Effect of reduced low-density lipoprotein receptor level on HepG2 cell cholesterol metabolism

Hepatocyte-like cells derived from induced pluripotent stem cells: A versatile tool to understand lipid disorders

Dyslipidemias are strongly linked to the development of atherosclerotic cardiovascular disease. Most dyslipidemias find their origin in the liver. In recent years, the differentiation of induced pluripotent stem cells (iPSCs) into hepatocyte-like cells has provided a versatile platform for the functional study of various dyslipidemias, both rare genetic dyslipidemia as well as common lipid disorders associated with insulin resistance or non-alcoholic fatty liver disease. In addition, iPSC-derived hepatocytes can serve as a cell model for developing novel lipid lowering therapies and have the potential of regenerative medicine. This review provides an overview of these developments.

Ellagic acid affects mRNA expression levels of genes that regulate cholesterol metabolism in HepG2 cells

Ellagic acid has been shown to improve cholesterol metabolism in animal studies, but the molecular mechanisms underlying this function have not been fully understood. We performed DNA microarray analysis to elucidate the effects of ellagic acid on cholesterol metabolism in HepG2 hepatocytes. This revealed that the expression levels of several genes related to cholesterol metabolism, including the low-density lipoprotein receptor (LDLR), were changed by ellagic acid treatment. Using a real-time PCR and immunoblot we confirmed that ellagic acid treatment up-regulated mRNA and protein expression level of the LDLR. Moreover, In the presence of 25 μM ellagic acid, extracellular apoB protein and MTP mRNA levels were significantly decreased. These findings indicate that ellagic acid improves cholesterol metabolism through the up-regulation of LDLR, down-regulation of MTP mRNA and reduces extracellular apoB levels. The ellagic acid-induced up-regulation of LDLR occurred via the extracellular signal-regulated kinase (ERK) signaling pathway in HepG2 hepatocytes. Abbreviations: LDLR: low-density lipoprotein receptor; apoB: apolipoprotein B; PKC: diacylglycerol-protein kinase C; MAPK: mitogen-activated protein kinase; ERK: p42/44 extracellular signal-regulated kinase; JNK: c-Jun N-terminal kinase; VLDLR: very low density lipoprotein receptor; PPARδ: peroxisome proliferator-activated receptor δ; SREBPs: sterol regulatory element-binding proteins; MTP: microsomal triacylglycerol transfer protein; LPDS: lipoprotein-deficient serum.

Systems proteomics of liver mitochondria function

Recent improvements in quantitative proteomics approaches, including Sequential Window Acquisition of all Theoretical Mass Spectra (SWATH-MS), permit reproducible large-scale protein measurements across diverse cohorts. Together with genomics, transcriptomics, and other technologies, transomic data sets can be generated that permit detailed analyses across broad molecular interaction networks. Here, we examine mitochondrial links to liver metabolism through the genome, transcriptome, proteome, and metabolome of 386 individuals in the BXD mouse reference population. Several links were validated between genetic variants toward transcripts, proteins, metabolites, and phenotypes. Among these, sequence variants in Cox7a2l alter its protein's activity, which in turn leads to downstream differences in mitochondrial supercomplex formation. This data set demonstrates that the proteome can now be quantified comprehensively, serving as a key complement to transcriptomics, genomics, and metabolomics--a combination moving us forward in complex trait analysis.

A simple and high-throughput in-cell Western assay using HepG2 cell line for investigating the potential hypocholesterolemic effects of food components and nutraceutics

Since saving time and money are critical issues while developing innovative functional foods and nutraceutics, the use of specific and high-throughput assays for the fast screening of potentially bioactive ingredients is crucial. In this context, the aim of the present investigation was the development of an in-cell Western (ICW) assay, a quantitative colorimetric cell-based technique, at the HepG2 cell line for screening and evaluating the effects of potentially bioactive compounds on the low density lipoprotein (LDL) receptor (LDLR). It is known that LDLR plays a pivotal role in the binding and endocytosis of circulating LDL, increasing its plasma clearance. The ICW was optimised and validated using monacolin K, the main hypocholesterolemic component of red yeast rice. This provided a robust and reproducible assay useful for characterising the cholesterol-lowering properties of bioactive food components. To our knowledge, this is the first application of the ICW technique in the field of functional foods and nutraceutics.

