International Immunopharmacology 11 (2011) 212–219
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International Immunopharmacology
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Selective Impairment of CD4+CD25+Foxp3+Regulatory T cells by paclitaxel isexplained by Bcl-2/Bax mediated apoptosis
Nan Liu 1, Yijie Zheng 1, Ying Zhu, Shudao Xiong, Yiwei Chu ⁎Department of Immunology, Shanghai Medical College, Key Laboratory of Molecular Medicine of Ministry of Education, Fudan University, Shanghai, People's Republic of China
⁎ Corresponding author. Department of ImmunologFudan University, 138 Yixueyuan Road, mail box 22Republic of China. Tel./fax: +86 21 54237324.
E-mail address: [email protected] (Y. Chu).1 Liu Nan and Zheng Yijie contributed equally to th
Paclitaxel has become one of the most effective and widely used chemotherapeutic agents over the pastdecades. Although it has shown promise to selectively deplete regulatory T (Treg) cells in our previous study,the underlying molecular mechanism remains to be further elucidated. The present study focused on theeffect of paclitaxel on Treg cells in 3LL Lewis tumor model and explored the possible molecular pathwaysinvolved in this process. We found that paclitaxel significantly decreased the percentage of Treg cells in CD4+
cells and impaired their suppressive functions, but effector T (Teff) cells remained unaffected. Compared withTeff cells, Treg cells exhibited a high sensitivity to paclitaxel-mediated apoptosis in vitro. Interestingly, thoughpaclitaxel has been characterized as a mitotic inhibitor, tubulin was not involved in the selective function ofpaclitaxel. Treg cells exposed to paclitaxel displayed downregulation of Bcl-2 and upregulation of Bax.Blocking the Bcl-2 pathway eliminated the difference between Treg and Teff cells responding to paclitaxel.These results suggest that Bcl-2 rather than tubulin contributes to the distinctive effect of paclitaxel on Tregcells. Therefore, we here identify a molecular pathway through which paclitaxel selectively ablates Treg cells.
y, Shanghai Medical College,6 Shanghai, 200032, People's
Paclitaxel is currently used as the front-line chemotherapeuticagent that has achieved prominence in clinical oncology for its efficacyagainst a range of cancers, including breast, ovarian, and non-smallcell lung cancers. It is a hydrophobic diterpenoid isolated from thePacific yew tree (Taxus brevifolia) and acts as a microtubule-targetingdrug by hindering the depolymerization of tubulin within cancer cells[1,2].
Traditionally, chemotherapy strategy is deemed to destroy notonly cancer cells, but also immune-related cells and bone marrowcells. Such kind of destruction may result in immunosuppression anddisturbance of hematopoietic homeostasis [3,4]. However, recentstudies demonstrated that paclitaxel could enhance immuneresponses by acting on a variety of immune cells. In paclitaxel-treatedmacrophages, the expression of inducible nitric oxide synthase (iNOS)was elevated and the production of interleukin-12 (IL-12) wasincreased [5]. It was also demonstrated that paclitaxel couldstrengthen the cytotoxic activity of natural killer cell (NK cell) andinduce altered maturation of dendritic cell (DC) by enhancing surfacematuration markers [6–8]. Our previous clinical study found that
paclitaxel selectively decreased the size of Treg cell population ratherthan other subsets including Teff cell in non-small cell lung cancer(NSCLC) patients following paclitaxel-based chemotherapy [9]. Thealtered pattern of tumor immunity provides new strategies tocombine paclitaxel treatment with immunotherapies to improveclinical efficacy of cancer therapies.
Treg cell, a subpopulation comprising 3%–5% of CD4+T cells, is themain contributor to the maintenance of peripheral self-tolerance [10,11].However, under pathologic conditions, Treg cells can also curtailantitumor immune responses. Treg cells inhibit antitumor immunity bysuppressing tumor-specific Teff cells, and functions through cell–cellcontact and/or production of cytokines such as IL-10 or TGF-β. Thenumber of functional Treg cells is elevated in tumor beds and tumordraining lymph nodes, leading to the observed immunosuppression[11–14]. For these reasons, depleting Treg cells may be beneficial topotentiate elimination of tumors by the immune system.
Thoughpaclitaxel has shownpromise as a drug to target Treg cells, theunderlying molecular mechanism remains to be further elucidated.Therefore, in the present study, we aim to investigate theimmunoregulatory effect of paclitaxel and explore the possible molecularpathways involved in this process.
