Morphology of Cap Formation in Ehrlich Ascites Tumor Cells Induced by Concanavalin A

Abstract

The redistribution of Concanavalin A (Con A) receptor sites on Ehrlich ascites tumor cells was studied by fluorescence and electron microscopy. The fluorochrome of fluorescein isothiocyanate (FITC)-Con A was distributed diffusely on the cell surface (as a ring) at 0°C, whereas it was concentrated at one pole of the cell (cap formation or capping) at 37°C. Cap formation occurred within 10 min when FITC-Con A was added to cells at 37°C or when cells, preincubated with FITC-Con A at 0°C, were warmed at 37°CC. Binding of FITC-Con A to cells was inhibited by the addition of 50 mM a-methyl glucoside. Upon incubating the cells with FITC-Con A for 2 h, concentrated fluorochrome appeared to be endocytosed at the cap region and much fluorescence in granular form remained at this locus in the cytoplasm even after the addition of α-methyl glucoside. This process was completely inhibited with 5 mM sodium azide.Under the electron microscope, control cells showed a diffuse and random distribution of microvilli and Con A receptors on their surfaces. In contrast, a large bundle of microvilli with bound Con A at the base of each microvillus was observed at one pole of the Con A-treated cells, indicating the gathering of Con A receptors corresponding to cap formation.The significance of cap formation is discussed in relation to the phagocytotic mechanism based on results of the present study.