Acetylation of WRN protein regulates its stability by inhibiting ubiquitination

Response to Replication Stress and Maintenance of Genome Stability by WRN, the Werner Syndrome Protein

Werner syndrome (WS) is an autosomal recessive disease caused by loss of function of WRN. WS is a segmental progeroid disease and shows early onset or increased frequency of many characteristics of normal aging. WRN possesses helicase, annealing, strand exchange, and exonuclease activities and acts on a variety of DNA substrates, even complex replication and recombination intermediates. Here, we review the genetics, biochemistry, and probably physiological functions of the WRN protein. Although its precise role is unclear, evidence suggests WRN plays a role in pathways that respond to replication stress and maintain genome stability particularly in telomeric regions.

Abnormal protein post-translational modifications induces aggregation and abnormal deposition of protein, mediating neurodegenerative diseases

Protein post-translational modifications (PPTMs) refer to a series of chemical modifications that occur after the synthesis of protein. Proteins undergo different modifications such as phosphorylation, acetylation, ubiquitination, and so on. These modifications can alter the protein's structure, function, and interaction, thereby regulating its biological activity. In neurodegenerative diseases, several proteins undergo abnormal post-translational modifications, which leads to aggregation and abnormal deposition of protein, thus resulting in neuronal death and related diseases. For example, the main pathological features of Alzheimer's disease are the aggregation of beta-amyloid protein and abnormal phosphorylation of tau protein. The abnormal ubiquitination and loss of α-synuclein are related to the onset of Parkinson's disease. Other neurodegenerative diseases such as Huntington's disease, amyotrophic lateral sclerosis, and so on are also connected with abnormal PPTMs. Therefore, studying the abnormal PPTMs in neurodegenerative diseases is critical for understanding the mechanism of these diseases and the development of significant therapeutic strategies. This work reviews the implications of PPTMs in neurodegenerative diseases and discusses the relevant therapeutic strategies.

Targeting succinylation-mediated metabolic reprogramming as a potential approach for cancer therapy

Metabolic reprogramming is a common hallmark of cancers and involves alterations in many metabolic pathways during tumor initiation and progression. However, the cancer-specific modulation of metabolic reprogramming requires further elucidation. Succinylation, a newly identified protein posttranslational modification (PTM), participates in many cellular processes by transferring a succinyl group to a residue of the target protein, which is related to various pathological disorders including cancers. In recent years, there has been a gradual increase in the number of studies on the regulation of tumors by protein succinylation. Notably, accumulating evidence suggests that succinylation can mediate cancer cell metabolism by altering the structure or activity of metabolism-related proteins and plays vital roles in metabolic reprogramming. Furthermore, some antitumor drugs have been linked to succinylation-mediated tumor-associated metabolism. To better elucidate lysine succinylation mediated tumor metabolic reprogramming, this review mainly summarizes recent studies on the regulation and effects of protein succinylation in tumors, focusing on the metabolic regulation of tumorigenesis and development, which will provide new directions for cancer diagnosis as well as possible therapeutic targets.

Post-Translational Modifications in Atopic Dermatitis: Current Research and Clinical Relevance

Atopic dermatitis (AD) is a chronic and relapsing cutaneous disorder characterized by compromised immune system, excessive inflammation, and skin barrier disruption. Post-translational modifications (PTMs) are covalent and enzymatic modifications of proteins after their translation, which have been reported to play roles in inflammatory and allergic diseases. However, less attention has been paid to the effect of PTMs on AD. This review summarized the knowledge of six major classes (including phosphorylation, acetylation, ubiquitination, SUMOylation, glycosylation, o-glycosylation, and glycation) of PTMs in AD pathogenesis and discussed the opportunities for disease management.

Structure-based prediction of HDAC6 substrates validated by enzymatic assay reveals determinants of promiscuity and detects new potential substrates

Histone deacetylases play important biological roles well beyond the deacetylation of histone tails. In particular, HDAC6 is involved in multiple cellular processes such as apoptosis, cytoskeleton reorganization, and protein folding, affecting substrates such as ɑ-tubulin, Hsp90 and cortactin proteins. We have applied a biochemical enzymatic assay to measure the activity of HDAC6 on a set of candidate unlabeled peptides. These served for the calibration of a structure-based substrate prediction protocol, Rosetta FlexPepBind, previously used for the successful substrate prediction of HDAC8 and other enzymes. A proteome-wide screen of reported acetylation sites using our calibrated protocol together with the enzymatic assay provide new peptide substrates and avenues to novel potential functional regulatory roles of this promiscuous, multi-faceted enzyme. In particular, we propose novel regulatory roles of HDAC6 in tumorigenesis and cancer cell survival via the regulation of EGFR/Akt pathway activation. The calibration process and comparison of the results between HDAC6 and HDAC8 highlight structural differences that explain the established promiscuity of HDAC6.

Werner Syndrome Protein (WRN) Regulates Cell Proliferation and the Human Papillomavirus 16 Life Cycle during Epithelial Differentiation

Human papillomaviruses recruit a host of DNA damage response factors to their viral genome to facilitate homologous recombination replication in association with the viral replication factors E1 and E2. We previously demonstrated that SIRT1 deacetylation of WRN promotes recruitment of WRN to E1-E2 replicating DNA and that WRN regulates both the levels and fidelity of E1-E2 replication. The deacetylation of WRN by SIRT1 results in an active protein able to complex with replicating DNA, but a protein that is less stable. Here, we demonstrate an inverse correlation between SIRT1 and WRN in CIN cervical lesions compared to normal control tissue, supporting our model of SIRT1 deacetylation destabilizing WRN protein. We CRISPR/Cas9 edited N/Tert-1 and N/Tert-1+HPV16 cells to knock out WRN protein expression and subjected the cells to organotypic raft cultures. In N/Tert-1 cells without WRN expression, there was enhanced basal cell proliferation, DNA damage, and thickening of the differentiated epithelium. In N/Tert-1+HPV16 cells, there was enhanced basal cell proliferation, increased DNA damage throughout the epithelium, and increased viral DNA replication. Overall, the results demonstrate that the expression of WRN is required to control the proliferation of N/Tert-1 cells and controls the HPV16 life cycle in these cells. This complements our previous data demonstrating that WRN controls the levels and fidelity of HPV16 E1-E2 DNA replication. The results describe a new role for WRN, a tumor suppressor, in controlling keratinocyte differentiation and the HPV16 life cycle.IMPORTANCE HPV16 is the major human viral carcinogen, responsible for around 3 to 4% of all cancers worldwide. Our understanding of how the viral replication machinery interacts with host factors to control/activate the DNA damage response to promote the viral life cycle remains incomplete. Recently, we demonstrated a SIRT1-WRN axis that controls HPV16 replication, and here we demonstrate that this axis persists in clinical cervical lesions induced by HPV16. Here, we describe the effects of WRN depletion on cellular differentiation with or without HPV16; WRN depletion results in enhanced proliferation and DNA damage irrespective of HPV16 status. Also, WRN is a restriction factor for the viral life cycle since replication is disrupted in the absence of WRN. Future studies will focus on enhancing our understanding of how WRN regulates viral replication. Our goal is to ultimately identify cellular factors essential for HPV16 replication that can be targeted for therapeutic gain.

