Persistent DNA damage (genotoxic stress) triggers signaling cascades that drive cells into apoptosis or senescence to avoid replicating a damaged genome. Sp1 has been found to play a role in double strand break (DSB) repair, and a link between Sp1 and aging has also been established, where Sp1 protein, but not RNA, levels decrease with age. Interestingly, inhibition ATM reverses the age-related degradation of Sp1, suggesting that DNA damage signaling is involved in senescence-related degradation of Sp1. Proteasomal degradation of Sp1 in senescent cells is mediated via sumoylation, where sumoylation of Sp1 on lysine 16 is increased in senescent cells. Taking into consideration our previous findings that Sp1 is phosphorylated by ATM in response to DNA damage and that proteasomal degradation of Sp1 at DSBs is also mediated by its sumoylation and subsequent interaction with RNF4, we investigated the potential contribution of Sp1’s role as a DSB repair factor in mediating cellular senescence. We report here that Sp1 expression is decreased with a concomitant increase in senescence markers in response to DNA damage. Mutation of Sp1 at serine 101 to create an ATM phospho-null mutant, or mutation of lysine 16 to create a sumo-null mutant, prevents the sumoylation and subsequent proteasomal degradation of Sp1 and results in a decrease in senescence. Conversely, depletion of Sp1 or mutation of Sp1 to create an ATM phosphomimetic results in premature degradation of Sp1 and an increase in senescence markers. These data link a loss of genomic stability with senescence through the action of a DNA damage repair factor.

持续的 DNA 损伤（基因毒性压力）触发信号级联反应，驱动细胞凋亡或衰老，以避免复制受损的基因组。已发现 Sp1 在双链断裂 (DSB) 修复中发挥作用，并且 Sp1 与衰老之间的联系也已确立，其中 Sp1 蛋白而非 RNA 水平随着年龄的增长而降低。有趣的是，抑制 ATM 逆转了与年龄相关的 Sp1 降解，表明 DNA 损伤信号参与了与衰老相关的 Sp1 降解。衰老细胞中 Sp1 的蛋白酶体降解是通过 sumoylation 介导的，其中 Sp1 在赖氨酸 16 上的 sumoylation 在衰老细胞中增加。考虑到我们之前的研究结果，即 Sp1 被 ATM 磷酸化以响应 DNA 损伤，并且 DSB 处 Sp1 的蛋白酶体降解也由其 sumoylation 和随后与 RNF4 的相互作用介导，我们研究了 Sp1 作为 DSB 修复因子的作用的潜在贡献在介导细胞衰老方面。我们在此报告 Sp1 表达降低，同时衰老标志物响应 DNA 损伤而增加。Sp1 在丝氨酸 101 的突变以产生 ATM 磷酸缺失突变体，或赖氨酸 16 的突变以产生 sumo-null 突变体，可防止 Sp1 的 sumoylation 和随后的蛋白酶体降解，并导致衰老减少。反过来，Sp1 的消耗或 Sp1 的突变以产生 ATM 磷模拟物导致 Sp1 的过早降解和衰老标志物的增加。这些数据通过 DNA 损伤修复因子的作用将基因组稳定性的丧失与衰老联系起来。