Role of Niemann-Pick type C1 protein in intracellular trafficking of low density lipoprotein-derived cholesterol

Niemann-Pick type C (NPC) is a disease that affects intracellular cholester ol-trafficking pathways. By cloning the hamster ortholog of NPC1, we identi fied the molecular lesions in two independently isolated Chinese hamster ov ary cell mutants, CT60 and CT43, Both mutants lead to premature translation al terminations of the NPC1 protein. Transfecting hamster NPC1 cDNA complem ented the defects of the mutants, Investigation of the CT mutants, their pa rental cells, and an NPC1-stable transfectant allow us to present evidence that NPC1 is involved in a post-plasma membrane cholesterol-trafficking pat hway, We found that the initial movement of low density lipoprotein (LDL)-d erived cholesterol to the plasma membrane (PM) did not require NPC1. After reaching the PM and subsequent internalization, however, cholesterol traffi cking back to the PM did involve NPC1. Both LDL-derived cholesterol and cho lesterol originating from the PM accumulated in a dense, intracellular comp artment in the CT mutants. Cholesterol movement from this compartment to th e PM or endoplasmic reticulum was defective in the CT mutants, Our results functionally distinguish the dense, intracellular compartment from the earl y endocytic hydrolytic organelle and imply that NPC1 is involved in sorting cholesterol from the intracellular compartment back to the PM or to the en doplasmic reticulum.