Lysine acetylation regulates the activity of nuclear Pif1

In Saccharomyces cerevisiae, the Pif1 helicase functions in both nuclear and mitochondrial DNA replication and repair processes, preferentially unwinding RNA:DNA hybrids and resolving G-quadruplex structures. We sought to determine how the various activities of Pif1 are regulated in vivo Here, we report lysine acetylation of nuclear Pif1 and demonstrate that it influences both Pif1's cellular roles and core biochemical activities. Using Pif1 overexpression toxicity assays, we determined that the acetyltransferase NuA4 and deacetylase Rpd3 are primarily responsible for the dynamic acetylation of nuclear Pif1. MS analysis revealed that Pif1 was modified in several domains throughout the protein's sequence on the N terminus (Lys-118 and Lys-129), helicase domain (Lys-525, Lys-639, and Lys-725), and C terminus (Lys-800). Acetylation of Pif1 exacerbated its overexpression toxicity phenotype, which was alleviated upon deletion of its N terminus. Biochemical assays demonstrated that acetylation of Pif1 stimulated its helicase, ATPase, and DNA-binding activities, whereas maintaining its substrate preferences. Limited proteolysis assays indicate that acetylation of Pif1 induces a conformational change that may account for its altered enzymatic properties. We propose that acetylation is involved in regulating of Pif1 activities, influencing a multitude of DNA transactions vital to the maintenance of genome integrity.

Deacetylation of HSD17B10 by SIRT3 regulates cell growth and cell resistance under oxidative and starvation stresses

17-beta-hydroxysteroid dehydrogenase 10 (HSD17B10) plays an important role in mitochondrial fatty acid metabolism and is also involved in mitochondrial tRNA maturation. HSD17B10 missense mutations cause HSD10 mitochondrial disease (HSD10MD). HSD17B10 with mutations identified from cases of HSD10MD show loss of function in dehydrogenase activity and mitochondrial tRNA maturation, resulting in mitochondrial dysfunction. It has also been implicated to play roles in the development of Alzheimer disease (AD) and tumorigenesis. Here, we found that HSD17B10 is a new substrate of NAD-dependent deacetylase Sirtuin 3 (SIRT3). HSD17B10 is acetylated at lysine residues K79, K99 and K105 by the acetyltransferase CBP, and the acetylation is reversed by SIRT3. HSD17B10 acetylation regulates its enzymatic activity and the formation of mitochondrial RNase P. Furthermore, HSD17B10 acetylation regulates the intracellular functions, affecting cell growth and cell resistance in response to stresses. Our results demonstrated that acetylation is an important regulation mechanism for HSD17B10 and may provide insight into interrupting the development of AD.

MIB1-mediated degradation of WRN promotes cellular senescence in response to camptothecin treatment

Werner syndrome protein (WRN) plays critical roles in DNA replication, recombination, and repair, as well as transcription and cellular senescence. Ubiquitination and degradation of WRN have been reported, however, the E3 ubiquitin ligase of WRN is little known. Here, we identify mindbomb E3 ubiquitin protein ligase 1 (MIB1) as a novel E3 ubiquitin ligase for WRN protein. MIB1 physically interacts with WRN in vitro and in vivo and induces ubiquitination and degradation of WRN in the ubiquitin-proteasome pathway. Camptothecin (CPT) enhances the interaction between MIB1 and WRN, and promotes WRN degradation in a MIB1-dependent manner. In addition, CPT-induced cellular senescence is facilitated by the expression of MIB1 and attenuated by WRN expression. Our results show that MIB1-mediated degradation of WRN promotes cellular senescence and reveal a novel model executed by MIB1 and WRN to regulate cellular senescence.

SIRT5 stabilizes mitochondrial glutaminase and supports breast cancer tumorigenesis

The mitochondrial enzyme glutaminase (GLS) is frequently up-regulated during tumorigenesis and is being evaluated as a target for cancer therapy. GLS catalyzes the hydrolysis of glutamine to glutamate, which then supplies diverse metabolic pathways with carbon and/or nitrogen. Here, we report that SIRT5, a mitochondrial NAD⁺-dependent lysine deacylase, plays a key role in stabilizing GLS. In transformed cells, SIRT5 regulates glutamine metabolism by desuccinylating GLS and thereby protecting it from ubiquitin-mediated degradation. Moreover, we show that SIRT5 is up-regulated during cellular transformation and supports proliferation and tumorigenesis. Elevated SIRT5 expression in human breast tumors correlates with poor patient prognosis. These findings reveal a mechanism for increasing GLS expression in cancer cells and establish a role for SIRT5 in metabolic reprogramming and mammary tumorigenesis.

Acetylation of Werner protein at K1127 and K1117 is important for nuclear trafficking and DNA repair

Werner syndrome is a rare autosomal recessive disorder where Werner (WRN) gene is mutated. Being a nucleolar protein, during DNA damage, WRN translocates at the damage site where its catalytic function is required in DNA repair. Several studies have indicated that WRN acetylation may modulate WRN trafficking and catalytic function (Blander et al., 2002; Lozada et al., 2014). Among the six acetylation sites in WRN protein identified by mass-spectrometry analysis (Li et al., 2010) we here explore the role of acetylation sites in C-terminal of WRN (K1127, K1117, K1389, K1413) because the C- terminal domain is the hub for protein- protein interaction and DNA binding activity (Brosh et al. [4]; Muftuoglu et al., 2008; Huang et al., 2006). To explore their functional activity, we created mutations in these sites by changing the acetylation residue lysine (K) to a non-acetylation residue arginine (R) and expressed them in WRN mutant cell lines. We observed that K1127R and K1117R mutants are sensitive to the DNA damaging agents etoposide and mitomycin C and display deficient DNA repair. Importantly, deacetylation of WRN by SIRT1 (Mammalian Sir2) is necessary for restoration of WRN localization at nucleoli after completion of DNA repair. Among all putative acetylation sites, K1127R, K1117R and the double mutant K1127R/K1117R showed significantly delayed re-entry to the nucleolus after damage recovery, even when SIRT1 is overexpressed. These mutants showed partial interaction with SIRT1 compared to WT WRN. Thus, our results suggest that K1127 and K1117 are the major sites of acetylation, necessary for DNA repair. These results elucidate the mechanism by which SIRT1 regulates WRN trafficking via these acetylation sites during DNA damage.

