Physiological and coordinate downregulation of the NPC1 and NPC2 genes are associated with the sequestration of LDL-derived cholesterol within endocytic compartments

• Published in: Journal of cellular biochemistry Vol. 108; no. 5; pp. 1102 - 1116
• Main Authors: Jelinek, David, Patrick, Sarah Mount, Kitt, Khameeka N., Chan, Teddy, Francis, Gordon A., Garver, William S.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.12.2009
• Subjects: ACAT-accessible pool; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Line; cholesterol; Cholesterol, LDL - metabolism; cholesteryl ester; Down-Regulation; early endosomes; Endosomes - metabolism; fibroblasts; Fibroblasts - cytology; Fibroblasts - metabolism; Glycoproteins - genetics; Glycoproteins - metabolism; Humans; late endosomes/lysosomes; low-density lipoprotein; Lysosomes - metabolism; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Niemann-Pick type C; Signal Transduction; Sterol Regulatory Element Binding Proteins - metabolism; sterol regulatory pool
• ISSN: 0730-2312; 1097-4644; 1097-4644
• DOI: 10.1002/jcb.22339

The Niemann‐Pick C1 and C2 (NPC1 and NPC2) proteins have a central role in regulating the transport of lipoprotein‐derived cholesterol from endocytic compartments to the endoplasmic reticulum for esterification by acyl‐CoA:cholesterol acyltransferase (ACAT) and feedback inhibition of the sterol regulatory element‐binding protein (SREBP) pathway. Since the NPC1 gene/protein has recently been shown to be downregulated by feedback inhibition of the SREBP pathway, the present study was performed to determine whether physiological downregulation of the NPC1 gene/protein alters the transport and metabolism of low‐density lipoprotein (LDL)‐derived cholesterol in human fibroblasts. To perform this study, three different culture conditions were used that included fibroblasts grown in lipoprotein‐deficient serum (LPDS), LPDS supplemented with LDL, and LPDS supplemented with LDL, followed by equilibration in the absence of LDL to allow the transport of LDL‐derived cholesterol from endocytic compartments and equilibration of cellular sterol pools. The results from this study indicated that in addition to the NPC1 gene/protein, the NPC2 gene/protein was also downregulated by LDL‐derived cholesterol‐dependent feedback inhibition and that downregulation of both the NPC1 and NPC2 genes/proteins was associated with the sequestration of LDL‐derived cholesterol within endocytic compartments, including late endosomes/lysosomes after equilibration. Therefore, it is proposed that physiological and coordinate downregulation of the NPC1 and NPC2 genes/proteins promotes the sequestration of LDL‐derived cholesterol within endocytic compartments and serves a role in maintaining intracellular cholesterol homeostasis. J. Cell. Biochem. 108: 1102–1116, 2009. © 2009 Wiley‐Liss, Inc.