Induction of autophagy by concanavalin A and its application in anti-tumor therapy.

Concanavalin A (Con A), a lectin from Jack bean seeds that, once bound to the mannose moiety on the cell membrane glycoprotein, is internalized preferentially to the mitochondria. A BNIP3-mediated mitochondria autophagy is then induced, and causes the tumor cells to undergo autophagic cell death. Con A is also a T cell mitogen that can induce autoimmune hepatitis in mice. Because of the dual properties (autophagic cytotoxicity and immunomodulation) via the specific mannose binding, Con A can exert a potent anti-hepatoma therapeutic effect by inhibiting tumor nodule formation in the liver and prolonging the survival of the tumor-bearing mice. The anti-tumor effect is primarily mediated by activated CD8(+) T cells, and will also establish a tumor antigen-specific immune memory during the hepatic inflammation. This finding provides a novel mechanism in which Con A can be used as an anti-hepatoma agent, and also gives support for the search for natural lectins as anti-cancer compounds.