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Mol Med Rep. 2014 May;9(5):1773-9. doi: 10.3892/mmr.2014.2054. Epub 2014 Mar 14.

Cholera toxin, a typical protein kinase A activator, induces G1 phase growth arrest in human bladder transitional cell carcinoma cells via inhibiting the c-Raf/MEK/ERK signaling pathway.

Author information

1
Department of Pathology, The First Affiliated Hospital, Sun Yat‑Sen University, Guangzhou, Guangdong 510089, P.R. China.
2
Department of Cardiovascular Epidemiology, Guangdong General Hospital, Guangzhou, Guangdong 510080, P.R. China.
3
Department of Pharmacology, Zhongshan School of Medicine, Sun Yat‑Sen University, Guangzhou, Guangdong 510089, P.R. China.
4
Department of Biochemistry, Zhongshan Medical College, Sun Yat‑Sen University, Guangzhou, Guangdong 510089, P.R. China.
5
Department of Microbiology, Zhongshan School of Medicine, Sun Yat‑Sen University, Guangzhou, Guangdong 510089, P.R. China.

Abstract

The biotoxin cholera toxin has been demonstrated to have anti-tumor activity in numerous types of cancer, including glioma. However, the role of cholera toxin in the tumorigenesis of transitional cell carcinoma (TCC), the most common malignant tumor of the bladder, remains to be elucidated. To address this, in the present study, two TCC cell lines, T24 and UM-UC-3, were treated with cholera toxin [protein kinase A (PKA) activator] and KT5720 (PKA inhibitor). Cell survival and proliferation, cell cycle alterations and apoptosis were analyzed using Hoechst staining, the MTT assay, fluorescence microscopy and flow cytometry. Western blot analysis was used to detect the expression of proteins involved in cell cycle regulation. The results revealed that cholera toxin significantly induced G1 arrest and downregulated the expression of cyclin D1 and cyclin-dependent kinase 4/6 in the TCC cell lines, and this was rescued by KT5720. Furthermore, it was demonstrated that cholera toxin downregulated the activation of the c-Raf/Mek/Erk cascade, an important mediator of tumor cell proliferation, via the PKA-dependent c-Raf phosphorylation at Ser-43. Furthermore, inhibition of Mek activity with UO126 mimicked the effects of cholera toxin. In conclusion, these results confirmed that cholera toxin specifically inhibited proliferation and induced G1 phase arrest in human bladder TCC cells. This effect was due to PKA-dependent inactivation of the c-Raf/Mek/Erk pathway. This suggested that cholera toxin may be a viable therapeutic treatment against tumorigenesis and proliferation in bladder cancer.

PMID:
24626525
DOI:
10.3892/mmr.2014.2054
[Indexed for MEDLINE]

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