Significance of Nuclear Relocalization of ERK1/2 in Reactivation of c-fos Transcription and DNA Synthesis in Senescent Fibroblasts

Joo-Ri Kim-Kaneyama,Kiyoshi Nose,Motoko Shibanuma

doi:10.1074/jbc.m908723199

Abstract

Two of mitogen-activated protein kinases (MAPK), p44(mapk)/p42(mapk) extracellular signal-regulated kinases (ERK1/2), translocate into nuclei following activation and play critical roles in connecting the signal to gene expression and allowing cell-cycle entry. Here we found that the nuclear translocation of ERK1/2 in response to growth stimuli was significantly inhibited in senescent cells that were irreversibly growth arrested, compared with presenescent cells. The activation step of these enzymes was not impaired, since ERK1/2 were phosphorylated and activated in senescent cells as efficiently as in presenescent cells. By elaborately localizing ERK2 in the nuclei of senescent cells, we could restore c-fos transcriptional activity upon growth stimuli, which was repressed in senescent cells. Furthermore, the nuclear localization of ERK1/2 has been suggested to potentiate the proliferative activity of the senescent cells in collaboration with adenovirus E1A protein. More importantly, SV40 large T antigen, the strong inducer of DNA synthesis, had the inherent ability to restore nuclear relocalization of active ERK1/2 in senescent cells, which was essentially required for the reinitiation of DNA synthesis. Thus, manipulating the relocalization of ERK1/2 into nuclei was expected to open the way to overcome some of the senescent phenotypes.

Highlights

Cellular senescence is a postmitotic state which normal cells reach after a finite number of cell divisions [1]
We show evidence that nuclear localization but not activation of ERK1/2 is impaired in the senescent cells and that relocalization of ERK1/2 in the nuclei of the senescent cells is sufficient or required for overcoming some of the senescent phenotypes
The results of Western blotting using the antibody that recognizes the dually phosphorylated ERK1/2 clearly showed that both ERK1/2 were phosphorylated in senescent cells in response to 10% fetal calf serum (FCS) as efficiently as in presenescent cells with the same time course (Fig. 1A)

Summary

Introduction

Cellular senescence is a postmitotic state which normal cells reach after a finite number of cell divisions [1]. The phosphorylation of Elk-1 in the nuclei was significantly inhibited in the senescent cells when the constitutive active form of MAPKK was expressed to activate ERK1/2 instead of the PDGF treatment (Fig. 4C).

Results

Conclusion