Gadd45β silencing impaired viability and metastatic phenotypes in cholangiocarcinoma cells by modulating the EMT pathway

Growth arrest and DNA damage-inducible-beta (Gadd45 beta) is a stress-response protein involved in a number of processes, including cell cycle control, DNA repair, survival and death control, and stress signaling, depending on its interactions. Gadd45 beta expression is dysregulated in numerous types of cancer, functioning as either a tumor promoter or a tumor suppressor. However, the functions of Gadd45 beta in cholangiocarcinoma (CCA), particularly in metastasis, has not been studied. The immunohistochemical analysis of Gadd45 beta expression revealed that 75% of histological specimens from patients with CCA expressed high levels of Gadd45 beta, and that high Gadd45 beta expression was associated with metastasis. The role of Gadd45 beta in CCA was examined using siRNA-mediated gene knockdown in HuCCA-1, a human CCA cell line established from a Thai patient. The effects of Gadd45 beta downregulation upon cell viability and death, invasion, migration, matrix metalloproteinase (MMP) activity and epithelial-mesenchymal transition (EMT) marker expression were investigated. Gadd45 beta knockdown impaired cell viability, which was associated with the induction of apoptosis. In addition, there was a marked reduction in invasion and migration, although MMP activity was unaffected. Impairment of these metastatic properties was accompanied by the decreased expression of EMT markers, including Slug, vimentin, claudin-1 and zona occludens protein 1, whereas E-cadherin expression was increased. The present study suggests that Gadd45 beta is involved in regulating the viability and the metastatic potential of CCA cells, which may be mediated by the modulation of the EMT pathway.