SUPPRESSION OF MANGANESE SUPEROXIDE DISMUTASE ACTIVITY IN ROTENONE-TREATED HUMAN GLIOBLASTOMA T98G CELLS REDUCES CELL VIABILITY

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1 Vol 11, Issue 1, 2018 Online Print Reserch Article SUPPRESSION OF MANGANESE SUPEROXIDE DISMUTASE ACTIVITY IN ROTENONE-TREATED HUMAN GLIOBLASTOMA T98G CELLS REDUCES CELL VIABILITY SEPTELIA INAWATI WANANDI 1 *, NOVI SILVIA HARDIANY 1, NURJATI CHAIRANI SIREGAR 2, MOHAMAD SADIKIN 1 1 Deprtment of Biochemistry nd Moleculr Biology, Fculty of Medicine, Universits Indonesi, Jkrt, Indonesi. 2 Deprtment of Antomic Pthology, Fculty of Medicine, Universits Indonesi, Jkrt, Indonesi. Emil: septeli@gmil.com/septeli.inwti@ui.c.id ABSTRACT Received:05 July 2017, Revised nd Accepted: 23 Septemer 2017 Ojective: Gliom is the most common humn primry rin tumor which is highly resistnt to oxidtive stress-sed nticncer. The im of this study ws to nlyze the effect of rotenone-induced rective oxygen species (ROS) on the modultion of mngnese superoxide dismutse (MnSOD) expression nd cell viility in humn gliolstom (GBM) T98G cells. Methods: In this in vitro experimentl study, T98G cells were treted with high-dose rotenone (0.5, 5, nd 50 μm, respectively). Following rotenone tretment nd intrcellulr ROS, oth peroxide nd superoxide rdicls were determined. Moreover, we nlyzed MnSOD mrna expression, protein, nd specific ctivity, s well s cell survivl including viility, prolifertion, poptosis, nd mitochondril structure. Results: High-dose rotenone tretment of T98G cells significntly incresed intrcellulr ROS nd MnSOD mrna, ut its protein nd specific ctivity definitely decresed. The tretment lso led to reduction of cell viility, enhncement of poptosis, nd disruption of mitochondril integrity. Conclusion: Overproduction of ROS in rotenone-treted humn GBM T98G cells could suppress the MnSOD protein level nd ctivity even though mrna synthesis hs een incresed. This modultion led to reduced survivl of T98G cells through induction of cell deth rther thn inhiition of cell prolifertion. Keywords: Cell viility, Gliolstom multiforme, Mngnese superoxide dismutse, Rotenone The Authors. Pulished y Innovre Acdemic Sciences Pvt Ltd. This is n open ccess rticle under the CC BY license ( org/licenses/y/4. 0/) DOI: INTRODUCTION Gliom is the most common humn primry rin tumor which rises from glil cells [1]. Nowdys, the use of conventionl tretments such s chemotherpy nd rdition does not significntly enhnce the life expectncy of gliom ptients, prticulrly those with high-grde mlignnt (the WHO Grde IV) multiforme gliolstom (GBM) ptients, which is highly resistnt to therpy [2]. Comintoril tretment strtegy hs een reported to hve improved the chemotherpeutic delivery to tumor cells in the rin [3,4]. Nevertheless, ccumulting evidence suggests tht dysregultion of cell cycle nd poptosis could led to rdiotherpy resistnce [5]. A plusile mechnism for this resistnce might involve high ntioxidnt sttus in tumor cells which could ffect cell survivl in response to rdition-induced oxidtive stress [6]. Mngnese superoxide dismutse (MnSOD) is mjor cellulr ntioxidnt locted in the mitochondril mtrix. This enzyme ctlyzes the rective superoxide nion into hydrogen peroxide which will e lter eliminted y ctlse or peroxidse. The previous studies hve reported tht the upregultion of MnSOD expression could inhiit the phenotype of vrious cncer cells, suggesting tht MnSOD is tumor suppressor [7-10]. However, this ssumption is still controversil, since it hs een demonstrted tht MnSOD ws overexpressed in severl humn cncers including GBM [11]. Furthermore, MnSOD hs een reported to hve n importnt role on tumor cell growth nd prolifertion in ovrin cncer