Biological significance of the expression of HIV-related chemokine coreceptors (CCR5 and CXCR4) and their ligands by human hematopoietic cell lines

How filopodia respond to calcium in the absence of a calcium-binding structural protein: non-channel functions of TRP

Background

For many cell types, directional locomotion depends on their maintaining filopodia at the leading edge. Filopodia lack any Ca²⁺-binding structural protein but respond to store-operated Ca²⁺ entry (SOCE).

Methods

SOCE was induced by first replacing the medium with Ca²⁺-free salt solution with cyclopiazonic acid (CPA). This lowers Ca²⁺ in the ER and causes stromal interacting molecule (STIM) to be translocated to the cell surface. After this priming step, CPA was washed out, and Ca²⁺ influx restored by addition of extracellular Ca²⁺. Intracellular Ca²⁺ levels were measured by calcium orange fluorescence. Regulatory mechanisms were identified by pharmacological treatments. Proteins mediating SOCE were localized by immunofluorescence and analyzed after image processing.

Results

Depletion of the ER Ca²⁺ increased filopodia prevalence briefly, followed by a spontaneous decline that was blocked by inhibitors of endocytosis. Intracellular Ca²⁺ increased continuously for ~ 50 min. STIM and a transient receptor potential canonical (TRPC) protein were found in separate compartments, but an aquaporin unrelated to SOCE was present in both. STIM1- and TRPC1-bearing vesicles were trafficked on microtubules. During depletion, STIM1 migrated to the surface where it coincided with Orai in punctae, as expected. TRPC1 was partially colocalized with Vamp2, a rapidly releasable pool marker, and with phospholipases (PLCs). TRPC1 retreated to internal compartments during ER depletion. Replenishment of extracellular Ca²⁺ altered the STIM1 distribution, which came to resemble that of untreated cells. Vamp2 and TRPC1 underwent exocytosis and became homogeneously distributed on the cell surface. This was accompanied by an increased prevalence of filopodia, which was blocked by inhibitors of TRPC1/4/5 and endocytosis.

Conclusions

Because the media were devoid of ligands that activate receptors during depletion and Ca²⁺ replenishment, we could attribute filopodia extension to SOCE. We propose that the Orai current stimulates exocytosis of TRPC-bearing vesicles, and that Ca²⁺ influx through TRPC inhibits PLC activity. This allows regeneration of the substrate, phosphatidylinositol 4,5 bisphosphate (PIP2), a platform for assembling proteins, e. g. Enabled and IRSp53. TRPC contact with PLC is required but is broken by TRPC dissemination. This explains how STIM1 regulates the cell’s ability to orient itself in response to attractive or repulsive cues.

A biophysical perspective on receptor-mediated virus entry with a focus on HIV

As part of their entry and infection strategy, viruses interact with specific receptor molecules expressed on the surface of target cells. The efficiency and kinetics of the virus-receptor interactions required for a virus to productively infect a cell is determined by the biophysical properties of the receptors, which are in turn influenced by the receptors' plasma membrane (PM) environments. Currently, little is known about the biophysical properties of these receptor molecules or their engagement during virus binding and entry. Here we review virus-receptor interactions focusing on the human immunodeficiency virus type 1 (HIV), the etiological agent of acquired immunodeficiency syndrome (AIDS), as a model system. HIV is one of the best characterised enveloped viruses, with the identity, roles and structure of the key molecules required for infection well established. We review current knowledge of receptor-mediated HIV entry, addressing the properties of the HIV cell-surface receptors, the techniques used to measure these properties, and the macromolecular interactions and events required for virus entry. We discuss some of the key biophysical principles underlying receptor-mediated virus entry and attempt to interpret the available data in the context of biophysical mechanisms. We also highlight crucial outstanding questions and consider how new tools might be applied to advance understanding of the biophysical properties of viral receptors and the dynamic events leading to virus entry.

Chemokines – role in inflammatory and cancer diseases

Over 50 human chemokines are known at present; the number of the newly discovered compounds from this group still grows. These proteins of low molecular weight, belonging to the family of cytokines with chemotactic properties. Chemokines participate in the physiological and pathological processes of the organism. Recent papers show their role in the processes of embryogenesis, organogenesis, allergies, wound healing, angiogenesis and apoptosis, the course of viral and bacterial infections, autoimmune diseases and cancerogenesis. Chemokines play crucial role in activation and migration of immune cells. Being a key player in chronic inflammation, chemokines may interfere the processes of cellular differentiation and contribute to loss of control over proliferation. Coexistence of inflammatory and cancerogenesis processes, impact of chemokines on cells associated with the tumor and stromal cells, mechanisms of immunological escape is considered to be a current scientific issue. Newly discovered functions of chemokines may reveal their new roles and create the new therapeutic perspectives. It is important to understand the relationship between the structure and function of chemokine receptors, the regulation of their signaling pathways and the genetic and epigenetic mechanisms that regulate the expression of chemokines and their receptors. This article presents the current state of knowledge regarding the construction and classification of chemokines and summarizes the most prominent roles of chemokines. Chemokines are still the subject of many scientific studies, new functions are being discovered. It gives an opportunity to limit the development of many dangerous diseases.

