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M Kellum

Publications and source records attributed to M Kellum.

16 recordsLinked to original sources
PubMed2006

ISG15 enhances the innate antiviral response by inhibition of IRF-3 degradation.

The transcription factor, interferon regulatory Factor 3 (IRF-3) plays a critical role in the activation of an antiviral innate immune response. However the transcriptional activity of IRF-3 is tightly regulated by a proteosome mediated degradation. We describe here a novel mechanism by which the activity of IRF-3 is stabilized in infected cells. We have shown that both interferon treatment and NDV infection profoundly increase conjugation of interferon induced ubiquitin- like protein ISG15 to cellular proteins. ISGylated IRF-3 could be detected both in interferon treated and virus-infected cells. ISG15, subverts the ubiquitin mediated degradation of IRF-3 in NDV infected 2fTGH cells and enhances the NDV mediated transactivation of interferonbeta promoter and the translocation of activated IRF-3 to the nucleus. The relative levels of IRF-3 were significantly lower in NDV infected ISG15 null MEF, than in wt MEF. While ISG15 null MEF were more permissive to VSV replication their sensitivity to the antiviral effect of interferon was not modulated. These results reveal that virus mediated subversion of the antiviral response by proteolysis of IRF-3 is counteracted by induction of ISG15 expression and that ISGylation provides a feedback mechanism, which enhances the host innate antiviral response via IRF-3 stabilization.

Active Transport, Cell Nucleus↗
PubMed1999

Functional analysis of human herpesvirus 8-encoded viral interferon regulatory factor 1 and its association with cellular interferon regulatory factors and p300.

Human herpesvirus 8/Kaposi sarcoma-associated virus (HHV-8/KSHV) contains, in addition to genes required for viral replication, a unique set of nonstructural genes which may be part of viral mimicry and contribute to viral replication and pathogenesis in vivo. Among these, HHV-8 encodes four open reading frames (ORFs) that showed homology to the transcription factors of the interferon regulatory factor (IRF) family. The ORF K9, viral IRF 1 (vIRF-1), has been cloned, and it was shown that, when overexpressed, it down modulates the interferon-mediated transcriptional activation of the interferon-stimulated gene 15 (ISG 15) promoter, and the role of vIRF-1 in viral mimicry was implied. However, the molecular mechanism of this effect has not been clarified. Here, we extend this observation and show that vIRF-1 also downregulates the transcriptional activity of IFNA gene promoter in infected cells by interfering with the transactivating activity of cellular IRFs, including IRF-1 and IRF-3. We further show that ectopic expression of vIRF-1 in NIH 3T3 cells confers resistance to tumor necrosis factor alpha-induced apoptosis. While vIRF-1 is unable to bind DNA with the same specificity as cellular IRFs, we demonstrate by in vitro binding assay that it can associate with the family of cellular IRFs, such as IRF-1 and the interferon consensus sequence binding protein. vIRF-1 interaction domain was localized between amino acids (aa) 152 and 243. While no binding between the full-size IRF-3 and vIRF-1 could be detected by the same assay, we show that vIRF-1 also targets the carboxy-terminal region (aa 1623 to 2414) of the transcriptional coactivator p300 which could also bind IRF-3 and IRF-1. These results demonstrate that vIRF-1 can modulate the transcription of the IFNA genes by direct heterodimerization with members of the IRF family, as well as by competitive binding with cellular transcription factors to the carboxy-terminal region of p300.

3T3 Cells↗
PubMed1998

Primary activation of interferon A and interferon B gene transcription by interferon regulatory factor 3.