Werner Helicase Control of Human Papillomavirus 16 E1-E2 DNA Replication Is Regulated by SIRT1 Deacetylation

Human papillomaviruses (HPV) are double-stranded DNA viruses causative in a host of human diseases, including several cancers. Following infection, two viral proteins, E1 and E2, activate viral replication in association with cellular factors and stimulate the DNA damage response (DDR) during the replication process. E1-E2 uses homologous recombination (HR) to facilitate DNA replication, but an understanding of host factors involved in this process remains incomplete. Previously, we demonstrated that the class III deacetylase SIRT1, which can regulate HR, is recruited to E1-E2-replicating DNA and regulates the level of replication. Here, we demonstrate that SIRT1 promotes the fidelity of E1-E2 replication and that the absence of SIRT1 results in reduced recruitment of the DNA repair protein Werner helicase (WRN) to E1-E2-replicating DNA. CRISPR/Cas9 editing demonstrates that WRN, like SIRT1, regulates the quantity and fidelity of E1-E2 replication. This is the first report of WRN regulation of E1-E2 DNA replication, or a role for WRN in the HPV life cycle. In the absence of SIRT1 there is an increased acetylation and stability of WRN, but a reduced ability to interact with E1-E2-replicating DNA. We present a model in which E1-E2 replication turns on the DDR, stimulating SIRT1 deacetylation of WRN. This deacetylation promotes WRN interaction with E1-E2-replicating DNA to control the quantity and fidelity of replication. As well as offering a crucial insight into HPV replication control, this system offers a unique model for investigating the link between SIRT1 and WRN in controlling replication in mammalian cells.IMPORTANCE HPV16 is the major viral human carcinogen responsible for between 3 and 4% of all cancers worldwide. Following infection, this virus activates the DNA damage response (DDR) to promote its life cycle and recruits DDR proteins to its replicating DNA in order to facilitate homologous recombination during replication. This promotes the production of viable viral progeny. Our understanding of how HPV16 replication interacts with the DDR remains incomplete. Here, we demonstrate that the cellular deacetylase SIRT1, which is a part of the E1-E2 replication complex, regulates recruitment of the DNA repair protein WRN to the replicating DNA. We demonstrate that WRN regulates the level and fidelity of E1-E2 replication. Overall, the results suggest a mechanism by which SIRT1 deacetylation of WRN promotes its interaction with E1-E2-replicating DNA to control the levels and fidelity of that replication.

Isotopic Labeling and Quantitative Proteomics of Acetylation on Histones and Beyond

Lysine acetylation is an important posttranslational modification (PTM) that regulates the function of proteins by affecting their localization, stability, binding, and enzymatic activity. Aberrant acetylation patterns have been observed in numerous diseases, most notably cancer, which has spurred the development of potential therapeutics that target acetylation pathways. Mass spectrometry (MS) has become the most adopted tool not only for the qualitative identification of acetylation sites but also for their large-scale quantification. By using heavy isotope labeling in cell culture combined with MS, it is now possible to accurately quantify newly synthesized acetyl groups and other PTMs, allowing differentiation between dynamically regulated and steady-state modifications. Here, we describe MS-based protocols to identify acetylation sites and quantify acetylation rates on both proteins in general and in the special case of histones. In the experimental approach for the former, ¹³C-glucose and D₃-acetate are used to metabolically label protein acetylation in cells with stable isotopes, thus allowing isotope incorporation to be tracked over time. After protein extraction and digestion, acetylated peptides are enriched via immunoprecipitation and then analyzed by MS. For histones, a similar metabolic labeling approach is performed, followed by acid extraction, derivatization with propionic anhydride, and trypsin digestion prior to MS analysis. The procedures presented may be adapted to investigate acetylation dynamics in a broad range of experimental contexts, including different cell types and stimulation conditions.

Lysine Acetylation of Proteins and Its Characterization in Human Systems

Posttranslational acetylation modifications of proteins have important consequences for cell biology, including effects on protein trafficking and cellular localization as well as on the interactions of acetylated proteins with other proteins and macromolecules such as DNA. Experiments to uncover and characterize protein acetylation events have historically been more challenging than investigating another common posttranslational modification, protein phosphorylation. More recently, high-quality antibodies that recognize acetylated lysine residues present in acetylated proteins and improved proteomic methodologies have facilitated the discovery that acetylation occurs on numerous cellular proteins and allowed characterization of the dynamics and functional effects of many acetylation events. This article summarizes some established biochemical information about how protein acetylation takes place and is regulated, in order to lay the foundation for subsequent descriptions of strategies used by our lab and others either to directly study acetylation of an individual factor or to identify groups of proteins targeted for acetylation that can then be examined in isolation.

MDM2-mediated degradation of WRN promotes cellular senescence in a p53-independent manner

MDM2 (Murine double minute 2) acts as a key repressor for p53-mediated tumor-suppressor functions, which includes cellular senescence. We found that MDM2 can promote cellular senescence by modulating WRN stability. Werner syndrome (WS), caused by mutations of the WRN gene, is an autosomal recessive disease, which is characterized by premature aging. Loss of WRN function induces cellular senescence in human cancer cells. Here, we found that MDM2 acts as an E3 ligase for WRN protein. MDM2 interacts with WRN both in vivo and in vitro. MDM2 induces ubiquitination of WRN and dramatically downregulates the levels of WRN protein in human cells. During DNA damage response, WRN is translocated to the nucleoplasm to facilitate its DNA repair functions; however, it is degraded by the MDM2-mediated ubiquitination pathway. Moreover, the senescent phenotype induced by DNA damage reagents, such as Etoposide, is at least in part mediated by MDM2-dependent WRN degradation as it can be significantly attenuated by ectopic expression of WRN. These results show that MDM2 is critically involved in regulating WRN function via ubiquitin-dependent degradation and reveal an unexpected role of MDM2 in promoting cellular senescence through a p53-independent manner.

