14-3-3 proteins are a family of homologous eukaryotic molecules with seven distinct isoforms in mammalian cells. Isoforms of 14-3-3 proteins interact with diverse ligands and are involved in the regulation of mitogenesis, cell cycle progression, and apoptosis. However, whether different 14-3-3 isoforms are responsible for distinct functions remains elusive. Here we report that multiple isoforms of 14-3-3 proteins were capable of binding to several ligands, Bad, Raf-1, and Cbl. In a functional assay of 14-3-3 isoforms, all mammalian 14-3-3 isoforms could inhibit Bad-induced apoptosis. Thus, 14-3-3 function in regulating one of its ligands, Bad, is conserved among mammalian isoforms. We addressed whether 14-3-3 isoforms are differentially expressed in tissues, which may in part determine isoform-specific interactions. In situ hybridization revealed that 14-3-3zeta was present in most tissues tested, but sigma was preferentially expressed in epithelial cells. Thus, isoforms of 14-3-3 can interact and control the function of selected protein ligands, and differential tissue distribution of 14-3-3 isoforms may contribute to their specific interactions and subsequent downstream signaling events.
Copyright 2001 Academic Press.