Survival Of Gastric Cancer Cells Research Articles

A role for Cdkl1 in the development of gastric cancer

Background. Cyclin-dependent kinase-like1 (CDKL1) is known as a new member of cyclin-dependent kinases. Whether genetic alterations of CDKL1 gene are involved in the development and/or progression of gastric cancer is still unknown. Material and methods. Here, the expression of CDKL1 protein in paired specimens of gastric cancer tissues and corresponding normal gastric tissue (n = 66) was assessed by immunohistochemistry assay. We then used lentivirus-mediated knock down to specifically inhibit CDKL1 expression in human gastric cancer cell lines. Cell proliferation potential in vitro was measured by MTT and clonogenic assays. Cell apoptosis was assessed by flow cytometry. Results. We show for the first time that high expression of CDKL1 protein was observed in gastric cancer tissues compared with matched adjacent tissues. Loss of CDKL1 function in both SGC7901 and MGC-803 gastric cancer cells significantly decreases cellular proliferation and increases apoptosis (p < 0.01). Furthermore, we show that the reduction of CDKL1 with its siRNA stimulates the activation of Bcl-2-interacting killer (Bik) pro-apoptotic protein and attenuated the expression of proliferating cell nuclear antigen PCNA. Conclusion. In summary, our data suggest that CDKL1 plays an important regulatory role in gastric cancer cell proliferation and survival, and therefore, may represent a new target for therapeutic intervention.

The role of transient receptor potential channel blockers in human gastric cancer cell viability

Transient receptor potential cation channel, subfamily M, receptor 7 (TRPM7) is a ubiquitous divalent-selective ion channel with its own kinase domain. Human gastric cancer cells express the TRPM7 channel, and the presence of this channel is essential for cell survival. Recent studies have suggested that 5-lipoxygenase (5-LOX) inhibitors are potent blockers of the TRPM7 channels. The aim of this study was to show the effects of 5-LOX inhibitors on the growth and survival of gastric cancer cells. Among 5-LOX inhibitors, nordihydroguaiaretic acid (NDGA), 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861), and 3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-tert-butylthioindol-2-yl]-2,2-dimethylpropanoic acid (MK886) were potent blockers of TRPM7-like currents in gastric cancer cells and also induced cell death. However, zileuton was ineffective in suppressing TRPM7-like current activity and inducing cell death. Moreover, a specific transient receptor potential cation channel, subfamily C, member 3 (TRPC3) inhibitor, a pyrazole compound (Pyr3), and a specific melastatin TRP (TRPM4) inhibitor, 9-phenanthrol, did not affect TRPM7-like currents or induce cell death. We conclude that TRPM7 has an important role in the growth and survival of gastric cancer cells and a likely potential target for the pharmacological treatment of gastric cancer.

Autophagy-mediated HMGB1 release antagonizes apoptosis of gastric cancer cells induced by vincristine via transcriptional regulation of Mcl-1

Autophagy-associated release of HMGB1 is known to protect cancer cells from many chemotherapeutics. However, the detailed molecular mechanism(s) responsible remains largely undefined. We show in this study that HMGB1 released into the extracellular space protects gastric cancer cells from apoptosis induced by the microtubule-targeting drug vincristine through transcriptional upregulation of Mcl-1. Extracellular HMGB1 appeared essential for autophagy-mediated inhibition of apoptosis, in that siRNA knockdown of HMGB1 or inhibition of its release abolished the protective effect of autophagy. Strikingly, vincristine upregulated the Mcl-1 mRNA expression through a transcriptional increase, but did not alter the expression levels of the Mcl-1 protein. Inhibition of HMGB1 release blocked the increase in the Mcl-1 transcript and caused reduction in Mcl-1 at the protein level, indicating that HMGB1-mediated signaling was necessary for transcriptional upregulation of Mcl-1. This seemed critical for maintaining sufficient Mcl-1 protein expression required for survival of gastric cancer cells exposed to vincristine. The effect of extracellular HMGB1 on transcriptional regulation of Mcl-1 was confirmed in gastric cancer cells treated with recombinant HMGB1. Taken together, these results identify HMGB1-mediated upregulation of Mcl-1 transcription as an important mechanism by which autophagy protects gastric cancer cells from apoptosis induced by vincristine.

