Functional significance of globotriaosyl ceramide in interferon‐α2/type 1 interferon receptor‐mediated antiviral activity

Abstract

The N-terminus of the type 1 interferon receptor subunit, IFNAR1, has high amino acid sequence similarity to the receptor binding B subunit of the Escherichia coli-derived verotoxin 1, VT1. The glycolipid, globotriaosyl ceramide (Gb3: Gal α1 → 4 Gal β 1 → 4 Glu β 1 → 1 Cer) is the specific cell receptor for VT1. Gb3-deficient variant cells selected for VT resistance are cross-resistant to interferon-α (IFN-α)–mediated antiproliferative activity. The association of eIFNAR1 with Gal α 1 → 4 Gal containing glycolipids has been previously shown to be important for the receptor-mediated IFN-α signal transduction for growth inhibition. The crucial role of Gb3 for the signal transduction of IFN-α–mediated antiviral activity is now reported. IFN-α–mediated antiviral activity, nuclear translocation of activated Stat1, and increased expression of PKR were defective in Gb3-deficient vero mutant cells, although the surface expression of IFNAR1 was unaltered. The VT1B subunit was found to inhibit IFN-α–mediated antiviral activity, Stat1 nuclear translocation and PKR upregulation. Unlike VT1 cytotoxicity, IFN-α–induced Stat1 nuclear translocation was not inhibited when RME was prevented, suggesting that the accessory function of Gb3 occurs at the plasma membrane. IFN-α antiviral activity was also studied in Gb3-positive MRC-5 cells, which are resistant to IFN-α growth inhibition, partially resistant to VT1 but still remain fully sensitive to IFN-α antiviral activity, and two astrocytoma cell lines expressing different Gb3 fatty acid isoforms. In both systems, long chain fatty acid-containing Gb3 isoforms, which are less effective to mediate VT1 cytotoxicity, were found to correlate with higher IFN-α–mediated antiviral activity. Inhibition of Gb3 synthesis in toto prevented IFN-α antiviral activity in all cells. We propose that the long chain Gb3 fatty isoforms preferentially remain in the plasma membrane, and by associating with IFNAR1, mediate IFN-α antiviral signaling, whereas short chain Gb3 fatty acid isoforms are preferentially internalized to mediate VT1 cytotoxicity and IFNAR1-dependent IFN-α growth inhibition. J. Cell. Physiol. 182:97–108, 2000. © 2000 Wiley-Liss, Inc.