Possible involvement of chromosome 1 in in vitro immortalization: Evidence from progression of a human adenoma‐derived cell line in vitro

We have previously reported that continuous in vitro passage in the presence of 3T3 feeders of a non‐tumorigenic adenoma‐derived epithelial cell line, designated PC/AA, resulted in its becoming immortal. At early passage PC/AA was normal diploid, whereas every cell of PC/AA late passage had an isochromosome I(q) which led us to suggest that abnormalities of chromosome I may be involved in tumour progression. We now report the isolation of a 3T3‐feeder‐independent variant of early‐passage PC/AA, designated PC/AA/FI, which was immortal in vitro and remained non‐tumorigenic. Each cell of PC/AA/FI again has an isochromosome I(q), like the late‐passage PC/AA. However, with PC/AA/FI it is the other chromosome I of the homologous pair which is involved in the formation of the isochromosome I(q). This is possible to determine because of the polymorphic cen‐tromeric heterochromatin on chromosome I of the early‐passage PC/AA. With the late‐passage PC/AA (grown with 3T3 feeders) the homologue with the large C‐band has given rise to an isochromosome I(q) whereas with PC/AA/FI it is the other homologue with the smaller C‐band which has given rise to this isochromosome. Both the immortal PC/ AA/FI and the immortal PC/AA late passage, therefore, have independent abnormalities involving chromosome I. These results indicate that chromosome I may be involved in in vitro immortalization.