外泌体源性miR-675在胰腺癌细胞竞争中抑制肿瘤增殖的研究

The noncoding RNAs have been demonstrated to play vital role in the tumorigenesis, and they are mainly packaged in exosomes to be delivered. It is of high value to investigate the expression and functional role of exosome derived miRNA in cancer. Our previous study indicated that the expression of miR-675 was downregulated in pancreatic cancer tissues and patients’ sera. It had been demonstrated that miR-675 could significantly suppress the pancreatic cell proliferation. However, the cause for reduced miR-675 expression and action mode of miR-675 remain unclear. A typical phenomenon of cell competition must exist in the pancreatic cancer which has a pathological feature of tissue heterogeneity. We hypothesize that the growth inhibitory signals such as exosome derived miR-675 released by normal pancreatic cells could control the dysplasia of the surrounding tissues. The decrease of normal cells and the occurrence of secondary desmoplastic reaction lead to the reduced expression of exosome derived miR-675. In that case, the inhibition on the adjacent cells will be weakened. This study will be focused on revealing the differential expression of exosome derived miR-675 in the different types of cells in pancreatic cancer. The secretory miR-675 released by cancer cells and fibrous mesenchymal cells is remarkably less than that released by normal cells. Exosome derived miR-675 secreted by normal cells could be intook into the cancer cells to suppress cell proliferation. This research will conform that the characteristic structure and function of exosome derived miR-675 could make it the candidate for dynamic monitor and targeted agent of pancreatic cancer.

非编码RNA在肿瘤形成中发挥了重要的调控作用，外泌体是其主要转运工具，外泌体源性miRNA在肿瘤中的表达及功能有很高的研究价值。前期实验发现miR-675在胰腺癌组织和血清中表达下降，并可显著抑制细胞增殖，但其表达减少的原因及作用方式尚不明确。组织异型性显著的胰腺癌中存在典型的细胞竞争现象，申请人认为，正常胰腺细胞可通过释放外泌体源性miR-675调节周围组织的异常增生；但随着肿瘤中正常细胞的比例下降与继发性纤维增生性反应的出现，外泌体源性miR-675分泌减少，对周围细胞的抑制能力降低。本研究将通过实验证实，胰腺癌不同细胞成分释放的外泌体源性miR-675存在差异，肿瘤细胞及纤维间质细胞产生的分泌型miR-675明显少于正常细胞；由正常细胞释放的外泌体源性miR-675可被肿瘤细胞摄取后抑制增殖；外泌体源性miR-675已经具备了成为胰腺癌动态监测标志物和靶向治疗药物的结构与功能基础。

上调外泌体源性miR-675表达可抑制细胞增殖；而且，通过加入外泌体形成的抑制剂可以直接抑制细胞增殖，结合测序结果生信分析，胰腺癌细胞外泌体中差异表达的miRNA调控的靶基因富集于涉及细胞内吞及外泌体形成的信号通路。因此我们怀疑，与正常细胞相比，胰腺癌细胞中外泌体的形成与分泌机制已经受到影响，肿瘤可能通过将包括miR-675在内的功能性miRNA转运出细胞使其无法在细胞内发挥功能，从而干预自身的生物学行为，这可解释具备增殖抑制功能的miR-675在肿瘤外泌体中的水平升高，同时也提示干预胰腺肿瘤的外泌体形成与分泌可能有一定治疗价值。后续我们还将继续研究细胞内外miR-675的总量变化以明确外泌体的排出功能、外泌体形成相关信号通路在胰腺癌细胞中的变化、以及外泌体抑制剂在体内实验中对胰腺肿瘤的治疗价值。目前的主流研究多关注外泌体运载“货物”的能力，而忽略了其排出“垃圾”的功能，通过将具备重要调控功能的生物学分子排出细胞外从而影响细胞状态可能是肿瘤细胞新的调控模式，值得进行后续深入探索。