Cycloxygenase-2 is Essential for the Survival and Proliferation of Gastric Cancer Cells

Cycloxygenase-2 catalyzes the synthesis of prostaglandins from arachidonic acid and this enzyme has been implicated in the metastasis of gastric cancer. In order to examine the significance of cycloxygenase-2 (Cox-2) in the survival and proliferation of gastric cancer cells, we have stably overexpressed an antisense Cox-2 in two gastric cancer cell lines, SGC7901 and AGS, in order to reduce the expression of this protein. The sense and antisense Cox-2 expression vectors were created by cloning COX-2 cDNA, in pIRES2-EGFP plasmid. Cox-2 gene expression was monitored by RT-PCR and Western blotting and the results indicated that cells with antisense Cox-2 construct had significantly reduced Cox-2 expression in comparison to the cells that received sense-Cox-2 plasmid. Reduction of Cox-2 expression in SGC7901 and AGS gastric cancer cells led to markedly decreased proliferation. The metastatic capability of the two cell lines, as assessed by in vitro colony formation assay, is also significantly compromised by lowered Cox-2 expression. Thus, this study demonstrates that Cox-2 activity is necessary for the proliferation and metastasis of gastric cancer cells.

Transient receptor potential melastatin type 7 channels are involved in zinc-induced apoptosis in gastric cancer

Transient receptor potential melastatin 7 (TRPM7) channels are novel Ca2+-permeable non-selective cation channels that are ubiquitously expressed. Activation of TRPM7 channels has been shown to be involved in the survival of gastric cancer cells. Here we show evidence suggesting that TRPM7 channels play an important role in Zn2+-mediated cellular injury. Using a combination of electrophysiology, pharmacological analysis, small interfering RNA (siRNA) methods and cell death assays, we showed that activation of TRPM7 channels augmented Zn2+-induced apoptosis of AGS cells, the most common human gastric adenocarcinoma cell line. The Zn2+-mediated cytotoxicity was inhibited by the non-specific TRPM7 blockers Gd3+ or 2 aminoethoxydiphenyl borate (2-APB) and TRPM7 specific siRNA. In addition, we showed that overexpression of TRPM7 channels in HEK293 cells increased Zn2+-induced cell injury. Thus, TRPM7 channels may represent a novel target for physiological disorders where Zn2+toxicity plays an important role.

Highlights of This Issue

Peritoneal carcinomatosis is a frequent cause of death in patients with advanced gastric cancer. Here, Yasumoto and colleagues investigated whether EGFR ligands and/or the ErbB family of receptors are involved in the development of this condition. They found that the EGFR ligands amphiregulin and HB-EGF collaborated with the CXCR4/CXCL12 axis to promote peritoneal carcinomatosis by stimulating the migration, proliferation, and survival of CXCR4-expressing gastric cancer cells and stromal fibroblasts. Furthermore, these two EGFR ligands showed different biological activities in target cells. These findings provide a framework for future clinical trials of ErbB receptor inhibitors that target tumor cells and their environment.Metastases can differ greatly from primary tumor tissue in terms of genetic characteristics. However, taking biopsies from metastases in patients is an invasive procedure and is frequently not possible due to the lack of accessible lesions. Circulating tumor cells (CTCs) are found in the peripheral blood of patients and can thus be regarded as “liquid biopsies” of metastasizing cells. In this study, Sieuwerts and colleagues demonstrate the feasibility of performing an extensive molecular characterization of CTCs from breast cancer patients at both the mRNA and microRNA level. It is anticipated that this approach will improve currently available prognostic and predictive models.Growing evidence suggests that chronic stress can promote cancer growth and progression. In this study, Moreno-Smith and colleagues show that dopamine can block the stimulatory effects of chronic stress on ovarian cancer tumor growth. They found that dopamine retards tumor growth by inhibiting tumor angiogenesis and stimulating tumor cell apoptosis. Further, dopamine depletion during chronic stress created a permissive microenvironment for tumor growth that could be reversed by dopamine replacement. Based on these findings, dopamine analogues may represent a novel therapeutic strategy for blocking the deleterious effects of chronic stress.Host immune reactivity to Pseudomonas exotoxin (PE)-based immunotoxins limits the ability to deliver repetitive immunotoxin doses that are needed for optimal anticancer effects. Here, Mossoba and coworkers show that administration of pentostatin plus cyclophosphamide in a murine model safely depleted host lymphocytes and abrogated host capacity to form antibodies to a PEbased immunotoxin through nine consecutive immunotoxin doses. These results suggest that novel host preparative therapy, such as the pentostatin plus cyclophosphamide regimen, represents an approach to deliver prolonged immunotoxin therapy for enhanced anticancer effects against a wide range of malignancies.

