EFFECT OF MITOCHONDRIAL-DNA TRANSMITTED CYTOPLASMICALLY FROM NONTUMORIGENIC TO TUMORIGENIC RAT-CELLS ON THE PHENOTYPIC-EXPRESSION OF TUMORIGENICITY

Abstract

The effect of mitochondrial DNA (mtDNA) on the phenotypic expression of tumorigenicity was examined by its cytoplasmic transmission from nontumorigenic cells to tumorigenic cells. Enucleated cells of the rat embryonic cell line 3Y1CAP, which are nontumorigenic and resistant to chloramphenicol, were fused with whole cells of the rat glioma C6BU-1 line, which are tumorigenic and resistant to 5-bromodeoxyuridine and the cybrid colonies growing in selective medium with 5-bromodeoxyuridine (30 .mu.g/ml) and chloramphenicol (50 .mu.g/ml) were isolated clonally. Cytoplasmic transmission of 3Y1CAP mtDNA to C6BU-1 cells was confirmed by quantitative analysis of their mtDNA with restriction endonuclease. Subclones containing various amounts of mtDNA from 3Y1CAP cells were isolated from 1 cybrid clone. Y22 and their tumorigenicities were examined by inoculating 2 .times. 106 cells s.c. into nude mice. The tumorigenicities of these cybrid subclones were almost identical to that of the nuclear donor C6BU-1 cells with respect to the tumor incidence (number of animals bearing tumors per number of animals inoculated), latent period and growth rates of tumors. Moreover, analysis of chromosomes and mtDNA of the cells recovered from the tumors obtained showed that the tumors were derived from the cells inoculated and that no selective overgrowth of segregants that had lost mtDNA from 3Y1CAP cells occurred in the nude mice. Expression of tumorigenicity of C6BU-1 cells was not suppressed by cytoplasmic transmission of nontumorigenic 3Y1CAP mtDNA.