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Lin YW, Chiu HC, Syu JJ, Jian YT, Chen CY. Abstract A33: Enhancement of thymidine phosphorylase downregulation by erlotinib enhances cytotoxicity affected by tamoxifen in human non-small cell lung cancer cells. Mol Cancer Res 2014. [DOI: 10.1158/1557-3125.rasonc14-a33] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Tamoxifen is a triphenylethylene nonsteroidal antiestrogen used worldwide as an adjuvant chemotherapeutic agent in the treatment of breast cancer. However, the molecular mechanism of tamoxifen also could induce cytotoxicity in non-small cell lung cancer (NSCLC) cells have not been proved. In this study, tamoxifen treatment inhibited cell survival in two NSCLC cells, H520 and H1975. Treatment with tamoxifen decreased TP mRNA and protein levels in an AKT inactivation-dependent manner. Furthermore, expression of constitutively active AKT (AKT-CA) vectors significantly rescued the decreased TP protein and mRNA levels in tamoxifen-treated NSCLC cells. In contrast, a combination of PI3K inhibitors (LY294002 or wortmannin) further decreased the TP expression and cell viability induced by tamoxifen. Moreover, knocking down TP expression by transfection with small interfering RNA of TP enhanced the cytotoxicity and growth inhibition of tamoxifen. Erlotinib (Tarceva, OSI-774), an orally available inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, is approved for clinical use in the NSCLC therapy. Compared to each single treatment, the combining tamoxifen with erlotinib resulted in a synergistically inhibited the cell viability and cell growth, accompanied with the reduction of phospho-AKT, phosph-ERK1/2, and TP protein levels. An enhancement of AKT or ERK1/2 activation by transfecting the cancer cells with constitutively active AKT or MKK1/2 expression vectors significantly restored the two drugs combination-reduced TP protein levels as well as cell viability. Taken together, our results suggest that the down-modulation of AKT and ERK1/2-mediated TP expression by erlotinib represents a key factor in enhancing the cytotoxic effects of tamoxifen in NSCLC cells.
Citation Format: Yun-Wei Lin, Hsien-Chun Chiu, Jhan-Jhang Syu, Yun-Ting Jian, Chien-Yu Chen. Enhancement of thymidine phosphorylase downregulation by erlotinib enhances cytotoxicity affected by tamoxifen in human non-small cell lung cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A33. doi: 10.1158/1557-3125.RASONC14-A33
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Ko JC, Chiu HC, Syu JJ, Jian YJ, Chen CY, Jian YT, Huang YJ, Wo TY, Lin YW. Tamoxifen enhances erlotinib-induced cytotoxicity through down-regulating AKT-mediated thymidine phosphorylase expression in human non-small-cell lung cancer cells. Biochem Pharmacol 2014; 88:119-27. [DOI: 10.1016/j.bcp.2014.01.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Revised: 01/10/2014] [Accepted: 01/10/2014] [Indexed: 12/12/2022]
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Ko JC, Chiu HC, Wo TY, Huang YJ, Tseng SC, Huang YC, Chen HJ, Syu JJ, Chen CY, Jian YT, Jian YJ, Lin YW. Inhibition of p38 MAPK-dependent MutS homologue-2 (MSH2) expression by metformin enhances gefitinib-induced cytotoxicity in human squamous lung cancer cells. Lung Cancer 2013; 82:397-406. [PMID: 24138903 DOI: 10.1016/j.lungcan.2013.09.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Revised: 09/12/2013] [Accepted: 09/18/2013] [Indexed: 12/29/2022]
Abstract
OBJECTIVES Gefitinib, a quinazoline-derived tyrosine kinase inhibitor, has anti-tumor activity in vivo and in vitro. Human MutS homologue-2 (MSH2) plays a central role in promoting genetic stability by correcting DNA replication errors. The present study investigated the effects of p38 mitogen-activated protein kinase (MAPK) signal on gefitinib-induced MSH2 expression in two human non-small cell lung squamous cancer cell lines. MATERIALS AND METHODS After the gefitinib treatment, the expressions of MSH2 mRNA were determined by real-time PCR and RT-PCR analysis. Protein levels of MSH2, phospho-MKK3/6, phospho-p38 MAPK were determined by Western blot analysis. We used specific MSH2, and p38 MAPK small interfering RNA to examine the role of p38 MAPK-MSH2 signal in regulating the chemosensitivity of gefitinib. Cell viability was assessed by MTS assay, trypan blue exclusion, and colony-forming ability assay. RESULTS Exposure of gefitinib increased MSH2 protein and mRNA levels, which was accompanied by MKK3/6-p38 MAPK activation in H520 and H1703 cells. Moreover, blocking p38 MAPK activation by SB202190 significantly decreased gefitinib-induced MSH2 expression by increasing mRNA and protein instability. In contrast, enhancing p38 activation using constitutively active MKK6 (MKK6E) increased MSH2 protein and mRNA levels. Specific inhibition of MSH2 expression by siRNA enhanced gefitinib-induced cytotoxicity. Metformin, an anti-diabetic drug, might reduce cancer risk. In human lung squamous cancer cells, metformin decreased gefitinib-induced MSH2 expression and augmented the cytotoxic effect and growth inhibition by gefitinib. Transient expression of MKK6E or HA-p38 MAPK vector could abrogate metformin and gefitinib-induced synergistic cytotoxic effect in H520 and H1703 cells. CONCLUSION Together, down-regulation of MSH2 expression can be a possible strategy to enhance the sensitivity of gefitinib to human lung squamous cancer cells.