2. Materials and methods
2.1. Mice and cell lines
Female C57BL/6 aged 6 to 8 weeks were purchased from ShanghaiExperimental Center, Chinese Academy of Science, and maintained
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under specific pathogen-free condition. All animal experiments wereperformed according to the Guide for the Care and Use of MedicalLaboratory Animals (Ministry of Health. P.R. China, 1998) and theguidelines of Shanghai Medical Laboratory Animal Care and UseCommittee. 3LL tumor cells were cultured at 37 °C under 5% CO2 incomplete RPMI1640 medium containing 10% heat-inactivated FetalBovine Serum (FBS), 2 μM glutamine, 100 IU/ml penicillin, and100 μg/ml streptomycin sulfate.
2.2. Reagents
Paclitaxel were purchased from Lukang (Qingdao, Shandong, P.R.China). RPIM1640 and FBS were from GIBICO (Grandland, NY, USA). IL-2wasobtained fromInvitrogen(Carlsbad, CA,USA).DAPIused for apoptosisanalysis was bought from Sigma (St. Louis, MO, USA). CD4+CD25hi TregCell Isolation Kit, T Cell Activation/Expansion Kit and Annexin v-FITC Kitwere from Phoenix Flow Systems (San Diego, CA, USA). The followingreagents were all supplied by eBioscience (San Diego, CA, USA):FITC-conjugated anti-CD3, PE/FITC-conjugated anti-CD4, PE-Cy5conjugated Foxp3, and appropriate isotype control mAbs, FounctionalGrade Purified Anti-mouse CD3 and CD28 mAbs, Enzyme-LinkedImmunosorbent Assay (ELISA) Kit for IL-10, TGF-β, IL-2 and IFN-γ,Fixation and Permeabilization Kit.
2.3. Tumorigenesis and paclitaxel treatment in vivo
Naive female C57BL/6 mice aged 6–8 weeks were subcutaneously(s.c.) injected with 2×105 3LL tumor cells in 100 μl Phosphate-BufferedSaline (PBS) per mouse on day 0. On day 11, these tumor-bearing micewere randomly divided into two groups (n=6 per group) and treated
Fig. 1. Paclitaxel decreased the percentage of Treg cells both in vivo and in vitro. Tumor-beaday 4. Percentage of CD4+Foxp3+ (Treg cell) and CD4+Foxp3(Teff cell) cells in the CD4+
derived from tumor-bearing C57BL/6 mice were treated with 0.1 μM paclitaxel for 24 h afteCells were double-labeled with anti-CD4 and anti-Foxp3 mAb to analyze the percentageexperiments. *pb0.05.
with orwithout paclitaxel intraperitoneally injection (i.p, 10 mg/kg) for3 days.
2.4. Isolation and culture of T cells and paclitaxel treatment in vitro
Before the isolation of T cells, the nylon wool fiber column waswashed with PBS containing 10% FCS gently to ensure the wool is wetand free of air bubbles. Nonadherent T-cells were collected by 5 mlmedium washes after adding 3×107 viable cells per column in avolume of 0.5 ml medium. Then the purified T cells were stimulated for48 h by the plate-bound anti-CD3 antibody (300 μl, 5 μg/ml), anti-CD28antibody (2 μg/ml), and cocultured with0.1 μM paclitaxel for another24 h.
2.5. Isolation and culture of Treg and Teff cells
Splenocytes from C57BL/6 mice were obtained to isolate CD4+CD25hi Treg cells and CD4+CD25-T cells by a Magnetic Activated CellSorting (MACS) system (Miltenyi Biotec.) according to the manufac-turer's protocol. CD4+CD25hi lymphocytes were routinely 95% pureas determined by flow cytometry. Purified CD4+CD25-T cells werecultured at a density of 2×106 cells/ml in 96-well plates with RPMI1640 supplemented with 10% FCS and CD3ε/28-Biotin MACSiBeadParticles for 24 h (bead-to-cell ratio 1:1), which was considered to beactivated effector T cells (Teff). The culture of purified Treg cells wassimilar to that of Teff cells, and the medium was additionallysupplemented with 200 U/ml IL-2. The MACSiBead Particles wereloadedwith CD3ε/28-Biotin and the process was performed accordingto the protocol provided by the manufacturer' protocol.
