Functional screening of yeast artificial chromosomes was previously used to isolate and clone the accessory factor, or second chain, of the human IFN-␥ 1 receptor (Soh et al., 1993(Soh et al., , 1994a(Soh et al., , 1994bCook et al., 1993Cook et al., , 1994 and more recently to identify a YAC (the F136C5 YAC or ␣YAC) which contains the genes required for responsiveness to human interferon ␣ (Hu-IFN-␣), human interferon ␤ (Hu-IFN-␤), and human interferon (Hu-IFN-), the type I interferons (Soh et al., 1994b). The ␣YAC encodes components of the type I interferon receptor (also called the IFN-␣ receptor) and contains at least two genes encoding subunits of this receptor complex (Soh et al., 1994b;Cleary et al., 1994;Emanuel, 1995): the first subunit identified, designated Hu-IFN-␣R1 (Uzé et al., 1990), and a second receptor subunit designated Hu-IFN-␣R2 (Novick et al., 1994). In addition, the ␣YAC encodes the gene for CRFB4, a transmembrane protein which, like the aforementioned subunits, is a member of the cytokine type II receptor family (Lutfalla et al., 1993), but which so far has no defined role in signal transduction in response to the type I interferons.In the process of isolating cDNA clones for the Hu-IFN-␣R1 chain, a splice variant of the Hu-IFN-␣R1 chain was discovered. This splice variant, designated Hu-IFN-␣R1s, was shown to be missing exons 4 and 5, which encode one of four subdomains of the extracellular domain of the receptor (Cleary et al., 1992;Cleary, 1995). The function of the Hu-IFN-␣R1s chain could not be readily ascertained because the individual components of the Hu-IFN-␣ receptor have not been identified. However, Cleary et al. (1994) reported that hamster cells containing a disrupted ␣YAC (or ⌬␣YAC) are incapable of responding to Hu-IFN-␣A and Hu-IFN-␣B2, but become fully responsive when transfected with an expression vector for the Hu-IFN-␣R1 chain. Therefore, the ⌬␣YAC expresses all genes required for human IFN-␣ responsiveness except for IFNAR1. These cells containing the ⌬␣YAC, designated 16-9/⌬␣YAC, made it possible to examine the function of Hu-IFN-␣R1s and the interaction of various type I human interferons with the Hu-IFN-␣R1 and Hu-IFN-␣R1s chains as described in this report. EXPERIMENTAL PROCEDURESCells-The 16-9 cell line is a human ϫ hamster hybrid containing the long arm of human chromosome 6 and a transfected HLA-B7 gene (Cook et al., 1994). The 16-9/␣YAC cells were obtained by transforming 16-9 cells with the ␣YAC (F136C5) as described (Soh et al., 1994b); 16-9/ ⌬␣YAC cells contain the deleted ⌬␣YAC whose IFNAR1 gene was disrupted by homologous recombination (Cleary et al., 1994); 16-9/ ⌬␣YAC/␣R1 cells are the 16-9/⌬␣YAC cell line transfected with the cDNA clone for Hu-IFN-␣R1; and the 16-9/⌬␣YAC/␣R1s cell line is a 16-9/⌬␣YAC cell line transfected with the cDNA clone for the Hu-IFN␣R1s. The 16-9 cell line was maintained in F12 medium plus 10% fetal bovine serum. The 16-9/␣YAC and 16-9/⌬␣YAC cell lines were grown in F12 plus 10% fetal bovine serum and 350 g/ml antibiotic G418....

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A murine monoclonal IgG2b with high affinity and specificity for O6-methylguanine was developed. This allowed visualization of this adduct in paraffin-embedded sections by indirect fluorescence or immunoperoxidase methods. The antibody was used to study and compare the formation and persistence of this adduct detected by immunohistochemistry and the presence of 14C methyl by autoradiography in sections from adult human pancreas explants exposed to [14C methyl]dimethylnitrosamine (DMN) and organ-cultured for up to 7 days. O6-methylguanine was detectable randomly and with varied intensity in parenchymal cell nuclei and cytoplasms, 6 h after exposure to DMN. Following RNase treatment, however, only 7.5% of nuclei revealed measurable staining. The positive nuclei decreased to 2.5% within 24 h and remained about the same throughout the 7 days of culture. This correlated well with the change in percentage of positive nuclei for 14C methyl autoradiographic grains which were selectively condensed over the O6-methylguanine-stained nuclei. The data demonstrate a subpopulation of repair-deficient parenchymal cells of human pancreas exposed to DMN.

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