Regulation of WRN Protein Cellular Localization and Enzymatic Activities by SIRT1-mediated Deacetylation

Abstract

Werner syndrome is an autosomal recessive disorder associated with premature aging and cancer predisposition caused by mutations of the WRN gene. WRN is a member of the RecQ DNA helicase family with functions in maintaining genome stability. Sir2, an NAD-dependent histone deacetylase, has been proven to extend life span in yeast and Caenorhabditis elegans. Mammalian Sir2 (SIRT1) has also been found to regulate premature cellular senescence induced by the tumor suppressors PML and p53. SIRT1 plays an important role in cell survival promoted by calorie restriction. Here we show that SIRT1 interacts with WRN both in vitro and in vivo; this interaction is enhanced after DNA damage. WRN can be acetylated by acetyltransferase CBP/p300, and SIRT1 can deacetylate WRN both in vitro and in vivo. WRN acetylation decreases its helicase and exonuclease activities, and SIRT1 can reverse this effect. WRN acetylation alters its nuclear distribution. Down-regulation of SIRT1 reduces WRN translocation from nucleoplasm to nucleoli after DNA damage. These results suggest that SIRT1 regulates WRN-mediated cellular responses to DNA damage through deacetylation of WRN. Werner syndrome (WS)3 is a human autosomal recessive disorder that displays symptoms of premature aging, including graying and loss of hair, wrinkling and ulceration of skin, atherosclerosis, osteoporosis, and cataracts. WS patients also exhibit an increased incidence of diabetes mellitus type 2, hypertension, and are highly disposed to cancers (1). WS results from mutation of the WRN gene, a member of the RecQ DNA helicase family (2). Mutations in other family members, BLM and RECQ4, are responsible for the two other cancer-prone and premature aging syndromes, Bloom (3) and Rothmund-Thomson (4), respectively. Consistent with other RecQ helicases, WRN protein possesses 3Ј to 5Ј DNA helicase activity; however, it is the only human RecQ member to also have a 3Ј to 5Ј exonuclease activity. Although its physiological substrate is not yet clear, WRN appears to preferentially act on replication and recombination structures. Cells from WS patients show premature replicative senescence compared with cells derived from normal individuals (5). WS cells also show hypersensitivity to selected DNA-damaging agents including 4-nitroquinoline-1-oxide (4NQO; 6), topoisomerase inhibitors (7), and certain DNA cross-linking agents (8). Compared with normal cells, WS cells also exhibit increased genomic instability including higher levels of DNA deletions, translocations, and chromosomal breaks (9, 10), suggesting that WRN plays an important role in one or more genome maintenance pathways (11).WRN protein shows dynamic relocalization within the nucleus under different conditions of growth. The WRN protein localizes to the nucleoli in a variety of cell types (12), and this localization is modulated by DNA damage and cell cycle. Upon serum starvation or treatment with hydroxyurea (HU), aphidicolin, 4NQO, etoposide, or camptothecin, WRN migrates from nucleoli to discrete nuclear foci (13-17). ...

p300-mediated acetylation of the Rothmund-Thomson-syndrome gene product RECQL4 regulates its subcellular localization

“…For example, it is possible that deacetylation of RECQL4 by the as-yet-unidentified deacetylase regulates its acetylation status. Indeed, Li et al recently reported that deacetylation of WRN helicase by the SIRT1 deacetylase regulates WRN-mediated cellular responses to DNA damage (Li et al, 2008). Additional experiments are planned in our laboratory to determine the possible effects of deacetylation of RECQL4 on its cellular localization and other roles in DNA metabolism.…”

Emerging Roles of SIRT1 in Cancer Drug Resistance

“…SIRT1 regulates these pathways through deacetylating Ku70, [59][60][61] Nijmegen breakage syndrome protein (NBS1), 25 apurinic/apyrimidinic endonuclease-1 (APE1), 62 xeroderma pigmentosum group A/C (XPA/XPC), 63,64 and Werner syndrome protein. 65 As a result, inhibition of SIRT1 can sensitize cancer cells to several types of DNA damageinducing agents. 46,66,67 …”

SIRT1 Is Downregulated in Gastric Cancer and Leads to G1-phase Arrest via NF-κB/Cyclin D1 Signaling

“…First, acetylation of H3K56, a substrate for SIRT1, is increased in multiple cancers (12). Second, SIRT1 has been reported to play a key role in repairing DNA-breaks and maintaining genome stability (13,14). Moreover, SIRT1 has been shown to suppress the growth of colon cancer by inhibiting E2F1 or b-catenin (15,16).…”