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Lin YW, Tseng SC, Huang YC, Chiu HC, Chen HJ, Weng SH, Huang YJ, Wo TY. Abstract 1283: Role of ERCC1 in metformin enhancing paclitaxel-induced cytotoxicity. Cancer Res 2013. [DOI: 10.1158/1538-7445.am2013-1283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Metformin, an extensively used and well-tolerated drug for treating individuals with type 2 diabetes, has recently gained significant attention as an anticancer drug. On the other hand, paclitaxel (taxol) is a new antineoplastic drug that has shown promise in the treatment of non-small cell lung cancer (NSCLC). High expression levels of excision repair cross-complementary 1 (ERCC1) in cancers have been positively associated with the DNA repair capacity and a poor prognosis in NSCLC patients treated with platinum-containing chemotherapy. In this current study, paclitaxel was found to increase phosphorylation of mitogen-activated protein kinase (MAPK) kinase 3/6 (MKK3/6)-p38 MAPK as well as protein and mRNA levels of ERCC1 in H1650 and H1703 cells. Moreover, paclitaxel-induced ERCC1 protein and mRNA levels significantly decreased via the downregulation of p38 activity by either a p38 MAPK inhibitor SB202190 or p38 knockdown with specific small interfering RNA (siRNA). Specific inhibition of ERCC1 with siRNA was found to enhance the paclitaxel-induced cytotoxic effect and growth inhibition. Furthermore, metformin was able to not only decrease the paclitaxel-induced p38 MAPK-mediated ERCC1 expression, but also augment the cytotoxic effect induced by paclitaxel. Finally, expression of constitutive activate MKK6 or HA-p38 MAPK vectors in lung cancer cells was able to abrogate ERCC1 downregulation by metformin and paclitaxel as well as cell viability and DNA repair capacity. Overall, our results suggest that inhibition of the p38 MAPK signaling by metformin coupled with paclitaxel therapy in human NSCLC cells may be a clinically useful combination, which however will require further validation.
Citation Format: Yun-Wei Lin, Sheng-Chieh Tseng, Yu-Ching Huang, Hsien-Chun Chiu, Huang-Jen Chen, Shao-Hsing Weng, Yi-Jhen Huang, Ting-Yu Wo. Role of ERCC1 in metformin enhancing paclitaxel-induced cytotoxicity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1283. doi:10.1158/1538-7445.AM2013-1283
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Lin YW, Huang YC, Tseng SC, Chiu HC, Chen HJ, Huang YJ, Wo TY, Weng SH, Ko JC. Abstract 1301: Metformin induces cytotoxicity by TP and ERCC1 decrease. Cancer Res 2013. [DOI: 10.1158/1538-7445.am2013-1301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Metformin is an anti-diabetic drug recently shown to inhibit cancer cell proliferation and growth, although the involved molecular mechanisms have not been elucidated. In many cancer cells, highly expression of thymidine phosphorylase (TP) and ERCC1 are associated with poor prognosis. We used A549 and H1975 huamn non-small cell lung cancer (NSCLC) cell lines to investigate the role of TP and ERCC1 expression in metformin-induced cytotoxicity. Metformin treatment decreased cellular TP and ERCC1 protein and mRNA levels by down-regulating phosphorylated MEK1/2-ERK1/2 protein levels in a dose- and time-dependent manner. The enforced expression of the constitutively active MEK1 (MEK1-CA) vectors significantly restored cellular TP and ERCC1 protein levels and cells viability. Specific inhibition of TP and ERCC1 expression by siRNA enhanced the metformin-induced cytotoxicity and growth inhibition. In conclusion, metformin induces cytotoxicity by down-regulating TP and ERCC1 expression in NSCLC cells.
Citation Format: Yun-Wei Lin, Yu-Ching Huang, Sheng-Chieh Tseng, Hsien-Chun Chiu, Huang-Jen Chen, Yi-Jhen Huang, Ting-Yu Wo, Shao-Hsing Weng, Jen-Chung Ko. Metformin induces cytotoxicity by TP and ERCC1 decrease. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1301. doi:10.1158/1538-7445.AM2013-1301
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Ko JC, Huang YC, Chen HJ, Tseng SC, Chiu HC, Wo TY, Huang YJ, Weng SH, Chiou RYY, Lin YW. Metformin induces cytotoxicity by down-regulating thymidine phosphorylase and excision repair cross-complementation 1 expression in non-small cell lung cancer cells. Basic Clin Pharmacol Toxicol 2013; 113:56-65. [PMID: 23362830 DOI: 10.1111/bcpt.12052] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 01/02/2013] [Indexed: 01/22/2023]
Abstract
Metformin is an antidiabetic drug recently shown to inhibit cancer cell proliferation and growth, although the involved molecular mechanisms have not been elucidated. In many cancer cells, high expression of thymidine phosphorylase (TP) and Excision repair cross-complementation 1 (ERCC1) is associated with poor prognosis. We used A549 and H1975 human non-small cell lung cancer (NSCLC) cell lines to investigate the role of TP and ERCC1 expression in metformin-induced cytotoxicity. Metformin treatment decreased cellular TP and ERCC1 protein and mRNA levels by down-regulating phosphorylated MEK1/2-ERK1/2 protein levels in a dose- and time-dependent manner. The enforced expression of the constitutively active MEK1 (MEK1-CA) vectors significantly restored cellular TP and ERCC1 protein levels and cell viability. Specific inhibition of TP and ERCC1 expression by siRNA enhanced the metformin-induced cytotoxicity and growth inhibition. Arachidin-1, an antioxidant stilbenoid, further decreased TP and ERCC1 expression and augmented metformin's cytotoxic effect, which was abrogated in lung cancer cells transfected with MEK1/2-CA expression vector. In conclusion, metformin induces cytotoxicity by down-regulating TP and ERCC1 expression in NSCLC cells.
