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. How do you suppose that overexpression of this protein accounts for the survival of tumor cells?

Group of answer choices

Protein will inactivate executioner caspases

Protein will inhibit release of Cytochrome c from the mitochondria

Protein will inhibit Bax and Bak-mediated pore formation in the mitochondria

Protein binds to Fas ligand

Answer 1

Apoptosis is programmed cell death which is energy dependent process. There is one intrinsic pathway in apoptosis and one extrinsic pathway both of which are caspases protein dependent. In extrinsic pathway Fas receptor(fatty acid synthase)and Fas ligand are involved.

FasR Receptor is present on target cells and FasL ligand on cytotoxic T lymphocytes and natural killer cells. Cells expressing FasR interect with cytotoxic T cells with there FasL and interaction lead to activation of FADD ( Fas- association Death domain) activation. FADD then recruit initiator caspases procaspase 8 which is cleaved to form active caspase 8. Caspase 8 activates executional caspases ( caspase 3 , caspase 7) which cleaves cell material and lead to cell death.

c - FLIP is protein which bind to FADD and caspases8 to inhibit them.

Protein can bind to executional caspases and make them inactive leading to no apoptosis. It can also bind to Fas ligand making it unable to bind to Fas receptor leading no acrivation of FADD domain. So first and forth Option both are correct choices for this question . Cyt c and bax and bak protein both options are wrong because they are involved in intrinsic pathway of apoptosis not in extrinsic pathway mediated by Fas ligand and Fas receptor.