Transformation-enhancing factor(s) released from chicken rous sarcoma cells: Effect on some transformation parameters

The medium of chick embryo fibroblasts (CEF) transformed by Schmidt-Ruppin strain of Rous sarcoma virus (SR-RSV) contains a factor(s) which complements the expression of some transformation parameters depending on the src gene. Notably, it reverses the block by puromycin of morphological transformation of cells infected with three ts-T mutants after shift-down from restrictive (41.5°) to permissive (37°) temperature. This reversal is not due to the release of inhibition of protein synthesis produced by puromycin, and is accompanied by the expression of two other src-dependent transformation parameters: disorganization of the cytoskeleton and loss of cell surface-associated fibronectin. The factor(s) able to overcome the puromycin block of morphological transformation was operationally called transformation-enhancing factor (TEF) like a previously reported factor favoring transformation by RSV ( Krycève et al., Int. J. Cancer 17, 370–379, 1976 ). It is lacking in media of untransformed cells, uninfected or infected with a nontransforming virus (RAV-1), and its production by RSV-infected cells seems to depend on the acquisition of the transformed phenotype, therefore on the expression of the src gene. Its effect was also shown to persist beyond the period of contact with the cells. It appears to be a glycoprotein which can be resolved by gel filtration into two peaks of 250K and 190K, apparently distinct from other known factors spontaneously released by transformed cells. A similar activity was also found in the medium of mammalian (rodent) cells transformed by SR-RSV and by other RNA and DNA oncogenic viruses, but not in the medium of untransformed controls.