Metalloproteinases Are Involved in Lipopolysaccharide– and Tumor Necrosis Factor-–Mediated Regulation of CXCR1 and CXCR2 Chemokine Receptor Expression

Abstract

The neutrophil-specific G-protein–coupled chemokine receptors, CXCR1 and CXCR2, bind with high affinity to the potent chemoattractant interleukin-8 (IL-8). The mechanisms of IL-8 receptor regulation are not well defined, although previous studies have suggested a process of ligand-promoted internalization as a putative regulatory pathway. Herein, we provide evidence for two distinct processes of CXCR1 and CXCR2 regulation. Confocal microscopy data showed a redistribution of CXCR1 expression from the cell surface of neutrophils to internal compartments after stimulation with IL-8, whereas stimulation with bacterial lipopolysaccharide (LPS) or tumor necrosis factor- (TNF-) did not induce CXCR1 internalization but instead mediated a significant loss of membrane-proximal CXCR1 staining intensity. To investigate whether proteolytic cleavage was the mechanism responsible for LPS- and TNF-–induced downmodulation of IL-8 receptors, we tested a panel of proteinase inhibitors. The downmodulation of CXCR1 and CXCR2 by LPS and TNF- was most dramatically inhibited by metalloproteinase inhibitors; 1,10-phenanthroline and EDTA significantly attenuated LPS- and TNF-–induced loss of CXCR1 and CXCR2 cell surface expression. Metalloproteinase inhibitors also blocked the release of CXCR1 cleavage fragments into the cell supernatants of LPS- and TNF-–stimulated neutrophils. In addition, while treatment of neutrophils with LPS and TNF- inhibited IL-8 receptor–mediated calcium mobilization and IL-8–directed neutrophil chemotaxis, both 1,10-phenanthroline and EDTA blocked these inhibitory processes. In contrast, metalloproteinase inhibitors did not affect IL-8–mediated downmodulation of CXCR1 and CXCR2 cell surface expression or receptor signaling. Thus, these findings may provide further insight into the mechanisms of leukocyte regulation during immunologic and inflammatory responses.

Expression and role of adiponectin receptor 1 in lipopolysaccharide‐induced proliferation of cultured rat adventitial fibroblasts

“…LPS-induced systemic inflammatory responses could increase neointima formation after balloon injury and stent implantation, with the resulting proliferation of smooth muscle cells playing a key role in atherogenesis (Danenberg et al, 2002). Bacterial substances and inflammatory cytokines can down-regulate leucocyte chemokine receptors and chemokine responsiveness (Bhattacharya et al, 1997;Khandaker et al, 1999). In our study, LPS treatment of rat AFs down-regulated Adipo1 expression in a dose-and time-dependent manner and increased the proliferation of AFs.…”

The mechanism for activation of the neutrophil NADPH‐oxidase by the peptides formyl‐Met‐Leu‐Phe and Trp‐Lys‐Tyr‐Met‐Val‐Met differs from that for interleukin‐8

“…This down-regulation of CXCRs, induced by TNF-a, has been suggested by others to be caused by receptor internalization and/or proteolytic cleavage of surface-exposed receptors. 32,33 The difference in localization of FPRs and CXCRs probably reflects the different nature of their agonists as being end-point or intermediate chemoattractants, respectively. In the first stage of migration, neutrophils sense mainly intermediate chemoattractants, such as IL-8, and thus it is reasonable that the corresponding receptors are expressed on the cell surface.…”

International Union of Basic and Clinical Pharmacology. LXXXIX. Update on the Extended Family of Chemokine Receptors and Introducing a New Nomenclature for Atypical Chemokine Receptors

“…3. Expression of CXCR1 and CXCR2 is tightly regulated in neutrophils by external signals such as tumor necrosis factor (TNF)-a, lipopolysaccharide (LPS), Toll-like receptor (TLR) agonists, and nitric oxide (Khandaker et al, 1999;Alves-Filho et al, 2009).…”