CD45RO-CD8+ T cell-derived exosomes restrict estrogen-driven endometrial cancer development via the ERβ/miR-765/PLP2/Notch axis.

Rationale: Estrogen-dependent cancers (e.g., breast, endometrial, and ovarian cancers) are among the leading causes of morbidity and mortality in women worldwide. Recently, exosomes released by tumor-infiltrating CD8+ T cells have been under the spotlight in the field of cancer immunotherapy. Our study aims at elucidating the underlying mechanisms of the crosstalk between estrogen signaling and CD8+ T cells, and possible intervention values in uterine corpus endometrial cancer (UCEC). Methods: Micro RNA-seq was conducted to screen differentially expressed micro RNA in UCEC. Bioinformatic analysis was processed to predict the target of miR-765. RNA silencing or overexpressing and pharmacologic inhibitors were used to assess the functions of ERβ/miR-765/PLP2/Notch axis in UCEC cell proliferation and invasion in vivo and in vitro. In vivo imaging was performed to evaluate the metastasis of tumor in mice. Combined fluorescent in situ hybridization for miR-765 and immunofluorescent labeling for CD8 was carried out to prove the co-localization between miR-765 and CD8+ T cells. Exosomes derived from CD45RO-CD8+ T cells were isolated to detect the regulatory effects on UCEC. Results: miR-765 is characterized as the most downregulated miRNA in UCEC, and there is a negative correlation between miR-765 and Proteolipid protein 2 (PLP2) in UCEC lesion. Estrogen significantly down-regulates miR-765 level, and facilitates the development of UCEC by estrogen receptor (ER) β. Mechanistically, this process is mediated through the miRNAs (e.g., miR-3584-5p, miR-7-5p, miR-150-5p, and miR-124-3p) cluster-controlled regulation of the PLP2, which further regulates Ki-67 and multiple epithelial-mesenchymal transition (EMT)-related molecules (e.g, E-cadherin and Vimentin) in a Notch signaling pathway-dependent manner. Interestingly, the selective ER degrader Fulvestrant alleviates estrogen-mediated miR-765/PLP2 expression regulation and UCEC development in ERβ-dependent and -independent manners. Additionally, CD45RO-CD8+ T cell-derived exosomes release more miR-765 than that from CD45RO+CD8+ T cells. In therapeutic studies, these exosomes limit estrogen-driven disease development via regulation of the miR-765/PLP2 axis. Conclusions: This observation reveals novel molecular mechanisms underlying estrogen signaling and CD8+ T cell-released exosomes in UCEC development, and provides a potential therapeutic strategy for UCEC patients with aberrant ERβ/miR-765/PLP2/Notch signaling axis.