ring C57BL/6 mice were injected with PBS or paclitaxel (10 mg/kg) i.p and sacrificed atcell population were determined by flow cytometry (A). For in vitro experiment, T cellsr stimulating with monoclonal plate-bound anti-CD3 and soluble anti-CD28 antibodies.of Treg and Teff cells by FACS (B). Values represent the mean±SD of three separate
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2.6. Flow cytometry analysis
For the in vivo experiment, splenocytes derived from C57BL/6 miceinjected with or without paclitaxel were prepared as a single-cellsuspension. For surface stain, samples were incubatedwith appropriatevolumes of FITC-conjugated anti-CD3, PE-conjugated anti-CD4 mAbdiluted to 100 μl in PBS in the dark for 30 min, at 4 °C. Then, sampleswere washed twice with PBS and intracellularly stained with PE-Cy5-conjugated Foxp3 mAb by the Fixation and Permeabilization Kit.Purified T cells for in vitro experiment were stained in the same waydescribed above.
All the cells were analyzed by flow cytometry with CXP Analysissoftware (CYTOMICS FC500, Beckman, USA). Before analysis, sampleswere washed twice with PBS. Each sample was done in triplicate.
2.7. Cytokine quantification by ELISA
MACS sorted Teff cells and Treg cells were treated with differentconcentrations of paclitaxel (0, 0.1 μM, 1 μM) after 2 days' culturewhich were performed according to the protocol addressed above.Supernatants were collected for the cytokine level analysis of IL-2,IFN-γ (from Teff cells) and IL-10, TGF-β (from Treg cells) by the ELISAKit according to the manufacturer's protocol. The supernatants weredouble diluted before IL-2 and IFN-γ detection.
Fig. 2. Paclitaxel inhibited cytokine secretion and Foxp3 expression of Treg cells. Purified Trwith 0.1 μM and 1 μM paclitaxel for 24 h after stimulation with monoclonal plate-bound asecretion determination by ELISA: IL-10 and TGF-β (A), IL-2 and IFN-γ (B). Expression of Forepresent the mean±SD of three separate experiments. *pb0.05,**pb0.01.
2.8. Immunofluorescence
After treatingwith paclitaxel for 24 h, cell smearswere prepared ata concentration of 5×106 cells/ml, then washed with PBS and fixedwith 3% paraformal-dehyde for 30 min at room temperature. Cellswere immunostained with an anti-β-tubulin mouse monoclonalantibody (CalBiochem, USA) followed by secondary FITC-conjugatedanti-mouse antibody (CalBiochem, USA). Coverslips were mountedonto glass slides and analysed with a confocol microscope.
2.9. Western blot
Paclitaxel treated T cells were lysed in ice-cold RIPA lysis buffer(20 mMTris-HCl [pH7.5], 150 mMNaCl, 1 mMNa2EDTA, 1 mMEGTA, 1%Triton, 2.5 mM sodium pyrophosphate, 1 mM beta-glycerophosphate,1 mMNa3VO4, and1 μg/mL leupeptin) for 30minutes. Insolublematerialwas removed by centrifugation, and lysates were used for Westernblotting. Equal amounts of protein were separated by SDS-PAGE,transferred onto PVDF membrane (Invitrogen Corporation), andincubated with first antibodies BCL-2 and BAX (1:1000), Signals weredetected using the corresponding secondary HRP-conjugated antibody(1:10000) purchased from Amersham (GE Healthcare Bio-Sciences,Piscataway, NJ, USA) and enhanced chemiluminescence purchased fromPierce (Thermo Fisher, Rockford, IL, USA). Antibodies used for western
eg and Teff cells from tumor-bearing C57BL/6 mice were either untreated or incubatednti-CD3 and soluble anti-CD28 antibodies. Supernatants were harvested for cytokinexp3 (C) in the CD4+Foxp3 cell population was determined by flow cytometry. Values
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blot were rabbit anti-Bcl-2 and rabbit anti-BAK from Santa Cruz (SantaCruz, CA, USA).
2.10. Statistical analysis
Analyses were done with Graphpad Prism version 4.0 (GraphpadSoftware, Inc., San Diego, CA). Analysis of intergroup differences fortwo groups was performed using Student's t-test while analysis ofmore than two groups was using ANOVA. Differences at Pb0.05 wereconsidered to be significant. All values were presented as mean±standard error of the mean (S.E.M.).
