The role of beta-2 microglobulin in temperature-sensitive and interferon-gamma-induced exocytosis of HLA class I molecules.
The passage of MHC class I heavy chains through the exocytic pathway is promoted by association with beta 2 microglobulin (beta 2m). In order to analyze the structural basis of this phenomenon, processing and cell surface expression of HLA class I molecules have been investigated in the beta 2m null human melanoma cell line FO-1 transfected with either the human or mouse beta 2m genes. These natural structural variants of beta 2m display 30% amino acid sequence divergence. In comparison with a human beta 2m transfectant of the FO-1 cell line (designated FO-1H), FO-1 cells transfected with the mouse beta 2m gene (FO-1C) express HLA class I molecules that are processed with grossly altered kinetics and are present on the cell surface at reduced levels. The suboptimal expression of HLA class I heavy chains encoded by FO-1C cells reflects a defect in heavy chain stability since cell surface expression of HLA class I antigens was increased following incubation at 30 degrees C. The increased cell surface expression paralleled accelerated processing of HLA class I heavy chains by FO-1C cells. In contrast, no induction in either cell surface expression or processing of HLA class I heavy chains was observed for the beta 2m-negative FO-1 parent cell line, which remained HLA class I antigen null when cultured at 30 degrees C, or the FO-1H human beta 2m transfectant, which expressed equivalent levels of HLA class I antigens on the cell surface at 37 degrees C and 30 degrees C. Further up-regulation of the temperature-sensitive induction of HLA class I antigen expression was accomplished by treatment of the FO-1C transfectant with interferon-gamma; this latter effect appears to be active at a posttranscriptional step for FO-1 cells since IFN-gamma was not as potent a transcriptional activator at 30 degrees C as it was at 37 degrees C. These results indicate that HLA class I heavy chains expressed by FO-1C cells are subject to temperature-sensitive and cytokine-inducible stabilization that increases their affinity for the structural variant of beta 2m and promotes exocytosis of the HLA class I heterodimer to the cell surface. Furthermore, beta 2m non-conformed MHC class I heavy chains undergo stabilization that is not associated with enhanced cell surface expression, indicating that the exocytosis of putative "empty" HLA class I antigens is a process dependent upon association with beta 2m.
Tatake
R J
RJ
Department of Pathology, University of Connecticut Health Center, Farmington 06030.
Ferrone
S
S
Zeff
R A
RA
D000818:Animals; D001483:Base Sequence; D005089:Exocytosis / Q000187:drug effects*; D015395:Histocompatibility Antigens Class I / Q000502:physiology*; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D008545:Melanoma; D051379:Mice; D008969:Molecular Sequence Data; D013696:Temperature; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000276:immunology / Q000502:physiology; D001613:beta 2-Microglobulin / Q000502:physiology*
D015395:Histocompatibility Antigens Class I; D001613:beta 2-Microglobulin; D007371:Interferon-gamma