MAP2K5 and neoplasm: In this regard, we observed that accelerated G1–S and S–G2/M cell cycle transition and increased tumour cell migration in CA-MEK5 cells were accompanied by a significant increase of NF-κB activation, along with a decrease in the total levels of IκB. Together with the results from our patient data, where IκB expression was inversely correlated with ERK5 expression, our data suggested that ERK5 activation promotes NF-κB activation, possibly through IκB degradation.