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

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 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.

Role of lipoproteins in growth of human adult arterial endothelial and smooth muscle cells in low lipoprotein‐deficient serum

“…We previously reported that the HDL requirement for growth of a variant cell line of a rat embryonic fibroblast (REF52) transformed with SV40 virus was effectively replaced by either apoHDL or highly purified apoC-111 in serum-free medium (Chen et al, 1986a). This suggested a role of the protein elements of HDL on cell growth that was independent of the lipids in the particle.…”

“…Lipoprotein and apolipoprotein fractions were analyzed by SDS polyacrylamide gel electrophoresis and were found to contain trace amounts of serum albumin (Chen et al, 1986a). Lipoproteins prepared in this manner were unable to support the monolayer growth of REF52 cells, which required, among other factors, HDL or LDL and EGF, and anchorage-independent growth of NRK cells, which required, among other factors, HDL, EGF, and p-TGF, in serum-free medium (unpublished observations).…”

“…Apolipoprotein solutions were extensively dialyzed against PBS and sterilized by filtration through 0.22 pm Millex filters for bioassay. Chromatography of apoHDL on Sephacryl S-200 columns was performed as previously described (Chen et al, 1986a). Apolipoprotein A-I (apoA-I) and apolipoprotein C (apoC) fractions were pooled, dialyzed against PBS, sterilized as described, and stored at 4°C.…”

“…ApoLDL, which contains 98% of apolipoprotein B, was insoluble (Schaefer et al, 1979) and could not be compared. Apolipoprotein fractions were analyzed for lipid contamination (Chen et al, 1986a) and were essentially free of cholesterol, cholesterol ester, and phospholipid in quantities that would stimulate proliferation of responsive cells. per/dish) and SMC (2 X 104/dish) were plated into 1.5 ml of medium MCDB 107, EGF, BDGF, and the indicated supplements.…”

High-Density Lipoprotein Cholesterol, Obesity, and Mammographic Density in Korean Women: The Healthy Twin Study

“…4 , 5 However, studies of this association have reported inconsistent results: some noted that high HDL-C increased the risk of breast cancer, 1 , 6 , 7 whereas others reported that lower levels of serum HDL-C were associated with an increased risk of breast cancer. 2 , 8 – 12 In one study, significant associations were observed only in specific groups, such as overweight or obese women.…”