Abstract
The connexin (Cx) 32 gene, a member of the gap junction gene family, acts as a tumour suppressor gene in human renal cell carcinoma (RCC) and is down-regulated by the hypermethylation of CpG islands in a promoter region of the Cx gene. The current study investigated whether the restoration of Cx32 silenced by hypermethylation in RCC by a DNA demethylating agent could be an effective treatment against RCC. Using nude mice bearing Caki-1 cells (a human metastatic RCC cell line), the effects of 5-aza-2'-deoxycytidine (5-aza-CdR), a DNA demethylase inhibitor, on Cx32 mRNA expression and tumour growth were examined by RT-PCR, and by measuring tumour weight and volume. Cx32 expression in Caki-1 tumours was inhibited by Cx32 short interfering (si) RNA, and the effect of siRNA on 5-aza-CdR-dependent suppression of tumour growth in nude mice was evaluated. 5-aza-CdR treatment inhibited the growth of Caki-1 cells in nude mice by 70% and increased 7-fold the level of Cx32 mRNA. The intratumour injection of Cx32 siRNA almost totally inhibited the expression of Cx32 mRNA and significantly reduced the suppression of tumour growth in 5-aza-CdR-treated nude mice. 5-aza-CdR suppressed the growth of Caki-1 tumours in a xenograft model, by restoring Cx32 expression. This finding suggests that treatment with 5-aza-CdR could be a new effective therapy against human metastatic RCC and that Cx32 could be a potential target for the treatment of RCC.
Highlights
Gap junctions are aqueous channels that connect the cytoplasm of contiguous cells, enabling the cells to directly share small metabolites by a process called gap junction intercellular communication (GJIC) or cell coupling
We showed that connexin 32 (Cx32) is prominently expressed in normal human renal epithelial cells, a progenitor cell of Renal cell carcinoma (RCC), whereas, of Cx subtypes, Cx32 is downregulated in several types of human RCC cell lines as well as cancerous regions of human kidneys (Yano et al, 2003)
We showed that c-Src is a key target in the regulation of vascular endothelial growth factor (VEGF) production in metastatic RCC cells and that Cx32 reduces the production of VEGF by cells via inactivation of c-Src (Fujimoto et al, 2005; Yonezawa et al, 2005). c-Src is a member of the Src family of kinases, intracellular non-receptor tyrosine kinases, widely expressed in tissues and shown to play an important role in the regulation of cell adhesion, cell growth and differentiation (Stein et al, 1994; Brown and Cooper, 1996)
Summary
Gap junctions are aqueous channels that connect the cytoplasm of contiguous cells, enabling the cells to directly share small metabolites by a process called gap junction intercellular communication (GJIC) or cell coupling It has Restoration of methylated Cx32 in RCC H Hagiwara et al cell coupling, individual cancer cells can propagate celldeath signals into adjacent cells, which die by apoptosis, and that the bystander effect can enhance the cytotoxicity of anticancer agents in cancer cells (Mesnil et al, 1997; Yamasaki and Katoh, 1998; Wilson et al, 2000). Conclusions and implications: 5-aza-CdR suppressed the growth of Caki-1 tumours in a xenograft model, by restoring Cx32 expression This finding suggests that treatment with 5-aza-CdR could be a new effective therapy against human metastatic RCC and that Cx32 could be a potential target for the treatment of RCC. British Journal of Pharmacology (2008) 153, 1373–1381; doi:10.1038/bjp.2008.17; published online 11 February 2008
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