Epigallocatechin gallate changes mRNA expression level of genes involved in cholesterol metabolism in hepatocytes

Catechins, compounds derived from green tea, have been shown to improve cholesterol metabolism in animal studies, but the molecular mechanisms underlying this function have not been fully understood. We performed DNA microarray analysis in order to clarify the effects of epigallocatechin gallate (EGCG), the dominant catechin in green tea, on cholesterol metabolism in HepG2 hepatocytes. This revealed that the expression levels of several genes related to cholesterol metabolism, including the LDL receptor, were changed by EGCG treatment. Using a real-time PCR technique, we confirmed that EGCG treatment up-regulated mRNA expression level of the LDL receptor. Moreover, EGCG decreased extracellular apoB levels. These findings indicated that EGCG improves cholesterol metabolism through the up-regulation of LDL receptor and also reduces extracellular apoB levels.

CD28 signaling in T regulatory precursors requires p56lck and rafts integrity to stabilize the Foxp3 message

Naturally occurring CD4(+)25(high)Foxp3(+) T regulatory (T-reg) cells are critical for maintaining tolerance to self and non-self Ags. The Foxp3 master-regulatory gene and CD28 costimulation are both required for thymic development and suppressogenic function of CD4(+)25(high)Foxp3(+) T-regs. Herein, we show that the sole CD28 stimulation of T-reg thymic precursors augments Foxp3 expression through the increase in Foxp3 mRNA life span by a mechanism involving p56(lck) and its binding motif on CD28 cytosolic tail, as well as the lipid rafts. We found that 1) the glycosphingolipids and cholesterol components of lipid rafts were highly expressed and unusually partitioned in T-reg thymic precursors as compared with the conventional T cell precursors, 2) the CD28 receptor density on cell membrane is proportional with the content of cholesterol in lipid rafts and with the level of Foxp3 mRNA expression in T-reg precursors, and 3) the CD28-mediated increase of Foxp3 mRNA life span was paralleled by an increased proliferative and suppressogenic capacity of terminally differentiated CD4(+)25(high)Foxp3(+) T-reg precursors. Thus, the functional integrity of CD28 receptor p56(lck) and plasma membrane lipid rafts are all prerequisites for up-regulation and long-term expression of Foxp3 mRNA transcripts in CD4(+)25(high)Foxp3(+) T-reg precursors.

Protein kinase C activation stabilizes LDL receptor mRNA via the JNK pathway in HepG2 cells

LDL is the most abundant cholesterol transport vehicle in plasma and a major prognostic indicator of atherosclerosis. Hepatic LDL receptors limit circulating LDL levels, since cholesterol internalized by the liver can be excreted. As such, mechanisms regulating LDL receptor expression in liver cells are appealing targets for cholesterol-lowering therapeutic strategies. Activation of HepG2 cells with phorbol esters enhances LDL receptor mRNA levels through transcriptional and posttranscriptional mechanisms. Here, we show that 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced stabilization of receptor mRNA requires the activity of protein kinase C and is accompanied by activation of the major mitogen activated protein kinase pathways. Inhibitor studies demonstrated that receptor mRNA stabilization is independent of the extracellular signal-regulated kinase or p38(MAPK), but requires activation of the c-Jun N-terminal kinase (JNK). An essential role for JNK in stabilizing receptor mRNA was further confirmed through small interfering RNA (siRNA) experiments and by activating JNK through two protein kinase C-independent mechanisms. Finally, prolonged JNK activation increased steady-state levels of receptor mRNA and protein, and significantly enhanced cellular LDL-binding activity. These data suggest that JNK may play an important role in posttranscriptional control of LDL receptor expression, thus constituting a novel mechanism to enhance plasma LDL clearance by liver cells.

