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.