Role of tyrosine phosphorylation in ligand-independent sequestration of CXCR4 in human primary monocytes-macrophages

Aberrant regulation of CXCR4 in cancer via deviant microRNA-targeted interactions

CXCR4 is involved in many facets of cancer, including being a major player in establishing metastasis. This is in part due to the deregulation of CXCR4, which can be attributed to many genetic and epigenetic mechanisms, including aberrant microRNA-CXCR4 interaction. MicroRNAs (miRNAs) are a type of small non-coding RNA that primarily targets the 3' UTR of mRNA transcripts, which in turn suppresses mRNA and subsequent protein expression. In this review, we reported and characterized the many aberrant miRNA-CXCR4 interactions that occur throughout human cancers. In particular, we reported known target sequences located on the 3' UTR of CXCR4 transcripts that tumour suppressor miRNAs bind and therefore regulate expression by. From these aberrant interactions, we also documented affected downstream genes/pathways and whether a particular tumour suppressor miRNA was reported as a prognostic marker in its respected cancer type. In addition, a limited number of cancer-causing miRNAs coined 'oncomirs' were reported and described in relation to CXCR4 regulation. Moreover, the mechanisms underlying both tumour suppressor and oncomir deregulations concerning CXCR4 expression were also explored. Furthermore, the miR-146a-CXCR4 axis was delineated in oncoviral infected endothelial cells in the context of virus-causing cancers. Lastly, miRNA-driven therapies and CXCR4 antagonist drugs were discussed as potential future treatment options in reported cancers pertaining to deregulated miRNA-CXCR4 interactions.

Demystifying the CXCR4 conundrum in cancer biology: Beyond the surface signaling paradigm

The oncogenic chemokine duo CXCR4-CXCL12/SDF-1 (C-X-C Receptor 4-C-X-C Ligand 12/ Stromal-derived factor 1) has been the topic of intense scientific disquisitions since Muller et al., in her ground-breaking research, described this axis as a critical determinant of organ-specific metastasis in breast cancer. Elevated CXCR4 levels correlate with distant metastases, poor prognosis, and unfavourable outcomes in most solid tumors. Therapeutic impediment of the axis in clinics with Food and Drug Administration (FDA) approved inhibitors like AMD3100 or Plerixafor yield dubious results, contrary to pre-clinical developments. Clinical trials entailing inhibition of CXCR7 (C-X-C Receptor 7), another convicted chemokine receptor that exhibits affinity for CXCL12, reveal outcomes analogous to that of CXCR4-CXCL12 axis blockade. Of note, the cellular CXCR4 knockout phenotype varies largely from that of inhibitor treatments. These shaky findings pique great curiosity to delve further into the realm of this infamous chemokine receptor to provide a probable explanation. A multitude of recent reports suggests the presence of an increased intracellular CXCR4 pool in various cancers, both cytoplasmic and nuclear. This intracellular CXCR4 protein reserve seems active as it correlates with vital tumor attributes, viz. prognosis, aggressiveness, metastasis, and disease-free survival. Diminishing this entire intracellular CXCR4 load apart from the surface signals looks encouraging from a therapeutic point of view. Transcending beyond the classically accepted concept of ligand-mediated surface signaling, this review sheds new light on plausible associations of intracellularly compartmentalised CXCR4 with various aspects of tumorigenesis. Besides, this review also puts forward a comprehensive account of CXCR4 regulation in different cancers.

Predicting Human Protein Subcellular Locations by Using a Combination of Network and Function Features

Given the limitation of technologies, the subcellular localizations of proteins are difficult to identify. Predicting the subcellular localization and the intercellular distribution patterns of proteins in accordance with their specific biological roles, including validated functions, relationships with other proteins, and even their specific sequence characteristics, is necessary. The computational prediction of protein subcellular localizations can be performed on the basis of the sequence and the functional characteristics. In this study, the protein-protein interaction network, functional annotation of proteins and a group of direct proteins with known subcellular localization were used to construct models. To build efficient models, several powerful machine learning algorithms, including two feature selection methods, four classification algorithms, were employed. Some key proteins and functional terms were discovered, which may provide important contributions for determining protein subcellular locations. Furthermore, some quantitative rules were established to identify the potential subcellular localizations of proteins. As the first prediction model that uses direct protein annotation information (i.e., functional features) and STRING-based protein-protein interaction network (i.e., network features), our computational model can help promote the development of predictive technologies on subcellular localizations and provide a new approach for exploring the protein subcellular localization patterns and their potential biological importance.

Tumor-Associated Macrophage Promotes the Survival of Cancer Cells upon Docetaxel Chemotherapy via the CSF1/CSF1R-CXCL12/CXCR4 Axis in Castration-Resistant Prostate Cancer

Castration-resistant prostate cancer (CRPC) is an advanced stage of prostate cancer that can progress rapidly even in patients treated with castration. Previously, we found that tumor-associated macrophages (TAM) can be recruited by CSF-1 secreted by docetaxel-treated prostate cancer cells and promote the survival of cancer cells in response to chemotherapy. The inhibition of CSF-1R can impede this effect and significantly prolong survival in xenograft mice. However, the actual mechanism of how TAM improves cancer cell survival still remains elusive and controversial. Here, for the first time, we found that the enhanced survival of cancer cells achieved by TAM was mainly mediated by CXCR4 activation from the increased secretion of CXCL12 from CSF-1 activated TAM. This finding helps to clarify the mechanism of chemoresistance for second-line chemotherapy using docetaxel, facilitating the development of novel drugs to overcome immune tolerance in castration-resistant prostate cancer.

Rab5 regulates macropinocytosis by recruiting the inositol 5-phosphatases OCRL and Inpp5b that hydrolyse PtdIns(4,5)P2

Rab5 is required for macropinosome formation, but its site and mode of action remain unknown. We report that Rab5 acts at the plasma membrane, downstream of ruffling, to promote macropinosome sealing and scission. Dominant-negative Rab5, which obliterates macropinocytosis, had no effect on the development of membrane ruffles. However, Rab5-containing vesicles were recruited to circular membrane ruffles, and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent endomembrane fusion was necessary for the completion of macropinocytosis. This fusion event coincided with the disappearance of PtdIns(4,5)P2 that accompanies macropinosome closure. Counteracting the depletion of PtdIns(4,5)P2 by expression of phosphatidylinositol-4-phosphate 5-kinase impaired macropinosome formation. Importantly, we found that the removal of PtdIns(4,5)P2 is dependent on Rab5, through the Rab5-mediated recruitment of the inositol 5-phosphatases OCRL and Inpp5b, via APPL1. Knockdown of OCRL and Inpp5b, or APPL1, prevented macropinosome closure without affecting ruffling. We therefore propose that Rab5 is essential for the clearance of PtdIns(4,5)P2 needed to complete the scission of macropinosomes or to prevent their back-fusion with the plasmalemma.

ERK1/2 Signaling Induces Upregulation of ANGPT2 and CXCR4 to Mediate Liver Metastasis in Colon Cancer

Carcinoma development in colorectal cancer is driven by genetic alterations in numerous signaling pathways. Alterations in the RAS-ERK1/2 pathway are associated with the shortest overall survival for patients after diagnosis of colorectal cancer metastatic disease, yet how RAS-ERK signaling regulates colorectal cancer metastasis remains unknown. In this study, we used an unbiased screening approach based on selection of highly liver metastatic colorectal cancer cells in vivo to determine genes associated with metastasis. From this, an ERK1/2-controlled metastatic gene set (EMGS) was defined. EMGS was associated with increased recurrence and reduced survival in patients with colorectal cancer tumors. Higher levels of EMGS expression were detected in the colorectal cancer subsets consensus molecular subtype (CMS)1 and CMS4. ANGPT2 and CXCR4, two genes within the EMGS, were subjected to gain-of-function and loss-of-function studies in several colorectal cancer cell lines and then tested in clinical samples. The RAS-ERK1/2 axis controlled expression of the cytokine ANGPT2 and the cytokine receptor CXCR4 in colorectal cancer cells, which facilitated development of liver but not lung metastases, suggesting that ANGPT2 and CXCR4 are important for metastatic outgrowth in the liver. CXCR4 controlled the expression of cytokines IL10 and CXCL1, providing evidence for a causal role of IL10 in supporting liver colonization. In summary, these studies demonstrate that amplification of ERK1/2 signaling in KRAS-mutated colorectal cancer cells affects the cytokine milieu of the tumors, possibly affecting tumor-stroma interactions and favoring liver metastasis formation. SIGNIFICANCE: These findings identify amplified ERK1/2 signaling in KRAS-mutated colorectal cancer cells as a driver of tumor-stroma interactions that favor formation of metastases in the liver.

