The mechanism for synthesis and secretion of apo A-IV in CaCo-2 cells

Human apo A-IV is an unique apolipoprotein which is synthesized only in enterocytes and is involved in lipid absorption。However，the mechanism for synthesis and secretion of apo A-IV has not been fully explored。In this study，the effect of two kinds of fatty acid，oleic(C I D 218：1 I D 2)and caprylic(C I D 28：0 I D 2)acids，on apo A-IV synthesis and sedretion was examined in CaCo-2 cells.CaCo-2cells，which are cell line origenated from human colon cancer cells and show characteristics of intestinal epithelim，were cultured on the filter mambrane of Transwell for 6hr at 37℃with 3.0 mM of oleic or caprylic acid with a micellar form。Oleic acid increased triglyceride secretion by 4times，whereas caprylic acid increased by 1.3 times，compared to control。Apo A-IV concentration in the medium was significantly decreased in oleic acid，compared to caprylic acid.In contrast，apo A-IV mRNA level in cells is significantly increased in oleic acid compared to caprylic acid.It is suggested that caprylic acid enhances the secretion of apo A-IV without the increase in synthesis and oleic acid increases the transcription rate of apo A-IV，at least in CaCo-2cells.These different effects of fatty acids on apo A-IV depends on the different carbon number of fatty acids。

Human apo A-IV is an unique apolipoprotein which is synthesized only in enterocytes and is involved in lipid absorption. However, the mechanism for synthesis and secretion of apo A-IV has not been fully explored. In this study, the effect of two kinds of fatty acid, oleic (CィイD218:1ィエD2) and caprylic (CィイD28:0ィエD2) acids, on apo A-IV synthesis and sedretion was examined in CaCo-2 cells. CaCo-2 cells, which are cell line origenated from human colon cancer cells and show characteristics of intestinal epithelim, were cultured on the filter mambrane of Transwell for 6 hr at 37℃ with 3.0 mM of oleic or caprylic acid with a micellar form. Oleic acid increased triglyceride secretion by 4 times, whereas caprylic acid increased by 1.3 times, compared to control. Apo A-IV concentration in the medium was significantly decreased in oleic acid, compared to caprylic acid. In contrast, apo A-IV mRNA level in cells is significantly increased in oleic acid compared to caprylic acid. It is suggested that caprylic acid enhances the secretion of apo A-IV without the increase in synthesis and oleic acid increases the transcription rate of apo A-IV, at least in CaCo-2 cells. These different effects of fatty acids on apo A-IV depends on the different carbon number of fatty acids.