Regulation of multidrug resistance by MGr1-antigen in gastric cancer cells

MGr1-Antigen/37 kDa laminin receptor precursor promotes cellular prion protein induced multi-drug-resistance of gastric cancer

Cellular prion protein (PrP^C), the infective agent of transmissible spongiform encephalopathies, is thought to be related to several cellular physiological and physiopathological processes. We have previously reported that PrP^C participates in multi-drug-resistance of gastric cancer. As the salient ligand molecule of PrP for participating in internalization and propagation of the scrapie form of prion protein (PrP^Sc), 37 kDa laminin receptor precursor protein (37LRP) shared the same gene coding sequence of MGr1-Ag, another protein previously found to be involved in multi-drug-resistance of gastric cancer in our lab. In the present study, we explored whether MGr1-Ag/37LRP contributed to PrP^C mediated multi-drug-resistance in gastric cancer. Immunohistochemical staining showed similar expression patterns of MGr1-Ag/37LRP and PrP^C in gastric cancer tissue serial sections. Western blot and immunohistochemistry also demonstrated correlative expression of MGr1-Ag/37LRP and PrP^C in gastric cancer cell lines. Interaction between MGr1-Ag/37LRP and PrP^C in gastric cancer cell lines and gastric cancer tissues were verified by immunofluorescence and co-immunoprecipitation. Furthermore, knockdown of MGr1-Ag/37LRP significantly attenuated PrP^C induced multi-drug-resistance by sensitizing drug-induced apoptosis through inhibition of AKT activation. In conclusion, MGr1-Ag/37LRP may interact with PrP^C and promote the PrP^C induced multi-drug-resistance in gastric cancer through PI3K/AKT pathway. The current study elucidates the mechanism of how PrP^C triggers intracellular signaling cascade resulting in multi-drug-resistance phenotype and provides a novel candidate molecular target against gastric cancer.

The 37-kDa laminin receptor precursor regulates the malignancy of human glioma cells

Glioma is one of the most common brain tumors and one of the most aggressive cancers. Although extensive progress has been made regarding to the diagnosis and treatment, the mortality in glioma patients is still high. Therefore, finding new therapeutic targets to the glioma is critical to the advancement in cancer treatment. Recently, the 37-kDa laminin receptor precursor (37LRP) was reported to play important roles in occurrence of some types of cancer, indicating that this molecule may function as a key regulator in the tumor migration and metastasis. However, there is still no report to elucidate the correlation between 37LRP expression and glioma genesis and development. In this study, we found the higher expression of 37LRP in the glioma cells compared with the normal brain cells. We also indicated that the downregulation of 37LRP could affect the glioma biomarker expression and also weaken the proliferative, migratory, and metastatic capacity of glioma cells in vitro. Furthermore, 37LRP silencing inhibited the glioma tumor growth in vivo. Collectively, these data demonstrated that 37LRP regulates the metastasis of glioma cells in vitro and tumor growth in vivo, suggesting that 37LRP may function as a potential molecular target in the glioma treatment.

MGr1-Ag/37LRP promotes growth and proliferation of gastric cancer in vitro and in vivo

Gastric carcinoma (GC) is an aggressive cancer with a poor prognosis. We previously reported that MGr1-Ag was involved in multidrug resistance and anti-apoptosis in GC. However, the exact function of MGr1-Ag in GC proliferation is not clear. In this study, we found that MGr1-Ag was highly expressed in GC tissues and four GC cell lines compared with nontumor gastric tissues or gastric epithelial mucosa cells. The high expression of MGr1-Ag/37LRP was also consistent with the decreased median survival time of GC patients. We employed lenti-mediated RNA interference technique to knock down MGr1-Ag expression in SGC7901 and MKN45 cells, respectively, and observed its effects on GC cells growth in vitro and in vivo. Further study showed that knockdown of MGr1-Ag could inhibit GC cell proliferation by inhibiting the cell cycle S-phase entry and induced apoptosis. Soft agar colony formation assay indicated that the colony formation ability of SGC7901 and MKN45 cells decreased after lenti-MGr1-Ag small interfering RNA (siRNA) infection. Western blot revealed that cyclin D1 and Bcl-2 expression were downregulated whereas p27 and Bax were upregulated in lenti-MGr-siRNA-infected GC cells. Further study demonstrated that the proliferation effect of MGr1-Ag in GC is dependent on its laminin-binding region. Taken together, these data revealed a novel function of MGr1-Ag that can possibly be used as an independent prognostic factor and a potential therapeutic target for GC.

