The role of Y-box binding protein-1 (YB-1) in regulation of DDX3 expression

• Main Authors: Min-Shiou Yang, 楊旻修
• Other Authors: Yan-Hwa Wu Lee
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/88452208586233895443

碩士 === 國立陽明大學 === 生化暨分子生物研究所 === 98 === Human DDX3 belongs to the DEAD box family which possesses DEAD box motif and ATP-dependent RNA helicase activity. DDX3 plays important roles in many biological functions. For example, DDX3 enhances p21 promoter activity via interacting with Sp1 to repress cell proliferation in liver cancer cell line. However, the regulation of DDX3 expression remains largely unknown. YB-1 (Y-box binding protein 1) is a member of cold-shock domain (CSD) family. YB-1 has nucleic-acid-binding activity and modulates the gene expression through transcriptional regulation. Moreover, the nuclear localization is important for transcription activity of YB-1. It has been shown that AKT could promote nuclear localization of YB-1 by phosphorylating Ser102 of YB-1. In recent studies, YB-1 translocates to nucleus and upregulates many growth related genes expression to enhance proliferation of cancer cells, such as breast cancers, ovarian cancer and lung cancer. In this study, our data showed that DDX3 expression was enhanced in HeLa cells but repressed in HuH-7 cells by YB-1. By using semi-quantitative RT-PCR, real-time quantitative PCR and reporter assay, we demonstrated that YB-1 could modulate DDX3 promoter activity, thereby enhancing or repressing DDX3 expression level in HeLa or HuH-7 cells, respectively. Furthermore, we also found that YB-1 could repress p21 promoter activity in a Sp1-dependent manner in HuH-7 cells, which might result from the inhibition of DDX3 expression and the reduction of DDX3-Sp1 interaction on p21 promoter. In contrast, YB-1 might activate the p21 promoter activity in both Sp1-dependent and Sp1-independent manners in HeLa cells. Consistent with the observation described above, the Ser102 phosphorylation of YB-1 was increased by elevated AKT activity under serum stimulation condition, and DDX3 expression was enhanced in HeLa cells but was repressed in HuH-7 cells. Therefore, the nuclear localization of YB-1 plays an important role in regulation of DDX3 expression. In summary, our findings suggest that YB-1 enhances DDX3 and p21 protein expressions in HeLa cells, but represses them in HuH-7 cells. Therefore, YB-1 protein is a potential regulator of DDX3 protein expression.