through regultion of superoxide level [12]. Our recent study hs confirmed tht MnSOD mrna expression nd specific ctivity in humn gliom cells isolted from clinicl specimens were higher thn those in norml rin cells. In ddition, the oxidtive stress iomrkers, i.e., mlondildehyde, cronyl compounds nd 8-OHdG, were notly enhnced [8]. Interestingly, when these cells were ctegorized sed on tumor grde, we found tht the high-grde mlignnt gliom cells expressed MnSOD mrna t higher levels compred to the low-grde ut hd lower specific ctivity. The differentil etween MnSOD mrna level nd specific ctivity in high-grde gliom prompted line of inquiry to investigte whether this ws ssocited with rective oxygen species (ROS) levels in these cells. Therefore, the im of this study ws to nlyze the effect of rotenoneinduced ROS in humn GBM on the modultion of MnSOD expression nd its ssocition with cell viility. High-dose rotenone ws pplied to humn GBM T98G cells to induce overproduction of intrcellulr ROS, which is n expected consequence of rdiotherpy. Rotenone is n inhiitor of mitochondril complex I electron trnsport chin, which increses the mitochondril ROS genertion, prticulrly superoxide rdicls, nd leds to cytotoxicity [13-15]. It hs lso een reported tht this toxin could e used s n nticncer gent [15]. Finlly, this study is lso projected to elorte on the role of MnSOD in high mlignnt GBM ptients who re resistnt to rdiotherpy. The outcome of this study hs the potentil for improving the mngement of GBM. MATERIAL AND METHODS Cell culture The humn GBM cell line T98G (kindly provided y Prof. Alexnder Brehm from Institutfuer Molekulriology und Tumorforschung Philipps Universität Mrurg, Germny; ATCC No. CRL-1690 TM ) ws mintined in high glucose DMEM contining 10% of hetinctivted fetl ovine serum, 3.7 g/l of sodium icronte, 1% Streptomycin - Penicillin, nd 1% mphotericin B t 37 C in humidified tmosphere of 95 % ir nd 5% CO 2. The cells were sucultured with 0.25% trypsin nd 1 % ethylenediminetetrcetic cid (EDTA) whenever the culture reched confluence. A sucultivtion

2 rtio ws 1:2 1:5. Cells were utilized for nlysis within 15 pssges since it hs een demonstrted tht ntioxidnt enzyme levels in tumor cells sucultured up to 50 pssges did not chnge [8]. Rotenone tretment Rotenone powder (Sigm Aldrich, USA) ws first dissolved in dimethyl sulfoxide (DMSO) to otin 10 mm stock solution. One dy efore rotenone tretment, 5 X 10 4 T98G cells were plted triplicte in 24- well plte nd grown in the sme medium without free serum. Cells were treted with vrious concentrtions of rotenone nd incuted for 6 h, s descried previously [12]. Negtive controls were T98G cells without rotenone or DMSO tretment, s well s T98G cells treted with the sme volume of vehicle DMSO used to dissolve rotenone. Rotenone tretment ws repeted 3 times t different time points. After the tretment, cells were wshed with phosphte-uffered sline (PBS), hrvested nd then centrifuged t 1000 rpm for 5 min. Finlly, cells were counted nd prepred either for the cell viility or prolifertion nlysis, s well s for the isoltion of totl RNA nd protein, followed y the nlysis of MnSOD mrna expression, protein level, nd specific ctivity, respectively. Determintion of intrcellulr ROS level Intrcellulr ROS ws mesured t the level of hydrogen peroxide nd superoxide nions. For peroxide level mesurement, dichlorodihydrofluorescein dicette (DCFH-DA) ssy (Moleculr Proes, USA) ws performed sed on the intrcellulr peroxidedependent oxidtion of 2,7 -(DCFH-DA to form the fluorescent compound 2,7 -dichlorofluorescein DCF, s descried previously [16]. Dihydroethidium (DHE) (Invitrogen) ssy could detect the presence of superoxide nion which enzymticlly converts