Gastric cancer cell adhesion to laminin enhances acquired chemotherapeutic drug resistance mediated by MGr1-Ag/37LRP

Adhesion of cancer cells to the extracellular matrix (ECM) causes a novel acquired chemotherapeutic drug‑resistant phenotype, referred to as cell adhesion-mediated drug resistance (CAM-DR). Our previous studies suggested that the adhesion molecule MGr1-Ag/37LRP may promote multidrug resistance in gastric cancer cells. Therefore, we investigated MGr1-Ag/37LRP binding-induced adhesion, and its role in CAM-DR. Initial studies revealed that, after adhesion to the ECM, the multidrug-resistant gastric cancer cell lines SGC7901/VCR and SGC7901/ADR showed significantly higher mean adhesive cell numbers than non‑resistant SGC7901 cells. We then investigated expression of MGr1-Ag/37LRP in gastric cancer cells adhering to laminin. Western blotting, RT-PCR and dual-luciferase reporter assays showed that laminin induced MGr1-Ag/37LRP expression and activity. In vitro and in vivo assays revealed that small interfering RNA against MGr1-Ag/37LRP significantly reduced CAM-DR in SGC7901/VCR cells. In vivo and in vitro analyses revealed that binding of MGr1-Ag/37LRP decreased intracellular drug accumulation by increasing P-glycoprotein and multidrug-associated protein expression, and inhibited drug-induced apoptosis by regulating Bcl-2 and Bax expression. These results indicate that MGr1-Ag/37LRP contributes to laminin-mediated CAM-DR in gastric cancer cells, and is a potentially effective target for reversing this phenomenon in gastric cancer.

MGr1-Ag/37LRP induces cell adhesion-mediated drug resistance through FAK/PI3K and MAPK pathway in gastric cancer

It is well known that tumor microenvironment plays a vital role in drug resistance and cell adhesion-mediated drug resistance (CAM-DR), a form of de novo drug resistance. In our previous study, we reported that MGr1-Ag/37LRP ligation-induced adhesion participated in protecting gastric cancer cells from a number of apoptotic stimuli caused by chemotherapeutic drugs. Further study suggested that MGr1-Ag could prompt CAM-DR through interaction with laminin. However, the MGr1-Ag-initiated intracellular signal transduction pathway is still unknown. In this study, our experimental results showed that gastric cancer MDR cell lines mediated CAM-DR through upregulation of Bcl-2 by MGr1-Ag interaction with laminin. Further study found that, as a receptor of ECM components, MGr1-Ag/37LRP may activate the downstream signal pathway PI3K/AKT and MAPK/ERK through interaction with phosphorylated FAK. Moreover, the sensitivity to chemotherapeutic drugs could be significantly enhanced by inhibiting MGr1-Ag/37LRP expression through mAbs, siRNA, and antisense oligonucleotide. According to these results, we concluded that the FAK/PI3K and MAPK signal pathway plays an important role in MGr1-Ag-mediated CAM-DR in gastric cancer. MGr1-Ag/37LRP might be a potential effective reversal target to MDR in gastric cancer.

37-kDa laminin receptor precursor promotes lung adenocarcinoma cell invasion and metastasis by epithelial-to-mesenchymal transition

37-kDa laminin receptor precursor (37LRP) has a crucial role in migration of some human cancers. Epithelial-to-mesenchymal transition (EMT) has received much attention in invasion and metastasis of lung cancer. Nevertheless, the role of 37LRP is not entirely clear in EMT promotion of lung cancer at present. In this study, we firstly examined the possible role of 37LRP in the invasiveness and metastasis process of lung cancer using immunohistochemistry of 80 lung adenocarcinoma cases, western blot and real-time PCR of 12 fresh lung adenocarcinoma tissues. The results showed that 37LRP significantly correlated with clinical stage and were highly expressed in metastatic lung adenocarcinomas compared with nonmetastatic ones. In vitro, we observed that 37LRP significantly increased the adhesive, invasive and metastatic abilities of human lung adenocarcinoma cell lines A549 by 37LRP-lentivirus interference. Furthermore, inoculation of A549 cells transduced with 37LRP-lentivirus in nude mice resulted in multi-metastases including the lung. In addition, western blotting and immunofluorescence were used to detect the significant difference in expression of E-cadherin and fibronectin in A549 by 37LRP-lentivirus interference compared with 37LRP-small interference RNA-lentivirus interference in vitro and vivo. The data indicated that A549 cells of epithelial cell characteristics might be induced to undergo EMT by 37LRP. A549 cells transduced with 37LRP-lentivirus showed marked morphological changes, accompanied by the decrease of epithelial marker E-cadherin and the increase of mesenchymal marker fibronectin. These results indicated that 37LRP may promote lung adenocarcinoma invasion and metastasis via the mechanism of EMT.

