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. Overall design: ATRX binding was analyzed in dedifferentiated liposarcoma cell lines under cycling, quiescent and senescent (using two unique inducers) conditions via ChIP-seq

细胞衰老（Senescence）是一种稳定的细胞周期退出状态，其对发育、生理过程及疾病发生均具有重要意义。该状态与细胞静息（quiescence）截然不同，静息状态下的细胞可被诱导重新进入细胞周期。尽管学界已明确衰老细胞的异染色质会发生广泛改变，但介导可逆性静息向不可逆性衰老转变的分子机制仍未明确。本研究证实，染色质重塑酶ATRX是细胞衰老过程所必需的。在复制性衰老与细胞性衰老过程中，ATRX均会在细胞核灶（nuclear foci）中聚集。本研究通过染色质免疫共沉淀测序（ChIP-seq）与RNA测序（RNA-seq），鉴定出HRAS属于受ATRX调控且与细胞衰老相关的基因表达程序之一。抑制HRAS的表达足以推动静息细胞向衰老细胞转变。据此我们认为，HRAS的表达抑制很可能是ATRX结合的直接结果，且对ATRX介导细胞衰老的功能至关重要。实验整体设计：本研究通过染色质免疫共沉淀测序（ChIP-seq），对去分化脂肪肉瘤细胞系在增殖、静息及两种独特诱导剂诱导的衰老状态下的ATRX结合情况进行了分析。