ATRX is necessary for cellular senescence and represses HRAS to drive cells from quiescence into senescence [ChIP-Seq]

Senescence is a state of stable cell cycle exit that has important implications for development, physiology and disease. It is distinct from quiescence in which cells can be induced to re-enter the cell cycle. Although it is well known that there are massive changes in the heterochromatin of senescent cells, the molecular mechanisms underpinning the transition from reversible quiescence into irreversible senescence have remained elusive. Here, we demonstrate that the chromatin-remodeling enzyme ATRX is required for senescence. ATRX accumulates in nuclear foci during both replicative and cellular senescence. Using ChIP-seq and RNA-seq we identified HRAS as part of an ATRX regulated gene expression program associated with senescence. Repression of HRAS is sufficient to promote the transition of quiescent cells into senescence. Thus we conclude that the repression of HRAS is likely a direct consequence of ATRX binding and critical to how it mediates its role in senescence. ATRX binding was analyzed in dedifferentiated liposarcoma cell lines under cycling, quiescent and senescent (using two unique inducers) conditions via ChIP-seq