Occurrence of the Tumor-specific, Calcium-binding Protein, Oncomodulin, in Virally Transformed Normal Rat Kidney Cells¹

Oncomodulin, an apparently tumor-specific calcium-binding protein, has been detected in many chemically induced rat hepatomas. It is now possible to detect, by radioimmunoassay and immunofluorescence, the presence of oncomodulin in normal rat kidney cells virally transformed by avian sarcoma virus. By contrast, it was not detected in uninfected, nonneoplastic normal rat kidney cells. The protein was isolated and purified by a novel high-performance liquid chromatography procedure and shown to be identical to that isolated previously from rat hepatoma. The cellular levels of oncomodulin approached the levels of calmodulin in avian sarcoma virus-transformed normal rat kidney cells, suggesting that the total calcium-binding activity of the cell may play a role in expression of the transformed phenotype.