PF4 inhibits the binding, endocytosis, and degradation of LDL.

¹²⁵I-LDL (5 nM) was incubated with LDL-R–transfected CHO cells in the presence of increasing concentrations of PF4 for 4 hours at 37°C. Cells were chilled to 4°C for 30 minutes, after which surface bound (●), internalized (▴), and degraded (■) LDL were measured as described in “Materials and methods.” Data are the mean ± SEM of 4 independent experiments, each performed in triplicate. (Inset) Indirect Hill plot of degradation data. D₀ represents LDL degradation in the absence of PF4. D represents LDL degradation in the presence of PF4 at a given concentration.