MHC CLASS-I EXPRESSION AND TRANSPORT IN A CALNEXIN-DEFICIENT CELL-LINE

The human leukemic cell line, GEM, and an NK-resistant variant of GEM, called CEM-NKR, were analyzed for protein differences by two-dimensio nal gel electrophoresis. One protein was found to be completely absent in CEM-NKR. This protein has been identified as calnexin. CEM-NKR als o completely lacks calnexin RNA. Calnexin is thought to act as a molec ular chaperone by assisting in the assembly and/or retention of MHC cl ass I and many other membrane and secreted proteins. The surface expre ssion of class I molecules on CEM-NKR was compared with CEM by several Abs. There was no significant class I expression differences between CEM and CEM-NKR using w6/32 (a conformational and beta(2)-microglobuli n-dependent mAb), HC-10 (a conformational and beta(2)-microglobulin-in dependent mAb), and an anti-class I antiserum that reacts with native and denatured class I. The transport rate of class I in both cell line s was examined by pulse-chase experiments, immunoprecipitating class I with w6/32 and anticlass I antiserum. The results show that class I m olecules in the calnexin-deficient cell line and its parent cell line are transported at similar rates. These results indicate that calnexin is not absolutely required for the viability of CEM or the transport and surface expression of human MHC class I molecules.