Resveratrol prevents hypoxia-induced retinal ganglion cell death related with ErbB2.

AIM: To confirm the changes in proteins related with hypoxia-induced retinal cell death and to assess the effects of resveratrol (Res). METHODS: The therapeutic effect of Res was verified using an ischemic/reperfusion (I/R) model in vivo and a hypoxia modelin retinal ganglion cells (RGCs) in vitro. Death of RGCs were confirmed by TUNEL assay. Protein expression was confirmed by Western blotting and immunohistochemistry. In addition, flow cytometric analysis was used to confirm the response in the cell unit to obtain more accurate data. RESULTS: ErbB2 expression and apoptosis in the ganglion cell layer (GCL) increased after I/R injury. Treatment of Res rescued I/R-induced ganglion cell death, downregulated apoptosis and ErbB2 protein expression in the retina. In subsequent in vitro models, Res affects apoptosis by regulating the phosphorylation and expression of mouse double minute 2 homolog (MDM2), along with those of ErbB2. These results suggest that Res reverses GCL-specific apoptosis via downregulation of ErbB2 in ischemic injury. CONCLUSION: In light of Res favorable properties, it should be evaluated in the treatment of RGC death and related retinal disease characterized by ErbB2 and MDM2 expression. Therefore, Res is appropriate therapeutic agent for treating ischemic injury-related eye diseases by targeting the expression of ErbB2 and MDM2.

Phosphorylation of STAT3 and ERBB2 mediates hypoxia­induced VEGF release in ARPE­19 cells.

Neovascularization in the retina can cause loss of vision. Vascular endothelial growth factor (VEGF) serves an important role in the pathogenesis of retinal vascular diseases. Hypoxia is a notable cause of VEGF release and both STAT3 and ERBB2 are known to be associated with VEGF. In addition, STAT3 and ERBB2 interact with each other. In the present study, it was hypothesized that signal transducer and activator of transcription 3 (STAT3) and erbB­2 receptor tyrosine kinase 2 (ERBB2) may be involved in the regulation of hypoxia­induced VEGF in the retina. Cells of the retinal pigment epithelium (RPE) are an important source of VEGF. Therefore, the RPE­derived human cell line ARPE­19 was exposed to hypoxia. Hypoxia­induced phosphorylation of STAT3 and ERBB2 in ARPE­19 cells was decreased by AG490, an inhibitor of Janus kinase 2, as were hypoxia­induced VEGF release and tube formation in human umbilical vein endothelial cells. Thus, phosphorylation of ERBB2 and STAT3 regulates hypoxia­induced VEGF release in ARPE­19 cells. The results of the present study suggested that inhibition of ERBB2 and STAT3­mediated pathways under hypoxia may represent a new strategy for treating retinal vascular disease.

Cross-talk between CD38 and TTP Is Essential for Resolution of Inflammation during Microbial Sepsis.

The resolution phase of acute inflammation is essential for tissue homeostasis, yet the underlying mechanisms remain unclear. We demonstrate that resolution of inflammation involves interactions between CD38 and tristetraprolin (TTP). During the onset of acute inflammation, CD38 levels are increased, leading to the production of Ca2+-signaling messengers, nicotinic acid adenine dinucleotide phosphate (NAADP), ADP ribose (ADPR), and cyclic ADPR (cADPR) from NAD(P)+. To initiate the onset of resolution, TTP expression is increased by the second messengers, NAADP and cADPR, which downregulate CD38 expression. The activation of TTP by Sirt1-dependent deacetylation, in response to increased NAD+ levels, suppresses the acute inflammatory response and decreases Rheb expression, inhibits mTORC1, and induces autophagolysosomes for bacterial clearance. TTP may represent a mechanistic target of anti-inflammatory agents, such as carbon monoxide. TTP mediates crosstalk between acute inflammation and autophagic clearance of bacteria from damaged tissue in the resolution of inflammation during sepsis.

Chung Hun Wha Dam Tang attenuates atherosclerosis in apolipoprotein E-deficient mice via the NF-κB pathway.

