FIGURE 6.

Inhibitors of lipid-raft mediated endocytosis block TβRIII down-regulation. A, COS7 cells transiently expressing TβRIIIΔgag and wild-type dynamin or mutant dynamin-K44A were bound and cross-linked with ¹²⁵I-labeled TGF-β1 followed by a 5-h time course at 37 °C. TβRIII down-regulation was quantified by densitometry (ImageJ). The average of three independent experiments was graphed (right); bars = S.E. B, HepG2 cells either untransfected (UT) or transfected with wild-type dynamin (WT) or dynamin K44A (K44A) were bound and cross-linked with ¹²⁵I-labeled TGF-β1 followed by a 22-h time course at 37 °C, and TβRIII was immunoprecipitated with a TβRIII antibody. TβRIII down-regulation was quantified by densitometry and normalized to β-actin (ImageJ). C, COS7 cells transiently expressing TβRIIIΔgag were bound and cross-linked with ¹²⁵I-labeled TGF-β1 and either untreated or treated with increasing amounts of nystatin ± cholesterol over a time course at 37 °C.