Abrogation of B-RafV600E induced senescence by FoxM1 expression.

B-RafV600E oncogene mutation occurs in various cancers and is associated with tumor initiation. However, genetic modification of B-RafV600E in cells induces MAPK activation and results in oncogene-induced senescence. Overcoming the oncogene-induced senescence by B-RafV600E requires activation of another oncogene pathway, such as AKT signaling. In the present study, we explored the factors involved in overcoming the senescence program in cells activated by B-RafV600E and AKT signaling. B-RafV600E activation caused a feedback inhibition of AKT phosphorylation and resulted in downregulation of FoxM1, one of the AKT downstream components. AKT activation by PTEN downregulation induced FoxM1 expression, and co-expression of B-RafV600E and FoxM1 overcame the cellular senescence. These observations suggested that FoxM1 is critical downstream gene of AKT and functions to overcome B-RafV600E-induced senescence.