Jan 2, 2014 - suggests that p53 activity is inhibited by Topors-mediated sumoylation of p53. Using co-immunoprecipitation. Figure 3: Role of thioredoxin in ...
Oncoscience 2014, Vol.1, No.1
www.impactjournals.com/oncoscience/
Cross talk between two antioxidant systems, Thioredoxin and DJ-1: consequences for cancer Prahlad V. Raninga1,2, Giovanna Di Trapani1, Kathryn F. Tonissen1,2 1
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Correspondence to: Kathryn F. Tonissen, email .7RQLVVHQ#JULIÀWKHGXDX Keywords: Thioredoxin, DJ-1, redox signalling, oxidative stress, antioxidants, cancer Received: December 4, 2013
Accepted: December 31, 2013
Published -DQXDU\
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
ABSTRACT: Oxidative stress, which is associated with an increased concentration of reactive oxygen species (ROS), is involved in the pathogenesis of numerous diseases including cancer. In response to increased ROS levels, cellular antioxidant molecules such as thioredoxin, peroxiredoxins, glutaredoxins, DJ-1, and superoxide dismutases DUHXSUHJXODWHGWRFRXQWHUDFWWKHGHWULPHQWDOHϑHFWRI526+RZHYHUFDQFHUFHOOV take advantage of upregulated antioxidant molecules for protection against ROS- induced cell damage. This review focuses on two antioxidant systems, Thioredoxin and DJ-1, which are upregulated in many human cancer types, correlating with tumour proliferation, survival, and chemo-resistance. Thus, both of these antioxidant PROHFXOHVVHUYHDVSRWHQWLDOPROHFXODUWDUJHWVWRWUHDWFDQFHU+RZHYHUWDUJHWLQJRQH RIWKHVHDQWLR[LGDQWVDORQHPD\QRWEHDQHϑHFWLYHDQWLFDQFHUWKHUDS\%RWKRIWKHVH antioxidant molecules are interlinked and act on similar downstream targets such as 1)Ȓǃ37(1DQG1UIWRH[HUWF\WRSURWHFWLRQ,QKLELWLQJHLWKHUWKLRUHGR[LQRU'- alone may allow the other antioxidant to activate downstream signalling cascades leading to tumour cell survival and proliferation. Targeting both thioredoxin and DJ-1 in conjunction may completely shut down the antioxidant defence system regulated by these molecules. This review focuses on the cross-talk between thioredoxin and DJ-1 and highlights the importance and consequences of targeting thioredoxin and '-WRJHWKHUWRGHYHORSDQHϑHFWLYHDQWLFDQFHUWKHUDSHXWLFVWUDWHJ\
INTRODUCTION
cellular ROS results in oxidative stress, which induces cell death by caspase activation, activation of Bcl-2 family proteins, and modulation of protein kinases [8]. ROS- induced oxidative stress is involved in the pathogenesis of a wide-variety of diseases including neurodegenerative GLVHDVHVLQÀDPPDWLRQFDUGLDFGLVHDVHDQGFDQFHU6LQFH an excess of ROS is detrimental to the cells or tissues, WKHLUGHWR[L¿FDWLRQLVHVVHQWLDO:LWKLQWKHFHOOVWKHUHLV a gambit of antioxidant molecules including thioredoxins [9, 10], glutaredoxins [11], peroxiredoxins [12] and other enzymes such as superoxide dismutase that detoxify ROS and maintain the balance between the generation and removal of oxidative species. During the past decade, DJ-1 has also emerged as an antioxidant molecule playing a crucial role in regulating cellular redox signalling cascades and inducing other antioxidants under oxidative stress FRQGLWLRQV > @ 6XFK DQWLR[LGDQW PROHFXOHV VHQVH
Cancer is currently one of the most deadly diseases worldwide. Amongst the many factors that cause cancer, oxidative stress is one of the most important and well- studied factors that give rise to the conditions leading to tumour development and progression [1]. Oxidative stress is associated with an increased concentration of reactive oxygen species (ROS). Depending on the cellular context, amount and exposure time, ROS can be either detrimental to the cells or important players in regulating various cellular responses including cell proliferation, differentiation, and apoptosis [2, 3]. It has been shown that low levels of ROS promote cell proliferation and differentiation by activating transcription factors, such as QXFOHDU IDFWRUɤȕ 1)ɤȕ >@ DQG DFWLYDWRU SURWHLQ (AP-1) [5-7]. On the other hand, excessive generation of www.impactjournals.com/oncoscience
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SK\VLRORJLFDOÀXFWXDWLRQVDQGLPEDODQFHRILQWUDFHOOXODU redox state and respond to such imbalance by activating appropriate signalling cascades. Despite the presence of such antioxidant defence systems within the cells, ROS generation often exceeds the antioxidant capacity of the cells leading to oxidative stress and ROS-induced cell death. In response to increased ROS levels, cells have evolved a number of survival pathways to counteract the toxic effect of ROS, which includes upregulation of antioxidant molecules and stress-response proteins. Upregulation of antioxidant molecules offer an advantage to the cells to eliminate the detrimental effects of ROS. However, cancer cells exploit this advantage and use it for their own protection against increased ROS levels. Antioxidant molecules have been shown to be upregulated in many human cancer types, correlating with tumour proliferation, survival, and drug resistance [15- 19]. Inhibition of elevated antioxidants inhibits tumour growth and metastasis, promotes tumour apoptosis, and reverses tumour resistance to chemotherapy, further implicating the functionality of antioxidant systems in cancer development and progression [20-23]. Thus, such deregulated antioxidants may serve as potential molecular targets to develop new single or combinatory anti-cancer therapy. In this review, we describe the role of DJ-1 and thioredoxin in cellular redox signalling and discuss the cross-talk between these two antioxidant systems to balance the cellular redox state. An understanding of the FURVVWDONEHWZHHQ'-DQG7U[PD\KHOSXVLQ¿QGLQJ novel therapeutic targets for the treatment of many types of human cancers, where antioxidants are upregulated.
