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 P1-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-i remained constant during the decline. The decrease may be a result of a partial conversion of Thy-1 from a P1-PLC-sensitive to a P1-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 P1-PLC.