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Tseng SC, Huang YC, Chen HJ, Chiu HC, Huang YJ, Wo TY, Weng SH, Lin YW. Metformin-mediated downregulation of p38 mitogen-activated protein kinase-dependent excision repair cross-complementing 1 decreases DNA repair capacity and sensitizes human lung cancer cells to paclitaxel. Biochem Pharmacol 2012; 85:583-94. [PMID: 23228696 DOI: 10.1016/j.bcp.2012.12.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Revised: 12/03/2012] [Accepted: 12/03/2012] [Indexed: 10/27/2022]
Abstract
Metformin, an extensively used and well-tolerated drug for treating individuals with type 2 diabetes, has recently gained significant attention as an anticancer drug. On the other hand, paclitaxel (Taxol) is a new antineoplastic drug that has shown promise in the treatment of non-small cell lung cancer (NSCLC). High expression levels of excision repair cross-complementary 1 (ERCC1) in cancers have been positively associated with the DNA repair capacity and a poor prognosis in NSCLC patients treated with platinum-containing chemotherapy. In this current study, paclitaxel was found to increase phosphorylation of mitogen-activated protein kinase (MAPK) kinase 3/6 (MKK3/6)-p38 MAPK as well as protein and mRNA levels of ERCC1 in H1650 and H1703 cells. Moreover, paclitaxel-induced ERCC1 protein and mRNA levels significantly decreased via the downregulation of p38 activity by either a p38 MAPK inhibitor SB202190 or p38 knockdown with specific small interfering RNA (siRNA). Specific inhibition of ERCC1 with siRNA was found to enhance the paclitaxel-induced cytotoxic effect and growth inhibition. Furthermore, metformin was able to not only decrease the paclitaxel-induced p38 MAPK-mediated ERCC1 expression, but also augment the cytotoxic effect induced by paclitaxel. Finally, expression of constitutive activate MKK6 or HA-p38 MAPK vectors in lung cancer cells was able to abrogate ERCC1 downregulation by metformin and paclitaxel as well as cell viability and DNA repair capacity. Overall, our results suggest that inhibition of the p38 MAPK signaling by metformin coupled with paclitaxel therapy in human NSCLC cells may be a clinically useful combination, which however will require further validation.
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Ko JC, Chen HJ, Huang YC, Tseng SC, Weng SH, Wo TY, Huang YJ, Chiu HC, Tsai MS, Chiou RYY, Lin YW. HSP90 inhibition induces cytotoxicity via down-regulation of Rad51 expression and DNA repair capacity in non-small cell lung cancer cells. Regul Toxicol Pharmacol 2012; 64:415-24. [PMID: 23069143 DOI: 10.1016/j.yrtph.2012.10.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Revised: 10/02/2012] [Accepted: 10/07/2012] [Indexed: 12/20/2022]
Abstract
Heat shock protein 90 (HSP90) is an exciting new target in cancer therapy. Repair protein Rad51 is involved in protecting non-small cell lung cancer (NSCLC) cell lines against chemotherapeutic agent-induced cytotoxicity. This study investigated the role of Rad51 expression in HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG)-induced cytotoxicity in two NSCLC cell lines, A549 and H1975. The 17-AAG treatment decreased cellular Rad51 protein and mRNA levels and phosphorylated MKK1/2-ERK1/2 protein levels, and disrupted the HSP90 and Rad51 interaction. This triggered Rad51 protein degradation through the 26S proteasome pathway. The 17-AAG treatment also decreased the NSCLC cells' DNA repair capacity, which was restored by the forced expression of the Flag-Rad51 vector. Specific inhibition of Rad51 expression by siRNA further enhanced 17-AAG-induced cytotoxicity. In contrast, enhanced ERK1/2 activation by the constitutively active MKK1/2 (MKK1/2-CA) vector significantly restored the 17-AAG-reduced Rad51 protein levels and cell viability. Arachidin-1, an antioxidant stilbenoid, further decreased Rad51 expression and augmented the cytotoxic effect and growth inhibition of 17-AAG. The 17-AAG and arachidin-1-induced synergistic cytotoxic effects and decreased DNA repair capacity were abrogated in lung cancer cells with MKK1/2-CA or Flag-Rad51 expression vector transfection. In conclusion, HSP90 inhibition induces cytotoxicity by down-regulating Rad51 expression and DNA repair capacity in NSCLC cells.
