Aberrant MEK5/ERK5 signalling contributes to human colon cancer progression via NF-κB activation.

This study was designed to evaluate MEK5 and ERK5 expression in colon cancer progression and to ascertain the relevance of MEK5/ERK5 signalling in colon cancer. Expression of MEK5 and ERK5 was evaluated in 323 human colon cancer samples. To evaluate the role of MEK5/ERK5 signalling in colon cancer, we developed a stable cell line model with differential MEK5/ERK5 activation. Impact of differential MEK5/ERK5 signalling was evaluated on cell cycle progression by flow cytometry and cell migration was evaluated by wound healing and transwell migration assays. Finally, we used an orthotopic xenograft mouse model of colon cancer to assess tumour growth and progression. Our results demonstrated that MEK5 and ERK5 are overexpressed in human adenomas (P<0.01) and adenocarcinomas (P<0.05), where increased ERK5 expression correlated with the acquisition of more invasive and metastatic potential (P<0.05). Interestingly, we observed a significant correlation between ERK5 expression and NF-κB activation in human adenocarcinomas (P<0.001). We also showed that ERK5 overactivation significantly accelerated cell cycle progression (P<0.05) and increased cell migration (P<0.01). Furthermore, cells with overactivated ERK5 displayed increased NF-κB nuclear translocation and transcriptional activity (P<0.05), together with increased expression of the mesenchymal marker vimentin (P<0.05). We further demonstrated that increased NF-κB activation was associated with increased IκB phosphorylation and degradation (P<0.05). Finally, in the mouse model, lymph node metastasis was exclusively seen in orthotopically implanted tumours with overactivated MEK5/ERK5, and not in tumours with inhibited MEK5/ERK5. Our results suggested that MEK5/ERK5/NF-κB signalling pathway is important for tumour onset, progression and metastasis, possibly representing a novel relevant therapeutic target in colon cancer treatment.

NF-kappaB and apoptosis in colorectal tumourigenesis.

BACKGROUND: Nuclear factor-kappaB (NF-kappaB) may play an important role in colorectal tumourigenesis, controlling cell cycle and apoptosis gene expression. In addition, imbalances between cell proliferation and cell death are thought to underlie neoplastic development. The aims of this study were to investigate apoptosis and expression of several apoptosis-related proteins, and to determine correlations with colorectal tumour progression. MATERIALS AND METHODS: Apoptosis was evaluated by the TUNEL assay in 48 patient samples, including adenomas, adenocarcinomas and adjacent normal mucosas. Immunohistochemistry was performed for Bcl-2 and NF-kappaB. Expression levels of p53, Bax and IkappaB proteins were determined by immunoblotting. Cultured human colon cancer cells were used to evaluate NF-kappaB expression and nuclear translocation by immunocytochemistry and immunoblotting. RESULTS: Apoptosis and NF-kappaB immunoreactivity were significantly higher in tumour tissue compared with normal mucosa (P < 0.01), increasing in association with histological tumour progression (P < 0.01). Bcl-2 was consistently higher in normal mucosa (P < 0.01) and inversely correlated with the percentage of apoptosis (P < 0.01). Phosphorylated p53 and Bax levels were similar in tumour tissue and normal mucosa; however, the NF-kappaB inhibitor, IkappaB, tended to decrease in tumours. In vitro, nuclear translocation of NF-kappaB was greater in proliferative than in resting phases of colon cancer cells. CONCLUSIONS: NF-kappaB expression and apoptosis are increased from adenoma to poorly differentiated adenocarcinoma tissues. Apoptosis is correlated with suppression of Bcl-2 expression, but appears to proceed through a p53- and Bax-independent pathway. Activation of NF-kappaB may play an important role in colorectal tumour progression.