KLRK1 and neoplasm: The specific binding of NKG2D to the high expression of MICA, MICB, and ULBP on the surface of hepatoma cells can trigger multiple signaling pathways, such as phosphatidylinositol 3-hydroxy kinase (PI3K), phospholipase C Gamma 2 (PLCã2), c-Jun-NH(2)-terminal kinase (JNK), and others, which also further promote the anti-tumor effects of NK cells by secreting cytokines, enhancing ADCC effects, and initiates the apoptosis process [108].