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Lin YW, Weng SH, Ko JC, Chen HJ, Tseng SC, Huang YC, Tsai MS, Chiou RYY. Abstract 2554: HSP90 inhibition induced cytotoxicity via downregulation of Rad51 expression and DNA repair capacity in non-small cell lung cancer cells. Cancer Res 2012. [DOI: 10.1158/1538-7445.am2012-2554] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Heat shock protein 90 (HSP90) is an exciting target in cancer therapy. Our previous studies indicated that repair protein Rad51 involved in protecting non-small lung cancer (NSCLC) cell lines against chemotherapeutic agents induced cytotoxicity. In this study, the role of Rad51 expression in HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) induced cytotoxicity in two NSCLC cell lines, A549 and H1975, were investigated. 17-AAG treatment decreased cellular Rad51 protein and mRNA levels and phosphorylated MKK1/2-ERK1/2 protein levels. 17-AAG treatment disrupted the HSP90 and Rad51 interaction and triggered Rad51 protein degradation through 26S proteasome pathway. Moreover, 17-AAG treatment decreased DNA repair capacity in NSCLC cells, which could restore by enforced expression of Flag-Rad51 vector. Specific inhibition of Rad51 expression by siRNA could further enhance the 17-AAG-induced cytotoxicity. Enhancement of ERK1/2 activation by constitutively active MKK1/2 (MKK1/2-CA) vector significantly restored the 17-AAG-reduced Rad51 protein levels as well as cell viability. Moreover, arachidin-1, antioxidant stilbenoids, has demonstrated beneficial effects on human health. It could further decrease Rad51 expression and augment the cytotoxic effect and growth inhibition by 17-AAG. Moreover, 17-AAG and arachidin-1-induced synergistic cytotoxic effect and DNA repair capacity decrease could be abrogated in lung cancer cells with MKK1/2-CA or Flag-Rad51 expression vector transfection. Our results suggested that HSP90 inhibition induced cytotoxicity via downregulation of Rad51 expression and DNA repair capacity in NSCLC cells.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2554. doi:1538-7445.AM2012-2554
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Chen YK, Chang YS, Lin YW, Wu MY. First Report of Cucumber mosaic virus in Desert Rose in Taiwan. PLANT DISEASE 2012; 96:593. [PMID: 30727436 DOI: 10.1094/pdis-11-11-0917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Desert rose (Adenium obesum (Forssk.) Roem. & Schult, family Apocynaceae) is native to southeastern Africa, and is a perennial potted ornamental with colorful flowers that are popular in Taiwan. Symptoms of mosaic and chlorotic ringspots and line patterns on leaves were observed in July 2010, on all eight plants in a private garden in Potzu, Chiayi, Taiwan. Spherical virus particles with a diameter of approximately 28 nm were observed in crude sap prepared from symptomatic leaves. Virus culture was established by successive local lesion isolation in Chenopodium quinoa and was maintained in the systemic host Nicotiana tabacum van Hicks. The virus was mechanically transmissible to indicator plants and induced symptoms similar to those incited by Cucumber mosaic virus (CMV). Observed symptoms included local lesions on inoculated leaves of C. amaranticolor and systemic mosaic in Cucumis sativus, Lycopersicon esculentum, N. benthamiana, N. glutinosa, and N. rustica. On N. tabacum, necrotic ringspots developed on inoculated leaves followed by systemic mosaic. Serological tests using ELISA assays and western blotting indicated that the virus reacted positively to a rabbit antiserum prepared to CMV (4). Amplicons of an expected size (1.1 kb) were obtained in reverse transcription-PCR with primers specific to the 3'-half of CMV RNA 3 (3) using total RNA extracted from infected desert rose and N. tabacum. The amplified cDNA fragment was cloned and sequenced (GenBank Accession No. AB667971). Nucleotide sequences of the coat protein open reading frame (CP ORF) (657 nt) had 92 to 96% and 76 to 77% sequence identity to those of CMV in subgroups I (GenBank Accession Nos. NC_001440, D00385, M57602, D28780, and AB008777) and II (GenBank Accession Nos. L15336, AF127976, AF198103, and M21464), respectively. Desert roses infected by Tomato spotted wilt virus (TSWV) (1) and CMV (2) have been reported previously. In spite of the plants showing mosaic symptoms similar to that caused by CMV (2) and chlorotic ringspots and line patterns caused by TSWV (1), only CMV was detected in and isolated from these infected desert roses. However, the possibility of mixed infection of CMV and other viruses were not excluded in this research. To our knowledge, this is the first report of CMV infection in desert rose plants occurring in Taiwan. References: (1) S. Adkins and C. A. Baker. Plant Dis. 89:526, 2005. (2) C. A. Baker et al. Plant Dis. 87:1007, 2003. (3) Y. K. Chen et al. Arch. Virol. 146:1631, 2001. (4) Y. K. Chen and C. C. Yang. Plant Dis. 89:529, 2005.
