Hydrophilic anchor-deficient Thy-1 is secreted by a class E mutant T lymphoma

To investigate the mechanism of glycophospholipid anchoring of the surface antigen Thy-1, we have undertaken a comparative biosynthetic study using a wild-type Thy-1+ murine T lymphoma (BW5147) and a mutant T lymphoma (class E) that synthesizes Thy-1 but fails to express it on the plasma membrane. Labelling experiments with D-2-3H]mannose demonstrate that, unlike the wild type, the mutant cells are secreting large amounts of Thy-1 and that the secreted molecules are hydrophilic. Moreover, unlike the wild type, they fail to incorporate 3H]palmitic acid into Thy-1. Both wild-type and mutant cells do incorporate labeled galactose and fucose into Thy-1. We conclude that the lack of surface expression of Thy-1 by this mutant results from the failure to add anchor components to Thy-1.