Export and stabilization of AU-rich element containng mRNA in oral cancer cells

富含AU的元件（ARE）存在于癌基因、细胞因子等生长相关基因转录的mRNA中。含有ARE的mRNA（ARE-mRNA）在病毒癌蛋白转化的细胞中被证明是输出和稳定的。HuR是一种RNA结合蛋白，在口腔癌细胞中，ARE-mRNA以不依赖CRM 1的方式输出到细胞质中，HuR的敲低导致口腔癌细胞的性质改变，免疫组化和生化分析显示，在口腔癌细胞如HSC 3和Ca 922中，HuR主要分布于细胞质和细胞核，而正常细胞HuR几乎全部分布于细胞核。ARE-mRNA也被输出并稳定在口腔癌细胞中。CRM 1依赖性输出通路抑制剂Leptomycin B对HSC 3细胞HuR和ARE-mRNA的输出无明显影响。我们利用RNAi技术建立了一个对口腔癌细胞有效的敲除系统。在HuR基因敲低的细胞中，ARE-mRNA的输出受到抑制。这些结果表明，HuR和ARE-mRNA在口腔癌细胞中通过破坏正常的输出途径而输出到细胞质中，HuR基因敲除有望成为口腔癌治疗的新途径。

AU-rich element (ARE) exists in the mRNA transcribed from growth-related genes such as oncogene and cytokine. ARE-containning mRNA (ARE-mRNA) has been shown to be exported and stabilized in the cells transformed with virus oncoprotein. HuR is an RNA-binding protein which has ARE-mRNA are exported to the cytoplasm in oral cancer cells in a CRM1-independent manner and that the knockdown of HuR resulted in changing the characters of oral cancer cells.Immunohistochemical and biochemical analysis revealed that, in oral cancer cells such as HSC3 and Ca922, HuR existed in the cytoplasm and the nucleus whereas almost all HuR was located in the nucleus in normal cells. ARE-mRNAs were also exported and stabilized in oral cancer cells. The export of HuR and ARE-mRNA was not affected by Leptomycin B, which is the inhibitor of CRM1 dependent export pathway, in HSC3 cells. We developed a knockdown system, which is effective for oral cancer cells, using RNAi technique. In HuR-knockdown cells, the export of ARE-mRNA was inhibited. Additionally, those cells failed to make colonies in soft-agar.These findings suggest that HuR and ARE-mRNA are exported to the cytoplasm in oral carcinoma cells by purturbing the normal export pathway and that HuR knockdown has potential as a new therapeutic approach for oral cancer.