Chung Hun Wha Dam Tang (CHWDT), a traditional Korean herbal formula, has been used for hundreds of years for alleviating dizziness, phlegm, and inflammation. The inhibitory effects of CHWDT on obesity have been reported. However, the effects of CHWDT in atherosclerosis have not yet been explored. Therefore, the aim of the study was to investigate whether CHWDT could confer protection from oxidative stress and inflammation in a high fat diet (HFD)-induced atherosclerosis model. Atherosclerosis was induced by feeding ApoeE-/- mice with HFD for 6 weeks. To examine the in vivo effects of CHWDT on HFD-induced atherosclerosis, mice on HFD for 6 weeks were orally administrated with CHWDT (400 or 800 mg/kg) every other day for an additional 6 weeks and histological features of aorta were determined by Sudan IV and H&E staining. The mRNA levels of TNF-α, SOD1, SOD2, iNOS or eNOS were determined with RT-PCR analysis or western blot analysis for protein levels. ROS generation was measured by CM-2DCFDA or MitoSox staining using FACS analysis or confocal microscopy. CHWDT decreased the mRNA levels of TNF-α and increased the mRNA levels of SOD1, SOD2 and catalase in both aorta and liver tissues of atherosclerotic mice. CHWDT attenuated TNF-α and iNOS expression in RAW 264.7 cells, U937 cells and HUVECs, and restored eNOS expression in HUVECs. CHWDT decreased H2O2-induced cellular ROS generation in RAW 264.7 cells and U937 cells, and also decreased H2O2-induced mitochondrial ROS generation in RAW 264.7 cells. Furthermore, SOD1, SOD2 and catalase mRNA levels were increased by pre-treatment with CHWDT in H2O2 and LPS-stimulated RAW 264.7 cells, as well as in LPS-treated U937 and HUVECs. CHWDT not only decreased LPS-induced NF-κB p65 phosphorylation but also inhibited the translocation of p65 from the cytosol to the nucleus in RAW 264.7 macrophages. These results suggest that CHWDT exerts inhibitory effects on atherosclerosis-induced oxidative stress and inflammation via the NF-κB pathway.

Anti-obesity Activity of Ethanol Extract from Bitter Melon in Mice Fed High-Fat Diet.

In many cases, obesity is associated with metabolic disorders. Recently, natural compounds that may be beneficial for improving obesity have received increasing attention. Bitter melon has received attention as a diabetes treatment. NAD+-dependent deacetylase (Sirtuin 1, SIRT1) has emerged as a novel therapeutic target for metabolic diseases. In this study, ethanol extract of bitter melon (BME) suppressed adipocyte differentiation and significantly increased the expression of SIRT1 in fully differentiated 3T3-L1 cells. Moreover, it enhanced the activation of AMP-activated protein kinase (AMPK). In high-fat diet (HFD)-fed induced-obesity mice, BME suppressed HFD-induced increases in body weight and white adipose tissue (WAT) weight. BME also increased the expression of SIRT1 and suppressed peroxisome proliferator-activated receptor and sterol regulatory element binding protein 1 expressions of WAT from HFD-fed mice. These findings suggest that BME prevents obesity by activating the SIRT1 and AMPK pathway and that it may be a useful dietary supplement for preventing obesity.

Resveratrol epigenetically regulates the expression of zinc finger protein 36 in non­small cell lung cancer cell lines.

Zinc finger protein 36 (ZFP36) is an AU­rich element protein that binds to 3'­untranslated regions and promotes the decay of target mRNAs. Downregulation of ZFP36 expression in turn results in stabilization of target mRNAs. A recent study indicated that downregulation of ZFP36 expression in human liver cancer is caused by epigenetic mechanisms. The purpose of the present study was to investigate the potential of resveratrol (Res) to induce ZFP36 expression. Promoter methylation was analyzed using methylation­sensitive restriction analysis. It was determined that Res treatment increased ZFP36 expression and decreased the mRNA levels of ZFP36 target genes in A549 lung cancer cells. Additionally, Res suppressed the expression of DNA (cytosine­5)­methyltransferase 1 and induced demethylation of the ZFP36 promoter. Collectively, the present results demonstrated that Res has anticancer activity through its epigenetic regulation of ZFP36 in non­small cell lung cancer.

