Formation, turnover, and sensitivity to phosphatidylinositol-specific phospholipase C of Thy-1 of a rat neuronal tumor cell line.

We have investigated the formation, turnover, and sensitivity to phosphatidylinositol-specific phospholipase C (PI-PLC) of Thy-1 in the rat neuronal tumor cell line BN-1010-1. It was initially established that a relatively short labeling time (1.5 h) using [3H]mannose yielded much more highly labeled PI-PLC-releasable glycoproteins than a longer labeling time (18 h). Labeled Thy-1 was released from the cell surface as early as 30 min postlabeling, increased to a maximum at 2.0 h, and then decreased to 50% of maximum by 5.5 h. The decrease may be due to degradation or spontaneous release into the medium, since total cellular Thy-1 remained constant during the decline. The decrease may be a result of a partial conversion of Thy-1 from a PI-PLC-sensitive to a PI-PLC-insensitive state. This resistance of the plasma membrane-associated Thy-1 was not due to a chemical modification of the glycoprotein, since detergent-extracted Thy-1 was completely sensitive to PI-PLC.