表观遗传修饰高甲基化癌基因1（HIC1)调控前列腺癌的发生、发展

Prostate cancer (PCa) is mostly common malignancy in Western male, which has recently been found in Chinese male with markedly increasing incidence; however, the mechanism underlying its initiation, progression still remains unclear.Our previous results indicated that the methylation status of 11 CpG sites within Hypermethylatioted in cancer 1(HIC1) by BSP sequencing were abundantly methylated in tissues of PCa patients compared with those of normal controls. Similar results were observed in PCa cell lines. In vitro and in vivo assays, restoring HIC1 expression in PCa cells markedly inhibited proliferation, migration, and invasion and induced the apoptosis in these cells.In contrast, knockdown of HIC1 expression by shRNA, these phenotypes in PCa cell are more markedly enhanced. Moreover, mice bearing PCa cells with overexpression of HIC1 had a significant effect on reducing tumor growth and osseous metastases. Notably, we also identified that chemokine receptor CXCR7 is a potential downstream target gene of HIC1 in PCa cells by microarray and ChIP assays. CXCR7 promoter in PCa cells is negatively regulated by HIC1, which may contribute to PCa progression. Based on these findings, we set out to constuct PCa model of mice by conditional double knock out Pten and HIC1 supressors in mice prostate epithenial whereby the machanism of HIC1 in PCa initiation, progression is further explored. On the other hand, We are interested to investigate whether cancer-associated fibroblasts(CAFs) within PCa microenviroment make contributes to regulating HIC1 expression in tumor cells by secretion of many factors. In summary, these results suggest that HIC1 is featured as a new biomarker capable of preventing metastasis and provides a more effective therapeutic strategy for PCa.

前列腺癌是西方男性最常见的恶性肿瘤之一，近年来它在我国男性中发病率快速增高，但其发病的机制仍不清楚。我们前期研究表明癌高甲基化基因1（HIC1）受表观遗传学修饰在前列腺癌细胞和癌组织中呈高甲基化状态，使其表达降低；体内外实验表明恢复表达HIC1可显著降低癌细胞增殖、侵袭、转移及成瘤等能力；相反， shRNA沉默HIC1的表达后，癌细胞这些特性被显著增强。深入研究发现趋化因子受体CXCR7是HIC1在前列腺癌发生、发展过程中潜在的一个重要下游靶点，机制上HIC1可能通过与CXCR7启动子特定区域结合反向调控其表达。以此为基础，在拟构建Ptenpc-/-HIC1pc-/-双敲除小鼠前列腺癌模型中，深入研究HIC1在前列腺癌发生、发展过程中的分子机制；同时探讨微环境中癌相关的成纤维细胞（CAFs）可能在调控肿瘤细胞HIC1的表达中发挥作用。这些研究有助于为前列腺癌的早期诊断和治疗提供新的思路。

背景：.肿瘤转移是前列腺癌致死的第一要素。研究发现，癌高甲基化基因1（Hypermethylated in cancer 1, HIC1）在前列腺癌组织中受到表观遗传学调控，但它与前列腺癌转移关系的分子机制目前鲜见报道。.研究内容：.我们利用大样本数据库（The Cancer Genome Atlas， TCGA数据库和Taylor’数据库）分析HIC1基因启动子在肿瘤和癌旁组织中甲基化和表达差异，以及HIC1表达量的高低与前列腺癌患者生存预后关系；体外实验中，在前列腺癌细胞系中沉默HIC1表达，分析HIC1表达缺失后细胞的侵袭、迁移能力的变化；使用生物发光活体成像和X光影像方法，检测HIC1表达缺失后前列腺癌细胞在裸鼠体内转移能力的变化，在自发性前列腺癌小鼠模型中，前列腺上皮特异性敲除HIC1后，使用免疫组化和H&E染色实验观察HIC1缺失后肿瘤侵袭能力变化；使用表达谱基因芯片、Western blot和Realtime RT-PCR方法检测HIC1表达缺失后前列腺癌细胞上皮-间质转化（Epithelial-Mesenchymal Transition，EMT）变化以及分子机制；荧光素酶报告基因实验和染色质免疫共沉淀实验检测HIC1调控Slug 和 CXCR4表达的分子机理。.重要结果：.实验证实，HIC1基因启动子在前列腺癌组织中高度甲基化，甲基化程度与表达量负相关；同时发现在转移性前列腺癌组织中HIC1表达明显低于原位癌和癌旁组织，HIC1表达低的患者生存期低于表达高的患者。基因敲除小鼠模型中发生，HIC1特异性敲除可以促进前列腺癌细胞发生局部侵袭。体外实验发现，HIC1表达缺失能够促进前列腺癌细胞侵袭和迁移能力，并促进EMT发生；动物实验发现，沉默HIC1表达可以促进前列腺癌细胞在小鼠体内转移，特别是骨转移，并明显降低了受试小鼠的生存期。进一步实验发现，Slug 和CXCR4表达上调与HIC1表达缺失后前列腺癌EMT发生和转移有关。同时也发现，CXCL12/CXCR4趋化因子轴可以通过活化ERK1/2信号通路促进Slug表达。.科学意义：.本研究证实，HIC1基因启动子甲基化导致其表达缺失，使Slug 和CXCR4表达升高，促进了前列腺癌细胞的侵袭和转移，揭示了前列腺癌转移发生新的调控机制，并为前列腺癌治疗提供了新的策略。