Telomere Protection by TPP1/POT1 Requires Tethering to TIN2

Abstract

SUMMARY To prevent ATR activation, telomeres deploy the single-stranded DNA binding activity of TPP1/POT1a. POT1a blocks the binding of RPA to telomeres, suggesting that ATR is repressed through RPA exclusion. However, comparison on the DNA binding affinities and abundance of TPP1/POT1a and RPA indicates that TPP1/POT1a by itself is unlikely to exclude RPA. We therefore analyzed the central shelterin protein TIN2, which links TPP1/POT1a (and POT1b) to TRF1 and TRF2 on the double-stranded telomeric DNA. Upon TIN2 deletion, telomeres lost TPP1/POT1a, accumulated RPA, elicited an ATR signal, and showed all other phenotypes of POT1a/b deletion. TIN2 also affected the TRF2-dependent repression of ATM kinase signaling but not to TRF2-mediated inhibition of telomere fusions. Thus, while TIN2 has a minor contribution to the repression of ATM by TRF2, its major role is to stabilize TPP1/POT1a on the ss telomeric DNA, thereby allowing effective exclusion of RPA and repression of ATR signaling.

Trypanosoma brucei TIF2 suppresses VSG switching by maintaining subtelomere integrity

“…This is consistent with the notion that telomere proteins are important for protecting chromosome ends [11]. Loss of mammalian TIN2 led to both chromatid-type and chromosome-type telomere fusions [51]. It is possible that TbTIF2 depletion results in similar telomere fusions and subsequent breakage-fusionbridge cycle, which can result in DNA amplification and large terminal deletions [57].…”

“…FACS analysis showed that depletion of TbTIF2 led to a decrease in G1 cells (2C) and an increase in G2/M (4C) and polyploidy cells (6C and 8C) (Supplementary information, Figure S3). This is similar to the situation in mouse cells, where deletion of TIN2 leads to polyploidization resulting from endoreduplication [51].…”

Human TEN1 Maintains Telomere Integrity and Functions in Genome-wide Replication Restart

“…6, D and E). Moreover, in both cell types, the telomere signal appeared as discrete spots in a well stained DAPI bridge rather than the elongated signals that might be expected if the bridges were caused by replication failure in the telomere duplex and subsequent stretching of the intertwined sisters (55). Overall, our results indicate that TEN1 depletion causes genome-wide instability that leads to defects in chromosome segregation.…”

Replication of Telomeres and the Regulation of Telomerase

“…Binding of hnRNPA1 to TERRA may in turn allow binding of the telomeric 3 0 overhang by Pot1 -Tpp1. On the other hand, it has been argued that the higher local concentration of Pot1 -Tpp1 near telomeres is sufficient to trigger Pot1 -Tpp1 binding once semiconservative telomere replication is completed (Takai et al 2011).…”