NPC1L1 (NPC1 like intracellular cholesterol transporter 1; HGNC:7898, NCBI Gene ID 29881) is a human locus mapped to chromosome band 7p13 that encodes 13-transmembrane sterol-sensing transporter NPC1L1 (1,332 aa). NPC1L1 acts in intestinal brush-border dietary/biliary cholesterol absorption & hepatic canalicular reuptake, together with LDLR (Low-Density Lipoprotein Receptor Gene), HMG-CoA Reductase (HMGCR Statin Target), and APOB (Apolipoprotein B Gene). Encodes the intestinal brush-border and hepatobiliary sterol transporter NPC1L1, the direct molecular target of ezetimibe.
Direct molecular target of ezetimibe; inactivating mutations lower LDL-C and reduce CHD risk by ~50%
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 20-exon gene on chromosome 7p13 homologous to the lysosomal Niemann-Pick C1 (NPC1) protein, encoding a 1,332-amino-acid polytopic membrane glycoprotein featuring an extracellular N-terminal cholesterol-binding domain, 13 transmembrane helices including a conserved 5-helix sterol-sensing domain (SSD), and a C-terminal YVNxxF endocytic motif.
Cellular & Tissue Expression Profile: Abundantly expressed at the apical brush-border microvillar membrane of jejunal enterocytes in the small intestine and, in humans (unlike mice), on the apical canalicular membrane of hepatic hepatocytes facing the bile canaliculus.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Binds unesterified dietary and biliary cholesterol (as well as non-cholesterol phytosterols) via its N-terminal domain, transfers the sterol through an intramolecular tunnel into a cholesterol-rich microdomain, and recruits the clathrin adaptor NUMB and flotillin-1/2 to internalize cholesterol into the endocytic recycling compartment for ACAT2 esterification and chylomicron packaging.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Exome sequencing of over 90,000 individuals revealed that heterozygous carriers of naturally occurring inactivating NPC1L1 mutations have 12 mg/dL lower plasma LDL-cholesterol and a 53% lower risk of coronary heart disease, while reduced NPC1L1 activity also lowers biliary cholesterol reuptake and slightly increases gallstone susceptibility.
Therapeutic & Clinical Pharmacology: Direct molecular target of ezetimibe (Zetia), which binds the middle extracellular loop of NPC1L1 to block sterol-induced conformational tunneling and endocytosis, reducing intestinal cholesterol absorption by ~50% and providing additive LDL-C and cardiovascular event reduction when combined with statins (IMPROVE-IT trial).