Spontaneous and 5-azacytidine-induced revertants of methionine-dependent tumor-derived and H-ras-1-transformed cells.
Methionine dependence is a metabolic defect affecting several tumor-derived and transformed cell lines; it is defined as the inability of cells to grow in a medium where methionine has been depleted and replaced by its immediate metabolic precursor, homocysteine. This defect is acquired by normal epithelial Clone 9-3 cells upon transformation by the activated H ras-1 oncogene. We report that these H-ras-1-transformed cells (as well as some other tumor or transformed cells) spontaneously revert to methionine dependence at a high frequency. These revertants still express the H-ras-1 oncogene and retain their anchorage-independent growth: this reversion is thus not associated with a complete reversion to the normal phenotype. Furthermore, the reversion frequency is dramatically increased (up to 400-fold) by treatment of the cells with 5-azacytidine, a strong demethylating agent. Methionine dependence might thus be a consequence of hypermethylation of a critical gene involved in methionine metabolism and possibly in the methylation processes themselves.
Vanhamme
L
L
Département de Biologie Moléculaire, Université Libre de Bruxelles, Rhode-St-Genèse, Belgium.
Szpirer
C
C
D000818:Animals; D001374:Azacitidine / Q000494:pharmacology*; D002455:Cell Division; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic; D003470:Culture Media; D005020:Ethyl Methanesulfonate / Q000494:pharmacology; D006710:Homocysteine / Q000378:metabolism; D008715:Methionine / Q000378:metabolism*; D008745:Methylation; D009857:Oncogenes; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000378:metabolism*
D003470:Culture Media; D006710:Homocysteine; D005020:Ethyl Methanesulfonate; D008715:Methionine; D001374:Azacitidine