In what one of the principal investigators refers to as "one of life's gentle ironies," two teams of researchers recently simultaneously announced the identification of a protein product of an oncogene (Science 1983; 221:275-276; Nature 1983;304:35-39).
The oncogene, sis, is associated with the simian sarcoma virus; its product appears to be plateletderived growth factor (PDGF). The linking of the two represents the first association of a previously identified oncogene with a protein known to have a normal physiological function—in this case, the stimulation of fibroblastic and neuroglial cell proliferation.
The discovery has intriguing implications on several levels. It provides long-sought evidence that an oncogene codes for a cellular growth factor. Because PDGF stimulates growth in normal cells, its overproduction could be a factor in the genesis of tumor cells. This possibility is reinforced by the fact that sarcomas and gliomas, human tumors in which there is evidence of heavy sis