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 ␤lox5. 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.

Generation of Human Pulmonary Microvascular Endothelial Cell Lines

“…Only a small fraction of these cells survive a subsequent crisis and proliferate indefinitely. Furthermore, the introduction of telomerase into cells expressing SV40 large T antigen enabled human fibroblasts and embryonic kidney and pancreatic cells to escape from crisis (Counter et al, 1998;Halvorsen et al, 1999;Zhu et al, 1999).…”

Characterization of ataxia telangiectasia fibroblasts with extended life-span through telomerase expression

“…The normal human primary ®broblasts (HFF) used in these studies were Basinger cells (Halvorsen et al, 1999). Cells were cultured according to the procedure described recently (Smilenov et al, 1999).…”

“…We determined the e ects of ectopic expression of hTERT in two primary A-T ®broblast cell strains GM02052 and GM05823. Stable GM02052 and GM05823 cell populations (hTERT+) were generated by infection of GM02052 cells at 36 PD and GM05823 at 40 PD with hTERT-expressing retrovirus as previously described (Halvorsen et al, 1999;Ouellette et al, 1999). GM02052 and GM05823 cells were also infected with control empty retroviral construct.…”

Reconstitution of telomerase activity combined with HPV-E7 expression allow human preadipocytes to preserve their differentiation capacity after immortalization

“…Indeed, it has been recently shown that overexpression of the human telomerase reverse transcriptase (h-TERT) allows SV40 T-Ag-transformed cells, derived from different tissues, to bypass the crisis step and to promote indefinite life span. 4,5 Nevertheless, the differentiation process of certain cell types, such as preadipocytes, is clearly blocked by SV40 T-Ag expression. 6 Differentiation of preadipocytes into adipocytes (i.e.…”