TANK2, a New TRF1-associated Poly(ADP-ribose) Polymerase, Causes Rapid Induction of Cell Death upon Overexpression

Abstract

Tankyrase (TANK1) is a human telomere-associated poly(ADP-ribose) polymerase (PARP) that binds the telomere-binding protein TRF1 and increases telomere length when overexpressed. Here we report characterization of a second human tankyrase, tankyrase 2 (TANK2), which can also interact with TRF1 but has properties distinct from those of TANK1. TANK2 is encoded by a 66-kilobase pair gene (TNKS2) containing 28 exons, which express a 6.7-kilobase pair mRNA and a 1166-amino acid protein. The protein shares 85% amino acid identity with TANK1 in the ankyrin repeat, sterile ␣-motif, and PARP catalytic domains but has a unique N-terminal domain, which is conserved in the murine TNKS2 gene. TANK2 interacted with TRF1 in yeast and in vitro and localized predominantly to a perinuclear region, similar to the properties of TANK1. In contrast to TANK1, however, TANK2 caused rapid cell death when highly overexpressed. TANK2-induced death featured loss of mitochondrial membrane potential, but not PARP1 cleavage, suggesting that TANK2 kills cells by necrosis. The cell death was prevented by the PARP inhibitor 3-aminobenzamide. In vivo, TANK2 may differ from TANK1 in its intrinsic or regulated PARP activity or its substrate specificity.Telomeres are the repetitive DNA sequences and specialized proteins that cap the ends of linear chromosomes and protect them from end-to-end fusion. In mammalian cells, loss or disruption of a telomere can cause cellular senescence, cell death, or genomic instability, depending on the genotype and cell context. A variety of events can lead to dysfunctional telomeres. Telomeres can be damaged directly by genotoxic agents and/or faulty DNA repair processes. In addition, the telomeric structure can be disrupted by changes in the expression or function of certain telomere-associated proteins. Finally, telomeres can erode owing to the biochemistry of DNA replication, which leaves 50 -200 bp 1 of 3Ј-telomeric DNA unreplicated upon completion of each S phase. Thus, in the absence of the enzyme telomerase, or another mechanism to replenish telomeric DNA, proliferating cells progressively lose telomeric DNA and eventually acquire one or more critically short or dysfunctional telomeres (1-3).Most normal mammalian cells respond to a critically short or dysfunctional telomere by undergoing cellular senescence (4 -7). This process results in an irreversible arrest of cell proliferation and striking changes in cell function (8). Dysfunctional telomeres can also induce apoptotic cell death, particularly in cells that harbor mutations in one or more cell cycle or DNA damage checkpoints (9 -11). Very little is known about how telomeres signal cells to undergo senescence or apoptosis. However, the recent discovery of a telomere-associated poly(ADPribose) polymerase (PARP) (12) provides a potential mechanism by which telomeres transmit signals to cellular proteins that regulate the senescence and apoptotic responses.PARPs catalyze the formation of branched chains of ADPribose polymers on selected proteins, using NAD ϩ ...

Cancer and aging: the importance of telomeres in genome maintenance

“…TRF1, for example, binds two highly related poly-ADP ribosylases (PARPs), TANK1 and TANK2 [68,69] ( Fig. 3).…”

“…3). Although the TANKs can be found at telomeres, and even ADP-ribosylate TRF1 in vitro [68,70], these proteins reside predominantly in Golgi-type vesicles, and have also been identified at centrosomes [69,[71][72][73]. The precise functions of TANKs are not known.…”

“…The precise functions of TANKs are not known. The majority of endogenous TANKs reside outside the nucleus, where they interact with the Grb14 adaptor protein and/or IRAP in GLUT4 vesicles [69,71,73], but the functional consequences of these interactions is not known. At telomeres, one function of TANKs might be the inactivation by ADP-ribosylation of TRF1.…”

PARP1 is activated at telomeres upon G4 stabilization: possible target for telomere-based therapy

“…Several of the PARP family proteins may be associated with telomeres. Tankyrases 1 and 2, as well as PARP1 and 2, can directly bind to and poly-ADP ribosylate the telomeric repeat binding factors 1 (TRF1) and 2 (TRF2) and affect their association to telomeric DNA, acting as positive regulators for telomere elongation (Smith and de Lange, 1999;Kaminker et al, 2001;Cook et al, 2002;Rippmann et al, 2002). In addition, upon DNA damage, PARP1 may be recruited to the damaged telomeres, helping to protect telomeres against chromosome end-to-end fusions and genomic instability (Gomez et al, 2006).…”

Functional Interaction between Poly(ADP-Ribose) Polymerase 2 (PARP-2) and TRF2: PARP Activity Negatively Regulates TRF2

“…In addition, tankyrase 1 localizes to different subcellular compartments in a cell-cycle-dependent manner, including nuclear pore complexes, mitotic centrosomes, and the Golgi complex (14,51). A closely related protein named tankyrase 2 was identified recently and was shown to interact and colocalize with tankyrase 1, thus suggesting that both proteins might perform overlapping functions (33,47).…”