Temperature-sensitive changes in surface modulating assemblies of fibroblasts transformed by mutants of Rous sarcoma virus.

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Abstract
The hypothesis that surface modulating assemblies containing microfilaments and microtubules are altered after cellular transformation was tested on cells infected with temperature-sensitive mutants of avian sarcoma virus. Untransformed cells (mouse 3T3 and chick fibroblasts), cells transformed by simian virus 40 (SV 3T3), and chick fibroblasts infected with Schmidt-Ruppin strain of Rous sarcoma virus (SR-RSV-A-infected cells) were first compared for differences in microfilament and microtubule patterns after treatment with fluorescein-labeled antibodies to actin and tubulin. Transformed cells showed disappearance of ordered stress microfilaments and thickened or diffuse alterations of microtubular arrays. At restrictive temperatures (41.degree.), chick fibroblasts infected with a temperature-sensitive mutant (ts 68) of Rous sarcoma virus showed normal patterns of stress filaments and radial microtubular arrays originating in 1 or 2 centrioles. At permissive temperatures (37.degree.), these patterns were disordered and resembled those of SR-RSV-A-infected cells. After a shift from 41.degree. to 37.degree., the changes in microtubules were observed in the majority of cells within 1 h. These changes were reversible and did not result from the inability of tubulin to polymerize. In ts 68-infected cells at permissive temperatures, concanavalin A induced much less surface modulation (inhibition of receptor mobility) than at restrictive temperatures. Cellular transformation probably alters both the structure and function of surface modulating assemblies and prompts the hypothesis that products of viral transforming genes may affect these assemblies with a consequent loss of growth control.