VITAMIN-A TRAFFICKING IN CACO-2 CELLS STABLY TRANSFECTED WITH CELLULAR RETINOL-BINDING PROTEINS

During intestinal vitamin A absorption, retinol is esterified by long- chain fatty acids and secreted in chylomicron particles. Stable transf ectants of the human intestinal Caco-2 cell line overexpressing cellul ar retinol binding protein II (CRBP II) or coexpressing CRBP II and CR BP were established to study their role in intestinal vitamin A traffi cking. Compared with control cell lines, retinol uptake increased up t o twofold by overexpression of CRBP TI and up to 2.9-fold by coexpress ion of CRBP and CRBP IT. Retinyl ester synthesis was increased proport ionate to the increase in retinol absorption in all cell lines. Retiny l ester secretion was directly correlated with retinyl ester synthesis in control and CRBP II-transfected cell lines. However, transfection with CRBP increased the proportion secreted. Expression of CRBP and CR BP II also affected the polarity of retinyl ester secretion by increas ing the proportion secreted basolaterally. Thus these studies provide evidence that intestinal retinol uptake, retinyl ester synthesis, and retinyl ester secretion are correlated with levels of CRBP and CRBP II and that the effects of CRBP on retinyl ester secretion can be distin guished from those of CRBP II.