HIV-1 gp120-CXCR4 recognition probed with synthetic nanomolar affinity D-peptides containing fragments of gp120 V3 loop

The human immunodeficiency virus type 1 (HIV-1) recognizes one of its principal coreceptors, the CXC chemokine receptor 4 (CXCR4) on the host cell via the third variable loop (V3 loop) of HIV-1 envelope glycoprotein gp120 during the viral entry process. Here, we investigated the stereochemical mechanism of the molecular recognition of HIV-1 gp120 V3 loop with coreceptor CXCR4 by using peptide probes containing important fragments of the V3 loop. The tip and base/stem fragments of the V3 loop critical for V3 loop function were linked individually with the fragment derived from another CXCR4's chemokine ligand, vMIP-II to generate nanomolar affinity peptide probes of the interactions of CXCR4-V3 loop fragments. When the amino acid residues of the V3 loop fragments in these combinational peptides were changed from L-to D-configurations, the resulting peptides remarkably retained or had even enhanced recognition by CXCR4 as shown by competitive ligand-receptor binding. The ability of these peptides, regardless of the different l- or d-amino acids used, in binding CXCR4 and antagonizing CXCR4 functions was demonstrated by their blockade of calcium influx, cell migration, and CXCR4 internalization triggered by the activation of CXCR4 signaling by its endogenous ligand SDF-1α. The structural mechanisms of CXCR4 interactions with these peptides were examined with site-directed mutagenesis and molecular modeling. These results indicate that CXCR4's interface with key segments of HIV-1 gp120 V3 loop is flexible in terms of stereospecificity of ligand-receptor interaction which may have implication on understanding the viral entry mechanism and how the virus evades immune detection with V3 loop mutations and retains effective recognition of the host cell's coreceptor.

Novel bivalent ligands carrying potential antinociceptive effects by targeting putative mu opioid receptor and chemokine receptor CXCR4 heterodimers

The functional interactions between opioid and chemokine receptors have been implicated in the pathological process of chronic pain. Mounting studies have indicated the possibility that a MOR-CXCR4 heterodimer may be involved in nociception and related pharmacologic effects. Herein we have synthesized a series of bivalent ligands containing both MOR agonist and CXCR4 antagonist pharmacophores with an aim to investigate the functional interactions between these two receptors. In vitro studies demonstrated reasonable recognition of designed ligands at both respective receptors. Further antinociceptive testing in mice revealed compound 1a to be the most promising member of this series. Additional molecular modeling studies corroborated the findings observed. Taken together, we identified the first bivalent ligand 1a showing promising antinociceptive effect by targeting putative MOR-CXCR4 heterodimers, which may serve as a novel chemical probe to further develop more potent bivalent ligands with potential application in analgesic therapies for chronic pain management.

Chemokine receptor CXCR4: An important player affecting the molecular-targeted drugs commonly used in hematological malignancies

INTRODUCTION

A variety of molecular-targeted drugs have been widely used in hematological malignancies and have shown great advances. Nevertheless, as the use of drugs in clinical practice increases, the problem of relapse or of the disease being refractory to treatment is becoming apparent. This problem is closely related to the C-X-C chemokine receptor 4 (CXCR4).

AREAS COVERED

This review focuses mainly on the effect of CXCR4 on molecular-targeted drug resistance in hematological malignancies as well as the clinical efficacy of CXCR4 antagonists combined with molecular-targeted drugs. Relevant literatures published between 2006 and 2020 were searched using PubMed/Medline for this review.

EXPERT OPINION

Monoclonal antibodies and non-antibody molecular-targeted drugs provide new therapeutic approaches for B-lineage malignancies and leukemia, but the clinical activity of these drugs is affected by CXCR4. In general, high CXCR4 expression or mutation inhibits the effects of molecular-targeted drugs, but there are exceptions, and in studies of proteasome inhibitors bortezomib (Bz) in multiple myeloma (MM), low CXCR4 expression or loss of CXCR4 was associated with Bz resistance (BzR) and poor treatment outcomes. Given that CXCR4 is a critical mediator of molecular-targeted drug resistance, numerous studies have combined molecular-targeted drugs with CXCR4 antagonists, which synergistically enhance the anti-proliferative/pro-apoptotic effect of molecular-targeted drugs.

Attenuation of chemokine receptor function and surface expression as an immunomodulatory strategy employed by human cytomegalovirus is linked to vGPCR US28

Background

Some herpesviruses like human cytomegalovirus (HCMV) encode viral G protein-coupled receptors that cause reprogramming of cell signaling to facilitate dissemination of the virus, prevent immune surveillance and establish life-long latency. Human GPCRs are known to function in complex signaling networks involving direct physical interactions as well as indirect crosstalk of orthogonal signaling networks. The human chemokine receptor CXCR4 is expressed on hematopoietic stem cells, leukocytes, endothelial and epithelial cells, which are infected by HCMV or display reservoirs of latency.

Results

We investigated the potential heteromerization of US28 with CXCR4 as well as the influence of US28 on CXCR4 signaling. Using Bioluminescence Resonance Energy Transfer and luciferase-complementation based methods we show that US28 expression exhibits negative effects on CXCR4 signaling and constitutive surface expression in HEK293T cells. Furthermore, we demonstrate that this effect is not mediated by receptor heteromerization but via signaling crosstalk. Additionally, we show that in HCMV, strain TB40E, infected HUVEC the surface expression of CXCR4 is strongly downregulated, whereas in TB40E-delUS28 infected cells, CXCR4 surface expression is not altered in particular at late time points of infection.