Expression and functional roles of the chemokine receptor CXCR7 in acute myeloid leukemia cells

BACKGROUND

The C-X-C chemokine receptor 7 (CXCR7) has been shown to be a decoy receptor for CXCR4 in certain cell types. We investigated the expression status and functional roles of CXCR7 in acute myeloid leukemia (AML) cells in vitro.

METHODS

CXCR7 mRNA was knocked down in AML cells by using small interfering RNA (siRNA) technology, and subsequent biological alterations in the cells were evaluated in vitro.

RESULTS

All AML cell lines examined in this study (U937, K562, KG1a, HL-60, and MO7e) and primary CD34(+) cells obtained from patients with AML expressed CXCR7 mRNA at various levels. Western blotting showed that all AML cells produced CXCR7. Furthermore, all AML cells expressed CXCR7 in both the cytoplasm and on the cell surface at various levels. Stromal cell-derived factor-1 (SDF-1; C-X-C motif ligand 12 (CXCL12)) induced internalization of cell surface CXCR7. However, neither hypoxia nor the examined hematopoietic growth factors (interleukin-1β (IL-1β), IL-3, IL-6, granulocyte-colony-stimulating factor, granulocyte, macrophage-colony-stimulating factor, and stem cell factor) and proinflammatory cytokines (interferon-γ, transforming growth factor-β, and tumor necrosis factor-α) were found to alter cell surface CXCR7 expression. The transfection of AML cells with CXCR4 siRNA, but not CXCR7 siRNA, significantly impaired the CXCL12-induced transmigration of the cells. The transfection of AML cells with CXCR7 siRNA did not affect the survival or proliferation of these cells. Knockdown of CXCR7, but not CXCR4, induced the upregulation of CXCL12 mRNA expression and CXCL12 production in AML cells.

CONCLUSION

CXCR7 is involved in the regulation of autocrine CXCL12 in AML cells.

Trivalent ligands for CXCR4 bearing polyproline linkers show specific recognition for cells with increased CXCR4 expression

The trivalent ligand with rigid linkers designed for exploration of GPCR multimerization shows specific recognition for overexpressed CXCR4.

Endogenous stromal cell-derived factor-1 (CXCL12) supports autonomous growth of acute myeloid leukemia cells

We investigated the role of endogenous stromal cell-derived factor-1 (SDF-1; CXCL12) in the survival and proliferation of acute myeloid leukemia (AML) cells in vitro. CD34(+) cells from the peripheral blood of five patients with AML, as well as five AML cell lines, produced and secreted SDF-1. Knock-down of endogenous SDF-1 expression using siRNA technology downregulated the constitutive phosphorylation of SDF-1-related signaling molecules and significantly inhibited spontaneous proliferation of the AML cell lines during a 3-day incubation in serum-free conditions. These results indicate that endogenous SDF-1 expression by AML cells plays a role in the autonomous growth of the cells.

LEDGF/p75-independent HIV-1 replication demonstrates a role for HRP-2 and remains sensitive to inhibition by LEDGINs

Lens epithelium–derived growth factor (LEDGF/p75) is a cellular cofactor of HIV-1 integrase (IN) that interacts with IN through its IN binding domain (IBD) and tethers the viral pre-integration complex to the host cell chromatin. Here we report the generation of a human somatic LEDGF/p75 knockout cell line that allows the study of spreading HIV-1 infection in the absence of LEDGF/p75. By homologous recombination the exons encoding the LEDGF/p75 IBD (exons 11 to 14) were knocked out. In the absence of LEDGF/p75 replication of laboratory HIV-1 strains was severely delayed while clinical HIV-1 isolates were replication-defective. The residual replication was predominantly mediated by the Hepatoma-derived growth factor related protein 2 (HRP-2), the only cellular protein besides LEDGF/p75 that contains an IBD. Importantly, the recently described IN-LEDGF/p75 inhibitors (LEDGINs) remained active even in the absence of LEDGF/p75 by blocking the interaction with the IBD of HRP-2. These results further support the potential of LEDGINs as allosteric integrase inhibitors.

