The role of exosomal miR-141 in stromal-tumor crosstalk and ovarian cancer metastasis

Abstract

Epithelial ovarian cancer is the major type of ovarian cancers and causes one of the most lethal gynaecologic malignancies in women. The high mortality rate of this cancer is due to the lack of reliable screening biomarkers, leading to most ovarian cancer patients diagnosed at advanced stages, accompanied by acquired chemoresistance, peritoneal metastasis, and high recurrence. Similar to other solid tumors, ovarian cancer metastasis is the major cause of cancer-related death. Indeed, a successful cancer metastasis requires not only the adaptation and the aggressiveness of cancer cells, but also affected the formation and suitability of pre-metastatic niches. However, previous studies mainly focused on the formation of the metastatic tumor cells, while the underlying molecular mechanisms for establishing a pre-metastatic niche remain elusive. Recent evidence has proposed that miRNA-exosomes not only mediate cell-to-cell communication but also remodel the recipient cells for facilitating metastatic progression. Our laboratory has recently reported that Hsa-miR-141-3p (miR-141), one member of miR-200 family, is frequently upregulated and secreted by the ovarian cancer cells. It was characterized by exosomal miR-141 secretion from ovarian cancer cells and involved in stromal cell reprogramming. Evidence has suggested stromal cells are the key component of pre-metastatic niche in various human cancers because they provide the source of pro-tumorigenic cytokines. As expected, the exosomal miR-141 has shown to remodel stromal cells specifically and induce stromal cells by producing cytokines including the Growth-Related Oncogene-alpha (GROα) and Matrix Metalloproteinase Inducer (EMMPRIN), which are frequently detected in ovarian cancer ascites and cancerous omentum. The dominant roles in clinical samples and conditioned media were further confirmed by testing the tumorigenic effects of recombinant proteins of GROα and EMMPRIN. Functionally, ovarian cancer cells cultured in miR-141 expressed stromal-conditioned media or the recombinant GROα and EMMPRIN exhibited enhanced oncogenic capacities of ovarian cancer cell proliferation, cell migration/ invasion and tumor colonization in the ex vivo murine omental model. These findings suggest that the exosomal miR-141 is a key messenger in the interaction of the ovarian cancer cells and stromal cells. Understanding the underlying mechanisms of miR-141 remodel stromal cells, a proteomic profiling analysis using high-resolution mass spectrometry was performed. Results showed that Yes-Associated Protein 1 (YAP1), a Hippo pathway key effector, is frequently silenced by miR-141. Depletion of YAP1 expression in stromal cells by miR-141 or shRNAi approach causing the induction of nuclear Tafazzin (TAZ) accumulation. Further examination by YAP/ TAZ responsive reporter 8xGTIIC-luciferase assay and QPCR analyses demonstrated that YAP1 depletion or miR-141 overexpression caused transcriptional activated the gene expressions of GROα and EMMPRIN in stromal cells. Consistently, IHC analysis of the cancerous ovarian and normal endometrial stroma confirmed the reduction of YAP1 and upregulation of GROα and EMMPRIN in cancerous stroma are clinically correlated. Taken together, this is the first report showing the exosomal miR-141 is able to reprogram the stromal cells by inducing the secretion of the pro-tumorigenic cytokines. In future, to investigate the roles of miR-141/ YAP1/ TAZ signaling cascade in facilitating tumor-stromal interaction and enhancing cancer metastasis in vivo are warranted.