ABSTRACT
UNLABELLED: Surgical resection is the first-line treatment for hepatocellular carcinoma (HCC) patients with well-preserved liver function. Nevertheless, the rate of postoperative recurrence at 5 years is as high as 70%, and this gravely jeopardizes the therapeutic outcome. Clearly, new approaches are needed for preventing the relapse of this deadly disease. Taking advantage of a luciferase-labeled orthotopic xenograft model of HCC, we examined the role of sorafenib, the first systemic drug approved for advanced HCC patients, in the prevention of HCC recurrence. We found that sorafenib suppressed the development of postsurgical intrahepatic recurrence and abdominal metastasis and consequently led to prolonged postoperative survival of mice in this model. Furthermore, hyperactivity of extracellular signal-regulated kinase signaling caused by elevated levels of growth factors associated with postoperative liver regeneration enhanced the sensitivity of HCC cells to sorafenib; this provides a plausible explanation for the observation that recurrent tumors are more responsive to growth inhibition by sorafenib. CONCLUSION: Our results strongly suggest that by effectively reducing postoperative recurrence, sorafenib has a potential application in early-stage HCC patients who have undergone hepatectomy with curative intention.
Subject(s)
Antineoplastic Agents/therapeutic use , Benzenesulfonates/therapeutic use , Carcinoma, Hepatocellular/surgery , Liver Neoplasms/surgery , Neoplasm Metastasis/prevention & control , Neoplasm Recurrence, Local/prevention & control , Pyridines/therapeutic use , Animals , Antineoplastic Agents/pharmacology , Apoptosis/drug effects , Benzenesulfonates/pharmacology , Carcinoma, Hepatocellular/metabolism , Carcinoma, Hepatocellular/pathology , Cell Line, Tumor , Cell Movement/drug effects , Cell Proliferation/drug effects , Disease Models, Animal , Extracellular Signal-Regulated MAP Kinases/metabolism , Humans , Liver Neoplasms/metabolism , Liver Neoplasms/pathology , Male , Mice , Mice, Inbred BALB C , Mice, Nude , Niacinamide/analogs & derivatives , Phenylurea Compounds , Pyridines/pharmacology , Sorafenib , Transplantation, Heterologous , Treatment OutcomeABSTRACT
The transcription factor NF-κB plays a pivotal role in innate immunity in response to a variety of stimuli, and the coordinated regulation of this pathway determines the proper host responses to extracellular signals. In this study, we identified RACK1 as a novel negative regulator of NF-κB signaling, NF-κB-mediated cytokine induction and inflammatory reactions. RACK1 physically associates with the IKK complex in a TNF-triggered manner. This interaction interferes with the recruitment of the IKK complex to TRAF2, which is a critical step for IKK phosphorylation and subsequent activation triggered by TNF. By modulating the interaction between TRAF2 and IKK, RACK1 regulates the levels of NF-κB activation in response to different intensities of stimuli. Our findings suggest that RACK1 plays an important role in controlling the sensitivity of TNF-triggered NF-κB signaling by regulating IKK activation and provide new insight into the negative regulation of inflammatory reactions.
Subject(s)
GTP-Binding Proteins/metabolism , I-kappa B Kinase/metabolism , NF-kappa B/metabolism , Neoplasm Proteins/metabolism , Receptors, Cell Surface/metabolism , TNF Receptor-Associated Factor 2/metabolism , Cytokines/metabolism , Enzyme Activation/drug effects , GTP-Binding Proteins/antagonists & inhibitors , GTP-Binding Proteins/chemistry , HEK293 Cells , HeLa Cells , Humans , I-kappa B Kinase/chemistry , Neoplasm Proteins/antagonists & inhibitors , Neoplasm Proteins/chemistry , Phosphorylation/drug effects , Protein Binding , Protein Structure, Tertiary , RNA Interference , RNA, Small Untranslated/metabolism , Receptors for Activated C Kinase , Receptors, Cell Surface/antagonists & inhibitors , Receptors, Cell Surface/chemistry , Signal Transduction/drug effects , TNF Receptor-Associated Factor 2/chemistry , Tumor Necrosis Factor-alpha/pharmacologyABSTRACT
Eph receptors are implicated in regulating the malignant progression of cancer. Here we find that despite overexpression of EphB3 in human non-small-cell lung cancer, as reported previously, the expression of its cognate ligands, either ephrin-B1 or ephrin-B2, is significantly downregulated, leading to reduced tyrosine phosphorylation of EphB3. Forced activation of EphB3 kinase in EphB3-overexpressing non-small-cell lung cancer cells inhibits cell migratory capability in vitro as well as metastatic seeding in vivo. Furthermore, we identify a novel EphB3-binding protein, the receptor for activated C-kinase 1, which mediates the assembly of a ternary signal complex comprising protein phosphatase 2A, Akt and itself in response to EphB3 activation, leading to reduced Akt phosphorylation and subsequent inhibition of cell migration. Our study reveals a novel tumour-suppressive signalling pathway associated with kinase-activated EphB3 in non-small-cell lung cancer, and provides a potential therapeutic strategy by activating EphB3 signalling, thus inhibiting tumour metastasis.
Subject(s)
Carcinoma, Non-Small-Cell Lung/metabolism , GTP-Binding Proteins/metabolism , Gene Expression Regulation, Neoplastic , Lung Neoplasms/metabolism , Neoplasm Proteins/metabolism , Neuropeptides/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Receptor, EphB3/metabolism , Receptors, Cell Surface/metabolism , Animals , Carcinoma, Non-Small-Cell Lung/pathology , Cell Movement , HEK293 Cells , Humans , Ligands , Lung Neoplasms/pathology , Mice , Mice, Nude , Models, Biological , Mutation , Neoplasm Metastasis , Neoplasm Transplantation , Phosphorylation , Photons , Receptors for Activated C Kinase , Signal Transduction , Tyrosine/chemistryABSTRACT
Eph receptors, the largest subfamily of transmembrane tyrosine kinase receptors, have been increasingly implicated in various physiologic and pathologic processes, and the roles of the Eph family members during tumorigenesis have recently attracted growing attention. Until now, research on EphB3 function in cancer is limited to focusing on tumor suppression by EphB receptors in colorectal cancer. However, its function in other types of cancer remains poorly investigated. In this study, we explored the function of EphB3 in non-small-cell lung cancer (NSCLC). We found that the expression of EphB3 was significantly upregulated in clinical samples and cell lines, and the expression level correlated with the patient pathologic characteristics, including tumor size, differentiation, and metastasis. Overexpression of EphB3 in NSCLC cell lines accelerated cell growth and migration and promoted tumorigenicity in xenografts in a kinase-independent manner. In contrast, downregulation of EphB3 inhibited cell proliferation and migration and suppressed in vivo tumor growth and metastasis. Furthermore, we showed that silencing of EphB3 inhibited cell growth by reducing DNA synthesis and caspase-8-mediated apoptosis and suppressed cell migration by increasing accumulation of focal adhesion formation. Taken together, our findings suggest that EphB3 provides critical support to the development and progression of NSCLC by stimulating cell growth, migration, and survival, thereby implicating EphB3 as a potential therapeutic target in NSCLC.