3. Results
3.1. Paclitaxel decreased the percentage of Treg cells both in vivo andvitro
We have previously demonstrated that paclitaxel could augmentvaccine induced antitumor immunity in tumor-bearing mice [15]. Ourpreclinical research further showed paclitaxel-based chemotherapyinduced a selective reduction of the circulating Treg population inNSCLC patients [9]. To explore the mechanisms behind the selectivedepletion of Treg cells, we focused on the effect of paclitaxel in 3LL
Fig. 3. Paclitaxel induced apoptosis of Treg cells. Purified Treg and Teff cells from tumor-bearingafter stimulationwithmonoclonal plate-boundanti-CD3 and soluble anti-CD28 antibodies. Cellincubated with AnnexinV and PI according to the manufacture's protocols after treating with p
Lewis tumor model in the present study. Therefore, we first analyzedthe alteration of the percentage ratios of Treg and Teff cells in CD4+
cell following paclitaxel treatment. Three days after 3LL Lewistumor-bearing C57BL/6 mice were injected with paclitaxel (10 mg/kg)i.p, their splenocytes were double-labeled with anti-CD4 and anti-Foxp3mAb to analyze the percentage of Treg cells by FACS. As shown in Fig. 1A,we observed a significant decrease of the percentage of Treg cells inT cells from 12±1.5% to 5±0.8%(Pb0.05),while that of Teff cellsexhibited no significant changed(PN0.05).
To confirm the result above, we performed a corresponding invitro experiment to investigate the direct effect of paclitaxel onsplenic T cells. Splenic T cells were treated with 0.1 μM paclitaxel for24 h after anti-CD3/28 mAb stimulation. As expected, FACS analysisrevealed similar results to the data in vivo. The percentage of Tregcells in CD4+ cells dropped from 5±1.3% to 3±0.7% (Fig. 1B). Theseresults suggested that paclitaxel decreased the percentage of Tregcells both in vivo and in vitro (pb0.05).
3.2. Paclitaxel downregulated suppressive functions of Treg cells
In order to examine whether paclitaxel affected the immunosup-pressive function of Treg cells and the immunoenhancing function ofTeff cells, cytokine secretion was assessed. Since Treg cells were well
C57BL/6micewere either untreated or incubatedwith 0.1 μMand 1 μMpaclitaxel for 24 hviabilitywasmeasuredwith trypanblue exclusion test (A). PurifiedTreg andTeff cellswereaclitaxel and were analyzed by FACS for apoptosis detection (B). **pb0.01.
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acknowledged to exert their regulatory role through secretion ofTGF-β and IL-10 while Teff cells through IL-2 and IFN-γ [10], thesecytokines were analyzed in this study. We first isolated splenic Tregand Teff cells from 3LL Lewis tumor-bearing C57BL/6 mice by MACSbeads. Subsequently, CD4+CD25+T cells and CD4+CD25−T cells,considered as Treg and Teff cells respectively, were stimulated withanti-CD3 and CD28 antibodies. Approximately 95% of CD4+CD25+Tcells expressed Foxp3 (data not shown), a well established functionalmarker of Treg cells [11,13]. Exposure to paclitaxel for 24 h led to thedose-dependent decrease in the cytokine secretion of both TGF-β andIL-10 by Treg cells. The amount of TGF-β dropped from 5100±100(pg/ml) to 3820±250(pg/ml) at the dose of 0.1 μM and 2350±50(pg/ml) at the dose of 1 μM (Fig. 2A), respectively. Similarly, theamount of IL-10 descended from4410±59(pg/ml) to 3950±50(pg/ml)at the concentration of 0.1 μMand 3690±79(pg/ml) at the dose of 1 μM(Fig. 2A). However, IL-2 and IFN-γ of Teff cells showed no significantchanges (PN0.05) (Fig. 2B).
Foxp3 is an important regulatory molecule of Treg cells, involvedin the change of inhibitory function of Treg [11,13]. The MeanFluorescence Intensity (MFI) representing the density of Foxp3expression in Treg at the cellular level was determined. Resultshowed that the MFI of Foxp3 expression of paclitaxel-treated Tregcells was lower than that of untreated ones when equal cell numbersof Treg cells were examined (Pb0.05) (Fig. 2C).
