Telomerase activity is sufficient to allow transformed cells to escape from crisis

The introduction of simian virus 40 large T antigen (SVLT) into human prima ry cells enables them to proliferate beyond their normal replicative life s pan. In most cases, this temporary escape from senescence eventually ends i n a second proliferative block known as "crisis," during which the cells ce ase growing or die. Rare immortalization events in which cells escape crisi s are frequently correlated with the presence of telomerase activity. We te sted the hypothesis that telomerase activation is the critical step in the immortalization process by studying the effects of telomerase activity in m o mortal SVLT-Ras(val12)-transformed human pancreatic cell lines, TRM-6 and beta lox5. The telomerase catalytic subunit, hTRT, was introduced into lat e-passage cells via retroviral gene transfer. Telomerase activity was succe ssfully induced in infected cells, as demonstrated by a telomerase repeat a mplification protocol assay. In each of nine independent infections, telome rase-positive cells formed rapidly dividing cell lines while control cells entered crisis. Telomere lengths initially increased, but telomeres were th en maintained at their new lengths for at least 20 population doublings. Th ese results demonstrate that telomerase activity is sufficient to enable tr ansformed cells to escape crisis and that telomere elongation in these cell s occurs in a tightly regulated manner.