Synthesis and secretion of apoC-I and apoE by human SW872 liposarcoma cells
Apolipoprotein C-I (apoC-I) plays an important role in the metabolism of plasma triglyceride levels and cholesterol metabolism. Little is known about the regulation of apoC-I production by human adipocytes. Aim. To investigate the effect of different tissue culture conditions on the synthesis and secretion of apoC-I and apoE in human SW872 liposarcoma cells and to study the effects of apoC-I overexpression in these same cells. Methods. SW872 cells were grown in DMEM/F-12 (3:1, v/v). QPCR was used to quantify mRNA synthesis. ELISAs were used to quantify intracellular and extracellular proteins. Colorimetric reaction kits were used to analyze intracellular cholesterol and triglyceride concentrations. Results . Maturation experiments revealed that after 17 days in culture, SW872 cells contained significantly more cholesterol (100%) and triglyceride (3-fold). Cell maturation was associated with significantly higher levels of apoE mRNA (+200%) but not apoC-I mRNA (-50%). The cells secreted more apoC-I (+110%) and apoE (+340%). Cellular apoC-I increased 620% and apoE increased 1540%. Treatment of cells during maturation with insulin (0, 10 or 1000 nM) significantly reduced the secretion of apoC-I and apoE (-14% and -56%, respectively) and intracellular apoC-I and apoE (-10% and -12%, respectively. Overexpression of apoC-I in SW872 cells resulted in increased cell number (+70%) and decreased lipids per cell (-32% triglyceride, -36% cholesterol) as compared to controls. Conclusion. These results suggest that apoC-I and apoE production is differentially regulated at the transcriptional level in adipocytes and that apoC-I and apoE play a role in the maturation of human adipocytes and may have an important role in mediating or regulating cell lipid accumulation. As well, overexpression of apoC-I in SW872 cells impedes cellular lipid accumulation and stimulates cellular proliferation.
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