A CHINESE-HAMSTER OVARY CELL MUTANT RESISTANT TO PHOSPHATIDYLSERINE IS DEFECTIVE IN TRANSBILAYER MOVEMENT OF CELL-SURFACE PHOSPHATIDYLSERINE

A mammalian plasma membrane protein(s) which catalyzes ATP-dependent t ransbilayer movement (hip-hop) of phosphatidylserine (PS) has been sug gested to be involved in the formation and maintenance of membrane lip id asymmetry. Flip-flop of PS in the cell surface of nucleated cells w as first described by O. C. Martin and R. E. Pagano (1987, J. Biol. Ch em. 262, 5890-5898). It has been suggested that flip-flop is involved in the internalization of exogenous PS in cultured cells. In the prese nt study we report that incubation with an excess amount of PS is cyto toxic to Chinese hamster ovary (CHO) cells, while the same amount of p hosphatidylcholine gives no effect. This effect allowed us to obtain P S-resistant cells among mutagenized CHO cells. Endocytosis-independent internalization of exogenous fluorescent PS analog was defective in 4 0% of the PS-resistant mutants. One of the mutants, PSR (phosphatidyls erine resistant) 406 was further characterized. Unlike wild-type CHO c ells, this mutant did not transport fluorescent PS significantly at 15 degrees C. Fluorescent PS was not metabolized at 15 degrees C in eith er wild-type or mutant cells. These results suggest that transbilayer movement of cell surface PS is defective in PS-resistant cells. (C) 19 96 Academic Press, Inc.