Isolation method affects transformed cell line karyotype

Abstract

NEOPLASTIC cells frequently have a karyotype deviant from the normal diploid state¹. Transformation of cells in culture by tumour viruses can be used as a model of neoplastic transformation^2,3 and is generally considered to be accompanied by extensive changes in chromosome number and morphology^4–7. It has not been clear whether these changes are the cause or the result of transformation. It has been suggested that for one DNA tumour virus, simian virus 40 (SV40), the initial step in transformation is the formation of polyploid cells^5,8,9 and near-diploid cells in some SV40-transformed cell lines are thought to arise from multipolar mitoses⁹. In contrast, stable diploid, or occasionally pseudodiploid transformed cell lines have been obtained after transformation by various tumour viruses^10–17. Explanations for these apparently contrasting results could be based on differences in the origin of the transformed material¹⁸ or on the method of transformation. We have used Chinese hamster Kupffer cell clones to demonstrate that two common methods of isolating transformed cell lines—either from colonies with irregular morphology or from dense foci²—can result in different degrees of karyotypic change in the isolated cell lines.