H[DPSOH/3LVUHVSRQVLEOHIRUVHYHUHGHVWDELOLVDWLRQ RIWKH'-SURWHLQ>@ Structure, Expression and Function of DJ-1 DJ-1 is a 189 amino acid protein dimer consisting of QLQHĮKHOLFVDQGVHYHQȕVWUDQGV> @7KHVWUXFWXUHRI the DJ-1 protein is similar to the monomer subunit of the intracellular cysteine protease from Pyrococcushorikoshii, SURWHDVH>@EXW'-FRQWDLQVDQH[WUDĮKHOL[DW the C-terminal region blocking the putative catalytic site RI'-XQGHUQRUPDOFRQGLWLRQV7KLVDGGLWLRQDOĮKHOL[ may undergo conformational changes under oxidative stress leading to the activation of DJ-1 catalytic site [35, 37]. DJ-1 is abundantly present in the majority of cells DQGWLVVXHVLQWKHERG\>@WKHUHIRUHWKHUHDUHQRFOXHV IRU FHOO RU WLVVXH VSHFL¿F IXQFWLRQV RI '- '- LV located in the cytosol, nucleus and mitochondria of the cells and it has also been reported to be secreted from the cells or tissues in cancer and Parkinson’s disease patient’s VHUXPDQGIURPDVWURF\WHV> @8SRQH[SRVXUH to growth factors and oxidative stress stimuli, DJ-1 translocates to the nucleus when cells are in the S phase of WKHFHOOF\FOH>@ DJ-1 has been implicated in many biological IXQFWLRQVLQFOXGLQJWUDQVFULSWLRQDOUHJXODWLRQ>@ FKDSHURQHDFWLYLW\UHJXODWLRQ> @SURWHDVHIXQFWLRQ UHJXODWLRQ >@ DQG PLWRFKRQGULDO UHJXODWLRQ > @ 2IPRVWVLJQL¿FDQFHFRQVLVWHQW¿QGLQJVGHPRQVWUDWHDQ antioxidant activity as well as a cytoprotective function against oxidative stress [52, 53] and a role in increasing cell survival under pro-apoptotic stimuli challenge >@ (YLGHQFH IRU DQ DQWLR[LGDQW IXQFWLRQ RI '- LQ neuronal cells comes from various studies. Rotenone DQG K\GUR[\GRSDPLQHLQGXFHG R[LGDWLYH VWUHVV LQ neuroblastoma cells have upregulated endogenous DJ-1 SURWHLQ DQG P51$ OHYHOV DQG LQGXFHG WUDQVORFDWLRQ of DJ-1 from the cytoplasm to the mitochondria to H[HUW QHXURSURWHFWLRQ IXQFWLRQ >@ 2YHUH[SUHVVLRQ of wild-type DJ-1, but not the mutant forms including /3 &6 0, DQG 5 4 SURWHFWV QHXURQV against ROS producing stress insult [55]. Several reports describe different mechanisms by which DJ-1 exerts its neuroprotective effects. DJ-1 protects primary dopaminergic neurons against hydrogen peroxide (H2O2)
DJ-1 '- ZDV LGHQWL¿HG \HDUV DJR DV D SXWDWLYH RQFRJHQHWUDQVIRUPLQJPRXVH1,+7FHOOVZHDNO\RQ LWV RZQ DQG VWURQJO\ LQ FRPELQDWLRQ ZLWK +5DV >@ Several studies have shown that the expression of DJ-1 is increased in several cancer types as compared to non- cancerous cells. High DJ-1 expression has been observed LQSULPDU\OXQJDQGSURVWDWHFDQFHUELRSVLHV>@LQ non-small cell lung carcinoma patients [27] as well as in endometrial cancer patients [28]. Proteomic studies have LGHQWL¿HG '- DV D VHFUHWHG WXPRXU DQWLJHQ LQ EUHDVW cancer patients [29] and as a potential biomarker secreted in uveal malignant melanoma patients [30]. '- ZDV ¿UVW DVVRFLDWHG ZLWK QHXURGHJHQHUDWLRQ when a large deletion and missense mutation in the DJ-1 gene in Italian and Dutch Parkinson’s disease patients was IRXQGOHDGLQJWRLGHQWL¿FDWLRQRIWKH'-JHQHDVVRFLDWHG with autosomal recessive early-onset Parkinson’s disease [31]. Apart from the large genomic deletion within the DJ-1 coding region, there are other point mutations also responsible for the Parkinson’s disease condition for www.impactjournals.com/oncoscience
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Figure 1: Summary of DJ-1 functions by regulating redox sensitive transcription factors and signalling pathways. 96
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DQG K\GUR[\GRSDPLQHLQGXFHG R[LGDWLYH VWUHVV E\ upregulating intracellular glutathione synthesis via LQFUHDVLQJJOXWDPDWHF\VWHLQHOLJDVHHQ]\PH>@'- also protects dopaminergic neurons from the toxic effects RI PXWDQW KXPDQ ĮV\QXFOHLQ E\ LQFUHDVLQJ KHDW VKRFN SURWHLQH[SUHVVLRQZLWKLQWKHFHOOV>@7DNHQWRJHWKHU these results suggest DJ-1 may exert neuroprotective action by different mechanisms, which may depend on the type of stress stimuli. In contrast to DJ-1 overexpression, VL51$PHGLDWHGGRZQUHJXODWLRQRI'-UHQGHUVFHOOV VXVFHSWLEOHWRXQGHUJRGHDWKXQGHUR[LGDWLYHVWUHVV(5 VWUHVVDQGSURWHDVRPHLQKLELWLRQ>@FRQ¿UPLQJWKHUROH of DJ-1 in protecting cells against oxidative stress. The crystal structure of DJ-1 reveals the presence RIWKUHHUHGR[VHQVLWLYHF\VWHLQHUHVLGXHV&\V&\V DQG &\V $PRQJVW WKHVH WKUHH F\VWHLQH UHVLGXHV &\V LV WKH PRVW VXVFHSWLEOH WR R[LGDWLYH VWUHVV DQG can be oxidized to SOH, SO2H, and then SO3H [50, 57]. 0DQ\VWXGLHVKDYHFRQ¿UPHGWKDW'-UHTXLUHV&\V to exert its cytoprotection against oxidative stress [50, @ZKHUHDVRQO\RQHVWXG\LGHQWL¿HV&\VDVWKH IXQFWLRQDOO\DFWLYHDQGHVVHQWLDOUHVLGXH>@0XWDWLRQ RI &\V DEROLVKHV DOO IXQFWLRQV RI '- > @ 0LOG R[LGDWLRQ RI &\V WR 622H is critical for the F\WRSURWHFWLYH IXQFWLRQ RI '- > @ 2[LGDWLRQ RI &\VWR622H increases the mitochondrial localization of DJ-1 and allows the direct binding of DJ-1 to apoptosis signal-regulating kinase 1 (ASK1) to inhibit the activation RI$6.PHGLDWHGDSRSWRVLV>@)XUWKHUR[LGDWLRQRI &\VIURP622H to SO3H results in the aggregation of '-ZKLFKOHDYHV'-LQLWVLQDFWLYHIRUP>@$QDO\VLV of the oxidation state of DJ-1 in post-mortem brain tissue
