Effect of microtubule-destroying drugs on the spreading and shape of cultured epithelial cells.

The role of microtubules in the spreading of cells from the liver-derived IAR2 rat cell line was studied. Cells in the control medium seeded on a flat isotropic glass surface rapidly spread to form discoid shapes. Spreading in colcemid-containing medium was disorganized and delayed; partial reversal of spreading was observed. Nevertheless, even in the presence of colcemid the cells finally spread to discoid flattened shapes. IAR2 cells in medium without colcemid spread not to discoid but to elongated shapes under three different sets of conditions: (1) when the cells were forced to spread on narrow strips of adhesive glass surface between two non-adhesive lipid films; (2) when the cells spread on the poorly adhesive surface of poly(HEMA)-covered glass; (3) when the cells spread on the usual glass surfaces in medium containing cytochalasin D. Addition of colcemid to the media reversed the polarized spreading under the first two conditions; colcemid did not reverse the formation of the elongated cell shape acquired by the cells spreading in cytochalasin-containing medium. Effects of microtubule-destroying drugs on the spreading of epithelial and fibroblast cells are compared and discussed. It is suggested that microtubules are essential for the stabilization of the spread state of those attached cytoplasmic processes and lamellae that do not have numerous and stable-cell substratum contacts, e.g. the processes formed at the early stages of spreading or the elongated processes of polarized cells. Possibly, microtubules stabilize the non-contracted state of the actin cytoskeleton in these processes.