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

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 coinciding 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 micrograms/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 micrograms/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.