Exosomal miR-32在癌相关成纤维细胞和髓源抑制性细胞促进胃癌腹膜转移中的作用机制研究

Peritoneal metastasis is one of the major obstacles in the way of gastric cancer therapy, and peritoneal microenvironment plays an important role during the metastasis process. Previous studies frequently focused on the soluble factors released by tumor and stromal cells. However, recent studies have pointed to a novel mechanism by which tumor-derived exosomes offered an efficient platform for transfer of cross-talk signals in promoting tumor metastasis. To date, the role of gastric cancer exosomes in regulating peritoneal microenvironment remains to be elucidated. In our previous work, we have already found gastric cancer exosomes contributing to production of cancer-associated fibroblasts (CAFs) and accumulation of MDSCs in peritoneal tissues, as well as promoting tumor metastasis. Furthermore, knockdown of E3 ubiquitin ligases Cbl-b in gastric cancer cells could potentiate the effect of exosomes on CAFs and MDSCs, and upregulate the expression of exosomal miR-32. Collectively, we try to demonstrate that gastric cancer cells regulate the peritoneal microenvironment through exosome-mediated delivery of miRNA-32, which target PTEN/Akt pathway in CAFs and MDSCs. The results of the present study would provide new ideas and potential targets for prevention and treatment of peritoneal metastasis for gastric cancer.

腹膜转移是胃癌预后不良的主要原因，腹膜微环境在转移过程中发挥着重要作用。既往研究主要围绕肿瘤和基质细胞释放的可溶性因子展开。然而，最新研究显示，肿瘤细胞释放的exosomes在肿瘤的定向转移过程中可能发挥更大的作用。我们在前期工作中首次发现，胃癌细胞分泌的exosomes能诱导腹膜癌相关成纤维细胞（CAFs）的形成和动员髓源抑制性细胞（MDSCs）在腹膜聚集，促进胃癌腹膜转移。抑制胃癌细胞泛素连接酶Cbl-b表达后，其分泌的exosomes诱导CAFs和动员MDSCs的能力进一步增强，同时出现exosomal miR-32表达上调。本研究拟通过体内外实验，证实胃癌细胞分泌的exosomes介导miR-32在肿瘤和间质细胞间转运，调节间质细胞中PTEN/Akt通路，诱导腹膜CAFs形成，动员MDSCs在腹膜聚集，从而促进胃癌腹膜转移。研究结果将为认识胃癌腹膜转移的机制与临床防治提供科学依据。

腹膜转移是胃癌预后不良的主要原因。研究显示腹膜转移是一个涉及到肿瘤生物学行为和靶器官特性等多因素的复杂过程。既往研究主要围绕肿瘤和基质细胞释放的可溶性因子展开。然而，最新研究显示，肿瘤细胞释放的exosomes在肿瘤的定向转移过程中可能发挥更大的作用。但是，有关exosomes与胃癌腹膜转移的关系仍未见报道。我们之前的研究发现，胃癌细胞分泌的exosomes能促进肿瘤细胞增殖，诱导免疫耐受。在此基础上，我们进一步探讨了胃癌细胞分泌的exosomes对腹膜微环境的影响。我们的研究证实：胃癌细胞分泌的exosomes通过诱导腹膜癌相关性成纤维细胞（CAFs）形成和骨髓来源的抑制性细胞（MDSCs）的募集，营造了适宜肿瘤细胞定植和生长的转移前微环境，从而促进腹膜转移的发生。进一步探讨其机制，发现胃癌细胞分泌的exosomes通过介导miR-32在肿瘤细胞和间质细胞间的转运，调节间质细胞中PTEN/Akt和ERK通路，诱导腹膜CAFs形成、动员MDSCs在腹膜聚集，进而促进胃癌腹膜转移。Cbl-b能调节胃癌细胞exosomal miR-32的表达，从而调控胃癌腹膜转移的发生。另外，研究发现胃癌细胞来源的Exosomal PD-L1能诱导T细胞凋亡，Cbl-b通过抑制STAT5a抑制Exosomal PD-L1的生成，从而调控胃癌腹膜转移的发生。胃癌患者血浆中Exosomal PD-L1表达与预后不良有关。研究结果将有助于明确exosomes在胃癌腹膜转移中的作用机制，同时也有望为胃癌腹膜转移的临床防治找出潜在的预后标志物，并为今后发现新的治疗靶点提供依据。