LOCATION AND REGULATION OF LOW-DENSITY-LIPOPROTEIN RECEPTORS IN INTESTINAL EPITHELIUM

The expression, distribution, and some aspects of the regulation of low-density lipoprotein (LDL) receptors in rat intestinal epithelial cells were examined. Cells prepared by a perfusion technique provided a pure preparation of epithelial cells and could be manipulated to produce crypt-villus units or villi alone. On a total protein basis, the abundance of LDL receptors in villus cell membranes was half that in hepatic membranes. The level of receptors in both tissues was reduced by feeding an atherogenic diet but was increased only in the liver by ethinyl estradiol-induced hypocholesterolemia. The level of LDL receptor mRNA in intestinal epithelial cells was somewhat lower than in liver. Regulation of LDL receptor mRNA was similar to that of protein. Judged by the ratio of mRNA in villus cells to the villus-crypt unit and nuclear run-on assay for LDL receptor gene transcription, we conclude that LDL receptor mRNA is produced in the villus cells. The effect of fat feeding was regulated at the level of transcription. Expression in villus cells in ileum was several fold higher than in jejunum and higher than in the liver. Together the results suggest serum cholesterol level is not the prime determinant of LDL receptor level in intestine, but LDL degradation in this organ may be regulated by factors in the lumen.