Generation of metastatic variants by transfection of a nonmetastatic rat mammary epithelial cell line with DNA from a metastatic rat mammary cell line

Transfection of rat mammary (Rama) 37 epithelial cells, which yield nonmetastasizing adenomas in syngeneic Wistar-Furth rats, with HindlΠ-fragmented cellular DNA and the drug-resistance plasmids pSV2, gpí or <i>pSV2neo</i> yields drug-resistant transformants with a frequency of 10^-4–10^-5. Transformant cell lines transfected with the following, <i>pSV2gpt</i> alone, <i>pSV2gpt</i> and Rama 37 DNA, <i>pSV2gpt</i> and DNA from a metastasizing cell line Rama 800 (CT set), <i>pSVlneo</i> and salmon sperm DNA, pSV2ne&#248; and Rama 800 DNA (C set), all yield tumors when injected subcutaneously into syngeneic rats. A few transformants obtained by cotransfection with DNA from Rama 800 cells produce metastases in lungs and/or lymph nodes. The incidence of such metastases for two transfectants, termed CT4–41 and C18P, is significant at 20 and 24%, respectively, but only half (48%) that achieved with Rama 800 cells. Reintroduction into rats of cells cultured from a metastatic tumor of CT4–41 and of C18P, and from their lung or lymph node metastases, produces either a similar incidence (20–24%) or a significantly higher (48–52%) incidence of metastasis than that of the original transfectants. Cells cultured from nonmetastatic tumors fail to produce any metastatic lesions. When [³²P]-labeled <i>gpt</i> or <i>neo</i> DNAs are hybridized to EcoRI-digested cellular DNA of the CT4–41 or C18P series of cell lines, tumors or metastases, <i>gpt</i> binds to one major fragment of 3,800 basepairs, and <i>neo</i> to two major fragments of 5,700 and 4,200 basepairs. The same cell lines produce hybridizing mRNAs of 1,500 and 1,900 bases for the CT4–41 series and 2,000–2,400 bases for the C18P series. It is suggested that transfection of DNA from the metastatic cells causes the nonmetastatic cells to become metastatic, in a genetically dominant manner, but additional steps are required for this process to become established and expressed at a level equivalent to that of the original, metastastasizing donor cells