Role And Molecular Mechanism Of Cullin4A In Regulating Progression And Metastasis Of Hepatocellular Carcinoma

Hepatocelluar carcinoma(HCC) is one of the most prevalent malignant cancers in our country. The development and progression of HCC is a complicated process involving multiple genes and multiple steps in human bodies. Surgical operation excision is one of the most effective treatment for HCC, but most of HCC patients have liver metastasis and vascular invasion when they have been suffered from hepatocellular carcinoma. Therefore, in order to change the present situation of poor prognosis of HCC patients,we need to investigate the mechanism of HCC and identify new molecular targets for the treatment of HCC.Ubiquitin-mediated proteolysis of cellular proteins plays avital role in maintain-ing the balance between normal growth, uncontrolled proliferation and cell cycle regulation. CUL4A (cullin4A) belongs to the family of cullin proteins that are essential components of a multifunctional ubiquitin-protein ligase E3complex, CUL4A showed distinct amplification and consequent over-expression at13q34in HCC. It is reported that CUL4A physically associates with MDM2and participates in the proteolysis of p53. In our study, we additionally investigate the mechanism by which CUL4A regulation in HCC.The epithelial-mesenchymal transition (EMT), in which epithelial cancer cells lose their polarity and become motile mesenchymal cells, has been implicated in carcinoma metastasis/invasion. Recently, several studies have reported that cancer cells undergoing EMT appear to override oncogeneinduced premature senescence and apoptosis, and contribute to immunosuppression, which reveals the vital role of EMT in tumor recurrence and provides a clue regarding the significance of the underlying mechanism of EMT. It recently was shown that hepatocellular EMT appears to play a pivotal role in the dissemination of malignant hepatocytes during HCC progression. In our study, we found that up-regulation CUL4A in HCC show less robust cell-to-cell adhesion, and undergo some measure of EMT.Nuclear transcription factor-kpa B (NF-κB) is activated in many human tumors and plays a key roles in survival, adherence, transformation and proliferation of tumor cells. Activation NF-κB signal pathway can be divided into classical pathway and non-classical pathway. Classical pathway was activated by degradating IkBs.Studies show that NF-κB plays all essential role in the induction of EMT in mammary epitholial cells. In our research,we found that up-regulating CUL4A induced the low expression of ikba and high expression P65. We further investigated the expression levels of CUL4A and P65in clinical HCC samples. Tissue microarray analysis of62HCC patient specimens revealed a strong correlation of CUL4A expression with P65levels, All of these results clearly demonstrated that the NF-κB-EMT induced by CUL4A is an important mechanism underlying HCC development and metastasis.In our study,we found that overexpression of CUL4A was detected in approximately85%the human HCC samples analyzed. Investigation of clinical HCC specimens showed that CUL4A were markedly overexpressed in metastatic HCC tissue compared with healthy tissue. Increased expression of CUL4A was often observed at the invasive front of HCC tumors and correlated with liver cirrhosis, microsatellite tumor nodule formation, serum AFP level,tumor encapsulation, edmondson grade, pathologic TNM stage, pathological thrombosis, vascular invasion. In vitro and in vivo functional studies in mice showed that CUL4A contributed to tumor cell migration, invasion, and metastasis by increasing cell motility and inducing epithelial-mesenchymal transition (EMT) via NF-κB signal pathway activation. Silencing CUL4A expression by siRNA effectively abolished the invasive and metastatic abilities in mice. These findings suggest that CUL4A-NF-κB-EMT might be a novel pathway involved in HCC progression and metastasis.The study shows that the high expression of CUL4A are major contributors to the invasion-prone phenotype of HCC. It defines both the protein and NF-κB signal as particularly suitable candidates for therapeutic agents in a subgroup of HCC patients.