Pterostilbene 4'-ß-Glucoside Attenuates LPS-Induced Acute Lung Injury via Induction of Heme Oxygenase-1.

Heme oxygenase-1 (HO-1) can exert anti-inflammatory and antioxidant effects. Acute lung injury (ALI) is associated with increased inflammation and influx of proinflammatory cells and mediators in the airspaces and lung parenchyma. In this study, we demonstrate that pterostilbene 4'-ß-glucoside (4-PG), the glycosylated form of the antioxidant pterostilbene (PTER), can protect against lipopolysaccharide- (LPS-) or Pseudomonas aeruginosa- (P. aeruginosa-) induced ALI when applied as a pretreatment or therapeutic post-treatment, via the induction of HO-1. To determine whether HO-1 mediates the antioxidant and anti-inflammatory effects of 4-PG, we subjected mice genetically deficient in Hmox-1 to LPS-induced ALI and evaluated histological changes, HO-1 expression, and proinflammatory cytokine levels in bronchoalveolar lavage (BAL) fluid. 4-PG exhibited protective effects on LPS- or P. aeruginosa-induced ALI by ameliorating pathological changes in lung tissue and decreasing proinflammatory cytokines. In addition, HO-1 expression was significantly increased by 4-PG in cells and in mouse lung tissues. The glycosylated form of pterostilbene (4-PG) was more effective than PTER in inducing HO-1 expression. Genetic deletion of Hmox-1 abolished the protective effects of 4-PG against LPS-induced inflammatory responses. Furthermore, we found that 4-PG decreased both intracellular ROS levels and mitochondrial (mt) ROS production in a manner dependent on HO-1. Pharmacological application of the HO-1 reaction product carbon monoxide (CO), but not biliverdin or iron, conferred protection in Hmox-1-deficient macrophages. Taken together, these results demonstrate that 4-PG can increase HO-1 expression, which plays a critical role in ameliorating intracellular and mitochondrial ROS production, as well as in downregulating inflammatory responses induced by LPS. Therefore, these findings strongly suggest that HO-1 mediates the antioxidant and anti-inflammatory effects of 4-PG.

Carbon monoxide-induced TFEB nuclear translocation enhances mitophagy/mitochondrial biogenesis in hepatocytes and ameliorates inflammatory liver injury.

Carbon monoxide (CO) can confer protection against cellular stress, whereas the potential involvement of autophagy and lysosomal biogenesis remains incompletely understood. We demonstrate here that the activation of protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK) with CO increased the nuclear translocation of transcription factor EB (TFEB). PERK activation by CO increased intracellular Ca2+ concentration and the phosphatase activity of calcineurin against TFEB. Moreover, we found that in the deficiency of TFEB, CO not only failed to recruit Parkin to the mitochondria but also failed to increase expression of lysosomal genes such as Lamp1, CathB, and TPP1. Therefore, we suggest that CO increases mitophagy through TFEB nuclear translocation by PERK-calcinuerin activation. In addition, the inhibition of TFEB with siRNA against TFEB abrogated the increase of mtDNA with CO, markers of mitochondrial biogenesis such as PGC1α, NRF1, and TFAM, and the mitochondrial proteins COX II, COX IV, and cytochrome c. To investigate the effects of CO on mitochondrial homeostasis in vivo, mice were treated with lipopolysaccharide (LPS)/D-galactosamine (D-GalN). CO inhalation reduced liver injury after challenge with LPS/GalN. Furthermore, CO inhalation increased TFEB activation, mitophagy and mitochondrial biogenesis in mice treated with LPS/GalN. Our findings describe novel mechanisms underlying CO-dependent cytoprotection in hepatocytes and liver tissue via activation of TFEB-dependent mitophagy and associated induction of both lysosomal and mitochondrial biogenesis.