The family of interferon (IFN) regulatory factors (IRFs) encodes DNA-binding transcription factors, some of which function as modulators of virus-induced signaling. The IRF-3 gene is constitutively expressed in many tissues and cell types, and neither virus infection nor IFN treatment enhances its transcription. In infected cells, however, IRF-3 protein is phosphorylated at the carboxyl terminus, which facilitates its binding to the CBP/p300 coactivator. In the present study, we demonstrate that overexpression of IRF-3 significantly enhances virus-mediated transcription of the IFNA and IFNB genes in infected cells as well as IFN synthesis. IRF-3-mediated activation of IFN genes depends in part on carboxyl-terminal phosphorylation of a cluster of Ser/Thr residues, because a mutant with Ser/Thr to Ala substitutions activates the IFN promoter less efficiently. However, overexpression of IRF-3 in human 2FTGH cells alone results in the induction of an antiviral state, which depends on functional IFN signaling, because IRF-3 does not induce an antiviral state in mutant 2FTGH cells defective in either JAK-1 or p48 functions; also no antiviral effect of IRF-3 could be demonstrated in Vero cells that lack the IFNA and IFNB genes. This finding indicates that the observed antiviral activity of IRF-3 in 2FTGH cells results mainly from the induction of IFNs. Furthermore, E1A protein inhibited IRF-3-mediated stimulation of the IFNA4 promoter in transient expression assays; this inhibition could be reversed partially by overexpression of CBP/p300 and was not demonstrated with the mutant of E1A that does not bind p300. These results identify IRF-3 and CBP/p300 as integral components of the virus-induced complex that stimulates type 1 IFN gene transcription. The observation that adenovirus E1A antagonizes IRF-3 mediated activation suggests that E1A and IRF-3 may compete for binding to CBP/p300 and implicates a novel mechanism by which adenovirus may overcome the antiviral effects of the IFN pathway.

Adenoviridae↗
PubMed1998

Differential use of the betaL subunit of the type I interferon (IFN) receptor determines signaling specificity for IFNalpha2 and IFNbeta.

The signaling specificity for cytokines that have common receptor subunits is achieved by the presence of additional cytokine-specific receptor components. In the type I interferon (IFN) family, all 14 subtypes of IFNalpha, IFNbeta, and IFNomega bind to the same alpha and betaL subunits of the type I IFN-R, yet differences in signaling and biological effects exist among them. Our data demonstrate that IFNalpha2 and IFNbeta utilize different regions of the betaL subunit for signaling. Thus, in contrast to other cytokine systems, signal diversity in the type I IFN system can be accomplished within the same receptor complex by utilizing different regions of the same receptor subunits.

Animals↗
PubMed1997

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.

Animals↗
PubMed1995

Cloning and expression of a long form of the beta subunit of the interferon alpha beta receptor that is required for signaling.

The interferon alpha beta receptor (IFN alpha R) or type I IFN-R is formed by a 110-kDa alpha subunit or IFNAR and by a beta subunit, which has short and long forms (molecular masses of 55 and 95-100 kDa, respectively). In this report, we demonstrate that the IFN alpha/beta R cDNA recently cloned corresponds to the 55-kDa or short form of the beta subunit, while the 95-100-kDa species reported here corresponds to a longer form of the IFN alpha/beta R cDNA that is probably produced by alternative splicing of the same gene. Stable transfection of the alpha subunit with either form of the beta subunit results in the expression of low and high affinity receptors, while expression of either form of the beta subunit alone only produces low affinity receptors. More important, only expression of the alpha and long form of the human beta subunits in mouse L-929 cells reconstitutes the activation of the Jak kinases and the Stat factors, as well as the antiviral response to human type I IFNs.

Amino Acid Sequence↗
PubMed1989

Upstream regulatory elements of murine alpha 4-interferon gene confer inducibility and cell type-restricted expression.

