Epithelial tumors express MIC proteins on their cell surfaces

Question

A. Why does this make the tumor cells susceptible to attack by NK cells, ?:? T cells, and cytotoxic CD8 T cells?
B. How do the tumor cells evade such attack?

Answer 1

A. MIC proteins are ligands for the activating receptor NKG2D, which is expressed by NK cells, γ:δ T cells, and cytotoxic CD8 T cells, and activates these cells to kill the tumor cells.
B. Some of the tumor cells evade being killed by expressing a protease that cleaves MIC from the cell surface. When the soluble MIC product binds to the NKG2D receptors on NK cells, γ:δ T cells, and cytotoxic T cells it induces receptor-mediated endocytosis, thus reducing the level of NKG2D on the surface of these cells. Together with the removal of MIC from tumor-cell surfaces, this helps the tumor cells evade cell-mediated killing.