Seon Young Nam

Upregulation of FLIPS by Akt, a possible inhibition mechanism of TRAIL‐induced apoptosis in human gastric cancers

Tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL) is a potent inducer of apoptosis in some, but not all cancer cells. To assess the regulation of TRAIL‐resistance in the human gastric cancer cells, we examined TRAIL sensitivity, TRAIL receptor expression, and intracellular signaling events induced by TRAIL. All the gastric cancer cell lines tested were susceptible to TRAIL to some extent except for SNU‐216 cell line, which was completely resistant. TRAIL receptor expression was not related to the TRAIL‐sensitivity. Of the cell lines tested, SNU‐216 showed the highest level of constitutively active Akt and the short form of FLICE inhibitory protein (FLIPS). Treatment with the phosphatidylinositol 3‐kinase (PI3K) inhibitor LY294002 or with the protein synthesis inhibitor cycloheximide induced a suppression of constitutive Akt activation in SNU‐216 cells and a concomitant decrease in the expression of FLIPS. The reduction of Akt activity by LY294002 affected the transcriptional level of FLIPS, but not the mRNA stability. As a result, LY294002 or cycloheximide significantly enhanced TRAIL‐induced apoptosis. Moreover, the overexpression of constitutively active Akt in the TRAIL‐sensitive cell line, SNU‐668, rendered the cell line resistant to TRAIL. In addition, infection of the same cell line with retrovirus expressing FLIPS completely inhibited TRAIL‐induced apoptosis by blocking the activation of caspase‐8. Therefore, our results suggest that Akt activity promotes human gastric cancer cell survival against TRAIL‐induced apoptosis via upregulation of FLIPS, and that the cytotoxic effect of TRAIL can be enhanced by modulating the Akt/FLIPS pathway in human gastric cancers.

Akt/PKB activation in gastric carcinomas correlates with clinicopathologic variables and prognosis.

Akt/protein kinase B (PKB) plays an important role in cell survival. However, the role of Akt in the biology of gastric cancer has not been well studied. We sought to investigate the expression of Akt or phosphorylated Akt (pAkt) in human gastric carcinomas and to analyze the relationship between Akt or pAkt and the clinicopathologic parameters. The expressions of Akt and pAkt were evaluated immunohistochemically in 311 gastric carcinomas using the tissue array method. Akt expression was detected in 74% of the tumors and pAkt expression in 78%. pAkt was highly expressed in the early stage of pTNM (p=0.011). We also found an inverse association between pAkt and lymphatic invasion (p=0.01) or lymph node metastasis (p=0.008). pAkt expression was significantly correlated with a higher survival in patients with stage I carcinomas (p=0.0003). Interestingly, combined evaluation revealed that the group with pAkt‐positive and lymph node‐negative carcinomas showed a better prognosis than the other groups (p<0.0001). In addition, pAkt was shown to correlate positively with APC (p=0.002) and Smad4 (p<0.0001) expression. These findings suggest that pAkt expression may help to predict the clinical outcome of gastric cancer patients.

Nuclear Factor-κB Activation Correlates with Better Prognosis and Akt Activation in Human Gastric Cancer

Purpose: Because the biological significance of constitutive nuclear factor-κB (NF-κB) activation in human gastric cancer is unclear, we undertook this study to clarify the regulatory mechanism of NF-κB activation and its clinical significance. Experimental Design: Immunohistochemistry for NF-κB/RelA was done on 290 human gastric carcinoma specimens placed on tissue array slides. The correlations between NF-κB activation and clinicopathologic features, prognosis, Akt activation, tumor suppressor gene expression, or Bcl-2 expression were analyzed. We also did luciferase reporter assay, Western blot analysis, and reverse transcription-PCR using the SNU-216 human gastric cancer cell line transduced with retroviral vectors containing constitutively active Akt or the NF-κB repressor mutant of IκBα. Results: Nuclear expression of RelA was found in 18% of the gastric carcinomas and was higher in early-stage pathologic tumor-node-metastasis (P = 0.019). A negative correlation was observed between NF-κB activation and lymphatic invasion (P = 0.034) and a positive correlation between NF-κB activation and overall survival rate of gastric cancer patients (P = 0.0228). In addition, NF-κB activation was positively correlated with pAkt (P = 0.047), p16 (P = 0.004), adenomatous polyposis coli (P < 0.001), Smad4 (P = 0.002), and kangai 1 (P < 0.001) expression. An in vitro study showed that NF-κB activity in gastric cancer cells is controlled by and controls Akt. Conclusions: NF-κB activation was frequently observed in early-stage gastric carcinoma and was significantly correlated with better prognosis and Akt activation. These findings suggest that NF-κB activation is a valuable prognostic variable in gastric carcinoma.