of Parkinson’s and Alzheimer’s patients as well as in healthy individuals has revealed that DJ-1 from diseased tissue was extensively oxidized as compared to healthy FHOOV>@,QFRQFOXVLRQWKHPLOGR[LGL]HGIRUPRI'-LV associated with its cytoprotective action by binding to its target molecules and regulating their activity, whereas the highly oxidized form of DJ-1 is associated with diseased conditions. Role of DJ-1 in regulating transcription factors under oxidative stress DJ-1 functions as an antioxidant when cells experience oxidative stress and acts to induce the H[SUHVVLRQRIVHYHUDODQWLR[LGDQWHQ]\PHV>@)RU example, DJ-1 increases the expression of glutamate cysteine ligase, which is a rate-limiting enzyme for LQWUDFHOOXODU JOXWDWKLRQH ELRV\QWKHVLV >@ ZKLOH GRZQ regulation of DJ-1 results in a decrease in expression of H[WUDFHOOXODUVXSHUR[LGHGLVPXWDVH 62' >@8QGHU oxidative stress conditions, DJ-1 has been shown by many studies to regulate various transcription factors and transmit downstream signals to respond to oxidative stress. )RUH[DPSOH'-KDVEHHQVKRZQWRUHJXODWHWKHVWHURO UHJXODWRU\ ELQGLQJ SURWHLQ 65(%3 D WUDQVFULSWLRQ IDFWRUWKDWUHJXODWHVFKROHVWHUROV\QWKHVLV>@5HSRUWHU gene assays were used to show that over expression of DJ-1 increased the promoter activity of the low-density lipoprotein receptor (LDLR) gene and this activity was IXUWKHU HQKDQFHG E\ R[LGDWLYH VWUHVV >@ %\ XVLQJ chromatin immunoprecipitation (ChIP), gel-mobility shift and co-immunoprecipitation, it has been shown that DJ-1 IRUPVDFRPSOH[ZLWK65(%3ZKLFKELQGVWRWKHVWHURO
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Figure 2: Regulation of ASK1/Trx1 by DJ-1 under oxidative stress. A. In the absence of DJ-1, ASK1 is dissociated from Trx1 XQGHUR[LGDWLYHVWUHVVFRQGLWLRQVDQGJHWVDFWLYDWHG$FWLYDWHG$6.DFWLYDWHV-1.DQGUHVXOWVLQFHOOGHDWK%2YHUH[SUHVVLRQRI'- inhibits dissociation of ASK1 from Trx1 under oxidative stress and thus, inhibits ASK1 activation and exerts cytoprotection. www.impactjournals.com/oncoscience
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UHJXODWRU\ HOHPHQW 65( LQ WKH /'/5 JHQH SURPRWHU >@ 6HYHUDOVWXGLHVKDYHLGHQWL¿HG'-DVDSRVLWLYH regulator of another transcription factor, the androgen UHFHSWRU $5 HLWKHULQGLUHFWO\>@RUGLUHFWO\> @ PIAS-alpha, a protein inhibiting androgen receptor WUDQVFULSWLRQDFWLYLW\KDVEHHQLGHQWL¿HGDVD'-ELQGLQJ SURWHLQE\D\HDVWWZRK\EULGVFUHHQ>@'-KDVEHHQ shown to bind to the AR-binding region of PIAS-alpha in vitro by co-immunoprecipitation and in vivo in human 293T cells resulting in the inhibition of PIAS-alpha and therefore, activation of androgen receptor transcription DFWLYLW\ >@ $QRWKHU VWXG\ XVLQJ D \HDVW WZRK\EULG screen has shown that DJ-1 can also directly bind to the DQGURJHQUHFHSWRU> @ 1XFOHDUIDFWRU HU\WKURLGGHULYHG OLNH 1UI is a redox-sensitive transcription factor, which serves as a master regulator of antioxidant and detoxifying genes under oxidative stress via the antioxidant response HOHPHQW $5( >@ 8QGHU QRUPDO FRQGLWLRQV 1UI LV localized in the cytoplasm and forms a complex with Kelch-like erythroid cell-derived protein-1 (Keap1) [71]. .HDSLVDQHJDWLYHUHJXODWRURI1UIDVLWWDUJHWV1UI IRUGHJUDGDWLRQE\WKHXELTXLWLQSURWHRVRPHV\VWHP>@ 7KUHH F\VWHLQH UHVLGXHV KDYH EHHQ LGHQWL¿HG LQ .HDS WKDWDUHLQYROYHGLQWKHUHJXODWLRQRI1UI>@7ZRRI WKHVH F\VWHLQH UHVLGXHV DUH UHTXLUHG IRU XELTXLWLQDWLRQ DQG GHJUDGDWLRQ RI 1UI LQ WKH F\WRSODVP ZKHUHDV WKH third cysteine residue acts as a redox sensor, leading to conformational changes of Keap1 under oxidative stress [72]. These changes result in the prevention of Keap1- GHSHQGHQWLQKLELWLRQRI1UI>@'-KDVEHHQVKRZQ WRVWDELOL]HWKH1UISURWHLQE\SUHYHQWLQJLWVDVVRFLDWLRQ with Keap1. Co-immunoprecipitation experiments
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pathway. Over-expression of DJ-1 leads to increased phosphorylation of P13K targets, leading to increased cell survival [27]. H2O2-induced oxidative stress inactivates 37(1 OHDGLQJ WR WKH DFWLYDWLRQ RI GRZQVWUHDP FHOO JURZWKVLJQDOOLQJPROHFXOHVLQFOXGLQJ$NWSURWHLQNLQDVH B [78]. Using co-immunoprecipitation and pull-down DVVD\VZLOGW\SHDQG&6PXWDQW'-ZHUHVKRZQWR LQWHUDFWGLUHFWO\ZLWK37(1LQPRXVH1,17FHOOV> @ Under oxidative stress, oxidized DJ-1 directly binds to 37(1GHFUHDVHVLWVSKRVSKDWDVHDFWLYLW\DQGLQFUHDVHV phosphorylation of AKT, resulting in the transmission RIFHOOVXUYLYDOVLJQDOVLQ1,+7FHOOV> @7KXV'- activates a cell growth signalling cascade by inhibiting 37(1DQGUHVXOWLQJLQDFWLYDWLRQRIWKH3,.VLJQDOOLQJ pathway. It can be hypothesized that inhibition of DJ-1 may prevent PI3K-regulated cell proliferation signalling pathways. This may result in a new therapeutic regime for the treatment of cancers where DJ-1 is over-expressed DQGOHDGVWRWKHDFWLYDWLRQRIWKH3,.$NW3.%VLJQDOOLQJ axis. DJ-1 exerts cytoprotective action against ultraviolet (UV)-induced oxidative stress by directly interacting with PLWRJHQDFWLYDWHG SURWHLQ NLQDVHH[WUDFHOOXODU VLJQDO UHJXODWHGNLQDVHNLQDVHNLQDVH 0(.. VXSSUHVVLQJ 0(.. DFWLYLW\ DQG DFWLQJ DV D QHJDWLYH UHJXODWRU RI WKH-1.VLJQDOOLQJFDVFDGHWRVXSSUHVVFHOOGHDWK> @ 7KH H[WUDFHOOXODU VLJQDOUHJXODWHG NLQDVH (5. LV WKH main pathway leading to cell-migration and is essential IRUQHXURSURWHFWLRQ7KH(5.VLJQDOOLQJFDVFDGHVFDQ EHPRGL¿HGZKHQWKHUHGR[VWDWHRIWKHFHOOVFKDQJHVLQ Parkinson’s disease. It was reported that over-expression of wild-type DJ-1 enhanced the phosphorylation of (5.DQGXSVWUHDPNLQDVH0(.>@'-LQGXFHG DFWLYDWLRQ RI WKH (5. VLJQDOOLQJ SDWKZD\ UHVXOWHG LQ increased cell viability and cytoprotection against H2O2 [80]. Conversely, another study has reported that DJ-1 LV XSUHJXODWHG E\ WKH DFWLYDWLRQ RI WKH 0$3 NLQDVH SDWKZD\YLDLQFUHDVHG(5.SKRVSKRU\ODWLRQLQKXPDQ neuroblastoma cells exposed to dopamine [52]. This FRQFOXVLRQ ZDV PDGH XVLQJ 0$3.. LQKLELWRUV ZKLFK prevented the dopamine induced DJ-1 up-regulation. However, a more recent study showed DJ-1 could protect dopaminergic neurons against rotenone-induced apoptosis E\LQFUHDVLQJSKRVSKRU\ODWLRQRI(5.DQGWKXVLQGXFLQJ mitophagy [81]. Thus, mounting evidence suggests that DJ-1 may exert its cytoprotective function through the (5.VLJQDOOLQJSDWKZD\WRSURPRWHFHOOVXUYLYDOXQGHU oxidative stress. Stable overexpression of DJ-1 protects cardiac cells against oxidative stress generated by increased ROS levels under hypoxic conditions [82]. The authors showed that RYHUH[SUHVVLRQRI'-LQFDUGLDFFHOOVUHGXFHVLVFKHPLD UHSHUIXVLRQ V,5 LQGXFHG526JHQHUDWLRQXSUHJXODWHV WKHH[SUHVVLRQRIDQWLR[LGDQWHQ]\PHVDQGSUHYHQWVV, R-induced oxidative stress [82]. The results from these cardiac cell studies suggest that DJ-1 has a potential role