All-trans-retinoic acid nanodisks

Nanodisks are nanoscale, disk-shaped phospholipid bilayers whose edge is stabilized by association of apolipoprotein molecules. Self-assembled ND particles enriched with all-trans-retinoic acid (ATRA) (phospholipid:ATRA molar ratio = 5.5:1) were generated wherein all reaction components were solubilized. ATRA-ND migrated as a single band (Stokes' diameter approximately 20 nm) on native gradient polyacrylamide gel electrophoresis. ATRA, phospholipid and apolipoprotein co-eluted from a Sepharose 6B gel filtration column, consistent with stable integration of ATRA into the ND particle milieu. Spectroscopic analysis of ATRA-ND in buffer yielded an absorbance spectrum characteristic of ATRA. ATRA-ND mediated time-dependent inhibition of cultured HepG2 cell growth more effectively than free ATRA. The nanoscale size of the formulation particles and the stable integration of biologically active ATRA suggest ND represent a potentially useful vehicle for solubilization and in vivo delivery of ATRA.

Primate-specific evolution of an LDLR enhancer

Analysis of primate-specific evolution of the LDL receptor enhancer demonstrates a molecular mechanism by which ancestral mammalian regulatory elements can evolve to perform new functions.

Background

Sequence changes in regulatory regions have often been invoked to explain phenotypic divergence among species, but molecular examples of this have been difficult to obtain.

Results

In this study we identified an anthropoid primate-specific sequence element that contributed to the regulatory evolution of the low-density lipoprotein receptor. Using a combination of close and distant species genomic sequence comparisons coupled with in vivo and in vitro studies, we found that a functional cholesterol-sensing sequence motif arose and was fixed within a pre-existing enhancer in the common ancestor of anthropoid primates.

Conclusion

Our study demonstrates one molecular mechanism by which ancestral mammalian regulatory elements can evolve to perform new functions in the primate lineage leading to human.

The role of scavenger receptor class B type I (SR-BI) in lipid trafficking. defining the rules for lipid traders

The scavenger receptor class B type I (SR-BI) is a 509-amino acid, 82 kDa glycoprotein, with two cytoplasmic C- and N-terminal domains separated by a large extracellular domain. The aim of this review is to define the role of SR-BI as a lipoprotein receptor responsible for selective uptake of cholesteryl esters (CE) from high density lipoprotein (HDL) and low density lipoprotein (LDL) and free cholesterol (FC) efflux to lipoprotein acceptors. These activities depend on lipoprotein binding to its extracellular domain and subsequent lipid exchange at the plasma membrane. CE selective uptake supplies cholesterol to liver and steroidogenic tissues, for biliary cholesterol secretion and steroid hormone synthesis. Genetically modified mice have confirmed SR-BI's major role in tissue cholesterol uptake and in reverse cholesterol transport, i.e. cholesterol turnover. Accordingly, cellular cholesterol level, estrogens and trophic hormones regulate SR-BI expression by both transcriptional and post-transcriptional mechanisms. Importantly, mouse SR-BI overexpression has both corrective and preventive effects on atherosclerosis. Human SR-BI has very similar tissue distribution, binding properties and lipid transfer activities compared to rodent SR-BI. However, human plasma has most of its cholesterol in LDL. Thus, there is considerable interest to develop anti-atherogenic strategies involving human SR-BI-mediated increases in reverse cholesterol transport through HDL and/or LDL.

Carbocyanine labeled LDL for optical imaging of tumors

RATIONALE AND OBJECTIVES

The purpose of this study was to define and characterize carbocyanine labeled low-density lipoprotein (LDL) to be used in the optical imaging of LDL receptor (LDLr)-overexpressing tumor models.

