Tetraspanin, extracellular domain or large extracellular loop (LEL), CD151_Like family. Tetraspanins are trans-membrane proteins with 4 trans-membrane segments. Both the N- and C-termini lie on the intracellular side of the membrane. This alignment model spans the extracellular domain between the 3rd and 4th trans-membrane segment. Tetraspanins are involved in diverse processes and their various functions may relate to their ability to act as molecular facilitators. Tetraspanins associate laterally with one another and cluster dynamically with numerous parnter domains in membrane microdomains, forming a network of multimolecular complexes, the "tetraspanin web". CD151strongly associates with integrins, especially alpha3beta1, alpha6beta1, alpha7beta1, and alpha6beta4; it may play roles in cell-cell adhesion, cell migration, platelet aggregation, and angiogenesis. For example, CD151 is is involved in regulation of migration of neutrophils, endothelial cells, and various tumor cell lines; it associates specifically with laminin-binding integrins and strengthens alpha6beta1 integrin-mediated adhesion to laminin-1; CD151 also specifically attenuates adhesion-dependent activation of Ras and correspdonding downstream effects, and is involved in epithelial cell-cell adhesion as a modulator of PKC- and Cdc42-dependent actin cytoskeletal reorganization.
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