Abstract
Lipid metabolism appears to play significant roles in the development of cancer. Numerous studies have shown that the evolution of malignancies, including breast, prostate, and colorectal cancers, involves cholesterol in a profound manner. A crucial part in the intestinal absorption of cholesterol is played by Niemann–Pick C1-like 1 (NPC1L1), a cholesterol transporter protein that is widely expressed in the small intestine and liver. The importance of NPC1L1 in tumor prognosis has been demonstrated in investigations in the interim. NPC1L1 also has the potential to develop into a new therapeutic target and a cancer marker. There is, however, no comprehensive review that summarizes NPC1L1’s function in cancer. To this end, we outlined NPC1L1’s functions in carcinogenesis and treatment, along with resources that can be used to further comprehend the connection between NPC1L1 and tumors.
1 Introduction
The body needs cholesterol for many functions, but too much cholesterol can create hypercholesterolemia, which can cause atherosclerosis, stroke, and coronary heart disease (). Due to the additional ways in which cholesterol encourages cell division, invasion, and proliferation, it is crucial to the growth and development of tumors. Studies have revealed that the upregulation of the cholesterol synthesis level, the rise in cholesterol absorption, and the abnormal accumulation of a large number of metabolites are the main manifestations of the improper regulation of cholesterol metabolism in tumor cells. This results in improved tumor cell growth, survival, invasion, metastasis, and tumor microenvironment adaption. Tumor occurrence and growth are further encouraged ().
Niemann–Pick type C1-like 1 (NPC1L1) is a protein that is essential for intestinal cholesterol absorption and plays vital roles in dietary cholesterol absorption and biliary cholesterol resorption. With remarkable specificity, NPC1L1 mediates cholesterol entrance into small intestinal absorptive cells. A vesicular endocytosis process, as demonstrated by the studies, mediated cholesterol absorption by the NPC1L1 protein. When the extracellular cholesterol concentration was high, the plasma membrane protein NPC1L1 would endocytose the extracellular cholesterol and transfer it to the endocytic cycle (). (Figure 1) As a specific target of NPC1L1, ezetimibe is a small molecule compound that can effectively and specifically inhibit the absorption of intestinal cholesterol. It is a medication used to treat coronary heart disease and hypercholesterolemia. According to research, it can lower plasma cholesterol by 15–20% (; ). It is also a medication used to treat dyslipidemia that does not respond to statin therapy ().
FIGURE 1
Obesity, hyperlipidemia, lipid storage disorders, and vascular diseases are all brought on by an abnormal cholesterol metabolism. Changes in cholesterol metabolism can significantly impact how quickly cancer develops and spreads. The current research on the association between NPC1L1 and cancer in carcinogenesis and cancer therapy is of utmost importance since NPC1L1 is a crucial member of cholesterol in intestinal absorption. First, we detailed the structure, usage, and distribution of the NPC1L1 protein in this article. Then, using the studies that were accessible, we summarized the connection between NPC1L1 and cancer for the first time.
2 Structure and function of NPC1L1
2.1 Structure of NPC1L1
NPC1L1 is a 1,332-amino acid membrane protein that is only found in primate hepatocyte tubular membranes and mammalian small intestinal brush membranes. The sequences of Niemann–Pick disease type C1 (NPC1) and NPC1L1 are comparable in 51 and 42 percent, respectively (). A membrane protein called NPC1 performs a job in late endosomes and lysosomes (). As a homolog of NPC1, NPC1L1 likewise possesses a transmembrane domain with 13 cysteines and three major luminal structural domains in the extracellular area, the N-terminal domain (NTD), the middle domain (MLD), and the cysteine-rich domain (CTD). Thirteen molecules of membrane-embedded transmembrane helices (TM) make up the transmembrane domain (TMD) (). The SSD domain is widely distributed in several regulatory protein substructures that are closely related to cholesterol metabolisms, such as NPC1, sterol regulatory element-binding protein cleavage activating protein (SCAP), and hydroxymethyl glutaryl-CoA reductase (HMG-CoA reductase) (). (Figure 2)
FIGURE 2
2.2 Distribution of NPC1L1
NPC1L1 is tissue-specific in its distribution and is highly expressed in tissues connected to the digestive system. Currently, NPC1L1 is being investigated more in rodents and humans, and it has been discovered that there are small species differences in the distribution of NPC1L1 in vivo. The human liver and small intestine are the tissues with the highest levels of the NPC1L1 expression, followed by the stomach, ovary, lung tissues, and even minimal amounts in the brain tissues (
2.3 Functions of NPC1L1
In humans, cholesterol is absorbed mainly in the proximal jejunum of the small intestine, where both dietary and biliary cholesterol types are absorbed (
3 Tumor suppression by NPC1L1 in cancer
3.1 Colorectal cancer
Colorectal cancer (CRC) is a malignant tumor of the colon and rectum. It is also the third most common cancer and the fourth leading cause of cancer-related deaths worldwide (
The development and prognosis of colorectal cancer have been shown to be associated with an altered lipid metabolism. High cholesterol intake is associated with an increased risk of colorectal cancer. Elevated serum cholesterol levels are associated with the risk of developing colorectal cancer (
FIGURE 3

