The endocytosis of low density lipoprotein (LDL) and α2-macroglobulin (α2M) has been examined simultaneously in human skin fibroblasts. Incubation of cells at 4 °C with rhodamine-α2M and LDL plus [(dichlorotriazinyl)amino]fluorescein-anti-LDL gave a weak fluorescence for α2M and a brighter, clustered fluorescence for LDL. Following warming to 37 °C, LDL and α2M were observed to be coincident within endocytotic vesicles in the cell. By electron microscopy, LDL-ferritin and α2M-colloidal gold were present in the same coated pit at 4 °C. After 7 min at 37 °C, both ligands were observed in the same receptosome. Pretreatment of fibroblasts at 37 °C with 200-300 μM dansylcadaverine or 50 mM methylamine blocked clustering and internalization of both LDL and α2M. Bacitracin (5 mg ml-) blocked clustering and endocytosis of α2M, but not of LDL. These data indicate that both LDL and α2M are processed via the same endocytotic pathway in skin fibroblasts.
ASJC Scopus subject areas
- Cell Biology