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Use of revertant cell lines to identify targets of v-fos transformation-specific alterations in gene expression.

Two proteins expressed in Rat-1 cells which are targets for v-fos transformation-specific alterations in gene expression were identified as alpha 1(I) and alpha 2(I) procollagen. While procollagen (I) proteins were synthesized in Rat-1 fibroblasts, their synthesis was dramatically reduced in Rat-1 cells transformed with the FBJ-v-fos oncogene. Revertant cell lines, which were previously shown to express a functional fos oncoprotein, resumed the synthesis of procollagen (I) at levels comparable to those seen in Rat-1 cells. Further results indicated that these procollagen proteins were also synthesized in Rat-1 cell lines that constitutively express high levels of a transfected c-fos protooncogene. Together, these observations suggested that constitutive fos protein expression was not sufficient to inhibit synthesis of these proteins. We have further demonstrated that Rat-1 cells transformed by most other oncogenes express abundant levels of procollagen (I), indicating that inhibition of procollagen (I) synthesis is not a general characteristic of transformed Rat-1 cells but is specifically associated with FBJ-v-fos-induced transformation. Northern blot analysis and runoff transcription assay data indicated that the alpha 1(I) procollagen, but not alpha 2(I) procollagen, is differentially regulated at the transcriptional level in Rat-1 fibroblasts, v-fos transformants, and revertants.