Cell shape and organization of cytoskeleton and surface fibronectin in non-tumorigenic and tumorigenic rat liver cultures

Abstract

Morphological changes associated with neoplastic transformation of epithelial cells were studied in a series of IAR cell lines derived from rat liver. The series included three independently obtained, non-tumorigenic lines and five derived, tumorigenic lines. The morphology of cell surfaces was observed by scanning electron microscopy; the distribution of actin, tubulin and fibronectin was determined by indirect immunofluorescence. All the non-tumorigenic lines had a typical epithelioid morphology: isolated cells of these lines spread on the substratum had a discoid shape and contained circular, marginal bundles of microfilaments and microtubules. In denser areas, the cells formed monolayered sheets with characteristic marginal bundles of microfilaments near the free edges. Decreased spreading of isolated cells on the substratum was the characteristic feature that distinguished tumorigenic lines from their non-tumorigenic parent lines. In particular a decrease in the size of the ring-like, peripheral lamella and its disintegration into several discrete lamellar zones were often observed; as a result, the cell shape was altered from discoid to polygonal or elongated. The altered distribution of microfilament bundles and microtubules was characteristic in elongated cells; the pattern of the cytoskeletal elements of these cells resembled that of polarized fibroblasts. Complete disappearance of microfilament bundles was observed in cells of only one tumorigenic line. Various degrees of disorganization of monolayered cell sheets were observed in tumorigenic cultures, accompanied by an altered distribution of microfilament bundles. The alterations in the fibronectin-containing structures were more complex: there were often fewer fibronectin “spots' and fibrils at the lower surfaces of cells of tumorigenic cultures as compared with those of non-tumorigenic ones; there were more fibrils in dense cultures of certain lines but fewer in others. It is concluded that alterations in the ability to spread on the substratum and to form cell-cell contacts are common features of morphologically transformed fibroblastic and epithelial cultures. However, the actual changes in the cytoskeletal structures that accompany these alterations are different in transformed cultures of various tissue types.