Figure 3.

Down-regulation of type II kinase mutant receptors depends upon cell type. Specific surface binding of ¹²⁵I-GM-CSF was determined in clones expressing a wild-type chimeric type I TGF-β receptor and point mutations in the type II TGF-β receptor at either K277 (▴) or P525 (●), when treated with 10 ng/ml GM-CSF at 37°C for the indicated times. Down-regulation of the normal heteromer (▪) containing wild-type type I and type II chimeric receptors is shown for comparison. (A) Data represent the mean (±SE) for each AKR-2B clone (wild-type A105 and P525L-13 and -22) assayed in duplicate from three separate experiments. (B) Data represent the mean (±SE) for each Mv1Lu clone (wild-type MB-9 and -18; K277R 102-1, -3, and -18, 117-7 and 9, 126-2 and -5; and P525L 102-5, -10, and -13, 117-10 and –15, and 126-1 and -12) assayed in duplicate from two separate experiments.