A small interfering RNA targeting the KLF6 splice variant, KLF6-SV1, as gene therapy for gastric cancer

Accumulating evidence suggests that the tumor suppressor gene Kruppel-like factor 6 (KLF6) and its dominant-negative splice form KLF6-SV1 play important roles in both the development and progression of cancer. However, the role of KLF6-SV1 in gastric cancer remains largely unknown. KLF6-SV1 expression was detected in various human gastric cancer cell lines and gastric cancer patient samples by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting. Small interfering RNA (siRNA) was used to inhibit KLF6-SV1 expression in BGC-823 and SGC-7901 cell lines. The effects of downregulation of KLF6-SV1 by siRNA on cell proliferation, migration, invasion, and tumor growth were examined in vitro and in vivo. Overexpression of KLF6-SV1 was detected in tumor samples from gastric cancer patients, and in various differentiated gastric cancer cell lines. In vitro downregulation of KLF6-SV1 by siRNA inhibited BGC-823 and SGC-7901 cell proliferation, anchorage-independent growth, migration, and invasion through the altered expression of Ki-67, vascular endothelial growth factor (VEGF), E-cadherin, and matrix metalloproteinase (MMP)-9. Also, KLF6-SV1 silencing promoted caspase-dependent apoptosis of BGC-823 and SGC-7901 cells via the regulation of phosphatidylinositol 3-OH kinase (PI3K)/Akt activity and Bcl-2-related protein expression. In vivo animal studies showed that KLF6-SV1 siRNA significantly inhibited the tumorigenicity of BGC-823 and SGC-7901 cells. Gene therapy with polyethylenimine/si-SV1 intratumoral injection also resulted in the suppression of tumor growth and prolonged animal survival in an established xenograft tumor model. These data demonstrate that KLF6-SV1 is an important regulator of the growth, migration, invasion, and survival of gastric cancer cells, and downregulation of KLF6-SV1 by siRNA may offer a new potential gene therapy approach for gastric cancer.

Abstract 1966: Regulation of RKIP function by Helicobacter pylori in gastric cancer cells

Abstract Raf kinase inhibitory protein (RKIP) is a negative regulator of the mitogen activated protein kinase (MAPK) cascade initiated by Raf-1 and nuclear factor kappa B (NF-κB) and is an activator of apoptosis in human cancers. STAT3 (signal transducer and activators of transcription) is often constitutively phosphorylated in gastric cancer. RKIP is a negative regulator of STAT3 and has been positively correlated with a higher survival rate in gastric cancer patients (Chatterjee, et al., Clin. Cancer Res., 14:2994-3001, 2008). Helicobacter pylori (H. pylori) infection is associated with high levels of activated STAT3 as well as activation of the transcription factor NF-κB in gastric epithelial cells, through mechanisms involving macrophage-derived IL-6. H. pylori infection led to a dose- and time-dependent increase in STAT3 activation and Snail, a protein that is a negative regulator of RKIP transcription. In addition, H. pylori and IL-6 treatment stimulated the phosphorylation of RKIP in a protein kinase C- (PKC) dependent manner. Interestingly, H. pylori stimulated RKIP transcription which was enhanced in the presence of the histone acetyl transferase, CBP, and inhibited in the presence of the PKC inhibitor. Surprisingly, RKIP stimulated STAT3 transcription in gastric cancer cells, an effect that was reversed in the presence of CBP. After H. pylori infection, RKIP localized to the nucleus and enhanced H. pylori-mediated apoptosis. Collectively, these results indicate that RKIP function is regulated by phosphorylation after H. pylori infection and acetylation by CBP. Moreover, our study demonstrates that RKIP post translational modifications regulate apoptosis induction (via phosphorylation) and inhibition of cell survival (via acetylation) in gastric cancer. These results also suggest the existence of a feedback loop between RKIP, H. pylori infection and STAT3 in gastric cancer. Supported, in part, by NIH COBRE Investigator Award Grant P20 RR17695 (DC and SM). 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 1966. doi:10.1158/1538-7445.AM2011-1966

