Suitability of LLC-PK1 pig kidney cells for the study of drug action on renal cell cholesterol uptake: identification and characterization of low-density lipoprotein receptors.
ABSTRACT The purpose of this study was to identify and characterize the presence of low-density lipoprotein receptors (LDLr) in LLC-PK(1) cells.
LLC-PK(1) cells were assessed for the presence of LDLr by conducting dose-response, LDL specific binding and competitive studies with DiI-LDL, and Western blot and RT-polymerase chain reaction (PCR) analyses. Assay conditions with IgG-C7, a monoclonal antibody (mAb) to the LDLr, were optimized, including temperature, preincubation time, and concentration in LLC-PK(1) cells.
LLC-PK(1) cells express LDL receptors as determined by LDL specific and competitive binding studies and Western blot and RT-PCR analysis (specific binding 0.5 ng DiI-LDL/mug of cellular protein).
Taken together, these findings confirm the presence of LDL receptors on LLC-PK1 cells and support the appropriateness of using these cells in studies involving renal cell cholesterol uptake and metabolism.
- Annual Review of Biochemistry 02/1994; 63:601-37. · 27.68 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: The aim of this study was to elucidate the possible causes of elevated low-density lipoprotein (LDL)-cholesterol levels in transplanted patients treated with the immunosuppressant drug, cyclosporine. HepG2 cells, from a well-differentiated cell-line of hepatoma cells, were cultured and used as a model for in vitro hepatocytic LDL uptake. Different concentrations of cyclosporine, which were within the range of concentrations found in humans treated with cyclosporine, were added to tissue culture medium together with 125I-LDL. The results showed that cyclosporine reduced LDL uptake and degradation in HepG2 cells by about 25%. The cells were also pretreated with cyclosporine for 1 to 24 hours and then incubated with new medium containing labeled LDL for 2 hours at 4 degrees C in an LDL-binding assay. The data showed that cyclosporine reduced the subsequent LDL binding. Cyclosporine has no toxic effects on HepG2 cells, as shown by unchanged growth capacity of the cells. By means of a 50-fold excess of unlabeled LDL, a monoclonal anti-LDL receptor antibody, and dextran sulfate, we also evaluated if this inhibition of LDL binding occurred through the LDL receptor-mediated pathway, through non-LDL receptor-mediated pathways, or through both. The results show that cyclosporine reduces LDL binding and uptake by mainly inhibiting the LDL receptor-mediated pathway. We also studied the effect of the LDL-cyclosporine complex on the binding of labelled LDL. The presence of cyclosporine in the LDL particle does not influence the binding behaviour of LDL to its receptor. We also found that cyclosporine reduces the expression of the LDL receptor messenger RNA (mRNA) by about 40%. Thus, the interpretation of this study is that cyclosporine can cause an increase in LDL-cholesterol in the plasma of transplantation patients by reducing the catabolism of LDL in the liver by inhibiting mainly the LDL receptor-mediated catabolism through an effect on LDL receptor synthesis.Hepatology 10/1996; 24(3):613-9. · 12.00 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: The mechanism of hepatic catabolism of human low density lipoproteins (LDL) by human-derived hepatoma cell line HepG2 was studied. The binding of 125I-labeled LDL to HepG2 cells at 4°C was time dependent and inhibited by excess unlabeled LDL. The specific binding was predominant at low concentrations of 125I-labeled LDL (< 50 pg protein/ml), whereas the nonsaturable binding prevailed at higher concentrations of substrate. The cellular uptake and degradation of 125I-labeled LDL were curvilinear functions of substrate concentration. Preincubation of HepG2 cells with unlabeled LDL caused a 56% inhibition in the degradation of 125I-labeled LDL. Reductive methylation of unlabeled LDL abolished its ability to compete with 125I-labeled LDL for uptake and degradation. Chloroquine (50 μM) and colchicine (1 μM) inhibited the degradation of 125I-labeled LDL by 64% and 30%, respectively. The LDL catabolism by HepG2 cells suppressed de novo synthesis of cholesterol and enhanced cholesterol esterification; this stimulation was abolished by chloroquine. When tested at a similar content of apolipoprotein B, very low density lipoproteins (VLDL), LDL and high density lipoproteins (HDL) inhibited the catabolism of 125I-labeled LDL to the same degree, indicating that in HepG2 cells normal LDL are most probably recognized by the receptor via apolipoprotein B. The current study thus demonstrates that the catabolism of human LDL by HepG2 cells proceeds in part through a receptor-mediated mechanism.Biochimica et Biophysica Acta 08/1984; · 4.66 Impact Factor