Isolation by fluorescence-activated cell sorting of Chinese hamster ovary cell lines with pleiotropic,...

We have isolated several Chinese hamster ovary cell lines with temperature-sensitive defects in the recycling of receptors after endocytosis. These cell lines were selected using fluorescence-activated cell sorting for retention of a pulse of labeled transferrin after a chase in the presence of unlabeled transferrin. One of these cell lines, TfT1.11, was selected for further characterization. In TfT1.11 the trapping of transferrin within the cells is paralleled by a loss of cell surface transferrin receptors. Within 4 h after the shift from 33 to 41 degrees C the surface binding of transferrin is reduced to 18% of parental cells at 41 degrees C. The trapping of transferrin and the loss of transferrin receptor from the cell surface are caused by a temperature-conditional 5.5-fold decrease in the initial rate of transferrin recycling. TfT1.11 cells also rapidly lose 89% of their ability to take up alpha 2-macroglobulin after the temperature shift to 41 degrees C. These data indicate that the TfT1.11 cell line has a pleiotropic defect in receptor recycling.