NPC1L1 expression in normal and CRC tissues. (A) NPC1L1 expression is higher in most CRC tissues than in normal tissues. The mean value of the NPC1L1 expression in normal tissues (blue box) is 7.00, and in CRC tissues (red box), it is 130.09. (B) Mean value of the NPC1L1 expression in normal tissues (blue box) is 22.69, and in CRC tissues (red box), it is 81.35 compared to normal tissues (GSE9348) (
FIGURE 4

OS of CRC patients with a high NPC1L1 expression was significantly lower than that of CRC patients with a low NPC1L1 expression. The results of the two datasets (GSE17536 and GSE129451) collated in the CRC patients stratified into NPC1L1-low and NPC1L1-high groups also showed results consistent with those obtained from the analysis of TCGA dataset (
FIGURE 5

NPC1L1-knockout mice have significantly lower intestinal inflammation scores than wild-type mice (
FIGURE 6

pc-Jun, p-ERK, and caspase-1 p20 protein expressions in tumors measured by protein blotting. pc-Jun, p-ERK and caspase-1 p20 were significantly reduced by NPC1L1 knockdown. pc-Jun, p-ERK, and caspase-1 p20 were also reduced by NPC1L1 knockdown (
3.2 Head and neck squamous cell carcinoma
With more than 550,000 new cases and 300,000 fatalities each year, head and neck squamous cell carcinoma (HNSCC), which comprises oral cavity cancer (OC) and oropharyngeal cancer (OPC), is the sixth most prevalent cancer worldwide (
According to several observational studies, statin use is associated negatively with cancer survival and HNSCC risk. Other research studies, however, have shown scant evidence of any impact. Using two-sample Mendelian randomization (MR), the relationship between the targets of genetically proxied cholesterol-lowering drugs and other circulating lipid profiles with OC and OPC risks was evaluated. Germline genetic variations in the genes for HMGCR, NPC1L1, CETP, PCSK9, and LDLR were utilized to simulate the effects of low-density lipoprotein cholesterol-lowering treatments in the initial analysis. There is scant evidence that inherited NPC1L1 increases the chance of developing OC and OPC (
3.3 Ovarian cancer
One of the world’s most dangerous malignant tumors is ovarian cancer due to the early stages of ovarian cancer’s lack of visible signs. The so-called “silent killer” is frequently identified in advanced stages in patients. Based on the genetic alterations and the cell shape of epithelial ovarian cancer, type I and type II ovarian tumors can be distinguished. Low-grade plasmacytomas, endometrioid carcinomas, clear cell carcinomas, and mucinous carcinomas are examples of type I tumors. High-grade plasmacytomas and undifferentiated carcinomas are examples of type II tumors (
When the analysis was limited to the general population or BRCA1/2 mutation carriers, there was no significant association between genetically close NPC1L1 or PCSK9 inhibition or low-density lipoprotein cholesterol levels and epithelial ovarian cancer in the Mendelian randomized analysis of 22,406 women with invasive epithelial ovarian cancer and 40,941 control individuals (
3.4 Hepatocellular carcinoma
Liver cancer accounts for 8.2% of all cancer deaths globally, ranking sixth in cancer incidence. Additionally, it ranks third in the world for cancer-related fatalities (Siegel, Miller, and Jemal). Intrahepatic cholangiocarcinoma, hepatocellular carcinoma (HCC), fibrous lamellar carcinoma, and hepatoblastoma are several types of primary liver cancer. These classifications differ significantly in terms of their molecular, histological, and pathological traits. Of the instances of liver cancer, 85 to 90 percent are caused by HCC alone (
FIGURE 7