β-arrestin 1 transfection induced cell death in high grade glioma in vitro

The best known functions of β-arrestins (β-arr) are to regulate G protein-coupled receptors (GPCR) signaling through receptor desensitization and internalization. Many reports also suggest that β-arrs play important role in immune regulation and inflammatory responses, under physiological and pathological conditions. Recent studies have shown that β-arr 1 silencing halts proliferation and increases temozolomide (TMZ) response in glioblastoma (GBM) cells. The focus of this paper is to analyze the role of β-arr 1 overexpression in the 18 high grade glioma (HGG) cell line in terms of viability and their response to TMZ treatment. For this reason, the cell line was transfected with β-arr 1 and the effect was analyzed after 24 h, 48 h and 72 h in terms of proliferation and treatment response. We observed that β-arr 1 overexpression induced a time and dose dependant inhibition in the HGG cells. Unexpectedly, β-arr transfection resulted in a very mild increase in TMZ toxicity after 24 h, becoming non-statistically significant at 72 h. In conclusion, we showed that β-arr 1 overexpression inhibits cell proliferation in the 18 cell line but only has a very modest effect on treatment response with the alkylating agent TMZ.

Biclustering-based association rule mining approach for predicting cancer-associated protein interactions

Protein-protein interactions (PPIs) have been widely used to understand different biological processes and cellular functions associated with several diseases like cancer. Although some cancer-related protein interaction databases are available, lack of experimental data and conflicting PPI data among different available databases have slowed down the cancer research. Therefore, in this study, the authors have focused on various proteins that are directly related to different types of cancer disease. They have prepared a PPI database between cancer-associated proteins with the rest of the human proteins. They have also incorporated the annotation type and direction of each interaction. Subsequently, a biclustering-based association rule mining algorithm is applied to predict new interactions with type and direction. This study shows the prediction power of association rule mining algorithm over the traditional classifier model without choosing a negative data set. The time complexity of the biclustering-based association rule mining is also analysed and compared to traditional association rule mining. The authors are able to discover 38 new PPIs which are not present in the cancer database. The biological relevance of these newly predicted interactions is analysed by published literature. Recognition of such interactions may accelerate a way of developing new drugs to prevent different cancer-related diseases.

Constitutive and stimulated macropinocytosis in macrophages: roles in immunity and in the pathogenesis of atherosclerosis

Macrophages respond to several stimuli by forming florid membrane ruffles that lead to fluid uptake by macropinocytosis. This type of induced macropinocytosis, executed by a variety of non-malignant and malignant cells, is initiated by transmembrane receptors and is involved in nutrient acquisition and mTOR signalling. However, macrophages also perform a unique type of constitutive ruffling and macropinocytosis that is dependent on the presence of extracellular calcium. Calcium-sensing receptors are responsible for this activity. This distinct form of macropinocytosis enables macrophages to continuously sample their microenvironment for antigenic molecules and for pathogen- and danger-associated molecular patterns, as part of their immune surveillance functions. Interestingly, even within the monocyte lineage, there are differences in macropinocytic ability that reflect the polarized functional roles of distinct macrophage subsets. This review discusses the shared and distinct features of both induced and constitutive macropinocytosis displayed by the macrophage lineage and their roles in physiology, immunity and pathophysiology. In particular, we analyse the role of macropinocytosis in the uptake of modified low-density lipoprotein (LDL) and its contribution to foam cell and atherosclerotic plaque formation. We propose a combined role of scavenger receptors and constitutive macropinocytosis in oxidized LDL uptake, a process we have termed 'receptor-assisted macropinocytosis'. This article is part of the Theo Murphy meeting issue 'Macropinocytosis'.

Pancreatic adenocarcinoma up-regulated factor (PAUF) enhances the accumulation and functional activity of myeloid-derived suppressor cells (MDSCs) in pancreatic cancer

Pancreatic cancer is characterized by an immunosuppressive tumor microenvironment (TME) with a profound immune infiltrate populated by a significant number of myeloid-derived suppressor cells (MDSCs). MDSCs have been increasingly recognized for their role in immune evasion and cancer progression as well as their potential as a target for immunotherapy. However, not much is known about the mechanisms regulating their behavior and function in the pancreatic TME. Here we report that pancreatic adenocarcinoma up-regulated factor (PAUF), a soluble protein involved in pancreatic tumorigenesis and metastasis, plays a role as an enhancer of tumor-infiltrating MDSC and its functional activity. We show that PAUF enhanced the accumulation of MDSCs in the spleen and tumor tissues of PAUF-overexpressing tumor cell-injected mice. In addition, PAUF was found to enhance the immunosuppressive function of MDSCs via the TLR4-mediated signaling pathway, which was demonstrated by PAUF-induced increased levels of arginase, nitric oxide (NO), and reactive oxygen species (ROS). The role of PAUF in modulating the functional properties of MDSCs was further demonstrated by the use of a PAUF-neutralizing antibody that caused a decreased number of tumor-infiltrating MDSCs and reduced MDSC immunosuppressive activity. The observations made in mice were confirmed in human pancreatic cancer patient-derived MDSCs, supporting the clinical relevance of our findings. Collectively, we conclude that the PAUF is a powerful and multifunctional promoter of tumor growth through increase and functional activation of MDSCs, suggesting therapeutic potential for targeting PAUF in pancreatic cancers.

Overexpression of GRK3, Promoting Tumor Proliferation, Is Predictive of Poor Prognosis in Colon Cancer

Deregulation of G protein-coupled receptor kinase 3 (GRK3), which belongs to a subfamily of kinases called GRKs, acts as a promoter mechanism in some cancer types. Our study found that GRK3 was significantly overexpressed in 162 pairs of colon cancer tissues than in the matched noncancerous mucosa (P < 0.01). Based on immunohistochemistry staining of TMAs, GRK3 was dramatically stained positive in primary colon cancer (130/180, 72.22%), whereas it was detected minimally or negative in paired normal mucosa specimens (50/180, 27.78%). Overexpression of GRK3 was closely correlated with AJCC stage (P = 0.001), depth of tumor invasion (P < 0.001), lymph node involvement (P = 0.004), distant metastasis (P = 0.016), and histologic differentiation (P = 0.004). Overexpression of GRK3 is an independent prognostic indicator that correlates with poor survival in colon cancer patients. Consistent with this, downregulation of GRK3 exhibited decreased cell growth index, reduction in colony formation ability, elevated cell apoptosis rate, and impaired colon tumorigenicity in a xenograft model. Hence, a specific overexpression of GRK3 was observed in colon cancer, GRK3 potentially contributing to progression by mediating cancer cell proliferation and functions as a poor prognostic indicator in colon cancer and potentially represent a novel therapeutic target for the disease.

TGF-β Family Signaling in Tumor Suppression and Cancer Progression

Transforming growth factor-β (TGF-β) induces a pleiotropic pathway that is modulated by the cellular context and its integration with other signaling pathways. In cancer, the pleiotropic reaction to TGF-β leads to a diverse and varied set of gene responses that range from cytostatic and apoptotic tumor-suppressive ones in early stage tumors, to proliferative, invasive, angiogenic, and oncogenic ones in advanced cancer. Here, we review the knowledge accumulated about the molecular mechanisms involved in the dual response to TGF-β in cancer, and how tumor cells evolve to evade the tumor-suppressive responses of this signaling pathway and then hijack the signal, converting it into an oncogenic factor. Only through the detailed study of this complexity can the suitability of the TGF-β pathway as a therapeutic target against cancer be evaluated.

VEGF gene therapy cooperatively recruits molecules from the immune system and stimulates cell homing and angiogenesis in refractory angina

BACKGROUND

New vessels are formed in response to stimuli from angiogenic factors, a process in which paracrine signaling is fundamental.

OBJECTIVE

To investigate the cooperative paracrine signaling profile in response to Vascular Endothelial Growth Factor (VEGF) gene therapy in patients with coronary artery disease (CAD) and refractory angina.

METHOD

A cohort study was conducted in which plasma was collected from patients who underwent gene therapy with a plasmid expressing VEGF 165 (10) and from surgical procedure controls (4). Blood samples were collected from both groups prior to baseline and on days 3, 9 and 27 after the interventions and subjected to systemic analysis of protein expression (Interleukin-6, IL-6; Tumor Necrosis Factor-α, TNF-α; Interleukin-10, IL-10; Stromal Derived Factor-1 α, SDF-1α; VEGF; Angiopoietin-1, ANGPT-1; and Endothelin-1, ET-1) using the enzyme-linked immunosorbent assay (ELISA).

