Mechanistic study of ADAM17 in cell senescence of HCC cells

• Main Authors: Yun-Ju Fu, 傅韻如
• Other Authors: Ann-Ping Tsou
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/13490850999118331577

碩士 === 國立陽明大學 === 醫學生物技術暨檢驗學系暨研究所 === 98 === ADAM17 (A disintegrin and metalloprotease domain 17), a transmembrane proteinase, mediates the ectodomain shedding of many ligands specially that of the EGFR family members. It affects cell proliferation, survival, migration and invasion. ADAM17 has been reported to be up-regulated in HCC. Our previous findings showed that ADAM17 mRNA is elevated in T3 stage of HCC tissues and silencing of ADAM17 reduced tumor angiogenesis and metastasis in vivo. Altered actin organization is responsible for reduced cell migration activity. We further demonstrated that silencing of ADAM17 in non-migratory and p53 (-) PLC/PRF/5cells, led to cell senescence. The detailed molecular mechanism in shADAM17-induced cell senescence, however, is not well characterized. In this study, we investigated the mechanisms involved in shADAM17-induced cell senescence. We found that ectopically overexpression of a constitutively-active EGFR in shADAM17-PLC drastically reduced cell senescence, suggesting that EGFR signaling was disabled in shADAM17-PLC. We further tested the role of ADAM17 in other non-migratory HCC cells. In addition to reduce the transforming activity, knockdown of ADAM17 in HepG2 triggered G1 blockade and increased SA-β-gal activity. This result suggests that elevated expression of ADAM17 is anti-senescence in two HCC cell lines tested so far. In p53 (+) HepG2 cells, we detected decreased phosphorylation of Rb protein, enhanced phosphorylation of p53 and p21 expression early after shADAM17 viral infection. Double knockdown of ADAM17 and p53 can effectively prevent the progression of cell senescence. This result shows that ADAM17-knockdown induced senescence in HepG2 is likely to be mediated via the p53 dependent p21-Rb pathway. Since p53 in PLC is mutated the ADAM17 knockdown-induced cell senescence in PLC is likely directed by a p53-independent mechanism. Moreover, we found that autophagy marker LC3 was elevated in ADAM17-knockdowned HCC cell, suggesting that autophagy may be involved in ADAM17 knockdown-induced cell senescence. Our work on ADAM17 in HCC is novel and is the first evidence linking ADAM17 directly to tumor metastasis and to cell senescence. Our current results imply that ADAM17 knockdown can induce either p53-dependent or p53-independent cell senescence. The findings from this project have potential to provide alternative therapeutic strategies for HCC.