Resveratrol Ameliorates Retinal Ischemia/Reperfusion Injury in C57BL/6J Mice via Downregulation of Caspase-3.

PURPOSE: Ischemia/reperfusion (I/R) injury induces apoptosis in retinal ganglion cells (RGCs). Resveratrol (Res) is a potent natural antioxidant with beneficial effects in many ocular diseases, such as age-related macular degeneration, diabetic retinopathy, and glaucoma. Because caspase-3 expression is highly correlated with activation of the apoptotic pathway, the present study aimed to determine whether Res regulates the expression of caspase-3 using an I/R retinal injury mouse model. METHODS: Male C57BL/6J mice were injected with Res for 2 consecutive days before I/R retinal injury. I/R retinal injury was induced by increasing the intraocular pressure for 1 h. Res was then injected for 3 consecutive days. Changes in retinal morphology were monitored for 3 days after injury by histochemistry using hematoxylin and eosin staining. mRNAs and proteins were extracted 2 days after injury. The expression levels of caspase-8 and caspase-3 mRNA and protein were determined using reverse-transcriptase polymerase chain reaction (RT-PCR) and western blot analyses. RESULTS: I/R injury induced declines in retinal thickness and number of RGCs during 5 days after injury. Caspase-8 and caspase-3 mRNA and protein activation increased. Res treatment reduced the significant loss of retinal morphology and downregulated the expression of mRNA and activation of caspase-8 and caspase-3 protein. CONCLUSIONS: The observed changes in retinal morphology suggest that I/R injury promotes retinal degeneration. Increased expression of caspase-8 and caspase-3 mRNA indicates apoptosis activation. Res, however, suppresses apoptosis via downregulation of caspase-8 and caspase-3 expression.

Carbon monoxide protects against hepatic steatosis in mice by inducing sestrin-2 via the PERK-eIF2α-ATF4 pathway.

Nonalcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, has emerged as one of the most common causes of chronic liver disease in developed countries over the last decade. NAFLD comprises a spectrum of pathological hepatic changes, including steatosis, steatohepatitis, advanced fibrosis, and cirrhosis. Autophagy, a homeostatic process for protein and organelle turnover, is decreased in the liver during the development of NAFLD. Previously, we have shown that carbon monoxide (CO), a reaction product of heme oxygenase (HO) activity, can confer protection in NAFLD, though the molecular mechanisms remain unclear. We therefore investigated the mechanisms underlying the protective effect of CO on methionine/choline-deficient (MCD) diet-induced hepatic steatosis. We found that CO induced sestrin-2 (SESN2) expression through enhanced mitochondrial ROS production and protected against MCD-induced NAFLD progression through activation of autophagy. SESN2 expression was increased by CO or CO-releasing molecule (CORM2), in a manner dependent on signaling through the protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor-2 alpha (eIF2α)/ activating transcription factor-4 (ATF4)-dependent pathway. CO-induced SESN2 upregulation in hepatocytes contributed to autophagy induction through activation of 5'-AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin (mTOR) complex I (mTORC1). Furthermore, we demonstrate that CO significantly induced the expression of SESN2 and enhanced autophagy in the livers of MCD-fed mice or in MCD-media treated hepatocytes. Conversely, knockdown of SESN2 abrogated autophagy activation and mTOR inhibition in response to CO. We conclude that CO ameliorates hepatic steatosis through the autophagy pathway induced by SESN2 upregulation.

Carbon monoxide decreases interleukin-1ß levels in the lung through the induction of pyrin.

