Intracellularly expressed granulysin induced apoptosis in hepatoma cells and role of mitochondrial apoptotic pathway

Granulysin expressed in a humanized mouse model induces apoptotic cell death and suppresses tumorigenicity

Granulysin (GNLY) is a cytolytic and proinflammatory protein expressed in activated human cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Conventional mouse models cannot adequately address the triggering mechanism and immunopathological pathways in GNLY-associated diseases due to lack of the GNLY gene in the mouse genome. Therefore, we generated a humanized immune system (HIS) mouse model by transplanting human umbilical cord blood mononuclear cells into NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ (NSG) mice after sublethally irradiation. We examined the GNLY expression and its effects on tumor growth using this system. Our HIS mice expressed human CD45⁺, CD4⁺, CD8⁺ and CD56⁺ cells in the peripheral blood and spleen. A high expression level of human Th1/Th2 and NK cytokines was detected, indicating the activation of both T and NK cells. Importantly, we found an elevated level of GNLY in the serum and it was produced by human CTLs and NK cells obtained from the peripheral blood mononuclear cells and spleen cells in the HIS mice. The serum level of GNLY was negatively correlated with the proliferation of transplanted tumor cells in HIS mice. Collectively, our findings strongly supported that HIS mouse as a valuable model for studying human cancer under an intact immune system and the role of GNLY in tumorigenesis.

The Role of Granulysin in Cancer Immunology

Granulysin is a cytotoxic granule expressed in cytotoxic T cells and natural killer cells. Although its cytotoxic effect against a number of tumor cell lines has been demonstrated in vitro, recent studies with transgenic mice, and a number of clinical studies, have further established its significance in cancer immunology. Furthermore, granulysin-induced in vitro chemotaxis and activation of both human and mouse dendritic cells have been reported. Given the results in recent clinical studies, granulysin may offer a useful indicator in the prognosis of cancer. Taken together, an understanding of the mechanism by which granulysin destroys target cells would provide vital information in the development of new therapies for the treatment of this disease.