ERK/MAPK activation involves hypoxia-induced MGr1-Ag/37LRP expression and contributes to apoptosis resistance in gastric cancer

We previously demonstrated that hypoxia increased the hypoxia-inducible factor (HIF-1)-dependent MGr1-Ag/37LRP expression, which enhanced adhesion of gastric cancer cells to laminin, inhibited drug-induced apoptosis and caused cell adhesion-mediated drug resistance (CAM-DR). Here, we investigated the role of extracellular-regulated kinase (ERK) 1/2 in the signaling mechanisms underlying these events. We found that hypoxia activated ERK activity in vitro and in vivo. Overexpression of mitogen-activated protein kinase (MAPK) kinase (MEK), which preferentially activated ERK, mimics, in a nonadditive way, hypoxia-induced activity of MGr1-Ag/37LRP promoter and expression of MGr1-Ag/37LRP. Furthermore, U0126, the MEK inhibitor, inhibited hypoxia- and MEK-induced MGr1-Ag/37LRP promoter activity in a dose-dependent manner. MEK inhibition also reversed hypoxia- and MEK-induced HIF-1 protein and its activity in a dose-dependent manner. We also investigated reactive oxygen species signaling this response. Exogenous addition of H(2)O(2) was sufficient to activate ERK in a dose-dependent profile. Reactive oxygen species scavengers of H(2)O(2) significantly inhibited hypoxia-induced ERK or HIF-1 activation and sequential expression of MGr1-Ag/37LRP. We also investigated the signaling in hypoxia-induced cell adhesion and apoptosis induced by vincristine. Hypoxia significantly enhanced adhesion of SGC7901 cells to laminin in a time-dependent manner, which might be inhibited by the MEK inhibitor U0126 and MGr1-Ag/37LRP siRNA. Consistent with results of adhesion assay, hypoxia-resistant apoptosis might be reversed by U0126 in a dose-dependent manner. Our results suggest that hypoxia-elicited MGr1-Ag/37LRP expression activated by HIF-1 depends on ERK activation. These events are dependent of reactive oxygen intermediates.

Screening and Identification of Recombinant Anti-Idiotype Antibodies against Gastric Cancer and Colon Cancer Monoclonal Antibodies by a Phage-Displayed Single-Chain Variable Fragment Library

Several monoclonal antibodies (McAbs) have been developed that show high sensitivity and specificity to gastric cancer and colorectal cancer. However, few of the antigens recognized by these antibodies have been identified. The authors now report the selection of anti-idiotype (anti-id) antibodies of MGb1 McAb against gastric cancer and MC5 McAb against colorectal cancer using phage-displayed single-chain variable fragment (ScFv) libraries. After purification, the anti-id antibodies were approximately 30 kd and could be recognized by MGb1/MC5 McAb. Anti-id antibodies significantly blocked the binding of MGb1 and MC5 to gastric cancer/colorectal cancer cells, respectively, suggesting that the antibodies were specific to MGb1 and MC5. Antibodies against gastric and colorectal cancer could be detected in mice at 6 weeks after immunization with the anti-id antibodies. At week 8, antibody titers reached 1:400. The anti-id antibodies may be useful as novel reagents for developing vaccines against gastric cancer and colorectal cancer.

Comparative proteomic analysis of colon cancer cells in response to oxaliplatin treatment

Colon cancer is one of the most common malignancies in the world. Oxaliplatin, a third-generation platinum compound, is widely used in clinical chemotherapy of colon cancer. Although the mechanisms of the antitumor effect of Oxaliplatin have been investigated in recent years, the proteomic changes that are associated with the cellular response to this compound are poorly understood. In this study, we performed a comparative proteomic analysis to survey the global changes in protein expression levels after Oxaliplatin treatment in three colon cancer cell lines: HT29, SW620, and LoVo. Two-dimensional gel electrophoresis coupled with MALDI-TOF/TOF mass spectrometry revealed 57, 48, and 53 differentially expressed proteins in the three cell lines (HT29, SW620 and LoVo, respectively) after Oxaliplatin treatment. Of these proteins, 21 overlapped among all three cell lines. These overlapping proteins participate in many cellular processes, such as apoptosis, signal transduction, transcription and translation, cell structural organization, and metabolism. Additionally, the expression levels of ezrin (EZRI), heat-shock protein beta-1 (HSPB1), translationally controlled tumor protein (TCTP), and cell division control protein 2 homolog (CDC2) were confirmed by immunoblotting. This is the first direct proteomic analysis of Oxaliplatin-treated colon cancer cells. Several interesting proteins that we found warrant further investigation owing to their potential significant functions in the antitumor effect of Oxaliplatin.