Requirement of Osteopontin in the migration and protection against Taxol-induced apoptosis via the ATX-LPA axis in SGC7901 cells

BackgroundAutotaxin (ATX) possesses lysophospholipase D (lyso PLD) activity, which converts lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA). The ATX-LPA signaling axis has been implicated in angiogenesis, chronic inflammation and tumor progression. Osteopontin (OPN) is an important chemokine involved in the survival, proliferation, migration, invasion and metastasis of gastric cancer cells. The focus of the present study was to investigate the relationship between the ATX-LPA axis and OPN.ResultsIn comparison with non-treated cells, we found that the ATX-LPA axis up-regulated OPN expression by 1.92-fold in protein levels and 1.3-fold in mRNA levels. The ATX-LPA axis activates LPA2, Akt, ERK and ELK-1 and also protects SGC7901 cells from apoptosis induced by Taxol treatment.ConclusionsThis study provides the first evidence that expression of OPN induced by ATX-LPA axis is mediated by the activation of Akt and MAPK/ERK pathways through the LPA2 receptor. In addition, OPN is required for the protective effects of ATX-LPA against Taxol-induced apoptosis and ATX-LPA-induced migration of SGC7901 cells.

Enhanced proliferation, invasion, and epithelial-mesenchymal transition of nicotine-promoted gastric cancer by periostin

To investigate the contribution of periostin in nicotine-promoted gastric cancer cell proliferation, survival, invasion, drug resistance, and epithelial-mesenchymal transition (EMT). Gastric cancer cells were treated with nicotine and periostin protein expression was determined by immunoblotting. Periostin mRNA in gastric cancer cells was silenced using small interfering RNA (siRNA) techniques and periostin gene expression was evaluated by quantitative reverse transcription-polymerase chain reaction. Gastric cancer cells transfected with control or periostin siRNA plasmid were compared in terms of cell proliferation using the methylthiazolyldiphenyl-tetrazolium bromide assay. Cell apoptosis was compared using annexin V-fluoresceine isothiocyanate and propidium iodine double staining. Tumor invasion was determined using the Boyden chamber invasion assay, and the EMT marker Snail expression was evaluated by immunoblotting. Nicotine upregulated periostin in gastric cancer cells through a COX-2 dependent pathway, which was blocked by the COX-2-specific inhibitor NS398. Periostin mRNA expression was decreased by ~87.2% by siRNA in gastric cancer cells, and stable periostin-silenced cells were obtained by G418 screening. Periostin-silenced gastric cancer cells exhibited reduced cell proliferation, elevated sensitivity to chemotherapy with 5-fluorouracil, and decreased cell invasion and Snail expression (P < 0.05). Periostin is a nicotine target gene in gastric cancer and plays a role in gastric cancer cell growth, invasion, drug resistance, and EMT facilitated by nicotine.

Effects of propranolol in combination with radiation on apoptosis and survival of gastric cancer cells in vitro

BackgroundThe National Comprehensive Cancer Network (NCCN) guidelines recommend radiotherapy as a standard treatment for patients with a high risk of recurrence in gastric cancer. Because gastric cancer demonstrates limited sensitivity to radiotherapy, a radiosensitizer might therefore be useful to enhance the radiosensitivity of patients with advanced gastric carcinoma. In this study, we evaluated if propranolol, a β-adrenoceptor (β-AR) antagonist, could enhance radiosensitivity and explored its precise molecular mechanism in gastric cancer cells.MethodsHuman gastric adenocarcinoma cell lines (SGC-7901 and BGC-823) were treated with or without propranolol and exposed to radiation. Cell viability and clonogenic survival assays were performed, and cell apoptosis was evaluated with flow cytometry. In addition, the expression of nuclear factor κB (NF-κB), vascular endothelial growth factor (VEGF), cyclooxygenase 2 (COX-2), and epidermal growth factor receptor (EGFR) were detected by western blot and real-time reverse transcription polymerase chain reaction (PCR).ResultsPropranolol combined with radiation decreased cell viability and clonogenic survivability. Furthermore, it also induced apoptosis in both cell lines tested, as determined by Annexin V staining. In addition, treatment with propranolol decreased the level of NF-κB and, subsequently, down-regulated VEGF, COX-2, and EGFR expression.ConclusionsTaken together, these results suggested that propranolol enhanced the sensitivity of gastric cancer cells to radiation through the inhibition of β-ARs and the downstream NF-κB-VEGF/EGFR/COX-2 pathway.