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Weng SH, Tsai MS, Chiu YF, Kuo YH, Chen HJ, Lin YW. Enhancement of Mitomycin C-Induced Cytotoxicity by Curcumin Results from Down-Regulation of MKK1/2-ERK1/2-Mediated Thymidine Phosphorylase Expression. Basic Clin Pharmacol Toxicol 2011; 110:298-306. [DOI: 10.1111/j.1742-7843.2011.00806.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Shen YH, Chen BR, Cherng SH, Chueh PJ, Tan X, Lin YW, Lin JC, Chuang SM. Cisplatin transiently up-regulates hHR23 expression through enhanced translational efficiency in A549 adenocarcinoma cells. Toxicol Lett 2011; 205:341-50. [DOI: 10.1016/j.toxlet.2011.06.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2011] [Revised: 06/22/2011] [Accepted: 06/23/2011] [Indexed: 10/18/2022]
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Ko JC, Tsai MS, Weng SH, Kuo YH, Chiu YF, Lin YW. Curcumin enhances the mitomycin C-induced cytotoxicity via downregulation of MKK1/2–ERK1/2-mediated Rad51 expression in non-small cell lung cancer cells. Toxicol Appl Pharmacol 2011; 255:327-38. [DOI: 10.1016/j.taap.2011.07.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 07/06/2011] [Accepted: 07/15/2011] [Indexed: 01/20/2023]
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Lin YW, Tsai MS, Chiu YF, Weng SH, Kuo YH, Chuang SM. Abstract 1699: Thymidylate synthase and thymidine phosphorylase expression contributes to cisplatin resistance. Cancer Res 2011. [DOI: 10.1158/1538-7445.am2011-1699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Chemotherapy for advanced human non-small cell lung cancer (NSCLC) includes platinum-containing compound such as cisplatin in combination with a second- or third-generation cytotoxic agents. 5-Fluorouracil (5-FU) belongs to anti-metabolite chemotherapeutics, and its mechanism of cytotoxicity is involved in inhibition of thymidylate synthase (TS). TS and thymidine phosphorylase (TP) were key enzymes of the pyrimidine salvage pathway. In this study, we have examined the molecular mechanism of TS and TP in regulating the drug sensitivity to cisplatin in NSCLC cell lines. Cisplatin could increase the phosphorylation of MKK1/2-ERK1/2 and the protein levels of TS and TP through enhancing the protein stability in A549 and H1975 cells. Blocking ERK1/2 activation by MKK1/2 inhibitor (U0126) decreases TS and TP protein levels in both cell lines treated with cisplatin. Depletion of endogenous TS or TP expression by specific small interfering RNA transfection significantly increases cisplatin-induced cell death and growth inhibition. Moreover, pemetrexed (TS inhibitor) enhances cisplatin-induced cytotoxic effects. Combined treatment with 5-FU can decrease cisplatin-induced ERK1/2 activation and the induction of TS and TP, which can subsequently result in synergistic cytotoxic effects. Enforced expression of constitutive active MKK1/2 vectors rescue the protein levels of phospho-ERK1/2, TS and TP, and the cell viability which were decreased by cisplatin and 5-FU combination. In contrast, U0126 enhances the drug sensitivity to cisplatin and/or 5-FU in lung cancer cells. We conclude that the up-regulation of ERK1/2-dependent TS and TP can protect human lung cancer cells from cisplatin-induced cytotoxicity.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1699. doi:10.1158/1538-7445.AM2011-1699
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Tsai MS, Weng SH, Kuo YH, Chiu YF, Lin YW. Synergistic effect of curcumin and cisplatin via down-regulation of thymidine phosphorylase and excision repair cross-complementary 1 (ERCC1). Mol Pharmacol 2011; 80:136-46. [PMID: 21493726 DOI: 10.1124/mol.111.071316] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Curcumin (diferuloylmethane), a phenolic compound obtained from the rhizome of Curcuma longa, is known to have antiproliferative and antitumor properties. Thymidine phosphorylase (TP), an enzyme of the pyrimidine salvage pathway, is considered an attractive therapeutic target, and its expression could suppress cancer cell death induced by DNA damage agents. Excision repair cross-complementary 1 (ERCC1) is a protein involved the process of nucleotide excision repair. The ERCC1 gene is expressed at high levels in cancers and has been associated with resistance to platinum-based chemotherapy. In this study, the effects of curcumin on TP and ERCC1 expression induced by cisplatin in non-small-cell lung cancer (NSCLC) cell lines was investigated. Exposure of the NSCLC cells to various concentrations of curcumin (5-40 μM) down-regulates the mRNA and protein levels of TP and ERCC1 through destabilization of the mRNA and proteins via a mechanism involving inactivation of MKK1/2-extracellular signal-regulated kinase (ERK1/2). Depletion of endogenous TP or ERCC1 expression by transfection with specific small interfering RNAs significantly decreases cell viability in curcumin-exposed NSCLC cells. Curcumin enhances the sensitivity of cisplatin treatment for NSCLC through inactivation of ERK1/2 and by decreasing the TP and ERCC1 protein levels. Enhancement of ERK1/2 signaling by constitutively active MKK1/2 causes an increase in TP and ERCC1 protein levels and promotes cell viability after cotreatment with curcumin and cisplatin. Enhancement of the cytotoxicity to cisplatin by administration of curcumin is mediated by down-regulation of the expression levels of TP and ERCC1 and by inactivation of ERK1/2.
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Ko JC, Tsai MS, Chiu YF, Weng SH, Kuo YH, Lin YW. Up-regulation of extracellular signal-regulated kinase 1/2-dependent thymidylate synthase and thymidine phosphorylase contributes to cisplatin resistance in human non-small-cell lung cancer cells. J Pharmacol Exp Ther 2011; 338:184-94. [PMID: 21444628 DOI: 10.1124/jpet.111.179663] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Chemotherapy for advanced human non-small-cell lung cancer (NSCLC) includes platinum-containing compound such as cisplatin in combination with a second- or third-generation cytotoxic agent. 5-Fluorouracil (5-FU) belongs to antimetabolite chemotherapeutics, and its mechanism of cytotoxicity is involved in the inhibition of thymidylate synthase (TS). TS and thymidine phosphorylase (TP) are key enzymes of the pyrimidine salvage pathway. In this study, we have examined the molecular mechanism of TS and TP in regulating drug sensitivity to cisplatin in NSCLC cell lines. Cisplatin could increase the phosphorylation of mitogen-activated protein kinase kinase 1/2 (MKK1/2)-extracellular signal-regulated kinase 1/2 (ERK1/2) and the protein levels of TS and TP through enhancing the protein stability in A549 and H1975 cells. Blocking ERK1/2 activation by MKK1/2 inhibitor [U0126; 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene)] decreased TS and TP protein levels in both cell lines treated with cisplatin. Depletion of endogenous TS or TP expression by specific small interfering RNA transfection significantly increased cisplatin-induced cell death and growth inhibition. Combined treatment with 5-FU could decrease cisplatin-induced ERK1/2 activation and the induction of TS and TP, which subsequently resulted in synergistic cytotoxic effects. Enforced expression of constitutive active MKK1/2 vectors rescued the protein levels of phospho-ERK1/2, TS, and TP, and the cell viability that were decreased by cisplatin and 5-FU combination. In contrast, U0126 enhanced drug sensitivity to cisplatin and/or 5-FU in lung cancer cells. In conclusion, the up-regulation of ERK1/2-dependent TS and TP can protect human lung cancer cells from cisplatin-induced cytotoxicity.
