龐瑞萍, 胡品津, 曾志榮, 陳 為
(中山大學(xué)1中山醫(yī)學(xué)院生理教研室,2第一附屬醫(yī)院消化內(nèi)科,廣東 廣州 510080)
流行病學(xué)研究表明長期使用非甾體類消炎藥(non -steroidal anti- inflammatory drugs,NSAIDs)可預(yù)防結(jié)腸癌、食管癌、胃癌等腫瘤的發(fā)生[1,2]。許多臨床前實驗也證實此觀點[3,4]。盡管目前NSAIDs在消化道腫瘤防治中的作用已被廣泛認(rèn)可,但其作用機(jī)制尚未完全闡明。傳統(tǒng)觀點認(rèn)為NSAIDs是通過抑制環(huán)氧合酶(cyclooxygenase,COX)而發(fā)揮抑制腫瘤的作用,但越來越多的研究表明非COX依賴途徑在其中也發(fā)揮了很重要的作用[5]?,F(xiàn)已證實,除COX外,還有10多個靶點可介導(dǎo)NSAIDs的作用[6],如核因子 κB(nuclear factor κB,NF - κB)、3 - 磷酸肌醇依賴性激酶1(3-phosphoinositide-dependent kinase 1,PDK1)/Akt、過氧化物酶體增殖子活化受體(peroxisome proliferator - activated receptor,PPAR)、NSAID活化基因(non-steroidal anti-inflammatory drug-activated gene,NAG-1)等。其中磷脂酰肌醇3激酶/蛋白激酶B/Akt(phosphatidylinositol 3-kinase/protein kinase B/Akt,PI3K/PKB/Akt)通路既可調(diào)節(jié)細(xì)胞增殖和存活,又可以調(diào)節(jié)糖原合成,而這些都是腫瘤預(yù)防和治療的重要靶點[7,8]。我們前期的研究發(fā)現(xiàn)COX抑制劑可抑制胃癌細(xì)胞的增殖,誘導(dǎo)胃癌細(xì)胞凋亡[9];在體實驗表明COX抑制劑可明顯抑制大鼠胃腺癌的發(fā)生[10]。進(jìn)一步研究我們發(fā)現(xiàn),COX抑制劑的上述作用與COX-2的表達(dá)并無明顯關(guān)系[9,11]。本研究從細(xì)胞學(xué)角度觀察吲哚美辛對胃癌細(xì)胞株生長的作用,并在此基礎(chǔ)上探討了吲哚美辛的作用與Akt/GSK3β/NAG-1信號通路的關(guān)系。
1.1 細(xì)胞培養(yǎng) 胃癌細(xì)胞株MGC-803由中科院上海細(xì)胞所贈送。細(xì)胞用含10%新生小牛血清(Hyclone)的DMEM培養(yǎng)基(Gibco)于37℃、5%CO2的培養(yǎng)箱內(nèi)培養(yǎng)。以0.125%胰蛋白酶+0.020%EDTA(Sigma)消化傳代。
1.2 蛋白表達(dá)的檢測 蛋白表達(dá)測定按我們已報道的方法進(jìn)行[9]。即細(xì)胞經(jīng)各種處理后,用冰浴的PBS洗滌2遍,隨后加入裂解緩沖液(150 mmol/L NaCl,50 mmol/L Tris - HCl,1 g/L SDS,0.2 g/L NaN3,5 mg/L aprotinin,1.0 mmol/L PMSF,1.0 g/L NP40,5.0 g/L 脫氧膽酸鈉,pH 8.0),混勻后冰浴30 min,刮取細(xì)胞。樣品經(jīng)4℃、12000×g離心5 min后,取上清即蛋白提取液。蛋白定量后分別通過SDS-PAGE電泳分離蛋白和電轉(zhuǎn)使蛋白轉(zhuǎn)移至PVDF膜。用PBST洗脫P(yáng)VDF膜5 min后,室溫下封閉1 h。加入不同稀釋的Ⅰ抗,室溫溫育2 h或4℃過夜。經(jīng)PBST洗3次后加入相對應(yīng)的Ⅱ抗,室溫孵育2 h。PBST洗脫后經(jīng)曝光、顯影和定影,吸光度值(absorbance,A)通過凝膠成像系統(tǒng)及相應(yīng)軟件分析。
1.3 MTT法測定吲哚美辛對胃癌細(xì)胞活力的影響按我們已報道的方法進(jìn)行[9]。將細(xì)胞(105cells/well)接種于96孔板,24 h后,依不同處理因素處理相應(yīng)時間后,加入5 g/L MTT(四甲基偶氮唑鹽,上海生物工程公司)10 μL/well,培養(yǎng)箱內(nèi)繼續(xù)孵育,4 h后吸去培養(yǎng)基,加入 DMSO(Sigma)100 μL/well,置酶標(biāo)儀上(測定波長570 nm)測定A值。細(xì)胞活力(%)=(處理組A值-空白組A值)/(對照組A值-空白組A值)×100%。