assays, DJ-1 was shown to bind to p53 in vivo as well as in vitro. Using luciferase assays and co-immunoprecipitation experiments, DJ-1 was shown to restore the transcriptional DFWLYLW\RISWKURXJK6802FRQMXJDWLRQVXJJHVWLQJ WKDW '- PD\ DFW DV D SRVLWLYH UHJXODWRU RI S >@ Conversely, other studies have shown that DJ-1 inhibits the transcriptional activity of p53. Co-immunoprecipitation studies have shown that DJ-1 physically interacts with p53 in vitro as well as in vivo resulting in the inhibition of SWUDQVFULSWLRQDFWLYLW\>@'-PHGLDWHGUHSUHVVLRQ of p53 transcription activity leads to the down-regulation RI%D[DQGVXSSUHVVLRQRIFDVSDVHFOHDYDJH>@$QRWKHU study has reported that the oxidized form of DJ-1 binds WR WKH '1$ELQGLQJ UHJLRQ RI S DQG LQKLELWV S WUDQVFULSWLRQDFWLYLW\ZKHQ'1$ELQGLQJDI¿QLW\RIS LVORZ>@:KHWKHU'-DFWVDVDSRVLWLYHRUQHJDWLYH regulator of p53 transcriptional activity may depend on the extent of oxidation of DJ-1. Another important transcription factor regulated E\ '- LV QXFOHDU IDFWRUɤȕ 1)ɤ% '- GLUHFWO\ interacts with one of its binding partners, Cezanne, which is a physiological inhibitor of the transcription activity of 1)ɤȕ>@7KHLQWHUDFWLRQRI'-ZLWK&H]DQQHZDV shown by mass spectrometry and co-immunoprecipitation. 7KLVLQWHUDFWLRQLQKLELWVWKHGHXELTXLWLQDWLRQDFWLYLW\RI &H]DQQHDOORZLQJWKHDFWLYDWLRQRI1)ɤȕWUDQVFULSWLRQ activity. Thus, DJ-1 has been reported to be a positive UHJXODWRU RI 1)ɤȕ ZKLFK KLJKOLJKWV DQRWKHU SRWHQWLDO mechanism by which DJ-1 promotes cell survival in cancer >@$VXPPDU\RIWKHWUDQVFULSWLRQIDFWRUVUHJXODWHGE\ '-DQGLWVGRZQVWUHDPIXQFWLRQVDUHGHVFULEHGLQ)LJXUH 7DNHQ DOO WRJHWKHU WKHVH ¿QGLQJV VXSSRUW WKH suggestion that DJ-1 might be a master upstream regulator of various transcription factors and pathways regulating various cellular responses including cell proliferation and apoptosis. Therefore, DJ-1 can serve as a potential therapeutic target for different cancer types where such transcription factors are deregulated. DJ-1-Induced Signal Transduction under Oxidative Stress In addition to the roles of DJ-1 in the regulation of various transcription factors, many studies have reported an involvement of DJ-1 in various signalling pathways and interactions with different signalling molecules. Several studies have reported the role of DJ-1 in regulating the tumour suppressor protein, phosphatase and tensin KRPRORJ 37(1 > @8VLQJDJHQHWLFVFUHHQRI Drosophila gain-of-function mutants, DJ-1 was shown to EHDQHJDWLYHUHJXODWRURI37(1IXQFWLRQVUHVXOWLQJLQWKH XSUHJXODWLRQRIWKHSKRSKRLQRVLWLGHNLQDVH 3,. $NW VLJQDOOLQJSDWKZD\>@7KH3,.$NWSDWKZD\LVDUHGR[ sensitive growth signalling pathway [78]. Once activated, 3,. FDXVHV SKRVSKRU\ODWLRQ RI $NWSURWHLQ NLQDVH % 3.% ZKLFK VWLPXODWHV FHOO JURZWK 37(1 LQKLELWV 3,. DQG QHJDWLYHO\ UHJXODWHV WKH 3,.$NW VLJQDOOLQJ
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in inhibiting hypoxia-induced cell death and thus, emerges as a possible novel therapeutic target for the treatment of hypoxic tumour cells. Another important signalling pathway that gets activated under oxidative stress is the Apoptosis Signal- regulating Kinase 1 (ASK1) pathway. ASK1 is an important component in activating the apoptosis signalling machinery induced by ROS generating cytotoxic stress > @ 2[LGDWLYH VWUHVV LQGXFHG E\ +2O2 causes dimerization of ASK1 and leads to its activation [85]. There are many studies showing the involvement of DJ-1 with ASK1 signalling cascades under oxidative VWUHVV>@8QGHUR[LGDWLYHVWUHVVFRQGLWLRQV 'HDWKDVVRFLDWHGSURWHLQ 'D[[ WUDQVORFDWHVIURPWKH nucleus to the cytoplasm and interacts directly with ASK1, resulting in activation of the ASK1-mediated apoptotic VLJQDOOLQJ SDWKZD\ >@ 2WKHU VWXGLHV KDYH VKRZQ that wild-type DJ-1 exerts a cytoprotective action by VHTXHVWHULQJ'D[[LQWKHQXFOHXVLQ+2O2-treated cultured PDPPDOLDQFHOOVDVZHOODVLQ0373WUHDWHG3DUNLQVRQ¶V GLVHDVHPRGHOPLFH>@6HTXHVWUDWLRQRI'D[[E\ DJ-1 impedes its translocation into the cytoplasm, resulting LQ WKH SUHYHQWLRQ RI $6.'D[[ FRPSOH[ IRUPDWLRQ such that activation of apoptotic signal transmission does not occur. DJ-1 also binds directly to ASK1 under oxidative stress and inhibits its kinase activity, resulting in the inhibition of p38 mitogen-activated protein kinase 0$3. VLJQDOOLQJ FDVFDGH DQG SUHYHQWLQJ FHOO GHDWK VLJQDOV >@ 8QGHU EDVDO FRQGLWLRQV$6. LV ERXQG WR and inhibited by a physiological inhibitor, Thioredoxin1 (Trx1). Upon oxidative stress, Trx1 dissociates from ASK1 and thus ASK1 is activated, resulting in the transmission of apoptosis-inducing signals through its kinase activity > @'-KDVEHHQVKRZQWREHDUHJXODWRURIWKH$6.