Like other viruses, HIV has a limited genome and needs to exploit the machinery of the host cell to complete its replication cycle. The elucidation of virus-host interactions not only sheds light on pathogenesis but also provides opportunities in a limited number of cases to develop novel antiviral drugs. A prototypical example is the interaction between the cellular protein LEDGF/p75 and HIV-1 integrase (IN). Here we generated a human somatic LEDGF/p75 knockout cell line to demonstrate that HIV-1 replication is highly dependent on its cofactor. We show that the residual replication of laboratory strains is predominantly mediated by a LEDGF/p75-related protein, HRP-2. Interestingly, the recently developed HIV-1 IN inhibitors that target the LEDGF/p75-IN interaction interface, LEDGINs, remain active even in the absence of LEDGF/p75. We demonstrate that LEDGINs efficiently block the interaction between IN and HRP-2. In case HIV-1 would be able to bypass LEDGF/p75-dependent replication using HRP-2 as an alternative tether, LEDGINs would remain fully active.

Microvesicles in health and disease

Microvesicles (or MVs) are plasma membrane-derived vesicles released from most eukaryotic cells constitutively during early apoptosis or at higher levels after chemical or physical stress conditions. This review looks at some of the functions of MVs in terms of intercellular communication and ensuant signal transduction, including the transport of proteins (unconventional protein export) as well as of mRNA and microRNA. MVs also have roles in membrane repair, the removal of misfolded proteins, and in the control of apoptosis. We also discuss the role MVs have been shown to have in invasive growth and metastasis as well as in hypoxia in tumours and cerebral ischaemia. The association of MVs in infectious and autoimmune disease is also summarised together with their possible use as therapeutic agents.

Differential effects of CXCR4 antagonists on the survival and proliferation of myeloid leukemia cells in vitro

BACKGROUND

Antagonists of CXC chemokine receptor 4 (CXCR4), including AMD3100, induce peripheral mobilization of hematopoietic stem cells and have been approved for clinical use. We explored whether the CXCR4 antagonists affected the survival and proliferation of myeloid leukemia cells in vitro.

METHODS

The effects of CXCR4 antagonists AMD3100 and T140 on the survival and proliferation of myeloid leukemia cell lines (U937, HL-60, MO7e, KG1a, and K562) as well as CD34(+) cells obtained from patients with AML and CML were analyzed by flow cytometry by using annexin V and a colorimetric cell proliferation assay.

RESULTS

AMD3100, but not T140, stimulated the proliferation of leukemia cells in vitro in a dose-dependent manner for up to 5 days (~2-fold increase at a concentration of 10(-5) M), which was not abrogated by pretreatment of the cells with pertussis toxin, but was attenuated by RNAi knockdown of CXCR7 transcripts. In contrast, AMD3100 induced a marked decrease in the cell numbers after 5-7 days. AMD3100, but not T140, induced phosphorylation of MAPK p44/p42. AMD3100 increased the number and size of leukemia cell colonies and reduced cell apoptosis during the first 5-7 days of incubation, but the phenomena were reversed during the later period of incubation.

CONCLUSION

The effects of CXCR4 antagonists on the proliferation of myeloid leukemia cells are not uniform. AMD3100, but not T140, exerts dual effects, initially enhancing and subsequently inhibiting the survival and proliferation of the cells in vitro.

Overlapping and distinct role of CXCR7-SDF-1/ITAC and CXCR4-SDF-1 axes in regulating metastatic behavior of human rhabdomyosarcomas

We have demonstrated that the α-chemokine stromal-derived factor (SDF)-1-CXCR4 axis plays an important role in rhabdomyosarcoma (RMS) metastasis. With the recent description of CXCR7, a new receptor for SDF-1 that also binds the interferon-inducible T-cell α chemoattractant (ITAC) chemokine, we became interested in the role of the CXCR7-SDF-1/ITAC axis in RMS progression. To address this issue, we evaluated 6 highly metastatic alveolar (A)RMS and 3 less metastatic embryonal (E)RMS cell lines and found that all these cell lines express CXCR7. Although CXCR4 was expressed at a much higher level by highly metastatic ARMS lines, CXCR7 was present at a high level on ERMS lines. We also noticed that CXCR7 expression on RMS cells was downregulated in hypoxic conditions. More importantly, the CXCR7 receptor on RMS cell lines was functional after stimulation with ITAC and SDF-1 as evidenced by mitogen-activated protein kinase (MAPK)p42/44 and AKT phosphorylation as well as CXCR7 internalization, chemotaxis, cell motility and adhesion assays. Similarly to CXCR4, signaling from activated CXCR7 was not associated with increased RMS proliferation or cell survival. Moreover, CXCR7(+) RMS cells responded to SDF-1 and I-TAC in the presence of CXCR4 antagonists (T140, AMD3100). Furthermore, while intravenous injection of RMS cells with overexpressed CXCR7 resulted in increased seeding efficiency of tumor cells to bone marrow, CXCR7 downregulation showed the opposite effect. In conclusion, the CXCR7-SDF-1/ITAC axis is involved in the progression of RMS; targeting of the CXCR4-SDF-1 axis alone without simultaneous blockage of CXCR7 will be an inefficient strategy for inhibiting SDF-1-mediated prometastatic responses of RMS cells.