MATERIALS AND METHODS

1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was used to label LDL (DiI-LDL). Scatchard plots were generated to determine the maximum binding capacity B(max) and dissociation constants K(D) of DiI-LDL in B16 melanoma (B16) and hepatoblastoma G(2) (HepG(2)) cell lines. Selective uptake of DiI-LDL into both tumor cells and corresponding subcutaneous tumors in mice were demonstrated by confocal microscopy and three-dimensional Cryo-imaging, respectively.

RESULTS

The labeling efficiency of DiI-LDL was 61 ng DiI/microg LDL protein (34 mol DiI/mol LDL protein). B(max) and K(D) for B16 cells were 6.311 ng LDL/mg cell protein and 60.38 microg protein/mL (117 nM), respectively. B(max) and K(D) were 7.573 ng LDL/mg cell protein and 26.79 microg protein/mL (52 nM) for HepG(2) cells, respectively. Confocal microscopic images showed specific uptake of DiI-LDL throughout the cytoplasm in the B16/HepG(2) cells. Cryo-imaging demonstrated preferential accumulations of DiI-LDL in the viable tumor regions of both B16 and HepG(2) tumors compared with their adjacent normal tissues and corresponding necrotic tumor regions. In addition, uptake of DiI-LDL by the HepG(2) tumor was much higher than that of the B16 tumor, consistent with the fact that the probe binding affinity for LDLrs of HepG(2) cells is 2.3 times that of B16 cells.

CONCLUSION

This study suggested that carbocyanine labeled LDL could be used for optical imaging of tumors overexpressing LDLr.

The role of human and mouse hepatic scavenger receptor class B type I (SR-BI) in the selective uptake of low-density lipoprotein-cholesteryl esters

Low-density lipoprotein (LDL)-cholesteryl ester (CE) selective uptake has been demonstrated in nonhepatic cells overexpressing the scavenger receptor class B type I (SR-BI). The role of hepatic SR-BI toward LDL, the main carrier of plasma CE in humans, remains unclear. The aim of this study was to determine if SR-BI, expressed at its normal level, is implicated in LDL-CE selective uptake in human HepG2 hepatoma cells and mouse hepatic cells, to quantify its contribution and to determine if LDL-CE selective uptake is likely to occur in the presence of human HDL. First, antibody blocking experiments were conducted on normal HepG2 cells. SR-BI/BII antiserum inhibited (125)I-LDL and (125)I-HDL(3) binding (10 microg of protein/mL) by 45% (p < 0.05) and CE selective uptake by more than 85% (p < 0.01) for both ligands. Second, HepG2 cells were stably transfected with a eukaryotic vector expressing a 400-bp human SR-BI antisense cDNA fragment. Clone 17 (C17) has a 70% (p < 0.01) reduction in SR-BI expression. In this clone, (3)H-CE-LDL and (3)H-CE-HDL(3) association (10 microg of protein/mL) was 54 +/- 6% and 45 +/- 7% of control values, respectively, while (125)I-LDL and (125)I-HDL(3) protein association was 71 +/- 3% and 58 +/- 5% of controls, resulting in 46% and 55% (p < 0.01) decreases in LDL- and HDL(3)-CE selective uptake. Normalizing CE selective uptake for SR-BI expression reveals that SR-BI is responsible for 68% and 74% of LDL- and HDL(3)-CE selective uptake, respectively. Thus, both approaches show that, in HepG2 cells, SR-BI is responsible for 68-85% of CE selective uptake. Other pathways for selective uptake in HepG2 cells do not require CD36, as shown by anti-CD36 antibody blocking experiments, or class A scavenger receptors, as shown by the lack of competition by poly(inosinic acid). However, CD36 is a functional oxidized LDL receptor on HepG2 cells, as shown by antibody blocking experiments. Similar results for CE selective uptake were obtained with primary cultures of hepatic cells from normal (+/+), heterozygous (-/+), and homozygous (-/-) SR-BI knockout mice. Flow cytometry experiments show that SR-BI accounts for 75% of DiI-LDL uptake, the LDL receptor for 14%, and other pathways for 11%. CE selective uptake from LDL and HDL(3) is likely to occur in the liver, since unlabeled HDL (total and apoE-free HDL(3)) and LDL, when added in physiological proportions, only partially competed for LDL- and HDL(3)-CE selective uptake. In this setting, human hepatic SR-BI may be a crucial molecule in the turnover of both LDL- and HDL(3)-cholesterol.