Werner Syndrome Protein and DNA Replication

Werner Syndrome (WS) is an autosomal recessive disorder characterized by the premature development of aging features. Individuals with WS also have a greater predisposition to rare cancers that are mesenchymal in origin. Werner Syndrome Protein (WRN), the protein mutated in WS, is unique among RecQ family proteins in that it possesses exonuclease and 3' to 5' helicase activities. WRN forms dynamic sub-complexes with different factors involved in DNA replication, recombination and repair. WRN binding partners either facilitate its DNA metabolic activities or utilize it to execute their specific functions. Furthermore, WRN is phosphorylated by multiple kinases, including Ataxia telangiectasia mutated, Ataxia telangiectasia and Rad3 related, c-Abl, Cyclin-dependent kinase 1 and DNA-dependent protein kinase catalytic subunit, in response to genotoxic stress. These post-translational modifications are critical for WRN to function properly in DNA repair, replication and recombination. Accumulating evidence suggests that WRN plays a crucial role in one or more genome stability maintenance pathways, through which it suppresses cancer and premature aging. Among its many functions, WRN helps in replication fork progression, facilitates the repair of stalled replication forks and DNA double-strand breaks associated with replication forks, and blocks nuclease-mediated excessive processing of replication forks. In this review, we specifically focus on human WRN's contribution to replication fork processing for maintaining genome stability and suppressing premature aging. Understanding WRN's molecular role in timely and faithful DNA replication will further advance our understanding of the pathophysiology of WS.

Acidic domain of WRNp is critical for autophagy and up-regulates age associated proteins

Impaired autophagy may be associated with normal and pathological aging. Here we explore a link between autophagy and domain function of Werner protein (WRNp). Werner (WRN) mutant cell lines AG11395, AG05229 and normal aged fibroblast AG13129 display a deficient response to tunicamycin mediated endoplasmic reticulum (ER) stress induced autophagy compared to clinically unaffected GM00637 and normal young fibroblast GM03440. Cellular endoplasmic reticulum (ER) stress mediated autophagy in WS and normal aged cells is restored after transfection with wild type full length WRN, but deletion of the acidic domain from wild type WRN fails to restore autophagy. The acidic domain of WRNp was shown to regulate its transcriptional activity, and here, we show that it affects the transcription of certain proteins involved in autophagy and aging. Furthermore, siRNA mediated silencing of WRN in normal fibroblast WI-38 resulted in decrease of age related proteins Lamin A/C and Mre11.

CREBBP and p300 lysine acetyl transferases in the DNA damage response

The CREB-binding protein (CREBBP, or in short CBP) and p300 are lysine (K) acetyl transferases (KAT) belonging to the KAT3 family of proteins known to modify histones, as well as non-histone proteins, thereby regulating chromatin accessibility and transcription. Previous studies have indicated a tumor suppressor function for these enzymes. Recently, they have been found to acetylate key factors involved in DNA replication, and in different DNA repair processes, such as base excision repair, nucleotide excision repair, and non-homologous end joining. The growing list of CBP/p300 substrates now includes factors involved in DNA damage signaling, and in other pathways of the DNA damage response (DDR). This review will focus on the role of CBP and p300 in the acetylation of DDR proteins, and will discuss how this post-translational modification influences their functions at different levels, including catalytic activity, DNA binding, nuclear localization, and protein turnover. In addition, we will exemplify how these functions may be necessary to efficiently coordinate the spatio-temporal response to DNA damage. CBP and p300 may contribute to genome stability by fine-tuning the functions of DNA damage signaling and DNA repair factors, thereby expanding their role as tumor suppressors.

Histone acetyltransferase CBP promotes function of SCF FBXL19 ubiquitin E3 ligase by acetylation and stabilization of its F-box protein subunit

Ubiquitin E3 ligases mediate ubiquitination and degradation of intracellular proteins. We have shown that a relatively new Skp, Cullin, F-box (SCF) protein E3 ligase, SCF FBXL19, has an anti-inflammatory effect and controls actin cytoskeleton dynamics via targeting cell membrane receptor and small GTPases for their ubiquitination and degradation, but the molecular regulation of its subunit FBXL19 stability remains unclear. Here we show that FBXL19 degradation is controlled by the balance between its ubiquitination and acetylation. FBXL19 is an unstable protein with a half-life of ∼3 h. FBXL19 can be polyubiquitinated, and the proteasome inhibitor MG-132 prolongs FBXL19 half-life, suggesting that FBXL19 degradation is mediated in the ubiquitin-proteasome system. FBXL19 can also be acetylated, and enhancing acetylation of FBXL19 by a deacetylase inhibitor reduces FBXL19 ubiquitination levels. Acetylation-mimic FBXL19 mutant exhibits a longer half-life than wild type. An acetyltransferase CBP catalyzes acetylation of FBXL19. Inhibition or down-regulation of CBP reduces FBXL19 stability, whereas it is increased in CBP-overexpressing cells. Taken together, the data indicate that CBP-mediated acetylation reduces ubiquitination and stabilizes FBXL19. Further, we demonstrate that FBXL19 targets small GTPase Cdc42 for its ubiquitination and degradation, whereas this effect is reversed by inhibition of CBP, suggesting that CBP increases the effect of SCF FBXL19 E3 ligase through acetylation and stabilization of FBXL19. Our study reveals a new molecular model for regulation of SCF E3 ligase function by acetylation and stabilization of its subunit F-box protein.-Wei, J., Dong, S., Yao, K., Martinez, M. F. Y. M., Fleisher, P. R., Zhao, Y., Ma, H., Zhao, J. Histone acetyltransferase CBP promotes function of SCF FBXL19 ubiquitin E3 ligase by acetylation and stabilization of its F-box protein subunit.

Camptothecin targets WRN protein: mechanism and relevance in clinical breast cancer

Werner syndrome protein (WRN) is a RecQ helicase that participates in DNA repair, genome stability and cellular senescence. The five human RecQ helicases, RECQL1, Bloom, WRN, RECQL4 and RECQL5 play critical roles in DNA repair and cell survival after treatment with the anticancer drug camptothecin (CPT). CPT derivatives are widely used in cancer chemotherapy to inhibit topoisomerase I and generate DNA double-strand breaks during replication. Here we studied the effects of CPT on the stability and expression dynamics of human RecQ helicases. In the cells treated with CPT, we observed distinct effects on WRN compared to other human RecQ helicases. CPT altered the cellular localization of WRN and induced its degradation by a ubiquitin-mediated proteasome pathway. WRN knockdown cells as well as CPT treated cells became senescent and stained positive for senescence-associated β-galactosidase at a higher frequency compared to control cells. However, the senescent phenotype was attenuated by ectopic expression of WRN suggesting functional implication of WRN degradation in CPT treated cells. Approximately 5-23% of breast cancer tumors are known to respond to CPT-based chemotherapy. Interestingly, we found that the extent of CPT-induced WRN degradation correlates with increasing sensitivity of breast cancer cells to CPT. The abundance of WRN decreased in CPT-treated sensitive cells; however, WRN remained relatively stable in CPT-resistant breast cancer cells. In a large clinical cohort of breast cancer patients, we find that WRN and topoisomerase I expression correlate with an aggressive tumor phenotype and poor prognosis. Our novel observations suggest that WRN abundance along with CPT-induced degradation could be a promising strategy for personalizing CPT-based cancer chemotherapeutic regimens.

