Phosphatase and tensin homolog (PTEN) is frequently inactivated in cancers and is associated with advanced stages of cancers or metastasis. However, the molecular mechanism of PTEN in hepatocellular carcinoma (HCC) metastasis is unclear. In this study, we found frequent (47.5%, n = 40) protein underexpression of PTEN in human HCCs compared with their corresponding nontumorous livers. Significantly, PTEN underexpression was associated with larger tumor size (P = 0.021), tumor microsatellite formation (P = 0.027), and shorter overall survival of patients (P = 0.035). Using different cell models, we observed that PTEN-knockdown HCC cells and PTEN-knockout mouse embryonic fibroblasts (MEFs) had enhanced cell migratory and invasive abilities. In addition to activation of AKT, there was up-regulation of the Sp1 transcription factor (SP1) and matrix metalloproteinase 2 (MMP2), as well as MMP2 activation in PTEN-knockdown HCC cells and PTEN(-/-) MEFs. With dual luciferase reporter assay, exogenous expression of SP1 in HCC cells led to enhanced MMP2 promoter activity by up to 74%, whereas deletion of the putative SP1 binding site on the MMP2 promoter led to reduced promoter activity by up to 65%. Using chromatin immunoprecipitation assay, we documented increased binding of SP1 to the MMP2 promoter in PTEN-knockdown HCC cells. Overexpression of SP1 and MMP2 was significantly but negatively associated with PTEN underexpression in human HCCs.
Conclusion: Our results show that PTEN was underexpressed in HCCs, and this underexpression was associated with more aggressive biological behavior and poorer patient survival. We have provided the first evidence that MMP2 up-regulation upon PTEN loss is SP1-dependent. Our findings indicate that PTEN plays a significant role in down-regulating HCC cell invasion via the AKT/SP1/MMP2 pathway.
Copyright © 2011 American Association for the Study of Liver Diseases.