Progression to Immortality in Rat Tracheal Epithelial Cells Nonrandom Chromosome Alterations That Correlate with

Primary rat trachea! epithelial cells can be transformed in vitro by V methyl-/V'-nitro-/V-nitrosoguanidine. The earliest recognizable morpho logical transformant is the enhanced growth variant (EGV), characterized by enhanced proliferative capacity. Transformed EGV colonies can pro gress 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 (•!()()population doublings). Early passages of all fire 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 Iq) and chromosome 3 (3q) also occurred in four out of five immortalized cultures. In all cases, structural alterations involving Iq 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 (/' : 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.