Fig. 5. MK-TRAP acts by blocking MK-LRP1 interaction. (A) CHO-derived cells were exposed to ¹²⁵I-MK and treated with the chemical crosslinker BS³. The ¹²⁵I-MK-crosslinked band appeared in CHO-mLRP4 but not CHO-LRP^– cells. MK-TRAP- or sLRP3-containing medium was added to CHO-mLRP4 cells to assess their effects on crosslinking. CHO-LRP cells are deficient in LRP1 expression; CHO-mLRP4 is a stable transfectant expressing LRP1-binding domain IV in the background of CHO-LRP^– cells. The arrowhead indicates the unprocessed form of the protein; the arrow indicates the mature form of the protein. (B) GST-RAP, an inhibitor of LRP1, and GST control were administered to M1 and control C1 cells, and the total numbers of colonies in each group were counted and compared by Student's t-test. n=3; error bars, ± s.e.m.; **, P<0.01.