hydroethidine to ethidium. T98G cell pellets contining cells were resuspended in PBS contining 20 µm DCFH-DA or 20 µm DHE nd incuted for 30 min t 37 C [17,18]. Cells were then rinsed with PBS (2 times) nd centrifuged 1000 rpm for 5 min. Cell pellets were resuspended in 3 ml PBS. Fluorescence intensity ws mesured using the Microplte Fluorometer (Vrioskn Flsh, Thermo Scientific, Finlnd) t 485 nm nd 488 nm excittion, s well s 530 nm nd 585 nm emission for DCFH-DA nd DHE ssys, respectively. Anlysis of cell viility T98G cell viility ws determined using MTS ssy ccording to the mnufcturer s protocol (Cell Titer 96Non-Rdioctive Cell Prolifertion Assy kit ; Promeg, USA). Briefly, ten thousnd cells fter rotenone tretment were wshed with PBS nd dded with 20 µl of MTS/PMS mixture (MTS:PMS=20:1) to ech well nd incuted for 1-4 h under stndrd conditions (5% CO 2 t 37 C). The quntity of formzn product ws mesured using spectrophotometer t 490 nm, nd the sornce ws directly proportionl to the numer of living cells in culture. Anlysis of cell prolifertion T98G cell prolifertion ws nlyzed using the Cell Prolifertion ELISA, BrdU kit (Roche, Germny) ccording to the mnufcturer s protocol. After rotenone tretment, cells in ech 24-well plte were leled with 20 µl/well of BrdU nd incuted for 24 h. The rection product ws quntified y mesuring the sornce t 490 nm using the Microplte Reder (Vrioskn Flsh, Thermo Scientific, Finlnd). The developed color nd therey the sornce vlues directly correlted to the mount of DNA synthesis nd herey to the numer of proliferting cells. Anlysis of cell poptosis Cell poptosis ws nlyzed using terminl deoxynucleotidyltrnsferse (TdT) dutp Nick-End Leling (TUNEL) ssy (In Situ Cell Deth Detection kit, POD) ccording to the mnufcturer s protocol. This ssy hs een designed to detect poptotic cells tht undergo extensive DNA frgmenttion during the lte stges of poptosis. Fifty thousnd T98G cells were plted in slide chmer one dy efore rotenone tretment. The counterstining process ws performed using methyl green solution, s descried previously [19]. Cells were oserved under light microscope (Nikon ECLIPSE 80i). Drk rown cells were identified s poptotic cells nd clculted using Imge J cell counter softwre (NCBI). Anlysis of MnSOD mrna expression using rel-time polymerse chin rection (RT-PCR) Totl RNA ws isolted from hrvested T98G cell culture using Tripure Isoltion kit (Roche) ccording to the mnufcturer s protocol. The concentrtion of totl RNA ws determined using spectrophotometry t 260 nm wvelength. cdna of MnSOD ws synthesized from 200 ng of totl RNA smples nd mplified using iscript one-step RT-PCR Kit with SYBR Green (BioRd), ccording to the mnufcturer s protocol. 18S rrna ws used s reference gene. The mplifiction protocol ws performed using primers for MnSOD or 18SrRNA gene, s descried in our previous report [20]. Aquidest ws used s nontemplte control to exclude the flse-positive result. The level of mrna expression in rotenone-treted or DMSO-treted cells ws reltively determined using Livk formul nd normlized to tht in the cells without ny tretment s control. Anlysis of MnSOD protein Totl protein ws isolted from hrvested T98G cell culture using Tripure Isoltion kit (Roche) ccording to mnufcturer s protocol. Totl protein concentrtion in ech smple ws first mesured using spectrophotometer t 280 nm wvelength nd plotted to the ovine serum lumin stndrd curve. The humn MnSOD stndrd stocksolution ws reconstituted y dding the dilution uffer to otin MnSOD concentrtion of 1600, 800, 400, 200, 100, 50, 25, nd 0 pg/ml. MnSOD protein levels were determined using spectrophotometer t 450 nm nd clculted using the concentrtion of stndrds provided in the kit nd the totl