Maguire JA, Reagan JW. Silencing of the mutant SCAP allele accounts for restoration of a normal phenotype in CT60 cells selected for NPC1 expression.
J Lipid Res 2005;
46:1840-8. [PMID:
15995170 DOI:
10.1194/jlr.m500198-jlr200]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The sterol regulatory element binding protein (SREBP)/SREBP cleavage-activating protein (SCAP) complex regulates the transcription of numerous genes involved in cellular cholesterol metabolism. The CHO mutant, CT60, and its parental cell line, 25RA, possess a gain-of-function mutation in one allele of the SCAP gene that renders the cells resistant to sterol-mediated suppression of cholesterol synthesis and uptake. In addition, CT60 cells do not express a functional Niemann-Pick type C1 (NPC1) protein, which leads to lysosomal accumulation of free cholesterol. Correction of the NPC1 defect by expression of a yeast artificial chromosome (YAC) containing the NPC1 genetic interval restored normal mobilization of cholesterol from the lysosomal compartment. Unexpectedly, the YAC-containing cell lines have overall cellular cholesterol concentrations that are comparable to wild-type levels, despite the assumed presence of the SCAP mutation. This phenotypic change results from a reduction in endogenous sterol synthesis, LDL receptor message, and HMG-CoA reductase message. Genetic analysis of the SCAP gene revealed that the YAC-expressing CT60 cells have normal regulation of these sentinel cholesterogenic genes as a result of selective silencing of the mutant SCAP allele, which appears to be independent of functional NPC1 expression.
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