Dipartimento di Scienze, Università "Roma Tre", Italy.
FEBS Open Bio. 2023 Sep;13(9):1683-1698. doi: 10.1002/2211-5463.13680. Epub 2023 Aug 3.
Telomere length can be maintained either by the telomerase enzyme or by alternative lengthening of telomeres (ALT), which is based on telomeric recombination. However, both mechanisms are inactive in most human somatic cells. ATRX has been previously identified as an ALT repressor gene. Nonetheless, TP53 is also deficient in most ALT cell lines, and previous works showed that it is an inhibitor of homologous recombination (HR). Despite this, the role of p53 as an ALT repressor has not been previously examined. Therefore, we investigated the effects of p53 and ATRX inhibition on normal human fibroblasts (devoid of any mutation), in the presence or absence of X-ray-induced telomeric damage. Performing immunofluorescence with antibodies for RAD51, H2AX, and TRF1 (for studying HR-mediated DNA damage repair) and CO-FISH (for telomeric sister chromatid exchanges), we observed that HR is a normal mechanism for the repair of telomeric damage, present also in noncancer cells. Moreover, we discovered that telomeric HR, as for HR in general, is significantly inhibited by p53. Indeed, we observed that inhibition of p53 drastically increases telomeric sister chromatid exchanges. We also confirmed that ATRX inhibition increases telomeric recombination. In particular, we observed an increase in crossover products, but a much higher increase in noncrossover products.
端粒长度可以通过端粒酶或端粒的非经典延长（ALT）来维持，后者基于端粒重组。然而，这两种机制在大多数人类体细胞中都不活跃。ATRX 先前被鉴定为 ALT 抑制基因。尽管如此，TP53 在大多数 ALT 细胞系中也缺失，并且先前的研究表明它是同源重组（HR）的抑制剂。尽管如此，p53 作为 ALT 抑制剂的作用尚未得到先前的研究。因此，我们研究了在存在或不存在 X 射线诱导的端粒损伤的情况下，p53 和 ATRX 抑制对正常人类成纤维细胞（没有任何突变）的影响。通过用 RAD51、H2AX 和 TRF1（用于研究 HR 介导的 DNA 损伤修复）和 CO-FISH（用于端粒姐妹染色单体交换）的抗体进行免疫荧光，我们观察到 HR 是修复端粒损伤的正常机制，在非癌细胞中也存在。此外，我们发现端粒 HR 与一般的 HR 一样，被 p53 显著抑制。事实上，我们观察到 p53 的抑制会大大增加端粒姐妹染色单体交换。我们还证实 ATRX 抑制会增加端粒重组。特别是，我们观察到交叉产物增加，但非交叉产物增加更多。
