肝癌组织中Raf激酶抑制蛋白和磷酸化Raf 激酶抑制蛋白的表达及其意义

 目的探讨Raf激酶抑制蛋白（Raf kinase inhibitor protein,RKIP）和磷酸化Raf激酶抑制蛋白（Phosphorylated raf kinase inhibitor protein,P-RKIP）在肝细胞癌中的表达及其临床意义。方法应用组织芯片和免疫组织化学方法检测RKIP蛋白和磷酸化的RKIP蛋白在72例肝细胞癌组织、50例癌旁肝组织及16例正常肝组织中的表达,并分析RKIP的表达与肝细胞癌临床病理学特征的关系。采用Western blot方法检测36例肝细胞癌、36例癌旁组织及12例正常肝组织中RKIP蛋白和磷酸化的RKIP蛋白的表达。结果免疫组化结果显示肝细胞癌、癌旁及正常肝组织中RKIP的阳性率分别为22.2％、86％、93.8％,P-RKIP为29.2％、84％、93.8％;肝癌组织中RKIP和P-RKIP的表达显著低于癌旁及正常肝组织,差异有统计学意义（P<0.05）,而且肝癌组织和癌旁肝组织中两者蛋白的表达均呈显著正相关（P=0.000,P=0.005）;RKIP和P-RKIP的表达均与肝癌有无肝内或淋巴结转移及分化程度有关（P<0.05）。Western blot结果显示肝癌组织中RKIP和P-RKIP的表达显著低于癌旁及正常肝组织。结论RKIP和 P-RKIP表达的减少或缺失与肝癌的发生发展、侵袭转移密切相关。     

Reduction in Raf kinase inhibitor protein expression is associated with increased Ras-extracellular signal-regulated kinase signaling in melanoma cell lines

Mutations in the Raf signaling pathway are known to play a pivotal role in the progression of malignant melanoma. In this study, we provide evidence that the Raf-1 kinase inhibitory protein (RKIP) and its effects on Raf-1-mediated activation of mitogen-activated protein/extracellular signal-regulated kinase kinase are important for the metastatic potential of malignant melanoma. Screening nine melanoma cell lines at mRNA and protein levels, we detected significant down-regulation of RKIP expression in comparison with normal melanocytes. Loss of RKIP expression in transformed cells in vivo was confirmed in immunohistochemical analyses demonstrating reduction of RKIP expression already in primary melanoma and even stronger down-regulation or complete loss in melanoma metastases. Stable transfection of the melanoma cell line Mel Im with an RKIP expression plasmid blocked the Raf kinase pathway, resulting in down-regulation of extracellular signal-regulated kinase 1/2 and activator protein 1 activity. In very good agreement with the in vivo finding that down-regulation of RKIP expression is most obvious in melanoma metastasis, overexpression of RKIP in the highly invasive Mel Im cell line leads to a significant inhibition of invasiveness in vitro. Taken together, our results suggest that loss of RKIP in malignant melanoma contributes to enhanced invasiveness of transformed cells and therefore to progression of the disease.     

Reduction of Raf-1 kinase inhibitor protein expression correlates with breast cancer metastasis.

PURPOSE: Raf-1 kinase inhibitor protein (RKIP) was originally identified as the first physiologic inhibitor of the Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) pathway. This pathway regulates fundamental cellular functions, including those that are subverted in cancer cells, such as proliferation, transformation, survival, and metastasis. Recently, RKIP has been recognized as a strong candidate for a metastasis suppressor gene in cell and animal model systems. Therefore, we investigated whether RKIP expression is altered in clinical specimens of human primary breast cancers and their lymph node metastases. EXPERIMENTAL DESIGN: Paraffin-embedded tumor samples from 103 breast cancer patients were examined immunohistochemically for the expression of RKIP, activated ERK, and apoptosis. The specificity of the antibodies used was validated by competition experiments with purified recombinant RKIP protein. RESULTS: RKIP expression was high in breast duct epithelia and retained to varying degrees in primary breast tumors. However, in lymph node metastases, RKIP expression was highly significantly reduced or lost (P = 0.000003). No significant correlations were observed between RKIP expression and histologic type, tumor differentiation grade, size, or estrogen receptor status. CONCLUSION: This is the first study of RKIP expression in a large clinical cohort. It confirms the results of cell culture and animal studies, suggesting that in human breast cancer, RKIP is a metastasis suppressor gene whose expression must be down-regulated for metastases to develop. RKIP expression is independent of other markers for breast cancer progression and prognosis.     

