Background：

Atypical E2F transcription factor that participates in various processes such as angiogenesis and polyploidization of specialized cells. Mainly acts as a transcription repressor that binds DNA independently of DP proteins and specifically recognizes the E2 recognition site 5’-TTTC[CG]CGC-3’. Directly represses transcription of classical E2F transcription factors such as E2F1: component of a feedback loop in S phase by repressing the expression of E2F1， thereby preventing p53/TP53-dependent apoptosis. Plays a key role in polyploidization of cells in placenta and liver by regulating the endocycle， probably by repressing genes promoting cytokinesis and antagonizing action of classical E2F proteins (E2F1， E2F2 and/or E2F3). Required for placental development by promoting polyploidization of trophoblast giant cells. Acts as a promoter of sprouting angiogenesis， possibly by acting as a transcription activator: associates with HIF1A， recognizes and binds the VEGFA promoter， which is different from ca