7U[ LQWHUDFWLRQ :LOGW\SH '- KDV EHHQ UHSRUWHG WR prevent the dissociation of ASK1 from Trx1 under H2O2- induced oxidative stress in a cultured mammalian cell line as well as in mice whole brain homogenates using co-immunoprecipitation experiments [58]. DJ-1, by KLQGHULQJ $6.7U[ GLVVRFLDWLRQ KDV EHHQ VKRZQ WR VXSUHVVHV-1.DFWLYDWLRQDQGWKXVSUHYHQWV+2O2-induced cell death [58]. Thus, it is interesting to note that DJ-1 and thioredoxin, known for antioxidant functions, are linked together and play a role in cytoprotection. A schematic representation of the interaction of ASK-1 and Trx and the regulation of this complex by DJ-1 under oxidative stress LVLOOXVWUDWHGLQ)LJXUH Thus, DJ-1 is involved in multiple redox signalling SDWKZD\V LQFOXGLQJ WKH '-$6.7U[ D[LV ZKLFK transmit cell proliferation signals. This indicates that targeted inhibition of DJ-1 may help in deactivating redox- responsive signalling events, altering the antioxidant activity of Trx1 and other antioxidant molecules to VWLPXODWHFHOOGHDWKLQFDQFHUDQGRWKHUGLVHDVHV)LJXUH 1 summarises the action of DJ-1 on various signalling molecules and its function.
The Thioredoxin System The thioredoxin system is one of the most important antioxidant system present in all species [9, 10]. The thioredoxin system is comprised of thioredoxin reductase 7U[5 HQ]\PH1$'3+DQGWKLRUHGR[LQ 7U[ 7U[KDV a conserved Cys-Gly-Pro-Cys redox catalytic site, which reduces the target proteins [9]. TrxR transfers reducing HTXLYDOHQWVIURP1$'3+WR7U[DQGUHGXFHVWKHDFWLYH VLWHGLVXO¿GHRIR[LGL]HG7U[ 7U[62) to a dithiol (Trx-
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Nrf2 Ubiquitination
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Figure 4: Induction of Trx1 expression by DJ-1 via the Nrf2 pathway. Under oxidative stress, DJ-1 inhibits the interaction EHWZHHQ1UIDQGLWVLQKLELWRU.HDSUHVXOWLQJLQDFWLYDWLRQRI1UI$FWLYDWHG1UIWUDQVORFDWHVWRWKHQXFOHXVDQGELQGVWKH$5(HOHPHQW LQWKH7U[SURPRWHUDQGLQGXFHV7U[H[SUHVVLRQ)LJXUHDGDSWHGDQGXVHGZLWKSHUPLVVLRQIURPWKHDXWKRUV>@ www.impactjournals.com/oncoscience
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(SH)2 7KH PDPPDOLDQ WKLRUHGR[LQ V\VWHP LV TXLWH complex and both Trx and TrxR are expressed as different isoforms;; Trx as Trx1 and Trx2, and TrxR as TrxR1 and TrxR2. Trx1 and TrxR1 are predominantly expressed in the cytosol, whereas Trx2 and TrxR2 are expressed in the mitochondria. All four of these genes are essential, since knockout mice lacking any of these four genes die early, during embryogenesis [90-93]. Another mammalian 7U[5KDVDOVREHHQLGHQWL¿HGSUHGRPLQDQWO\H[SUHVVHGLQ testis, which has the potential to reduce not only Trx but DOVRJOXWDWKLRQHGLVXO¿GH7KHUHIRUHWKLV7U[5LVRIRUPLV WHUPHGWKHWKLRUHGR[LQJOXWDWKLRQHUHGXFWDVH 7*5 > @ Amongst all the members of thioredoxin system, Trx1 and TrxR1 have emerged as critical redox regulators and as potential therapeutic targets for many human cancer types [17, 20, 95].
Several studies have reported the involvement of Trx1 in regulating the activity of p53 [105-108]. By using electrophoretic mobility shift assays, it was shown that Trx HQKDQFHGWKHVHTXHQFHVSHFL¿F'1$ELQGLQJDFWLYLW\RI p53 in a Ref-1 dependent as well as independent manner [105]. Using luciferase assays, Trx was shown to stimulate the Ref-1 mediated transactivation of p53, which suggests an importance of functional coupling between Trx and Ref-1 in activating the p53 signalling cascade [105]. )XUWKHUPRUH7U[ KDV DOVR EHHQ VKRZQ WR EH SRVLWLYHO\ DVVRFLDWHGZLWKSLQGXFHG'1$UHSDLULQEUHDVWFDQFHU FHOOV>@ Trx1 has been implicated in the regulation of the WXPRXUVXSSUHVVRUDFWLYLW\RI37(1> @EXWWKHUH LVDGLVFUHSDQF\LQWKHGDWD37(1LVDUHGR[VHQVLWLYH tumour suppressor, which is inactivated by H2O2-induced 526JHQHUDWLRQ37(1H[SRVXUHWR526UHVXOWVLQWKH formation of an intramolecular disulphide bond involving D UHGR[ VHQVLWLYH F\VWHLQH UHVLGXH &\V SUHVHQW LQ WKH DFWLYH VLWH RI 37(1 ZKLFK LQKLELWV 37(1 WXPRXU suppressor activity [109]. As described earlier, inhibition RI37(1UHVXOWVLQWKHDFWLYDWLRQRI$NWSURWHLQNLQDVH% and promotes cell survival. Using co-immunoprecipitation assays, Trx was shown to bind to an inactive oxidized IRUPRI37(1DQGWRUHGXFHLWUHVXOWLQJLQWKHDFWLYDWLRQ RI 37(1 DFWLYLW\ > @$QRWKHU VWXG\ XVHG PROHFXODU docking studies and site-directed mutagenesis to also show that the reduced form of Trx1 directly binds to the C2 GRPDLQRI37(1E\IRUPLQJDGLVXOSKLGHERQGEHWZHHQ WKH&\VRI7U[DQG&\VRI37(1>@,QFRQWUDVW WRWKHSUHYLRXVVWXG\WKLVELQGLQJRI7U[WR37(1UHVXOWV in the inactivation of the lipid phosphatase activity