Induced expression of MELK is implicated in hepatocarcinogenesis
| Autor: | Cheng-Kuo Lai, 賴正國 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 Protein kinases play key regulatory roles in numerous cell physiological and pathological activities in eukaryotic cells. We investigated expression of protein kinases with an expression microarray approach. Expression of 68 kinases was highly elevated, in which MELK, maternal embryonic leucine zipper kinase, showed the highest induction in HCC tumors. Further validation with a larger set of HCC samples (104 pairs) confirmed an association of elevated expressions of MELK with development of HCC. Thus overexpression of MELK is a potential diagnostic marker for HCC. MELK is involved in self-renewing multipotent neural progenitors and in regulating the cell cycle of many cell types but the biochemical characterization of MELK is still in its early stage. We explored the functional roles of MELK in HCC with RNA interference using VSV-G pseudotyped lentivirus system. With shMELK-lentivirus, we down regulated MELK expression in HCC cell lines expressing high levels of MELK mRNA and protein. In HuH7, PLC/PRF/5 and Hep3B cells, knock-down of MELK resulted in alteration of cell morphology, reduced cell growth and apoptotic cell death as shown by increased cell population in sub-G1 and presence of cleavage form of PARP. The protein level of survivin, an anti-apoptotic protein, was reduced in shMELK-treated cells. These results suggested that MELK is a survival kinase in HCC cells. We further tested the combined effect of shMELK and four chemodrugs (5-FU, mitoxantrone, cisplatin and taxol) in HCC cells. Cells become more sensitive to the drug effects when MELK expression was suppressed. This result suggests that high level expression of MELK may confer chemo-resistance of HCC cells. An emerging protein complex involving MELK, ZRP9 and MYBL2 provided a different viewpoint of how MELK modulates cell growth. We observed a down-regulation of MYBL2 mRNA in MELK knock-down PLC/PRF/5 and HepG2 cells. Since MYBL2 is a transcription factor highly induced in the metastatic HCC, understanding MELK modulation of MYBL2 can shed more light on the regulation of HCC cell survival. For HCC, when most of conventional chemotherapeutic agents have not proven to be effective, new anti-cancer strategies are urgently needed. The hope for a “magic bullet” of the future for HCC patients persists. Essential kinases, such as MELK holds the promise. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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