We have previously shown that myosin light chain phosphatase (MLC PPase) is a key determinant in the regulation of endothelial cell (EC) permeability. Most of the functional characteristics of MLC PPase are determined by its regulatory subunit-MYPT1 and include binding to the catalytic subunit and targeting it to MLC insuring substrate specifity. In addition, it was recently discovered that MLC PPase activity can be regulated by several endogenous inhibitory proteins. The inhibitory subunits/proteins include MYPT3, protein inhibitor CPI-17, and a recently discovered TIMAP (TGF-b-inhibited membrane-associated protein). Hence regulation of EC MLC PPase may involve several targeting subunits and endogenous inhibitory proteins, as well as other cytoskeletal proteins. TIMAP shares significant domain homology with MYPT3, which specifically inhibits PPase activity toward MLC and myosin in vitro. TIMAP is highly expressed in EC and may be involved in endothelial cytoskeletal and barrier regulation. However, the exact role of TIMAP in regulation of MLC PPase activity has not been yet reported. BacterioMatch Two-Hybrid System (Stratagene) was applied for screening of human lung cDNA library in order to identify potential human TIMAP interaction proteins in the lung. Seven potential TIMAP interacting partner proteins were identified. Four of identified proteins, cysteine- and glycine-rich protein 1, eukaryotic translation elongation factor 2, U5 snRNP-specific protein 116 kD, and solute carrier family 3 member 2, are involved in actin cytoskeleton organization, cell adhesion or translation, and transcriptional regulation. However, the exact role of these regulatory proteins in endothelial cytoskeletal and barrier regulation is yet to be found. Collectively, these data suggest involvement of TIMAP in the regulation of EC cytoskeleton.
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