and PHPEUDQHELQGLQJRI37(1 )LJXUH >@+HQFH7U[ KDVEHHQUHSRUWHGWRLPSHGH37(1DFWLYLW\DVZHOODVWR VWLPXODWH37(1IXQFWLRQV:KLOHWKHH[DFWUROHRI7U[ LQUHJXODWLQJ37(1DFWLYLW\UHPDLQVDWRSLFRIGHEDWHD UHFHQWVWXG\KDVVKRZQWKDW7U[LQKLELWV37(1DFWLYLW\LQ QHXUREODVWRPDFHOOV>@7KXV7U[E\LQKLELWLQJ37(1 activity, may result in tumour cell proliferation. Taken all WRJHWKHU WKH7U[37(1 D[LV PD\ EH FRQVLGHUHG DV DQ effective molecular target for the treatment of cancers with KLJKHU7U[OHYHOVDQGORZHUHG37(1DFWLYLW\ Another target of Trx is ASK1 [89]. In the cytoplasm Trx1 has been shown to directly bind to Cys-250 in the 1WHUPLQDO UHJLRQ RI $6. FDXVLQJ LQKLELWLRQ RI LWV kinase activity [112]. In the mitochondria Trx2 has been VKRZQWRGLUHFWO\ELQGWR&\VLQWKH1WHUPLQDOUHJLRQ of ASK1, resulting in the inhibition of ASK1 activity [112]. Thus, ASK1 is regulated by both cytosolic and mitochondrial thioredoxin in an independent manner. ASK1 is activated by a variety of external stress stimuli including ROS. Under normal conditions the reduced form of Trx1 [Trx1-(SH)2] binds to ASK1, but under oxidative stress conditions the reduced form of Trx1 is converted to its oxidized form (Trx1-S2) and results in the dissociation of Trx1 from ASK1 [89, 112, 113]. This dissociation
Regulation of thioredoxin system under oxidative stress Under oxidative stress conditions, the induction of WKLRUHGR[LQ H[SUHVVLRQ LV UHJXODWHG E\ DQ$5( SUHVHQW in the promoter region of the Trx1 gene, which is bound E\1UI> @8SRQDFWLYDWLRQ1UILVWUDQVORFDWHGWRWKH nucleus where it forms a heterodimer with maf proteins. 6HYHUDOVWXGLHVKDYHUHSRUWHGWKDWWKH1UI0DIFRPSOH[ WKHQELQGVWRWKH$5(HOHPHQWLQWKHSURPRWHUUHJLRQRI the target antioxidant genes [97] including thioredoxin > @DQGWKLRUHGR[LQUHGXFWDVH> @DQGLQFUHDVHVWKHLU expression. Role of Trx in intracellular redox signalling pathways Being critical redox regulators, Trx and TrxR are involved in a number of intracellular redox signalling pathways by activating a number of redox-sensitive WUDQVFULSWLRQ IDFWRUV UHTXLUHG IRU YDULRXV FHOOXODU processes. Trx is usually present in the cytoplasm, but under certain circumstances it is translocated to the nucleus. In the nucleus, Trx has been shown to activate redox sensitive WUDQVFULSWLRQIDFWRUVLQFOXGLQJ1)ɤȕ>@8QGHUQRUPDO FRQGLWLRQV1)ɤȕLVSUHVHQWLQWKHF\WRSODVPZKHUHLWLV LQKLELWHGDQGVHTXHVWHUHGE\LWVSK\VLRORJLFDOLQKLELWRU LQKLELWRURIɤȕ ,ɤȕ 8QGHUR[LGDWLYHVWUHVV526UHOHDVHV ,ɤȕ VXEXQLW IURP 1)ɤȕ ZKLFK LV WKHQ WUDQVORFDWHG WR WKHQXFOHXV>@,QWKHQXFOHXV7U[UHGXFHV&\VLQ WKH 1)ɤȕ VXEXQLW S DOORZLQJ 1)ɤȕ WR ELQG WR WKH recognition site present on the promoter region of its target genes, which are involved in cellular processes including, FHOOJURZWKDQGVXUYLYDO )LJXUH >@7U[DOVR regulates the activity of other transcription factors such as Activator protein-1 (AP-1), via Redox factor-1 (Ref-1). Trx reduces Ref-1 in the nucleus, which in turn reduces F\VWHLQH UHVLGXHV SUHVHQW LQ WKH '1$ELQGLQJ GRPDLQV RI)RVDQG-XQDQGWKXVDFWLYDWHV$3 )LJXUH >@ Using in vitro diamide-induced cross-linking study and in vivo mammalian two-hybrid assays, Trx1 was shown to directly bind to Ref-1 in the nucleus and to activate the WUDQVFULSWLRQDODFWLYLW\RI$3>@ www.impactjournals.com/oncoscience
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results in the activation of ASK1 kinase activity, which stimulates the apoptotic signalling cascade in the cells )LJXUH$ 7KH(5.SDWKZD\LVDOVRUHGR[UHJXODWHGE\7U[ Recent evidence suggests that the loss of Trx1 or TrxR1 VHQVLWLVHGDPRXVHPDPPDU\FDUFLQRPDFHOOOLQH (07 WRWXPRXUQHFURVLVIDFWRU±Į 71)Į LQGXFHGDSRSWRVLV E\ LQFUHDVLQJ QXFOHDU ORFDOL]DWLRQ RI S(5. LQ D 3,. GHSHQGHQW PDQQHU >@ 7KLV PD\ VXJJHVW WKDW increased Trx1 or TrxR1 levels in cancer cells prevents QXFOHDUWUDQVORFDWLRQRIS(5.DQGWKHUHIRUHSURWHFWV FHOOV DJDLQVW 71)ĮPHGLDWHG DSRSWRVLV ,QWHUHVWLQJO\ F\WRSODVPLFDQGPLWRFKRQGULDOORFDOL]DWLRQRIS(5. LQ7U[RU7U[5GH¿FLHQW(07FHOOVKDYHQRWVHQVLWLVHG FHOOVWR71)ĮLQGXFHGDSRSWRVLV7KHVHUHVXOWVLQGLFDWH WKDWWKHVXEFHOOXODUORFDOL]DWLRQRIS(5.LVDFULWLFDO determinant of whether cancer cells with compromised Trx levels or activity will undergo stress stimuli-induced DSRSWRVLV>@ Thus, Trx1 is involved in multiple redox-regulated signalling pathways in cancer by regulating redox- sensitive transcription factors and signalling molecules )LJXUH 7DNHQWRJHWKHUPRGXODWLRQRI7U[H[SUHVVLRQ and activity in diseased cells leads to the modulation of the signal transmission regulated by various transcription factors and may emerge as an effective therapeutic
approach to overcome cancer.