Prognostic Value of Raf Kinase Inhibitor Protein in Esophageal Squamous Cell Carcinoma

Raf kinase inhibitory protein (RKIP, also PEBP1) is involved in regulation of multiple cellular signaling processes and suppressing metastasis in animal models. Downregulation of RKIP expression has been shown to promote tumor progression in a variety of human cancers. However, its role and clinical significance in resectable esophageal squamous cell carcinoma (ESCC) is still scanty. The purpose of this study was to investigate the prognostic significance of RKIP expression by immunohistochemistry in a group of patients with ESCC treated with surgical resection. RKIP expression in 233 surgically resected ESCC specimens and 49 cases of adjacent normal tissues was detected by using immunohistochemical staining. The clinical and prognostic significance of RKIP expression was statistically analyzed. Kaplan-Meier analysis was used to compare the postoperative survival between groups. Significant downregulation was noted for RKIP protein in ESCCs, compared to adjacent normal tissues (p < 0.001). A lower disease-free survival and overall survival of ESCC was found in patients whose tissues had low RKIP expression (both P < 0.001). In addition, RKIP expression could stratify the patient survival (disease-free survival/overall survival) in stage II (P = 0.01 and 0.02, repectively). The Cox proportionate hazard regression model also established that low expression of RKIP was significantly correlated with increased risk (RR = 3.572) of recurrence compared with high RKIP expression (P < 0.001). Furthermore, the results of multivariate analysis suggested that RKIP expression (P < 0.001) was an independent factor that affected overall survival. These findings suggest that the low expression of RKIP be associated with poor survival in resectable ESCC patients.     

Prognostic value of RKIP and p-ERK in gastric cancer

Background

The mitogen-activated protein kinase (MAPK) signaling pathway participates in several steps of tumour development and is considered a prominent therapeutic target for the design of chemotherapeutic agents. We evaluated the expressions of extracellular signal-regulated kinase (ERK), mitogen-activated protein kinase (MEK), an upstream regulator of ERK, and Raf kinase inhibitor protein (RKIP), and investigated correlations of these expressions with clinicopathological features and outcomes in gastric cancer.

Methods

Tumour samples were obtained from 105 patients with gastric adenocarcinomas who underwent radical gastrectomy. The expressions of phosphorylated ERK (p-ERK), phosphorylated MEK (p-MEK), and RKIP were analysed by immunohistochemical staining.

Results

Expression of RKIP, p-MEK, and p-ERK was found in 69 (66%), 54 (51%), and 64 (61%) of all tumours, respectively. RKIP expression negatively correlated with the depth of invasion (p < 0.001), lymph node involvement (p = 0.028), and Union for International Cancer Control (UICC) stage (p = 0.007). RKIP expression was associated with significantly longer relapse-free survival (RFS) (p = 0.0033), whereas p-MEK was not (p = 0.79). Patients with p-ERK expression had slightly, but not significantly shorter RFS than those without such expression (p = 0.054). Patients with positive p-ERK and negative RKIP expression had significantly shorter RFS than the other patients (p < 0.001). The combination of RKIP and p-ERK expression was an independent prognostic factor (hazard ratio, 2.4; 95% confidence interval, 1.3 - 4.6; p = 0.008).

Conclusions

Our results demonstrated that loss of RKIP was associated with tumour progression and poor survival. Negative RKIP expression combined with positive p-ERK expression was an independent predictor of poor outcomes in patients with gastric cancer.     

