Internalization and transport of mouse beta-interferon into the cell nucleus

Type I IFN receptor controls activated TYK2 in the nucleus: implications for EAE therapy

Recent studies have suggested that activated wild-type and mutant Janus kinase JAK2 play a role in the epigenetics of histone modification, where it phosphorylates histone H3 on tyrosine 41(H3pY41). We showed that type I IFN signaling involves activated TYK2 in the nucleus. ChIP-PCR demonstrated the presence of receptor subunits IFNAR1 and IFNAR2 along with TYK2, STAT1, and H3pY41 specifically at the promoter of the OAS1 gene in IFN treated cells. A complex of IFNAR1, TYK2, and STAT1α was also shown in the nucleus by immunoprecipitation. IFN treatment was required for TYK2 activation in the nucleus. The presence of IFNAR1, IFNAR2, and activated STAT1 and STAT2, as well as the type I IFN in the nucleus of treated cells was confirmed by the combination of Western blotting and confocal microscopy. Trimethylated histone H3 lysine 9 underwent demethylation and subsequent acetylation specifically in the region of the OAS1 promoter. Resultant N-terminal truncated IFN mimetics functioned intracellularly as antivirals as well as therapeutics against experimental allergic encephalomyelitis without the undesirable side effects that limit the therapeutic efficacy of IFNβ in treatment of multiple sclerosis. The findings indicate that IFN signaling is complex like that of steroid signaling.

Cytoplasmic and nuclear cytokine receptor complexes

Much of our understanding on how hormones and cytokines transmit their message into the cell is based on the receptor activation at the plasma membrane. Many experimental in vitro models have established the paradigm for cytokine action based upon such activation of their cell surface receptor. The signaling from the plasma membrane activated cytokine receptor is driven to the nucleus by a rapid ricochet of protein phosphorylation, ultimately integrated as a differentiative, proliferative, or transcriptional message. The Janus kinase (JAK)--signal transducers and activators of transcription (STAT) pathway that was first thought to be cytokine receptor specific now appears to be activated by other noncytokine receptors. Also, evidence is accumulating showing that cytokines modulate the signal transduction machinery of the tyrosine kinase receptors and that of the heterotrimeric guanosine triphosphate (GTP)-binding protein-coupled receptors. Thus cytokine receptor signaling has become much more complex than originally hypothesized, challenging the established model of specificity of the action of a given cytokine. This review is focused on another level of complexity emerging within cytokine receptor superfamily signaling. Over the past 10 years, data from different laboratories have shown that cytokines and their receptors localize to intracellular compartments including the nucleus, and, in some cases, biological responses have been correlated with this unexpected location, raising the possibility that cytokines act as their own messenger through inter-actions with nuclear proteins. Thus, the interplay between cytokine receptor engagement and cellular signaling turns out to be more dynamic than originally suspected. The mechanisms and regulations of intracellular translocation of the cytokines, their receptors, and their signaling proteins are discussed in the context that such compartmentalization provides some of the specificity of the responses mediated by each cytokine.

Identification of an adenine-nucleotide-binding site on interferon alpha2

Using 32P-labeled 2-azidoadenosine 5'-triphosphate (2N3ATP) and 8-azidoadenosine 5'-triphosphate (8N3ATP), we have identified a site on human interferon alpha2 (IFN-alpha2) that binds adenine nucleotides. The results from saturation and competition experiments demonstrated the specificity of the nucleotide interaction. Half-maximal saturation of IFN-alpha2 was observed at 10 microM 2N3ATP or 35 microM 8N3ATP. ATP effectively decreased photoinsertion of both photoaffinity analogs of ATP. Photoinsertion of 8N3ATP was enhanced by MgCl2, independent of the ionic strength, and exhibited an optimum pH between 7.0 and 7.5. Immobilized-Al3+ affinity chromatography and HPLC were used to purify the modified peptides from IFN-alpha2 that had been photolabeled with 8N3ATP and digested with trypsin or chymotrypsin. Overlapping-sequence analysis localized the sites of photoinsertion to the region corresponding to Lys121-Tyr135 in the amino acid sequence of IFN-alpha2, which almost perfectly overlaps a nuclear-localization signal (R120KYFQRITLYLKEKKY135).

