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.     

Cloning and sequence analyses of cDNAs for interferon- and virus-induced human Mx proteins reveal that they contain putative guanine nucleotide-binding sites: functional study of the corresponding gene promoter.

The human protein p78 is induced and accumulated in cells treated with type I interferon or with some viruses. It is the human homolog of the mouse Mx protein involved in resistance to influenza virus. A full-length cDNA clone encoding the human p78 protein was cloned and sequenced. It contained an open reading frame of 662 amino acids, corresponding to a polypeptide with a predicted molecular weight of 75,500, in good agreement with the Mr of 78,000 determined on sodium dodecyl sulfate gels for the purified natural p78 protein. The cloned gene was expressed in vitro and corresponded in size, pI, antigenic determinant(s), and NH2 terminus sequence to the natural p78 protein. A second cDNA was cloned which encoded a 633-amino-acid protein sharing 63% homology with human p78. This p78-related protein was translated in reticulocyte lysates where it shared an antigenic determinant(s) with p78. A putative 5' regulatory region of 83 base pairs contained within the gene promoter region upstream of the presumed p78 mRNA cap site conferred human alpha interferon (IFN-alpha) inducibility to the cat reporter gene. The p78 protein accumulated to high levels in cells treated with IFN-alpha. In contrast, the p78-related protein was not expressed at detectable levels. The rate of decay of p78 levels in diploid cells after a 24-h treatment with IFN-alpha was much slower than the rate of decay of the antiviral state against influenza A virus and vesicular stomatitis virus, suggesting that the p78 protein is probably not involved in an antiviral mechanism. Furthermore, we showed that these proteins, as well as the homologous mouse Mx protein, possess three consensus elements in proper spacing, characteristic of GTP-binding proteins.     

trans activation of type 1 interferon promoters by simian virus 40 T antigen.

A human transient expression system was used to measure the influence of simian virus 40 T antigen and adenovirus E1a proteins on the activation of alpha interferon subtype 1 (IFN-alpha 1) and IFN-beta promoters linked to the reporter chloramphenicol acetyltransferase gene. Large T-antigen production, amplified by expression plasmid replication in transfected 293 cells, was able to trans activate the IFN-beta promoter 5- to 10-fold, increasing both the constitutive and Sendai virus-induced levels of expression. Surprisingly, the previously quiescent transfected IFN-alpha 1 promoter in T-antigen-expressing cells displayed a level of inducibility similar to IFN-beta. The endogenous IFN-alpha 1 gene was also inducible to a limited extent in cells expressing T antigen. A truncated IFN-beta promoter deleted to position -37 relative to the CAP site was neither inducible nor trans activated by T antigen, suggesting that sequences required for efficient induction were also needed for trans activation. Since 293 cells express adenoviral E1a proteins, experiments were also performed in HeLa cells to assess the relative contribution of T antigen and E1a proteins to IFN trans activation. In HeLa cells, T-antigen coexpression increased the constitutive level of IFN-beta and IFN-alpha 1 promoter activity without augmenting relative inducibility. Coexpression of T antigen and E1a proteins did not have a cooperative effect on type 1 IFN expression.     

Organization, structure and expression of murine interferon alpha genes.

Using a human interferon-alpha probe we have isolated recombinant phages containing murine interferon-alpha (Mu IFN-alpha) genes from a genomic library. One of these phages contained two complete Mu IFN-alpha genes and part of a third gene. The insert of a second phage held two IFN genes. This indicates that the Mu IFN-alpha genes are clustered in the genome as is the case for the analogous human genes. The nucleotide sequences of these 5 genes were determined. They show that the genes are all different, albeit highly homologous. The deduced amino acid sequences show that four of the five genes contain a putative glycosylation site. Three genes were transiently expressed in COS cells and they gave rise to protein products showing antiviral properties. The expression of the five Mu IFN-alpha genes and the Mu IFN-beta gene was studied in virus-induced mouse L cells. The individual mRNAs were visualized in a nuclease S1 experiment, using a specific probe for each gene. In RNA preparations from induced cells mRNAs for each of the five alpha genes and the beta gene were present. However, substantial differences in the amounts of the individual mRNAs were observed.