SIRT6 delays cellular senescence by promoting p27Kip1 ubiquitin-proteasome degradation

Sirtuin6(SIRT6) has been implicated as a key factor in aging and aging-related diseases. However, the role of SIRT6 in cellular senescence has not been fully understood. Here, we show that SIRT6 repressed the expression of p27^Kip1 (p27) in cellular senescence. The expression of SIRT6 was reduced during cellular senescence, whereas enforced SIRT6 expression promoted cell proliferation and antagonized cellular senescence. In addition, we demonstrated that SIRT6 promoted p27 degradation by proteasome and SIRT6 decreased the acetylation level and protein half-life of p27. p27 acetylation increased its protein stability. Furthermore, SIRT6 directly interacted with p27. Importantly, p27 was strongly acetylated and had a prolonged protein half-life with the reduction of SIRT6 when cells were senescent, compared with those young cells. Finally, SIRT6 markedly rescued senescence induced by p27. Our findings indicate that SIRT6 decreases p27 acetylation, leading to its degradation via ubiquitin-proteasome pathway and then delays cellular senescence.

Replication stress induced site-specific phosphorylation targets WRN to the ubiquitin-proteasome pathway

Faithful and complete genome replication in human cells is essential for preventing the accumulation of cancer-promoting mutations. WRN, the protein defective in Werner syndrome, plays critical roles in preventing replication stress, chromosome instability, and tumorigenesis. Herein, we report that ATR-mediated WRN phosphorylation is needed for DNA replication and repair upon replication stress. A serine residue, S1141, in WRN is phosphorylated in vivo by the ATR kinase in response to replication stress. ATR-mediated WRN S1141 phosphorylation leads to ubiquitination of WRN, facilitating the reversible interaction of WRN with perturbed replication forks and subsequent degradation of WRN. The dynamic interaction between WRN and DNA is required for the suppression of new origin firing and Rad51-dependent double-stranded DNA break repair. Significantly, ATR-mediated WRN phosphorylation is critical for the suppression of chromosome breakage during replication stress. These findings reveal a unique role for WRN as a modulator of DNA repair, replication, and recombination, and link ATR-WRN signaling to the maintenance of genome stability.

CCAR2 Is Required for Proliferation and Tumor Maintenance in Human Squamous Cell Carcinoma

CCAR2 is a widely expressed protein involved in the regulation of a variety of transcriptional complexes. High expression of CCAR2 correlates with poor outcomes in many human tumor types such as squamous cell carcinoma (SCC). Paradoxically, loss of Ccar2 in the mouse results in an increased tumor burden, suggesting that CCAR2 may in fact function as a tumor suppressor. This tumor suppressor function is dependent on p53, a protein that is inactivated in the vast majority of SCC tumors, leaving the role of CCAR2 in p53-null tumors unclear. We sought to identify p53-independent CCAR2 functions in SCC and to examine its role in tumorigenesis. We found that CCAR2 is highly overexpressed in p53-deficient SCC cell lines compared with normal primary keratinocytes due to increased protein stability. We identify a role for CCAR2 in promoting the stability of the transcription factors RFX1 and CREB1, which are both required for proliferation. Finally, we show that CCAR2 is required for proliferation in vitro and in established SCC tumors in vivo. Our data suggest an important role for CCAR2 in maintaining cell cycle progression and promoting SCC tumorigenesis.

Deacetylation of tumor-suppressor MST1 in Hippo pathway induces its degradation through HBXIP-elevated HDAC6 in promotion of breast cancer growth

Reduction or loss of tumor-suppressor mammalian STE20-like kinase 1 (MST1) in Hippo pathway contributes to the tumorigenesis. However, the mechanism leading to reduction of MST1 in cancers remains poorly understood. In this study, we explored the hypothesis that the oncoprotein hepatitis B X-interacting protein (HBXIP) is involved in the reduction of MST1 in breast cancer. Immunohistochemical analysis of tissue microarrays revealed that the expression of HBXIP was negatively associated with that of MST1 in 98 clinical breast tissue samples. Then we found that HBXIP could posttranslationally downregulate MST1 in breast cancer cells. Mechanistically, we identified that MST1 could be acetylated on its lysine 35 residue in the cells. Strikingly, the treatment with trichostatin A, an inhibitor of histone deacetylases (HDACs), markedly increased the levels of MST1 acetylation and protein in the cells. Interestingly, the oncoprotein HBXIP could significantly inhibit acetylation of MST1, resulting in the reduction of MST1 protein. Notably, we revealed that the HDAC6 could reduce the protein levels of MST1 through deacetylation modification of MST1 in the cells. Moreover, our data revealed that HBXIP upregulated HDAC6 at the levels of mRNA and protein by activating transcription factor nuclear factor-κB. Deacetylation of MST1 promoted the interaction of MST1 with HSC70 in the cells, resulting in a lysosome-dependent degradation of MST1 via chaperone-mediated autophagy (CMA). Functionally, the reduction of tumor-suppressor MST1 mediated by HBXIP promoted the growth of breast cancer cells in vitro and in vivo. Thus we conclude that the deacetylation of MST1 mediated by HBXIP-enhanced HDAC6 results in MST1 degradation in a CMA manner in promotion of breast cancer growth. Our finding provides new insights into the mechanism of tumor-suppressor MST1 reduction in breast cancer.

Stem cell aging in adult progeria

Aging is considered an irreversible biological process and also a major risk factor for a spectrum of geriatric diseases. Advanced age-related decline in physiological functions, such as neurodegeneration, development of cardiovascular disease, endocrine and metabolic dysfunction, and neoplastic transformation, has become the focus in aging research. Natural aging is not regarded as a programmed process. However, accelerated aging due to inherited genetic defects in patients of progeria is programmed and resembles many aspects of natural aging. Among several premature aging syndromes, Werner syndrome (WS) and Hutchinson–Gilford progeria syndrome (HGPS) are two broadly investigated diseases. In this review, we discuss how stem cell aging in WS helps us understand the biology of aging. We also discuss briefly how the altered epigenetic landscape in aged cells can be reversed to a “juvenile” state. Lastly, we explore the potential application of the latest genomic editing technique for stem cell-based therapy and regenerative medicine in the context of aging.

