Actin assembly plays a variable, but not obligatory role in receptor-mediated endocytosis in mammalian cells

Three cell-permeant compounds, cytochalasin D, latrunculin A and jasplakino lide. which perturb intracellular actin dynamics by distinct mechanisms, we re used to probe the role of filamentous actin and actin assembly in clathr in-mediated endocytosis in mammalian cells. These compounds had variable ef fects on receptor-mediated endocytosis of transferrin that depended on both the cell line and the experimental protocol employed. Endocytosis in A431 cells assayed in suspension was inhibited by latrunculin A and jasplakinoli de, but resistant to cytochalasin D. whereas neither compound inhibited end ocytosis in adherent A431 cells. In contrast. endocytosis in adherent CHO c ells was more sensitive to disruption of the actin cytoskeleton than endocy tosis in CHO cells grown or assayed in suspension. Endocytosis in other cel l types, including nonadherent K562 human erythroleukemic cells or adherent Cos-7 cells was unaffected by disruption of the actin cytoskeleton. While it remains possible that actin filaments can play an accessory role in rece ptor-mediated endocytosis, these discordant results indicate that actin ass embly does not play an obligatory role in endocytic coated vesicle formatio n in cultured mammalian cells.