HIV-1 infection inhibits cytokine production in human thymic macrophages

OBJECTIVE

The thymus serves as a critical site of T-lymphocyte ontogeny and selection. Thymic infection by HIV-1 is known to disrupt thymocyte maturation by both direct and indirect means; however, the mechanism behind these effects remains poorly defined. Macrophages represent one of the most important peripheral targets of HIV-1 infection, are resident in the thymic stroma, and play a central role in thymocyte maturation.

MATERIALS AND METHODS

Studies presented here define three primary features and outcomes of thymic macrophages (TM) and HIV-1 infection: (1) The distinctive TM phenotype (surface markers and cytokine production measured by immunofluorescence, fluorescence-activated cell sorting, and reverse transcriptase polymerase chain reaction) relative to macrophages from other sources (blood [monocyte-derived macrophages] and bone marrow); (2) infection of TM by different HIV-1 subtypes (X4, R5, and X4/R5) measured by enzyme-linked immunosorbent assay and polymerase chain reaction; and (3) consequences of HIV-1 infection on cytokine production by TM measured by reverse transcriptase polymerase chain reaction.

RESULTS

The results demonstrate that TM display a distinctive phenotype of HIV-1 receptors (CD4(lo), CXCR4(lo), CCR5(med), CCR3(hi)), chemokine production (macrophage inflammatory protein-1α(+); regulated on activation, normal T expressed and secreted(+); macrophage inflammatory protein-1b(-); stromal cell-derived factor -1(-)); and cytokine production (tumor necrosis factor-α(+), interleukin-8(+), macrophage colony-stimulating factor(+), interleukin-6(-)) relative to either monocyte-derived macrophages or bone marrow. TM were infected in vitro with R5 and X4/R5-tropic HIV-1 subtypes, and developed syncytia formation during long-term X4/R5 culture. In contrast, TM supported only transient replication of X4-tropic HIV-1. Lastly, infection of TM with HIV-1 abolished the production of all cytokines tested in long-term in vitro cultures.

CONCLUSIONS

Taken together, these results indicate that TM are a potential direct target of in situ HIV-1 infection, and that this infection may result in the disruption of macrophage functions that govern normal thymocyte maturation.

Bivalent ligands of CXCR4 with rigid linkers for elucidation of the dimerization state in cells

To date, challenges in the design of bivalent ligands for G protein-coupled receptors (GPCRs) have revealed difficulties stemming from lack of knowledge of the state of oligomerization of the GPCR. The synthetic bivalent ligands with rigid linkers that are presented here can predict the dimer form of CXCR4 and be applied to molecular probes in cancerous cells. This "molecular ruler" approach would be useful in elucidating the details of CXCR4 oligomer formation.

Macrophage migration inhibitory factor is secreted by rhabdomyosarcoma cells, modulates tumor metastasis by binding to CXCR4 and CXCR7 receptors and inhibits recruitment of cancer-associated fibroblasts

The overexpression of macrophage migration inhibitory factor (MIF) has been observed in many tumors and is implicated in oncogenic transformation and tumor progression. MIF activates CXCR2 and CD74 receptors and, as recently reported, may also bind to the stromal-derived factor-1 (SDF-1)-binding receptor CXCR4. Here, we report that human rhabdomyosarcoma (RMS) cell lines secrete MIF and that this chemokine (a) induces phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 and AKT, (b) stimulates RMS cell adhesion, (c) enhances tumor vascularization, but surprisingly (d) decreases recruitment of cancer-associated fibroblasts (CAF). Because RMS cells used in our studies do not express CXCR2 and CD74 receptors, the biological effects of MIF on RMS cells depend on its interaction with CXCR4, and as we report here for the first time, MIF may also engage another SDF-1-binding receptor (CXCR7) as well. Interestingly, downregulation of MIF in RMS cells inoculated into immunodeficient mice led to formation of larger tumors that displayed higher stromal cell support. Based on these observations, we postulate that MIF is an important autocrine/paracrine factor that stimulates both CXCR4 and CXCR7 receptors to enhance the adhesiveness of RMS cells. We also envision that when locally secreted by a growing tumor, MIF prevents responsiveness of RMS to chemoattractants secreted outside the growing tumor (e.g., SDF-1) and thereby prevents release of cells into the circulation. On the other hand, despite its obvious proangiopoietic effects, MIF inhibits in CXCR2/CD74-dependent manner recruitment of CAFs to the growing tumor. Our data indicate that therapeutic inhibition of MIF in RMS may accelerate metastasis and tumor growth.

