TLR4 induces CCR7-dependent monocytes transmigration through the blood-brain barrier.

In this study, we examined whether bacterial pathogen-associated molecular patterns recognized by toll-like receptors (TLRs) can modify the CCR7-dependent migration of human monocytes. MonoMac-1 (MM-1) cells and freshly isolated human monocytes were cultivated in the presence of agonists for TLR4 (which senses lipopolysaccharides from gram-negative bacteria), TLR1/2 (which senses peptidoglycan from gram-positive bacteria), and TLR9 (which recognizes bacterial DNA rich in unmethylated CpG DNA). CCR7 mRNA transcription was measured using quantitative reverse transcription polymerase chain reaction and protein expression was examined using flow cytometry. CCR7 function was monitored using migration and transmigration assays in response to CCL19/CCL21, which are natural ligands for CCR7. Our results show that TLR4 strongly increases monocyte migratory capacity in response to CCL19 in chemotaxis and transmigration assays in a model that mimics the human blood-brain barrier, whereas TLR1/2 and 9 have no effect. Examination of monocyte migration in response to TLRs that are activated by bacterial components would contribute to understanding the excessive monocyte migration that characterizes the pathogenesis of bacterial infections and/or neuroinflammatory diseases.

CCL19-induced chemokine receptor 7 activates the phosphoinositide-3 kinase-mediated invasive pathway through Cdc42 in metastatic squamous cell carcinoma of the head and neck.

Metastatic squamous cell carcinoma of the head and neck (SCCHN) has been shown to express chemokine receptor 7 (CCR7), which activates phosphoinositide-3 kinase (PI3K) to promote invasion and survival of SCCHN cells. We hypothesized that Cdc42 might be involved in the CCR7-PI3K pathway. Adhesion assays, migration assays, immunofluorescence staining, Western blotting and immunohistochemical analysis were used to find whether Cdc42 can be activated by CCL19 (the CCR7 ligand) and its role in SCCHN. Results showed that CCL19 induced polarized localization of Cdc42 and actin polymerization in the leading edge of migrating cells. The level of activated membrane-bound Cdc42 was elevated, as measured by the GTPase activity pull-down assay. The increased membrane localization and membrane-bound activity of Cdc42 were abolished by CCR7 and PI3K inhibition, indicating the involvement of Cdc42 in the CCR7-PI3K cascade. Knockdown of Cdc42 by small interfering RNA (siRNA) led to significant reduction in the activation of Rac, filamentous actin (F-actin) accumulation as well as in the migration and invasion induced by CCL19. Taken together, our data indicate the important role played by Cdc42 in CCL19-induced migration and invasion of SCCHN cells.

CCR7-dependent stimulation of survival in dendritic cells involves inhibition of GSK3beta.

Chemokine receptor CCR7 regulates chemotaxis and survival in mature dendritic cells (DCs). We studied the role of glycogen synthase kinase-3beta (GSK3beta) in the regulation of CCR7-dependent survival. We show that GSK3beta behaves as a proapoptotic regulator in cultured monocyte-derived human DCs and murine splenic DCs in vitro, and in lymph node DCs in vivo. In keeping with its prosurvival role, stimulation of CCR7 induced phosphorylation/inhibition of GSK3beta, which was mediated by the prosurvival regulator Akt1, but it was independent of ERK1/2, a key regulator of chemotaxis. Stimulation of CCR7 also induced translocation of two transcription-factor targets of Akt, prosurvival NF-kappaB and proapoptotic FOXO1, to the nucleus and cytosol, respectively, resulting in DCs with a phenotype more resistant to apoptotic stimuli. We analyzed if GSK3beta was able to modulate the mobilizations of these transcription factors. Using pharmacological inhibitors, small interfering RNA, and a construct encoding constitutively active GSK3beta, we show that active GSK3beta fosters and hampers the translocations to the nucleus of FOXO and NF-kappaB, respectively. Inhibition of GSK3beta resulted in the degradation of the NF-kappaB inhibitor IkappaB, indicating a mechanism whereby GSK3 can control the translocation of NF-kappaB to the nucleus. GSK3beta and FOXO interacted in vivo, suggesting that this transcription factor could be a substrate of GSK3. The results provide a novel mechanism whereby active GSK3beta contributes to regulate apoptosis in DCs. They also suggest that upon stimulation of CCR7, Akt-mediated phosphorylation/inhibition of GSK3beta may be required to allow complete translocations of FOXO and NF-kappaB that confer DCs an extended survival.

Synergy-inducing chemokines enhance CCR2 ligand activities on monocytes.

The migration of monocytes to sites of inflammation is largely determined by their response to chemokines. Although the chemokine specificities and expression patterns of chemokine receptors are well defined, it is still a matter of debate how cells integrate the messages provided by different chemokines that are concomitantly produced in physiological or pathological situations in vivo. We present evidence for one regulatory mechanism of human monocyte trafficking. Monocytes can integrate stimuli provided by inflammatory chemokines in the presence of homeostatic chemokines. In particular, migration and cell responses could occur at much lower concentrations of the CCR2 agonists, in the presence of chemokines (CCL19 and CCL21) that per se do not act on monocytes. Binding studies on CCR2(+) cells showed that CCL19 and CCL21 do not compete with the CCR2 agonist CCL2. Furthermore, the presence of CCL19 or CCL21 could influence the degradation of CCL2 and CCL7 on cells expressing the decoy receptor D6. These findings disclose a new scenario to further comprehend the complexity of chemokine-based monocyte trafficking in a vast variety of human inflammatory disorders.

IL-21 promotes survival and maintains a naive phenotype in human CD4+ T lymphocytes.

IL-21 is a key T-cell growth factor (TCGF) involved in innate and adaptive immune response. It contributes to the proliferation of naive, but not memory T lymphocytes. However, the full spectrum of IL-21 activity on T cells remains unclear. Here, we demonstrate that IL-21 primarily maintains the expression of specific naive cell surface markers such as CD45RA, CD27, CD62L and CCR7 on human CD4(+) T lymphocytes and that the expression of CCR7 induces cell migration by means of CCL21 chemoattraction. These effects contrast with those of IL-2 which induced the marked proliferation of CD4(+) T lymphocytes, leading to an activated-memory phenotype. Nevertheless, IL-21 maintained cell cycle activation and expression of proliferation markers, including proliferating cell nuclear antigen and Ki-67, and triggered T-cell proliferation via TCR and co-stimulation pathways. Unlike IL-2, IL-21 decreased the expression of the anti-apoptotic Bcl-2 protein, which correlated with the absence of activation of the phosphatidylinositol 3'-kinase/Akt signaling pathway. Thus, IL-21 is a TCGF whose function is the preservation of a pool of CD4(+) T lymphocytes in a naive phenotype, with a low proliferation rate but with the persistence of cell cycling proteins and cell surface expression of CCR7. These findings strongly suggest that IL-21 plays a part in innate and adaptive immune response owing to homeostasis of T cells and their homing to secondary lymphoid organs.