RESULTS

Analysis showed an increase in proinflammatory IL-6 (p=0.02) and ET-1 (p=0.05) on day 3 after gene therapy and in VEGF (p=0.02) on day 9. A strong positive correlation was found between mobilization of endothelial progenitor cells and TNF-α on day 9 (r=0.71; p=0.03). Furthermore, a strong correlation between β-blockers, antiplatelets, and vasodilators with SDF-1α baseline in the group undergoing gene therapy was verified (r=0.74; p=0.004).

CONCLUSION

Analysis of cooperative paracrine signaling after VEGF gene therapy suggests that the immune system cell and angiogenic molecule expression as well as the endothelial progenitor cell mobilization are time-dependent, influenced by chronic inflammatory process and continuous pharmacological treatment.

Variations in chemokine receptor and cytokine expression during pregnancy in multiple sclerosis patients

Although several T cell-mediated autoimmune diseases have shown a reduction in their clinical disease activity during pregnancy, the underlying mechanisms by which pregnancy causes such a beneficial effect on the disease activity are not fully understood. We performed a longitudinal study of chemokine receptors (CCR3, CCR4, CCR5, CXCR3, CXCR4) by flow cytometry in different subsets of peripheral blood mononuclear cells (PBMC) during pregnancy in multiple sclerosis (MS) patients. The levels of cytokine mRNA expression (IL-10, IFN-g) were also investigated by real-time quantitative reverse transcription polymerase chain reaction. The expression of CXCR3 by CD4 and CD8 positive T cells was decreased to a statistically significant extent during the second trimester of pregnancy. CD4 and CD8 T cells showed a statistically significant increase in the expression of CXCR4 during the third trimester of pregnancy. At the mRNA expression level, an increase in the IL-10/IFN-g ratio was observed during pregnancy, especially during the third trimester. These findings indicate immunomodulatory effects of pregnancy on the expression of chemokine receptors and cytokines, which may be related to changes in the clinical disease activity of T cell-mediated autoimmune diseases, such as MS.

Limited role for transforming growth factor-β pathway activation-mediated escape from VEGF inhibition in murine glioma models

BACKGROUND

The vascular endothelial growth factor (VEGF) and transforming growth factor (TGF)-β pathways regulate key biological features of glioblastoma. Here we explore whether the TGF-β pathway, which promotes angiogenesis, invasiveness, and immunosuppression, acts as an escape pathway from VEGF inhibition.

METHODS

The role of the TGF-β pathway in escape from VEGF inhibition was assessed in vitro and in vivo and by gene expression profiling in syngeneic mouse glioma models.

RESULTS

We found that TGF-β is an upstream regulator of VEGF, whereas VEGF pathway activity does not alter the TGF-β pathway in vitro. In vivo, single-agent activity was observed for the VEGF antibody B20-4.1.1 in 3 and for the TGF-β receptor 1 antagonist LY2157299 in 2 of 4 models. Reduction of tumor volume and blood vessel density, but not induction of hypoxia, correlated with benefit from B20-4.1.1. Reduction of phosphorylated (p)SMAD2 by LY2157299 was seen in all models but did not predict survival. Resistance to B20 was associated with anti-angiogenesis escape pathway gene expression, whereas resistance to LY2157299 was associated with different immune response gene signatures in SMA-497 and GL-261 on transcriptomic profiling. The combination of B20 with LY2157299 was ineffective in SMA-497 but provided prolongation of survival in GL-261, associated with early suppression of pSMAD2 in tumor and host immune cells, prolonged suppression of angiogenesis, and delayed accumulation of tumor infiltrating microglia/macrophages.

CONCLUSIONS

Our study highlights the biological heterogeneity of murine glioma models and illustrates that cotargeting of the VEGF and TGF-β pathways might lead to improved tumor control only in subsets of glioblastoma.

Injectable hydrogel delivery plus preconditioning of mesenchymal stem cells: exploitation of SDF-1/CXCR4 axis toward enhancing the efficacy of stem cells' homing

Clinical applications of mesenchymal stem cells (MSCs) rely on their capacity to home and engraft in the appropriate target injury tissues for the long term. However, their homing efficiency has been observed to be very poor because of the lack or modifications of homing factors SDF-1α and CXCR4 receptors. Hence, this study was designed to investigate the homing and retention of pretreated human adipose tissue-derived MSCs (hASCs) from three different delivery routes in response to SDF-1α, released from chitosan-based injectable hydrogels. After stimulation of ASCs with a hypoxia mimicking agent, the expression level and functionality of CXCR4 were analyzed by flowcytometric analysis (FACS), transwell migration assay and qPCR. Then, the homing/retention of pretreated DiI-labeled hASCs were compared through three different in vivo delivery routes, 2 weeks after transplantation in Wistar rats. The cells were tracked histologically by fluorescent microscope and by PCR for human-specific CXCR4 gene. Results showed CXCR4 has dynamic expression pattern and pretreatment of hASCs significantly up-regulates CXCR4, leading to an increase in migration capacity toward 100 ng/mL SDF-1α in vitro and homing into the subcutaneously implanted hydrogel releasing SDF-1α in vivo. Furthermore, it seems that SDF-1α is particularly important in the retention of ASCs, in addition to its chemoattraction role. In summary, the delivery route in which the ASCs were mixed with the hydrogel rather than systemic delivery and local injection and preconditioning undertaken to increase CXCR4 expression concomitant with SDF-1α delivery by the injectable hydrogel, allowed for further homing/retention of ASCs. This might be a promising way to get better therapeutic outcomes in stem cell therapy.

Post-Sepsis State Induces Tumor-Associated Macrophage Accumulation through CXCR4/CXCL12 and Favors Tumor Progression in Mice

Survivors from sepsis are in an immunosuppressed state that is associated with higher long-term mortality and risk of opportunistic infections. Whether these factors contribute to neoplastic proliferation, however, remains unclear. Tumor-associated macrophages (TAM) can support malignant cell proliferation, survival, and angiogenesis. We addressed the relationship between the post-sepsis state, tumor progression and TAM accumulation, and phenotypic and genetic profile, using a mouse model of sepsis resolution and then B16 melanoma in mice. In addition, we measured the serum concentrations of TNFα, TGFβ, CCL2, and CXCL12 and determined the effect of in vivo CXCR4/CXCL12 inhibition in this context. Mice that survived sepsis showed increased tumor progression both in the short and long term, and survival times were shorter. TAM accumulation, TAM local proliferation, and serum concentrations of TGFβ, CXCL12, and TNFα were increased. Naïve mice inoculated with B16 together with macrophages from post-sepsis mice also had faster tumor progression and shorter survival. Post-sepsis TAMs had less expression of MHC-II and leukocyte activation-related genes. Inhibition of CXCR4/CXCL12 prevented the post-sepsis-induced tumor progression, TAM accumulation, and TAM in situ proliferation. Collectively, our data show that the post-sepsis state was associated with TAM accumulation through CXCR4/CXCL12, which contributed to B16 melanoma progression.

Chemokine receptor Cxcr4 contributes to kidney fibrosis via multiple effectors

Kidney fibrosis is the final common pathway for virtually every type of chronic kidney disease and is a consequence of a prolonged healing response that follows tissue inflammation. Chronic kidney inflammation ultimately leads to progressive tissue injury and scarring/fibrosis. Several pathways have been implicated in the progression of kidney fibrosis. In the present study, we demonstrate that G protein-coupled chemokine (C-X-C motif) receptor (CXCR)4 was significantly upregulated after renal injury and that sustained activation of Cxcr4 expression augmented the fibrotic response. We demonstrate that after unilateral ureteral obstruction (UUO), both gene and protein expression of Cxcr4 were highly upregulated in tubular cells of the nephron. The increased Cxcr4 expression in tubules correlated with their increased dedifferentiated state, leading to increased mRNA expression of platelet-derived growth factor (PDGF)-α, transforming growth factor (TGF)-β1, and concurrent loss of bone morphogenetic protein 7 (Bmp7). Ablation of tubular Cxcr4 attenuated UUO-mediated fibrotic responses, which correlated with a significant reduction in PDGF-α and TGF-β1 levels and preservation of Bmp7 expression after UUO. Furthermore, Cxcr4(+) immune cells infiltrated the obstructed kidney and further upregulate their Cxcr4 expression. Genetic ablation of Cxcr4 from macrophages was protective against UUO-induced fibrosis. There was also reduced total kidney TGF-β1, which correlated with reduced Smad activation and α-smooth muscle actin levels. We conclude that chronic high Cxcr4 expression in multiple effector cell types can contribute to the pathogenesis of renal fibrosis by altering their biological profile. This study uncovered a novel cross-talk between Cxcr4-TGF-β1 and Bmp7 pathways and may provide novel targets for interrupting the progression of fibrosis.