RKIP在肺鳞癌组织中的表达及其意义

背景与目的 Raf激酶抑制蛋白(Raf kinase inhibitor protein,RKIP)属于磷脂酰乙醇胺结合蛋白家族的成员,可干扰Raf-1-MEK1/2-ERK1/2信号通路,抑制NF-κB和G蛋白偶联受体激酶等信号传导过程,且RKIP的表达减弱或丢失与多种肿瘤的发生发展以及侵润转移相关。本研究旨在探讨RKIP在肺鳞癌组织中的表达及其与肺鳞癌临床病理的相关性。方法应用RT-PCR方法检测56例肺鳞癌组织及其癌旁正常组织中RKIP基因的表达,计算其阳性率;并用Western blot方法检测肺鳞癌组织及其癌旁正常组织中RKIP蛋白的表达变化。结果 RKIP mRNA在肺鳞癌组织中表达的阳性率明显低于癌旁正常组织(P<0.05),在有淋巴结转移者中的表达阳性率明显低于无淋巴结转移者(P<0.05),但与患者的性别、年龄、肿瘤的大小及分化程度无明显关系(P>0.05)。RKIP蛋白在肺鳞癌组织中表达明显低于癌旁正常组织(P<0.05)。结论 RKIP的低表达可能与肺鳞癌的发生及侵袭转移有关。     

Impact of PTEN expression on the outcome of hepatitis C virus-positive cirrhotic hepatocellular carcinoma patients: possible relationship with COX II and inducible nitric oxide synthase

PTEN, a novel tumor suppressor, functions as a regulator of both cell cycle progression and apoptosis. PTEN gene is frequently mutated or deleted in several malignancies including human hepatocellular carcinoma (HCC). The clinical significance and prognostic value of PTEN expression in HCC or in the surrounding non-cancerous parenchyma remain obscure. Using immunohistochemistry, we analyzed the PTEN protein expression in 46 tissue sections collected from surgically resected hepatitis C virus (HCV)-positive cirrhotic HCC patients. Although the surrounding normal liver tissue was strongly expressing PTEN in 42 cases (91.3%), the immunostaining intensity was low in 29 (63.1%) and high in 17 (36.9%) of the HCCs. Additionally a significant positive correlation was identified between low PTEN expression in the HCC and increased expression of iNOS and COX II in the surrounding liver. The overall survival was significantly longer for the HCC-patients with high PTEN expression than patients with low PTEN expression. Univariate analysis revealed PTEN expression as an independent prognostic factor for patients survival. By Western blot analysis we also found that the Akt/PKB signaling, which is negatively regulated by PTEN, was upregulated in the HCCs in comparison to its expression in the surrounding liver tissue. These results demonstrate that downregulation of PTEN in the tumor is an important step in HCV-positive cirrhotic hepatocarcinogenesis and might result in concomitant upregulation of iNOS and COX II in the surrounding liver in favor of tumor promotion.     

Extracellular signal-regulated kinase induces cyclin D1 and Cdk-2 expression and phosphorylation of retinoblastoma in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies in Southeast Asia. Hyperphosphorylation of retinoblastoma (pRB) by cyclin/CDKs in G1/S transition is required for its inactivation and cell cycle progression. In the present study, we report that phosphorylation of pRB at Ser780 and Ser795 was detected in 71% (33 of 46) and 63% (29 of 46) of HCCs examined respectively. pRB protein was undetectable in 13% (6 of 46) of HCCs examined. Phosphorylated pRB was localized in the nuclei of hepatocarcinoma cells. Benign hepatocytes exhibited very weakly or no nuclear staining for phosphorylated pRB. Over-expression of E2F-1, cyclin D1, Cdk-2, Cdk-4 and cyclin A was found in 64% (30 of 46), 43% (26 of 46), 28% (11 of 46), 71% (33 of 46) and 63% (29 of 46) of HCCs examined respectively and this was correlated with elevation of ERK. Treatment of HepG2 cells with MEK1/2 inhibitor U0126 resulted in cell cycle arrest, downregulation of cyclin D1 and Cdk-2 expression and inhibition of pRB phosphorylation at Ser780 and Ser795. Ectopic expression of activated MEK1 in HepG2 cells increased cyclin D1 and Cdk-2 expression, phosphorylation of pRB at Ser780 and Ser795, and percentage of cells in S phase. Our data indicate that activated ERK plays an important role in cyclin D1 and Cdk-2 expression and phosphorylation of pRB at Ser780 and Ser795 in liver cancer cells.     