Akt is negatively regulated by the MULAN E3 ligase

The serine/threonine kinase Akt functions in multiple cellular processes, including cell survival and tumor development. Studies of the mechanisms that negatively regulate Akt have focused on dephosphorylation-mediated inactivation. In this study, we identified a negative regulator of Akt, MULAN, which possesses both a RING finger domain and E3 ubiquitin ligase activity. Akt was found to directly interact with MULAN and to be ubiquitinated by MULAN in vitro and in vivo. Other molecular assays demonstrated that phosphorylated Akt is a substantive target for both interaction with MULAN and ubiquitination by MULAN. The results of the functional studies suggest that the degradation of Akt by MULAN suppresses cell proliferation and viability. These data provide insight into the Akt ubiquitination signaling network.

Constitutive phosphorylation of the FOXO1A transcription factor as a prognostic variable in gastric cancer.

Increased phosphorylation of FOXO1A, a FOXO transcription factor, has been implicated in several human cancers; however, it has not been studied in the gastric cancer to date. To determine the status of pFOXO1A expression in human gastric cancers and to determine its relationship with other tumor-associated proteins, we performed immunohistochemical staining on tissue array slides containing 272 human gastric carcinoma specimens. In non-neoplastic gastric mucosa, the expression of pFOXO1A was observed primarily in cells in the proliferative zone and in areas of intestinal metaplasia. In gastric carcinomas, the expression of pFOXO1A was observed in 230 (84.6%) out of 272 cases examined, and was positively correlated with the Ki-67-labeling index (P=0.026). The expression of pFOXO1A was higher in the early stages of pTNM (P<0.001), and was inversely correlated with the intestinal type by Laurens classification (P=0.001), lymphatic invasion (P=0.017) and lymph node metastasis (P<0.001). Moreover, the expression of pFOXO1A was correlated with a longer patient survival (P=0.004). In addition, the expression of pFOXO1A was correlated with that of pAKT1 (P<0.001), PTEN (P=0.009), CDKN2A (P=0.012), APC (P=0.048), SMAD4 (P<0.001), CD82 (P=0.011), and BCL2 (P=0.011). In conclusion, our results showed that the expression of pFOXO1A is a frequent and early event in gastric tumorigenesis and that there is a significant correlation between pFOXO1A and better prognosis. Thus, our data suggest that the expression of pFOXO1A may serve as a valuable prognostic variable in gastric carcinoma and have significant implications for the development and application of targeted therapy.

Ret finger protein 2 enhances ionizing radiation-induced apoptosis via degradation of AKT and MDM2.

Ret finger protein 2 (RFP2), a gene frequently deleted in multiple tumor types, encodes a protein with a RING finger, B-box, and coiled-coil domain that belongs to the RBCC/TRIM protein family. Although RBCC proteins are involved in diverse cellular processes such as apoptosis, proliferation, differentiation, and transcriptional regulation, the biological function of RFP2 has not been well defined. Here, we demonstrate that overexpression of RFP2 in cells induced apoptosis through proteasomal degradation of MDM2 and AKT. The expression of RFP2, which possesses RING domain-dependent E3 ubiquitin ligase activity, was increased by ionizing radiation dose- and time-dependently, and RFP2 overexpression induced cell death with increased expression of apoptotic molecules (p53, p21, and Bax). These results depended on the E3 ubiquitin ligase activity of RFP2 because mutant RFP2, which contains a mutated RING domain, failed to drive apoptosis compared with wild-type RFP2. We observed that RFP2 formed a complex with MDM2, a negative regulator of the p53 tumor suppressor, and AKT, a regulator of apoptosis inhibition at the cellular level. Additionally, we found that the interaction of RFP2 with MDM2 and AKT resulted in ubiquitination and proteasomal degradation of MDM2 and AKT in vivo and in vitro. Thus, these data suggest that irradiation causes RFP2 overexpression, which enhances ionizing radiation-induced apoptosis by increasing p53 stability and decreasing AKT kinase activity through MDM2 and AKT degradation.

Genome-wide analysis of low-dose irradiated male Drosophila melanogaster with extended longevity.

Ionizing radiation generates oxidative stress, which is thought to be a major cause of aging. Although living organisms are constantly exposed to low levels of radiation, most studies examining the effect of radiation have focused on accelerated aging and diminished life span that result from high-dose radiation. On the other hand, several studies have suggested that low-dose radiation enhances the longevity of Drosophila melanogaster. Therefore, investigation of the biological effects of low-dose radiation could contribute to a more comprehensive understanding of the aging process. In this study, microarray and quantitative real time-PCR were used to measure genome-wide changes in transcript levels in low-dose irradiated fruit flies that showed enhanced longevity. In response to radiation, approximately 13% of the genome exhibited changes in gene expression, and a number of aging-related genes were significantly regulated. These data were compared with quantitative trait loci affecting life-span to identify candidate genes involved in enhanced longevity induced by low-dose radiation. This genome-wide survey revealed novel information about changes in transcript levels in low-dose irradiated flies and identified 39 new candidate genes for molecular markers of extended longevity induced by ionizing radiation. In addition, this study also suggests a mechanism by which low-dose radiation extends longevity.

