Differential regulation of apolipoprotein A-I/ATP binding cassette transporter A1-mediated cholesterol and phospholipid release.

We compared apolipoprotein A-I (apoA-I)-mediated release of cellular cholesterol and phospholipid among several fibroblast cell lines. ApoA-I induced phospholipid release from WI-38, MRC-5, BALB/3T3, L929 and CHO-K1, but not from COS-7, while cholesterol was released only from WI-38, MRC-5 and BALB/3T3 without correlation to the cellular cholesterol content. The reaction consequently generated cholesterol-rich high density lipoprotein (HDL) with WI-38, MRC-5 and BALB/3T3, cholesterol-poor HDL with L929 and CHO-K1, and no HDL from COS-7. In contrast, diffusion-mediated cholesterol efflux to cyclodextrin took place with all the cell lines tested in proportion to the cellular free cholesterol content. While caveolin-1 was expressed in all of these cell lines, ATP-binding cassette transporter (ABC) A1 was detected in all but COS-7. We concluded that (1) fibroblasts were categorized into three groups with respect to the interaction with apoA-I, (i) those to produce cholesterol-rich HDL, (ii) cholesterol-poor HDL and (iii) no HDL; (2) ABCAl was required for the assembly of HDL from phospholipid among the cell lines tested; (3) caveolin-1 alone did not induce cholesterol incorporation into the HDL generated.