Protein degradation pathways regulate the functions of helicases in the DNA damage response and maintenance of genomic stability

Degradation of helicases or helicase-like proteins, often mediated by ubiquitin-proteasomal pathways, plays important regulatory roles in cellular mechanisms that respond to DNA damage or replication stress. The Bloom’s syndrome helicase (BLM) provides an example of how helicase degradation pathways, regulated by post-translational modifications and protein interactions with components of the Fanconi Anemia (FA) interstrand cross-link (ICL) repair pathway, influence cell cycle checkpoints, DNA repair, and replication restart. The FANCM DNA translocase can be targeted by checkpoint kinases that exert dramatic effects on FANCM stability and chromosomal integrity. Other work provides evidence that degradation of the F-box DNA helicase (FBH1) helps to balance translesion synthesis (TLS) and homologous recombination (HR) repair at blocked replication forks. Degradation of the helicase-like transcription factor (HLTF), a DNA translocase and ubiquitylating enzyme, influences the choice of post replication repair (PRR) pathway. Stability of the Werner syndrome helicase-nuclease (WRN) involved in the replication stress response is regulated by its acetylation. Turning to transcription, stability of the Cockayne Syndrome Group B DNA translocase (CSB) implicated in transcription-coupled repair (TCR) is regulated by a CSA ubiquitin ligase complex enabling recovery of RNA synthesis. Collectively, these studies demonstrate that helicases can be targeted for degradation to maintain genome homeostasis.

Acetylation of Werner syndrome protein (WRN): relationships with DNA damage, DNA replication and DNA metabolic activities

Loss of Werner syndrome protein function causes Werner syndrome, characterized by increased genomic instability, elevated cancer susceptibility and premature aging. Although WRN is subject to acetylation, phosphorylation and sumoylation, the impact of these modifications on WRN's DNA metabolic function remains unclear. Here, we examined in further depth the relationship between WRN acetylation and its role in DNA metabolism, particularly in response to induced DNA damage. Our results demonstrate that endogenous WRN is acetylated somewhat under unperturbed conditions. However, levels of acetylated WRN significantly increase after treatment with certain DNA damaging agents or the replication inhibitor HU. Use of DNA repair-deficient cells or repair pathway inhibitors further increase levels of acetylated WRN, indicating that induced DNA lesions and their persistence are at least partly responsible for increased acetylation. Notably, acetylation of WRN correlates with inhibition of DNA synthesis, suggesting that replication blockage might underlie this effect. Moreover, WRN acetylation modulates its affinity for and activity on certain DNA structures, in a manner that may enhance its relative specificity for physiological substrates. Our results also show that acetylation and deacetylation of endogenous WRN is a dynamic process, with sirtuins and other histone deacetylases contributing to WRN deacetylation. These findings advance our understanding of the dynamics of WRN acetylation under unperturbed conditions and following DNA damage induction, linking this modification not only to DNA damage persistence but also potentially to replication stalling caused by specific DNA lesions. Our results are consistent with proposed metabolic roles for WRN and genomic instability phenotypes associated with WRN deficiency.

Valproic Acid Regulates α-Synuclein Expression through JNK Pathway in Rat Primary Astrocytes

Although the role of α-synuclein aggregation on Parkinson's disease is relatively well known, the physiological role and the regulatory mechanism governing the expression of α-synuclein are unclear yet. We recently reported that α-synuclein is expressed and secreted from cultured astrocytes. In this study, we investigated the effect of valproic acid (VPA), which has been suggested to provide neuroprotection by increasing α-synuclein in neuron, on α-synuclein expression in rat primary astrocytes. VPA concentrationdependently increased the protein expression level of α-synuclein in cultured rat primary astrocytes with concomitant increase in mRNA expression level. Likewise, the level of secreted α-synuclein was also increased by VPA. VPA increased the phosphorylation of Erk1/2 and JNK and pretreatment of a JNK inhibitor SP600125 prevented the VPA-induced increase in α-synuclein. Whether the increased α-synuclein in astrocytes is involved in the reported neuroprotective effects of VPA awaits further investigation.

A novel aromatic carboxylic acid inactivates luciferase by acylation of an enzymatically active regulatory lysine residue

Firefly luciferase (Luc) is widely used as a reporter enzyme in cell-based assays for gene expression. A novel aromatic carboxylic acid, F-53, reported here for the first time, substantially inhibited the enzymatic activity of Luc in a Luc reporter screening. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS/MS) analyses showed that F-53 modifies Luc at lysine-529 via amidation of the F-53 carboxyl group. The lysine-529 residue of Luc, which plays a regulatory catalytic role, can be acetylated. Luc also has a long-chain fatty acyl-CoA synthase activity. An in vitro assay that involved both recombinant Luc and mouse liver microsomes identified F-53-CoA as the reactive form produced from F-53. However, whereas the inhibitory effect of F-53 is observed in Hela cells that transiently expressed Luc, it is not observed in an in vitro assay that involves recombinant Luc alone. Therefore, insights into the activities of certain mammalian transferases can be translated to better understand the acylation by F-53. The insights from this study about the novel inhibitory modification mechanism might help not only to avoid misinterpretation of the results of Luc-based reporter screening assays but also to explain the pharmacological and toxicological effects of carboxylic acid-containing drugs.

Acetylation of drosha on the N-terminus inhibits its degradation by ubiquitination

The RNase III enzyme Drosha initiates microRNA (miRNA) biogenesis in the nucleus by cleaving primary miRNA transcripts into shorter precursor molecules that are subsequently exported into the cytoplasm for further processing. While numerous disease states appear to be associated with aberrant expression of Drosha, the molecular mechanisms that regulate its protein levels are largely unknown. Here, we report that ubiquitination and acetylation regulate Drosha protein levels oppositely. Deacetylase inhibitors trichostatin A (TSA) and nicotinamide (NIA) increase Drosha protein level as measured by western blot but have no effects on its mRNA level in HEK293T cells. TSA increases miRNA-143 production in a miRNA sensor assay and in a qPCR analysis in HEK293T cells. Treatment of AGS and HEK293T cells with proteasome inhibitors MG132 or Omuralide increases Drosha protein levels. Furthermore, the N-terminal, but not the C-terminal Drosha can be acetylated by multiple acetyl transferases including p300, CBP and GCN5. Acetylation of Drosha competes with its ubquitination, inhibiting the degradation induced by the ubiquitin-proteasome pathway, thereby increasing Drosha protein levels. Infection of the gastric mucosa AGS cells by H. pylori, the gastric cancer associated carcinogen, leads to the ubiquitination and reduction of Drosha protein levels. H. pylori infection of AGS cells has no significant effects on Drosha mRNA levels. Our findings establish a central mechanism of protein homeostasis as playing a critical role in miRNA biogenesis.

