BACKGROUND/AIMS: The developed liver is able to tightly control cellular proliferation, rapidly switching from quiescence to growth in response to specific stimuli. This suggests that growth inhibitors may be involved in the control of liver growth. We analyzed the role of the Spred-family of growth inhibitors in the liver. METHODS: We screened human EST databases for Spred-related sequences. Clones were isolated, sequenced, epitope-tagged and expressed. Subcellular localization of clones were determined and their effects on cellular signaling pathways analysed using specific antibodies. Cell cycle progression assays and protein interaction studies were initiated. Organ distribution of transcripts and their expression throughout liver development and in primary hepatocytes were recorded. RESULTS: We have identified a new, liver-restricted protein, Eve-3, containing a single Ena Vasp homology (EVH1) domain that can potently block activation of the Ras/MAPK pathway. Eve-3 is specific in inhibiting the Ras/MAPK pathway. Eve-3 can block serum-mediated cell cycle progression and its expression is highly regulated during liver development. CONCLUSIONS: The liver is the only organ that can regulate its growth and mass. Eve-3 may act as an inhibitor of proliferation pathways in the mature liver and be involved in modulating the unique regenerative capacity of this organ.