Retrograde transport from the Golgi complex to the ER of both Shiga toxin and the nontoxic Shiga B-fragment is regulated by butyric acid and cAMP

Endocytosed Shiga toxin is transported from the Golgi complex to the endoplasmic reticulum in butyric acid-treated A431 cells. We here examine the extent of this retrograde transport and its regulation. The short B fragment of Shiga toxin is sufficient for transport to the ER. The B fragment of cholera toxin, which also binds to glycolipids, is transported to all the Golgi cisterns, but cannot be localized in the ER even after butyric acid treatment. Under all conditions the toxic protein ricin was found predominantly in the trans-Golgi network. There is no transport of endocytosed fluid to the Golgi apparatus or to the ER even after butyric acid treatment and in the presence of Shiga toxin, indicating that transport to the ER, through the trans-Golgi network and the cisterns of the Golgi apparatus, involves several sorting stations. Since Shiga toxin receptors (Gb3) in butyric acid-treated A431 cells seem to have a ceramide moiety with longer fatty acids than in untreated cells, the possibility exists that fatty acid composition of the receptor is important for sorting to the ER. Both retrograde transport and intoxication with Shiga toxin can also be induced by cAMP, supporting the idea that retrograde transport from the Golgi to the ER is required for intoxication. The data suggest that transport to the ER in cells in situ may depend on fatty acid composition and is regulated by physiological signals.

Interferons in the persistence, pathogenesis, and treatment of HIV infection

Interferon (IFN) plays an important role in the treatment and pathogenesis of HIV disease. Recent studies show beneficial effects of IFN alpha in the treatment of HIV-associated Kaposi's Sarcoma and early HIV-infection. Moreover, cell culture studies support these beneficial effects. HIV infection of monocytes is blocked by IFN alpha administered at the time of viral challenge. The IFN alpha-treated cells show no evidence of HIV infection. Viral gene products produced in monocytes infected with HIV then treated with IFN alpha gradually decrease to baseline. Large quantities of proviral DNA are seen in the HIV-infected IFN alpha-treated cells with little evidence for viral transcription suggesting true microbiological latency. While most viral infections of cells result in IFN production, HIV is a notable exception. Indeed, HIV does not induce monocytes to produce IFN alpha and blocks its production following poly(I).poly(c) stimulation. This allows HIV yet another mechanism to evade an important host antiviral response. Paradoxically, the appearance of IFN activity in sera of HIV-infected patients is associated with disease progression, not resolution. Recent observations showing that the interaction between HIV-infected monocytes and PBMC results in the production of IFN alpha s with reduced anti-HIV activity may help explain this paradox. Thus, IFN alpha plays an important but complex role in HIV disease. The elucidation of cellular factors that regulate the antiretroviral effects of IFN alpha may lead to the development of novel therapeutic strategies for HIV infection.

Alpha/beta interferons fail to induce antiviral activity from within the nucleus

Electrophoretically pure murine alpha/beta interferons (IFN-alpha/beta) were microinjected directly into the nuclei of mouse L cells, each nucleus receiving 10 fl containing about 20,000 (IFN) molecules, an amount sufficient to induce the antiviral state when added to the culture medium of control cells. Three, six or 24 h after intranuclear delivery, the cells were challenged with vesicular stomatitis virus or Semliki Forest virus and the appearance of cytopathic effects was scored for each individual cell. The scoring of more than 1,000 intranuclearly injected cells in nine different experiments showed unambiguously that the intranuclear delivery of IFN-alpha/beta did not induce the antiviral state. The results argue strongly against the physiological importance of high-affinity nuclear binding sites for native IFN that have been recently described (V. M. Kushnaryov, H. S. MacDonald, G. P. Lemense, J. Debruin, J. J. Sedmak, and S. E. Grossberg, Cytobios 53:185-197, 1988). Together with earlier results of other groups describing the lack of IFN activity after intracytoplasmic injection (Y. Higashi and Y. Sokawa, J. Biochem. 91:2021-2028, 1982; G. Huez, M. Silhol, and B. Lebleu, Biochem. Biophys. Res. Commun. 110:155-160, 1983), these results lend weight to the hypothesis that the binding of IFN-alpha/beta to the plasma membrane receptor is sufficient to set into motion the complex mechanism of transmembrane signalling without requiring internalization of the bound IFN molecules.

