The E2F-1 Transcription Factor Promotes Caspase-8 and Bid Expression, and Enhances Fas Signaling in T Cells

The immune system depends on the extensive proliferation of rare Ag-specific precursor T lymphocytes, followed by their differentiation, the delivery of effector function, and finally death by apoptosis. T cells that lack the E2F-1 transcription factor, which is activated as cells pass the restriction point and enter S phase, show defects in activation-induced cell death. We now report that E2F-1 increases the activity of an apoptotic pathway that is important in murine primary T cells. Thus, E2F-1 promotes the transcription of Bid, a molecule that links death receptor signaling to the activation of apoptotic mechanisms in mitochondria. It also promotes the transcription of caspase-8, the enzyme that cleaves and activates Bid. Enforced expression of Bid can partially restore apoptosis in E2F-1-deficient T cells. Thus, E2F-1 integrates cell cycle progression with apoptosis.