3.3. Paclitaxel induced apoptosis of Treg cells
To explore how paclitaxel selectively decreased the amount of Tregcells, purified Treg or Teff cells were co-cultured with different doses ofpaclitaxel for 24 h. Cell viability was measured with trypan blueexclusion test. As shown in Fig. 3A, Treg cells displayed a high sensitivityto paclitaxel in a dose-dependent manner. Cell viability of Treg cellstreated with paclitaxel at the concentration of 0.1 μM and 1 μMdecreased to 65.4±4.5% and 47.2±2.3%, respectively. Importantly,both of these two doses of paclitaxel were not toxic to Teff cells(PN0.05). In addition, PI/Annexin V analysis revealed a high percentage
Fig. 4. Paclitaxel exerted no different effects on tubulin of Treg and Teff cells. Purified Treg an0.1 μM and 1 μMpaclitaxel for 24 h after stimulation with monoclonal plate-bound anti-CD3both Treg and Teff cells treated with paclitaxel was illustrated by the confocol fluorescence
of Treg cells underwent apoptosis after paclitaxel treatment for 24 h.The percentage of apoptotic Treg cells increased in a dose dependentmanner from the concentration of 0.1 μM to 1 μM(Fig. 3B). In contrast,no significant change in the percentage of apoptotic cells was observedin Teff cells (PN0.05). This result was also confirmed by DAPI staining.Dark blue particles (fragmented nuclei) of Treg cells increasedafter paclitaxel treatment, which was illustrated by laser confocalfluorescence microscopy in Fig. 4.
3.4. Selective impairment of Treg cells by paclitaxel was not mediated viatubulin
As it has been widely acknowledged that one of the mainmechanisms of paclitaxel is promoting tubulin polymerization, thusleading to mitotic arrest [1], we wonder whether it was involved in theremarkable susceptibility of Treg cells to paclitaxel-induced apoptosis.In the absence of paclitaxel, both Treg and Teff cells were characterizedas being relatively large, irregular shaped bodies with a readily visibledense network of tubulin often focusing around the centrosome (Fig. 4).Treatment of 0.1 μM and 1 μM paclitaxel resulted in distinct alterationsin both cell morphology andmicrotubule distribution. Many of the Tregand Teff cells became rounded with evidence of microtubulestabilization and no longer focused around the centrosome. However,treatment of paclitaxel had no distinguishable effects between Treg andTeff cells on morphology or microtubule stabilization indicating thattubulin was not involved in the selective apoptosis of Treg cells.
3.5. Bcl-2/Bax contributed to the paclitaxel induced apoptosis of Tregcells
Bcl-2, a molecule in the anti-apoptotic family, was recently deemedto be a new target of paclitaxel [16]. We found that bcl-2 expression ofTreg cells derived from 3LL Lewis tumor-bearing C57BL/6 mice wasdown-regulated significantly after paclitaxel treatment for both 24 hand 48 h by Western blot. As shown in Fig. 5A, unlike Treg cells, Bcl-2expression of Teff cells was not significantly alterated after paclitaxel
d Teff cells from tumor-bearing C57BL/6 mice were either untreated or incubated withand soluble anti-CD28 antibodies. Immunofluorescent staining of β-tubules and DAPI inmicroscopy. Results are representatives of at least three independent experiments.
Fig. 5. Paclitaxel down-regulated Bcl-2 expression and up-regulated Bax expression on Treg cells. Bcl-2 (A) and Bax (B) expression on Treg and Teff cells treated with paclitaxel(0.1 μM and 1 μM) for 24 h and 48 h respectively were analyzed byWestern blot. Purified Treg and Teff cells were cocultured with 0.1 μM, 1 μMpalitaxel, under the pre-treatment ofBcl-2 inhibitor ABT 737 (10 μM) for 24 h while the control group using DMSO (10 mM) instead. Cell viability was analyzed by the trypan blue exclusion test (C). Results arerepresentatives of at least three independent experiments and values represent the mean±SD of three separate experiments. *pb0.05, **pb0.01.
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treatment. Additionally, the apoptotic molecule Bax, a member of Bcl-2family, was up-regulated apparently in Treg cells following paclitaxelexprosure (Fig. 5B). The difference between Treg and Teff cellsresponding to paclitaxel vanished after blocking the Bcl-2 pathway byBcl-2 inhibitor ABT 737, which confirmed the results above (Fig. 5C).Hence, downregulation of Bcl-2 and upregulation of Bax in Treg cells areinvolved in the selective impairment of paclitaxel.
4. Discussion
Several chemotherapeutic agents have been shown to have dosedependent immunostimulatory activity [3,4]. There is increasing datato suggest that these compounds including paclitaxel are also capableof specifically inducing Treg cell depletion [15,17], however, themolecular basis of which remained to be further elucidated. In the
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present study, we provided evidence that Bcl-2/Bax mediatedapoptosis explained the selective killing of Treg cells by paclitaxel.
