Investigation On The Role Of STAT3 Signaling System In Invasion Of Colorectal Cancer

Backgrounds:Signal transducers and activator of transcription,STATs, are a family of transcription factors that transduce signals from cell surface receptors directly to the nucleus.Activation of all the STAT proteins is caused by phosphorylation of a single tyrosine residue that leads to dimerization via an intermolecular SH2 phosphotyrosine interaction. The dimerized STATs then translocate to the nucleus where they regulate gene expression by binding directly to high affinity DNA binding sites or by associating with other transcription factors. They play a critical role in mediating cytokine and growth factor signaling involved in cell growth, differentiation and survival. Among the seven members of mammalian STAT family, STAT3 has been most strongly implicated in oncogenesis.Some studies showed that constitutively activated STAT3 is found in a wide variety of human tumors including multiple myelomas, breast, ovarian,prostate, and head and neck squamous tumors. Inhibition of STAT3 signaling with either dominant negative or antisense oligonucleotides against STAT3 suppresses the transformation process in some tumors. Recent studies have shown that treatment of tumor cells with inhibitors of STAT signaling results in decreased cell viability and induces apoptosis. Together these findings demonstrate that STAT3 signaling plays a critical role in both the transformation process and tumor progression in some types of cancer.Recent report showed that STAT3 has a significant association with tumor invasion and metastasis of a few of cancer. In renal cell carcinoma,the positive rate of the expression of (phosphorylated-STAT3,p-STAT3)correlated well with the depth of tumor invasion and with metastasis.In colorectal adenocarcinoma, p-STAT3 protein was significantly correlated with the depth of tumour invasion, venous invasion,lymph node metastasis, and increasing stages of the Dukes' classification.In addition,blockade of activated STAT3 via ectopic expression of dominant-negative STAT3 significantly could suppressed angiogenesis, tumor growth, and metastasis in pancreatic cancer(?)Together these findings demonstrate that STAT3 activation might be a new potential target for therapy of human cancer metastasis.Recently it has been shown that STAT3 is constitutively activated in colon cancer,however, the role and mechanism of STAT3 signaling in metastasis of colon cancer remain elusive.Colorectal cancer is the third most common malignant neoplasm worldwide and the second leading cause of death due to cancer. Despite recent advances in diagnostic and therapeutic measures, the prognosis of colorectal cancer patients with distant metastasis still remains poor. Liver metastasis is a major cause of morbidity and mortality in patients with colon cancer. Colorectal liver metastasis is associated with a very poor prognosis;most patients die within 2 years of diagnosis despite the availability of numerous therapies. To improve the choice of therapeutic strategy, it is critical that the mechanism of invasion and metastasis of colon cancer be clarified. Here we will show that knockdown of STAT3 expression by siRNA inhibit invasion ability and reduces the resistance anoikis in colon cancer cells.Aim:To investigate the roles and mechanism of signal transducer and activator of transcription 3 (STAT3) in invasion of human colon cancer cell by RNA interference.Methods:Small interfering RNA (siRNA) targerting Signal transducer and activator of transcription 3 (STAT3) was transfected into HT29 colon cancer cell.STAT3 mRNA level and DNA-binding activity of STAT3 were evaluated by RT-PCR and electrophoretic mobility shift assay(EMSA),respectively. We studied the proliferation by MTT assay,and anchorage-independent growth by clon formation in soft agar,and invasion by Boyden chamber in vitro;To explore the mechanisms, anoikis of cancer cells by DNA fragmentation assay and terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL),respectively. Western blot assay was used to observe the protein expression of p-Akt in colon cancer HT29 cell.Results:RNA interference(RNAi) mediated by siRNA leads to supprsession of STAT3 expression and its activity in cancer cells.Suppression of STAT3 expression by siRNA could inhibit anchorage-independent growth,and invasion ability,and induces anoikis in colon cancer cell line HT29.It has been shown that knockdown of STAT3 expression by siRNA results in a reduction in expression of p-Akt and in HT29 cells.Conclusion:These results suggests that STAT3 siRNA can inhibit invasion ability of colon cancer cells through inducing anoikis,which p-Akt contributes to regulation of anoikis. These studies indicates STAT3 siRNA could be a useful therapeutic tool for the treatment of colon cancer.