Vitamin K enhancement of sorafenib-mediated HCC cell growth inhibition in vitro and in vivo

The multikinase inhibitor sorafenib is the first oral agent to show activity against human hepatocellular carcinoma (HCC). Apoptosis has been shown to be induced in HCC by several agents, including sorafenib as well as by the naturally occurring K vitamins (VKs). As few nontoxic agents have activity against HCC growth, we evaluated the activity of sorafenib and VKs, both independently and together on the growth of HCC cells in vitro and in vivo. We found that when VK was combined with sorafenib, the concentration of sorafenib required for growth inhibition was substantially reduced. Conversely, VK enhanced sorafenib effects in several HCC cell lines on growth inhibition. Growth could be inhibited at doses of VK plus sorafenib that were ineffective with either agent alone, using vitamins K1, K2 and K5. Combination of VK1 plus sorafenib induced apoptosis on FACS, TUNEL staining and caspase activation. Phospho-extracellular signal-regulated kinase (ERK) levels were decreased as was myeloid cell leukemia sequence 1 (Mcl-1), an ERK target. Sorafenib alone inhibited growth of transplantable HCC in vivo. At subeffective sorafenib doses in vivo, addition of VK1 caused major tumor regression, with decreased phospho-ERK and Mcl-1 staining. Thus, combination of VK1 plus sorafenib strongly induced growth inhibition and apoptosis in rodent and human HCC and inhibited the RAF/mitogen-activated protein kinase kinase/ERK pathway. VK1 alone activated PKA, a mediator of inhibitory Raf phosphorylation. Thus, each agent can antagonize Raf: sorafenib as a direct inhibitor and VK1 through inhibitory Raf phosphorylation. As both agents are available for human use, the combination has potential for improving sorafenib effects in HCC.     

TC21/R-Ras 2在肝癌中的表达、亚细胞定位及意义

目的:探讨TC21基因在肝癌细胞、肝癌及癌旁组织中的表达、亚细胞定位及意义。方法:用RT-PCR检测TC 21在肝癌细胞系及人肝癌及癌旁组织中mRNA水平的表达,用免疫组化及Western印迹检测TC21蛋白在肝癌相关组织中的表达差异,用组织芯片技术结合免疫组化检测TC21蛋白的亚细胞定位。结果:RT-PCR检测结果表明TC21 mRNA在SMMC-7721、BEL-7402、Huh-7、Hep3B、HepG2、MHCC-97L、MHCC-LM3 7个肝癌细胞系及L-02和Chang liver 2株永生化人肝细胞系、7对肝癌及对应癌旁肝组织中均有较高表达;Western印迹结果表明上述细胞系中TC21蛋白表达与mRNA表达一致,TC21在4对肝癌及癌旁组织中均呈较高水平的表达;免疫组化检测结果表明TC21在人原发性肝癌、癌旁组织、硬化肝组织与正常肝组织中的表达阳性率分别为84.2%、77.2%、41.7%、0%,肝癌与肝硬化、正常肝相比显著高表达(P<0.05,P<0.01),与癌旁组织比无统计学意义(P>0.05);统计学分析结果表明TC21蛋白表达与肿瘤大小呈正相关(P<0.05),与是否肝硬化呈负相关(P<0.05);肝癌组织中TC21主要定位于肝癌细胞核,部分定位于胞质,膜定位不明显,TC21蛋白在肝癌细胞中的核定位显著高于癌旁肝细胞(P<0.001)。结论:本研究首次揭示TC21蛋白在肝癌组织中的高表达及核定位预示其在肝细胞恶性转化及肝癌发生发展中发挥重要作用。     

A New p53 Target Gene,RKIP, Is Essential for DNA Damage-Induced Cellular Senescence and Suppression of ERK Activation

p53, a strong tumor suppressor protein, is known to be involved in cellular senescence, particularly premature cellular senescence. Oncogenic stresses, such as Ras activation, can initiate p53-mediated senescence, whereas activation of the Ras-mitogen-activated protein kinase (MAPK) pathway can promote cell proliferation. These conflicting facts imply that there is a regulatory mechanism for balancing p53 and Ras-MAPK signaling. To address this, we evaluated the effects of p53 on the extracellular signal-regulated kinase (ERK) activation and found that p53 could suppress ERK activation through de novo synthesis. Through several molecular biologic analyses, we found that RKIP, an inhibitor of Raf kinase, is responsible for p53-mediated ERK suppression and senescence. Overexpression of RKIP can induce cellular senescence in several types of cell lines, including p53-deficient cells, whereas the elimination of RKIP by siRNA or forced expression of ERK blocks p53-mediated cellular senescence. These results suggested that RKIP is an essential protein for cellular senescence. Moreover, modification of the p53 serine 46 residue was critical for RKIP induction and ERK suppression as well as cellular senescence. These results indicated that RKIP is a novel p53 target gene that is responsible for p53-mediated cellular senescence and tumor suppressor protein expression.     

