Medical Toxicology Commons^™

The Dna Structure And Sequence Preferences Of Wrn Underlie Its Function In Telomeric Recombination Events, Deanna N. Edwards, Amrita Machwe, Li Chen, Vilhelm A. Bohr, David K. Orren

Toxicology and Cancer Biology Faculty Publications

Telomeric abnormalities caused by loss of function of the RecQ helicase WRN are linked to the multiple premature ageing phenotypes that characterize Werner syndrome. Here we examine WRN's role in telomeric maintenance, by comparing its action on a variety of DNA structures without or with telomeric sequences. Our results show that WRN clearly prefers to act on strand invasion intermediates in a manner that favours strand invasion and exchange. Moreover, WRN unwinding of these recombination structures is further enhanced when the invading strand contains at least three G-rich single-stranded telomeric repeats. These selectivities are most pronounced at NaCl concentrations within …

Human Dna Exonuclease Trex1 Is Also An Exoribonuclease That Acts On Single-Stranded Rna, Fenghua Yuan, Tanmay Dutta, Ling Wang, Lei Song, Liya Gu, Liangyue Qian, Anaid Benitez, Shunbin Ning, Arun Malhotra, Murray P. Deutscher, Yanbin Zhang

Toxicology and Cancer Biology Faculty Publications

3' repair exonuclease 1 (TREX1) is a known DNA exonuclease involved in autoimmune disorders and the antiviral response. In this work, we show that TREX1 is also a RNA exonuclease. Purified TREX1 displays robust exoribonuclease activity that degrades single-stranded, but not double-stranded, RNA. TREX1-D200N, an Aicardi-Goutieres syndrome disease-causing mutant, is defective in degrading RNA. TREX1 activity is strongly inhibited by a stretch of pyrimidine residues as is a bacterial homolog, RNase T. Kinetic measurements indicate that the apparent K_m of TREX1 for RNA is higher than that for DNA. Like RNase T, human TREX1 is active in degrading native …

Acetylation Of Wrn Protein Regulates Its Stability By Inhibiting Ubiquitination, Kai Li, Rui Wang, Enerlyn Lozada, Wei Fan, David K. Orren, Jianyuan Luo

Toxicology and Cancer Biology Faculty Publications

BACKGROUND: WRN is a multi-functional protein involving DNA replication, recombination and repair. WRN acetylation has been demonstrated playing an important role in response to DNA damage. We previously found that WRN acetylation can regulate its enzymatic activities and nuclear distribution.

METHODOLOGY/PRINCIPAL FINDING: Here, we investigated the factors involved in WRN acetylation and found that CBP and p300 are the only major acetyltransferases for WRN acetylation. We further identified 6 lysine residues in WRN that are subject to acetylation. Interestingly, WRN acetylation can increase its protein stability. SIRT1-mediated deacetylation of WRN reverses this effect. CBP dramatically increases the half-life of wild …

Replication Fork Regression In Vitro By The Werner Syndrome Protein (Wrn): Holliday Junction Formation, The Effect Of Leading Arm Structure And A Potential Role For Wrn Exonuclease Activity, Amrita Machwe, Liren Xiao, Robert G Lloyd, Edward Bolt, David K. Orren

Toxicology and Cancer Biology Faculty Publications

The premature aging and cancer-prone disease Werner syndrome stems from loss of WRN protein function. WRN deficiency causes replication abnormalities, sensitivity to certain genotoxic agents, genomic instability and early replicative senescence in primary fibroblasts. As a RecQ helicase family member, WRN is a DNA-dependent ATPase and unwinding enzyme, but also possesses strand annealing and exonuclease activities. RecQ helicases are postulated to participate in pathways responding to replication blockage, pathways possibly initiated by fork regression. In this study, a series of model replication fork substrates were used to examine the fork regression capability of WRN. Our results demonstrate that WRN catalyzes …

Length-Dependent Degradation Of Single-Stranded 3' Ends By The Werner Syndrome Protein (Wrn): Implications For Spatial Orientation And Coordinated 3' To 5' Movement Of Its Atpase/Helicase And Exonuclease Domains, Amrita Machwe, Liren Xiao, David K. Orren

Toxicology and Cancer Biology Faculty Publications

BACKGROUND: The cancer-prone and accelerated aging disease Werner syndrome is caused by loss of function of the WRN gene product that possesses ATPase, 3' to 5' helicase and 3' to 5' exonuclease activities. Although WRN has been most prominently suggested to function in telomere maintenance, resolution of replication blockage and/or recombinational repair, its exact role in DNA metabolism remains unclear. WRN is the only human RecQ family member to possess both helicase and exonuclease activity, but the mechanistic relationship between these activities is unknown. In this study, model single-stranded and 3' overhang DNA substrates of varying length and structure were …

Competition Between The Dna Unwinding And Strand Pairing Activities Of The Werner And Bloom Syndrome Proteins, Amrita Machwe, Enerlyn M. Lozada, Liren Xiao, David K. Orren

Toxicology and Cancer Biology Faculty Publications

BACKGROUND: The premature aging and cancer-prone Werner and Bloom syndromes are caused by defects in the RecQ helicase enzymes WRN and BLM, respectively. Recently, both WRN and BLM (as well as several other RecQ members) have been shown to possess a strand annealing activity in addition to the requisite DNA unwinding activity. Since an annealing function would appear to directly oppose the action of a helicase, we have examined in this study the dynamic equilibrium between unwinding and annealing mediated by either WRN or BLM.

RESULTS: Our investigation into the competition between annealing and unwinding demonstrates that, under standard reaction …