HeLa cells contain intermediate-sized filaments of the prekeratin type

Abstract

Immunofluorescence microscopy using antibodies raised against protein constituents of the different types of intermediate-sized filaments has shown that in HeLa cells filaments containing a prekeratin-like protein (cytokeratin) predominate. The wavy filament bundles decorated by antibodies against prekeratin are similar to those described in other cells of epithelial origin. These bundles of intermediate-sized (6–11 nm) filaments are also described by electron microscopy in intact cells and in cytoskeletal preparations obtained by cell lysis and extraction with low and high salt buffers and Triton X-100. The occasional occurrence of desmosome-attached tonofibrillar bundles of intermediate-sized filaments is also shown. When HeLa cells are treated for long times with colcemid to induce perinuclear whorls of intermediate-sized filaments, these aggregates of filaments are strongly stained by antibody to vimentin, the major polypeptide of the intermediate-sized filaments of murine 3T3 cells. However, they are not stained by antibody to prekeratin, and the display of the prekeratin-containing tonofilament-like structures is similar to that seen in untreated cells. SDS-polyacrylamide gel electrophoresis of cytoskeletons prepared under conditions in which intermediate-sized filaments are retained show the presence of a polypeptide which co-migrates with one component of bovine prekeratin, and a second polypeptide which co-migrates with vimentin purified from mouse 3T3 cells. The data show ( i) that two different types of intermediate-sized filaments can be present in the same cell and can be distinguished immunologically; and ( ii) that the expression of a prominent epithelial structural marker, i.e. prekeratin-containing filaments, can be maintained in malignancy and continuing proliferation in vitro.