LIPOPROTEIN AND APOLIPOPROTEIN SECRETION BY A NEWBORN PIGLET INTESTINAL-CELL LINE (IPEC-1)

The aim of these studies was to characterize the synthesis and secreti on of lipoproteins and apolipoprotein B (ape B) and apo A-I by a newbo rn swine intestinal epithelial cell line (IPEC-1). Differentiated cell s exhibited enterocytic features, including microvilli. [H-3]oleic aci d was taken up and incorporated into cellular lipids and secreted into the basolateral medium in lipoproteins. Total apo B and apo A-I secre ted increased with oleic acid incubation. However, cellular apo B and apo A-I content did not change. Whereas undifferentiated cells synthes ized and secreted only apo B-100, both apo B-100 and apo B-48 were pro duced by differentiated cells. The ratio of radiolabeled apo B-48 to a po B-100 in both basolateral medium and cell homogenate increased with oleic acid treatment after 24-h steady-state labeling. However, apo B mRNA editing was unchanged, indicating posttranslational regulation o f this ratio. Pulse-chase radiolabeling demonstrated no major changes in cellular or basolateral medium apolipoprotein labeling kinetics wit h oleic acid or dexamethasone incubation. The dissociation of apo B an d apo A-I mass secretion from the secretion of radiolabeled apo B and apo A-I in response to oleic acid absorption suggests the presence of an intracellular pool of apolipoprotein with a slow turnover that is m obilized for secretion in response to fatty acid uptake.