Persistence of Ha-ras-induced metastatic potential of SP1 mouse mammary tumors despite loss of the Ha-ras shuttle vector.
Previous studies have shown that the SP1 mouse mammary adenocarcinoma cell line, which is tumorigenic but nonmetastatic, acquires metastatic potential when transfected with the activated human Ha-ras gene. In addition, the process of calcium phosphate-mediated DNA transfection, as well as treatment with the calcium ionophore A23187 or with phorbol 12-myristate 13-acetate, can also result in heritable changes in the malignant behavior of SP1 cells. It was of interest, therefore, to determine whether the metastatic consequences of Ha-ras oncogene expression in SP1 cells are a primary effect of the transfected gene or whether heritable secondary changes are induced by Ha-ras oncogene expression. In the latter case, continued expression of the Ha-ras oncogene would not be required to maintain the metastatic phenotype. To test this hypothesis we introduced the Ha-ras oncogene into SP1 cells on a shuttle vector in which maintenance of the vector was dependent on selection for resistance to the antibiotic G418. Subclones which had lost the transfected Ha-ras gene were subsequently isolated following growth in nonselective medium. The Ha-ras-transfected clones and the revertant subclones were found to be equally metastatic, indicating that transfection with the Ha-ras gene does induce stable secondary changes in the metastatic phenotype of SP1 cells.
Schlatter
B
B
Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
Waghorne
C G
CG
D000818:Animals; D015139:Blotting, Southern; D002460:Cell Line; D004273:DNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D005260:Female; D011905:Genes, ras; D005822:Genetic Vectors; D008325:Mammary Neoplasms, Experimental / Q000235:genetics* / Q000473:pathology*; D051379:Mice; D008808:Mice, Inbred CBA; D009362:Neoplasm Metastasis / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras) / Q000032:analysis / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D016283:Proto-Oncogene Proteins p21(ras)