A dynamic molecular link between the telomere length regulator TRF1 and the chromosome end protector TRF2

Background: Human telomeres are coated by the telomere repeat binding proteins TRF1 and TRF2, which are believed to function independently to regulate telomere length and protect chromosome ends, respectively. Results: Here, we show that TRF1 and TRF2 are linked via TIN2, a previously identified TRF1 -interacting protein, and its novel binding partner TINT1. TINT1 localized to telomeres via TIN2, where it functioned as a negative regulator of telomerase-mediated telomere elongation. TIN2 associated with TINT1, and TRF1 or TRF2 throughout the cell cycle, revealing a partially redundant unit in telomeric chromatin that may provide flexibility in telomere length control. Indeed, when TRF1 was removed from telomeres by overexpression of the positive telomere length regulator tankyrase 1, the TIN2/TINT1 complex remained on telomeres via an increased association with TRF2. Conclusions: Our findings suggest a dynamic cross talk between TRF1 and TRF2 and provide a molecular mechanism for telomere length homeostasis by TRF2 in the absence of TRF1.