Purified HDL‐apolipoproteins, A‐I and C‐III, substitute for HDL in promoting the growth of SV40‐transformed REF52 cells in serum‐free medium

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Abstract
The lipid‐free apolipoproteins of human high density lipoprotein (HDL) have been assayed for their ability to substitute for native HDL in promoting the growth of a SV40‐transformed REF52 cell line in serum‐free medium. Total HDL‐apolipoproteins (apoHDL) were found to mimic almost exactly the growth promoting effects of whole HDL. The apoHDL‐associated growth promoting activity eluted from a Sephacryl S‐200 column in two separate fractions coin‐ciding with the protein peaks of apolipoprotein A‐I and the C group of apolipoproteins. These two fractions, designated S‐II and S‐IV, respectively, acted additively in promoting WT1A cell growth when tested at saturating concentrations. The active component in the S‐II fraction maximally stimulated WT1A cell growth at 40–60 μg/ml and was identified as apolipoprotein A‐1 by NaDodSO4 polyacrylamide gel electrophoresis and affinity chromatography on anti‐(apoA‐I). The active component in the S‐IV fraction was maximally active at 1–2 μg/ml and was identified as apolipoprotein C‐III by DEAE ion exchange high pressure liquid chromatography and polyacrylamide gel electrophoresis (at pH 8.3) in 6 M urea. These results indicate that the growth promoting effect of HDL on WT1A cells is mediated via the HDL‐apolipoproteins, A‐I and C‐III, and that the mechanism responsible does not necessarily involve their participation in the uptake (or utilization) of HDL‐associated lipids.

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