Annexin VI is one of a family of
calcium-dependent
phospholipid-
binding proteins. Although the function of this
protein is not known, various physiological roles have been proposed, including a role in the budding of
clathrin-coated pits (Lin et al., 1992. Cell. 70:283-291.). In this study we have investigated a possible endocytotic role for
annexin VI in intact cells, using the human
squamous carcinoma cell line A431, and report that these cells do not express endogenous
annexin VI, as judged by Western and Northern blotting and PCR/Southern blotting. To examine whether endocytosis might in some way be either facilitated or inhibited by the presence of
annexin VI, a series of A431 clones were isolated in which
annexin VI expression was achieved by stable transfection. These cells expressed
annexin VI at similar levels to other human cell types. Using assays for endocytosis and recycling of the
transferrin receptor, we report that each of these cellular processes occurs with identical kinetics in both transfected and wild-type A431 cells. In addition, purified
annexin VI failed to support the scission of coated pits in permeabilized A431 cells. We conclude that
annexin VI is not an essential component of the endocytic pathway, and that in A431 cells,
annexin VI fails to exert any influence on internalization and recycling of the
transferrin receptor.