HCV E2-caused down-regulation of IRS-1 may be through an ubiquitination. In the absence or presence of MG132 (10 and 20 nM), Huh7 cells were transfected with FLAG-CMV2 or FLAG-E2 for 24 hours and then subjected to immunoblotting with the indicated antibodies (A). Results indicated that MG132, proteosomal proteolysis inhibitor, may restore the E2-related down-regulation of IRS1. Furthermore, cell lysates were subjected to immunoprecipitation with IRS-1 followed by immunoblotting with anti-ubiquitin antibody. Results in (B) indicated that HCV E2 caused an accumulation of ubiquitin-conjugated IRS-1.