A partially transformed cell line (NRK-PT14) was isolated from normal rat kidney (NRK) cells. Like NRK cells, NRK-PT14 cells required epidermal growth factor for anchorage-independent growth, but lost the additional requirement for exogenous type beta transforming growth factor (TGF-beta). Compared to NRK cells, NRK-PT14 cells did not secrete elevated levels of TGF-beta, but exhibited an altered response to this growth factor. Monolayer growth of NRK cells in a serum-free medium was inhibited by TGF-beta, whereas growth of NRK-PT14 cells was stimulated by TGF-beta. In addition, TGF-beta stimulated epidermal growth factor binding to high affinity sites in NRK cells, but decreased epidermal growth factor binding to NRK-PT14 cells during growth of the cells in serum-free medium. These qualitative changes in the response to TGF-beta may be representative of an intermediate stage in the spontaneous transformation of NRK cells.
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