PF4 promotes the binding of soluble LDL-R to the cell surface.

(A) ¹²⁵I–sLDL-R (250 nM) was incubated with LDL-R–deficient CHO cells (▪, ▴) or with XT⁻ CHO cells, which lack HS and CS chains (●), in the presence of increasing concentrations of PF4 (▪, ●) or NAP2 (▴; dashed line). (B)¹²⁵I-LDL (50 nM) was incubated with LDL-R–deficient CHO cells as in (A) in the presence of PF4 (80 μg/mL), sLDL-R (2.5 μM), or both PF4 and sLDL-R. Data are the mean ± SEM of 3 to 6 independent experiments, each performed in triplicate.