protein concentrtion in ech smple. Anlysis of the MnSOD enzyme-specific ctivity MnSOD enzyme ctivity ws mesured using xnthine oxidse inhiition ssy (RnSOD kit, Rndox), s previously descried [19]. To inhiit the Cu/ZnSOD, first, ntrium cynide (5 mm) ws dded into ech smple, nd the mixture ws incuted for 5 min in room temperture [21]. MnSOD enzyme ctivity ws expressed s percentge (%) inhiition of the smples plotted to the stndrd curve. The specific ctivity of MnSOD enzyme ws clculted s enzyme ctivity (in Unit) per mg totl protein. Anlysis of trnsmission electron microscopy (TEM) The mitochondril ultrstructure of T98G cells-treted rotenone ws otined y TEM. Cells were firstly fixed in 2.5 % glutrldehyde contining 3% sucrose in 0.1 M sodium ccodylte uffer (ph 7.4) for 24 h t 4 C, then in 2.5 % glutrldehyde contining 3% sucrose in 0.1 M sodium ccodylte uffer (ph 7.4) for 3 h t 4 C, nd finlly in 2% osmium tetroxide nd 2.5% K 3 Fe(CN) 6 in 0.1 M ccodylte uffer (ph 7.4) for 2 h t 4 C [22]. Afterwrd, smples were dehydrted in grded ethnol for 15 min, emedded in Spurr s resin for 24 h t room temperture nd exmined under JEOL 1010 trnsmission electron microscope. Sttisticl nlysis Sttisticl nlysis ws performed using Student s t-test (for comprison etween rotenone- nd DMSO-treted cells) or Wilcoxon test (for comprison of non-prmetric dt). Dt were presented s men ± SE, nd p vlues of <0.05 were considered s eing sttisticlly significnt. RESULTS Genertion of intrcellulr ROS y rotenone in T98G cells To determine the optiml rotenone concentrtion which could induce the overccumultion of oth superoxide nd peroxide rdicls intrcellulr, T98G cells were first treted with vrious concentrtions of rotenone (0.5 µm, 5 µm nd 50 µm) for 6 h. Fig. 1 demonstrtes tht rotenone could induce the production of oth superoxide rdicls 49

3 (mesured using DHE) nd hydrogen peroxide (mesured using DCFH- DA) in T98G cells. When compred with the DMSO-treted T98G cells, superoxide levels were considerly enhnced in T98G cells treted with rotenone t concentrtion of 0,5 µm (1.37-fold, p<0.05) nd grdully incresed t the concentrtion of 5 µm (1.56-fold, p<0.05) nd 50 µm (1.97-fold, p<0.01). In ddition, we could demonstrte in this study tht high-dose rotenone could lso significntly increse the peroxide level (1.77-fold, p<0.01 t 50 µm). Effect of rotenone tretment on cell survivl In this study, we investigted the effect of rotenone tretment on the survivl of T98G cells. To nlyze T98G cell viility following rotenone tretment, n MTS ssy ws performed. The result demonstrted tht the viility of T98G cells treted with rotenone of either 5 or 50 µm ws lower Fig. (~0.5 or 0.7-fold, p<0.05) thn their counterprts treted with DMSO (Fig. 2). These dt were consistent with the superoxide level, reveling tht superoxide rdicls generted y rotenone were le to lessen T98G cell viility. To verify whether the decrese of T98G cell viility ws triggered y the reduction of cell prolifertion or induction of cell deth, we performed BrdU ssy for cell prolifertion nd TUNEL ssy for cell poptosis. The result demonstrted tht T98G cells prolifertion following rotenone tretment ws slightly decresed (~0.9-fold; p>0.05) compred with the cells treted with DMSO (Fig. 2). In contrst to the result of cell prolifertion, TUNEL ssy in T98G cells treted with high-dose rotenone (50 µm) detected remrkle increse of drk rown cells (~1.6-fold; p<0.05) compred with the control (non-treted cells) nd DMSO-treted cells, respectively (Fig. 3). This indictes tht high-dose rotenone provoked cell poptosis which ws most likely cused y overproduction of oth superoxide nd peroxide rdicls. reltive expression level of MnSOD mrna in 50 µm rotenone-treted T98G