Summary: | 博士 === 國立清華大學 === 分子與細胞生物研究所 === 103 === Protein Shugoshin-1 (Sgo1) functions to protect centromeric cohesion and is essential for proper chromosome segregation and genomic integrity. During mitosis, Plk-1 phosphorylates SA2 subunit of cohesin, and thereby cohesin dissociates from chromosome arm. In contrast, centromeric cohesin is still kept at centromere due to the reason that Sgo1-protein phosphatase 2A (PP2A) counteracts Plk1-mediated phosphorylation at centromeric cohesin. Therefore, centromeric cohesin still tethers sister chromatids together until the onset of anaphase. In this study, we find that protein stability and localization of Sgo1 are independent of Plk1 activity during mitosis. In addition, we examined expression levels of Sgo1 isoforms in normal tissue cDNA and transformed cell lines by conventional reverse transcription-PCR. All Sgo1 isoforms are detected in the transformed cell lines, but not in most normal tissues, expect for thymus and testis. In contrast to hTERT-immortalized cell lines, we find that Sgo1 protein is highly expressed in transformed cell lines, such as HeLa, HuH-7, WRL-68, HepG2, and HepaRG. We also demonstrate that mRNA and the protein levels of Sgo1 significantly increased in HCC, compared with in adjacent non-HCC regions. The depletion of Sgo1 induces chromosome instability and mitotic cell death in HeLa and HuH-7 cells, as a result of spindle assembly checkpoints activation. This effect is not detected in hTERT-immortalized cell lines such as RPE-1 and NeHepLxHT. Notably, hepatitis B virus (HBV) is positively correlated with Sgo1 expression at non-HCC regions. Overexpression of viral large surface proteins (LHBS) increases Sgo1 expression on NeHepLxHT cells along with increased chromosome instabilities. These results demonstrated that Sgo1 is an important modulator for mitotic progression in transformed cells and hepatocytes carrying HBV-LHBS protein. We suggest that Sgo1 is a promising and novel therapeutic target for HCC, especially those related to HBV infection.
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