Analysis of low-density lipoprotein catabolism by primary cultures of hepatic cells from normal and low-density lipoprotein receptor knockout mice

Low-density lipoproteins (LDL) are taken up by LDL receptor (LDLr)-dependent and -independent pathways; the role and importance of the latest being less well defined. We analyzed the importance of these pathways in the mouse by comparing LDL binding to primary cultures of hepatocytes from LDLr knockout (LDLr KO) and normal C57BL/6J mice. Saturation curve analysis shows that (125)I-LDL bind specifically to normal and LDLr KO mouse hepatocytes with similar dissociation constants (K(d)) (31.2 and 22.9 microg LDL-protein/ml, respectively). The maximal binding capacity (B(max)) is, however, reduced by 48% in LDLr KO mouse hepatocytes in comparison to normal hepatocytes. Conducting the assay in the presence of a 200-fold excess of high-density lipoprotein-3 (HDL3) reduced by 39% the binding of (125)I-LDL to normal hepatocytes and abolished the binding to the LDLr KO mouse hepatocytes. These data indicate that in normal mouse hepatocytes, the LDLr is responsible for approximately half of the LDL binding while a lipoprotein binding site (LBS), interacting with both LDL and HDL3, is responsible for the other half. It can also be deduced that both receptors/sites have a similar affinity for LDL. The metabolism of LDL-protein and cholesteryl esters (CE) was analyzed in both types of cells. (125)I-LDL-protein degradation was reduced by 95% in LDLr KO hepatocytes compared to normal hepatocytes. Comparing the association of (125)I-LDL and (3)H-CE-LDL revealed a CE-selective uptake of 35.6- and 22-fold for normal and LDLr KO mouse hepatocytes, respectively. Adding a 200-fold excess of HDL3 in the assay reduced by 71% the CE-selective uptake in LDLr KO hepatocytes and by 96% in normal hepatocytes. This indicates that mouse hepatocytes are able to selectively take up CE from LDL by the LBS. The comparison of LDL-CE association also showed that the LBS pathway provides 5-fold more LDL-CE to the cell than the LDLr. Overall, our results indicate that in mouse hepatocytes, LDLr is almost completely responsible for LDL-protein degradation while the LBS is responsible for the major part of LDL-CE entry by a CE-selective uptake pathway.

Low density lipoprotein uptake: holoparticle and cholesteryl ester selective uptake

Low density lipoproteins (LDL) contain apolipoprotein B-100 and are cholesteryl ester-rich, triglyceride-poor macromolecules, arising from the lipolysis of very low density lipoproteins. This review will describe the receptors responsible for uptake of whole LDL particles (holoparticle uptake), and the selective uptake of LDL cholesteryl ester. The LDL-receptor mediates the internalization of whole LDL through an endosomal-lysosomal pathway, leading to complete degradation of LDL. Increasing LDL-receptor expression by pharmacological intervention efficiently reduces blood LDL concentrations. The lipolysis stimulated receptor and LDL-receptor related protein may also lead to complete degradation of LDL in presence of free fatty acids and apolipoprotein E- or lipase-LDL complexes, respectively. Selective uptake of LDL cholesteryl ester has been demonstrated in the liver, especially in rodents and humans. This activity brings five times more LDL cholesteryl ester than the LDL-receptor to human hepatoma cells, suggesting that it is a physiologically significant pathway. The lipoprotein binding site of HepG2 cells mediates this process and recognizes all lipoprotein classes. Scavenger receptor class B type I and CD36, which mediate the selective uptake of high density lipoprotein cholesteryl ester, are potentially involved in LDL cholesteryl ester selective uptake, since they both bind LDL with high affinity. It is not known whether they are identical to the uncloned lipoprotein binding site and if the selective uptake of LDL cholesteryl ester produces a less atherogenic particle. If this is verified, pharmacological up-regulation of LDL cholesteryl ester selective uptake may become another therapeutic approach for reducing blood LDL-cholesterol levels and the risk of atherosclerosis.