Cross-talk between two antioxidant molecules: DJ-1 and Thioredoxin Oxidative stress is one of the major factors giving rise to diseased conditions. As discussed above, DJ-1 and Trx are two important antioxidant molecules that play crucial roles in maintaining the intracellular redox state and provide cytoprotection against oxidative stress. DJ-1 has been shown to exert cytoprotection against R[LGDWLYHVWUHVVLQ3DUNLQVRQ¶VGLVHDVH>@'- protein levels are increased in a number of human cancer types as compared to normal cells or tissues and promote cell survival and resistance against apoptosis [25-30]. 6LPLODUO\7U[SURWHLQOHYHOVDUHVLJQL¿FDQWO\XSUHJXODWHG in many human cancer cell types including gastric, lung, colon, liver, and pancreatic cancers [17, 115-117] to provide protection against ROS-mediated cell death. Both DJ-1 and Trx1 were considered as two separate intracellular antioxidant systems until two independent studies reported the interaction between DJ-1 and Trx1 [58, 118]. DJ-1 has been shown to enhance Trx1 expression by activating the transcriptional activity RI 1UI in vitro as well as in vivo )LJXUH >@
Cytoprotection
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Figure 5: Consequences of targeting each antioxidant, Trx1 and DJ-1, alone or in combination in cancer. Both Trx1 DQG'-H[HUWF\WRSURWHFWLRQE\LQGHSHQGHQWPHFKDQLVPVDVZHOODVE\DFWLQJRQFRPPRQWDUJHWVVXFKDV1)ɤ%DQG37(17DUJHWLQJ '-DORQHPD\QRWEHVXI¿FLHQWWRLQGXFHFHOOGHDWKVLQFH1UIFDQDOVREHDFWLYDWHGE\RWKHUVWUHVVVWLPXOLOHDGLQJWR7U[XSUHJXODWLRQ 0RUHRYHU7U[DOVRDFWLYDWHV1)ɤ%DQGLQKLELWVWKHWXPRXUVXSSUHVVRUDFWLYLW\RI37(1OHDGLQJWRFHOOVXUYLYDODQGWXPRXUJURZWK7KXV even after inhibition of DJ-1, all other cytoprotective machineries are functional and may promote tumour growth. Similarly, targeting Trx1 DORQHPD\QRWLQGXFHFDQFHUFHOOGHDWKVLQFH'-PD\DFWLYDWHRWKHU1UIWDUJHWHGF\WRSURWHFWLYHJHQHVRUDFWLYDWHV1)ɤ%RULQKLELWV WXPRXUVXSSUHVVRUDFWLYLW\RI37(1UHVXOWLQJLQFHOOVXUYLYDODQGWXPRXUJURZWK2QWKHRWKHUKDQGWDUJHWLQJ7U[DQG'-WRJHWKHUPD\ completely shut down all the cytoprotective machineries regulated by these antioxidants and leads to cancer cell apoptosis. Hence, targeting two or more antioxidants in conjunction may prove an effective therapy to treat cancer.. www.impactjournals.com/oncoscience
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Overexpression of wild-type DJ-1 induced the expression of Trx1 protein in HeLa cells, suggesting that DJ-1 may regulate the expression of Trx1 [118]. This result was IXUWKHU FRQ¿UPHG ZKHQ LQKLELWLRQ RI '- H[SUHVVLRQ in neuroblastoma cells and DJ-1 knockout in mice VLJQL¿FDQWO\UHGXFHG7U[SURWHLQDQGP51$OHYHOV>@ 2YHUH[SUHVVLRQRI'-HQKDQFHG1UISURWHLQOHYHOVDQG LQFUHDVHGLWVQXFOHDUWUDQVORFDWLRQZKLFKZDVFRQ¿UPHG by western blot analysis [118]. Using promoter assay and chromatin co-immunoprecipitation (ChIP) assays, it was VKRZQ WKDW '- HQKDQFHG WKH UHFUXLWPHQW RI 1UI RQ WKH$5(UHJLRQRIWKH7U[SURPRWHUDQGLQFUHDVHG7U[ P51$H[SUHVVLRQ>@+RZHYHU'-ZDVQRWERXQG WRWKH$5(7KXV'-PD\H[HUWLWVF\WRSURWHFWLYHHIIHFW against oxidative stress by inducing expression of Trx1 YLD1UI>@)LJXUHLOOXVWUDWHVWKHDFWLRQRI'-RQ Trx1 expression. It was shown that the treatment of cells ZLWK FKORUR GLQLWUREHQ]HQH D SKDUPDFRORJLFDO LQKLELWRU RI 7U[5 DQG 7U[ VSHFL¿F VL51$ UHVXOWHG LQ the partial loss of DJ-1-mediated cytoprotection against oxidative stress [118]. Although DJ-1 was reported to VWLPXODWH WKH WUDQVFULSWLRQDO DFWLYLW\ RI 1UI WKH H[DFW mechanism still remains elusive. DJ-1 has been shown to LQFUHDVH1UISURWHLQOHYHOVZLWKRXWDIIHFWLQJ1UIP51$ H[SUHVVLRQ E\ SUHYHQWLQJ WKH LQWHUDFWLRQ EHWZHHQ 1UI and Keap1 [13, 119]. By using co-immunoprecipitation H[SHULPHQWVLWZDVVKRZQWKDW.HDSZDVERXQGWR1UI but the presence of DJ-1 eliminated this association in Huh7 cells [13]. This data demonstrates that DJ-1 hinders WKHDVVRFLDWLRQEHWZHHQ1UIDQG.HDSKRZHYHULWGRHV not prove the physical interaction of DJ-1 with either 1UIRU.HDS>@,QFRQWUDVWDQRWKHUVWXG\E\XVLQJ co-immunoprecipitation and chemical cross-linking experiments, has shown that DJ-1 neither physically LQWHUDFWV ZLWK 1UI RU .HDS QRU LQWHUIHUHV ZLWK WKH LQWHUDFWLRQ EHWZHHQ 1UI DQG .HDS >@ 7KXV D TXHVWLRQRIKRZ'-DFWLYDWHV1UILVVWLOORSHQDQGVHHNV PRUH XQGHUVWDQGLQJ RI WKH PHFKDQLVP 7KHVH ¿QGLQJV suggest that, Trx1 and DJ-1 are not only independent antioxidant molecules but DJ-1 may serve as an upstream regulator of Trx1, at least for some stress conditions. $SDUW IURP WKH '-7U[ LQWHUDFWLRQ WKHUH are no reports describing any role for DJ-1 in regulating expression and activity of other members of the thioredoxin system, including Trx2. Trx2 is a mitochondrial thioredoxin and exerts cytoprotection against external stress stimuli. Trx2 has been shown to bind mitochondrial ASK1 and inhibits mitochondrial $6.PHGLDWHGDSRSWRVLVLQD-1.LQGHSHQGHQWIDVKLRQ [112]. Based on the observations that DJ-1 regulates the F\WRVROLF$6.7U[FRPSOH[WRLQKLELW$6.PHGLDWHG apoptosis [58] and its mitochondrial localization [50, 51] to exert neuroprotection, it would be interesting to GHWHUPLQHLI'-DOVRUHJXODWHVWKHPLWRFKRQGULDO7U[ $6.FRPSOH[,WLVSRVVLEOHWKDWWKH'-7U[$6. axis may serve as a novel molecular mechanism to protect www.impactjournals.com/oncoscience
cells against mitochondrial ROS-induced apoptosis. An understanding of these molecular signalling pathways may open new avenues for the therapeutic intervention of cancers.