cells ws significntly upregulted (~3.8-fold; p<0.01). In contrst to the mrna expression, high-dose rotenone led to remrkle decrese in the protein levels (~6.2-fold lower; p<0.01) nd specific ctivity of MnSOD in T98G cells (~1.4-fold; p<0.05). This reveled tht high-dose rotenone modulted the MnSOD expression in T98G cells, leding to the modultions in its mrna, protein, nd ctivity levels. Effect of rotenone tretment on the mitochondril structure To evlute whether rotenone - n inhiitor of the mitochondril trnsport electron chin - could disrupt the mitochondril integrity of T98G cells, we oserved the ultrstructure of mitochondri using TEM. The result illustrted tht mitochondri of T98G cells treted with highdose rotenone were swollen nd exhiited irregulr criste with loss of lipid ilyer memrne (Fig. 5c), in contrst to the non-treted (Fig. 5) nd DMSO-treted cells (Fig. 5), respectively. In the T98G cells treted with DMSO solely, lthough the mitochondri lso tended to e swelling nd irregulr, the lipid ilyer memrne nd criste remined intct indicting tht the mitochondri integrity ws mintined (Fig. 5). This oservtion demonstrted tht rotenone tretment in T98G cells could led to mitochondril dmge nd cell deth. DISCUSSION Rotenone is n herl pesticide tht locks electrons flow from complex I to coenzyme Q of the electron trnsport chin in mitochondri [23]. As lipophilic molecule, rotenone cn freely penetrte through the cell Effect of rotenone tretment on MnSOD expression To determine whether high-dose rotenone ws efficient in stimulting the ntioxidnt response ginst the overproduction of ROS, we ssessed the expression of MnSOD - mjor ntioxidnt enzyme locted in mitochondri - y gthering its level of mrna nd protein expression s well s its specific ctivity levels. In Fig. 4 nd, we found tht the Fig. 1: Effect of vrious rotenone concentrtions on the rective oxygen species (ROS) production. T98G cells were treted either with vrious concentrtions of rotenone (0.5, 5, nd 50 µm, respectively) in dimethyl sulfoxide (DMSO) or with the sme volume of DMSO (s vehicle) used for dissolving rotenone. ROS levels were determined using DCFH-DA nd DHE ssy s descried under mteril nd methods. Fluorescence intensity of oxidized dichloro-dihydro-fluorescein dicette nd dihydroethidium in treted cells ws expressed s rtio to control (cells without ny tretment). All vlues re mens, n=3. Student s t-test showed significnt differences t *(p<0.05) nd **(p<0.01) compred to those of DMSO-treted cells. D: DMSO, R: Rotenone Fig. 2: Effect of rotenone tretment on cell viility () nd prolifertion () on vrious concentrtion. T98G cells ( cells) were first treted with 0.5 µm, 5 µm, nd 50 µm rotenone in dimethyl sulfoxide (DMSO) or with DMSO (s vehicle) solely. Then, MTS ssy ws performed for the cell viility nd BrdU ssy for cell prolifertion, respectively, s descried under the forementioned mteril nd methods section. Dt were clculted s percentge of the control (cells without ny tretment). All vlues re mens±stndrd error, n=9. Student s t-test showed significnt differences t *(p<0.05) compred to the cells treted with DMSO 50

4 c d e f g Fig. 3: Effect of rotenone tretment on DNA frgmenttion. () T98G cells ( cells) were first treted with vrious concentrtions of rotenone in dimethyl sulfoxide (DMSO) nd with n equivlent volume of DMSO (s vehicle), respectively. Susequently, TUNEL ssys were performed s descried under the mteril nd methods sectopm. Dt were clculted s percentge of control (cells without ny tretment). All vlues re mens±stndrd error, n=9. Student s t-test showed significnt differences t **(p<0.01) compred to the cells treted with DMSO. (-i) microgrphs of TUNEL-stined T98G treted with rotenone. Cells