Transport of exogenous fluorescent phosphatidylserine analogue to the Golgi apparatus in cultured fibroblasts

We have examined intracellular transport and metabolism of the fluorescent analogue of phosphatidylserine, 1-palmitoyl-2-(N-12(7-nitrobenz-2-oxa-1,3-diazole-4-yl)amino] dodecanoyl])-phosphatidylserine (palmitoyl-C12-NBD]-PS) in cultured fibroblasts. When monolayer cultures were incubated with liposomes containing (palmitoyl-C12-NBD)-PS at 37 degrees C, fluorescent PS was transported to the Golgi apparatus. NBD-containing analogues of phosphatidylcholine, phosphatidylethanolamine (PE), or phosphatidic acid did not accumulate in the Golgi apparatus under the same experimental conditions. We suggest that the transport is not due to endocytosis, but is the result of incorporation and trans-bilayer movement of the (palmitoyl-C12-NBD)-PS at the plasma membrane followed by translocation of the lipid from plasma membrane to the Golgi apparatus via nonvesicular mechanisms. Uptake of fluorescent PS was inhibited by depletion of cellular ATP and was blocked by structural analogues of the lipid or by pretreatment of cells with glutaraldehyde or N-ethylmaleimide. After incorporation into the cell, fluorescent PS was metabolized to fluorescent PE. The intracellular distribution of fluorescence changed during the conversion. In addition to the Golgi apparatus, mitochondria also became labeled.