[Cytoplasmic microfilaments in laryngeal carcinoma malignant keratinocytes (author's transl)]

The fine structure of malignant keratinocytes of invasive squamous cell carcinoma of the human larynx was studied by electron microscopy. In these malignant cells a system organized 50--70 A microfilaments is prominent in the cortical cytoplasm of the lateral and basal cell surfaces. The microfilaments are arranged either in oriented bundles or form a complex filamentous network. The bundles may lie parallel to the plasma membrane and to the long axis of the cell. The microfilaments are situated at the base of the pseudopodia-like cell processes or are found extending into microvillous cytoplasmic extensions. In some places the bundles are some associated with the plasmalemma displaying electron-dense attachment sites. Desmosomes or other types of junctional complexes invariably remain free of microfilaments. At higher magnification the individual microfilaments are seen to be interconnected transversely by a polygonal interfilamentous meshwork. Within the bundles of microfilaments focal regions of increased electron density, similar to the Z-band of sarcomeres, are observed. Organized bundles of oriented 50--70 A microfilaments do not occur in normal squamous epithelial cells of laryngeal mucosa. By analogy with various motile microfilament containing cell systems which have been shown biochemically to contain the contractile protein actin, these cytoplasmic microfilaments may be the structural elements responsible for the migratory invasive properties of malignant keratinocytes in cancer of the larynx.