microRNA（miRNA）是一类长约22个核苷酸的内源性小分子RNA，它对基因的表达调控发挥重要作用。我们之前的研究表明，miRNA在人类血清和血浆中稳定存在并有潜力作为肿瘤的指纹图谱。进一步的研究发现，细胞分泌的miRNA是一种新型的细胞间交流通讯的手段。在本项研究中，我们猜想肿瘤细胞为了维持生存，能主动的通过分泌miRNA的途径排出不利己的miRNA，以获得无限增殖及抗凋亡的能力，以及获得更强的迁移和侵袭的能力，维持肿瘤的生长。另一方面，肿瘤细胞也能将另一类miRNA释放到细胞外，这些肿瘤分泌miRNA将在microvesicle的传输作用下进入靶细胞，从而抑制这些靶细胞中一些关键蛋白的表达，使这些靶细胞发生变异，向利于肿瘤细胞生存的方向发生转化。本项研究将揭示肿瘤分泌miRNA的生物学功能并拓展人们对肿瘤miRNA的认识。

microRNAs (miRNAs) are endogenous small non-coding RNAs of 22 nucleotides in length. They play an important role in regulation of gene expression. In previous studies, we showed that miRNAs are present in human serum and plasma in a remarkably stable form and that their unique expression patterns can serve as "fingerprints" of tumors. Moreover, we reported that secreted miRNAs can serve as novel signaling molecules mediating intercellular communication. Since some miRNAs generally function as tumor suppressor genes to target oncogenes, we herein propose that tumor cells may secrete these tumor-suppressive miRNAs into the extracellular environment via microvesicles to reduce the anti-tumorigenic effect within the cells, which lead to maintain their oncogenic and metastatic propensities. Moreover, we hypothesize that another type of tumor-secreted miRNAs, delivered by tumor-derived microvesicles, can efficiently target some essential genes and downregulate their expression in target cells, which finally facilitate tumor growth. This project may reveal the biological functions of tumor-secreted miRNAs and significantly extend our understanding of tumor miRNAs.