(A) NPC1L1 and NPC2 expressions were detected in 10 pairs of HCC tissues (T) and peritumoral tissues (p) by Western blot analysis. The expressions of NPC1L1 and NPC2 were significantly decreased in HCC tissues. Meanwhile, the mRNA expressions of NPC1L1 and NPC2 expression levels were also decreased in HCC tissues compared with peritumoral tissues. (B) Quantitation of proteins from Western blot analyses shows that both NPC1L1 and NPC2 expressions were significantly reduced in the HCC tissue (T) (
FIGURE 8

Scatter plot showing paired peritumor tissues shows that NPC1L1 and NPC2 expressions in HCC tumor tissues are usually lower than those in peritumor tissues (NPC1L1 p < 0.0001; NPC2 p = 0.0001) (
3.5 Pancreatic cancer
As one of the 14 most prevalent malignancies worldwide, pancreatic cancer is the seventh most common cause of cancer-related deaths (
FIGURE 9

(A) Representative image of the PDAC012T-derived spheroids treated with ezetimibe (50 µM) or vehicle after 3 days. (B) Cell viability of spheroids was measured by CellTiter-Glo and expressed as a percentage of the vehicle-treated spheroids (∗∗p < 0.01) (
4 Conclusion and outlook
Cholesterol aids in the proliferation, invasion, and subduction of cells and is crucial for the development and growth of tumors. As a crucial protein in intestinal cholesterol absorption, NPC1L1 plays vital functions in the development and spread of tumors. The most recent research indicates that NPC1L1 can be employed as a standalone prognostic marker in colorectal cancer. Additionally, it proved to be a reliable prognostic factor for hepatocellular carcinoma. Additionally, NPC1L1 may be a valuable therapeutic target for pancreatic cancer. The association between NPC1L1 and other malignancies has not been proven by recent investigations. The significance of NPC1L1 in carcinogenesis and cancer therapy, however, merits additional research to offer new therapeutic avenues for clinical cancers due to the role of cholesterol in tumorigenesis and development.
Overall, the current studies on the connection between NPC1L1 and cancers are deficient, however, due to the function of NPC1L1 in cholesterol uptake and the link between cholesterol and cancer. Future research examining this connection might reveal other targets to impede the progression of cholesterol-dependent cancer.
Statements
Author contributions
Conceptualization, RZ; writing—original draft preparation, RZ and JZ; writing—review and editing, RZ, JZ, and WL; supervision, DX All authors have read and agreed to the published version of the manuscript.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Publisher’s note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
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Summary
Keywords
NPC1L1, tumor, cholesterol, tumor therapy, cancer marker
Citation
Zhang R, Zeng J, Liu W, Meng J, Wang C, Shi L, Yang S, Chang J and Xing D (2022) The role of NPC1L1 in cancer. Front. Pharmacol. 13:956619. doi: 10.3389/fphar.2022.956619
Received
30 May 2022
Accepted
11 July 2022
Published
10 August 2022
Volume
13 - 2022
Edited by
Ting Wang, Sichuan Cancer Hospital, China
Reviewed by
Inamul Kabir, Yale University, United States
Eri Saki H. Hayakawa, Jichi Medical University, Japan
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© 2022 Zhang, Zeng, Liu, Meng, Wang, Shi, Yang, Chang and Xing.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Dongming Xing, xdm_tsinghua@163.com
† These authors share first authorship
This article was submitted to Pharmacology of Anti-Cancer Drugs, a section of the journal Frontiers in Pharmacology
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.