Further study of β‐tgfs released by virally transformed and non‐transformed cells

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Abstract
Chicken embryo fibroblasts sensitized by ts RSV respond to TGFs present in the media of non‐transformed FR3T3 and NRK‐4 rat cells and of the same cells transformed by KiMSV or RSV. They also respond to TGFs present in the media of BHK hamster cells transformed by MoMSV, PyV or RSV. Two other indicator rat cell lines, untransformed NRK‐4 and FR3T3, sensitized by ts KiMSV, respond to the same TGF‐containing media, and this response is increased by exogenous EGF. Normal FR3T3 cells failed to respond to any of the media. The most sensitive target cells were the ts KiMSV‐FR3T3 cells at the restrictive temperature (39.5°C). All the media tested on NRK‐49F target cells required EGF for their TGF activity which was essentially dependent on prior activation by acidification. These data show that the above media from non‐transformed or transformed cells contain β‐TGFs, with no detectable accompanying α‐TGF activity. The release of and the response to these TGFs are not interdependent. A function of ts mutant src and k‐ras viral oncogenes, still expressed at the restrictive temperature, can sensitize non‐responsive cells, without there being any specificity towards the TGF producer cells.