Selective uptake of cholesteryl ester from low density lipoprotein is involved in HepG2 cell cholesterol homeostasis

Low density lipoprotein (LDL) can follow either a holoparticle uptake pathway, initiated by the LDL receptor (LDLr), and be completely degraded, or it can deliver its cholesteryl esters (CE) selectively to HepG2 cells. Although high density lipoprotein-CE selective uptake has been shown to be linked to cell cholesterol homeostasis in nonhepatic cells, there is no available information on the effect of LDL-CE selective uptake on hepatic cell cholesterol homeostasis. In order to define the role of the LDL-CE selective uptake pathway in hepatic cell cholesterol homeostasis, we used a cellular model that expresses constitutively a LDLr antisense mRNA and that shows LDLr activity at 31% the normal level (HepG2-all cells). The addition of a specific antibody anti-LDLr (IgG-C7) reduces LDL protein degradation (LDLr activity) to 7%. This cellular model therefore reflects, above all, LDL-CE selective uptake activity when incubated with LDL. The inactivation of LDLr reduces LDL-protein association by 78% and LDL-CE association by only 43%. The LDL-CE selective uptake was not reduced by the inactivation of LDLr. The activities of the various enzymes involved in cell cholesterol homeostasis were measured in normal and LDLr-deficient cells during incubation in the absence or presence of LDL as a cholesterol source. Essentially, 3-hydroxy-3-methylglutaryl coenzyme A reductase and acyl coenzyme A:cholesterol acyltransferase (ACAT) activities responded to LDL in LDLr-deficient cells as well as in normal HepG2 cells. Inhibition of lysosomal hydrolysis with chloroquine abolished the effect measured on ACAT activity in the presence of LDL, suggesting that CE of LDL, but not free cholesterol, maintains cell cholesterol homeostasis. Thus, in HepG2 cells, when LDLr function is virtually abolished, LDL-CE selective uptake is coupled to cell cholesterol homeostasis.

Low density lipoprotein-receptor plays a major role in the binding of very low density lipoproteins and their remnants on HepG2 cells

The binding to HepG2 cells of very low density lipoproteins (VLDL) and their remnants (IDL) was alternatively, in the past, attributed to the low density lipoprotein receptor (LDLr) or to an apoE-specific receptor. In order to resolve this issue, we have compared the binding of those lipoproteins labelled with iodine-125 to normal and LDLr deficient HepG2 cells. Those deficient cells were obtained by a constitutive antisense strategy and their LDLr level is 14% the level of normal HepG2 cells. By saturation curve analysis, we show that VLDL and IDL bind to high and low affinity sites on cells. The low affinity binding was eliminated by conducting the assay in presence of a 200-fold excess of HDL3 respective to the concentrations of 125I-labelled VLDL and IDL. For 125I-VLDL high affinity binding to normal HepG2 cells, we found a dissociation constant (Kd) of 21.2 +/- 3.7 micrograms prot./ml (S.E., N = 5) and a maximal binding capacity (Bmax) of 0.0312 +/- 0.0063 microgram prot./mg cell prot, while we have measured a Kd of 5.3 +/- 0.8 and a Bmax of 0.0081 +/- 0.0014 with LDLr deficient cells. This indicates that LDLr is responsible for 74% of VLDL binding to HepG2 cells and that the non-LDLr high affinity receptor has a higher affinity for VLDL than LDLr. A 53% loss of 125I-IDL binding capacity was measured with LDLr deficient cells compared with normal cells (Bmax: 0.028 +/- 0.005 versus 0.059 +/- 0.006), while no significant statistical difference was found between affinities. The study shows that the LDLr is almost the only contributor in VLDL binding, while it shares IDL binding capacity with another high affinity receptor. The physiological importance of LDLr is confirmed by an almost equivalent loss of IDL and VLDL degradation in LDLr deficient cells.

