Ultrastructural immunocytochemical localization of the transferrin receptor using a monoclonal antibody in human KB cells.

Abstract

Using a monoclonal antibody (HB21) against the human transferrin receptor, we have localized this receptor in cultured KB human carcinoma cells by fluorescence and ultrastructural immunocytochemistry. The receptor was found diffusely distributed on the cell surface, concentrated in clathrin-coated pits of the cell surface, in intracellular endocytic vesicles (receptosomes) derived from coated pits, in tubular elements of the trans-reticular Golgi system, and in microtubule-associated membranous elements thought to be part of the constitutive exocytic system. This distribution is the same as that previously shown for labeled transferrin in these same cells (Willingham MC, Hanover JA, Dickson BB, Pastan J: Proc Natl Acad Sci USA 81:175, 1984). No significant amounts of receptor were found in lysosomes. An aggregation of membranous elements containing this receptor was found in the pericentriolar region of cells during mitosis. Together with the previous data on the immunocytochemical localization of transferrin, these results suggest that the transferrin receptor may constitutively enter and exit KB cells by endocytosis and exocytosis, carrying bound transferrin into and out of the cell for the purpose of supplying iron from the extracellular environment for cell growth.

Alveolar type II cells express a high-affinity receptor for pulmonary surfactant protein A.

“…The high-affinity binding is not accompanied by A. degradation as is observed for the low density lipoprotein (LDL)-receptor system (27). The lack of degradation and the potential reutilization of SP-A may place this receptor system in the same category as the transferrin receptor (30)(31)(32). The binding of SP-A is dependent upon the extracellular Ca2+ concentration and can occur at 0C (albeit to a lesser extent than at 370C).…”

Localization of TGN38 to the trans-Golgi network: involvement of a cytoplasmic tyrosine-containing sequence.

“…The recycling pool of transferrin receptors in CV-I cells was marked by incubation of intact cells for 2 h at 37~ with rhodamineconjugated transferrin. Under these conditions, intracellular transferrin would be expected to be bound to recycling receptors (Klausner et al, 1983;Dautry-Varsat et al, 1983), and to be localized mainly to early endosomes (Hopkins, 1983), with smaller amounts present in coated vesicles and tubules in the area of TGN (Willingham and Pastan, 1985;Fishman and Fine, 1987;Stoorvogel et al, 1988). Cells were then fixed, permeabilized, and stained for T-G-G using an antibody to Tac and a fluorescein-conjugated second antibody (Fig.…”

Internalization of a monoclonal antibody against human breast cancer by immunoelectron microscopy

“…After warming at 37°C the transferrin receptor molecules displayed their proper pathway of internalization. Warming for two minutes was sufficient to induce the formation of coated pits, as previously described (Willingham & Pastan, 1985) and the transferrin receptors reached the lysosomes through vesicles in a few minutes. Therefore, it seemed unlikely that the trypsin treatment could have caused a profound peturbation of the cell membrane structure or that the cell line used had acquired some endocytotic defect while in culture.…”