We have identified and functionally characterized DNA sequences that are required for the inducible and cell-restricted expression of the murine alpha 4-interferon gene. Hybrid plasmids in which the alpha 4 promoter region or its 5' deletions were inserted upstream of the CAT gene were constructed, and the expression of these hybrid genes was studied in mouse L-cells both in permanent and transient assays with comparable results. Inducible expression was not affected by deletions up to -109; however, when the deletion was extended to -96, inducibility by Newcastle disease virus was abolished; however, this hybrid plasmid was expressed constitutively. Further deletion to -88 did not permit either constitutive or inducible expression. Insertion of the 35-base pair-long sequence (-109 to -75 base pairs) from the alpha 4 promoter region 5' of the minimal alpha 4 or human immunodeficiency virus promoter region, conferred inducibility to these two inactive promoters. The 5' deleted hybrids or plasmids containing the inducible element were induced only at low levels in transfected NIH/3T3 cells that do not express endogenous alpha 4 gene efficiently, indicating that the inducible region also determines the cell-specific expression. A tandem repeat of AGTGAA, which is present in the -109 to -88 region of alpha 4 in two copies, showed both basal levels of expression and inducibility in L-cells, while its analogue AATGAA was highly inducible but was not expressed constitutively. The inducibility of the synthetic hexamer repeats did not show cell type-restricted expression, suggesting that their response does not fully reflect the range of expression observed for the inducible region and the endogenous alpha genes.

Animals↗
PubMed1986

Synthesis of fusion and mature murine alpha interferons in Escherichia coli.

Four murine interferon-alpha (MuIFN-alpha) genes (alpha 1, alpha 4, alpha 5, alpha 6) were previously identified and characterized. The coding regions of these IFN-alpha genes were inserted into bacterial expression vectors behind the lpp promoter under the control of the lac promoter-operator region, resulting in fusion peptides containing additional N-terminal amino acids (aa). Plasmids coding for the expression of mature IFN-alpha 1 and alpha 5 were also constructed using the same vector system, by inserting a 30-bp synthetic oligodeoxynucleotide, which contains a stop codon for the lpp gene, a ribosome-binding sequence and an ATG start codon for the IFN peptides. The amounts of IFN polypeptides synthesized in Escherichia coli were estimated in the maxi-cell system and their biological activities were measured on mouse and other mammalian cells. The yields of mature IFN produced in this vector were 2 to 4 X 10(6) units/liter; the antiviral activity of the majority of the MuIFNs on human and bovine cells was 100- to 1000-fold lower than on mouse cells. IFN-alpha 4, which contains an internal deletion of 5 aa, showed a lower antiviral activity than other MuIFNs on mouse cells.

Amino Acid Sequence↗
PubMed1985

Differential regulation of interferon synthesis in lymphoblastoid cells.

We have examined the molecular mechanisms involved in the induction and regulation of expression of alpha and beta 1 human interferons (HuIFN) in Namalva cells. Cloned IFN-alpha and -beta 1 cDNAs, and antisera to purified IFN-alpha and -beta 1 were used as specific probes to determine the expression of HuIFN genes both on the RNA and protein levels. The rates of gene transcription were correlated with the relative levels of HuIFN mRNA present in induced cells and with the amounts of HuIFN peptides synthesized by these cells. The comparative rate of transcription of HuIFN-alpha and -beta 1 genes was measured in nuclei isolated from Namalva cells before and after induction. No transcription of HuIFN-alpha and -beta 1 genes was detected in nuclei isolated from the uninduced cells. The correspondence in the rate of HuIFN-alpha and -beta 1 genes transcription after virus infection with the relative levels of HuIFN mRNA in the induced cells indicates that the stimulation of HuIFN synthesis by viral infection results from the activation of the transcription of HuIFN genes. The relative levels of alpha and beta 1 induced transcripts were the same in spite of the differences in the number of copies of HuIFN-alpha and -beta 1 genes indicating that the beta 1 gene is transcribed more efficiently than the alpha genes. The steady-state levels of HuIFN-alpha and -beta 1 mRNAs in induced Namalva cells are comparable, however, the overall amount of HuIFN-beta 1 synthesized (as determined by radioimmunoassay and biological activity) is approximately 10-fold lower than that of IFN-alpha. No evidence has been found that would indicate that HuIFN-beta 1 mRNA induced in Namalva cells is different from that induced in human fibroblasts. The data indicate, however, that in Namalva cells, the IFN-beta 1 polypeptide has a higher turnover rate and slower rate of release into medium than the HuIFN-alpha polypeptides, indicating that the observed difference in the overall amounts of these two types of interferons present in the medium is due to regulation on posttranslational level.