Novel role for NFAT3 in ERK-mediated regulation of CXCR4

The G-protein coupled chemokine (C-X-C motif) receptor CXCR4 is linked to cancer, HIV, and WHIM (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) syndrome. While CXCR4 is reported to be overexpressed in multiple human cancer types and many hematological cancer cell lines, we have observed poor in vitro cell surface expression of CXCR4 in many solid tumor cell lines. We explore further the possible factors and pathways involved in regulating CXCR4 expression. Here, we showed that MEK-ERK signaling pathway and NFAT3 transcriptional factor plays a novel role in regulating CXCR4 expression. When cultured as 3D spheroids, HeyA8 ovarian tumor cells showed a dramatic increase in surface CXCR4 protein levels as well as mRNA transcripts. Furthermore, HeyA8 3D spheroids showed a decrease in phospho-ERK levels when compared to adherent cells. The treatment of adherent HeyA8 cells with an inhibitor of the MEK-ERK pathway, U0126, resulted in a significant increase in surface CXCR4 expression. Additional investigation using the PCR array assay comparing adherent to 3D spheroid showed a wide range of transcription factors being up-regulated, most notably a > 20 fold increase in NFAT3 transcription factor mRNA. Finally, chromatin immunoprecipitation (ChIP) analysis showed that direct binding of NFAT3 on the CXCR4 promoter corresponds to increased CXCR4 expression in HeyA8 ovarian cell line. Taken together, our results suggest that high phospho-ERK levels and NFAT3 expression plays a novel role in regulating CXCR4 expression.

EGFR phosphorylates and inhibits lung tumor suppressor GPRC5A in lung cancer

Background

GPRC5A is a retinoic acid inducible gene that is preferentially expressed in lung tissue. Gprc5a– knockout mice develop spontaneous lung cancer, indicating Gprc5a is a lung tumor suppressor gene. GPRC5A expression is frequently suppressed in majority of non-small cell lung cancers (NSCLCs), however, elevated GPRC5A is still observed in a small portion of NSCLC cell lines and tumors, suggesting that the tumor suppressive function of GPRC5A is inhibited in these tumors by an unknown mechanism.

Methods

In this study, we examined EGF receptor (EGFR)-mediated interaction and tyrosine phosphorylation of GPRC5A by immunoprecipitation (IP)-Westernblot. Tyrosine phosphorylation of GPRC5A by EGFR was systematically identified by site-directed mutagenesis. Cell proliferation, migration, and anchorage-independent growth of NSCLC cell lines stably transfected with wild-type GPRC5A and mutants defective in tyrosine phosphorylation were assayed. Immunohistochemical (IHC) staining analysis with specific antibodies was performed to measure the total and phosphorylated GPRC5A in both normal lung and lung tumor tissues.

Result

We found that EGFR interacted with GPRC5A and phosphorylated it in two conserved double-tyrosine motifs, Y317/Y320 and Y347/ Y350, at the C-terminal tail of GPRC5A. EGF induced phosphorylation of GPRC5A, which disrupted GPRC5A-mediated suppression on anchorage-independent growth of NSCLC cells. On contrary, GPRC5A-4 F, in which the four tyrosine residues have been replaced with phenylalanine, was resistant to EGF-induced phosphorylation and maintained tumor suppressive activities. Importantly, IHC analysis with anti-Y317/Y320-P sites showed that GPRC5A was non-phosphorylated in normal lung tissue whereas it was highly tyrosine-phosphorylated in NSCLC tissues.

Conclusion

GPRC5A can be inactivated by receptor tyrosine kinase via tyrosine phosphorylation. Thus, targeting EGFR can restore the tumor suppressive functions of GPRC5A in lung cancer.

The N-terminal region of the atypical chemokine receptor ACKR2 is a key determinant of ligand binding

The atypical chemokine receptor, ACKR2 is a pivotal regulator of chemokine-driven inflammatory responses and works by binding, internalizing, and degrading inflammatory CC-chemokines. ACKR2 displays promiscuity of ligand binding and is capable of interacting with up to 14 different inflammatory CC-chemokines. Despite its prominent biological role, little is known about the structure/function relationship within ACKR2, which regulates ligand binding. Here we demonstrate that a conserved tyrosine motif at the N terminus of ACKR2 is essential for ligand binding, internalization, and scavenging. In addition we demonstrate that sulfation of this motif contributes to ligand internalization. Furthermore, a peptide derived from this region is capable of binding inflammatory chemokines and inhibits their interaction with their cognate signaling receptors. Importantly, the peptide is only active in the sulfated form, further confirming the importance of the sulfated tyrosines for function. Finally, we demonstrate that the bacterial protease, staphopain A, can cleave the N terminus of ACKR2 and suppress its ligand internalization activity. Overall, these results shed new light on the nature of the structural motifs in ACKR2 that are responsible for ligand binding. The study also highlights ACKR2-derived N-terminal peptides as being of potential therapeutic significance.

CXC chemokine receptor 4 expression, CXC chemokine receptor 4 activation, and wild-type nucleophosmin are independently associated with unfavorable prognosis in patients with acute myeloid leukemia

BACKGROUND

CXC chemokine receptor 4 (CXCR4) is activated by phosphorylation and essential for migration of hematopoietic precursors to bone marrow. CXCR4 overexpression predicts unfavorable prognosis in patients with acute myeloid leukemia (AML). Nucleophosmin (NPM1) mutation is the most frequent genetic abnormality in patients with AML and predicts a favorable prognosis. In vitro studies have suggested that mutant nucleophosmin (NPM) decreases CXCR4-mediated chemotaxis by downregulating CXCR4, thereby linking the NPM and CXCR4 pathways.

PATIENTS AND METHODS

In a group of 117 untreated adults with AML, we used immunohistochemistry to assess bone marrow specimens for CXCR4 and phosphorylated CXCR4 (pCXCR4) expression. All cases also were analyzed for NPM1 mutations using polymerase chain reaction-based methods.

RESULTS

CXCR4 expression was detected in 75 patients (64%), and pCXCR4 expression was detected in 31 patients (26%). NPM1 mutations were detected in 63 patients (54%). NPM1 mutations did not correlate with CXCR4 (P = .212) or pCXCR4 (P = .355) expression. The median 5-year overall survival was 27% (95% confidence interval, 19-36), with a median follow-up of 8 months (95% confidence interval, 6-15). In a multivariate Cox proportional hazards model, reduced overall and progression-free survival rates were associated with a history of antecedent hematologic disorder, failure to achieve complete remission, thrombocytopenia, unfavorable cytogenetics, CXCR4 expression, and wild-type NPM1. pCXCR4 expression was independently associated with shorter progression-free survival.

CONCLUSIONS

There is no correlation between NPM1 mutations and CXCR4 or pCXCR4 expression, suggesting that the CXCR4 and NPM pathways act independently in adult AML.

β-Arrestins in the immune system

β-Arrestins regulate G protein-coupled receptors through receptor desensitization while also acting as signaling scaffolds to facilitate numerous effector pathways. Recent studies have provided evidence that β-arrestins play a key role in inflammatory responses. Here, we summarize these advances on the roles of β-arrestins in immune regulation and inflammatory responses under physiological and pathological conditions, with an emphasis on translational implications of β-arrestins on human diseases.

Incorporation of stromal cell-derived factor-1α in PCL/gelatin electrospun membranes for guided bone regeneration

The goal of this work was to evaluate the effect of membrane functionalization with a chemotactic factor on cell recruitment and bone formation in order to develop a bioactive membrane for guided bone regeneration (GBR) applications. To this end, GBR membranes were prepared by electrospinning using poly(ε-caprolactone) (PCL) blended with type B-gelatin, and functionalized with stromal cell derived factor-1α (SDF-1α) via physical adsorption. Firstly, the obtained membranes were evaluated in vitro for SDF-1α release and chemotactic effect on bone marrow stromal cells (BMSCs). Subsequently, in vivo BMSCs recruitment and bone regeneration in response to SDF-1α loaded PCL/gelatin electrospun membranes were assessed in rat cranial defects. The results showed that PCL/gelatin electrospun membranes provided a diffusion-controlled SDF-1α release profile. Furthermore, the membranes loaded with different amounts of SDF-1α (50-400 ng) significantly induced stimulated chemotactic migration of BMSCs in vitro without dose-dependent effects. Eight weeks after implantation in rat cranial defects, SDF-1α loaded membranes yielded a 6-fold increase in the amount of bone formation compared to the bare membranes, albeit that contribution of in vivo BMSCs recruitment to the bone regeneration could not be ascertained. In conclusion, the results of current study indicate the potential for using SDF-1α loaded PCL/gelatin electrospun membrane as a bioactive membrane, which is beneficial for optimizing clinical application of GBR strategies.