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Chen RS, Lu MC, Wang SD, Ke HS, Teng RH, Kao YL, Kuo CC, Kao ST, Lin YW, Shieh B, Li C, Liao HF. Two Chinese Herbal Regimens Safe for the Elderly on Inhibiting Liver and Bladder Tumor Cell Growth and Regulating Gene Expression. INT J GERONTOL 2011. [DOI: 10.1016/j.ijge.2011.01.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Lin YW, Yang FJ, Chen CL, Lee WT, Chen RS. Free radical scavenging activity and antiproliferative potential of Polygonum cuspidatum root extracts. J Nat Med 2010; 64:146-52. [PMID: 20082145 DOI: 10.1007/s11418-009-0387-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Accepted: 12/17/2009] [Indexed: 11/29/2022]
Abstract
Polygonum cuspidatum is widely used as a medicinal herb in Asia. In this study, ethanol and ethyl acetate extracts of P. cuspidatum root were assayed for their 1,1-diphenyl-2-hydrazyl (DPPH) and hydroxyl free radical scavenging activities, total phenolics content, protective effect against DNA damage, and antiproliferative activity on human lung cancer cells. The ethanol and ethyl acetate (lipophilic phase) extracts of P. cuspidatum had significant scavenging effects on DPPH and hydroxyl radicals. Total phenolics content of ethanol and ethyl acetate (lipophilic phase) extracts of P. cuspidatum were 276.78 +/- 39.31 and 231.73 +/- 5.04 mg/ml, respectively; both extracts protected against hydroxyl radical-induced DNA strand scission. Furthermore, the extracts of P. cuspidatum induced apoptosis and inhibited cell growth in A549 and H1650 cell lines, suggesting that P. cuspidatum root extracts exhibit an antiproliferative effect on human lung cancer cells.
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Tsai MS, Kuo YH, Chiu YF, Su YC, Lin YW. Down-regulation of Rad51 expression overcomes drug resistance to gemcitabine in human non-small-cell lung cancer cells. J Pharmacol Exp Ther 2010; 335:830-40. [PMID: 20855443 DOI: 10.1124/jpet.110.173146] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Gemcitabine (2',2'-difluorodeoxycytidine), a deoxycytidine analog, and erlotinib, an epidermal growth factor receptor-tyrosine kinase inhibitor, are used clinically to treat patients with non-small-cell lung cancer (NSCLC). However, the molecular mechanisms for the drug resistance of gemcitabine in NSCLC cells are poorly understood. In this study, we used constructs containing human Rad51 cDNA or specific Rad51 small interfering RNA (siRNA) to examine the role of Rad51 in chemoresistance of gemcitabine in three different human NSCLC cell lines. Exposure of human NSCLC cell lines to gemcitabine increased the phosphorylation levels of mitogen-activated protein kinase kinase (MKK) 1/2-extracellular signal-regulated kinase (ERK) 1/2 and AKT in a time- and dose-dependent manner, which was accompanied by an induction of Rad51 mRNA and protein expression. Gemcitabine increased the expression of Rad51 by increasing its mRNA and protein stability. Blockage of ERK1/2 or AKT activation by 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U0126; MKK1/2 inhibitor) or 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002; phosphatidyl inositol 3-kinase inhibitor), respectively, decreased the gemcitabine-induced Rad51 expression. Gemcitabine-induced cytotoxicity was significantly increased using siRNA depletion of Rad51 or blockage of ERK1/2 and AKT activation. Erlotinib enhanced the gemcitabine-induced cytotoxicity via the inactivation of ERK1/2 and AKT and the down-regulation of Rad51. Enforced expression of constitutively active MKK1/2 or AKT recovered cell viability and Rad51 protein levels that were decreased by the combination of erlotinib and gemcitabine. Suppression of Rad51 expression or the inactivation of ERK1/2 or AKT signaling may be considered potential therapeutic modalities for gemcitabine-resistant lung cancer.
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Ko JC, Su YJ, Lin ST, Jhan JY, Ciou SC, Cheng CM, Lin YW. Suppression of ERCC1 and Rad51 expression through ERK1/2 inactivation is essential in emodin-mediated cytotoxicity in human non-small cell lung cancer cells. Biochem Pharmacol 2010; 79:655-64. [PMID: 19799875 DOI: 10.1016/j.bcp.2009.09.024] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Revised: 09/22/2009] [Accepted: 09/22/2009] [Indexed: 01/20/2023]
Abstract
Emodin, a tyrosine kinase inhibitor, is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. Emodin exhibits anticancer effects against a variety of cancer cells, including lung cancer cells. ERCC1 and Rad51 proteins are essential for nucleotide excision repair and homologous recombination, respectively. Furthermore, ERCC1 and Rad51 overexpression induces resistance to DNA-damaging agents that promote DNA double-strand breaks. Accordingly, the aim of this study was to determine the role of ERCC1 and Rad51 in emodin-mediated cytotoxicity in human non-small cell lung cancer (NSCLC) cells. Both ERCC1 and Rad51 protein levels as well as mRNA levels were decreased in four different NSCLC cell lines after exposure to emodin. These decreases correlated with the inactivation of the MKK1/2-ERK1/2 pathway. Moreover, cellular ERCC1 and Rad51 protein and mRNA levels were specifically inhibited by U0126, a MKK1/2 inhibitor. We found that transient transfection of human NSCLC cells with si-ERCC1 or si-Rad51 RNA and cotreatment with U0126 could enhance emodin-induced cytotoxicity. In contrast, overexpression of constitutively active MKK1/2 vectors (MKK1/2-CA) was shown to significantly recover reduced phospho-ERK1/2, ERCC1, and Rad51 protein levels and to rescue cell viability upon emodin treatment. These results demonstrate that activation of the MKK1/2-ERK1/2 pathway is the upstream signal regulating the expressions of ERCC1 and Rad51, which are suppressed by emodin to induce cytotoxicity in NSCLC cells.
