Tubulin and actin in paired nonneoplastic and spontaneously transformed neoplastic cell lines in vitro: fluorescent antibody studies.

Pairs of nonneoplastic and spontaneously transformed neoplastic cells were derived from rat, mouse and hamster embryos. The neoplastic cells of each pair had poorly spread cellular morphology, grew in agarose in vitro and produced invasive sarcomas in vivo; the nonneoplastic cells exhibited none of these properties. The distribution of microtubules and microfilament bundles (stress fibers or actin cables) was examined in five such paired lines and in 3T3 and SV40-transformed 3T3 cells by indirect immunofluorescent microscopy of fixed cells treated with rabbit antibody prepared against bovine brain tubulin or guinea pig smooth muscle actin, respectively. Actin cables in all the neoplastic cells appeared thinner and more sparse than in the paired nonneoplastic cells. These differences were also observed in living cells with polarization microscopy. In contrast, microtubules appeared similar in neoplastic and nonneoplastic cells, both in areas of thin peripheral lamellar cytoplasm which allowed a clear visualization of fine, curving microtubules and in regions of thick, central endoplasm which obsecured individual microtubules. In fact, the main morphological difference between neoplastic and nonneoplastic cells was the relative amount of lamellar cytoplasm or endoplasm, rather than the appearance of microtubles in either region. Thus the distinctive growth properties and retracted cellular morphology of neoplastic cells in this study did not correlate with decreased or disorganized microtubules, but with thin and sparse actin cables.