Cellular and molecular biology of the liver

This paper highlights several key issues, ideas, and findings that significantly contribute to our understanding of the organization, communication, and molecular machinery of the liver. The functional anatomy of the liver has been studied in several ways that have revealed the extent of the biliary tree within the hepatic parenchyma, including identification of the canals of Hering as their most distal ramification. The canals of Hering are also considered as the potential residence of hepatic progenitor cells. Hepatocytes can "communicate" with each other via gap junctions, but might also deliver hormones and nucleotides downstream to cholangiocytes. The interaction of inflammatory cells and inflammatory mediators with hepatocytes is of particular importance in transplant immunology, infection, inflammation, viral hepatitis, and fibrogenesis. The role of these mediators as well as certain "toxic" bile acids in apoptosis has become clearer with the discovery of the mitochondrial permeability transition. Moreover, ursodeoxycholic acid can reduce apoptosis by minimizing the mitochondrial permeability transition. Two new nuclear hormone receptors, PXR and SXR, have been identified. These are both activated by a variety of chemically distinct ligands, whose final common goal is the activation of cytochrome P450-containing drug-metabolizing enzymes. Thus, these two receptors are critical to the body's ability to metabolize a variety of compounds properly. Additional insight into the role of cytokines and cytokine receptors in liver regeneration is presented. Finally, in vivo gene therapy of liver-expressed genes by chimeric oligonucleotides appears quite promising as a means of correcting single nucleotide gene defects.

Uptake and fate of class B scavenger receptor ligands in HepG2 cells

Class B scavenger receptors (SR-Bs) interact with native, acetylated and oxidized low-density lipoprotein (LDL, AcLDL and OxLDL), high-density lipoprotein (HDL3) and maleylated BSA (M-BSA). The aim of this study was to analyze the catabolism of CD36- and LIMPII-analogous-1 (CLA-1), the human orthologue for the scavenger receptor class B type I (SR-BI), and CD36 ligands in HepG2 (human hepatoma) cells. Saturation binding experiments revealed moderate-affinity binding sites for all the SR-B ligands tested with dissociation constants ranging from 20 to 30 microg.mL-1. Competition binding studies at 4 degrees C showed that HDL and modified and native LDL share common binding site(s), as OxLDL competed for the binding of 125I-LDL and 125I-HDL3 and vice versa, and that only M-BSA and LDL may have distinct binding sites. Degradation/association ratios for SR-B ligands show that LDL is very efficiently degraded, while M-BSA and HDL3 are poorly degraded. The modified LDL degradation/association ratio is equivalent to 60% of the LDL degradation ratio, but is three times higher than that of HDL3. All lipoproteins were good cholesteryl ester (CE) donors to HepG2 cells, as a 3.6-4.7-fold CE-selective uptake ([3H]CE association/125I-protein association) was measured. M-BSA efficiently competed for the CE-selective uptake of LDL-, OxLDL-, AcLDL- and HDL3-CE. All other lipoproteins tested were also good competitors with some minor variations. Hydrolysis of [3H]CE-lipoproteins in the presence of chloroquine demonstrated that modified and native LDL-CE were mainly hydrolyzed in lysosomes, whereas HDL3-CE was hydrolyzed in both lysosomal and extralysosomal compartments. Inhibition of the selective uptake of CE from HDL and native modified LDL by SR-B ligands clearly suggests that CLA-1 and/or CD36 are involved at least partially in this process in HepG2 cells.