Carbon monoxide (CO) can act as an anti-inflammatory effector in mouse models of lung injury and disease, through the downregulation of pro-inflammatory cytokines production, though the underlying mechanisms remain unclear. The nucleotide-binding oligomerization domain-, leucine-rich region-, and pyrin domain-containing-3 (NLRP3) inflammasome is a protein complex that regulates the maturation and secretion of pro-inflammatory cytokines, including interleukin-1ß (IL-1ß). In this report, we show that the CO-releasing molecule (CORM-2) can stimulate the expression of pyrin, a negative regulator of the NLRP3 inflammasome. CORM-2 increased the transcription of pyrin in the human leukemic cell line (THP-1) in the absence and presence of lipopolysaccharide (LPS). In THP-1 cells, CORM-2 treatment dose-dependently reduced the activation of caspase-1 and the secretion of IL-1ß, and increased the levels of IL-10, in response to LPS and adenosine 5'-triphosphate (ATP), an NLRP3 inflammasome activation model. Genetic interference of IL-10 by small interfering RNA (siRNA) reduced the effectiveness of CORM-2 in inhibiting IL-1ß production and in inducing pyrin expression. Genetic interference of pyrin by siRNA increased IL-1ß production in response to LPS and ATP, and reversed CORM-2-dependent inhibition of caspase-1 activation. CO inhalation (250 ppm) in vivo increased the expression of pyrin and IL-10 in lung and spleen, and decreased the levels of IL-1ß induced by LPS. Consistent with the induction of pyrin and IL-10, and the downregulation of lung IL-1ß production, CO provided protection in a model of acute lung injury induced by intranasal LPS administration. These results provide a novel mechanism underlying the anti-inflammatory effects of CO, involving the IL-10-dependent upregulation of pyrin expression.

Tristetraprolin regulates the decay of the hypoxia-induced vascular endothelial growth factor mRNA in ARPE-19 cells.

The aim of the present study was to investigate the effects of tristetraprolin (TTP) on the vascular endothelial growth factor (VEGF) mRNA and protein expression levels in retinal pigment epithelial cells under hypoxic conditions, and to consider the possibility of using TTP as a novel treatment tool for neovascular age­related macular degeneration (AMD). Overexpression of TTP reduced the expression and secretion levels of VEGF in ARPE­19 cells under hypoxic conditions. TTP destabilized the VEGF mRNA by binding to adenosine and uridine­rich elements regions in its 3'­untranslated region. Furthermore, conditioned medium (CM) from TTP­overexpressing ARPE­19 cells suppressed the tube formation in human umbilical vein endothelial cells compared with hypoxic CM. These findings indicate that regulation of TTP expression may be a promising therapeutic tool for neovascular AMD, however, further research is required.

Synergistic Effects of Cilostazol and Probucol on ER Stress-Induced Hepatic Steatosis via Heme Oxygenase-1-Dependent Activation of Mitochondrial Biogenesis.

The selective type-3 phosphodiesterase inhibitor cilostazol and the antihyperlipidemic agent probucol have antioxidative, anti-inflammatory, and antiatherogenic properties. Moreover, cilostazol and probucol can regulate mitochondrial biogenesis. However, the combinatorial effect of cilostazol and probucol on mitochondrial biogenesis remains unknown. Endoplasmic reticulum (ER) stress is a well-known causative factor of nonalcoholic fatty liver disease (NAFLD) which can impair mitochondrial function in hepatocytes. Here, we investigated the synergistic effects of cilostazol and probucol on mitochondrial biogenesis and ER stress-induced hepatic steatosis. A synergistic effect of cilostazol and probucol on HO-1 and mitochondrial biogenesis gene expression was found in human hepatocellular carcinoma cells (HepG2) and murine primary hepatocytes. Furthermore, in an animal model of ER stress involving tunicamycin, combinatorial treatment with cilostazol and probucol significantly increased the expression of HO-1 and mitochondrial biogenesis-related genes and proteins, whereas it downregulated serum ALT, eIF2 phosphorylation, and CHOP expression, as well as the lipogenesis-related genes SREBP-1c and FAS. Based on these results, we conclude that cilostazol and probucol exhibit a synergistic effect on the activation of mitochondrial biogenesis via upregulation of HO-1, which confers protection against ER stress-induced hepatic steatosis.

Effects of postnatal alcohol exposure on hippocampal gene expression and learning in adult mice.

