Figure 5.

(A) G418-selected, stable apoB48R-transfected, and vector-transfected control CHO were incubated with tryp-VLDL 100–400 S_f at the concentrations indicated for 4 h at 37°C and the cells processed to measure TG mass as previously reported (18). The upper curve (closed squares; apoB48R transfected) reflects a rapid, curvilinear accumulation of TG with increasing levels of tryp-VLDL. The lower curve (open squares; cells transfected with pcDNA 3.1 vector plus inverted insert) shows linear accumulation, representing low-affinity nonspecific uptake. Values are averages from duplicate dishes that differ by <10%; This represents one of four experiments with the apoB48R cDNA and four with the apoB48R minigene containing the first intron. (B) Transfections were as described in Fig. 5A. After a 2-h incubation with the indicated lipoprotein at 37°C, the cells were processed as above. The bar graph shows the amount of TG that accumulated relative to a buffer control, which was subtracted from the level for each lipoprotein. Like human THP-1 macrophages, the apoB48R-transfected cells accumulate significant TG when exposed to apoB48 only containing CM S_f 1,100–3,200 S (CMII) and to the model ligand, tryp-VLDL S_f 100–400 (t-V1), but not to VLDL S_f 100–400 from a donor with normal plasma TG levels (N-V1). The experiment was repeated twice with identical results. Concurrent experiments with control vector-transfected CHO showed no significant TG accumulation under the same experimental conditions (data not shown).