Reduced expression of syndecan-1 in human hepatocellular carcinoma with high metastatic potential

Syndecans comprise a gene family of transmembrane proteoglycans that regulate cellular behavior through interactions with various effectors, including heparin-binding growth factors and insoluble matrix components. Syndecan-1, the most extensively studied, localizes in epithelial cells and has been shown to present in normal hepatocytes. However, little is known about the change of syndecan-1 expression in human hepatocellular carcinoma (HCC). We investigated syndecan-1-protein expression by immunohistochemistry in 57 HCC tissue samples. Syndecan-1 gene expression was also determined. Syndecan-1 protein was expressed in cytoplasm and cell membrane of the hepatocytes and in the bile duct epithelial cells of liver with underlying hepatitis and cirrhosis. Conversely, among 57 HCC tissues, 39 HCC (68.4%) showed negative staining; 50% of well-differentiated HCC showed positive staining, whereas 82.4% of poorly differentiated HCC were negative. Loss of syndecan-1-protein expression was more prevalent in HCC with intra-hepatic metastasis (85.2%) than those without metastasis (48.0%). Similarly, syndecan-1 expression was significantly reduced in HCC with extra-hepatic metastasis (91.7%) as compared with the HCC without extra-hepatic metastasis (62.2%). The gene expression of syndecan-1 was significantly lower in HCC tissue than that in non-tumoral liver tissue. In 2 human HCC cell lines with poorly differentiated phenotype, HLE and HLF, syndecan-1 expression was markedly decreased both at the mRNA and the protein levels. These results suggest that the loss of syndecan-1 expression is a characteristic feature of HCC with high metastatic potential. Int. J. Cancer 74:482–491, 1997. © 1997 Wiley-Liss, Inc.     

Raf激酶抑制蛋白在非小细胞肺癌中的表达及其临床意义

背景与目的 Raf激酶抑制蛋白(Rafkinase inhibitor protein,RKIP)属于磷脂酰乙醇胺结合蛋白家族的成员,RKIP参与ERK/MAPK、G蛋白偶联受体和NF-κΒ等信号传导过程,且RKIP的表达减弱或丢失与多种肿瘤的发生发展及侵润转移相关。本研究旨在探讨RKIP在非小细胞肺癌(non-small cell lung cancer,NSCLC)组织中的表达及其与NSCLC临床病理特征的相关性。方法应用RT-PCR、Western blot及免疫组化方法检测83例NSCLC及其癌旁组织标本中RKIP的表达,并结合临床病理学资料进行统计学分析,所有病例均经病理诊断确诊,均无其它部位原发肿瘤,术前无化疗、放疗和免疫治疗史。结果 NSCLC中RKIP mRNA及蛋白的表达明显低于癌旁组织,差异有统计学意义(P<0.05)。RKIP与肿瘤分化程度、TNM分期、有无淋巴结转移及生存期有关(P<0.05),但与患者的性别、吸烟、年龄及肿瘤的大小无关(P>0.05)。结论 RKIP的低表达与NSCLC的发生及侵袭转移有关,可作为NSCLC预测及预后评估的指标。     

RKIP downregulates B-Raf kinase activity in melanoma cancer cells

The Raf-MEK-ERK protein kinase cascade is a highly conserved signaling pathway that is pivotal in relaying environmental cues from the cell surface to the nucleus. Three Raf isoforms, which share great sequence and structure similarities, have been identified in mammalian cells. We have previously identified Raf kinase inhibitor protein (RKIP) as a negative regulator of the Raf-MEK-ERK signaling pathway by specifically binding to the Raf-1 isoform. We show here that RKIP also antagonizes kinase activity of the B-Raf isoform. Yeast two-hybrid and coimmunoprecipitation experiments indicated that RKIP specifically interacted with B-Raf. Ectopic expression of RKIP antagonized the kinase activity of B-Raf. We showed that the effects of RKIP on B-Raf functions were independent of its known inhibitory action on Raf-1. The expression levels of RKIP in melanoma cancer cell lines are low relative to primary melanocytes. Forced expression of RKIP partially reverted the oncogenic B-Raf kinase-transformed melanoma cancer cell line SK-Mel-28. The low expression of RKIP and its antagonistic action on B-Raf suggests that RKIP may play an important role in melanoma turmorgenesis.     