were oserved under inverted microscope with 200 mgnifiction. () Negtive control (cells without tretment); (c) positive control (cells + DNAse); (d) cells + DMSO for 0.5 µm rotenone (vehicle); (e) cells µm rotenone; (f) cells + DMSO for 5 µm rotenone (vehicle); (g) cells + 5 µm rotenone; (h) Cells + DMSO for 50 µm rotenone (vehicle); (i) cells+50 µm rotenone. Apoptotic cells exhiiting DNA frgmenttion were stined drk rown. Slides were counter-stined with methyl green to identify ckground TUNEL-negtive cells h i memrne into the cytoplsm nd mitochondri nd esily trnsfer cross the lood-rin rrier [23]. It hs een reported tht rotenone tretment could induce free rdicl genertion, leding to oxidtive dmges, such s mitochondril dysfunction, uiquitin-dependent protesome dysfunction nd endoplsmic reticulum stress, s well s cell deth [25,26]. In the present study, we confirmed tht rotenone induced the ccumultion of mitochondril ROS, s reported previously [25,26]. Although superoxides were the min ROS generted s result of mitochondril complex I inhiition, here, we demonstrted tht highdose rotenone could stimulte the sustntil production of peroxides s well. This might e due to the incresed conversion of superoxides into hydrogen peroxides ctlyzed y MnSOD in mitochondri. The rotenone tretment of T98G cells performed in this study cn serve s model for oxidtive stress induction during rdiotherpy for gliom ptients. Rdiotherpy induces ROS production in tumor cells, either to fcilitte tumor cell deth through process of poptosis or to suppress the tumor growth through n inhiition of cell prolifertion. Here, we found tht rotenone concentrtion of 5 or 50 µm suppressed the viility of T98G cells, indicting high ROS levels [27]. The ssessment of cell viility should e considered to e one of the primry criteri for poptosis [28]. Through the use of TUNEL ssy, we oserve n increse in DNA frgmenttion which indicted cell deth induced y chromtin dysfunction in T98G cells fter high-dose rotenone tretment. Therefore, we suggested tht the decline of cell viility following rotenone tretment is more likely due to the stimultion of cell poptosis rther thn the inhiition of cell prolifertion since the BrdU ssy performed in this study hs indicted no significnt decrese of T98G cell prolifertion. Comprle results hve lso een reported y other previous studies, suggesting tht rotenone does not ffect the S-phse of cell prolifertion [29,30]. Menwhile, low-dose rotenone tretment (0.5-1 µm) for 18 h hs een demonstrted to enhnce poptosis in HL-60 cells through cytochrome c relese, cspse-3 ctivtion, nd DNA rekdown [26]. However, it should e considered tht ROS-medited DNA frgmenttion presented y the TUNEL ssy could e detected not only merely in poptosis ut lso in the necrosis process [31]. In ddition, using TEM ssy, we could oserve the mitochondril swelling with loss of criste structure nd loss of memrne integrity in the cells treted with highdose rotenone, which is more likely n indictor of necrosis rther thn poptotic cell deth, s descried previously [32,33]. It hs een suggested tht n inhiitor of the mitochondril electron trnsport chin such s rotenone-induced necrosis rther thn poptosis [33]. This effect ws surely unexpected nd should e tken into ccount during the mngement of cncer therpies in the future. 51

