The role of the MEK/ERK pathway in regulation of HDACI-induced senescence of transformed rat embryo fibroblasts

A key regulator of cellular senescence, mTORC1 complex, is a target of many signaling cascades, including Ras/Raf/MEK/ERK cascade. In this paper, we investigated the role of the MEK/ERK branch of this cascade in the process of cellular senescence induced by sodium butyrate (NaBut), a histone deacetylase inhibitor (HDACI), in transformed rat-embryo fibroblasts. Suppression of MEK/ERK activity by inhibitor PD0325901 did not prevent activation of mTORC1 complex induced by NaBut treatment. Inhibition of MEK/ERK increased mTORC1 activity and activated mTORC2 complex. Activation of mTOR-containing complexes was accompanied by reorganization of the actin cytoskeleton (formation of actin stress fibers) and the appearance of cellular senescence markers. In contrast to NaBut-induced senescence, no protein accumulation was observed, probably due to increased activity of the degradation processes. Furthermore, senescence induction under suppression of MEK/ERK drastically decreased the cell viability, Thus, NaBut-induced senescence upon suppressed activity of the MEK/ERK branch of MAP kinase cascade has a more pronounced tumor-suppressing effect that is manifested by activation of both mTOR complexes, reorganization of the actin cytoskeleton and protein degradation.