Increased expression of growth factor mRNAs accompanies viral transformation of rodent cells

Transforming growth factors-alpha and beta (TGF-alpha and -beta) and platelet-derived growth factor (PDGF), three distinct peptide hormones, acting together, are able to potentiate the phenotypic transformation of normal rat kidney (NRK) cells. Cells transformed by retroviruses have been shown to secrete increased levels of TGF-alpha, TGF-beta and PDGF. We report here that Harvey sarcoma virus-transformed NIH-3T3 cells and Moloney sarcoma virus-transformed NRK cells show increased expression of the mRNAs for TGF-alpha, TGF-beta, PDGF A-chain and nerve growth factor (NGF) compared to their untransformed counterparts. No amplification or rearrangement in the genomic DNA is seen in the transformed cells. In tumor tissue formed by subcutaneous injection of Ha-3T3 cells, this enhanced level of TGF-beta mRNA returns to the control level of the untransformed cells. The increase in TGF-beta mRNA in the transformed cells is paralleled by an increase in the level of TGF-beta protein as shown by immunoprecipitation and Western blotting procedures using specific TGF-beta antibodies.