1.4 吲哚美辛誘導(dǎo)胃癌細(xì)胞凋亡的檢測 細(xì)胞凋亡檢測按我們已報道的方法進(jìn)行[9]。①Hoechst 33258核染色法 細(xì)胞經(jīng)處理后,用多聚甲醛液(40 g/L,Sigma)固定10 min,蒸餾水洗滌后加入5 mg/L Hoechst33258(Promega),10 min后蒸餾水洗細(xì)胞2次,自然干燥后,細(xì)胞置于熒光顯微鏡下(340 nm激發(fā)光)觀察并拍照。②流式細(xì)胞儀檢測 細(xì)胞(1×109/L)用PBS洗2次,以70%乙醇(4℃)固定過夜。離心棄乙醇,細(xì)胞重懸于含有50 mg/L碘化丙啶和50 mg/L RNase A的染色液中避光染色30 min。以流式細(xì)胞儀測定,每樣品計數(shù)12000個細(xì)胞,記錄熒光強(qiáng)度值并以相應(yīng)軟件處理結(jié)果,計算凋亡率。
MTT檢測結(jié)果顯示100-600 μmol/L吲哚美辛處理MGC-803細(xì)胞12、24和48 h后,細(xì)胞的活力隨劑量增加和時間延長而降低,見圖1。
Figure 1.Effects of indomethacin on viability of MGC-803 cells.MGC -803 cells were treated with indomethacin(100 -600 μmol/L)or DMSO vehicle(0.1%)for 12,24 and 48 h.The cell viability showed a concentration-and time-dependent reduction..n=6.*P <0.05,**P <0.01 vs DMSO.圖1 吲哚美辛對MGC-803細(xì)胞活力的影響
Hoechst 33258核染色法結(jié)果表明,未加吲哚美辛的MGC-803細(xì)胞,胞核較大,淺染,呈彌散均勻熒光;500 μmol/L吲哚美辛處理12 h后胞核形態(tài)變得不規(guī)則,呈條紋狀或裂隙狀,并見部分細(xì)胞的染色質(zhì)濃縮;處理24 h后染色質(zhì)進(jìn)一步凝集;處理48 h后,可見染色質(zhì)裂解呈塊狀,見圖2。
流式細(xì)胞術(shù)檢測發(fā)現(xiàn)500 μmol/L吲哚美辛處理后各組均出現(xiàn)明顯的凋亡峰。對照組細(xì)胞凋亡百分率為(3.9±1.6)%,吲哚美辛處理12、24和48 h組細(xì)胞凋亡率分別為(19.6±3.5)%、(38.8±6.1)%和(56.6±9.7)%,P <0.01,見圖3。
Figure 2.Morphological changes of MGC -803 cells induced by indomethacin(×400).After treated with 500 μmol/L indomethacin for 12,24 and 48 h,apoptotic bodies could be observed under fluorescent microscope.圖2 吲哚美辛作用后MGC-803細(xì)胞形態(tài)學(xué)的變化
Figure 3.MGC -803 cell apoptosis after treatment with indomethacin(500 μmol/L)for 12,24 and 48 h analyzed by flow cytometry.圖3 流式細(xì)胞術(shù)檢測吲哚美辛處理后MGC-803細(xì)胞的凋亡率
500 μmol/L吲哚美辛處理細(xì)胞12、24和48 h后,caspase-3酶原被激活,蛋白免疫印跡顯示17 kD的活化caspase-3片段,其作用存在時間依賴性,見圖4A。廣譜caspase抑制劑zVAD-fmk 100 μmol/L可明顯抑制吲哚美辛引起的caspase-3酶原的活化,見圖4B。而且zVAD-fmk 100 μmol/L預(yù)處理后可顯著降低吲哚美辛誘導(dǎo)的細(xì)胞凋亡作用,見圖4C。這提示吲哚美辛主要通過caspase通路誘導(dǎo)胃癌細(xì)胞的凋亡。
Figure 4.Effects of z-VAD-fmk on indomethacin-induced apoptosis.MGC -803 cells were treated with 500 μmol/L indomethacin for 6,12 and 24 h(A)or 24 h in the presence or absence of 100 μmol/L z-VAD-fmk(z-VAD -fmk was added to the cells 2 h prior to indomethacin treatment;DMSO vehicle concentration:0.1%)(B).Proteins were extracted and used for the detection of caspase-3 cleavage by Western blotting.C:indomethacin-induced reduction of cell viability was partially prevented by pretreatment with z-VAD-fmk.Indo:indomethacin..n=6.*P<0.05,**P<0.01 vs indomethacin group.圖4 廣譜caspase抑制劑z-VAD-fmk對吲哚美辛誘導(dǎo)MGC-803細(xì)胞凋亡的作用
