Abstract

Lipoprotein synthesis by the colonic adenocarcinoma cell line Caco-2 was investigated to assess the utility of this cell line as a model for the in vitro study of human intestinal lipid metabolism. Electron micrographic analysis of conditioned medium revealed that under basal conditions of culture post-confluent Caco-2 cells synthesize and secrete lipoprotein particles. Lipoproteins of density (d) less than 1.063 g/ml consist of a heterogeneous population of particles (diameter from 10 to 90 nm). This fraction consists of very low density lipoproteins (d less than 1.006 g/ml) and low density lipoproteins (d = 1.019-1.063 g/ml). Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [35S]methionine-labeled Caco-2 lipoproteins revealed that very low density lipoproteins contain apolipoprotein E (apoE) and C apolipoproteins, while low density lipoproteins contained apoB-100, apoE, apoA-I, and C apolipoproteins. The 1.063-1.21 g/ml density fraction contained two morphological entities, discoidal (diameter 15.6 +/- 3.9 nm) and round high density lipoprotein particles (diameter 10.2 +/- 2.3 nm). The high density lipoproteins contained apoA-I, apoB-100, apoB-48, apoE, and the C apolipoproteins. Using isoelectric focusing polyacrylamide gel electrophoresis newly secreted apoA-I was identified as pro-apoA-I. ApoE and apoC-III released by Caco-2 cells were highly sialylated. mRNA species for apoA-I, apoC-III, and apoE, but not apoA-IV were identified by Northern blot analysis. ApoA-I, apoB, and apoE were visualized in Caco-2 cells by immunolocalization analysis. This intestinal cell line may be useful for in vitro studies of nutritional and hormonal regulation of lipoprotein synthesis.

Highlights

  • Lipoprotein synthesis by the colonic adenocarcinoma cell line Caco-2 was investigated to assess the utility of this cell line as a model for the in vitro study of human intestinal lipid metabolism

  • Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [36S]methionine-labeled Caco-2 lipoproteins revealed that very low density lipoproteinscontain apolipoprotein E and C apolipoproteins, while low density lipoproteins contained apoB-100, apoE, apoA-I, and C apolipoproteins

  • Been conducted in uivo [1,2,3,4,5,6] using intestinal segments ( 7, 8) and isolated intestinal epithelium [9,10,11], the study of human intestinal apolipoprotein synthesis and secretion has notbeen feasible. In general this area of study has lagged behind the investigation of hepatic lipoprotein metabolism, since the introduction of the human hepatoma cell line Hep G-2 [12]. This cell line (Hep G-2) has been very useful in the investigation of fully differentiated hepatocyte function and has been demonstrated to synthesize and secrete low density lipoprotein (LDL)’ and high density lipoprotein (HDL) particles similar to those produced by rat hepatocyte preparations in vitro as well as to particles derived from human plasma [13,14,15]

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Summary

Introduction

Lipoprotein synthesis by the colonic adenocarcinoma cell line Caco-2 was investigated to assess the utility of this cell line as a model for the in vitro study of human intestinal lipid metabolism. Been conducted in uivo [1,2,3,4,5,6] using intestinal segments ( 7 , 8) and isolated intestinal epithelium [9,10,11], the study of human intestinal apolipoprotein synthesis and secretion has notbeen feasible In general this area of study has lagged behind the investigation of hepatic lipoprotein metabolism, since the introduction of the human hepatoma cell line Hep G-2 [12]. This cell line (Hep G-2) has been very useful in the investigation of fully differentiated hepatocyte function and has been demonstrated to synthesize and secrete low density lipoprotein (LDL)’ and high density lipoprotein (HDL) particles similar to those produced by rat hepatocyte preparations in vitro as well as to particles derived from human plasma [13,14,15]

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