Question

One important role of Fas and Fas ligand is to mediate the elimination of tumor cells by killer lymphocytes. In a study of 35 primary lung and colon tumors, half the tumors were found to have amplified and overexpressed a gene for a secreted protein that binds to Fas ligand. How do you suppose that overexpression of this protein might contribute to the survival of these tumor cells? Explain your reasoning.

Answer 1

Fas and Fas Ligand (FasL, which is a type II transmembrane protein belongs to TNF family) are two molecules which are involved in the regulation of cell death.

The interaction of these two (Fas and Fas Ligand) leads to activation-induced cell death (a form of apoptosis) in tumor-specific lymphocytes induced by repeated TCR (T cell receptor) stimulation, responsible for the peripheral deletion of activated T cells.

Now since, we know that Fas and Fas Ligand is important for apoptosis. The downstream pathway for apoptosis gets activated after binding of these two. If FasL is blocked by some other protein then the downstream pathway leading to apoptosis will be blocked which could lead to tumor formations.

hence, in the half of the tumors it is found that the gene of a secreted protein that bind to FasL in place of Fas is overexpressed.