Mesenchymal stem cell secreted vesicles provide novel opportunities in (stem) cell-free therapy

Mesenchymal stem cells (MSCs) are adult multipotent cells that give rise to various cell types of the mesodermal germ layer. MSCs are of great interest in the field of regenerative medicine and cancer therapy because of their unique ability to home to damaged and cancerous tissue. These cells also regulate the immune response and contribute to reparative processes in different pathological conditions, including musculoskeletal and cardiovascular diseases. The use of MSCs for tissue repair was initially based on the hypothesis that these cells home to and differentiate within the injured tissue into specialized cells. However, it now appears that only a small proportion of transplanted MSCs actually integrate and survive in host tissues. Thus, the predominant mechanism by which MSCs participate in tissue repair seems to be related to their paracrine activity. Indeed, MSCs provide the microenvironment with a multitude of trophic and survival signals including growth factors and cytokines. Recent discoveries suggest that lipid microvesicles released by MSCs may also be important in the physiological function of these cells. Over the past few years the biological relevance of micro- and nano-vesicles released by cells in intercellular communication has been established. Alongside the conventional mediators of cell secretome, these sophisticated nanovesicles transfer proteins, lipids and, most importantly, various forms of RNAs to neighboring cells, thereby mediating a variety of biological responses. The physiological role of MSC-derived vesicles (MSC-MVs) is currently not well understood. Nevertheless, encouraging results indicate that MSC-MVs have similar protective and reparative properties as their cellular counterparts in tissue repair and possibly anti-cancer therapy. Thus, MSC-MVs represent a promising opportunity to develop novel cell-free therapy approaches that might overcome the obstacles and risks associated with the use of native or engineered stem cells.

SDF-1 activates papillary label-retaining cells during kidney repair from injury

The adult kidney contains a population of low-cycling cells that resides in the papilla. These cells retain for long periods S-phase markers given as a short pulse early in life; i.e., they are label-retaining cells (LRC). In previous studies in adult rat and mice, we found that shortly after acute kidney injury many of the quiescent papillary LRC started proliferating (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009; Oliver JA, Maarouf O, Cheema FH, Martens TP, Al-Awqati Q. J Clin Invest 114: 795-804, 2004) and, with cell-tracking experiments, we found upward migration of some papillary cells including LRC (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009). To identify molecular cues involved in the activation (i.e., proliferation and/or migration) of the papillary LRC that follows injury, we isolated these cells from the H2B-GFP mice and found that they migrated and proliferated in response to the cytokine stromal cell-derived factor-1 (SDF-1). Moreover, in a papillary organ culture assay, the cell growth out of the upper papilla was dependent on the interaction of SDF-1 with its receptor Cxcr4. Interestingly, location of these two proteins in the kidney revealed a complementary location, with SDF-1 being preferentially expressed in the medulla and Cxcr4 more abundant in the papilla. Blockade of Cxcr4 in vivo prevented mobilization of papillary LRC after transient kidney ischemic injury and worsened its functional consequences. The data indicate that the SDF-1/Cxcr4 axis is a critical regulator of papillary LRC activation following transient kidney injury and during organ repair.

HGF-induced PKCζ activation increases functional CXCR4 expression in human breast cancer cells

The chemokine receptor CXCR4 and its ligand CXCL12 have been shown to mediate the metastasis of many malignant tumors including breast carcinoma. Interaction between hepatocyte growth factor (HGF) and the Met receptor tyrosine kinase mediates development and progression of cancers. HGF is able to induce CXCR4 expression and contributes to tumor cell invasiveness in breast carcinoma. However, the mechanism of the CXCR4 expression modulated by c-Met-HGF axis to enhance the metastatic behavior of breast cancer cells is still unclear. In this study, we found that HGF induced functional CXCR4 receptor expression in breast cancer cells. The effect of HGF was specifically mediated by PKCζ activity. After transfection with PKCζ-siRNA, the phosphorylation of PKCζ and CXCR4 was abrogated in breast cancer cells. Interference with the activation of Rac1, a downstream target of HGF, prevented the HGF-induced increase in PKCζ activity and CXCR4 levels. The HGF-induced, LY294002-sensitive translocation of PKCζ from cytosol to plasma membrane indicated that HGF was capable of activating PKCζ, probably via phosphoinositide (PI) 3-kinases. HGF treatment also increased MT1-MMP secretion. Inhibition of PKCζ, Rac-1 and phosphatidylinositol 3-kinase may attenuate MT1-MMP expression in cells exposed to HGF. Functional manifestation of the effects of HGF revealed an increased ability for migration, chemotaxis and metastasis in MDA-MB-436 cells in vitro and in vivo. Our findings thus provided evidence that the process of HGF-induced functional CXCR4 expression may involve PI 3-kinase and atypical PKCζ. Moreover, HGF may promote the invasiveness and metastasis of breast tumor xenografts in BALB/c-nu mice via the PKCζ-mediated pathway, while suppression of PKCζ by RNA interference may abrogate cancer cell spreading.

Role of TGF-β and the tumor microenvironment during mammary tumorigenesis

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that functions to inhibit mammary tumorigenesis by directly inducing mammary epithelial cells (MECs) to undergo cell cycle arrest or apoptosis, and to secrete a variety of cytokines, growth factors, and extracellular matrix proteins that maintain cell and tissue homeostasis. Genetic and epigenetic events that transpire during mammary tumorigenesis typically inactivate the tumor suppressing activities of TGF-beta and ultimately confer this cytokine with tumor promoting activities, including the ability to stimulate breast cancer invasion, metastasis, angiogenesis, and evasion from the immune system. This dramatic conversion in TGF-beta function is known as the "TGF-beta paradox" and reflects a variety of dynamic alterations that occur not only within the developing mammary carcinoma, but also within the cellular and structural composition of its accompanying tumor microenvironment. Recent studies have begun to elucidate the critical importance of mammary tumor microenvironments in manifesting the TGF-beta paradox and influencing the response of developing mammary carcinomas to TGF-beta. Here we highlight recent findings demonstrating the essential function of tumor microenvironments in regulating the oncogenic activities of TGF-beta and its stimulation of metastatic progression during mammary tumorigenesis.

Genomics of Acute Lung Injury and Vascular Barrier Dysfunction

Acute lung injury (ALI) is a devastating ­syndrome of diffuse alveolar damage that develops via a variety of local and systemic insults such as sepsis, trauma, ­pneumonia, and aspiration. It is interestingly to note that only a subset of individuals exposed to potential ALI-inciting insults develop the disorder and the severity of the disease varies from complete resolution to death. In addition, ALI susceptibility and severity are also affected by ethnicity as evidenced by the higher mortality rates observed in African-American ALI patients compared with other ethnic groups in the USA. Moreover, marked differences in strain-specific ALI responses to inflammatory and injurious agents are observed in preclinical animal models. Together, these observations strongly indicate genetic components to be involved in the pathogenesis of ALI. The identification of genes contributing to ALI would potentially provide a better understanding of ALI pathobiology, yield novel biomarkers, identify individuals or populations at risk, and prove useful for the development of novel and individualized therapies. Genome-wide searches in animal models have identified a number of quantitative trait loci that associate with ALI susceptibility. In this chapter, we utilize a systems biology approach combining cellular signaling pathway analysis with population- based association studies to review established and suspected candidate genes that contribute to dysfunction of endothelial cell barrier integrity and ALI susceptibility.

Mesenchymal stem cells: Mechanisms of immunomodulation and homing

Mesenchymal stem cell (MSC) transplantation has been explored as a new clinical approach to repair injured tissue. A growing corpus of studies have highlighted two important aspects of MSC therapy: 1) MSCs can modulate T-cell-mediated immunological responses, and (2) systemically administered MSCs home to sites of ischemia or injury. In this review, we describe the known mechanisms of immunomodulation and homing of MSCs. First, we examine the low immunogenicity of MSCs and their antigen presentation capabilities. Next, we discuss the paracrine interactions between MSCs and innate [dendritic cells (DC)] and adaptive immune cells (T lymphocytes) with a focus on prostaglandin E(2) (PGE(2)), indoleamine 2,3-dioxygenase (IDO), and toll-like receptor (TLR) signaling pathways. We transition to outline the steps of activation, rolling/adhesion, and transmigration of MSCs into target tissues during inflammatory or ischemic conditions. These aspects of MSC grafts--immunomodulation and homing--are contextualized to understand a reported side effect of MSC therapy, cancer development.

The macrophage in HIV-1 infection: from activation to deactivation?

