Vault Poly(ADP-Ribose) Polymerase Is Associated with Mammalian Telomerase and Is Dispensable for Telomerase Function and Vault Structure In Vivo

Abstract

Vault poly(ADP-ribose) polymerase (VPARP) was originally identified as a minor protein component of the vault ribonucleoprotein particle, which may be involved in molecular assembly or subcellular transport. In addition to the association of VPARP with the cytoplasmic vault particle, subpopulations of VPARP localize to the nucleus and the mitotic spindle, indicating that VPARP may have other cellular functions. We found that VPARP was associated with telomerase activity and interacted with exogenously expressed telomerase-associated protein 1 (TEP1) in human cells. To study the possible role of VPARP in telomerase and vault complexes in vivo, mVparp-deficient mice were generated. Mice deficient in mVparp were viable and fertile for up to five generations, with no apparent changes in telomerase activity or telomere length. Vaults purified from mVparpdeficient mouse liver appeared intact, and no defect in association with other vault components was observed. Mice deficient in mTep1, whose disruption alone does not affect telomere function but does affect the stability of vault RNA, showed no additional telomerase or telomere-related phenotypes when the mTep1 deficiency was combined with an mVparp deficiency. These data suggest that murine mTep1 and mVparp, alone or in combination, are dispensable for normal development, telomerase catalysis, telomere length maintenance, and vault structure in vivo.Telomerase is a ribonucleoprotein (RNP) complex that replenishes telomere loss due to incomplete DNA replication in almost all eukaryotes. A loss of telomerase activity leads to an attrition of telomeric DNA which, in turn, is known to trigger end-to-end chromosome fusions, genomic instability, and cell arrest or death (31). Telomerase expression is thus critical to the prolonged viability of several human cell types and in the majority of human cancers (3). Elucidating the molecular machinery that regulates telomerase activity and its ability to maintain telomere length is critical to an understanding of malignant transformation.Telomerase contains two core components, telomerase reverse transcriptase (TERT) and telomerase RNA, the latter serving as an integral template for the de novo synthesis of telomeric DNA. Both TERT and telomerase RNA are required for the reconstitution of telomerase activity in vitro (2, 75). In mice, the disruption of either component also abolishes telomerase activity, leading to telomere attrition, genetic instability, and eventual infertility (4,15,26,44,48,61,76).Several other telomerase-associated proteins have been identified in mammals (22); these include telomerase-associated protein 1 (TEP1), which binds telomerase RNA (23, 55) and which was cloned based on its homology to ciliate Tetrahymena thermophila protein p80 (8,20,23,55). T. thermophila p80 was identified as a species copurifying with telomerase, although it subsequently was found unlikely to be a core telomerase component (8,20,49). Although deletion of the T. thermophila p80 gene resulted in slight telomere lengthening (51), ...

Tankyrase 2 Poly(ADP-Ribose) Polymerase Domain-Deleted Mice Exhibit Growth Defects but Have Normal Telomere Length and Capping

“…Other components of the vault complex include major vault protein, vault RNA, and telomerase-associated protein 1 (TEP1), which binds telomerase RNA (25). Studies of VPARP Ϫ/Ϫ mice and TEP1 Ϫ/Ϫ VPARP Ϫ/Ϫ mice, however, showed normal telomere length and structure (39). While it is possible that PARP-1, PARP-2, and VPARP could have functions redundant with tankyrases 1 and 2 in maintaining normal telomere length and capping of telomeres, we think it unlikely, since the only homology between these three PARPs and tankyrases 1 and 2 is in the PARP catalytic domain.…”

Major Vault Protein, in Concert with Constitutively Photomorphogenic 1, Negatively Regulates c-Jun–Mediated Activator Protein 1 Transcription in Mammalian Cells

“…In addition to their roles in DNA repair and chromatin remodeling, PARP-1 and PARP-2 also regulate gene expression through physical and functional interactions with specific transcription factors (28). The function of VPARP remains elusive (29). However, it was found to be able to ADP-ribosylate itself and MVP (30).…”

PARP1 Is a TRF2-associated Poly(ADP-Ribose)Polymerase and Protects Eroded Telomeres

“…Primary Parp2-deficient mouse embryonic fibroblasts (MEFs) show normal telomere length and telomere capping but display an increase in chromosome ends lacking detectable telomeric DNA (Dantzer et al, 2004). We recently reported that Vault poly(ADP-ribose) polymerase (VPARP), a minor protein component of cytoplasmic vault particles, associates with telomerase activity in cell extracts; nevertheless, mice deficient for mVparp have normal telomerase activity, telomere length, and telomere capping (Liu et al, 2004).…”

“…Several PARP family proteins associate with telomeres or telomerase (Smith et al, 1998;Kaminker et al, 2001;Cao et al, 2002;Sbodio et al, 2002;Dantzer et al, 2004;Liu et al, 2004). Tankyrases 1 and 2 can directly bind and poly(ADP-ribosyl)ate the telomere repeat binding factor 1 (TRF1) and affect its binding to telomeric DNA (Smith et al, 1998;Kaminker et al, 2001;Cook et al, 2002;Rippmann et al, 2002;Sbodio et al, 2002).…”