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P-selectin
P-selectin is a protein that in humans is encoded by the SELP gene. P-selectin functions as a cell adhesion molecule (CAM) on the surfaces of activated endothelial cells, which line the inner surface of blood vessels, and activated platelets. In unactivated endothelial cells, it is stored in granules called Weibel-Palade bodies. In unactivated platelets P-selectin is stored in α-granules. Other names for P-selectin include CD62P, Granule Membrane Protein 140 (GMP-140), and Platelet Activation-Dependent Granule to External Membrane Protein (PADGEM). It was first identified in endothelial cells in 1989. == Gene and regulation ==
P-selectin is located on chromosome 1q21-q24, spans > 50 kb and contains 17 exons in humans. P-selectin is constitutively expressed in megakaryocytes (the precursor of platelets) and endothelial cells. P-selectin expression is induced by two distinct mechanisms. First, P-selectin is synthesized by megakaryocytes and endothelial cells, where it is sorted into the membranes of secretory granules. When megakaryocytes and endothelial cells are activated by agonists such as thrombin, P-selectin is rapidly translocated to the plasma membrane from granules. Secondly, increased levels of P-selectin mRNA and protein are induced by inflammatory mediators such as tumor necrosis factor-a (TNF-a), LPS, and interleukin-4 (IL-4). Although TNF-a and LPS increase levels of both mRNA and protein in murine models, they do not appear to affect mRNA in human endothelial cells, while IL-4 increases P-selectin transcription in both species.〔Liu et al., J. Exp. Med. Vol. 207 No. 13 2975-2987 www.jem.org/cgi/doi/10.1084/jem.20101545〕〔Panes et al., Br J Pharmacol. 1999 February; 126(3): 537–550. at page 538 〕 The elevated synthesis of P-selectin may play an important role in the delivery of protein to the cell surface. In ischemic stroke patients, plasma P-selectin concentration was reported to be highly correlated to plasminogen activator inhibitor-1 activity and tissue plasminogen activator activity.
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