Actopaxin: a novel regulator of cell migration and invasion in human hepatocellular carcinoma

Abstract

Invasion and metastasis are the major causes of treatment failure and high mortality rate in hepatocellular carcinoma (HCC) patients. Cell motility is crucial to tumor invasion and metastasis, requiring the ability of tumor cells to interact with extracellular matrix, which is regulated by integrins and integrin-associated molecules at the focal adhesions. Recent studies have demonstrated the role of β1 integrin (CD29) overexpression in HCC and its correlation with cancer cell invasiveness and metastastic potential, as well as its protective role against cancer cells against chemotherapeutic drug-induced apoptosis, yet the mechanism is not fully known. Focal adhesion proteins serve as binding platforms for additional cytoskeletal and signaling molecules in the CD29 signaling pathway. Recently, Actopaxin has been demonstrated to form complex with numerous molecules at the focal adhesions, including ILK, which interacts with the cytoplasmic tail of CD29. Through these interactions, Actopaxin has been shown to regulate different cellular events, including cell survival, spreading and cell migration. In this study, the role of Actopaxin in HCC was investigated. In particular, its role in the regulation of tumor invasion and metastasis of HCC cells was demonstrated.

This study showed that Actopaxin expression was overexpressed in HCC specimens when compared with the adjacent non-tumorous liver, and that its overexpression positively correlated with tumor size, stage and metastasis in HCC specimens. Actopaxin expression was also correlated with the metastatic potential in HCC cell-lines. Functional studies established that overexpression of Actopaxin conferred invasive phenotypes in primary, non-metastatic HCC cells, whereas down-regulation of Actopaxin could revert the invasive phenotypes and metastatic potential of metastatic HCC cells in vitro and in vivo. Suppression of Actopaxin expression was associated with reduced expression of ILK, PINCH, Paxillin and cdc42, whereas expressions of E-cadherin, β-catenin and GSK3β were induced, indicative of a less invasive and invasive phenotype. Conversely, overexpression of Actopaxin in primary, non-metastasis HCC cells accordingly up-regulated the expression of ILK, PINCH, Paxillin and cdc42, and down-regulation of of E-cadherin, β-catenin and GSK3β, suggestive of an enhanced invasive phenotype. The expression of Actopaxin was found to be correlated with CD29 level, indicating that Actopaxin is a CD29-associated protein and involved in CD29-regulated signaling. Finally, Actopaxin down-regulation enhanced chemosensitivity of of HCC cells towards chemotherapeutic treatment. Treatment with Oxaliplatin was enhanced in Actopaxin-deficient HCC cells, which showed a stronger inhibitory effect on cell proliferation and cell cycle progression, accompanied with induction on apoptosis. The enhanced chemosensitivity effect was a collective result of suppression of Survivin protein, β-catenin and mTOR pathways; and up-regulation of p53.

To conclude, this study demonstrated for the first time that Actopaxin is involved in HCC invasion, metastasis and chemosensitization, providing the basis to further investigate the potential role of this protein or its downstream effectors as a therapeutic target for inhibiting the development of metastasis and enhancing chemotherapy efficacy to combat HCC, and perhaps other invasive cancers.