XIST是一种长链非编码RNA，它在早期胚胎发育中启动X染色体失活（XCI），异常表达是乳腺癌（BC）的常见特征。然而，后XCI XIST在乳腺癌发生中的作用仍不清楚。在这里，我们将XIST鉴定为乳腺癌干细胞（CSCs）的关键调控因子，这些干细胞表现为醛脱氢酶阳性（ALDH+）上皮细胞（E）和CD24loCD44hi类间质样（M）表型。XIST在BC亚型谱系上有不同的表达，Doxycycline（DOX）诱导的XIST敲低（KD）显著抑制了球体/群落形成能力，肿瘤生长和肿瘤发生潜能。这种表型归因于在泌乳管和三阴乳腺癌中受损的E-CSC和E和M-CSC活性。基因表达分析揭示了XIST KD对细胞因子-细胞因子受体相互作用的影响最大，导致在ALDH- 整体BC细胞中明显抑制了促炎性细胞因子IL-6和IL-8的表达。外源性IL-6而不是IL-8，可以挽救在XIST KD时，泌乳管和TN BC中的ALDH + E-CSCs的减少的球体形成能力和比例。XIST在细胞核中作为microRNA let-7a-2-3p的海绵来促进ALDH- 整体BC细胞中的IL-6的生成，以共生方式影响表达上调的IL-6受体（IL6R）表达的ALDH + E-CSCs。这通过STAT3激活和CSC因子c-MYC，KLF4和SOX9的表达促进了CSC的自我更新。本研究通过解除let-7控制的共生IL-6促炎信号来支持XIST的新作用。©2023年作者。

Aberrant expression of XIST, a long noncoding RNA (lncRNA) initiating X chromosome inactivation (XCI) in early embryogenesis, is a common feature of breast cancer (BC). However, the roles of post-XCI XIST in breast carcinogenesis remain elusive. Here we identify XIST as a key regulator of breast cancer stem cells (CSCs), which exhibit aldehyde dehydrogenase positive (ALDH+) epithelial- (E) and CD24loCD44hi mesenchymal-like (M) phenotypes. XIST is variably expressed across the spectrum of BC subtypes, and doxycycline (DOX)-inducible knockdown (KD) of XIST markedly inhibits spheroid/colony forming capacity, tumor growth and tumor-initiating potential. This phenotype is attributed to impaired E-CSC in luminal and E- and M-CSC activities in triple-negative (TN) BC. Gene expression profiling unveils that XIST KD most significantly affects cytokine-cytokine receptor interactions, leading to markedly suppressed expression of proinflammatory cytokines IL-6 and IL-8 in ALDH- bulk BC cells. Exogenous IL-6, but not IL-8, rescues the reduced sphere-forming capacity and proportion of ALDH+ E-CSCs in luminal and TN BC upon XIST KD. XIST functions as a nuclear sponge for microRNA let-7a-2-3p to activate IL-6 production from ALDH- bulk BC cells, which acts in a paracrine fashion on ALDH+ E-CSCs that display elevated cell surface IL-6 receptor (IL6R) expression. This promotes CSC self-renewal via STAT3 activation and expression of key CSC factors including c-MYC, KLF4 and SOX9. Together, this study supports a novel role of XIST by derepressing let-7 controlled paracrine IL-6 proinflammatory signaling to promote CSC self-renewal.© 2023. The Author(s).