Macrophages play a crucial role in innate and adaptative immunity in response to microorganisms and are an important cellular target during HIV-1 infection. Recently, the heterogeneity of the macrophage population has been highlighted. Classically activated or type 1 macrophages (M1) induced in particular by IFN-γ display a pro-inflammatory profile. The alternatively activated or type 2 macrophages (M2) induced by Th-2 cytokines, such as IL-4 and IL-13 express anti-inflammatory and tissue repair properties. Finally IL-10 has been described as the prototypic cytokine involved in the deactivation of macrophages (dM). Since the capacity of macrophages to support productive HIV-1 infection is known to be modulated by cytokines, this review shows how modulation of macrophage activation by cytokines impacts the capacity to support productive HIV-1 infection. Based on the activation status of macrophages we propose a model starting with M1 classically activated macrophages with accelerated formation of viral reservoirs in a context of Th1 and proinflammatory cytokines. Then IL-4/IL-13 alternatively activated M2 macrophages will enter into the game that will stop the expansion of the HIV-1 reservoir. Finally IL-10 deactivation of macrophages will lead to immune failure observed at the very late stages of the HIV-1 disease.

Transforming growth factor beta (TGF-beta) and inflammation in cancer

The transforming growth factor beta (TGF-beta) has been studied with regard to the regulation of cell behavior for over three decades. A large body of research has been devoted to the regulation of epithelial cell and derivative carcinoma cell populations in vitro and in vivo. TGF-beta has been shown to inhibit epithelial cell cycle progression and promote apoptosis that together significantly contribute to the tumor suppressive role for TGF-beta during carcinoma initiation and progression. TGF-beta is also able to promote an epithelial to mesenchymal transition that has been associated with increased tumor cell motility, invasion and metastasis. However, it has now been shown that loss of carcinoma cell responsiveness to TGF-beta stimulation can also promote metastasis. Interestingly, enhanced metastasis in the absence of a carcinoma cell response to TGF-beta stimulation has been shown to involve increased chemokine production resulting in recruitment of pro-metastatic myeloid derived suppressor cell (MDSC) populations to the tumor microenvironment at the leading invasive edge. When present, MDSCs enhance angiogenesis, promote immune tolerance and provide matrix degrading enzymes that promote tumor progression and metastasis. Further, the recruitment of MDSC populations in this context likely enhances the classic role for TGF-beta in immune suppression since the MDSCs are an abundant source of TGF-beta production. Importantly, it is now clear that carcinoma-immune cell cross-talk initiated by TGF-beta signaling within the carcinoma cell is a significant determinant worth consideration when designing therapeutic strategies to manage tumor progression and metastasis.

Impaired recruitment of Grk6 and beta-Arrestin 2 causes delayed internalization and desensitization of a WHIM syndrome-associated CXCR4 mutant receptor

WHIM (warts, hypogammaglobulinemia, infections, and myelokatexis) syndrome is a rare immunodeficiency syndrome linked to heterozygous mutations of the chemokine receptor CXCR4 resulting in truncations of its cytoplasmic tail. Leukocytes from patients with WHIM syndrome display impaired CXCR4 internalization and enhanced chemotaxis in response to its unique ligand SDF-1/CXCL12, which likely contribute to the clinical manifestations. Here, we investigated the biochemical mechanisms underlying CXCR4 deficiency in WHIM syndrome. We report that after ligand activation, WHIM-associated mutant CXCR4 receptors lacking the carboxy-terminal 19 residues internalize and activate Erk 1/2 slower than wild-type (WT) receptors, while utilizing the same trafficking endocytic pathway. Recruitment of β-Arrestin 2, but not β-Arrestin 1, to the active WHIM-mutant receptor is delayed compared to the WT CXCR4 receptor. In addition, while both kinases Grk3 and Grk6 bind to WT CXCR4 and are critical to its trafficking to the lysosomes, Grk6 fails to associate with the WHIM-mutant receptor whereas Grk3 associates normally. Since β-Arrestins and Grks play critical roles in phosphorylation and internalization of agonist-activated G protein-coupled receptors, these results provide a molecular basis for CXCR4 dysfunction in WHIM syndrome.

Strong expression of chemokine receptor CXCR4 by renal cell carcinoma correlates with advanced disease

Diverse chemokines and their receptors have been associated with tumor growth, tumor dissemination, and local immune escape. In different tumor entities, the level of chemokine receptor CXCR4 expression has been linked with tumor progression and decreased survival. The aim of this study was to evaluate the influence of CXCR4 expression on the progression of human renal cell carcinoma. CXCR4 expression of renal cell carcinoma was assessed by immunohistochemistry in 113 patients. Intensity of CXCR4 expression was correlated with both tumor and patient characteristics. Human renal cell carcinoma revealed variable intensities of CXCR4 expression. Strong CXCR4 expression of renal cell carcinoma was significantly associated with advanced T-status (P = .039), tumor dedifferentiation (P = .0005), and low hemoglobin (P = .039). In summary, strong CXCR4 expression was significantly associated with advanced dedifferentiated renal cell carcinoma.

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

The salivary glands (SG) provide a haven for persistent cytomegalovirus replication, and in this regard are a privileged site of virus immune evasion. The murine cytomegalovirus (MCMV) model has provided insight into the immunological environment of the SG and the unqiue virus-host relationship of this organ. In response to MCMV infection, a robust T cell-mediated immune response is elicited, comprised predominantly of CD8+ T cells that phenotypically and functionally appear activated. However, they fail to clear virus by an unknown evasion mechanism that is independent of inhibitory NKG2A- or Programmed Death 1-mediated signaling. Virus is eventually eliminated from the SG by effector CD4+ T cells expressing antiviral cytokines. However, this mechanism is severely dampened by high levels of the immunosuppressive cytokine IL-10, selectively expressed by SG CD4+ T cells.

Leukocyte analysis from WHIM syndrome patients reveals a pivotal role for GRK3 in CXCR4 signaling

Leukocytes from individuals with warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome, a rare immunodeficiency, and bearing a wild-type CXCR4 ORF (WHIM(WT)) display impaired CXCR4 internalization and desensitization upon exposure to CXCL12. The resulting enhanced CXCR4-dependent responses, including chemotaxis, probably impair leukocyte trafficking and account for the immunohematologic clinical manifestations of WHIM syndrome. We provided here evidence that GPCR kinase-3 (GRK3) specifically regulates CXCL12-promoted internalization and desensitization of CXCR4. GRK3-silenced control cells displayed altered CXCR4 attenuation and enhanced chemotaxis, as did WHIM(WT) cells. These findings identified GRK3 as a negative regulator of CXCL12-induced chemotaxis and as a candidate responsible for CXCR4 dysfunction in WHIM(WT) leukocytes. Consistent with this, we showed that GRK3 overexpression in both leukocytes and skin fibroblasts from 2 unrelated WHIM(WT) patients restored CXCL12-induced internalization and desensitization of CXCR4 and normalized chemotaxis. Moreover, we found in cells derived from one patient a profound and selective decrease in GRK3 products that probably resulted from defective mRNA synthesis. Taken together, these results have revealed a pivotal role for GRK3 in regulating CXCR4 attenuation and have provided a mechanistic link between the GRK3 pathway and the CXCR4-related WHIM(WT) disorder.

Glucocorticoids regulate innate immunity in a model of multiple sclerosis: reciprocal interactions between the A1 adenosine receptor and beta-arrestin-1 in monocytoid cells

Desensitization of seven transmembrane receptors (7TMRs), which are modulated by the beta-arrestins, leads to altered G protein activation. The A1 adenosine receptor (A1AR) is an antiinflammatory 7TMR exhibiting reduced expression and activity in both multiple sclerosis (MS) and the murine MS model, experimental autoimmune encephalomyelitis (EAE) in monocytoid cells. Herein, we report that beta-arrestin-1 expression was increased in brains of MS patients relative to non-MS brains, whereas A1AR expression was concomitantly reduced. This inverse relationship between beta-arrestin-1 and A1AR was confirmed in cultured monocytoid cells as beta-arrestin-1 overexpression resulted in a down-regulation of A1AR together with the internalization of the surface receptor. Moreover, a physical interaction between beta-arrestin-1 and A1AR was demonstrated in monocytoid cells. Proinflammatory cytokines regulated the A1AR/beta-arrestin-1 interactions, while A1AR activation also modulated proinflammatory cytokines expression. During EAE, beta-arrestin-1 and A1AR expression in the spinal cord displayed a similar pattern compared to that observed in MS brains. EAE-induced neuroinflammation and neurobehavioral deficits were suppressed by glucocorticoid treatments, accompanied by concurrent reduced beta-arrestin-1 and enhanced A1AR expression. Thus, the interplay between beta-arrestin-1 and A1AR in the central nervous system during neuroinflammation represents a reciprocal regulatory mechanism through which neuroprotective therapeutic strategies for neuroinflammatory diseases might be further developed.

