The role of elevated circulating cholesterol levels has been highlighted by an increased awareness of its role in causing heart disease. The cellular biology of cholesterol in normal cells is much less well understood, partly due to technical difficulties in assaying cholesterol synthesis and localization in intact cells.
Heino et al. developed techniques to allow them to examine the rate of transport of newly synthesized cellular cholesterol from its site of synthesis inside the cell--the endoplasmic reticulum--to the cell surface. They compared the rate at which cholesterol was transported to the cell surface with the delivery of a model cell surface protein. Their findings suggest that cholesterol follows at least two routes to the cell surface: 20% of newly synthesized cholesterol follows the classical secretory pathway from the endoplasmic reticulum through the Golgi complex to the cell surface, and the remainder follows another less well characterized pathway that appears to bypass the Golgi complex. The challenge remains to identify the membrane carriers for the bulk of newly synthesized cholesterol. -- SMH
Proc. Natl. Acad. Sci. U.S.A. 97, 8380 (2000).
