Role Of Insulin Receptor Substrate1in The Invasion And Metastasis Of Head And Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma（HNSCC）is the eighth most commoncancer and accounts for5%of all malignant tumors. It is one of the cancersthreatening the health of the people around the world. Lymph nodes metastasis is themain factor that affects the5-year survival rate. Despite the advances in combiningsurgery with chemotherapy and radiotherapy,5-year survival rate of patients withrecurrent and metastatic head and neck cancer remain poor. Therefore, identifying thecrucial proteins and clarifying mechanisms that contribute to metastasis will besignificant to provide biomarkers for prognosis and targets for treatment.IRS-1, the first of the family to be identified and cloned, is the quintessentialsignaling adaptor phosphorylated and activated by both IR and IGF-1R. Acting as anadaptor protein, IRS-1transduces extracellular stimuli to cytoplasm signals, andregulates cell growth, metabolism, survival and differentiation of the cells. Previousstudies mainly focused on its roles in metabolism, recently it was reported to beassociated with cancer progression and metastasis. As a major substrate of insulin andinsulin-like growth factor Ⅰ (IGF-Ⅰ) andmainly functioning through activatingPI3K/Akt and MAPK pathway, IRS-1has been considered oncogenic in cancerprogression. As well, elevated expression levels and the active form of IRS-1hasbeen reported in a variety of tumors, including hepatocellular carcinomas (HCCs),pancreatic cancer, breast cancers, leiomyomas, Wilms’ tumors, rhabdomyosarcomas,liposarcomas, leiomyosarcomas, and adrenal cortical carcinomas. Conversely, IRS-1has been confirmed to suppress tumor metastasis. However, IRS-1has been identifiedas both a positive and negative regulator of metastasis in breast cancer. Therefore, the studies of IRS-1in tumor metastasis are quite limited and controversial. To date, themechanism of IRS-1in invasion and metastasis of head and neck cancer is stillunclear.Epithelial-mesenchymal transition (EMT) plays initial and critical roles in tumormetastasis. Cells undergoing EMT lose their epithelial characteristics and phenotype,acquire mesenchymal properties, and thus gain enhanced motility. EMT isaccompanied by decreased E-cadherin expression, β-catenin nucleus translocation,and increased Vimentin, N-cadherin expression. Loss of E-cadherin expression is notonly the initial and essential step of EMT, but also a potential promoter of EMT.MicroRNAs (miRNAs) are~22nt short non-coding RNAs that negativelyregulate gene expression post-transcriptionally by directly cleaving target mRNAs orby suppressing their translation. They play key roles in many cellular processesincluding cell proliferation, differentiation and apoptosis. Lately, many evidencesshow that several different miRNAs are aberrant in tumor metastasis. Recently, miR-9has been shown to directly target E-cadherin to reduce its expression atpost-transcription levels and thus induce EMT.In this study, we investigated the role of IRS-1in head and neck cancermetastasis. First, we detected the expression levels of IRS-1in the tissues of HNSCCpatients with lymph node metastasis. Our results showed that IRS-1mRNAexpression levels decreased in metastatic lymph node tumor tissues compared toprimary tumor tissues. We then detected IRS-1expression levels in pairedpoorly-highly metastatic HNSCC cell lines. We found IRS-1expression levels weredecreased both at mRNA levels and at protein levels in highly metastatic686LN-M4ecells compared with paired poorly metastatic686LN cells, suggesting that IRS-1is asuppressor of HNSCC metastasis. Furthermore, we found that down-regulation ofIRS-1expression by siRNA increased the invasive potency of poorly metastatic 686LN cells (which express high levels of IRS-1). In addition, we founddown-regulation of E-cadherin and up-regulation of miR-9after IRS-1knocked down.These results suggest that decreased expression of IRS-1is correlated with HNSCCmetastasis and reduction of IRS-1expression promotes invasion and induces EMT ofHNSCC cells possibly through up-regulation of miR-9expression. IRS-1may bedeveloped as a new diagnostic marker and a new therapeutic target for metastasis ofHNSCC.