Molecular signature of oncogenic ras-induced senescence

Abstract

Senescence irreversibly arrests the proliferation of cells that have sustained significant cellular stress. Replicative senescence, due to the shortening and dysfunction of telomeres, appears to provide a barrier to the immortalization of cells and development of cancer. In normal human fibroblasts, senescence induced by oncogenic H-ras displays a nearly identical cellular phenotype to that of replicative senescence, suggesting the activation of a common senescence mechanism. In this study, we investigated the gene expression profile of oncogenic H-ras-induced senescent human diploid fibroblasts. We found altered gene expression of various cell cycle regulators in both oncogenic H-ras-induced senescent cells and replicative senescent cells. Similar to replicative senescent cells, H-ras-induced senescent cells exhibited specific downregulation of genes involved in G₂/M checkpoint control and contained tetraploid cells that were arrested in a G₁ state. This observation suggests that the inactivation of G₂/M checkpoints may be involved in senescence and may play a role in the generation of senescent G₁ tetraploid cells. Lastly, we have identified two genes, topoisomerase II and HDAC9, whose expression was specifically altered under several conditions associated with senescence, suggesting that these two molecules may be novel biomarkers for senescent human fibroblasts.