Flowing leukocytes use[unreadable] the glycoprotein PSGL-1 to tether to and roll on P-selectin on activated[unreadable] endothelial cells and platelets. These two proteins are a novel prototype[unreadable] for a lectin-glycoprotein interaction that mediates cell adhesion and[unreadable] signaling. The investigator and coworkers have obtained preliminary data[unreadable] suggesting that P-selectin and PSGL-1 dimerize in the membrane and interact[unreadable] with cytoplasmic proteins. They hypothesize that the transmembrane and[unreadable] cytoplasmic domains mediate these interactions, which in turn regulate the[unreadable] cell surface distributions, adhesive functions, and signaling capabilities[unreadable] of P-selectin and PSGL-1. There are five specific aims: 1) determine[unreadable] whether the cytoplasmic domain of P-selectin regulates its cell surface[unreadable] distribution and its adhesive function, 2) determine whether P-selectin[unreadable] dimerizes in the membrane, and if so, whether dimerization affects its[unreadable] adhesive function or internalization efficiency, 3) determine whether the[unreadable] cytoplasmic or transmembrane domain of PSGL-1 regulates its dimerization,[unreadable] cell surface distribution, or adhesive function, 4) identify proteins that[unreadable] are phosphorylated upon PSGL-1 engagement and determine whether the[unreadable] transmembrane and cytoplasmic domains of PSGL-1 are required for signaling,[unreadable] and 5) characterize proteins that bind to the cytoplasmic domains of PSGL-1.