Regulation by estrogen of synthesis and secretion of apolipoprotein A-I in the chicken hepatoma cell line,LMH-2A |
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Authors: | Hermann Marcela Foisner Roland Schneider Wolfgang J Ivessa N Erwin |
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Affiliation: | Department of Molecular Genetics, Institute of Medical Biochemistry, University and Biocenter Vienna, Dr. Bohr-Gasse 9/2, Vienna A-1030, Austria. mhermann@mol.univie.ac.at |
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Abstract: | The synthesis and secretion of apolipoprotein A-I (apoA-I) in response to the treatment with estrogen were investigated in the chicken hepatoma cell line, LMH-2A. Exposure of these cells to exogenous estrogen for up to 48 h results in a decrease of apoA-I production, as evident from Western blotting, immunoprecipitation, and immunofluorescence experiments. Likewise, the secretion of apoA-I is also decreased in estrogen-treated cells when compared to controls. However, under both conditions, the disappearance of the apoprotein from the cells occurs very rapidly and with similar kinetics. The bulk of apoA-I secreted from LMH-2A cells is recovered on lipoprotein particles with a buoyant density of > or =1.10 g/ml, corresponding to HDL and heavy LDL. Interestingly, apoA-I is detectable on apoB-containing lipoproteins by sequential immunoprecipitation, suggesting that the two apoproteins co-reside at least on a subfraction of the secreted particles, or that apoB- and apoA-I-containing particles interact. These interactions are more pronounced in estrogen-treated cells, most likely due to the dramatic estrogen-mediated induction of apoB synthesis and secretion. |
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