Misfolding of major histocompatibility complex class I molecules in activated T cells allows cis-interactions with receptors and signaling molecules and is associated with tyrosine phosphorylation.
Knowledge of the origin and biochemical status of beta(2)-microglobulin-free or misfolded major histocompatibility complex (MHC)-I molecules is essential for understanding their pleiotropic properties. Here we show that in normal human T cells, misfolding of MHC-I molecules is turned on upon activation and cell division and is proportional to the level of proliferation. Immunoprecipitation showed that a number of proteins are associated with MHC-I heavy chains at the surface of activated T cells, including the CD8alphabeta receptor and the chaperone tandem calreticulin/ERp57, associations that rely upon the existence of a pool of HC-10-reactive molecules. Biochemical analysis showed that misfolded MHC-I molecules present at the cell surface are fully glycosylated mature molecules. Importantly, misfolded MHC-I molecules are tyrosine phosphorylated and are associated with kinase activity. In vitro kinase assays followed by reprecipitation indicated that tyrosine phosphorylation of the class I heavy chain is probably mediated by a Src tyrosine kinase because Lck was found associated with HC-10 immunocomplexes. Finally, we show that inhibition of tyrosine phosphorylation by using the Src-family tyrosine kinase inhibitor PP2 resulted in enhanced release of MHC-I heavy chains from the cell surface of activated T cells and a slight down-regulation of cell surface W6/32-reactive molecules. This study provides new insights into the biology of MHC-I molecules and suggests that tyrosine phosphorylation may be involved in the regulation of MHC-I misfolding and expression.
Division of Human Genetics and Genetic Disorders, Institute for Molecular and Cell Biology, Ruua do Campo Alegre, 823, 4150-180 Porto, Portugal.
Susana G
SG
Santos
Simon J
SJ
Powis
Fernando A
FA
Arosa
D019921:Biotinylation; D015153:Blotting, Western; D016827:CD8 Antigens / Q000378:metabolism; D037282:Calreticulin / Q000378:metabolism; D049109:Cell Proliferation; D003101:Collodion / Q000737:chemistry; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D005805:Genes, MHC Class I; D006031:Glycosylation; D006801:Humans; D047468:Immunoprecipitation; D007700:Kinetics; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D017510:Protein Folding; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011743:Pyrimidines / Q000737:chemistry; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism*; D013997:Time Factors; D014443:Tyrosine / Q000737:chemistry*
C412373:AG 1879; D016827:CD8 Antigens; C433839:CD8alphabeta antigen; D037282:Calreticulin; D010455:Peptides; D011743:Pyrimidines; D014443:Tyrosine; D003101:Collodion; D011505:Protein-Tyrosine Kinases