Lin28A调控间质上皮转化（MET）与乳腺癌转移

EMT in cancer progression and metastasis has been widely studied in the last ten years. Mesenchymal–epithelial transition (MET) is suggested to participate in the process of metastatic tumor formation too. while the experimental data supportingthe role of MET in the process of carcinoma are still limited.Lin28A, an evolutionarily conserved RNA binding protein, is abundantly expressed in embryonic stem cells and is necessary for stem cell viability and pluripotency. Clinical data indicated that Lin28 overexpression is associated with advanced disease across multiple tumor types. Our results suggested that Lin28A promoted MET process in vitro, meanwhile, preliminarily indicated that Lin28A promoted the pulmonary metastasis of breast cancer via mammary fat pad graft. Histological examination found that high expression of Lin28A promoted TAM infiltration, which was indicative of high malignancy. The mechanism was initially determined that Lin28A up-regulatie the TAM and promote TAM M2 polarization to induce tumor invasion and pulmonary metastasis by directly binding to Let7 and miR-125a and inhibited its expression; moreover, Lin28A can upregulate PD-L1 both at primary and metastasis tumor. We will demonsrated that the molecular mechanism of Lin28A on Let7， miR-125a regulating . This work reveals a potential mechanism whereby , Lin28A, involves in MET process and TAM infiltration and impacts on the pulmonary metastasis of breast cancer. meanwhile, we show that the occurrence of lymphangiogennesis within mice breast cancers after mammary gland transplatation. Our results establish the of lymphangiogenesis in breast and identify lin28A-miR205-VEGFC as a molecuar link between tumor lymphangiogenesis and MET related metastasis.Nevertheless, this is a relatively new field of study and much remains to be established before the concept of TAM infiltration-induced lymphangiogenesis and lung metastasis are accepted as a viable anti-metastatic target. These observations will provide new targets for breast metastasis.

EMT在转移中的作用已获得广泛认可。但至今间质上皮转化（MET）在肿瘤中的作用却缺乏认识。Lin28A又叫多潜能因子，已知在胚胎干细胞具有重要作用。我们发现Lin28A是一种MET inducer，能促进细胞的上皮特征并抑制间质特性。我们用具有肺部微转移而无法形成转移灶的小鼠乳腺癌细胞系4TO7进行原位移植，发现lin28A可诱导肺部形成巨大转移灶，推测lin28A对乳腺癌的远端定值等后期转移相关。同时发现lin28A主要表达在上皮性乳腺癌细胞系中，符合其MET特性，并与干性增加相关。通过分子、细胞和动物水平，拟从两个方面阐述Lin28A调控乳腺癌转移的分子机制。一方面，Lin28A肿瘤调控TAM浸润可促进肿瘤肺转移，可能通过外泌体释放miR-125a和let7发挥作用。另一方面乳腺原位TAM浸润调控miR205，从而靶向VEGF-C信号并实现淋巴转移。以上作用可能均和MET转化密切相关。

Lin28A是已知的干性调节因子，其主要表达于胚胎干细胞，而在成体几乎不表达。研究表明，Lin28A在多个类型肿瘤中表达上调，流行病学数据也显示Lin28A的高表达往往预示其转移增加，而其调控肿瘤免疫微环境的机制仍不清楚。通过特定的4TO7小鼠乳腺癌原位移植模型，我们发现，Lin28A表达促进肿瘤微环境巨噬细胞M2转化，由于M2巨噬细胞被报道有免疫抑制作用。的确，我们进一步发现，Lin28A抑制4TO7肿瘤组织CD8+ T细胞浸润和活化相关细胞因子如IFN-γ、TNF-α等的表达，抑制CD8+ T细胞杀伤活性。此外，Lin28A还抑制4TO7肿瘤CD4+ T细胞浸润，抑制其Th1分化而上调其Treg分化，这一分化的改变将用以抑制CD8+ T细胞活性。机制上，我们发现，肿瘤细胞中Lin28A表达通过抑制miR-125a 和let-7s而上调IL-4表达，促使巨噬细胞M2转化。M2巨噬细胞自身有上调的PD-L2表达，这一增高的免疫检测点抑制子也将导致降低的CD8+ T细胞活性。我们推测，M2巨噬细胞和肿瘤细胞通过改变的的细胞因子表达谱，共同调节CD4+ T细胞分化。M2巨噬细胞由于异常的细胞因子分泌，导致增高的Treg群体比例，另一方面IL-4、IL-10可与M2巨噬细胞分泌的细胞因子一起，协同参与抑制CD4+ T细胞Th1分化，产生下游CD8+ T细胞杀伤活性抑制，M2巨噬细胞也能通过PD-L2直接参与抑制CD8+ T细胞。本研究揭示了Lin28A起始下，4TO7小鼠乳腺癌肿瘤细胞诱导巨噬细胞M2转化，肿瘤细胞和巨噬细胞协同作用于CD4+ T细胞，使其Th1比例降低而Treg比例升高，由此引起降低的CD8+ T细胞活性，从而促进肿瘤进展和转移。本文揭示了Lin28促进转移相关的抑制性免疫微环境新机制，相关免疫抑制通路的有效阻断将为乳腺癌转移防治提供新的思路。