The Molecular Mechanism Of Metastasis Inhibition By TIP30/CC3 In Human Hepatocellular Carcinoma

Object: To study the molecular mechanism of TIP30 in the transcriptional regulation of OPN and metastasis inhibition of hepatocellular carcinoma. Methods: we analyzed the mRNA levels of TIP30 and OPN in eight hepatocarcinoma cell lines, and the alteration of cell adhesion and invasion of HCC cells by TIP30. Then we analyzed the effect of TIP30 on the transcriptional activity of the OPN promoter and indentified the transcriptional factors binding on the OPN promoter region. The interaction between TIP30 and ETS1 were examined. Gene expression profiles were performed to search for HCC metastasis-related genes whose expression levels were altered by over-expression of TIP30. The expression levels of TIP30 and OPN in HCC tissue were detected. Results: There is an inverse correlation between the mRNA levels of TIP30 and OPN in eight hepatoearcinoma cell lines. Ectopic expression of TIP30/CC3 could downregulate both the mRNA and protein levels of OPN, resulting in decreased cell adhesion, suppressed invasion through Matrigel. TIP30 inhibits the transcription of OPN by suppressing the activity of OPN promoter region nt -266 to -221, which contain a consensus binding site of ETS1. TIP30 downregulates the transcription of OPN by interaction with the NH_2-terminal regions of ETS1 and repressing the synergistic action of ETS1 and AP-1 on the OPN promoter. TIP30 could repress the expression of many metastasis-related genes. There is an inverse correlation between the mRNA and protein levels of TIP30 and OPN from analysis of HCC tissue(p=0.031, 0.003, respectively). HCC patients with lower expression level of TIP30 have an higher recurrence rate and poorer prognosis(p=0.025, 0.033, respectively). Conclusions: TIP30 suppresses the expression of OPN, a metastasis-associated gene, through repressing the transcriptional activity of ETS1 and the synergistic action of ETS1 and AP-1 by the physical association with ETS1, and inhibits the metastasis of HCC. Our results demonstrate firstly that TIP30/CC3, as a metastasis suppressor gene, downregulates the expression of metastasis-related genes to inhibit the metastasis of tumor through repressing the function of oncogene ETS1, which reveal a new mechamism on tumor metastasis regulation.