异染色质蛋白HP1γ介导间充质干细胞对于膀胱癌细胞的干性维持调控机制研究

Mesenchymal stem cells (MSCs) are involved in the formation of tumor microenvironment during cancer development. Given that MSCs have potency to differentiate into various cell types, including cancer-associated fibroblast, pericytes, etc, they are thought to play essential roles in promoting cancer cell stemness. However, how MSCs regulates cancer cells, especially the maintenance of cancer cell stemness, remains unclear. We found that bladder cancer cells induce MSCs to express Cox2, which is essential for PGE2 production. The elevated PGE2 increases cancer cell stemness, with the concomitant increase of pHP1γ(S83) level. Hence, it is important to understand the molecular mechanisms underlying MSCs-cancer cells interaction for future cancer treatment. At first, we plan to identify the mechanism of paracrine effects from MSCs to cancer stem cells. Furthermore, we will test how HP1γ mediates PGE2 induced cancer cell stemness, especially identifying the target genes at global view. Moreover, we will also confirm the essential role of pHP1γ(S83) in the process in vitro and in vivo through Cas9/CRISP knockin approach. At last, we will test the association between pHP1γ(S83) and bladder cancer aggressiveness. Taken together, this research will reveal how the essential role of HP1γ in MSC-induced cancer cell stemness and examine whether HP1γ is a potential drug target for bladder cancer.

肿瘤干细胞与肿瘤复发和转移有密切关系。间充质干细胞参与肿瘤微环境的形成并影响肿瘤细胞的干性维持。但间充质干细胞影响肿瘤干细胞维持的分子机制现在了解甚少。以具有高复发特性的膀胱癌为研究对象，我们发现肿瘤细胞诱导间充质干细胞表达Cox2酶的产物PGE2，从而促进膀胱癌细胞的干性，并伴随异染色质蛋白HP1γ的磷酸化水平改变。所以我们提出HP1γ介导了间充质干细胞对膀胱癌细胞干性的维持。首先，我们拟在体内和体外建立的间充质干细胞与膀胱癌细胞的相互作用模型基础上，研究确定相互作用的分子；其次，分析PGE2对于翻译后调控HP1γ活性从而调控基因转录的机制；再者，确立HP1γS83磷酸化状态改变对于间充质干细胞维持膀胱癌细胞干性的体内外意义；最后，检测HP1γS83磷酸化水平与膀胱癌恶性程度相关性。以上研究将充分阐述HP1γ介导的微环境对于肿瘤细胞干性维持的重要分子机理，同时为膀胱癌的治疗提供靶点。

膀胱癌具有高复发的特征。肿瘤干细胞与肿瘤复发转移密切相关。但肿瘤微环境中间充质干细胞（MSCs）影响膀胱肿瘤干细胞维持的分子机制还不清楚。因此，本项目研究了微环境中MSCs对于肿瘤细胞干性维持的重要分子机理，同时寻找膀胱癌的治疗靶点。我们首先发现MSCs能趋向膀胱癌细胞并促进癌细胞的成瘤能力。膀胱肿瘤干性样细胞内HP1γ信号被激活。然后，体外和体内实验结果显示，敲除HP1γ后肿瘤干性和相关基因的表达明显下降；而过表达HP1γ可以明显促进肿瘤干性增强。这证明HP1γ对膀胱癌细胞干性维持有重要作用。随后，通过基因表达图谱鉴定和分析，验证了SCML2是介导HP1γ调控膀胱癌干性的下游效应分子。进一步机制研究证明HP1γ通过自身招募到SCML2基因的CpG1和3区段的组蛋白H3K9 me2/3，再通过结合DNA甲基转移酶DNMT3a，甲基化SCML2启动子并下调其表达。SCML2是介导HP1γ调控肿瘤干性的重要下游分子。最后，临床膀胱癌样本检测分析，结果显示HP1γ在膀胱癌组织中高表达，与膀胱癌进展呈正相关，可能作为膀胱癌不良预后的指标和潜在治疗靶点。并且，HP1γ和SCML2在mRNA的表达水平呈负相关。本项目阐述了HP1γ介导的微环境对于肿瘤细胞干性维持的重要分子机理，同时为膀胱癌的治疗提供了新的靶点。