5 Fig. 5: The ultrstructure of mitochondri ws evluted y trnsmission electron microscopy. () Typicl mitochondril structure (white rrow) showing regulr size nd shpe, s well s intct lipid ilyer memrne in T98G cells without tretment. () Swollen mitochondri (white rrow) with irregulr shpe nd size. Lipid ilyer memrne ws still visile in cells treted with dimethyl sulfoxide 50 μm for 6 h. (c) Vrious sizes of swollen mitochondri (white rrow) with irregulr criste in cells treted with rotenone 50 μm for 6 h. White rrows signed for mitochondri. Brs: D=500 nm c Fig. 4: Anlysis of mrna reltive expression, protein, nd specific ctivity of mngnese superoxide dismutse (MnSOD).T98G cells treted y 50 µm rotenone nd dimethyl sulfoxide (DMSO) (vehicle), respectively. Totl RNA ws extrcted from the cells, nd cdna product ws mplified using rel-time polymerse chin rection methods, s descried under the mteril nd methods section. () Expression level ws reltively clculted nd normlized with respect to the control group (cells without tretment). All vlues re mens±stndrd error (SE), n=9. Significnt differences t *(p<0.05). Totl protein ws extrcted from the cells s descried under the mteril nd methods section. MnSOD protein level ws determined using enzymelinked immunosorent ssy (NWLSSTM MnSOD ELISA kit). MnSOD-specific ctivity ws mesured using RnSOD kit (Rndox). All vlues re mens±se, n=9. Student s t-test showed significnt differences t *(p<0.05). () Gel electrophoresis grose 1% of cdna products. Lne 1, 5: Cells without tretment, lne 2, 6: Cells+rotenone, lne 3, 7: Cells+DMSO, lne 4: Non templte control To counterlnce the rotenone-induced ROS undnce in the cells, cellulr ntioxidnts re lso recruited to eliminte ROS. When there is n imlnce etween the cellulr ntioxidnt levels nd ROS ccumultion, it will induce stte of oxidtive stress which inflicts vrious oxidtive dmge on essentil mcromolecules in the cells, such s lipid, protein, nd DNA [34]. Therefore, we focused to nlyze the response of rotenone induction on the expression of MnSOD, the mjor free rdicl scvenging enzyme in the mitochondril mtrix. MnSOD ws initilly thought to hve tumor suppressor ctivity, ut the recent studies hve proved tht the expression of this enzyme ws upregulted in mny cncers which suggest tht it my ply role in incresing the invsive properties of tumor cells [12,35-38]. In primry GBM multiforme, upregultion of MnSOD gene expression hs een suggested s specific dignostic mrker through trnscriptome nlysis [39]. Severl studies hve proposed tht MnSOD cts s n nti-poptotic fctor. Thus, upregultion of MnSOD gene expression could led to ROS-sed therpy resistnce [40-42]. Indeed, our recent report hs found tht MnSOD mrna synthesis ws upregulted in high-grde GBM cells isolted from clinicl specimens, ut its protein nd specific ctivity levels were lower compred to norml rin cells [7]. In contrst to those results, other previous study tht used tissue microrry nlysis hs shown tht MnSOD protein expression in ovrin crcinom ws significntly higher thn in enign tumor nd norml tissue [12]. Interestingly, the present study hinted tht oth the protein level nd specific ctivity of MnSOD in the cells treted with high-dose rotenone were significntly lower thn those in control cells, which contrdicted findings in the previous reports [12,26]. In ddition, we specificlly employed the nlysis of MnSOD enzyme-specific ctivity with xnthine oxidse inhiition ssy nd inhiited Cu/ZnSOD ctivity y dding ntrium cynide [20]. It should e noted tht the rotenone dose optimized in this study ws higher thn the dosges used in the forementioned studies nd presuming tht the overccumultion of intrcellulr ROS my exceed the ntioxidnt cpcity of MnSOD, which reduces the vilility nd ctivity of MnSOD. More interestingly, the present study reveled tht high-dose rotenone (50 µm) could modulte mrna, protein, or specific ctivity levels of MnSOD in T98G cells. Although the synthesis of MnSOD mrna hs een upregulted, ccumultion of intrcellulr ROS ws elevted, s indicted y high superoxide nd peroxide levels, which led to insufficient levels of ctive