Manganese superoxide dismutase expression correlates with a poor prognosis in gastric cancer.

Objective: The biologic significance of superoxide dismutase (SOD) in transformed gastric carcinoma cells is unclear. The aim of this study was to examine the role of SOD as a prognostic indicator of gastric carcinomas and its association with other clinicopathological factors. Methods: Expression of MnSOD and Cu/ZnSOD was evaluated immunohistochemically in gastric carcinomas and adenomas using tissue-array methods. The correlation between SOD immunoreactivity and clinical outcome or clinicopathological factors was investigated. Results: MnSOD expression was associated with a poor patient prognosis and was strong in advanced gastric cancer, in the well-differentiated type and in the presence of lymphoid stroma (p < 0.05). On the other hand, there was no association between Cu/ZnSOD expression and patient survival. Cu/ZnSOD immunoreactivity was strong in advanced gastric cancer and in the presence of lymphoid stroma (p < 0.05) and was weak in signet ring cell type. Conclusion: MnSOD immunoreactivity is significantly associated with poor outcome in gastric carcinoma patients although both MnSOD and Cu/ZnSOD have a connection with several clinicopathological parameters with some overlap.

Immunohistochemical Analysis of Cell Cycle-Related Molecules in Gastric Carcinoma: Prognostic Significance, Correlation with Clinicopathological Parameters, Proliferation and Apoptosis

Objective: We aimed to investigate the biological significance of cell cycle regulators in gastric carcinoma. Methods: Immunohistochemistry and TUNEL staining were performed on tissue array slides containing 293 gastric carcinoma specimens. The relationship between the protein expression of each of the cell cycle regulators and prognosis, clinicopathological features, proliferation, or apoptosis was evaluated. Results: The nuclear immunoreactivity for cyclin D1, cyclin E, p21, and p27 was observed in 22, 14, 31 and 27% of cases, respectively. The expression of cyclin D1, p21, or p27 positively correlated with early pTNM stages, tumor cell proliferation (represented by Ki-67 labeling) and good prognosis, whereas it inversely correlated with the lymph node metastasis (p < 0.05). On the other hand, p27 expression inversely correlated with the apoptosis index represented by TUNEL staining (p < 0.001). In addition, the expression of cyclin D1 positively correlated with that of p21 or p27 (p < 0.05). Conclusions: Our results showed that the expression of cyclin D1, p21 and p27, alone or in combination, are early events in gastric tumorigenesis and may serve as a candidate molecular marker for the early gastric carcinoma.

Nuclear factor-κB dependency of doxorubicin sensitivity in gastric cancer cells is determined by manganese superoxide dismutase expression

The role of nuclear factor‐κB (NF‐κB) activation in cancer cell apoptosis appears to be tailored specifically for each cell type and the type of NF‐κB inducer. The present study aimed to determine whether or not NF‐κB activation is associated with chemosensitivity to doxorubicin (DOX) using the DOX‐sensitive SNU‐601 and DOX‐resistant SNU‐216 gastric cancer cell lines. The effect of NF‐κB activation on DOX (1 µg/mL) sensitivity was analyzed after the suppression of NF‐κB activation using transfection of the super‐suppressive mutant form of IκBα (mIκBα) or pretreatment with pyrrolidine dithiocarbamate. In addition, the association between NF‐κB and manganese superoxide dismutase (MnSOD) in relation to DOX sensitivity was analyzed after the modulation of MnSOD expression. The NF‐κB activity was much higher in DOX‐resistant SNU‐216 cells than in DOX‐sensitive SNU‐601 cells before and after DOX treatment. Overexpression of mIκBα or pyrrolidine dithiocarbamate pretreatment decreased the DOX resistance in SNU‐601 cells with low MnSOD expression, but not in SNU‐216 cells with high MnSOD expression. In comparison, the overexpression of MnSOD, which also suppressed NF‐κB activation in both cell lines, increased DOX resistance in SNU‐601 cells. Blocking of MnSOD expression using RNA interference techniques increased DOX sensitivity in SNU‐216 cells, which was further augmented by the additional inhibition of NF‐κB activity. Our results showed that whether NF‐κB contributes to DOX sensitivity in gastric cancer cells is determined by the level of MnSOD expression. Thus, targeting both MnSOD and NF‐κB may be helpful for increasing the efficacy of DOX treatment of DOX‐resistant SNU gastric cancer cells. (Cancer Sci 2008; 99: 1117–1124)