Recent progress in interferon research: molecular mechanisms of regulation, action, and virus circumvention

A complex system of cis regulatory elements exists by which induction of IFN gene expression is initiated in response to a variety of inducers; cis elements also appear to be involved in the down-regulation of IFN production. IFN gene activation or inhibition of expression may be tightly regulated by the specific binding of newly synthesized or modified proteins to be regulatory regions of the IFN genes. IFN itself acts as a potent modulator of multiple cellular activities. By binding to specific cell surface receptors and probable internalization via receptor-mediated endocytosis and transport into the dense chromatin, IFN treatment leads to activation of numerous genes, some of which possess known antiviral or immunoregulatory functions, whereas the function of others remains to be identified. As with the IFN genes themselves, many of the IFN-inducible genes appear to possess complex regulatory mechanisms, including domains for binding of specific trans-acting proteins. To add to this molecular complexity some viruses have successfully developed methods to circumvent, among other mechanisms, the 2',5'-A-mediated system and the P1 protein kinase system.

Interferon receptors and their role in interferon action

Interferon (IFN) proteins interact with cells through specific cell surface receptors, some of which have been purified and cloned. The alpha-IFNs and beta-IFN bind to a common receptor (type I), whereas gamma-IFN binds to a separate receptor (type II). Both types of high-affinity receptors have been demonstrated on a variety of receptors and the ways in which IFNs may affect cellular physiology and gene expression is discussed.

The cellular internalization of recombinant gamma interferon differs from that of natural interferon gamma

Purified natural and recombinant murine gamma interferons (MuIFN-gamma) bind at 4 degrees C to cultured L929 mouse fibroblasts with comparable receptor-binding affinity (Kd = 9 x 10(-10) M). Both 125I-labeled MuIFNs are rapidly internalized by cells at 37 degrees C, although recombinant IFN is internalized somewhat more slowly than natural IFN (t1/2 = 90 sec and 45 sec, respectively). Immunoelectronmicroscopy showed that the majority of bound recombinant MuIFN-gamma was located on the plasma membrane outside of coated areas, whereas natural interferon was found mainly in coated pits. At 37 degrees C most of the recombinant molecules entered the cytoplasm in pinocytotic vesicles, while natural interferon was internalized by the specific mechanism of receptor-mediated endocytosis [1]. However, nearly equal amounts of immunocytochemically detectable molecules of both IFNs were found in the cell nucleus within 2-3 min incubation at 37 degrees C. Thus, the process of translocation of the recombinant IFN-gamma appears to differ from that of the natural product.

Intracellular human gamma-interferon triggers an antiviral state in transformed murine L cells

Interaction of human gamma-interferon (IFN-gamma) with a cell-surface receptor is known to be essential for the cell to become resistant to viral infection. Here we demonstrate that IFN-gamma, when present inside the cell, is also capable of inducing a permanent antiviral state. Mouse cells transformed with a truncated human cDNA encoding a mature IFN-gamma protein lacking the signal peptide accumulate high levels of intracellular human IFN-gamma. Not only do these cells acquire a permanent resistance to viral infection, they also exhibit all the biochemical characteristics normally observed after exposure to exogenous IFN. The observed loss of species specificity normally associated with IFN-gamma suggests that this restriction is strictly dependent on the interaction of the molecule with the cell-surface receptor.

Bovine spleen, a convenient source for purifying a type I interferon receptor

Bovine spleen was investigated for the presence of receptors for radioiodinated human interferon-alpha 2 (125I-labeled HuIFN-alpha 2). Membranes were prepared by homogenization and differential centrifugation and analyzed for labeled IFN binding with recently developed tissue membrane assays. The characteristics of IFN binding included an affinity constant (Ka) of 3.1 +/- 0.99 X 10(10) M-1 and a receptor content of 8.4 +/- 0.74 fmoles/mg (wet weight) of bovine spleen membranes. The labeled IFN-receptor complex on these membranes was chemically cross-linked with 1.0 mM ethylene glycol bis(succinimidyl succinate (EGS), and subjected to SDS-PAGE and autoradiography. The formation of a 137-kD complex observed on autoradiographs was inhibited in a dose-dependent manner by unlabeled HuIFN-alpha 2 at concentrations that inhibited the binding of labeled IFN to the membranes. The products of the cross-linking reaction were purified by gel filtration on a column of Ultragel AcA34 in the presence of SDS and examined by SDS-PAGE and autoradiography. In addition to the 137-kD complex, several low-molecular-weight species were observed in the column profile of radioactivity which migrated to the bottom of 10% polyacrylamide gels. The fractions containing the 137-kD complex were pooled, concentrated, and utilized as a substrate for endoglycosidase digestion assays. Endoglycosidase H (EndoH) had no affect on the migration of the 137-kD complex while peptide:N-glycosidase F (PNGase F) increased the migration of the 137-kD band to a position with an Mr of 105 kD.(ABSTRACT TRUNCATED AT 250 WORDS)