Telomerase Activity Is Sufficient To Allow Transformed Cells To Escape from Crisis

Abstract

The introduction of simian virus 40 large T antigen (SVLT) into human primary cells enables them to proliferate beyond their normal replicative life span. In most cases, this temporary escape from senescence eventually ends in a second proliferative block known as “crisis,” during which the cells cease growing or die. Rare immortalization events in which cells escape crisis are frequently correlated with the presence of telomerase activity. We tested the hypothesis that telomerase activation is the critical step in the immortalization process by studying the effects of telomerase activity in two mortal SVLT-Ras^val12-transformed human pancreatic cell lines, TRM-6 and βlox5. The telomerase catalytic subunit, hTRT, was introduced into late-passage cells via retroviral gene transfer. Telomerase activity was successfully induced in infected cells, as demonstrated by a telomerase repeat amplification protocol assay. In each of nine independent infections, telomerase-positive cells formed rapidly dividing cell lines while control cells entered crisis. Telomere lengths initially increased, but telomeres were then maintained at their new lengths for at least 20 population doublings. These results demonstrate that telomerase activity is sufficient to enable transformed cells to escape crisis and that telomere elongation in these cells occurs in a tightly regulated manner.

ACKNOWLEDGMENTS

This work was supported by grants from the Stern Foundation and the Juvenile Diabetes Foundation International, and by a pilot grant from the Howard Hughes Medical Institute. T. Halvorsen is a recipient of a Medical Scientist Training Program Award. F. Levine is a member of the UCSD Center for Molecular Genetics, UCSD Cancer Center, and Whittier Institute for Diabetes.

We thank Camillo Recordi for providing adult human islets, L. Yu for providing reagents, and G. Beattie, A. Hayek, and members of the Levine laboratory for helpful discussions.