ARID1A and PI3-Kinase pathway mutations in the endometrium drive epithelial transdifferentiation and collective invasion [Mouse_RNA-seq]. ARID1A and PI3-Kinase pathway mutations in the endometrium drive epithelial transdifferentiation and collective invasion [Mouse_RNA-seq]

ARID1A and PI3-Kinase (PI3K) pathway alterations are common in neoplasms originating from the uterine endometrium. Here we show that monoallelic loss of ARID1A in the mouse endometrial epithelium is sufficient for vaginal bleeding when combined with PI3K activation. Sorted mutant epithelial cells display gene expression and promoter chromatin signatures associated with epithelial-to-mesenchymal transition (EMT). We further show that ARID1A is bound to promoters with open chromatin, but ARID1A loss leads to increased promoter chromatin accessibility and the expression of EMT genes. PI3K activation partially rescues the mesenchymal phenotypes driven by ARID1A loss through antagonism of ARID1A target gene expression, resulting in partial EMT and invasion. We propose that ARID1A normally maintains endometrial epithelial cell identity by repressing mesenchymal cell fates, and that coexistent ARID1A and PI3K mutations promote epithelial transdifferentiation and collective invasion. Broadly, our findings support a role for collective epithelial invasion in the spread of abnormal endometrial tissue. Overall design: EPCAM+ endometrial epithelial cells from hyperplastic LtfCre0/+; (Gt)Rosa26Pik3ca*H1047R; Arid1afl/fl and healthy control wild-type CD-1 mice were purified and assayed via RNA-seq. Mature female mice were euthanized prior to vaginal bleeding.

ARID1A与磷脂酰肌醇3-激酶（PI3-Kinase, PI3K）通路异常，在子宫内膜起源的肿瘤中十分常见。本研究发现，在小鼠子宫内膜上皮中，ARID1A的单等位基因缺失若联合PI3K激活，足以引发阴道出血。分选获得的突变上皮细胞，呈现出与上皮间质转化（epithelial-to-mesenchymal transition, EMT）相关的基因表达与启动子染色质特征。本研究进一步证实，ARID1A可结合开放染色质状态的启动子；而ARID1A缺失会提升启动子染色质的可及性，并上调EMT相关基因的表达。PI3K激活可通过拮抗ARID1A靶基因的表达，部分挽救ARID1A缺失所驱动的间质表型，进而引发部分上皮间质转化与侵袭行为。本研究提出，ARID1A通常通过抑制间质细胞命运程序，维持子宫内膜上皮细胞的细胞身份；而ARID1A与PI3K的共突变，则会促进上皮转分化与集体侵袭。总体而言，本研究结果证实，集体上皮侵袭在异常子宫内膜组织的播散中发挥作用。

实验整体设计：从增生性LtfCre0/+；(Gt)Rosa26Pik3ca*H1047R；Arid1afl/fl小鼠以及健康野生型CD-1对照小鼠中，分离纯化上皮细胞黏附分子（EPCAM）阳性子宫内膜上皮细胞，并通过RNA测序（RNA-seq）进行检测。本研究中的成熟雌性小鼠均在出现阴道出血前实施安乐死。