Animals↗
PubMed1982

Induction of human beta-interferon synthesis with poly(rI . rC) in mouse cells transfected with cloned cDNA plasmids.

Human genomic DNA and plasmids carrying portions of the cDNA gene for human beta-interferon have been introduced into mouse Ltk- cells by cotransfection with a herpes simplex virus thymidine kinase (TK) gene. One plasmid contains 840 base pairs of human DNA complementary to pre-beta-interferon mRNA inserted into pBR322, whereas the other plasmids have hybrid genes containing only the 560-base pair coding region inserted under the transcriptional control of the TK promoter. Constitutive interferon production could not be detected in any of the mouse TK+ cell lines tested. Nevertheless, synthesis of interferon could be induced by poly(rI . rC) treatment in at least 16 of these cell lines, including clones transfected with genomic DNA, the beta-interferon cDNA, and the TK-beta-interferon cDNA hybrid gene. The interferon produced was specific for human cells and could be neutralized by antiserum against human beta-interferon. In contrast to human fibroblast cells, in which the synthesis of induced beta-interferon is transient, the poly(rI . rC)-induced TK+ lines continued to produce beta-interferon for prolonged periods of time and did not respond to superinduction conditions. Therefore, in transfected mouse cells, the coding DNA sequence from the human beta-interferon gene, without any of the adjacent 3' or 5' flanking human DNA sequences, was sufficient both to direct synthesis of biologically active product and to respond to the specific induction system that operates in human cells. However, the mechanism that switches off the synthesis of induced interferon in human cells appears not to operate in mouse cells transfected with beta-interferon cDNA.

Cell Line↗
PubMed1976

The effect of feeding on oxygen consumption, RQ and plasma levels of glucose, FFA, and D-beta-hydroxybutyrate in newborn infants of diabetic mothers and small for gestational age infants.

Eight infants of strictly controlled diabetic mothers (IDM), 8 infants of gestational diabetic mothers (IGDM) and 6 small for gestational age infants (SGA) were studied before the first feeding and during an early feeding regimen. In IDMs and IGDMs continuous monitoring from 2 hours up to 7 1/2 hours after birth before feeding revealed no consistent changes of VO2 and RQ. The groups of infants were studied on 4 different occasions: (I) 2 to 16 hours, (II) 1 to 2 days, (III) 3 to 4 days, and (IV) 7 to 11 days. Prefeeding VO2-values were not significantly different between each of the groups, but mean RQ was higher in IGDMs than in IDMs. Age of the infant and prefeeding RQ were inversely correlated (r = -0.537, p less than 0.02). With increasing age and milk intake VO2 increased significantly in all groups. RQ decreased during the first 24 to 48 hours in all groups and rose thereafter with highest values at 7 to 11 days. Plasma levels of glucose, FFA, and D-beta-hydroxybutyrate were not significantly different between each of the group. The highest values for D-beta-hydroxybutyrate were found at 1-2 days when the lowest RQ values were also recorded. D-beta-hydroxybutyrate concentrations and RQ values (r = 0.648, p less than 0.001) were inversely correlated suggesting increasing oxidation of fat. Feeding resulted in a marked rise in RQ to values around unity, which preceded a distinct increase in VO2 that reached a maximum at 1 to 1 1/2 hour after the feed, then slowly returned to pretest values. The rise in VO2 was accompanied by an increase in rectal temperature (0.4 to 1.5 degrees C). VO2, RQ, and plasma levels of glucose, FFA, and D-beta-hydroxybutyrate, were almost identical for each of the groups. We suggest: 1) That differences in feeding practice is the most likely explantation for the discrepancy between reported values for VO2, RQ, and circulating substrates in normal and low birth weight newborns. 2) That the rise in VO2 during the neonatal period, caused by feeding, reflects the cost of growth.

Adult↗