Impairment of p53 is required for induction of epithelial-mesenchymal transition by knockdown of the human citrate synthase

• Main Authors: Chin-chih Lin, 林晋志
• Other Authors: Wen-Tsan Chang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/05809594388045609338

碩士 === 國立成功大學 === 生物化學研究所 === 96 === The bioenergetic organelle mitochondrial plays an important roles in a variety of cellular functions including growth, division, energy metabolism and apoptosis. Defects in mitochondrial bioenergetic will led the cell revert to a more primitive cytoplasmic glycolysis for energy generation and promote to tumor malignancy. Recently, we have shown that persistently knockdown the RNAi-mediated silencing of the human citrate synthase (CS), the first and rate-limiting enzyme of the tricarboxylic acid cycle (TCA), dramatically induced epithelial-mesenchymal transition (EMT), resulting in increased tumor migration and invasion in HeLa and SiHa human uterine cervix cancer cells. Although we have provided the concept about knockdown of the human CS expression disrupted the mitochondrial bioenergetic pathway and in turn promoted the cytosolic glycolysis metabolism, but the detailed mechanism of this abnormal metabolic alteration is not completely elucidated yet. In this study, we have first demonstrated that inhibition of the human CS expression induced EMT phenotype in human cervical carcinoma cell line HeLa (impaired p53). Besides, we have shown that this phenotypic switch could be revered by treatment with MG132, an ubiquitin-proteasome inhibitor, or knockdown of the human homolog of MDM2 (HDM2). In addition, we have also demonstrated that silencing of the human CS expression induced EMT phenotype in human breast cancer cell line MCF7 (wild type p53), under the only condition of co-knockdown of the human p53 expression. Silencing of neither the human CS expression nor the human p53 expression could induce EMT phenotype in MCF-7 cells, suggesting that the EMT phenotype was induced only by dysfunction of the both the human CS and p53 expression. Moreover, we have additionally shown that silencing of the human CS expression induced EMT phenotype in human prostate cancer cell line PC3 (null p53) and that this phenotype switch could not be reversed by knockdown of the human HDM2 expression .These results clearly indicate that impairment of p53 is required for induction of the MET phenotype by silencing of the human CS expression. It has been well characterized that the human p53 inhibits glycolysis through p53 induced glycolysis and apoptosis regulator (TIGAR) induction and promotes oxidative phosphorylation (OXPHOS) through synthesis of cytochrome c oxidase 2 (SCO2) activation. According to this effect, the human CS-knockdown cell lines exhibited a strong down-regulator of the TIGAR and SCO2 expression, resulting from rapid HDM2-mediated p53 degradation by ubiquitin-mediated p53 degradation switches the cellular bioenergetic metabolism form mitochondrial OXPHOS to cytosolic glycolysis that as an intrinsic carcinogenesis.