CD45 Modulation of CXCR1 and CXCR2 in Human Polymorphonuclear Leukocytes

All leukocytes express the cell surface glycoprotein CD45, which has intrinsic intracellular protein tyrosine phosphatase activity. CD45 is known to play a regulatory role in activation-induced signaling in lymphocytes; however, little is known of its role in non-lymphoid leukocytes. Therefore, we examined the potential effect of CD45 on chemokine-induced signaling in human neutrophils (polymorphonuclear cells, PMN). Treating isolated PMN for 2 h with an anti-CD45RB antibody (Bra11) down-modulated expression of the chemokine receptors CXCR1 and CXCR2 to 44 +/- 10% and 47 +/- 9% of their respective controls. The tyrosine kinase inhibitors genistein and herbimycin A significantly inhibited the Bra11-induced down-modulation of CXCR1 and CXCR2. Furthermore, Bra11-treated PMN were functionally inhibited in their capacity to exhibit IL-8-induced transient intracellular Ca2+ increases. Selected targeting of CXC receptors is indicated by the fact that N-formyl-Met-Leu-Phe (fMLP) receptor expression and function were not lost following Bra11 treatment. The effect of Bra11 on IL-8-mediated function and receptor expression was paralleled by decreased tyrosine phosphorylation of a 54- to 60-kDa protein. These findings indicate that CD45 can act to modulate PMN responses to chemokines; thus agents regulating CD45 can potentially modulate leukocyte traffic and may represent a novel therapeutic approach towards the treatment of inflammatory diseases

Identification of a Novel Mechanism for Endotoxin-mediated Down-modulation of CC Chemokine Receptor Expression

In the present study, we explored the molecular mechanisms by which bacterial endotoxin (LPS) mediates the down-regulation of CCR2 receptors on human monocytes. We found that LPS induced a marked reduction in CCR2 cell surface protein levels which was blocked by pretreatment with the tyrosine kinase inhibitors genistein and herbimycin A. The effector mechanism underlying LPS-induced CCR2 down-modulation appears to involve the enzymatic activity of proteinases since Western blot analysis of LPS-stimulated monocytes revealed the degradation of a 38-kDa species corresponding to the CCR2B monomer. In RBL cells expressing the CCR2B-green fluorescent protein (GFP) fusion chemokine receptor, LPS stimulated the internalization and degradation of CCR2. The serine proteinase inhibitor N-alpha-p-tosyl-L-lysine chloromethyl ketone blocked LPS-induced down-modulation of CCR2 in monocytes and CCR2B-GFP in RBL cells. This work describes a previously uncharacterized mechanism for CC chemokine receptor down-modulation that is dependent upon tyrosine kinase activation and serine proteinase-mediated receptor degradation and may provide further insight into the mechanisms of leukocyte regulation during immunological and inflammatory responses