FANCJ/BACH1 acetylation at lysine 1249 regulates the DNA damage response

BRCA1 promotes DNA repair through interactions with multiple proteins, including CtIP and FANCJ (also known as BRIP1/BACH1). While CtIP facilitates DNA end resection when de-acetylated, the function of FANCJ in repair processing is less well defined. Here, we report that FANCJ is also acetylated. Preventing FANCJ acetylation at lysine 1249 does not interfere with the ability of cells to survive DNA interstrand crosslinks (ICLs). However, resistance is achieved with reduced reliance on recombination. Mechanistically, FANCJ acetylation facilitates DNA end processing required for repair and checkpoint signaling. This conclusion was based on the finding that FANCJ and its acetylation were required for robust RPA foci formation, RPA phosphorylation, and Rad51 foci formation in response to camptothecin (CPT). Furthermore, both preventing and mimicking FANCJ acetylation at lysine 1249 disrupts FANCJ function in checkpoint maintenance. Thus, we propose that the dynamic regulation of FANCJ acetylation is critical for robust DNA damage response, recombination-based processing, and ultimately checkpoint maintenance.

The BRCA1–Fanconi anemia (FA) pathway is required for both tumor suppression and cell survival, particularly following treatment with DNA damaging agents that induce DNA interstrand crosslinks (ICLs). ICL processing by the BRCA–FA pathway includes promotion of homologous recombination (HR) and DNA damage tolerance through translesion synthesis. However, little is known about how the BRCA–FA pathway or these ICL processing mechanisms are regulated. Here, we identify acetylation as a DNA damage–dependent regulator of the BRCA–FA protein, FANCJ. FANCJ acetylation at lysine 1249 is enhanced by expression of the histone acetyltransferase CBP and reduced by expression of histone deacetylases HDAC3 or SIRT1. Furthermore, acetylation on endogenous FANCJ is induced upon treatment of cells with agents that generate DNA lesions. Consistent with this post-translation event regulating FANCJ function during cellular DNA repair, preventing FANCJ acetylation skews ICL processing. Cells have reduced reliance on HR factor Rad54 and greater reliance on translesion synthesis polymerase polη. Our data indicate that FANCJ acetylation contributes to DNA end processing that is required for HR. Furthermore, resection-dependent checkpoint maintenance relies on the dynamic regulation of FANCJ acetylation. The implication of these findings is that FANCJ acetylation contributes to DNA repair choice within the BRCA–FA pathway.

ASEB: a web server for KAT-specific acetylation site prediction

Protein lysine acetylation plays an important role in the normal functioning of cells, including gene expression regulation, protein stability and metabolism regulation. Although large amounts of lysine acetylation sites have been identified via large-scale mass spectrometry or traditional experimental methods, the lysine (K)-acetyl-transferase (KAT) responsible for the acetylation of a given protein or lysine site remains largely unknown due to the experimental limitations of KAT substrate identification. Hence, the in silico prediction of KAT-specific acetylation sites may provide direction for further experiments. In our previous study, we developed the acetylation set enrichment based (ASEB) computer program to predict which KAT-families are responsible for the acetylation of a given protein or lysine site. In this article, we provide KAT-specific acetylation site prediction as a web service. This web server not only provides the online tool and R package for the method in our previous study, but several useful services are also included, such as the integration of protein-protein interaction information to enhance prediction accuracy. This web server can be freely accessed at http://cmbi.bjmu.edu.cn/huac.

A novel acetylation cycle of transcription co-activator Yes-associated protein that is downstream of Hippo pathway is triggered in response to SN2 alkylating agents

Yes-associated protein (YAP) is a transcriptional co-activator that acts downstream of the Hippo signaling pathway and regulates multiple cellular processes. Although cytoplasmic retention of YAP is known to be mediated by Hippo pathway-dependent phosphorylation, post-translational modifications that regulate YAP in the nucleus remain unclear. Here we report the discovery of a novel cycle of acetylation/deacetylation of nuclear YAP induced in response to S(N)2 alkylating agents. We show that after treatment of cells with the S(N)2 alkylating agent methyl methanesulfonate, YAP phosphorylation mediated by the Hippo pathway is markedly reduced, leading to nuclear translocation of YAP and its acetylation. This YAP acetylation occurs on specific and highly conserved C-terminal lysine residues and is mediated by the nuclear acetyltransferases CBP (CREB binding protein) and p300. Conversely, the nuclear deacetylase SIRT1 is responsible for YAP deacetylation. Intriguingly, we found that YAP acetylation is induced specifically by S(N)2 alkylating agents and not by other DNA-damaging stimuli. These results identify a novel YAP acetylation cycle that occurs in the nucleus downstream of the Hippo pathway. Intriguingly, our findings also indicate that YAP acetylation is involved in responses to a specific type of DNA damage.

Interferon regulatory factor 1 transactivates expression of human DNA polymerase η in response to carcinogen N-methyl-N'-nitro-N-nitrosoguanidine

DNA polymerase η (Polη) implements translesion DNA synthesis but has low fidelity in replication. We have previously shown that Polη plays an important role in the genesis of nontargeted mutations at undamaged DNA sites in cells exposed to the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Here, we report that MNNG-induced Polη expression in an interferon regulatory factor 1 (IRF1)-dependent manner in human cells. Mutagenesis analysis showed that four critical residues (Arg-82, Cys-83, Asn-86, and Ser-87) located in the IRF family conserved DNA binding domain-helix α3 were involved in DNA binding and POLH transactivation by IRF1. Furthermore, Polη up-regulation induced by IRF1 was responsible for the increase of mutation frequency in a SupF shuttle plasmid replicated in the MNNG-exposed cells. Interestingly, IRF1 was acetylated by the histone acetyltransferase CBP in these cells. Lys → Arg substitution revealed that Lys-78 of helix α3 was the major acetylation site, and the IRF1-K78R mutation partially inhibited DNA binding and its transcriptional activity. Thus, we propose that IRF1 activation is responsible for MNNG-induced Polη up-regulation, which contributes to mutagenesis and ultimately carcinogenesis in cells.

Characterization and prediction of lysine (K)-acetyl-transferase specific acetylation sites

Lysine acetylation is a well-studied post-translational modification on both histone and nonhistone proteins. More than 2000 acetylated proteins and 4000 lysine acetylation sites have been identified by large scale mass spectrometry or traditional experimental methods. Although over 20 lysine (K)-acetyl-transferases (KATs) have been characterized, which KAT is responsible for a given protein or lysine site acetylation is mostly unknown. In this work, we collected KAT-specific acetylation sites manually and analyzed sequence features surrounding the acetylated lysine of substrates from three main KAT families (CBP/p300, GCN5/PCAF, and the MYST family). We found that each of the three KAT families acetylates lysines with different sequence features. Based on these differences, we developed a computer program, Acetylation Set Enrichment Based method to predict which KAT-families are responsible for acetylation of a given protein or lysine site. Finally, we evaluated the efficiency of our method, and experimentally detected four proteins that were predicted to be acetylated by two KAT families when one representative member of the KAT family is over expressed. We conclude that our approach, combined with more traditional experimental methods, may be useful for identifying KAT families responsible for acetylated substrates proteome-wide.

