The AP-2 family of transcription factors

The AP-2 family of transcription factors consists of five different proteins in humans and mice: AP-2 alpha,AP-2 beta, AP-2 gamma, AP-2 delta and AP-2 epsilon. Frogs and fish have known orthologs of some but not all of these proteins, and homologs of the family are also found in protochordates, insects and nematodes. The proteins have a characteristic helix-span-helix motif at the carboxyl terminus, which, together with a central basic region, mediates dimerization and DNA binding. The amino terminus contains the transactivation domain. AP-2 proteins are first expressed in primitive ectoderm of invertebrates and vertebrates; in vertebrates, they are also expressed in the emerging neural-crest cells, and AP-2 alpha(-/-) animals have impairments in neural-crest-derived facial structures. AP-2 beta is indispensable for kidney development and AP-2 gamma is necessary for the formation of trophectoderm cells shortly after implantation; AP-2 alpha and AP-2 gamma levels are elevated in human mammary carcinoma and seminoma. The general functions of the family appear to be the cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development.