Role of ES Cell-Expressed Ras (ERas) in Tumorigenicity of Gastric Cancer

ERas, a unique member of the Ras family, was initially found only in embryonic stem (ES) cells, where it plays a crucial role in the transformation of transplanted ES cells to teratomas. ERas is involved in ES cell survival, and unlike other Ras family members, is constitutively active without any mutations. The aim of this study was to investigate the expression and role of ERas in human gastric cancer. To test whether ERas played a significant role in human cancer cells, we examined its expression and function in gastric cancer. ERas was expressed in gastric cancer cell lines at different levels. Induction of ERas expression activated the phosphatidylinositol 3 kinase (PI3K)/Akt axis and then enhanced anchorage-independent growth and ERas knockdown by siRNA suppressed cell invasion. Immunohistochemical analyses revealed that ERas was expressed in 38.7% (55/142) of human gastric carcinoma tissues, and its expression was significantly associated with metastasis to the liver (P < 0.0001) and lymph nodes (P < 0.05). ERas up-regulated transcription regulatory factors including ZFHX1A, ZFHX1B, and TCF3, which repress E-cadherin. These data suggest that ERas is activated in a significant population of gastric cancer, where it may play a crucial role in gastric cancer cell survival and metastases to liver via down-regulation of E-cadherin.

Abstract 1770: Overexpression of fibroblast growth factor receptor 2 (FGFR2) in gastric cancer and basis for future FGFR2-targeted cancer therapy

Abstract Introduction: Fibroblast growth factors (FGFs) are potent mitogens and inducers of angiogenesis. FGF signalling pathway is closely associated with cancer development and progression. Fibroblast growth factor receptor 2 (FGFR2) gene, located at human chromosome 10q26, encodes FGFR2b and FGFR2c isoforms functioning as distinct FGF receptors. Gene amplification or missense mutation of FGFR2 occurs in gastric cancer (GC). Genetic alterations of FGFR2 may induce aberrant activation of FGFR2 signalling pathway, thereafter induce proliferation and survival of GC cells. FGFR2 plays an important role in gastric carcinogenesis. Patients and Methods: A total of 33 gastric cancer tissues with formalin-fixed, paraffin-embedded tumor slides were investigated by immunohistochemical staining with primary antibody against FGFR2. By Lauren's classification, there are 9 diffuse-type, 23 intestinal-type, and 1 mixed-type GC patients, respectively. Results: The FGFR2 immunohistochemical staining was classified as 0, 1+, 2+, and 3+ according to percentage of immunoreactive positive-staining FGFR2 cells in &amp;lt;10%, 10-25%, 25-50%, and &amp;gt;50% tumor cells, respectively. The relationship between the FGFR2 expression and the clinicopathological characteristics were analyzed. Among 33 GC patients, 13 patients (39.4%; 23-57%, 95% C.I.) had FGFR2 expression (1+, 2+, and 3+), and 11 patients (33.3%; 17-52%, 95% C.I.) had FGFR2 overexpression (2+ and 3+), respectively. FGFR2 expression was not correlated with diffuse-type versus intestinal-type GC patients (p=0.427, Fisher exact test). Conclusions: Overexpression of FGFR2 in gastric cancer forms the basis of the rational clinical application of future FGFR2-targeted cancer therapy for treatment of advanced GC. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1770.

