Signal Transduction in the Endothelium - Research Group Researchgroup

Vascular endothelial cell (EC) monolayer acts as a semiselective barrier between blood and the interstitium. EC barrier integrity is critical to tissue and organ function. Phosphorylation level of many cytoskeleton and cytoskeleton-associated proteins plays crucial role in the EC barrier function. We have shown the regulatory role of two major mammalian Ser/Thr-specific protein phosphatases (PP), type 1 and type 2A in maintaining EC cytoskeleton structure and barrier function. We also characterized the protein-protein interaction between the catalytic subunit of PP1 and TIMAP (TGF-beta inhibited membrane-associated protein, highly expressed in EC), and demonstrated the positive role of TIMAP in pulmonary EC barrier function. Our results indicated that phosphorylated or dephosphorylated forms of TIMAP mediate differently the phosphorylation level of the actin binding ERM (ezrin-radixin-moesin) proteins via regulation of PP1 in EC. ERM proteins serve as cross-linkers between actin filaments and plasma membranes and they are thought to be employed in cell adhesion, cell motility, etc. TIMAP contains ankyrin repeats allowing protein-protein interactions, therefore we intend to explore further potential interacting protein partners of TIMAP. ERM-binding phosphoprotein 50 (EBP50, aka NHERF1) is a member of the Na+/H+ exchanger regulatory factor (NHERF) family which consists of four related PDZ (postsynaptic density 95/discs-large/zona occludens-1) domain containing scaffolding proteins termed as NHERF1/EBP50, NHERF2/E3KARP, NHERF3/PDZK1, and NHERF4/IKEPP. Various type of proteins (transporters, ion channels, receptors, signaling proteins, structural proteins, etc.) may bind to the NHERF family proteins usually through the C-terminal PDZ binding domains of these target proteins. Only two of the NHERF family proteins, EBP50 and NHERF2, contain ERM binding domain at their C-termini.