Hypoxia-mediated up-regulation of MGr1-Ag/37LRP in gastric cancers occurs via hypoxia-inducible-factor 1-dependent mechanism and contributes to drug resistance

Our previous study demonstrated hypoxia-inducible factor-1(HIF-1) could prompt multidrug resistance (MDR) phenotype and MGr1-Ag/37LRP, a novel drug-resistance protein was reported by our labortary, associated with multidrug resistance in gastric cancer. Given this association, we hypothesized that MGr1-Ag/37LRP contributed to HIF-1-dependent hypoxia-induced MDR phenotype. Initial experiments revealed that blocking MGr1-Ag/37LRP expression by siRNA in gastric cancer cells effectively reversed multidrug resistance phenotype induced by hypoxia. Subsequent analysis of MGr1-Ag/37LRP mRNA and protein in gastric cancer cells revealed a time-dependent manner increase with hypoxia. While the up-regulation of MGr1-Ag/37LRP was abolished by HIF-1 inhibition with siRNA. Studies using luciferase promoter constructs revealed a significant increase in activity in cells subject to hypoxia and such hypoxia inducibility was lost in cells co-transfected siRNA targeting HIF-1. Analysis of the MGr1-Ag/37LRP promoter revealed several potential binding sites for HIF-1. Electrophoretic mobility shift assay and chromatin immunoprecipitation demonstrated a functional HIF-1 binding site within MGr1-Ag/37LRP gene regulatory sequence located at -16 to -11 relative to the transcriptional initiation point. These observations demonstrate that MGr1-Ag/37LRP is actively engaged by hypoxia and represent a novel HIF-1 target. Such results suggest hypoxia-elicited MGr1-Ag/37LRP expression as a pathway for resistance of gastric cancer to chemotherapeutics.

Multidrug resistance in gastric cancer: recent research advances and ongoing therapeutic challenges

Gastric cancer is the second leading cause of cancer mortality worldwide. The major cause of treatment failure for gastric cancer is the development of multidrug resistance (MDR) to chemotherapy, which is currently one of the primary treatment options. Recently, research into the MDR of gastric cancer has revealed that, in addition to the classical ATP-binding cassette transporters, such as P-glycoprotein (P-gp) and MDR-associated protein (MRP)1, a number of other molecules might mediate the drug resistance of human gastric cancer. The absence of P-gp and MRP1 expression in some gastric cancer cases also indicates that there might be other mechanisms responsible for human gastric cancer MDR. These molecules belong to different functional families and might work together to confer MDR phenotypes. The new findings may provide new clues to the mechanisms of MDR and enable the selection of new candidates for targeting MDR in human gastric cancer.

Involvement of MGr1-Ag/37LRP in the vincristine-induced HIF-1 expression in gastric cancer cells

Drug resistance is a major obstacle in the development of effective cancer therapy. It was reported that many chemotherapeutic drugs such as vincristine (VCR), a potent anti-tumor agent that associates with microtubules and disrupts the microtubular system, was found in acquisition of drug-resistance associated with an increase of HIF-1 expression via activating the NF-gammaB signal pathway. However, the multifactorial mechanism responsible for VCR increased HIF-1alpha expression remains to be fully elucidated. MGr1-Ag was previously reported by our laboratory as an upregulated protein in VCR-resistant cell lines SGC7901/VCR. In our study, detection of HIF-1 expression in SGC7901 cells and SGC7901/VCR cell or VCR-treated SGC7901cells showed that VCR could induce a significant expression of HIF-1alpha and VCR-resistant SGC7901/VCR cells had much higher expression of HIF-1alpha. Under nonhypoxic condition, VCR could enhance DNA binding activity and transcriptional activity of HIF-1alpha by 5.42- and 9.42-fold, respectively. Further study showed that forced expression of MGr1-Ag/37LRP upregulated HIF-1alpha protein expression and transcriptional activity in gastric cancer cell under nonhypoxic condition whereas siRNA targeting MGr1-Ag showed a markedly decreased VCR-induced HIF-1alpha expression and transcriptional activity (P < 0.05). SiRNA targeting FAK or inhibitors of phosphatidylinositol 3-kinase (PI3K) and MAPK could inhibit VCR-induced HIF-1alpha expression, suggesting FAK-PI3K and p42/44MAPK (Erk1/2) may be the major signaling molecules in MGr1-Ag/37LRP-induced HIF-1alpha expression and activity. These data support a model in which MGr1-Ag was a focal point for the convergence of VCR-mediated signaling events leading to HIF-1Alpha induction, thus revealing a novel aspect of HIF-1alpha regulation.