POT1 Association with TRF2 Regulates Telomere Length

Abstract

Deleting the OB folds encoding the telomeric single-stranded DNA (ssDNA)-binding activity of the human telomeric protein POT1 induces significant telomere elongation, suggesting that at least one critical aspect of the regulation of telomere length is disrupted by this POT1^ΔOB mutant protein. POT1 is known to associate with two proteins through the protein interaction domain retained in POT1^ΔOB—the telomeric double-stranded DNA-binding protein TRF2 and the telomere-associated protein TPP1. We report that introducing a mutation that reduces association of POT1 with TRF2, but not a mutation that reduces the association with TPP1, abrogates the ability of POT1^ΔOB to promote telomere elongation. Mechanistically, expression of POT1^ΔOB reduced the association of TRF2 with POT1, RAP1, and TIN2; however, of these proteins, only ectopic expression of POT1 suppressed the telomere elongation induced by POT1^ΔOB. Lastly, replacing endogenous POT1 with a full-length POT1 mutant defective in the association with TRF2 induced telomere elongation. Thus, we conclude that the association of POT1 with both ssDNA and TRF2 is critical for telomere length homeostasis.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank J. Campisi and Z. Songyang for constructs encoding TIN2 and RAP1, respectively, and members of the Counter lab for helpful discussions.

This research is supported by NIH grant CA082481 and the Edward Spiegel Fund of the Lymphoma Foundation.