Endocytosis of the class I major histocompatibility antigen via a phorbol myristate acetate-inducible pathway is a cell-specific phenomenon and requires the cytoplasmic domain.
Class I major histocompatibility (MHC) antigens are expressed by virtually all mammalian cells, yet their levels of expression and behavior on the cell surface vary in a cell-specific fashion. A panel of lymphoid (both B and T) and nonlymphoid cell lines was used to study the kinetics of internalization of the H-2Ld class I MHC in different cell types. These studies revealed that endocytosis of H-2Ld occurs by both constitutive and PMA-regulated pathways in lymphoid cells, but only by a PMA-refractory pathway in the nonlymphoid cells tested. Transfectant derivatives of the T lymphoma, EL4, which express wild-type or mutant H-2Ld class I MHC antigens, were used to investigate the requirement for the cytoplasmic domain of the class I MHC antigen for its endocytosis in T lymphocytes. These studies showed that modification or deletion of the cytoplasmic domain of H-2Ld abrogates endocytosis via a PMA-regulated pathway. The role of cytoplasmic domain phosphorylation in PMA-inducible endocytosis was examined. The wild-type H-2Ld antigen is phosphorylated in all cell types examined, and this phosphorylation is up-regulated by PMA treatment. In contrast, cytoplasmic domain mutants of H-2Ld fail to be phosphorylated in vivo, in the presence or absence of PMA. The universality of PMA-inducible hyperphosphorylation of the class I MHC antigen among diverse cell types leads us to conclude that phosphorylation of the cytoplasmic domain, while perhaps necessary, is not sufficient for triggering endocytosis via a PMA-inducible pathway. Furthermore, the results with the cytoplasmic domain mutants of H-2Ld suggest that a structural conformation of the class I MHC cytoplasmic domain is required for endocytosis via this route.
Capps
G G
GG
Department of Microbiology, University of Texas, Austin 78712-1095.
Van Kampen
M
M
Ward
C L
CL
Zúñiga
M C
MC
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D002872:Chromosome Deletion; D003593:Cytoplasm / Q000187:drug effects / Q000502:physiology; D004705:Endocytosis / Q000187:drug effects*; D005805:Genes, MHC Class I; D006183:H-2 Antigens / Q000235:genetics; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D006183:H-2 Antigens; D013755:Tetradecanoylphorbol Acetate