Expression of CCR5 receptors on Reed-Sternberg cells and Hodgkin lymphoma cell lines: involvement of CCL5/Rantes in tumor cell growth and microenvironmental interactions

The expression of CCL5/Rantes by Hodgkin (H) and Reed-Sternberg (RS) cells has been recently documented. In the present study we demonstrated that the CCL5 receptor (CCR5) is constitutively expressed by Hodgkin Lymphoma (HL)-derived cell lines (i.e. L-428, KM-H2, L-1236 and L-540) as shown by immunohistochemistry, flow cytometry and western blotting and also detected by immunohistochemistry on primary H-RS cells from lymph node tissues. sCD40L never significantly affected CCR5 expression, whereas a short exposure to doxorubicin down regulated its expression. CCR5 receptors on HL cell lines were functionally active, since neutralizing anti-CCL5 monoclonal antibodies inhibited basal proliferation of HL-derived cell lines and recombinant CCR5 ligands (CCL3/Mip-1 alpha, CCL4/Mip1 beta and CCL5/Rantes) increased their clonogenic growth. CCL5 secretion by L-1236, L-428 and KM-H2 cells was stimulated by CD40 engagement and also by coculturing L-1236 cells on primary stromal fibroblasts from HL-involved lymph nodes (HLF). Coculture experiments indicated that a direct contact of H-RS cells induces HLF cells to produce CCL5. Supernatants from L-1236, L-428 and KM-H2 cells stimulated migration of purified CD4+ T-cells and eosinophils in vitro. The migratory response to HL-cell lines supernatants was only partially neutralized (CD4+ cells: 70%; esinophils: 36%) by anti-CCL5 antibodies, reinforcing the notion that multiple chemokines are involved in the recruitment of nonmalignant reactive cells in HL tissues. Taken together, our results indicate a possible involvement of the CCR5/CCR5-ligands signaling in the regulation of H-RS cells growth and in the formation/maintenance of the typical tissue microenvironment of HL.

Mobilization studies in mice deficient in either C3 or C3a receptor (C3aR) reveal a novel role for complement in retention of hematopoietic stem/progenitor cells in bone marrow

The mechanisms regulating the homing/mobilization of hematopoietic stem/progenitor cells (HSPCs) are not fully understood. In our previous studies we showed that the complement C3 activation peptide, C3a, sensitizes responses of HSPCs to stromal-derived factor 1 (SDF-1). In this study, mobilization was induced with granulocyte colony-stimulating factor (G-CSF) in both C3-deficient (C3-/-) and C3a receptor-deficient (C3aR-/-) mice as well as in wild-type (wt) mice in the presence or absence of a C3aR antagonist, SB 290157. The data indicated (1) significantly increased G-CSF-induced mobilization in C3-/- and C3aR-/- mice compared with wt mice, (2) significantly accelerated and enhanced G-CSF-induced mobilization in wt, but not in C3-/- or C3aR-/-, mice treated with SB 290157, and (3) deposition of C3b/iC3b fragments onto the viable bone marrow (BM) cells of G-CSF-treated animals. Furthermore, mobilization studies performed in chimeric mice revealed that wt mice reconstituted with C3aR-/- BM cells, but not C3aR-/- mice reconstituted with wt BM cells, are more sensitive to G-CSF-induced mobilization, suggesting that C3aR deficiency on graft-derived cells is responsible for this increased mobilization. Hence we suggest that C3 is activated in mobilized BM into C3a and C3b, and that the C3a-C3aR axis plays an important and novel role in retention of HSPCs (by counteracting mobilization) by increasing their responsiveness to SDF-1, the concentration of which is reduced in BM during mobilization. The C3a-C3aR axis may prevent an uncontrolled release of HSPCs into peripheral blood. These data further suggest that the C3aR antagonist SB 290157 could be developed as a drug to mobilize HSPCs for transplantation.

