Gene expression in hemocyte from cancer-bearing or non-cancer control Drosophila larvae

The involvement of immunity in the prevention of cancer is apparent. Although the participation of both humoral and cellular immune reactions is presumed, underlying mechanisms are yet to be solved. This study was conducted to solve this issue using a Drosophila model where cancer was induced through the simultaneous inhibition of cell-cycle checkpoints and apoptosis. Hemocytes, blood cells of Drosophila equivalent to mammalian macrophages and granulocytes, play a role of immune cells. We first determined the location of hemocytes in cancer-bearing and normal larvae, but there was no significant difference between the two groups. When a gene expression pattern in hemocytes was examined, the expression of immunity-related genes including those encoding proteins necessary for phagocytosis was reduced in the cancer model. We then asked if hemocyte phagocytosis plays a role in the prevention of cancer. For this purpose, a cancer rate was determined in animals where phagocytosis, instead of apoptosis, was retarded, in addition to the inhibition of cell-cycle checkpoints. We found that a defect in phagocytosis augmented the occurrence of cancer caused by the inhibition of cell-cycle checkpoints to an extent seen after the simultaneous inhibition of apoptosis. These results indicated that phagocytosis plays a role in cancer prevention, and suggested that cancerous cells undergo apoptosis-dependent phagocytosis.