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Su YJ, Tsai MS, Kuo YH, Chiu YF, Cheng CM, Lin ST, Lin YW. Role of Rad51 down-regulation and extracellular signal-regulated kinases 1 and 2 inactivation in emodin and mitomycin C-induced synergistic cytotoxicity in human non-small-cell lung cancer cells. Mol Pharmacol 2009; 77:633-43. [PMID: 20042515 DOI: 10.1124/mol.109.061887] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. It is a tyrosine kinase inhibitor and has anticancer effects on lung cancer. Rad51 plays a central role in homologous recombination, and high levels of Rad51 expression are observed in chemo- or radioresistant carcinomas. Our previous studies have shown that the mitogen-activated protein kinase kinase (MKK) 1/2-extracellular signal-regulated kinase (ERK) 1/2 signal pathway maintains the expression of Rad51. Therefore, in this study, we hypothesized that emodin could enhance the effects of the antitumor antibiotic mitomycin C (MMC)-mediated cytotoxicity by decreasing the expression of Rad51 and the phosphorylation of ERK1/2. Exposure of the human non-small-cell lung cancer H1703 or A549 cell lines to emodin decreased the MMC-elicited phosphorylated ERK1/2 and Rad51 levels. Moreover, emodin significantly decreased the MMC-elicited Rad51 mRNA and protein levels by increasing the instability of Rad51 mRNA and protein. In emodin- and MMC-cotreated cells, ERK1/2 phosphorylation was enhanced by constitutively active MKK1/2 (MKK1/2-CA), thus increasing Rad51 protein levels and protein stability. The synergistic cytotoxic effects induced by emodin combined with MMC were remarkably decreased by MKK1-CA-mediated enhancement of ERK1/2 activation. Depletion of endogenous Rad51 expression by small interfering Rad51 RNA transfection significantly enhanced MMC-induced cell death and cell growth inhibition. In contrast, overexpression of Rad51 protects lung cancer cells from the synergistic cytotoxic effects induced by emodin and MMC. We conclude that suppression of Rad51 expression or a combination of emodin with chemotherapeutic agents may be considered as potential therapeutic modalities for lung cancer.
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Ko JC, Su YJ, Lin ST, Jhan JY, Ciou SC, Cheng CM, Chiu YF, Kuo YH, Tsai MS, Lin YW. Emodin enhances cisplatin-induced cytotoxicity via down-regulation of ERCC1 and inactivation of ERK1/2. Lung Cancer 2009; 69:155-64. [PMID: 19962780 DOI: 10.1016/j.lungcan.2009.10.013] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2009] [Revised: 10/22/2009] [Accepted: 10/26/2009] [Indexed: 12/11/2022]
Abstract
Emodin, a tyrosine kinase inhibitor, is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants; it exhibits an anticancer effect on many malignancies. The most important chemotherapeutic agent for patients with advanced non-small cell lung cancer (NSCLC) is a platinum-containing compound such as cisplatin or carboplatin. The molecular mechanism underlying decreased NSCLC cell viability after treatment with emodin and cisplatin is unclear. Therefore, the aim of this study was to assess the cytotoxic effect of combined emodin and cisplatin on NSCLC cell lines and to clarify underlying molecular mechanisms. Exposure of human NSCLC cells to emodin decreased cisplatin-elicited ERK1/2 activation and ERCC1 protein induction by increasing instability of ERCC1 protein. Cisplatin alone did not affect expression of ERCC1 mRNA. However, emodin alone or combined with cisplatin significantly decreased expression of ERCC1 mRNA levels. Enhancement of ERK1/2 activation by transfection with constitutively active MKK1/2 (MKK1/2-CA) vector increased ERCC1 protein levels and protein stability, as well as increasing viability of NSCLC cells treated with emodin and cisplatin. In contrast, blocking ERK1/2 activation by U0126 (an MKK1/2 inhibitor) decreased cisplatin-elicited ERCC1 expression and enhanced cisplatin-induced cytotoxicity. Depletion of endogenous ERCC1 expression by si-ERCC1 RNA transfection significantly enhanced cisplatin's cytotoxic effect. In conclusion, ERCC1 protein protects NSCLC cells from synergistic cytotoxicity induced by emodin and platinum agents. Further investigation of combined emodin and cisplatin may lead to novel therapy in the future for NSCLC through down-regulating expression of ERCC1.