Engraftment of Acute Myeloid Leukemia in NOD/SCID Mice Is Independent of CXCR4 and Predicts Poor Patient Survival

The aim of this study was to investigate factors influencing the engraftment potential of acute myeloid leukemia (AML) CD34+ cells in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. We examined the relationship between engraftment, CXCR4 expression on CD34+ and CD34+CD38- cells, and patient (Pt) clinical/laboratory characteristics in 44 samples from 11 Pts. Engraftment, evaluated by Southern blot and CD45 flow cytometric analyses, was observed in murine bone marrow of 6 of 11 Pt samples, ranging from 0.1% to 73.9% by Southern blot and from 0.1%-36.8% by flow cytometry. Poor Pt prognosis was inversely correlated with engraftment; the median overall survival was 95.9 weeks for Pts whose cells did not engraft and 26.1 weeks for those whose cells did engraft (p = 0.012, log-rank test). No other clinical/laboratory variable predicted engraftment. No correlation between the level of CXCR4 expression on AML cells and engraftment was observed. Cells with virtually absent CXCR4 expression were able to engraft, and cells from two Pts with high expression levels of CXCR4 did not engraft. Furthermore, anti-CXCR4 antibody failed to block the engraftment of AML cells into NOD/SCID mice. In conclusion, we demonstrated that CXCR4 is not critical for the engraftment of AML CD34+ cells in NOD/SCID mice. The model may, however, reflect the clinical course of the disease.

Platelet- and megakaryocyte-derived microparticles transfer CXCR4 receptor to CXCR4-null cells and make them susceptible to infection by X4-HIV

OBJECTIVE

Under some circumstances the HIV virus may infect cells that do not express receptors essential to HIV-entry. We hypothesized that platelet- and megakaryocyte-derived microparticles (MP) could play a role in such infections. MP are circular membrane fragments shed from the surface of eukaryotic cells. After adhesion to target cells, MP may transfer membrane-associated proteins to these cells. We found that peripheral blood platelet- (PMP) and megakaryocyte-derived MP (MegaMP) that highly express CXCR4 may transfer this receptor from the surface of platelets or megakaryocytes to the surface of CXCR4-null cells.

DESIGN

Since this mechanism could potentially allow CD4+/CXCR4-null cells to become infected by T-tropic HIV, we incubated several human CD4+/CXCR4-null cells such as normal erythroblasts, glioblastomas U87, MAGI and hematopoietic cell lines UT-7, HEL and TF-1 with PMP or MegaMP. We found that these cells became CXCR4+. We next exposed these cells to X4-HIV (IIIB) and evaluated their susceptibility to infection by PCR, ELISA, and morphological analysis.

RESULTS

We observed in all instances that after CD4+/CXCR4-null cell lines 'acquired' CXCR4 from PMP or MegaMP, they could became infected by X4 HIV.

CONCLUSIONS

We postulate that both PMP and MegaMP may play a novel and important role in spreading HIV-1 infection by transferring the CXCR4 co-receptor to CD4+/CXCR4-null cells.

HIV type 1 infection alters cytokine mRNA expression in thymus

We and others have previously shown that HIV infection of human thymus/liver implants in severe combined immunodeficient (SCID-hu Thy/Liv) mice results in a loss of CD4(+) thymocytes and a decreased recovery of human myeloid and erythroid colony-forming activity. Furthermore, our previous studies have shown that this decrease in colony-forming potential is due to indirect effects, rather than to massive loss of CD34(+) hematopoietic progenitor cells, suggesting that HIV infection might alter expression of hematopoietic cytokines. Herein we have investigated potential HIV-1-induced perturbations of hematolymphoid microenvironments by determining the effect of HIV-1 infection on levels of cytokine mRNAs in human stroma and thymocytes, using the reverse transcription-polymerase chain reaction (RT-PCR). The levels of interleukin 6 (IL-6), interferon gamma (IFN-gamma), and IL-2 RNAs increased and macrophage inflammatory protein 1beta (MIP-1beta) RNA decreased significantly in infected thymocytes. IL-6 RNA levels in stroma also increased somewhat with infection; however, expression of stromal cell-derived factor 1 (SDF-1) by stromal elements was not affected. IL-4 RNA levels were unaffected by infection in both stroma and thymocytes. Antiretroviral drug treatment of the infected animals, which results in restoration of colony-forming potential, tends to restore the cytokine mRNA levels in HIV-1-infected implants to those of mock-infected implants. These results indicate that HIV-1 infection can greatly distort the cytokine profiles in Thy/Liv implants, and suggest that cytokine perturbation could be involved in virus-induced inhibition of hematopoiesis.

