Primary Rat Embryo Cells Transformed by One or Two Oncogenes Show Different Metastatic Potentials

Abstract

Second-passage rat embryo cells were transfected with a neomycin resistance gene and the activated form of the c-Ha-ras I gene, or with these two genes plus the adenovirus type 2 E1a gene. Foci of morphologically transformed cells were observed in both cases; however, the frequency of transformation was at least ten times higher with two oncogenes than with the ras gene alone. All the transformed cell lines gave rise to rapidly growing tumors when injected subcutaneously into nude mice. All but one of the cell lines transformed by the ras oncogene alone formed metastatic nodules in the lungs of animals that had been injected subcutaneously with transformed cells. When transformed cells were injected intravenously, all the ras single-gene transformants gave rise to many metastatic lung nodules. In contrast, cell lines transformed with ras and E1a did not generate metastases after subcutaneous injection and gave rise to very few metastatic lung nodules after intravenous injection. These data demonstrate that a fully malignant cell with metastatic potential, as measured in an immunodeficient animal, can be obtained from early passage embryo cells by the transfection of the ras oncogene alone.

Gene expression profiles of primary breast tumors maintained in distant metastases

“…It has been shown that activation of a single gene, which in turn affects a process essential for metastasis, can be sufficient for inducing metastasis in vitro (10,11). This would imply that one gene, when activated early in its development, can empower the metastatic process once a primary tumor with additional genetic changes has been established.…”

“…Such a model implies that a metastasis arising from a selected subclone would be molecularly distinct from its primary tumor. The subpopulation concept by Fidler is widely accepted, although the metastatic process has also been described as a stochastic event, giving primary tumor cells an equal metastatic potential (7-9).It has been shown that activation of a single gene, which in turn affects a process essential for metastasis, can be sufficient for inducing metastasis in vitro (10,11). This would imply that one gene, when activated early in its development, can empower the metastatic process once a primary tumor with additional genetic changes has been established.…”

Transcriptional repression of the neu protooncogene by the adenovirus 5 E1A gene products.

“…Although transcriptional activation and transcriptional repression of nonadenoviral genes by the ElA proteins have been reported (13)(14)(15)(16)(17)(18)(19)(20), their functional significance and physiological impact are unclear in many cases. Recently, it has been shown that exogenously added ElA gene can reduce the metastatic potential of ras-transformed rat embryo cells by activating the cellular NM23 gene that is associated with a lower metastatic potential, thus identifying it as nonimmunologically related metastasis-inhibitory gene (21)(22)(23)(24). As ElA proteins are multifunctional transcription regulators and metastasis suppressors and overexpression of the human neu gene correlates with number of axillary lymph nodes positive for metastasis in breast cancer patients, we investigated the potential effects of the ElA products on the promoter activity of neu.…”

Molecular determinants of metastatic transformation.

“…As mentioned previously, myc-and p53-transformed NIH 3T3 cells are not metastatic (20). In addition, primary rat embryo fibroblasts transformed by the combination of ElA type 2 and ras were not metastatic, in contrast to these cells transforned by ras alone, which are highly malignant (11).…”

“…This question was being independently examined by several laboratories including our own (7) and was confirmed and then extended by demonstrating that introduction of ras into many types including primary rat fibroblasts also induced the metastatic phenotype (11,12). These experiments raised the question of whether ras was directly regulating metastatic behavior or was inducing a change in phenotypic stability that would cause metastatic dissemination in a ras-independent manner.…”