吲哚美辛(500 μmol/L)作用于MGC-803細(xì)胞后,總Akt蛋白表達(dá)無明顯變化,而Ser473位點磷酸化Akt的表達(dá)水平明顯降低,見圖5A、C。
吲哚美辛作用后,細(xì)胞總GSK3β的表達(dá)無顯著變化,而GSK3β Ser9磷酸化水平降低,見圖5B、D。
Figure 5.Effects of indomethacin on the phosphorylation of Akt and GSK3β in MGC -803 cells.Indomethacin(500 μmol/L)treatment inhibited the phosphorylation of Akt(Ser473)(A,C)and GSK3β (Ser9)(B,D)in MGC -803 cells,but did not change the total Akt and GSK3β.Indo:indomethacin..n=4.**P<0.01 vs corresponding control.圖5 吲哚美辛對MGC-803細(xì)胞Akt和GSK3β磷酸化的影響
吲哚美辛可以增加NAG-1的表達(dá),而單獨應(yīng)用PI3K抑制劑 LY294002(20 μmol/L)和 Akt抑制劑1L-6-h(huán)ydroxymethyl-chiro-inositol 2(R)-2-O -octadecylcarbonate(10 μmol/L)處理后,也可增加NAG-1蛋白表達(dá)。預(yù)先加入 GSK3β抑制劑SB216763(10 μmol/L)孵育1 h可完全取消PI3K抑制劑和Akt抑制劑誘導(dǎo)NAG-1表達(dá)的作用,見圖6A、C。PI3K 抑制劑 LY294002(20 μmol/L)和 Akt抑制劑(10 μmol/L)預(yù)孵育 1 h 后再加入500 μmol/L吲哚美辛,NAG-1的表達(dá)水平與單用吲哚美辛相比無顯著差異。而預(yù)先加入 GSK3β抑制劑SB216763(10 μmol/L)孵育1 h,則完全取消吲哚美辛誘導(dǎo)NAG-1表達(dá)的作用,見圖6B、D。
預(yù)先加入SB216763(10 μmol/L)孵育1 h可顯著抑制吲哚美辛誘導(dǎo)細(xì)胞凋亡的作用,見圖7。
Figure 6.Effects of PI3K,Akt and GSK3β inhibitors on NAG -1 expression induced by indomethacin in MGC -803 cells.MGC -803 cells were treated with 20 μmol/L LY294002,a specific PI3K inhibitor,or 10 μmol/L 1L -6 - hydroxymethyl- chiro - inositol 2(R)-2-O -octadecylcarbonate,a selective Akt inhibitor,or pre-addition of 10 μmol/L SB216763,a selective GSK3β inhibitor for 12 h in the presence(B,D)or absence(A,C)of 500 μmol/L indomethacin.The cell lysates were harvested for Western blotting analysis using anti-NAG-1 antibody..n=5.**P<0.01 vs control.圖6 PI3K、Akt和GSK3β抑制劑對吲哚美辛誘導(dǎo)MGC-803細(xì)胞NAG-1表達(dá)的影響
Figure 7.GSK3β inhibitor blocks the indomethacin-induced inhibition of cells growth.Indomethacin-induced reduction of cell viability was prevented by pretreatment with 10 μmol/L SB216763(SB216763 was added to the cells 1 h prior to indomethacin treatment;DMSO vehicle concentration:0.1%).Indo:indomethacin..n=6.*P<0.05,**P<0.01 vs indomethacin group.圖7 GSK3β抑制劑可阻斷吲哚美辛誘導(dǎo)的細(xì)胞凋亡作用
