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The type I interferons, interferon-alpha (IFN-alpha) and interferon-beta (IFN-beta), are situated on the short arm of chromosome 9, specifically 9p21-22. This locus lies very close to an area that is deleted or rearranged in nearly half of all melanomas tested. The identification of 9p rearrangements in both melanoma precursor lesions (dysplastic naevi) and primary lesions has implicated the 9p locus in the early stages of melanoma development. Recent evidence has demonstrated that metastatic melanoma cell lines have a specific loss of IFN-alpha gene expression, a defect that appears to occur at the level of transcription. In this study, we examined the expression of IFN-alpha in cell lines isolated from the various stages of melanoma progression, with a view to determine the prevalence of the IFN-alpha transcription defects exhibited by malignant melanoma, and to assess whether the loss of IFN-alpha expression was particular to a certain stage of melanoma progression. We showed that all the melanoma cell lines tested (n=20) demonstrated an inability to express IFN-alpha, a defect that was reflected in the apparent inactivity of the IFN-alpha promoter. These defects were found to occur in cells isolated from early melanomas, lending support to the hypothesis that IFN-alpha has a role in the aetiology of malignant melanoma.

Type I interferons constitute an important part of the innate immune response against viral infection. Unlike the expression of interferon (IFN) B gene, the expression of IFNA genes is restricted to the lymphoid cells. Both IFN regulatory factor 3 and 7 (IRF-3 and IRF-7) were suggested to play positive roles in these genes expression. However, their role in the differential expression of individual subtypes of human IFNA genes is unknown. Using various IFNA reporter constructs in transient transfection assay we found that overexpression of IRF-3 in virus infected 2FTGH cells selectively activated IFNA1 VRE, whereas IRF-7 was able to activate IFNA1, A2, and A4. The binding of recombinant IRF-7 and IRF-3 to these VREs correlated with their transcriptional activation. Nuclear proteins from infected and uninfected IRF-7 expressing 2FTGH cells formed multiple DNA-protein complexes with IFNA1 VRE, in which two unique DNA-protein complexes containing IRF-7 were detected. In 2FTGH cells, virus stimulated expression of IFNB gene but none of the IFNA genes. Reconstitution of IRF-7 synthesis in these cells resulted, upon virus infection, in the activation of seven endogenous IFNA genes in which IFNA1 predominated. These studies suggest that IRF-7 is a critical determinant for the induction of IFNA genes in infected cells.

Type-I interferons are encoded by a multigene family, the major members of which are at least 13 IFN A subtypes and a single IFN B gene. IFNs A and B are induced in response to similar stimuli, such as virus infection and double-stranded RNA, but in different cell types: the induction of IFN A is almost exclusively restricted to cells of lymphoid origin, while IFN B has been found to be induced in a variety of cell types including fibroblasts. The virus-responsive enhancer element in the promoter region of IFN A family members is largely responsible for the differential expression of individual subtypes in responsive cells. In this paper we describe experiments which address the issue of the differential expression of IFN A and IFN B in different cell types. We show that IFN-beta is induced in a variety of cells of different origin, while not all of these are able to secrete IFN-alpha. By transfection of reporter gene constructs comprising the virus-responsive enhancer from the IFN A1 and IFN B genes, we show that this differential response is mediated at the level of transcription via these control elements. More detailed analysis of the function of these regions identifies specific sequences within the IFN A1 virus response element that has an inhibitory effect on expression in cells that are normally inducible, and is also implicated in the overall suppression of IFN A induction in non-inducible cells.

This paper addresses the role of transcriptional regulation in the determination of the levels of expression of different interferon-alpha subtypes secreted from Namalwa cells following infection with Sendai virus. Using RT-PCR to determine the relative abundance of mRNA species coding for the various subtypes, we found a general correlation with corresponding protein levels, indicative of a role for transcriptional control in the determination of levels of individual subtypes. We have used reporter gene constructs to compare the inducibility of the virus-response elements from the IFNA1, A2, A4, and A14 subtype genes cloned upstream of a secreted alkaline phosphatase gene. The inducibility of these reporter gene constructs broadly correlated with the relative mRNA abundances in both transiently and stably transfected Namalwa cells. During work with stable cell lines, we found that G418, the drug used for the selection of transfected cells, inhibited the induction of interferon by both Sendai virus and double-stranded RNA. This inhibition was reversible when G418 was removed from the medium 24 h before the addition of virus.