Role of Tyrosine Phosphorylation in Ligand-independent Sequestration of CXCR4 in Human Primary Monocytes-Macrophages

Abstract

The chemokine stromal cell-derived factor (SDF)-1 and its receptor, CXCR4, play important roles in human immunodeficiency virus type 1 (HIV-1) pathophysiology, leukocyte trafficking, inflammation, hematopoiesis, embryogenesis, angiogenesis, and cancer metastasis. The effects of cytokines on the regulation of CXCR4 function were investigated in human primary monocytes-macrophages. The expression of functional CXCR4 on the cell surface was demonstrated by the detection of ligandinduced Ca 2؉ mobilization, chemotaxis, and ligand-induced receptor endocytosis. Surface CXCR4 expression was down-regulated by cytokines interleukin-4 (IL-4), IL-13, and granulocyte-macrophage colony-stimulating factor (GM-CSF) and up-regulated by IL-10 and transforming growth factor-␤1. Down-regulation was mediated post-translationally, in the absence of protein degradation, through an endocytotic mechanism. In contrast to SDF-1␣-induced CXCR4 endocytosis, cytokine-induced endocytosis of this receptor was independent of actin filament polymerization. GM-CSF increased the expression of G protein-coupled receptor kinase 3 (GRK3), ␤-arrestin-1, Pyk2, and focal adhesion kinase (FAK). Cytokine treatment also increased the total and tyrosine-specific phosphorylation of CXCR4 as well as the phosphorylation of FAK on tyrosine 397. It also induced the formation of GRK3⅐CXCR4 or FAK⅐CXCR4 complexes. Infection of macrophages by primary R5X4 and X4 isolates of HIV-1 was inhibited by IL-4, IL-13, and GM-CSF, an effect that was associated with down-regulation of surface CXCR4 expression. These data indicate that ligand-dependent and ligand-independent endocytoses of CXCR4 are mediated by different mechanisms. Cytokine-induced endocytosis of chemokine receptors may be of therapeutic value in HIV-1 infection, inflammation, tumor metastasis, and defective hematopoiesis.Macrophages and T lymphocytes are the major targets of HIV-1 1 infection and constitute the productive viral reservoirs (1, 2). Three types of HIV-1 isolates that infect macrophages have been identified and differ according to the chemokine receptor targeted for use as a viral coreceptor: (i) R5 viruses infect macrophages and primary CD4 ϩ T cells through CCR5 and constitute the principal virus type transmitted in vivo, as indicated by the resistance to HIV-1 infection of individuals who lack functional CCR5(3-5). (ii) Primary X4 viruses that have not been subjected to extensive passage in vitro use CXCR4 as a coreceptor and infect primary CD4 ϩ T cells, T cell lines, and macrophages (6). These viruses emerge later in infection than do R5 viruses and are associated with disease progression. Laboratory-adapted X4 viruses lose the ability to infect macrophages but still replicate in primary CD4 ϩ T cells and T cell lines. (iii) R5X4 viruses infect macrophages through either CCR5 or CXCR4 (7, 8) and may represent an important intermediate viral phenotype during the transition from R5 to X4 virus types (9) during the course of infection.Host factors are important contributors to the pathogenesi...

The Mechanism of Chemokine Receptor 9 Internalization Triggered by Interleukin 2 and Interleukin 4

“…But there are also exceptions, such as granulocyte-macrophage colony-stimulating factor increased the abundance of GRK3 and might contribute to the sequestration of CXCR4 in human primary monocytederived macrophages (31). The similar result was found in our experiments, as pan-GRK inhibitor (heparin) also prevented the CCR9 internalization triggered by IL-2 and IL-4 together.…”

Post‐translational and cell type‐specific regulation of CXCR4 expression by cytokines

“…For example, rapid internalization of CXCR4 was observed after stimulation of lymphocytes with phorbol esters [14,26]. Interestingly, for monocytes Wang et al reported a down-modulation of CXCR4 from the cell surface after overnight stimulation with GM-CSF, while lymphocytes were not affected [27]. Cytokine-induced down-regulation of CXCR4 from the cell surface of monocytes was mediated through an endocytotic mechanism in the absence of protein degradation, similar to our observations for cytokine-induced internalization of CXCR4 on neutrophils.…”

The salivary glands as a privileged site of cytomegalovirus immune evasion and persistence

“…However, this model using KO mice must consider the fact that these animals may be compromised in the ability of monocytes to traYc to SG, the primary means by which virus seeds this organ. Indeed, IL-10 modulates expression of chemokine receptors on at least human monocytes, with reports of IL-10 mediated upregulation of CCR2, CCR5, and CXCR4 [14,16,47,56,60]. It is possible therefore that in the absence of IL-10, less virus entered the SG, as opposed or in addition to more rapid and eYcient viral clearance.…”