STAT-3 correlates with lymph node metastasis and cell survival in gastric cancer

To investigate the correlation between gastric cancer growth and signal transducer and activator of transcription-3 (STAT3) expression. We assessed the expressions of STAT3, phosphor-STAT3 (pSTAT3), suppressor of cytokine signaling-1 (SOCS-1), survivin and Bcl-2 in gastric cancer patients after gastrectomy by immunohistochemical method. In addition, in situ hybridization was used to further demonstrate the mRNA expression of STAT3 in gastric cancer. With the univariate analysis, expressions of STAT3, pSTAT3, SOCS-1, survivin and Bcl-2, the size of primary tumor and the lymph node metastasis were found to be associated with the overall survival (OS) of gastric cancer patients. However, only pSTAT3 expression and the lymph node metastasis were identified as the independent factors of OS of gastric cancer with multivariate analysis. STAT3 expression was correlated with the lymph node metastasis. There were positive correlations between expressions of STAT3, survivin, Bcl-2 and pSTAT3 in gastric cancer, whereas there was negative correlation between STAT3 expression and SOCS-1 expression in gastric cancer. STAT3 can transform into pSTAT3 to promote the survival and inhibit the apoptosis of gastric cancer cells. SOCS-1 might be the valid molecular antagonist to inhibit the STAT3 expression in gastric cancer.

Hedgehog Signaling Regulates the Survival of Gastric Cancer Cells by Regulating the Expression of Bcl-2

Gastric cancer is the second most common cause of cancer deaths worldwide. The underlying molecular mechanisms of its carcinogenesis are relatively poorly characterized. Hedgehog (Hh) signaling, which is critical for development of various organs including the gastrointestinal tract, has been associated with gastric cancer. The present study was undertaken to reveal the underlying mechanism by which Hh signaling controls gastric cancer cell proliferation. Treatment of gastric cancer cells with cyclopamine, a specific inhibitor of Hh signaling pathway, reduced proliferation and induced apoptosis of gastric cancer cells. Cyclopamine treatment induced cytochrome c release from mitochondria and cleavage of caspase 9. Moreover, Bcl-2 expression was significantly reduced by cyclopamine treatment. These results suggest that Hh signaling regulates the survival of gastric cancer cells by regulating the expression of Bcl-2.

Midkine positively regulates the proliferation of human gastric cancer cells

Midkine (MDK), a heparin-binding growth factor, modulates the proliferation and migration of various cells, is often highly expressed in many malignant tumors, and may act as an oncoprotein. We found that MDK is overexpressed in clinical human gastric cancer tissues relative to its expression in adjacent noncancerous tissues. To further investigate the biological activities of MDK in gastric cancer, we introduced the MDK gene into human SGC7901 gastric cancer cells, where it contributed to the proliferation of SGC7901 cells in vitro and in vivo. Conversely, the knockdown of MDK expression by siRNA resulted in significantly reduced proliferation of BGC823 cells. Our study also shows that MDK activates both the Akt and ERK1/2 pathways and upregulates the expression of several cell-cycle-related proteins, including cyclin A, cyclin D1, Cdk2, Cdk4, and Cdk6, which in part explains the contribution of MDK to gastric cancer cell survival and growth. These results demonstrate that MDK contributes to gastric cancer cell proliferation and suggest that it plays an important role in the development of human gastric cancer.

Inhibition of PI3K/Akt partially leads to the inhibition of PrPC‐induced drug resistance in gastric cancer cells

Cellular prion protein (PrP(C)), a glycosyl-phosphatidylinositol-anchored membrane protein with unclear physiological function, was previous found to be upregulated in adriamycin (ADR)-resistant gastric carcinoma cell line SGC7901/ADR compared to its parental cell line SGC7901. Overexpression of PrP(C) in gastric cancer has certain effects on drug accumulation through upregulation of P-glycoprotein (P-gp), which is suggested to play an important role in determining the sensitivity of tumor cells to chemotherapy and is linked to activation of the phosphatidylinositol-3-kinase/Akt (PI3K/Akt) pathway. In the present study, we further investigate the role of the PI3K/Akt pathway in PrP(C)-induced multidrug-resistance (MDR) in gastric cancer. Immunohistochemistry and confocal microscope detection suggest a positive correlation between PrP(C) and phosphorylated Akt (p-Akt) expression in gastric cancer. Using established stable PrP(C) transfectant cell lines, we demonstrated that the level of p-Akt was increased in PrP(C)-transfected cells. Inhibition of PrP(C) expression by RNA interference resulted in decreased p-Akt expression. Inhibition of the PI3K/Akt pathway by one of its specific inhibitors, LY294002, or by Akt small interfering RNA (siRNA) resulted in decreased multidrug resistance of SGC7901 cells, partly through downregulation of P-gp induced by PrP(C). Taken together, our results suggest that PrP(C)-induced MDR in gastric cancer is associated with activation of the PI3K/Akt pathway. Inhibition of PI3K/Akt by LY2940002 or Akt siRNA leads to inhibition of PrP(C)-induced drug resistance and P-gp upregulation in gastric cancer cells, indicating a possible novel mechanism by which PrP(C) regulates gastric cancer cell survival.

