engleski

Backsorting of the cell surface MHC class I molecules by murine cytomegalovirus glycoproteins

Murine cytomegalovirus (MCMV) encodes glycoproteins that are responsible for down-regulation of the cell surface resident MHC class I molecules. The down-regulation occurs 6-7 hours post infection with the wild type MCMV. Two viral glycoproteins of 48 and 34 kDa coprecipitate with MHC class I molecules from the cell surface. Glycoprotein of 48 kDa, encoded by the MCMV m06 gene, directs newly synthesized MHC class I complexes for degradation in lysosomes. Glycoprotein of 34 kDa that is encoded by the m04 gene binds tightly to MHC class I molecules in the endoplasmic reticulum and the complex is exported to the cell surface. The function of these two glycoproteins in the down-regulation MHC class I molecules was tested. The down-regulated proteins were followed in the intracellular compartments by the cell-surface biotinylation and immunoprecipitation after different periods of time. The cell surface MHC class I molecules are backsorted into endosomal compartment, but they are not directed for degradation in lysosomes. Deletion of the m06 gene from MCMV prevents cell surface down-regulation indicating that the m06 protein participates in the backsorting but is not able to directs them to the lysosomes. Although the m04 protein binds strongly to cell surface MHC class I complexes it does not down-regulate MHC class I molecules, and it has no protective function on the MHC molecules that are backsorted by the m06 protein.

antigen presentation; ER retention; Gp34; MHC class I; murine cytomegalovirus

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