Local accumulation of α‐spectrin‐related protein under plasma membrane during capping and phagocytosis in acanthamoeba

Abstract

During capping and phagocytosis the interaction between clustered cell surface receptors and the submembraneous actin-based skeleton may be mediated by spectrin-like proteins. To test this possibility we examined the localization of an α-spectrin immunoanalogue, that had been previously identified in whole extracts of Acanthamoeba, during capping of Con A receptors and during phagocytosis of Con A-coated yeast. During capping α-spectrin and filamentous actin co-migrated with the Con A receptors and accumulated in the region of cap formation, as demonstrated by double immunofluorescence studies. Immunoelectron microscopy revealed submembraneous location of α-spectrin in cells exposed to Con A, both at the time of initial cross-linking and during accumulation of α-spectrin in the region of the cap. Phagocytosis studies showed that α-spectrin and actin filaments were concentrated around phagocytic cups that enclosed Con A-coated yeast upon internalization. The proteins also surrounded nascent phagosomes present in the vicinity of the plasma membrane but were absent at the later time point of phagosome maturation. These data demonstrate a correlation between clustering of cell surface receptors and submembraneous localization of α-spectrin, suggesting an involvement of spectrin-like proteins in mediating the interaction of receptor clusters with the actin cytoskeleton. Cell Motil. Cytoskeleton 36:253–265, 1997. © 1997 Wiley-Liss, Inc.