Knock‐down of methylenetetrahydrofolate reductase reduces gastric cancer cell survival: An in vitro study

The present study aimed to investigate the effect of knocking-down methylenetetrahydrofolate reductase (MTHFR) on the survival of the human gastric cancer cell line MKN45. Antisense and small interfering RNA (siRNA) plasmids were used to target MTHFR in MKN45. Meanwhile, we also constructed a wild-type MTHFR plasmid to assess the effect of over-expression of this protein on cell viability. The knock-down of MTHFR decreased cell survival by approximately 30% compared to the control and resulted in cell cycle arrest at the G2 phase. These cells also had lower levels of c-myc compared to control cells, while over-expression of MTHFR increased cell proliferation and induced the down-regulation of p21WAF1 and hMLH1. Inhibiting MTHFR with either antisense or siRNA decreases the viability of methionine-dependent transformed gastric cancer cells and suggests that MTHFR inhibition may be a novel anticancer approach.

FGFR2-Amplified Gastric Cancer Cell Lines Require FGFR2 and Erbb3 Signaling for Growth and Survival

We have identified a critical role for amplified FGFR2 in gastric cancer cell proliferation and survival. In a panel of gastric cancer cell lines, fibroblast growth factor receptor 2 (FGFR2) was overexpressed and tyrosine phosphorylated selectively in FGFR2-amplified cell lines KatoIII, Snu16, and OCUM-2M. FGFR2 kinase inhibition by a specific small-molecule inhibitor resulted in selective and potent growth inhibition in FGFR2-amplified cell lines, resulting in growth arrest in KatoIII cells and prominent induction of apoptosis in both Snu16 and OCUM-2M cells. FGFR2-amplified cell lines also contained elevated phosphotyrosine in EGFR, Her2, and Erbb3, but the elevated phosphorylation in EGFR could not be inhibited by gefitinib or erlotinib. We show that the elevated EGFR, Her2, and Erbb3 phosphotyrosine is dependent on FGFR2, revealing EGFR family kinases to be downstream targets of amplified FGFR2. Moreover, shRNA to Erbb3 resulted in a loss of proliferation, confirming a functional role for the activated EGFR signaling pathway. These results reveal that both the FGFR2 and EGFR family signaling pathways are activated in FGFR2-amplified gastric cancer cell lines to drive cell proliferation and survival. Inhibitors of FGFR2 or Erbb3 signaling may have therapeutic efficacy in the subset of gastric cancers containing FGFR2 amplification.

Growth arrest-specific gene 6 and Axl signaling enhances gastric cancer cell survival via Akt pathway.

Activation of tyrosine kinases is an important factor during cancer development. Axl, one of the receptor tyrosine kinases, binds to the specific ligand growth arrest-specific gene 6 (Gas6), which encodes a vitamin K-dependent gamma-carboxyglutamyl protein. Although many receptor tyrosine kinases and their ligands are involved in gastric carcinogenesis, whether Gas6-Axl signaling is involved in gastric carcinogenesis has not been elucidated. The aim of this study was to investigate the expression of Gas6 and Axl in gastric cancer and also their roles during gastric carcinogenesis. mRNA and protein of Gas6 and Axl were highly expressed in a substantial proportion of human gastric cancer tissue and cell lines, and Gas6 expression was significantly associated with lymph node metastasis. With recombinant Gas6 and a decoy-receptor of Axl in vitro, we demonstrated that Gas6-Axl signaling pathway enhanced cellular survival and invasion and suppressed apoptosis via Akt pathway. Our results suggests that Gas6-Axl signaling plays a role during gastric carcinogenesis, and that targeting Gas6-Axl signaling could be a novel therapeutic for gastric cancer.