Fetal alcohol syndrome (FAS) is a condition resulting from excessive drinking by pregnant women. Symptoms of FAS include abnormal facial features, stunted growth, intellectual deficits and attentional dysfunction. Many studies have investigated FAS, but its underlying mechanisms remain unknown. This study evaluated the relationship between alcohol exposure during the synaptogenesis period in postnatal mice and subsequent cognitive function in adult mice. We delivered two injections, separated by 2 h, of ethanol (3 g/kg, ethanol/saline, 20% v/v) to ICR mice on postnatal day 7. After 10 weeks, we conducted a behavioral test, sacrificed the animals, harvested brain tissue and analyzed hippocampal gene expression using a microarray. In ethanol-treated mice, there was a reduction in brain size and decreased neuronal cell number in the cortex, and also cognitive impairment. cDNA microarray results indicated that 1,548 genes showed a > 2-fold decrease in expression relative to control, whereas 974 genes showed a > 2-fold increase in expression relative to control. Many of these genes were related to signal transduction, synaptogenesis and cell membrane formation, which are highlighted in our findings.

Tristetraprolin suppresses the EMT through the down-regulation of Twist1 and Snail1 in cancer cells.

Inhibition of epithelial-mesenchymal transition (EMT)-inducing transcription factors Twist and Snail prevents tumor metastasis but enhances metastatic growth. Here, we report an unexpected role of a tumor suppressor tristetraprolin (TTP) in inhibiting Twist and Snail without enhancing cellular proliferation. TTP bound to the AU-rich element (ARE) within the mRNA 3'UTRs of Twist1 and Snail1, enhanced the decay of their mRNAs and inhibited the EMT of cancer cells. The ectopic expression of Twist1 or Snail1 without their 3'UTRs blocked the inhibitory effects of TTP on the EMT. We also observed that TTP overexpression suppressed the growth of cancer cells. Our data propose a new model whereby TTP down-regulates Twist1 and Snail1 and inhibits both the EMT and the proliferation of cancer cells.

Resveratrol Induces Glioma Cell Apoptosis through Activation of Tristetraprolin.

Tristetraprolin (TTP) is an AU-rich elements (AREs)-binding protein, which regulates the decay of AREs-containing mRNAs such as proto-oncogenes, anti-apoptotic genes and immune regulatory genes. Despite the low expression of TTP in various human cancers, the mechanism involving suppressed expression of TTP is not fully understood. Here, we demonstrate that Resveratrol (3,5,4'-trihydroxystilbene, Res), a naturally occurring compound, induces glioma cell apoptosis through activation of tristetraprolin (TTP). Res increased TTP expression in U87MG human glioma cells. Res-induced TTP destabilized the urokinase plasminogen activator and urokinase plasminogen activator receptor mRNAs by binding to the ARE regions containing the 3' untranslated regions of their mRNAs. Furthermore, TTP induced by Res suppressed cell growth and induced apoptosis in the human glioma cells. Because of its regulation of TTP expression, these findings suggest that the bioactive dietary compound Res can be used as a novel anti-cancer agent for the treatment of human malignant gliomas.

Resveratrol suppresses vascular endothelial growth factor secretion via inhibition of CXC-chemokine receptor 4 expression in ARPE-19 cells.

The present study characterizes the effects of resveratrol (Res) on vascular endothelial growth factor (VEGF) secretion in retinal pigment epithelial (RPE) cells. ARPE-19 cells were treated with CoCl2, a hypoxia mimetic agent. CoCl2 treatment increased protein levels of hypoxia inducible factor-1α (HIF-1α) and CXC-chemokine receptor 4 (CXCR4), and secretion of VEGF. To confirm the effects of Res on VEGF secretion, the human umbilical vein endothelial cell tube formation assay was performed with conditioned medium from Res-treated ARPE-19 cells. The well-known antioxidant Res effectively blocked these effects and reduced phosphorylation of nuclear factor (NF)-κB, an upstream activator of CXCR4. Furthermore, Res also suppressed VEGF secretion induced by SDF-1, a ligand of CXCR4. Conditioned medium from Res-treated ARPE-19 cells clearly suppressed tube formation compared with hypoxia-treated conditioned medium. The results demonstrated that Res inhibited the hypoxia mimetic CoCl2-induced expression of VEGF in ARPE-19 cells. Res suppressed CXCR4 expression through decreased phosphorylation of NF-κB, resulting in downregulation of VEGF secretion.