Treg cells suppress the antitumor effect of immune system inpatients and murine models. Several lines of evidence indicate thatthe interference in Treg biology or depletion of Treg cells is of criticalimportance in the treatment of cancer [3,14,18,19].On the basis ofresults from several clinical and preclinical murine studies, differentmethods of reducing Treg cell numbers or blocking their activitywithin the tumor microenvironment are currently being investigated.The commonly used chemotherapeutic agent paclitaxel as well ascyclophosphamide has been reported to have anti-Treg-cell activityand enhance immune responses at low dose [9,15,20]. We haveshown in the present study that low-dose paclitaxel (0.1 μM) mostlyaffects Treg cells rather than Teff cells. However, high-dose paclitaxel(concentration higher than 1 μM) may impair Teff cells at thesame time (data not shown). Therefore, the administration of singlehigh-dose paclitaxel kills Treg cells as well as other immune cells.However, paclitaxel can be metabolized within a short time in vivo,leading to the recovery of Treg cells. In contrast, metronomic low-dosepaclitaxel treatmentmay continue to selectively deplete Treg cells. Basedon our findings, we suggest that metronomic low-dose paclitaxeladministration is an ideal approach for Treg cell depletion, therebybreaking tumor immunotolerance and enhancing antitumor immuneresponses.
In this regard, our present study, shedding light on the underlyingmechanism of low-dose paclitaxel selectivity for Treg cells, hasimportant clinical significance. We found that paclitaxel inducedsignificant apoptosis in Treg cells, but not in Teff cells, which couldexplain thedifferential depletion of Treg cells followingpaclitaxel-basedchemotherapy. This result inmurine studywas in consistencewith thatin patients with NSCLC [9].
Paclitaxel was thought to link its induction of apoptosis touncharacterized cellular events arising frommicrotubule polymerizationand mitotic arrest. However, paclitaxel-induced microtubule bundlingandmitotic blockade have been functionally separated from its apoptoticand subsequent cytotoxic effects in someexperiments [21–23].Our studyshowed that tubulin in both Treg and Teff cells displayed no obviousdifference after exposure to paclitaxel, indicating the tubulin was notinvolved in the selective function of paclitaxel. It also validated themanifestation that apoptosis is an independent determinant of thecytotoxic efficacy of paclitxel caused by tubulin bundling and mitoticblockade.
It has recently been shown in vitro that paclitaxel could targetBcl-2 and therefore lead to apoptosis [16]. Subsequently, a number ofreports suggested Bcl-2 be an additional intracellular target ofpaclitxel besides microtubule [24–26]. It has been reported thatpaclitaxel can bind to the β-subunit of the tubulin heterodimer andstabilize themicrotubules by inhibiting their depolymerization, whichresults in cell division cycle arrest and eventually leads to theapoptosis of tumor cells. Bcl-2 family proteins are key regulators ofapoptosis, which are implicated in many physiological and pathologicprocesses. The members of this family can be divided into two groups,one with anti-apoptotic (i.e.Bcl-2, Bcl-XL, Bcl-w) and the other withpro-apoptotic (i.e.Bax, Bim, Bid) properties [26,27]. Bcl-2 is widelyreported to play an important role in tumorigenesis and multi-drugresistance by blocking apoptosis [28–31]. We found that paclitaxeldecreased the expression of anti-apoptotic molecule Bcl-2 in Tregcells while increased the corresponding pro-apoptotic member Bax.Such alteration could contribute to the apoptotic sensitivity of Tregtowards paclitaxel. Importantly, blocking the Bcl-2 pathway eliminatedthe difference between Treg and Teff cells responding to paclitaxel,suggesting that Bcl-2 is involved in the distinctive effect of paclitaxel onTreg and Teff cells.
In summary, our data show that Bcl-2/Bax, by virtue of theirdifferential expression levels induced by paclitaxel in Treg and Teff cells,contributes to the sensitivity of these cells to paclitaxel. These findings
provide a basic rationale for the use of paclitaxel in chemotherapycombined with immunotherapy.
Acknowledgments
This work was supported by the National Key Technologies R & DProgram of China during the eleventh Five-Year Plan Period(2009ZX10004-104, 2009ZX09301-011) and the National ScienceFoundation of China (No.30872378, J0730860), National 973 project(2010CB912603) in China.
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