β-elemene enhances the radiosensitivity of gastric cancer cells by inhibiting Pak1 activation

• Published in: World journal of gastroenterology : WJG Vol. 21; no. 34; pp. 9945 - 9956
• Main Author: Liu, Jun-Song
• Format: Journal Article
• Language: English
• Published: United States Baishideng Publishing Group Inc 14.09.2015
• Subjects: Apoptosis - drug effects; Apoptosis - radiation effects; Basic Study; cancer; Cell Line, Tumor; Cell Survival - drug effects; Cell Survival - radiation effects; cells;Cl; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases - metabolism; Humans; Intracellular Signaling Peptides and Proteins - metabolism; p21-Activated Kinases - antagonists & inhibitors; p21-Activated Kinases - metabolism; Phosphorylation; Protein Kinase Inhibitors - pharmacology; Proteomics - methods; Radiation Tolerance - drug effects; Radiation-Sensitizing Agents - pharmacology; Sesquiterpenes - pharmacology; Signal Transduction - drug effects; Stomach Neoplasms - enzymology; Stomach Neoplasms - pathology; Stomach Neoplasms - radiotherapy; Time Factors; β-elemene;Radiosensitivity;Gastric; β-elemene; p21-activated protein kinase 1; Clonogenic survival; Radiosensitivity; Gastric cancer cells; Apoptosis
• ISSN: 1007-9327; 2219-2840; 2219-2840
• DOI: 10.3748/wjg.v21.i34.9945

AIM:To explore the potential of β-elemene as a radiosensitizer for gastric cancer cells and the underlying mechanisms.METHODS:SGC7901,MKN45,MKN28,N87,and AGS human gastric cancer cell lines were used to screen for radioresistant gastric cancer cell lines. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium(MTT) assay was used to determine the effects of β-elemene and IPA-3 on cell viability in MKN45 and SGC7901 gastric cancer cell lines. A clonogenic survival assay and annexin V-FITC/PI apoptosis detection assay were used to evaluate cellular radiosensitivity and radiation-induced cell death,respectively. A proteomic method,isobaric tags for relative and absolute quantitation(i TRAQ),was employed to screen the proteins regulated by β-elemene pretreatment prior to ionizing radiation(IR) in SGC7901 gastric cancer cell line. IPA-3 was used as a specific small molecule inhibitor of p21-activated protein kinase 1(Pak1) to target Pak1 signaling. Protein levels of PAK1IP1(p21-activated protein kinase-interacting protein 1),total Pak1(t-Pak1),phospho-Pak1(T423),phospho-ERK1/2( Thr202/Tyr204),and cleaved caspase-3(17 k Da) were assessed by western blotting.RESULTS:MKN45 and SGC7901 gastric cancer cell lines were relatively more resistant to IR. β-elemene pretreatment decreased clonogenic survival following IR in MKN45 and SGC7901 gastric cancer cell lines. Additionally,β-elemene pretreatment prior to IR increased radiation-induced cell death compared with IR alone in MKN45(10.4% ± 0.9% vs 34.8% ± 2.8%,P < 0.05) and SGC7901(11.6% ± 0.9% vs 46.7% ± 5.2%,P < 0.05) human gastric cancer cell lines,respectively,consistent with the level of cleaved caspase-3(17 k Da). Through i TRAQ analysis and western blot validation,we found that β-elemene upregulated PAK1IP1 and downregulated phospho-Pak1(T423) and phosphoERK1/2 in SGC7901 gastric cancer cells. IR increased the level of phospho-Pak1(T423). Pretreatment with β-elemene decreased radiation-induced Pak1 and ERK1/2 phosphorylation. Inhibition of Pak1 using IPA-3 decreased clonogenic survival following IR. In addition,IPA-3 increased radiation-induced cell death in MKN45(13.4% ± 0.3% vs 26.6% ± 1.0%,P < 0.05) and SGC7901(16.0% ± 0.6% vs 37.3% ± 1.7%,P < 0.05) gastric cancer cell lines,respectively,consistent with the level of cleaved caspase-3(17 k Da). Western blotting showed that IPA-3 decreased radiation-induced Pak1 and ERK1/2 phosphorylation.CONCLUSION:This is the first demonstration that β-elemene enhances radiosensitivity of gastric cancer cells,and that the mechanism involves inhibition of Pak1 signaling.