| Tankyrase 1 is a poly(ADP-ribose) polymerase (PARP), which interacts with the telomeric DNA binding protein TRF1 at human telomeres. Tankyrase 1 poly(ADP-ribosyl)ates TRF1, inhibiting its binding to telomeric DNA, in vitro. Stable overexpression of tankyrase 1 leads to TRF1 loss and telomere elongation. To determine if the catalytic PARP activity of tankyrase 1 is required for telomere length regulation a catalytically inactive point mutant, tankyrase1.HE/A, was generated. Telomere length dynamics were studied in stable cell lines expressing tankyrase1.HE/A in telomerase positive and negative cell lines. Tankyrase 1-induced telomere elongation required telomerase, and both tankyrase 1-mediated telomere elongation and TRF1 loss required a catalytically active PARP domain. To further study tankyrase 1's telomeric function, its expression was inhibited by short interfering RNAs (siRNAs). Cells deficient for tankyrase 1 arrested in early anaphase, due to inappropriate telomere associations. Only a catalytically active tankyrase 1 could rescue the mitotic phenotype. Other telomeric proteins were inhibited by siRNA and assayed for their ability to rescue. Of these, only TIN2 resulted in a rescue. These studies suggest that telomeres, like chromosome arms and centromeres, require a distinct, tankyrase 1 poly(ADP-ribosyl)ation dependent, mechanism for sister chromatid resolution prior to anaphase. |
