Nonrandom chromosome alterations that correlate with progression to immortality in rat tracheal epithelial cells transformed with N-methyl-N'-nitro-N-nitrosoguanidine

Abstract

Primary rat tracheal epithelial cells can be transformed in vitro by N-methyl-N'-nitro-N-nitrosoguanidine. The earliest recognizable morphological transformant is the enhanced growth variant (EGV), characterized by enhanced proliferative capacity. Transformed EGV colonies can progress to give rise to immortal cell lines. The purpose of this study was to determine if specific chromosome changes occur which correlate with immortalization. A total of 34 EGV colonies were isolated, of which five were able to progress in culture to become immortal (greater than or equal to 100 population doublings). Early passages of all five immortalized cultures exhibited additional copies of chromosomes 4, 7, and 11 as a common or recurrent abnormality. These numerical alterations were rarely observed in the primary EGV colonies from which the cell lines were derived, suggesting that these alterations occurred during progression. Structural alterations involving chromosome 1 (resulting in a net gain of 1q) and chromosome 3(3q) also occurred in four out of five immortalized cultures. In all cases, structural alterations involving 1q and/or 3q were detected in the primary EGV colonies from which the immortal cell lines arose. Comparison of the frequency of the structural and numerical alterations observed in the immortalized cultures with their frequency in the 29 EGV colonies which did not become immortal indicated that these changes correlated (P less than or equal to 0.005) with the ability to become immortal. These results suggest that structural alterations occur in primary EGV colonies which predispose cells to immortalization and that subsequent numerical changes occur during progression that correlate with acquisition of the immortal phenotype.