CXCR4-SDF-1 signaling is active in rhabdomyosarcoma cells and regulates locomotion, chemotaxis, and adhesion

We hypothesized that the CXC chemokine receptor-4 (CXCR4)-stromal-derived factor-1 (SDF-1) axis may be involved in metastasis of CXCR4(+) tumor cells into the bone marrow and lymph nodes, which secrete the alpha-chemokine SDF-1. To explore this hypothesis, we phenotyped by fluorescence-activated cell sorter analysis various human tumor cell lines for expression of CXCR4 and found that it was highly expressed on several rhabdomyosarcoma (RMS) cell lines. We also observed that cell lines derived from alveolar RMS, which is characterized by recurrent PAX3- and PAX7-FKHR gene fusions and is associated with a poor prognosis, expressed higher levels of CXCR4 than lines derived from embryonal RMS. Furthermore, transfer of a PAX3-FKHR gene into embryonal RMS cell activates CXCR4 expression. Because alveolar RMS frequently metastasizes to the bone marrow and lymph nodes, it seems that the CXCR4-SDF-1 axis could play an important role in this process. These findings prompted us to determine whether SDF-1 regulates the metastatic behavior of RMS cells. Accordingly, we found that, although SDF-1 did not affect proliferation or survival of these cell lines, it induced in several of them (1) phosphorylation of mitogen-activated protein kinase p42/44; (2) locomotion; (3) directional chemotaxis across membranes covered by laminin, fibronectin, or Matrigel; (4) adhesion to laminin, fibronectin, and endothelial cells; and (5) increased MMP-2 and diminished tissue inhibitors of metalloproteinases secretion. The small-molecule CXCR4-specific inhibitor, T140, effectively blocked the in vitro responses of RMS cells to SDF-1. On the basis of these observations we suggest that the CXCR4-SDF-1 axis may play an important role in tumor spread and metastasis of RMS cells to bone marrow and that molecular strategies aimed at inhibiting this axis could thus prove to be useful therapeutic measures.

Treatment of circulating CD34(+) cells with SDF-1alpha or anti-CXCR4 antibody enhances migration and NOD/SCID repopulating potential

OBJECTIVE

Stromal cell-derived factor-1alpha (SDF-1alpha) has been implicated in homing and engraftment of primitive hematopoietic progenitor cells (HPC) in studies demonstrating reduced NOD/SCID repopulating potential of HPC exposed to supra-physiologic concentrations of SDF-1alpha or anti-CXCR4. Outcome of CXCR4 signaling in some cells has been shown to be dependent on the concentration of SDF-1alpha. We aimed to determine whether similar concentration-dependent responses to CXCR4 signaling are present in CD34(+)cells.

MATERIALS AND METHODS

Human peripheral blood (PB), mobilized PB (MPB), or bone marrow (BM) CD34(+) cells were incubated for 30 minutes with different concentrations of SDF-1alpha or anti-CXCR4, washed, then assessed for in vitro hematopoietic potential, migration, and NOD/SCID repopulating potential.

RESULTS

Exposure of MPB or PB CD34(+) cells to 100 ng/mL SDF-1alpha increased tyrosine phosphorylation without subsequent proliferation or apoptosis. Spontaneous and SDF-1alpha-directed migration also increased in pretreated cells, despite previous exposure to SDF-1alpha. Cells exposed to 1 microg anti-CXCR4/10(6) cells displayed similar increases in activation and migration as cells exposed to SDF-1alpha, demonstrating the ability of anti-CXCR4 to activate the CXCR4 receptor. Interestingly, chimerism in NOD/SCID mice transplanted with MPB CD34(+) cells pretreated with SDF-1alpha or anti-CXCR4 was increased, while exposure of these cells to 10- to 100-fold higher concentrations of these proteins inhibited in vitro migration and NOD/SCID repopulating potential. Migration and NOD/SCID repopulating potential of BM CD34(+) cells remained unchanged after treatment with either protein.

CONCLUSIONS

These results illustrate the ability of SDF-1alpha and anti-CXCR4 to augment repopulating potential of CD34(+) cells, and suggest that HPC function can be favorably modulated through specific CXCR4 signaling.

