title: The phenotype of five classes of T lymphoma mutants. Defective glycophospholipid anchoring, rapid degradation, and secretion of Thy-1 glycoprotein.
abstract: Thy-1 glycoprotein is a member of a class of proteins which are anchored to the plasma membrane via a covalently bound glycophospholipid. The biosynthesis and anchoring of Thy-1 were investigated in a family of wild-type and mutant (complementation groups A, B, C, E, and F) T lymphomas. The mutants all synthesize Thy-1 but fail to express it on the cell surface. Analysis of the size of D-[2-3H]mannose-labeled dolichol-linked oligosaccharides showed that the class E mutant is the only cell line which does not synthesize dolichol-P-P-Glc3Man9GlcNAc2. Turnover and possible secretion of Thy-1 by mutant T lymphoma cells were documented in D-[2-3H]mannose pulse-chase experiments. The turnover of [3H]Thy-1 for all wild-type cells is considerably slower than for the mutant cells. Class B and E cells release appreciably more [3H]Thy-1 than wild-type cells. Additional experiments were performed to determine the electrophoretic mobility and hydrophobicity of cell-associated and released forms of Thy-1 labeled overnight with [3H]mannose. All wild-type and class A, C, E, and F mutant cells contain a major Triton X-114 binding species of cell-associated [3H]Thy-1. All extracellular [3H]Thy-1 was almost exclusively hydrophilic. The presence of two Thy-1 anchor components, ethanolamine and palmitate, was investigated. Biosynthetic labeling with [3H]palmitic acid showed that all of the wild-type cells but none of the mutants incorporated this anchor precursor into Thy-1. In [3H]ethanolamine-labeling experiments, incorporation was detected in the Thy-1 of all wild-type cells and in two mutants, S1A-b and T1M1-c. Based on the above studies, the phenotype of Thy-1 negative T lymphoma mutants can be re-evaluated. In classes A and F, dolichol-linked oligosaccharides appear normal and no anchor is detected. In class B, dolichol-linked oligosaccharides appear normal, a partial anchor may be present, and a substantial amount of Thy-1 is released. In class C, dolichol-linked oligosaccharides appear normal and a partial anchor may be present. In class E, truncated dolichol-linked oligosaccharides are formed, no anchor is detected, but a substantial amount of newly synthesized Thy-1 is released. These observations are discussed with reference to the possibility that the lesions which characterize the mutants pertain to the biosynthesis of the glycophospholipid moiety of Thy-1.
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism*; D002460:Cell Line; D004286:Dolichols / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D019856:Ethanolamine; D004983:Ethanolamines / Q000378:metabolism; D007700:Kinetics; D008223:Lymphoma / Q000235:genetics*; D008358:Mannose / Q000378:metabolism; D051379:Mice; D009154:Mutation; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D010641:Phenotype; D013601:T-Lymphocytes; D018800:Thy-1 Antigens; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D000954:Antigens, Surface; D004286:Dolichols; D004983:Ethanolamines; D010169:Palmitic Acids; D018800:Thy-1 Antigens; D019308:Palmitic Acid; D019856:Ethanolamine; D008358:Mannose