Figure 6.

Effects of telomerase and a proposed model. (a) Telomerase does not rescue cell death by TIN2-15C. 5 × 10⁴ senescent cells were infected with lentiviruses expressing GFP (control), the telomerase catalytic subunit hTERT, TIN2-15C, or both TIN2-15C and hTERT. The cells were then infected with lenti-GSE-22. After 2 d, the cells were subcultured and plated for colony formation. Colonies were fixed and stained 61 d later. (b) Colonies were counted 5, 11, and 61 d after plating. Colonies were scored in two or three independent experiments for each transfection. Error bars represent the standard deviation. (c) Proposed model for TIN2 complexes at telomeres. Complex A and B cooperate, albeit at different positions on telomeres, to form t-loops or other terminal structures. Complex B may localize preferentially or uniquely near t-loop junctions, whereas A complexes may modulate the tertiary structure of telomeres and promote B complex stability. TIN2-13 disrupts complex A, thereby reducing the tertiary telomeric structure and destabilizing B complexes, resulting in partial or mild disruption of t-loops and telomere uncapping. TIN2-15C directly disrupts B complexes, resulting in severe disruption of t-loops and telomere uncapping. Cells expressing wild-type p53 and TIN2-13 or TIN2-15 undergo growth arrest, whereas cells lacking functional p53 undergo cell death. In both cases, the consequences of TIN2-15C expression are more severe than that of expressing TIN-13.