha/beta (type I) receptor, to human chromosome 21. Ifnabr colocalized with Ifnar to the distal region of q22.1. The presence of a chromosomal fragment encoding IFNABR and IFNAR was also not sufficient to confer sensitivity to human IFN. In contrast, hybrids carrying in addition the region 21q22.2 showed a full response to human IFN-alpha B, suggesting that a gene located in this region encodes a third factor required for type I IFN receptor activity

The mechanism by which the binding of growth hormone (GH) to its cell surface receptor elicits changes in gene transcription are largely unknown. The transcription factor Stat1/p91 has been shown to be activated by GH. Here we show that acute phase response factor or Stat3 f1p4an antigenically related protein), is also activated by GH. Stat3 has been implicated in the interleukin-6-dependent induction of acute phase response genes. GH promotes in 3T3-F442A fibroblasts the tyrosyl phosphorylation of a protein immunoprecipitated by antibodies to Stat3. This protein co-migrates with a tyrosyl phosphorylated protein from cells treated with leukemia inhibitory factor, a cytokine known to activate Stat3. Tyrosyl phosphorylated Stat3 is also observed in response to interferon-gamma. Stat3 is present in GH-inducible DNA-binding complexes that bind the sis-inducible element in the c-fos promoter and the acute phase response element in the alpha 2-macroglobulin promoter. The ability of GH to activate both Stat1 and Stat3 (i.e. increase their tyrosyl phosphorylation and ability to bind to DNA) suggests that gene regulation by GH involves multiple Stat proteins. Shared transcription factors among hormones and cytokines that activate JAK kinases provide an explanation for shared responses, while the ability of the different ligands to differentially recruit various Stat family members suggests mechanisms by which specificity in gene regulation could be achieved

Cytokines and growth factors elicit responses in target cells through induction of gene expression. Signaling mechanisms leading to gene transcription from cell surface receptors often require tyrosine phosphorylation. A family of transcription factors comprising the interferon (IFN)-stimulated gene factor 3 (ISGF3) multimeric complex are phosphorylated and activated in response to interferon. We describe a protein 50% identical to the 91-kDa subunit of ISGF3 that constitutes the acute phase response factor (APRF). This protein was rapidly activated by interleukin-6 to bind an enhancer element common to genes activated in liver cells during the acute phase response to inflammation. Remarkably, APRF was also activated by IFN alpha, IFN gamma, epidermal growth factor, platelet-derived growth factor, colony stimulating factor-1, and the cytokines leukemia inhibitory factor and oncostatin M. The growth factors also activated a third, distinct but related, DNA-binding protein in addition to APRF and p91. This novel factor or a closely related one, but neither APRF nor p91, was also activated in lymphoid cells by interleukin-2, erythropoietin, and interleukin-3. Activation of APRF, p91, and additional members of the ISGF3 family is thus a general feature of a wide variety of signaling pathways, integrating diverse signals through common transcriptional regulators

The ability of cytokines to activate distinct but overlapping sets of genes defines their characteristic biological response. We now show that IFN gamma, IL-3, IL-4, IL-6, erythropoietin, EGF, and CSF-1 activate differing members of a family of latent cytoplasmic transcription factors. Although these factors have distinct physical and functional properties and exhibit different patterns of expression, they share many important features, including recognition of a related set of enhancer elements, rapid activation, tyrosine phosphorylation, and cross-reactivity to antibodies against p91, a cytoplasmic signaling protein activated by IFN alpha, IFN gamma, and IL-6. These shared features point to either parallel or common patterns of signal transduction. A general model of cytokine signal transduction is presented, in which receptor-associated tyrosine kinases activate ligand-specific members of a family of signal-transducing factors. Once activated, these factors carry their signals to the nucleus, where they bind a family of related enhancer elements

Interferon (IFN) consensus sequence binding protein (ICSBP) is a transcription factor expressed mostly in the cells of the immune system. ICSBP belongs to the IFN regulatory factor (IRF) family, which also includes IRF-1, IRF-2, and the IFN-alpha-stimulated gene factor 3 gamma (ISGF3 gamma). We show here that ICSBP forms a complex with IRF-1 or IRF-2 both in vivo and in vitro and, in the presence or absence of the target DNA, with the IFN-stimulated response element (ISRE). Further, electrophoretic mobility shift assays show that this interaction greatly enhances the otherwise very low binding affinity of ICSBP to the ISRE. We show, on the other hand, that ICSBP inhibits binding of the IFN-alpha-stimulated gene factor 3 gamma to the ISRE. Through these interactions ICSBP is likely to exert complex modulatory functions in the regulation of IFN-stimulated genes

Many cytokines and growth factors trigger rapid changes in gene expression upon binding to their receptors. In many cases, the mechanism by which these changes are affected is unknown. In this report, we show that interleukin-2 (IL-2), IL-3, IL-4, IL-6, leukemia inhibitory factor (LIF), erythropoietin (Epo), and granulocyte-macrophage colony-stimulating factor (GM-CSF) treatment of cells causes rapid activation of DNA-binding activities that recognize a DNA sequence element previously implicated in regulation of gene expression by interferon gamma (IFN gamma). The IL-4-, IL-6-, and GM-CSF-induced complexes can be distinguished from the recently characterized IFN gamma-activated protein p91 on the basis of mobility in polyacrylamide gels, sequence preferences, and lack of reactivity with an anti-p91 antiserum. The IL-4- and GM-CSF-induced complexes react with antiphosphotyrosine antibodies, demonstrating the presence of phosphotyrosine-containing proteins in these DNA-binding complexes. Transcriptional activation of a reporter gene linked to a synthetic IFN gamma-responsive promoter is observed in response to IFN gamma, IL-6, and LIF. These data suggest a pathway by which cytokines induce rapid changes in gene expression