Therapeutic perspective The intracellular redox state regulates various cellular signalling pathways under oxidative stress conditions induced by internal and external stimuli. DJ-1 and Trx play a crucial role in maintaining intracellular redox homeostasis by involving and regulating various redox stress responsive signalling pathways. Thus, targeting either of these antioxidant molecules or both together, may serve as a novel and effective therapeutical DSSURDFK IRU WKH WUHDWPHQW RI FDQFHUV WKDW DFTXLUH resistance to the anti-cancer therapy acting by modulating ROS levels. DJ-1 and Trx play a protective role against oxidative stress and inhibit redox stress-induced cell death in many diseases. Genetic mutations of DJ-1 resulting in the loss or reduced DJ-1 functions lead to the onset of oxidative stress-related diseases including Parkinson’s disease [31, 120, 121], stroke [122], chronic obstructive pulmonary disease (COPD) [119], and type II diabetes >@([SUHVVLRQRI'-KDVEHHQVKRZQWREHLQFUHDVHG in many cancer types [25-27, 29, 77]. Therefore, the knowledge about the antioxidant and cytoprotective functions of DJ-1 obtained from other disease models can be readily translated into cancers where an expression of DJ-1 is upregulated. Similarly, Trx has been shown to act as a modulator of cell susceptibility under oxidative stress conditions and exerts protective effects on cancer FHOOV>@7U[H[SUHVVLRQKDVEHHQUHSRUWHGWRLQFUHDVH LQPDQ\FDQFHUFHOOW\SHV>@ZKHUHLWUHVXOWV in increased cell proliferation and resistance to cell death >@7KHWKLRUHGR[LQV\VWHPKDVHPHUJHGDVDSRWHQWLDO therapeutic target for the treatment of many human FDQFHUW\SHVXVLQJFRPSRXQGVWKDWVSHFL¿FDOO\WDUJHWWKH thioredoxin system to induce cancer cell apoptosis [20, @,QKLELWLRQRI7U[RU7U[5XVLQJVSHFL¿FLQKLELWRUV inhibits tumour cell proliferation, induces apoptosis, and increases the sensitivity of cancer cells to anti-cancer therapy [20, 21]. )LQGLQJV WKDW KDYH LPSOLFDWHG WKH UROH RI '- LQ LQGXFLQJ 7U[ H[SUHVVLRQ E\ LQFUHDVLQJ 1UI DFWLYLW\ have given another mechanism by which DJ-1 exerts cytoprotective function. Inhibition of Trx1 expression E\7U[VSHFL¿FVL51$KDVGHFUHDVHGWKH'-LQGXFHG cytoprotective effect against oxidative stress [118], but has not completely eliminated it. DJ-1 may increase H[SUHVVLRQDQGDFWLYLW\RIRWKHU1UIUHJXODWHGDQWLR[LGDQW or detoxifying enzymes including heme oxygenase 1 +2 DQG1$' 3 +TXLQLQHR[LGRUHGXFWDVH 142 which may protect cells against oxidative stress rendering WKHUDSLHVWDUJHWLQJ7U[DORQHOHVVHIIHFWLYH)XUWKHUPRUH WDUJHWLQJ '- DORQH PD\ QRW EH VXI¿FLHQW WR LQFUHDVH 103
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cell susceptibility to ROS-induced apoptosis because the 1UIUHJXODWHGVLJQDOOLQJFDVFDGHFDQDOVREHDFWLYDWHG by regulatory molecules other than DJ-1 such as the DXWRSKDJ\VXEVWUDWHSSWDUJHWHGSSURWHLQ> @7KHUHIRUHLQKLELWLRQRI'-RU7U[DORQHPD\QRW EHVXI¿FLHQWWRWUHDWFDQFHUVZLWKKLJKDQWLR[LGDQWOHYHOV 7DUJHWLQJ WKH '-1UI7U[ D[LV PD\ EH LPSRUWDQW in modulating cellular response to ROS-induced cell GHDWKLQFDQFHU)XUWKHUPRUHHOXFLGDWLRQRIWKHSRVVLEOH interactions of DJ-1 with the other members of Trx system PD\ DOVR OHDG WR WKH LGHQWL¿FDWLRQ RI QRYHO PROHFXODU therapeutic targets that can be used to develop anti-cancer therapies. $QRWKHUPROHFXODUD[LVWKDWPD\UDLVHDVLJQL¿FDQW interest for the treatment of various types of malignancies LVWKH7U['-37(1D[LV7XPRXUVXSSUHVVRU37(1LV reported to be lost or inhibited in many types of human cancers [127-131] and is deregulated in many other diseased conditions including, rheumatoid arthritis, FKURQLF SXOPRQDU\ GLVHDVH DQG SXOPRQDU\ ¿EURVLV >@6LQFHERWK7U[DQG'-WDUJHWWKHWXPRXU VXSSUHVVRUDFWLYLW\RI37(1FRLQKLELWLRQRIERWKRIWKHVH antioxidant molecules may prove an effective approach for the therapeutic intervention of chemotherapy-resistant forms of cancer. 1)ɤȕLVDUHGR[VHQVLWLYHWUDQVFULSWLRQIDFWRUWKDW LVSRVLWLYHO\UHJXODWHGE\ERWK'-DQG7U[>@ $V GLVFXVVHG HDUOLHU '- DFWLYDWHV 1)ɤȕ E\ ELQGLQJ WRLWVSK\VLRORJLFDOLQKLELWRU&H]DQQH>@ZKHUHDV7U[ ELQGV GLUHFWO\ WR WKH 1)ɤȕ LQ WKH QXFOHXV DQG UHGXFHV D NH\ F\VWHLQH UHVLGXH WR HQKDQFH WKH '1$ ELQGLQJ DFWLYLW\RI1)ɤȕ>@7KHUHIRUHWKHUHDUHWZRGLVWLQFW PHFKDQLVPVWKDWXSUHJXODWHV1)ɤȕDFWLYLW\7KXVWKH '-1)ɤȕ7U[D[LVLVDQRWKHUPROHFXODUD[LVWKDWPD\ be considered as a potential target to treat cancer where these antioxidants are upregulated. Thus, tumours having elevated levels of antioxidants, such as Trx1 and DJ-1, may not respond well to the therapies targeting only one of them. Inhibiting either Trx1 or DJ-1 alone may allow the other to activate downstream signalling cascade leading to the tumour cell survival and proliferation. On the other hand, targeting both Trx1 and DJ-1 in conjunction may completely shut down the antioxidant defence systems regulated by these antioxidants and render the cancer cells sensitive to ROS- LQGXFHGFHOOGHDWK)LJXUHVXPPDULVHVWKHFRQVHTXHQFHV of targeting Trx1 and DJ-1 alone or in combination in cancer cells.
elucidation of DJ-1 and Trx-dependent regulation of redox signalling cascades may provide an effective and a promising therapeutic regime to treat cancers with KLJK DQWLR[LGDQW OHYHOV )XUWKHUPRUH HOXFLGDWLRQ RI the cross-talk between DJ-1 and other members of the Trx superfamily in different tumour models, and the molecular mechanism of these interactions may lead to WKHLGHQWL¿FDWLRQRIPXOWLSOHPROHFXODUWDUJHWV'HWDLOHG XQGHUVWDQGLQJ RI WKH UROH RI '- LQ UHJXODWLQJ 1UI mediated signalling pathways and its targeted genes may OHDGWRWKHLGHQWL¿FDWLRQRIQRYHOWDUJHWVIRUWKHUDSHXWLF intervention of various human cancer types.
ACKNOWLEDGEMENTS 7KLVUHVHDUFKZDVVXSSRUWHGE\*ULI¿WK8QLYHUVLW\ 3RVWJUDGXDWH 5HVHDUFK 6FKRODUVKLS WR 35 D *ULI¿WK University International Postgraduate Research Scholarship (to P.R.).
REFERENCES 1. Robbins D and Zhao Y. Oxidative Stress Induced by 0Q62'S ,QWHUDFWLRQ 3UR RU $QWL7XPRULJHQLF" - 6LJQDO7UDQVGXFW )LQNHO72[LGDQWVLJQDOVDQGR[LGDWLYHVWUHVV&XUU2SLQ &HOO%LRO 0DUWLQGDOH -/ DQG +ROEURRN 1- &HOOXODU UHVSRQVH WR R[LGDWLYHVWUHVV VLJQDOLQJIRUVXLFLGHDQGVXUYLYDO-&HOO 3K\VLRO .DEH
