FIGURE 1.

Exogenous PCSK9 can induce degradation of the LDLR in the absence of APLP2. HepG2 (A) and Huh7 (B) cells were transfected with a control non-target siRNA (Ctrl) or 3 different siRNAs targeting APLP2. Cells were incubated overnight with serum-free conditioned media lacking or containing 1 μg/ml of PCSK9-V5. HepG2 and Huh7 cell lysates were then subjected to Western blotting using LDLR, APLP2, and β-actin antibodies. LDLR and APLP2 signals were normalized to that of β-actin. C, the input HEK293 conditioned medium was analyzed using mAb-V5 to detect PCSK9-V5. D, duplicate samples of Huh7 cells matching those in panel B were analyzed by FACS to assess the cell surface LDLR levels. Values were normalized to that of the first lane (control non-target siRNA in the absence of PCSK9). Error bars represent S.E. *, p < 0.05 (Student's t test). The data shown here are representative of two to three independent experiments.