TIMAP,a novel CAAX box protein regulated by TGF-beta1 and expressed in endothelial cells

Representational difference analysis ofthe glomerular endothelial cell response to transforming growthfactor-1 (TGF-1) revealed a novel gene, TIMAP (TGF--inhibitedmembrane-associated protein), which contains 10 exons and maps to humanchromosome 20.q11.22. By Northern blot, TIMAP mRNA is highly expressedin all cultured endothelial and hematopoietic cells. The frequency ofthe TIMAP SAGE tag is much greater in endothelial cell SAGE databasesthan in nonendothelial cells. Immunofluorescence studies of rat tissuesshow that anti-TIMAP antibodies localize to vascular endothelium.TGF-1 represses TIMAP through a protein synthesis- and histonedeacetylase-dependent process. The TIMAP protein contains five ankyrinrepeats, a protein phosphatase-1 (PP1)-interacting domain, aCOOH-terminal CAAX box, a domain arrangement similar to that of MYPT3,and a PP1 inhibitor. A green fluorescent protein-TIMAP fusion proteinlocalized to the plasma membrane in a CAAX box-dependent fashion.Hence, TIMAP is a novel gene highly expressed in endothelial andhematopoietic cells and regulated by TGF-1. On the basis of itsdomain structure, TIMAP may serve a signaling function, potentiallythrough interaction with PP1.