A BALB/c 3T3-transformed cell line suitable for transfection assay of metastasis-inducing genes

A clonal cell line, 1-1ras1000, transformed by the activated c-Ha-ras oncogene, does not form metastases after i.v. injection into mice (experimental metastasis assay). Here, we show that this cell line is useful as a recipient to detect metastasis-inducing genes, using a transfection assay. Cells (1-1ras1000) were susceptible to metastasis induction by transfection with either v-src or genomic DNA from a v-src-and v-fos-transferred highly metastatic rat cell line (SR202). The susceptibility of 1-1ras1000 cells for lung metastasis induction was suitable for a genomic transfection assay to detect a metastasis-inducing gene in the transfected cells which had incorporated genomic DNA from donor metastatic tumor cells. When DNAs extracted from 7 human tumors were tested for metastasis induction, 2 DNAs from nonmalignant tumors (non-tumorigenic tumors in athymic nude mice) (2/2) were negative and 4 DNAs from malignant tumors (4/5) were positive in 1-1ras1000 cells for primary transfection. in one of the resulting metastases, the ability to metastasize was also transferred in the second and third cycles of genomic DNA transfection at high frequencies. All of the resulting metastases carried the human repetitive Alu sequence. Neither re-arrangements of the endogenous c-Haras nor changes of protein amounts were detected. Recipient 1-1ras1000 cells had a negligible rate of spontaneously metastatic conversion during in vitro cultivation and transfection processes. The resulting metastasized cells were easily isolated from the lung after culturing in selection medium containing G418 (geneticin). Isolated cells stably retained the ability to form metastatic lung nodules when re-injected into mice. Thus, 1-1ras1000 cells appear to be a useful system for the isolation of metastasis-inducing genes from human metastatic tumors.