The Niemann-Pick C Proteins and Trafficking of Cholesterol Through the Late Endosomal / Lysosomal System

To maintain proper cellular function, the amount and distribution of cholesterol residing within cellular membranes must be regulated. The principal disorder affecting transport of cholesterol through the late endosomal / lysosomal system and intracellular cholesterol homeostasis is Niemann- Pick type C (NPC) disease. The genes responsible for NPC disease have been identified, and the encoded Niemann-Pick C1 (NPC1) and Niemann-Pick C2 (HE1 / NPC2) proteins are currently the subject of intense investigation. This review provides a detailed examination of NPC1 and HE1 / NPC2 in regulating the transport of cholesterol through the late endosomal / lysosomal system to other cellular compartments responsible for maintaining intracellular cholesterol homeostasis, and how defective function of these proteins may be responsible for the pathophysiology associated with NPC disease.