Fas "counterattack" by cancer cells
Fas-mediated apoptosis is blocked in tumors with mutations in Fas or in the tumor suppressor gene p53, in enzymes involved in the early caspase cascade, or in tumors expressing abnormal levels of proteins involved in signal transduction. For example, increased resistance towards Fas-mediated apoptosis results from down-regulation of caspase-1 and selective members of the apoptosis-inducing Bcl-2 family of molecules, or by upregulation of Bcl-2. In addition, some tumor cells can prevent Fas Ligand (FasL)-induced apoptosis by the release of soluble Fas (3).
Tumors may use FasL/Fas to eliminate Fas-expressing leukocytes, including cytotoxic T-cells (Tc). This may occur through constitutive expression of FasL, or by release of soluble FasL.