intrcellulr MnSOD enzyme. Thus, the imlnce etween high ROS level nd low ctivity of MnSOD found in the present study ws due to high-dose rotenone-induced oxidtive stress. On the other hnd, we should lso consider the possiility tht uiquitin-protesoml degrdtion of MnSOD protein is exggerted y the high undnce of intrinsic ROS leding to mitochondril dysfunction [25,26]. This ssumption is supported y the TEM ssy results in the present study demonstrting tht the mitochondril disruption in T98G cells is induced y high ROS levels. Alterntively, the discrepncy etween high MnSOD mrna nd low protein or specific ctivity level might e ssocited with the dysregultion of MnSOD protein synthesis influenced y overproduction of ROS. The stedy stte of mrna levels perceived using quntittive RT-PCR method is cumultive result of severl regultory mechnisms, including trnscription, RNA processing, nd RNA stility, wheres the protein level nd ctivity re predominntly influenced y trnsltionl nd post-trnsltionl processing, s well s innte vritions in stility. Severl comprtive trnscriptomics nd proteomics in mouse offer evidence tht there is low correltion etween trnscript nd encoded protein levels [43,44]. Here, we highlight the importnce of the MnSOD gene expression nlysis t the level of mrna nd protein, s well s enzyme ctivity. Unlike the previous report on ovrin cncer [12], our concomitnt study hs otined tht the suppression of MnSOD mrna expression in T98G cells through sirna trnsfection could reduce the protein level nd enzyme ctivity nd enhnce superoxide rdicls production, leding to cell deth [45]. Hence, we evidently suggest tht the impct of oxidtive stress induced y high-dose rotenone is most likely ssocited with low MnSOD expression t the level of protein nd enzyme ctivity. Incresed 52

6 MnSOD mrna levels which resulted in the incresed vilility of MnSOD ntioxidnts might e the result of cellulr dptive response to oxidtive stress. It should e considered tht the impct of rotenone on cell survivl is not only limited through enhncing the mount of intrcellulr ROS, oth superoxide nd peroxide rdicls, ut lso through the modultion of MnSOD gene expression. Bsed on the results of this study, we could elucidte tht the discrepncy etween high MnSOD mrna nd low protein or specific ctivity levels in humn high-grde gliom cells reported in our previous study might e due to oxidtive dmge triggered y excessive production of ROS, s demonstrted y the increse of protein cronyls s mrker of protein oxidtive dmge in the high-grde compred to low-grde gliom nd norml rin cells [7]. Nevertheless, in contrst to the present study, the rte of cell prolifertion ws higher, nd the rte of poptosis ws lower in the high-grde compred to lowgrde gliom cells. It seems tht the redox signling pthwy regulting cell viility ws not similr to tht oserved in this study. It hs een formerly reported tht moderte ROS levels were le to induce cell prolifertion through redox signling pthwy, which contriuted to tumor growth, wheres high ROS levels stimulted poptosis [27]. Furthermore, in tht study, we hve demonstrted tht cell survivl of high-grde gliom from clinicl specimens ws strongly correlted with the MnSOD mrna level [7]. Therefore, we presume tht MnSOD gene expression might e responsile for the modultion of redox signling mechnisms contriuting to tumor cell survivl in high-grde gliom cells, nd further ffecting tumor mlignncy nd ROS-sed cncer therpy resistnce. CONCLUSION Bsed on our findings, we conclude tht overproduction of ROS in rotenone-treted humn GBM T98G cells could suppress the MnSOD protein level nd ctivity even though its mrna synthesis hs incresed. 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