The formation of variants with a reversion of properties of transformed cells. 8. In vitro limited life span of variants isolated from tumors

Identification of a chromosome that controls malignancy in Chinese hamster cells

A chromosome that controls malignancy in Chinese hamster cells has been identified by analysis of the Giemsa banding pattern of a malignant cell line transformed by simian virus 40 (SV40), non-malignant revertants from this line, segregants from the revertants that were again malignant and a cell line transformed by methylcholanthrene. The malignant cell line transformed by SV40 was near diploid and had gained additional material of chromosome 3. Revertants with a suppression of malignancy and malignant revertants from which they were derived. Malignancy of these cells was associated with the ability to form colonies in agar. Cells of a line transformed by methylcholanthrene were malignant, formed almost no colonies in agar and the only chromosome change from the normal diploid chromosome banding complement was the addition of a long arm of chromosome 3. The results indicate that chromosome 3 carriers gene(s) that control malignancy in Chinese hamster cells in cell lines transformed by a viral or a chemical carcinogen and that malignancy was induced in both cell types by an increase of these genes.

Chromosome balance and the control of malignancy

The Giemsa banding pattern of the chromosomes has been analyzed in a line of transformed golden hamster cells, revertant and re-revertant cells and their tumors. The transformed and re-revertant cells were malignant in vivo and had gained an additional chromosome 5(7). Revertants with a suppression of malignancy lost this additional chromosome 5(7) and gained an additional chromosome 7(2). The tumors produced by segregants from the revertant cells were malignant, although to a lower degree than transformed and re-revertant cells. These tumors had lost the additional chromosome 7(2) found in revertants and gained one or two 5(12) chromosomes. The results support the hypothesis that the balance between genes for expression and suppression controls malignancy. The data indicate that chromosome 7(2) carries genes for suppression and that chromosomes 5(7) and 5(12) carry genes for expression of malignancy. The genes on chromosome 5(7) seem to result in a greater degree of expression than the genes on chromosome 5(12). The chromosome balance that controlled malignancy in these cells, also controlled the expression and suppression of transformed properties in vitro.