Intracellular cross-talk between the GPCR CXCR1 and CXCR2: role of carboxyl terminus phosphorylation sites

In the present study, we used the human chemokine receptors CXCR1 and CXCR2 as a model system for the study of intracellular cross-talk between two closely related G protein-coupled receptors (GPCR). In cells expressing either CXCR1 or CXCR2, exposure to the CXCL8 ligand resulted in prominent reduction in cell surface expression of the receptors. We have shown previously that the reduction in cell surface expression of CXCR1 and CXCR2, to be termed herein "down-regulation", is significantly lower in cells expressing both receptors together. Now we show that reduced receptor down-regulation was specific to the CXCR1+CXCR2 pair. Also, CXCR2 carboxyl terminus phosphorylation sites were required for inducing inhibition of CXCR1 down-regulation, and vice versa. Accordingly, phosphorylation of CXCR2 carboxyl terminus domain was intact when expressed together with CXCR1. Moreover, specific carboxyl terminus phosphorylation sites on each of the wild type receptors protected them from more severe inhibition of down-regulation, induced by joint expression with the other receptor. When concomitantly expressed, CXCR1 and CXCR2 were impaired in recycling to the plasma membrane, despite their undergoing intact dephosphorylation. Overall, we show that cross-talk between two GPCR is manifested by impairment of their intracellular trafficking, primarily of ligand-induced down-regulation, via carboxyl terminus phosphorylation sites.

Surface expression of neutrophil CXCR4 is down-modulated by bacterial endotoxin

The chemokine receptor CXCR4 and its unique ligand, stromal-derived factor 1 (SDF-1), play critical roles in the retention of hematopoietic cells within bone marrow and in their mobilization into the circulation. Surface CXCR4 down-regulation in hematopoietic cells is associated with a loss of retention of the cells in bone marrow. Lipopolysaccharide (LPS), commonly referred to as endotoxin, induces neutrophilia in vivo, but the mechanism of mobilization related to neutrophilia has not been fully clarified. We show that LPS reduces CXCR4 surface expression in a dose- and time-dependent manner in neutrophils and monocytes, but not in lymphocytes. Polymyxin B neutralization of LPS in culture supernatants still induced this down-modulation, and LPS-stimulated neutrophils released interferon gamma and interleukin 1beta. These results provide evidence that CXCR4 down-regulation can be attributed to soluble factors released by neutrophils upon LPS treatment. Moreover, LPS treatment increased CXCR4 messenger RNA in neutrophils, suggesting that the down-regulation of surface CXCR4 is caused by a posttranslational mechanism, and the chemotactic migration of neutrophils in response to SDF-1 was reduced by LPS pretreatment. Thus, the present study has shown that by down-regulating neutrophil CXCR4 expression and attenuating neutrophil responsiveness to SDF-1, LPS can mobilize neutrophils from bone marrow to the peripheral blood through reducing neutrophil retention in bone marrow.

T helper type 2 differentiation and intracellular trafficking of the interleukin 4 receptor-α subunit controlled by the Rac activator Dock2

The lineage commitment of CD4+ T cells is coordinately regulated by signals through the T cell receptor and cytokine receptors, yet how these signals are integrated remains elusive. Here we find that mice lacking Dock2, a Rac activator in lymphocytes, developed allergic disease through a mechanism dependent on CD4+ T cells and the interleukin 4 receptor (IL-4R). Dock2-deficient CD4+ T cells showed impaired antigen-driven downregulation of IL-4Ralpha surface expression, resulting in sustained IL-4R signaling and excessive T helper type 2 responses. Dock2 was required for T cell receptor-mediated phosphorylation of the microtubule-destabilizing protein stathmin and for lysosomal trafficking and the degradation of IL-4Ralpha. Thus, Dock2 links T cell receptor signals to downregulation of IL-4Ralpha to control the lineage commitment of CD4+ T cells.

Leptin requires canonical migratory signaling pathways for induction of monocyte and macrophage chemotaxis

The growing worldwide obesity epidemic is frequently linked to an increased risk of developing diseases such as diabetes, cardiovascular disease, and cancer. These diseases are associated with the infiltration of macrophages in white adipose tissue (WAT), the artery wall, and tumors, respectively; and these macrophages likely contribute to disease progression and pathogenesis. Abdominal WAT, adipose tissue surrounding the heart and artery wall, as well as carcinoma cells, secrete many factors that could induce macrophage infiltration. Leptin is an adipocyte-secreted hormone, and deficiency of either leptin or its receptor has been shown to cause morbid obesity in animals and in humans. However, what is more commonly noted in human obesity is the presence of central leptin resistance leading to hyperleptinemia. As leptin receptors are present on macrophages, we hypothesized that leptin could act as a monocyte/macrophage chemoattractant. Our current study demonstrates: 1) leptin is a potent chemoattractant for monocytes and macrophages, inducing maximal chemotactic responses at 1 ng/ml; 2) leptin-mediated chemotaxis requires the presence of full-length leptin receptors on migrating cells; 3) leptin causes increased influx of intracellular calcium in macrophages; and 4) activation of janus kinase/signal transducers and activators of transduction (JAK/STAT), mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3-kinase (PI3K) pathways are all necessary for leptin-induced macrophage migration. Taken together, these data demonstrate that leptin is a potent monocyte/macrophage chemoattractant in vitro and that canonical cell motility machinery is activated upon macrophage exposure to leptin. These data have implications for the impact of hyperleptinemia on obesity-related pathophysiological conditions such as diabetes, cardiovascular disease, and cancer.

Control of in vitro immune responses by regulatory oligodeoxynucleotides through inhibition of pIII promoter directed expression of MHC class II transactivator in human primary monocytes

Ag presentation is a key step in the initiation of adaptive immune responses that depends on the expression of MHC Ags and costimulatory molecules. Immune-enhancing CpG and non-CPG oligodeoxynucleotides (ODNs) stimulate Ag presentation by stimulating the expression of these molecules and by promoting dendritic cell maturation. In this report, we identify immunoregulatory orthophosphorothioate non-CpG molecules, referred to as regulatory ODNs (rODNs), by their ability to inhibit allogeneic monocyte-stimulated T cell responses and down-regulate HLA-DR in human primary monocytes. The rODNs promoted the survival of macrophages and were able to activate IL-8 secretion through a chloroquine-resistant pathway. Messenger RNAs for HLA-DR alpha and beta and the MHC CIITA were reduced by rODNs but not by stimulatory CpG ODN2006 and non-CpG ODN2006a. CIITA transcription in monocytes was controlled primarily by promoter III and not by promoter I or IV. rODNs blocked promoter III-directed transcription of CIITA in these cells. Under conditions that induced dendritic cell differentiation, rODNs also reduced HLA-DR expression. The activity of rODNs is phosphorothioate chemistry and G stretch dependent but TLR9 independent. G tetrads were detected by circular dichroism in active rODNs and associated with high m.w. multimers on nondenaturing gels. Heat treatment of rODNs disrupted G tetrads, the high m.w. aggregates, and the HLA-DR inhibitory activity of the ODNs. The inhibition of immune responses by regulatory oligodeoxynucleotides may be useful for the treatment of immune-mediated disorders including autoimmune diseases and graft rejection.

Regulation of CXCR4 signaling

The chemokine receptor CXCR4 belongs to the large superfamily of G protein-coupled receptors, and is directly involved in a number of biological processes including organogenesis, hematopoiesis, and immune response. Recent evidence has highlighted the role of CXCR4 in a variety of diseases including HIV, cancer, and WHIM syndrome. Importantly, the involvement of CXCR4 in cancer metastasis and WHIM syndrome appears to be due to dysregulation of the receptor leading to enhanced signaling. Herein we review what is currently known regarding the regulation of CXCR4 and how dysregulation contributes to disease progression.

Dimerization of CXCR4 in living malignant cells: control of cell migration by a synthetic peptide that reduces homologous CXCR4 interactions

Chemokine receptor CXCR4 (CD184) may play a role in cancer metastasis and is known to form homodimers. However, it is not clear how transmembrane regions (TM) of CXCR4 and receptor homotypic interactions affect the function of CXCR4 in living cells. Using confocal microscopy and flow cytometric analysis, we showed that high levels of CXCR4 are present in the cytoplasm, accompanied by lower expression on the cell surface in CXCR4 transfectants, tumor cells, and normal peripheral blood lymphocytes. CXCR4 homodimers were detected in tumor cells, both on the cell surface membrane and in the cytoplasm using fluorescence resonance energy transfer and photobleaching fluorescence resonance energy transfer to measure energy transfer between CXCR4-CFP and CXCR4-YFP constructs. Disruption of lipid rafts by depletion of cholesterol with methyl-beta-cyclodextrin reduced the interaction between CXCR4 molecules and inhibited malignant cell migration to CXCL12/SDF-1alpha. A synthetic peptide of TM4 of CXCR4 reduced energy transfer between molecules of CXCR4, inhibited CXCL12-induced actin polymerization, and blocked chemotaxis of malignant cells. TM4 also inhibited migration of normal monocytes toward CXCL12. Reduction of CXCR4 energy transfer by the TM4 peptide and methyl-beta-cyclodextrin indicates that interactions between CXCR4s may play important roles in cell migration and suggests that cell surface and intracellular receptor dimers are appropriate targets for control of tumor cell spread. Targeting chemokine receptor oligomerization and signal transduction for the treatment of cancer, HIV-1 infections, and other CXCR4 mediated inflammatory conditions warrants further investigation.

