Concanavalin A-induced autophagy in anti-hepatoma therapy and acute hepatitis

• Main Authors: Chih-Peng Chang, 張志鵬
• Other Authors: Huan-Yao Lei
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/12145455354626443215

博士 === 國立成功大學 === 基礎醫學研究所 === 96 === Hepatocellular carcinoma (HCC) is among the top two malignant cancers leading to death in Taiwan. There is no satisfactory therapy for HCC patients. Concanavalin A (Con A), a lectin with mannose and glucose binding specificity, was tested for anti-hepatoma effects. From in vitro observations, Con A was able to bind to splenocytes and tumor cells to induce cell proliferation and cell death, respectively. In an in situ murine hepatoma model, intravenous injection of Con A could inhibit liver tumor nodule formation through the CD8+ T cell-mediated activity, and establish an immune memory to prevent further challenge of the same tumor. Furthermore, the liver tumor growth was also partially inhibited in severe combined immune deficiency mice. The mechanisms of Con A-induced cell death on hepatoma cells were further studied. We found that Con A would be internalized to mitochondria through clathrin-mediated endocytosis to induce autophagic cell death once bound to the hepatoma cells. The characteristics of autophagic vacuoles, lysosomal activity, BNIP3 expression and LC3-II aggregation were observed. The class III PI3K inhibitor, 3-methyladenine, could both inhibit autophagosome formation and cell death induced by Con A. RNA interference studies shown that Con A-induced autophagic cell death on hepatoma cells was mediated through BNIP3 induction following by LC3-II formation whereas beclin-1 and ATG5 were not involved. Furthermore, it is known that Con A-induced acute hepatitis in mice is mediated through activation of NKT and T cells to cause liver damage. The observation of Con A-induced autophagy on hepatocytes made us to re-evaluate the effect of Con A in mice. Con A at 20 mg/kg induced acute hepatitis in BABL/c mice and became lethal when the dose was higher than 20 mg/kg. However in SCID or SCID/NOD mice, Con A could also induce acute hepatitis but needed higher dose than 30 or 40 mg/kg, respectively. The kinetics of acute hepatitis in immunodeficient mice is similar to that of immunocompetent BABL/c mice. No lymphocyte infiltrations were found in the livers of SCID or SCID/NOD mice, and the cytokine productions were different. An autophagy with LC3-II conversion was demonstrated in the liver post Con A injection with a quicker kinetics in BALB/c than in SCID/NOD mice. IFN-�� produced in BALB/c mice post Con A injection could enhance the autophagy of hepatocytes through the up-regulation of LC3 expression. Con A-induced acute hepatitis can be either T cell-dependent in BABL/c mice or T cell-independent in SCID/NOD mice, but both have an early autophagic induction. Due to the mannose/glucose-specific binding on cell membrane, Con A can cause both autophagic induction on hepatocytes and immunomodulation on T cells to inhibit tumor growth or induce acute hepatitis in mice. Con A-induced autophagy response provides a novel mechanism for the applications of lectins.