High expression of AP-4 predicts poor prognosis for hepatocellular carcinoma after curative hepatectomy

The aim of this study was to evaluate the association between activating enhancer binding protein 4 (AP-4) tissue expression and patient prognosis in hepatocellular carcinoma (HCC). The levels of AP-4 mRNA and protein in tumor and para-tumor tissue were evaluated in 30 HCC cases by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Additionally, AP-4 protein expression in 112 HCC was analyzed by immunohistochemistry. The correlation of AP-4 expression and patients’ clinicopathological parameters was evaluated. Survival analysis was performed using the Kaplan–Meier method and Cox’s proportional hazards model. By RT-PCR and Western blot, the levels of AP-4 mRNA and protein were significantly higher in HCC, compared to that in para-tumor tissue (p?<?0.001). Immunohistochemical staining revealed that AP-4 was highly expressed in 53.6 % of the HCC patients. The AP-4 expression level was closely associated with serum alpha fetoprotein elevation, tumor size, histological differentiation, tumor recurrence, tumor metastasis, and tumor stage. Kaplan–Meier survival analysis showed that a high expression level of AP-4 resulted in a significantly poor prognosis of HCC patients. Multivariate analysis revealed that AP-4 expression level was an independent prognostic parameter for the overall survival rate of HCC patients. These findings provide evidence that a high expression level of AP-4 serves as a biomarker for poor prognosis for HCC. Thus, we speculate that AP-4 may be a potential target of antiangiogenic therapy for HCC.     

Raf kinase inhibitor protein (RKIP) in cancer

Raf kinase inhibitory protein (RKIP) was initially identified as phosphatidylethanolamine binding protein in bovine brain. It was later identified as a protein that inhibits Raf kinase activation of MEK. Further exploration has revealed that RKIP modulates several other signaling pathways including NF–κB and G-protein signaling. A gene array screen revealed that RKIP expression was low in a metastatic compared with non-metastatic prostate cancer cell line. Further experiments revealed that RKIP fits the criteria for a metastasis suppressor gene. RKIP expression has been shown to be downregulated in metastatic tissues, compared with non-metastatic tissue in multiple cancers, suggesting that loss of RKIP metastasis suppressor activity is a broad mechanism leading to metastasis. Additionally, loss of RKIP has been shown to impact therapy through conferring radioresistance and chemoresistance. Taken together, these data indicate understanding RKIP’s contributions to cancer may lead to important therapeutic strategies to prevent metastasis and promote therapeutic efficacy.     

Reduction of RKIP expression promotes nasopharyngeal carcinoma invasion and metastasis by activating Stat3 signaling

The role and underlying mechanism of Raf kinase inhibitory protein (RKIP) in nasopharyngeal carcinoma (NPC) metastasis remain unclear. Here, we showed that RKIP was downregulated in the NPC with high metastatic potentials, and its decrement correlated with NPC metastasis and poor patient survival, and was an independent predictor for reduced overall survival. With a combination of loss-of-function and gain-of-function approaches, we observed that high expression of RKIP reduced invasion, metastasis and epithelial to mesenchymal transition (EMT) marker alternations of NPC cells. We further showed that RKIP overexpression attenuated while RKIP knockdown enhanced Stat3 phosphorylation and activation in NPC cells; RKIP reduced Stat3 phosphorylation through interacting with Stat3; Stattic attenuated NPC cell migration, invasion and EMT marker alternations induced by RKIP knockdown, whereas Stat3 overexpression restored NPC cell migration, invasion and EMT marker alternations reduced by RKIP overexpression. In addition, there was an inverse correlation between RKIP and phospho-Stat3 expression in the NPC tissues and xenograft metastases. Our data demonstrate that RKIP is a metastatic suppressor and predictor for metastasis and prognosis in NPC, and RKIP downregulation promotes NPC invasion, metastasis and EMT by activating Stat3 signaling, suggesting that RKIP/Stat3 signaling could be used as a therapeutic target for NPC metastasis.