Stromal-derived factor 1 inhibits the cycling of very primitive human hematopoietic cells in vitro and in NOD/SCID mice

Stromal-derived factor 1 (SDF-1) is a -CXC- chemokine that plays a critical role in embryonic and adult hematopoiesis, and its specific receptor, CXCR4, has been implicated in stem cell homing. In this study, it is shown that the addition of SDF-1 to long-term cultures (LTCs) of normal human marrow can selectively, reversibly, and specifically block the S-phase entry of primitive quiescent erythroid and granulopoietic colony-forming cells (CFCs) present in the adherent layer. Conversely, addition of anti-SDF-1 antibody or SDF-1(G2), a specific CXCR4 antagonist, to preactivated human LTCs prevented both types of primitive CFCs from re-entering a quiescent state, demonstrating that endogenous SDF-1 contributes to the control of primitive CFC proliferation in the LTC system. Interestingly, SDF-1 failed to arrest the proliferation of primitive chronic myeloid leukemia CFCs in the adherent layer of LTCs containing normal marrow stromal cells. In vivo, injection of SDF-1 arrested the cycling of normal human LTC-initiating cells as well as primitive CFCs in the marrow of nonobese diabetic/severe combined immunodeficient mice engrafted with human cord blood cells. Conversely, injection of the antagonist, SDF-1(G2), reactivated the cycling of quiescent primitive human CFCs present in the marrow of mice engrafted with human marrow cells. These studies are the first to demonstrate a potential physiological role of SDF-1 in regulating the cell-cycle status of primitive hematopoietic cells and suggest that the deregulated cycling activity of primitive chronic myeloid leukemia (CML) cells is due to the BCR-ABL-mediated disruption of a pathway shared by multiple chemokine receptors.

The SDF-1-CXCR4 axis stimulates VEGF secretion and activates integrins but does not affect proliferation and survival in lymphohematopoietic cells

To better define the role HIV-related chemokine receptor-chemokine axes play in human hematopoiesis, we investigated the function of the CXCR4 and CCR5 receptors in human myeloid, T- and B-lymphoid cell lines selected for the expression of these receptors (CXCR4(+), CXCR4(+) CCR5(+), and CCR5(+) cell lines). We evaluated the phosphorylation of MAPK p42/44, AKT, and STAT proteins and examined the ability of the ligands for these receptors (stromal-derived factor-1 [SDF-1] and macrophage inflammatory protein-1beta [MIP-1beta]) to influence cell growth, apoptosis, adhesion, and production of vascular endothelial growth factors (VEGF), matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in these cell lines. We found that A) SDF-1, after binding to CXCR4, activates multiple signaling pathways and that in comparison with the MIP-1beta-CCR5 axis, plays a privileged role in hematopoiesis; B) SDF-1 activation of the MAPK p42/44 pathway and the PI-3K-AKT axis does not affect proliferation and apoptosis but modulates integrin-mediated adhesion to fibronectin, and C) SDF-1 induces secretion of VEGF, but not of MMPs or TIMPs. Thus the role of SDF-1 relates primarily to the interaction of lymphohematopoietic cells with their microenvironment and does not directly influence their proliferation or survival. We conclude that perturbation of the SDF-1-CXCR4 axis during HIV infection may affect interactions of hematopoietic cells with the hematopoietic microenvironment.

New T-lymphocytic cell lines for studying cell infectability by human immunodeficiency virus

We identified five human T-lymphoid cell lines (PB-1, Sez-4, C19PL, HUT 102B and ATL-2) which highly express CD4 in addition to CXCR4 and CCR5. In order to evaluate if these cells are infectabile by human immunodeficiency virus (HIV) and could be employed as a model in HIV research we exposed these cell lines to X4 (T-cell tropic) and R5 (macrophage tropic) and subsequently tried to correlate their infectability with (i) level of chemokine coreceptor (CXCR4 and CCR5) expression, (ii) coreceptor functionality (calcium flux, chemotaxis and phosphorylation of MAPK p42/44 and AKT) and (iii) endogenous expression and secretion of HIV-related chemokines which compete with the virus for binding to CXCR4 (SDF-1/CXCL12) or CCR5 (MIP-1beta/CCL4, MIP-1alpha/CCL3, RANTES/CCL5, MCP-2/CCL8, MCP-3/CCL7 and MCP-4/CCL13). We demonstrated that while PB-1 cells are infectable by both X4 and R5 HIV, Sez-4, C91PL, HUT 102B and ATL-2 cells were infected by X4 HIV only. Moreover, we noticed that the susceptibility of these cells to HIV did not correspond either with the level of surface expression or with the functionality of CXCR4 or CCR5; however, it was modulated to some degree by the endogenously secreted HIV-related chemokines. Thus all five mature T-cell lines described here may provide useful new models for studying various aspects of HIV infection. In addition we demonstrate that the infectability of cells by HIV is modulated by so far unidentified intrinsic factors as well as some already known endogenously secreted chemokines. The identification of these factors may be important for developing new strategies to protect cells from HIV infection.