Dendrite-selective redistribution of the chemokine receptor CXCR4 following agonist stimulation

The chemokine SDF-1 is a secreted protein that plays a critical role in several aspects of neuron development through interaction with its unique receptor CXCR4. A key mechanism that controls neuron responsiveness to extracellular signals during neuronal growth is receptor endocytosis. Since we previously reported that SDF-1 regulates axon development without affecting the other neurites, we asked whether this could correlate with a compartment-selective trafficking of CXCR4. We thus studied CXCR4 behavior upon SDF-1 exposure in rat hippocampus slices and in transfected neuron cultures. A massive agonist-induced redistribution of CXCR4 in endosomes was observed in dendrites whereas no modification was evidenced in axons. Our data suggest that CXCR4 trafficking may play a role in mediating selective effects of SDF-1 on distinct neuronal membrane subdomains.

Tumour microenvironment: TGFbeta: the molecular Jekyll and Hyde of cancer

Transforming growth factor-beta (TGFbeta) signalling regulates cancer through mechanisms that function either within the tumour cell itself or through host-tumour cell interactions. Studies of tumour-cell-autonomous TGFbeta effects show clearly that TGFbeta signalling has a mechanistic role in tumour suppression and tumour promotion. In addition, factors in the tumour microenvironment, such as fibroblasts, immune cells and the extracellular matrix, influence the ability of TGFbeta to promote or suppress carcinoma progression and metastasis. The complex nature of TGFbeta signalling and crosstalk in the tumour microenvironment presents a unique challenge, and an opportunity to develop therapeutic intervention strategies for targeting cancer.

Regulation of stromal cell-derived factor-1 and exhaled nitric oxide in asthmatic children following montelukast and ketotifen treatment

BACKGROUND

Montelukast and ketotifen are oral anti-allergy medications in asthmatic children. This study investigates the modulation effect of montelukast and ketotifen on children with intermittent to mild persistent asthma as demonstrated by the levels of peak expiratory flow (PEF), asthma scores (AS), exhaled nitric oxide (eNO) and plasma stromal cell-derived factor-1 (SDF-1) concentration in a randomized, prospective study.

METHODS

Fifty asthmatic children were enrolled and received 8 weeks of treatment with oral montelukast sodium 5mg chewable tablet administered once daily, or 1mg ketotifen, and were followed for a 4-week post-treatment washout period. ENO concentration, AS and PEF were measured before, 2, 4, 6 and 8 weeks after initial treatment, and 4 weeks after cessation of treatment.

RESULTS

Montelukast therapy was showed to improve AS, PEF and eNO within 2 weeks and remained the improvement during the treatment period. Montelukast also significantly decreased plasma SDF-1 levels after 8 weeks of treatment. In contrast, the ketotifen treatment revealed no significant effects in these clinical parameters until 4 and 6 weeks of the therapy, and did not suppress plasma SDF-1 levels after 8 weeks of treatment. To prove whether montelukast directly suppressed SDF-1 induction, we studied effects of montelukast on the LPS-induced SDF-1 expression and SDF-1-induced chemotaxis of monocytic (THP-1) cells. Montelukast, but not ketotifen, could suppress SDF-1 expression and its related chemotaxis on THP-1 monocytic cells.

CONCLUSIONS

Leukotriene receptor antagonist, such as montelukast, may be a better non-steroid anti-inflammatory drug for mild childhood asthma in preventing airway inflammation.

Widespread CXCR4 activation in astrocytomas revealed by phospho-CXCR4-specific antibodies

The chemokine receptor CXCR4 is expressed in many cancers where it may regulate tumor cell growth and migration. The role of CXCR4 in cancer will depend on it being in an activated, signaling state. To better define the significance of CXCR4 expression in cancer, we developed an antibody that can distinguish CXCR4 phosphorylated on serine 339, a residue previously identified as a site for ligand-induced phosphorylation. With this antibody, we investigated the mechanisms of CXCR4 phosphorylation and evaluated the phosphorylation status of CXCR4 in human astrocytomas. In vitro, phosphorylation of serine 339 occurred in response to CXCL12 or epidermal growth factor (EGF) treatment and was increased by protein kinase C activation. In all grades of astrocytomas, CXCR4 was expressed in tumor cells and some endothelial cells, whereas CXCL12 was present in endothelial cells and infiltrating microglia. We found that CXCR4 phosphorylated on serine 339 was present in tumor cells and vascular endothelial cells in all grades of astrocytoma. These data indicate that CXCR4 is expressed and activated in astrocytomas and that phosphorylation of CXCR4 can occur through ligand activation or transactivation via the EGF receptor. These studies extend the potential roles of CXCR4 in cancer to include functions associated with benign (grade 1) tumors. The ability to distinguish phosphorylated CXCR4 will be invaluable for the continued analysis of the role of CXCR4 in cancer and the development of CXCR4 antagonist therapy for patients suffering with primary tumors of the brain and other sites.

Interleukin-18 primes the oxidative burst of neutrophils in response to formyl-peptides: role of cytochrome b558 translocation and N-formyl peptide receptor endocytosis

Using flow cytometry, we observed that interleukin-18 (IL-18) primed human neutrophils (PMNs) in whole blood to produce superoxide anion (O2 degrees-) in response to N-formyl peptide (fMLP) stimulation, whereas IL-18 alone had no significant effect. In contrast to tumor necrosis factor alpha (TNF-alpha), which is a cytokine known to strongly prime O2 degrees- production, IL-18 did not induce either p47phox phosphorylation or its translocation from the cytosol to the plasma membrane. However, IL-18 increased PMN degranulation, as shown by increased levels of cytochrome b558 and CD11b expression at the PMN surface. Moreover, addition of IL-18 to whole blood for 45 min reduced the ability of PMNs to bind to fMLP, suggesting endocytosis of fMLP receptors, as visualized by confocal microscopy. 2,3-Butanedione 2-monoxime, which inhibits endosomal recycling of plasma membrane components back to the cell surface, concomitantly accentuated the diminution of fMLP binding at the PMN surface and increased IL-18 priming of O2 degrees- production by PMNs in response to fMLP. This suggests that fMLP receptor endocytosis could account, at least in part, for the priming of O2 degrees- production. In addition, genistein, a tyrosine kinase inhibitor, and SB203580, a p38 mitogen-activated protein kinase (p38MAPK) inhibitor, completely reversed the decreased level of fMLP binding and increased the level of CD11b expression after IL-18 treatment. Flow cytometric analysis of intact PMNs in whole blood showed that IL-18 increased p38MAPK phosphorylation and tyrosine phosphorylation. In particular, IL-18 induced phosphorylation of focal adhesion kinase (p125FAK), which has been implicated in cytoskeleton reorganization. Taken together, our findings suggest several mechanisms that are likely to regulate cytokine-induced priming of the oxidative burst in PMNs in their blood environment.

Induction of 15-lipoxygenase-1 impairs expression of HIV-1 receptors CD4 and CXCR4 in monocytic cells

The lipoxygenase pathway of immunocompetent cells has been related to HIV infection and interleukins-4 and -13 have been described as major regulators of this metabolic route. To explore whether 15-lipoxygenase1 expression might impact the responsiveness of monocytic cells for HIV we induced expression of this enzyme by two independent ways (stable transfection of U937 cells and culturing of blood monocytes in vitro in the presence of granulocyte/monocyte colony stimulating factor and interleukin 4) and assayed the cellular content of the two HIV-1 receptors CD4 and CXCR4 (CD184) by real time RT-PCR and fluorescence-activated cell sorting. Wild-type U937 cells express CD4 and CXCR4 at high levels and expression was not altered when the cells were transfected with control plasmids. In contrast, expression of these proteins was strongly reduced when the cells were stably transfected with 15-lipoxygenase1. Similar effects were observed when blood monocytes were cultured in the presence of granulocyte/monocyte colony stimulating factor and interleukin-4. Under these conditions strong overexpression of 15-lipoxygenase1 was paralleled by downregulation of CD4 and CXCR4. Since these surface proteins are essential for the binding of T-tropic HIV-1 strains expression of 15-lipoxygenase1 may confer resistance against HIV infection to monocytic cells.