Tristetraprolin inhibits the growth of human glioma cells through downregulation of urokinase plasminogen activator/urokinase plasminogen activator receptor mRNAs.

Urokinase plasminogen activator (uPA) and urokinase plasminogen activator receptor (uPAR) play a major role in the infiltrative growth of glioblastoma. Downregulatoion of the uPA and uPAR has been reported to inhibit the growth glioblastoma. Here, we demonstrate that tristetraprolin (TTP) inhibits the growth of U87MG human glioma cells through downregulation of uPA and uPAR. Our results show that expression level of TTP is inversely correlated with those of uPA and uPAR in human glioma cells and tissues. TTP binds to the AU-rich elements within the 3' untranslated regions of uPA and uPAR and overexpression of TTP decreased the expression of uPA and uPAR through enhancing the degradation of their mRNAs. In addition, overexpression of TTP inhibited the growth and invasion of U87MG cells. Our findings implicate that TTP can be used as a promising therapeutic target to treat human glioma.

VEGF-C mediates RhoGDI2-induced gastric cancer cell metastasis and cisplatin resistance.

Rho GDP dissociation inhibitor 2 (RhoGDI2) expression is correlated with tumor growth, metastasis and chemoresistance in gastric cancer. However, the mechanisms by which RhoGDI2 promotes tumor cell survival and metastasis remain unclear. In this study, we clearly demonstrate that RhoGDI2 upregulates VEGF-C expression and RhoGDI2 expression is positively correlated with VEGF-C expression in human gastric tumor tissues as well as parental gastric cancer cell lines. VEGF-C depletion suppressed RhoGDI2-induced gastric cancer metastasis and sensitized RhoGDI2-overexpressing cells to cisplatin-induced apoptosis in vitro and in vivo. Secreted VEGF-C enhanced gastric cancer cell invasion and conferred cisplatin resistance to RhoGDI2-overexpressing cells. We also show that RhoGDI2 positively regulates Rac1 activity in gastric cancer cells. Inhibition of Rac1 expression suppressed RhoGDI2-induced VEGF-C expression, and this inhibition was associated with decreased invasiveness and increased sensitivity to cisplatin in RhoGDI2-overexpressing cells. Our results indicate that RhoGDI2 might be a potential therapeutic target for simultaneously reducing metastasis risk and enhancing chemotherapy efficacy in gastric cancer.

14-3-3σ attenuates RhoGDI2-induced cisplatin resistance through activation of Erk and p38 in gastric cancer cells.

Rho GDP dissociation inhibitor 2 (RhoGDI2) promotes tumor growth and malignant progression and enhances chemoresistance of gastric cancer. Recently, we noted an inverse correlation between RhoGDI2 and 14-3-3σ expression, which suggests that 14-3-3σ is a target of gastric cancer metastasis and the chemoresistance-promoting effect of RhoGDI2. Herein, we evaluated whether 14-3-3σ is regulated by RhoGDI2 and is functionally important for the RhoGDI2-induced cisplatin resistance of gastric cancer cells. We used highly metastatic and cisplatin-resistant RhoGDI2-overexpressing SNU-484 cells and observed decreased 14-3-3σ mRNA and protein expression. Depletion of 14-3-3σ in SNU-484 control cells enhanced cisplatin resistance, whereas restoration of 14-3-3σ in RhoGDI2-overexpressing SNU-484 cells impaired cisplatin resistance in vitro and in vivo. We also found that the phosphorylation levels of Erk and p38 kinases significantly decreased in RhoGDI2-overexpressing SNU-484 cells and recovered after 14-3-3σ expression, and that decreased activities of these kinases were critical for RhoGDI2-induced cisplatin resistance. In conclusion, 14-3-3σ is a RhoGDI2-regulated gene that appears to be important for suppressing the chemoresistance of gastric cancer cells.