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Cytoplasmic accumulation of connexin32 protein enhances motility and metastatic ability of human hepatoma cells in vitro and in vivo
Author(s) -
Li Qingchang,
Omori Yasufumi,
Nishikawa Yuji,
Yoshioka Toshiaki,
Yamamoto Youhei,
Enomoto Katsuhiko
Publication year - 2007
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.22696
Subject(s) - biology , cancer research , gap junction , connexin , cytoplasm , connexin 32 , motility , cell culture , clone (java method) , microbiology and biotechnology , hccs , carcinogenesis , intracellular , cancer , hepatocellular carcinoma , dna , genetics
Connexins have long been believed to suppress tumour development during carcinogenesis by exerting gap junctional intercellular communication (GJIC). Although GJIC is abrogated in hepatocellular carcinoma (HCC), connexin32 (Cx32) protein tends to remain expressed in cytoplasm, but not in cell–cell contact areas; thus, it is incapable of forming gap junctions. Hypothesising that cytoplasmic Cx32 protein that has accumulated in HCC should have its proper functions, which are independent of GJIC, we established an inducible expression system of Cx32 in human HuH7 HCC cells, which were unable to support the formation of Cx32‐mediated gap junctions, so that Cx32 protein could be overexpressed by doxycycline (Dox) withdrawal. Although the established clone HuH7 Tet‐off Cx32 cells exhibited a 4‐fold increase in Cx32 expression after Dox withdrawal, none of them were dye‐coupled, and Cx32 protein was retained in the Golgi apparatus. However, the proliferation rate of the HuH7 Tet‐off Cx32 cells was significantly higher in the Dox‐free medium than in the Dox‐supplemented one. Transwell assays also revealed that Dox withdrawal enhanced serum‐stimulated motility and invasiveness into Matrigel of the HuH7 Tet‐off Cx32 cells. Furthermore, when HuH7 Tet‐off Cx32 cells were xenografted into the liver of SCID mice, only the mice to which no Dox was administered developed metastatic lesions, indicating that overexpression of cytoplasmic Cx32 protein induced metastasis of HuH7 cells. Our results suggest that, while Cx32‐mediated GJIC suppresses the development of HCCs, cytoplasmic Cx32 protein exerts effects favourable for HCC progression, such as invasion and metastasis, once the cells have acquired a malignant phenotype. © 2007 Wiley‐Liss, Inc.