Distinct and overlapping roles for E2F family members in transcription, proliferation and apoptosis

Since the discovery almost fifteen years ago that E2F transcription factors are key targets of the retinoblastoma protein (RB), studies of the E2F family have uncovered critical roles in the control of transcription, cell cycle and apoptosis. E2F proteins are encoded by at least eight genes, E2F1 through E2F8. While specific roles for individual E2Fs in mediating the effects of RB loss are emerging, it is also becoming clear that there are no simple divisions of labor among the E2F family. Instead, an individual E2F can function to activate or repress transcription, promote or impede cell cycle progression and enhance or inhibit cell death, dependent on the cellular context. While functional redundancy among E2Fs and the striking influences of cellular context on the effects of E2F loss or gain of function have prevented a simple delineation of unique functions within the E2F family, these complexities undoubtedly reflect the extensive regulation and importance of this transcription factor family.