Combined exercise and insulin-like growth factor-1 supplementation induces neurogenesis in old rats, but do not attenuate age-associated DNA damage

We have investigated the effects of 2 weeks of insulin-like growth factor-1 (IGF-1) supplementation (5 μg/kg per day) and 6 weeks of exercise training (60% of the maximal oxygen consumption [VO₂ max]) on neurogenesis, DNA damage/repair, and sirtuin content in the hippocampus of young (3 months old) and old (26 months old) rats. Exercise improved the spatial memory of the old group, but IGF-1 supplementation eliminated this effect. An age-associated decrease in neurogenesis was attenuated by exercise and IGF-1 treatment. Aging increased the levels of 8-oxo-7,8-dihydroguanine (8-oxoG) and the protein Ku70, indicating the role of DNA damage in age-related neuropathology. Acetylation of 8-oxoguanine DNA glycosylase (OGG1) was detected in vivo, and this decreased with aging. However, in young animals, exercise and IGF-1 treatment increased acetylated (ac) OGG1 levels. Sirtuin 1 (SIRT1) and SIRT3, as DNA damage-associated lysine deacetylases, were measured, and SIRT1 decreased with aging, resulting in a large increase in acetylated lysine residues in the hippocampus. On the other hand, SIRT3 increased with aging. Exercise-induced neurogenesis might not be a causative factor of increased spatial memory, because IGF-1 plus exercise can induce neurogenesis in the hippocampus of older rats. Data revealed that the age-associated increase in 8-oxoG levels is due to decreased acetylation of OGG1. Age-associated decreases in SIRT1 and the associated increase in lysine acetylation, in the hippocampus, could have significant impact on function and thus, could suggest a therapeutic target.

Physical and functional HAT/HDAC interplay regulates protein acetylation balance

The balance between protein acetylation and deacetylation controls several physiological and pathological cellular processes, and the enzymes involved in the maintenance of this equilibrium—acetyltransferases (HATs) and deacetylases (HDACs)—have been widely studied. Presently, the evidences obtained in this field suggest that the dynamic acetylation equilibrium is mostly maintained through the physical and functional interplay between HAT and HDAC activities. This model overcomes the classical vision in which the epigenetic marks of acetylation have only an activating function whereas deacetylation marks have a repressing activity. Given the existence of several players involved in the preservation of this equilibrium, the identification of these complex networks of interacting proteins will likely foster our understanding of how cells regulate intracellular processes and respond to the extracellular environment and will offer the rationale for new therapeutic approaches based on epigenetic drugs in human diseases.

Aberrant cytoplasm localization and protein stability of SIRT1 is regulated by PI3K/IGF-1R signaling in human cancer cells

SIRT1, an NAD-dependent histone/protein deacetylase, has classically been thought of as a nuclear protein. In this study, we demonstrate that SIRT1 is mainly localized in the nucleus of normal cells, but is predominantly localized in the cytoplasm of the cancer / transformed cells we tested. We found this predominant cytoplasmic localization of SIRT1 is regulated by elevated mitotic activity and PI3K/IGF-1R signaling in cancer cells. We show that aberrant cytoplasmic localization of SIRT1 is due to increased protein stability and is regulated by PI3K/IGF-1R signaling. In addition, we determined that SIRT1 is required for PI3K-mediated cancer cell growth. Our study represents the first identification that aberrant cytoplasm localization is one of the specific alternations to SIRT1 that occur in cancer cells, and PI3K/IGF-1R signaling plays an important role in the regulation of cytoplasmic SIRT1 stability. Our findings suggest that the over-expressed cytoplasmic SIRT1 in cancer cells may greatly contribute to its cancer-specific function by working downstream of the PI3K/IGF-1R signaling pathway.

Werner syndrome as a hereditary risk factor for exocrine pancreatic cancer: potential role of WRN in pancreatic tumorigenesis and patient-tailored therapy

Advanced age is considered a risk factor for pancreatic cancer, but this relationship at the molecular and genetic level remains unclear. We present a clinical case series focusing on an association between pancreatic adenocarcinoma and Werner syndrome (WS) that is an autosomal recessive genetic disorder characterized by accelerated aging and cancer predisposition, and is caused by loss-of-function mutations in the WS RecQ helicase gene (WRN). Although pancreatic adenocarcinoma mostly occurs in a sporadic fashion, a minority of cases occurs in the context of susceptible individuals with hereditary syndromes. While WS has not been previously recognized as a risk factor for developing malignant tumors of the exocrine pancreas, the clinicopathologic features of three reported patients suggest a contributory role of WRN deficiency in pancreatic carcinogenesis. Molecular genetic analyses support the role of WRN as a tumor suppressor gene, although recent evidence reveals that WRN can alternatively promote oncogenicity depending on the molecular context. Based upon the clinico-pathologic features of these patients and the role of WRN in experimental models, we propose that its loss-of-function predisposes the development of pancreatic adenocarcinoma through epigenetic silencing or loss-of-heterozygosity of WRN. To test this hypothesis, we are investigating the mechanistic role of WRN in pancreatic cancer models including a pancreatic adenocarcinoma cell line generated from a human with WS. These studies are expected to provide new insight into the relationship between aging and pancreatic tumorigenesis, and facilitate development of novel strategies for patient-tailored interventions in this deadly malignancy.

Novel polymorphisms of nuclear receptor SHP associated with functional and structural changes

We identified three heterozygous nonsynonymous single nucleotide polymorphisms in the small heterodimer partner (SHP, NROB2) gene in normal subjects and CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy)-like patients, including two novel missense mutations (p.R38H, p.K170N) and one of the previously reported polymorphism (p.G171A). Four novel heterozygous mutations were also identified in the intron ((Intron)1265T-->A), 3'-untranslated region ((3'-UTR)101C-->G, (3'-UTR)186T-->C), and promoter ((Pro)-423C-->T) of the SHP gene. The exonic R38H and K170N mutants exhibited impaired nuclear translocation. K170N made SHP more susceptible to ubiquitination mediated degradation and blocked SHP acetylation, which displayed lost repressive activity on its interacting partners ERRgamma and HNF4alpha but not LRH-1. In contrast, G171A increased SHP mRNA and protein expression and maintained normal function. In general, the interaction of SHP mutants with LRH-1 and EID1 was enhanced. K170N also markedly impaired the recruitment of SHP, HNF4alpha, HDAC1, and HDAC3 to the apoCIII promoter. Molecular dynamics simulations of SHP showed that G171A stabilized the nuclear receptor boxes, whereas K170N promoted the conformational destabilization of all the structural elements of the receptor. This study suggests that genetic variations in SHP are common among human subjects and the Lys-170 residue plays a key role in controlling SHP ubiquitination and acetylation associated with SHP protein stability and repressive function.