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Huang S, Chueh PJ, Lin YW, Shih TS, Chuang SM. Disturbed mitotic progression and genome segregation are involved in cell transformation mediated by nano-TiO2 long-term exposure. Toxicol Appl Pharmacol 2009; 241:182-94. [PMID: 19695278 DOI: 10.1016/j.taap.2009.08.013] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Revised: 08/10/2009] [Accepted: 08/11/2009] [Indexed: 10/20/2022]
Abstract
Titanium dioxide (TiO2) nano-particles (<100 nm in diameter) have been of interest in a wide range of applications, such as in cosmetics and pharmaceuticals because of their low toxicity. However, recent studies have shown that TiO2 nano-particles (nano-TiO2) induce cytotoxicity and genotoxicity in various lines of cultured cells as well as tumorigenesis in animal models. The biological roles of nano-TiO2 are shown to be controversial and no comprehensive study paradigm has been developed to investigate their molecular mechanisms. In this study, we showed that short-term exposure to nano-TiO2 enhanced cell proliferation, survival, ERK signaling activation and ROS production in cultured fibroblast cells. Moreover, long-term exposure to nano-TiO2 not only increased cell survival and growth on soft agar but also the numbers of multinucleated cells and micronucleus (MN) as suggested in confocal microscopy analysis. Cell cycle phase analysis showed G2/M delay and slower cell division in long-term exposed cells. Most importantly, long-term TiO2 exposure remarkably affected mitotic progression at anaphase and telophase leading to aberrant multipolar spindles and chromatin alignment/segregation. Moreover, PLK1 was demonstrated as the target for nano-TiO2 in the regulation of mitotic progression and exit. Notably, a higher fraction of sub-G1 phase population appeared in TiO2-exposed cells after releasing from G2/M synchronization. Our results demonstrate that long-term exposure to nano-TiO2 disturbs cell cycle progression and duplicated genome segregation, leading to chromosomal instability and cell transformation.
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Ko JC, Ciou SC, Jhan JY, Cheng CM, Su YJ, Chuang SM, Lin ST, Chang CC, Lin YW. Roles of MKK1/2-ERK1/2 and phosphoinositide 3-kinase-AKT signaling pathways in erlotinib-induced Rad51 suppression and cytotoxicity in human non-small cell lung cancer cells. Mol Cancer Res 2009; 7:1378-89. [PMID: 19671683 DOI: 10.1158/1541-7786.mcr-09-0051] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Erlotinib (Tarceva) is a selective epidermal growth factor receptor tyrosine kinase inhibitor in the treatment of human non-small cell lung cancer (NSCLC). In this study, we investigated the roles of ERK1/2 and AKT signaling pathways in regulating Rad51 expression and cytotoxic effects in different NSCLC cell lines treated with erlotinib. Erlotinib decreased cellular levels of phosphorylated ERK1/2, phosphorylated AKT, Rad51 protein, and mRNA in erlotinib-sensitive H1650, A549, and H1869 cells, leading to cell death via apoptosis, but these results were not seen in erlotinib-resistant H520 and H1703 cells. Erlotinib decreased Rad51 protein levels by enhancing Rad51 mRNA and protein instability. Enforced expression of constitutively active MKK1 or AKT vectors could restore Rad51 protein levels, which were inhibited by erlotinib, and decrease erlotinib-induced cytotoxicity. Knocking down endogenous Rad51 expression by si-Rad51 RNA transfection significantly enhanced erlotinib-induced cytotoxicity. In contrast, overexpression of Rad51 by transfection with Rad51 vector could protect the cells from cytotoxic effects induced by erlotinib. Blocking the activations of ERK1/2 and AKT by MKK1/2 inhibitor (U0126) and phosphoinositide 3-kinase inhibitor (wortmannin) suppressed the expression of Rad51 and enhanced the erlotinib-induced cell death in erlotinib-resistant cells. In conclusion, suppression of Rad51 may be a novel therapeutic modality in overcoming drug resistance of erlotinib in NSCLC.
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Chen RS, Jhan JY, Su YJ, Lee WT, Cheng CM, Ciou SC, Lin ST, Chuang SM, Ko JC, Lin YW. Emodin enhances gefitinib-induced cytotoxicity via Rad51 downregulation and ERK1/2 inactivation. Exp Cell Res 2009; 315:2658-72. [PMID: 19505457 DOI: 10.1016/j.yexcr.2009.06.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Revised: 05/12/2009] [Accepted: 06/03/2009] [Indexed: 01/24/2023]
Abstract
Emodin, a tyrosine kinase inhibitor, is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. It reportedly exhibits an anticancer effect on lung cancer. Gefitinib (Iressa) is a selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor for human non-small cell lung cancer (NSCLC). However, the molecular mechanism of how emodin combined with gefitinib decreases NSCLC cell viability is unclear. The recombinase protein Rad51 is essential for homologous recombination repair, and Rad51 overexpression is resistant to DNA double-strand break-inducing cancer therapies. In this study, we found that emodin enhanced the cytotoxicity induced by gefitinib in two NSCLC cells lines, A549 and H1650. Emodin at low doses of 2-10 microM did not affect ERK1/2 activation, mRNA, and Rad51 protein levels; however, it enhanced a gefitinib-induced decrease in phospho-ERK1/2 and Rad51 protein levels by enhancing Rad51 protein instability. Expression of constitutively active MKK1/2 vectors (MKK1/2-CA) significantly rescued the reduced phospho-ERK1/2 and Rad51 protein levels as well as cell viability on gefitinib and emodin cotreatment. Blocking of ERK1/2 activation by U0126 (an MKK1/2 inhibitor) lowered Rad51 protein levels and cell viability in emodin-treated H1650 and A549 cells. Knockdown of Rad51 expression by transfection with si-Rad51 RNA enhanced emodin cytotoxicity. In contrast, Rad51 overexpression protected the cells from the cytotoxic effects induced by emodin and gefitinib. Consequently, emodin-gefitinib cotreatment may serve as the basis for a novel and better therapeutic modality in the management of advanced lung cancer.
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