8.A.130. The Transmembrane Protein 204 (TMEM204) Family
TMEM204, a 4 TMS (1 + 3 TMS arrangement) of Homo sapiens can influence paracellular permeability, and it appears to be involved in cell-cell interactions through adherens. Ir is a hypoxically regulated junctional protein (claudin-like protein of 24 kDa, CLP24) (Kearsey et al. 2004). It shows homology to the myelin protein 22/epithelial membrane protein 1/claudin family of cell junction proteins, which are involved in the modulation of paracellular permeability. The CLP24 protein contains a C-terminal protein-protein interaction domain, characteristic of the four transmembrane spanning (tetraspan) family of proteins, which includes myelin protein 22, and are involved in cell adhesion at tight, gap and adherens junctions. Expression profiling analyses showed that CLP24 is highly expressed in lung, heart, kidney and placental tissues. Cellular studies confirmed that the CLP24 protein localizes to cell-cell junctions and co-localizes with the beta-catenin adherens junction-associated protein but not with tight junctions. Over-expression of CLP24 results in decreased adhesion between cells, and functional paracellular flux studies confirm that over-expression of the CLP24 protein modulates the junctional barrier function (Kearsey et al. 2004).