Akt(PKB)是細(xì)胞存活和凋亡的重要調(diào)節(jié)因子,Akt的磷酸化可保護(hù)多種類型細(xì)胞的凋亡。越來越多的證據(jù)顯示Akt可通過促進(jìn)細(xì)胞的增殖和抑制細(xì)胞凋亡參與腫瘤的發(fā)生和發(fā)展[12]。在肺癌和肝癌細(xì)胞,研究表明Akt的磷酸化參與了COX-2介導(dǎo)的促細(xì)胞存活過程[12,13]。Akt的磷酸化位點包括催化結(jié)構(gòu)域的Thr308位點和調(diào)節(jié)結(jié)構(gòu)域的Ser473位點。Thr308位點的磷酸化只能部分激活A(yù)kt,只有2個位點的磷酸化才能使Akt充分活化。已有研究表明,NSAIDs誘導(dǎo)前列腺癌、肝細(xì)胞肝癌等的凋亡作用與抑制Akt Thr308和Ser473位點的磷酸化水平相關(guān)[14,15]。在人結(jié)腸癌細(xì)胞株 HT -29 細(xì)胞,celecoxib誘導(dǎo)細(xì)胞凋亡作用同時Akt和GSK3β磷酸化水平均被明顯抑制[16]?;罨蟮腁kt主要通過對含有絲氨酸/蘇氨酸殘基的底物磷酸化而發(fā)揮作用。GSK3β是Akt的重要底物之一,它作為細(xì)胞凋亡的上游調(diào)節(jié)因子,參與調(diào)控多種細(xì)胞的凋亡過程[17]。在基礎(chǔ)狀態(tài)下,GSK3β即有較高的活性。Akt通過磷酸化GSK3β的Ser9而抑制其活性。最近有報道認(rèn)為celecoxib可通過抑制PI3K/Akt/GSK3β通路誘導(dǎo)結(jié)腸癌細(xì)胞的凋亡[18]。本實驗中,我們在MGC-803細(xì)胞檢測到基礎(chǔ)狀態(tài)Akt Ser473位點和GSK3β Ser9位點的磷酸化,吲哚美辛可明顯抑制 Akt Ser473和GSK3β Ser9的磷酸化水平,而對總的 Akt和總GSK3β表達(dá)水平無影響。進(jìn)一步研究發(fā)現(xiàn),GSK3β選擇性抑制劑 SB216763可幾乎完全逆轉(zhuǎn)吲哚美辛誘導(dǎo)MGC-803細(xì)胞凋亡的作用。這些結(jié)果說明吲哚美辛是通過Akt/GSK3β信號通路誘導(dǎo)MGC-803細(xì)胞凋亡。但GSK3β的信號下游底物尚未明了。
NAG-1又稱為巨噬細(xì)胞抑制因子1(macrophage inhibitory factor 1,MIF-1)、生長分化因子15(growth differentiation factor 15,GDF-15)等,屬于轉(zhuǎn)化生長因子β(transforming growth factor β,TGF-β)超家族成員。已有的研究表明,NAG-1過表達(dá)可抑制乳腺癌細(xì)胞、上皮腫瘤細(xì)胞和前列腺癌細(xì)胞的增殖[18,19],而且 NAG -1 過表達(dá)的人結(jié)腸癌和膠質(zhì)瘤細(xì)胞種植于裸鼠后,其成瘤能力明顯降低[20,21]。進(jìn)一步研究顯示,NAG-1過表達(dá)可引起前列腺癌細(xì)胞產(chǎn)生 caspase依賴性的凋亡[22]。這些結(jié)果提示NAG-1與腫瘤的發(fā)生密切相關(guān)。但NAG-1的調(diào)控機(jī)制尚未完全清楚。已知NSAIDs可誘導(dǎo)NAG-1蛋白表達(dá)的上調(diào)。已有研究認(rèn)為NSAIDs主要是通過早期生長反應(yīng)基因-1(early growth response gene-1,EGR -1)上調(diào) NAG -1的表達(dá)[23]。最近有研究提示 NAG -1的表達(dá)受 PI3K/Akt/GSK3β[24]信號通路調(diào)控。我們的實驗發(fā)現(xiàn),在MGC-803細(xì)胞,吲哚美辛可誘導(dǎo)NAG-1的表達(dá)上調(diào)。單用PI3K抑制劑和Akt抑制劑亦可明顯上調(diào)NAG-1的表達(dá),預(yù)先加入GSK3β抑制劑則完全取消PI3K抑制劑和Akt抑制劑對 NAG-1的作用,提示 PI3K/Akt/GSK3β信號通路參與調(diào)控MGC-803細(xì)胞NAG-1的表達(dá)。我們的結(jié)果與結(jié)腸癌細(xì)胞上的研究結(jié)果相一致[23]。如預(yù)先加入GSK3β抑制劑則可取消吲哚美辛上調(diào)NAG-1表達(dá)的作用,而在PI3K抑制劑和Akt抑制劑作用的基礎(chǔ)上,吲哚美辛對NAG-1表達(dá)的上調(diào)作用與單用吲哚美辛相比并無差異。提示在胃癌細(xì)胞株MGC-803細(xì)胞,吲哚美辛主要是通過Akt/GSK3β信號通路上調(diào)NAG-1的表達(dá)。
綜上所述,我們的結(jié)果表明,在胃癌細(xì)胞株MGC-803細(xì)胞,非選擇性COX抑制劑吲哚美辛主要是通過Akt/GSK3β信號通路上調(diào)NAG-1的表達(dá),進(jìn)而誘導(dǎo)細(xì)胞的凋亡。
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