Implications on Cell Function and Differentation

Abstract

Does morphology contribute to the function of intermediate filaments? As cell type specific markers, they have the reputation of being nondynamic parts of the cytoskeleton in contrast to the microfilaments and microtubules which play a well-established role in the cell (Lazarides 1980). Experimental disruption of the intermediate filament cytoskeleton in cultured cells by means of a microinjection of antibodies directed at specific intermediate filament proteins (Klymkowsky 1981, 1982; Lane and Klymkowsky 1982; Toelle et al. 1986) showed, besides the collapse of filaments around the nucleus, no effects on cell morphology, organelle transport, cell locomotion, or mitosis. Whereas vimentin filaments remain intact during mitosis (Blose and Bushnell 1982), cytokeratins are transiently disaggregated in the cell division process (Lane et al. 1982). Biologically functioning cells exist which obviously lack intermediate filament proteins, as was observed in, for example, some normal vimentin-negative lymphocytes in the germinal center of lymph nodes (Moeller et al. 1988), in tumor cells of pituitary adenomas (see Sect. 9.1), and in some neuroendocrine neoplasms (Blobel et al. 1985). Under pathological conditions, as in the case of alcoholic liver disease, the cytokeratin cytoskeleton of hepatocytes is destroyed and Mallory’s bodies containing the remnants are found. These cells, however, have undiminished metabolic activities (Hazan et al. 1986). Recent reports on intermediate filaments suggest a more functional involvement in the cell and a more dynamic role in cell differentiation.