Conclusions

We show that the vGPCR US28 is leading to severely disturbed signaling and surface expression of the chemokine receptor CXCR4 thereby representing an effective mechanism used by vGPCRs to reprogram host cell signaling. In contrast to other studies, we demonstrate that these effects are not mediated via heteromerization.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-016-0154-x) contains supplementary material, which is available to authorized users.

Exploration of labeling by near infrared dyes of the polyproline linker for bivalent-type CXCR4 ligands

We have previously used poly-L-proline linkers for the development of bivalent-type ligands for the chemokine receptor, CXCR4. The bivalent ligands with optimum linkers showed specific binding to CXCR4, suggesting the existence of CXCR4 possibly as a dimer on the cell membrane, and enabled definition of the amount of CXCR4 expressed. This paper reports the synthesis by a copper-catalyzed azide-alkyne cycloaddition reaction as the key reaction, of bivalent CXCR4 ligands with near infrared (NIR) dyes at the terminus or the center of the poly-L-proline linker. Some of the NIR-labeled ligands, which would be valuable probes useful in studies of the behavior of cells expressing CXCR4, have been obtained. The information concerning the effects of the labeling positions of NIR dyes on their binding properties is useful for the design of modified bivalent-type CXCR4 ligands.

The presence of CXCR4+ CD1a+ cells at onset of Langerhans cell histiocytosis is associated with a less favorable outcome

PURPOSE

Langerhans Cell Histiocytosis (LCH) is a neoplastic disorder characterized by tissue accumulating CD1a⁺ histiocytes which frequently carry somatic mutations. Irrespective of mutation status, these LCH-cells display constitutively active kinases belonging to the MAPK pathway. We evaluated, in retrospect, the contribution of individual components of the MAPK-activating and chemotaxis-promoting TNF-CXCR4-CXCL12 axis to LCH manifestation and outcome.

EXPERIMENTAL DESIGN

CXCR4, CXCL12 and TNF protein expression was immunohistochemically analyzed in 70 LCH-affected biopsies. The presence of CXCR4⁺CD1a⁺ cells in peripheral blood (PB) and/or bone marrow (BM) samples was evaluated by flowcytometry in 13 therapy-naive LCH-patients.

RESULTS

CXCL12 was detected in 68/70 (97%) biopsies. CXCR4⁺LCH-cells were present in 50/70 (71%) biopsies; their presence was associated with higher levels of intralesional TNF. Circulating CD1a⁺CXCR4⁺ cells were detected in 4/13 (31%) therapy-naïve LCH-patients which displayed BRAF^V600E (2/4), MAP2K1 (1/4) or no (1/4) mutations in their tissues. These CD11c co-expressing CD1a⁺CXCR4⁺cells migrated to CXCL12 in chemotaxis assays. Lesional CXCR4⁺LCH-cells were detected in 18/20 cases who presented with LCH manifestation at multiple sites and in 5/23 (22%) patients who developed additional lesions after initially presenting with a single lesion. The CXCR4 status at onset proved to be an independent risk factor for LCH reactivation in multivariate analysis (odds ratio 10.4, p = 0.034).

CONCLUSIONS

This study provides the first evidence that CXCR4 is involved in the homing and retention of LCH-cells in CXCL12-expressing tissues and qualifies CXCR4 as a candidate prognostic marker for less favorable disease outcome.

Effect of specific suppression of chemokine receptor CXCR4 by short interference RNA on the invasion capability and proliferation of colorectal cancer cells

AIM: To study the inhibitory effect of chemokine receptor CXCR4 short interference RNA (siRNA) on the invasion capability and proliferation of colorectal cancer cell line SW480.

METHODS: SiRNA specifically targeting CXC chemokine receptor CXCR4 was designed in vitro using T7 RNA polymerase. Colorectal cancer SW480 cells were cultured under standard condition and the siRNA was transfected into SW480 cells with Lipofectamine 2000. Negative control and mock control were used at the same time. The levels of CXCR4 mRNA and protein were detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting 48 h after transfection respectively. The changes of invasion capability and MT1-MMP protein in SW480 cells were evaluated using Boyden Chamber invasion assay and Western blotting respectively. The cell cycle distribution and proliferation status were detected by flow cytometry and MTT assay respectively.

RESULTS: Forty-eight hours after transfection with CXCR4 siRNA, in comparison with those in negative and mock control group, the levels of CXCR4 mRNA (51.53% ± 6.1% vs 78.4% ± 3.3%, P < 0.01; 51.53% ± 6.1% vs 87.4% ± 5.3%, P < 0.01) and protein (47.3% ± 3.7% vs 107.2% ± 3.6%, P < 0.01; 47.3% ± 3.7% vs 114.7% ± 4.8%, P < 0.01) decreased significantly (47.3% ± 3.7% vs 107.2% ± 3.6%, P < 0.01; 47.3% ± 3.7% vs 114.7% ± 4.8%, P < 0.01); the invasion capability (26.5% ± 6.1% vs 73.7% ± 3.4%, P < 0.01; 26.5% ± 6.1% vs 64.5% ± 5.7%, P < 0.01) and the MT1-MMP protein expression (43.8% ± 2.5% vs 64.4% ± 4.4%, P < 0.01; 43.8% ± 2.5% vs 67.0% ± 2.9%, P < 0.01) in SW480 cells decreased significantly, but the cell cycle distribution didn't change remarkably. At the absence of SDF-1, cell proliferation status was similar to that in control and mock control group. After stimulation by SDF-1, the proliferation of SW480 cells increased in all the groups, but it was much less active in the CXCR4 siRNA group than in the other two control groups.

CONCLUSION: CXCR4 siRNA can inhibit the expression of CXCR4 and decrease the invasion capability and proliferation of SW480 cells.

Expression of CXC chemokine receptor CXCR4 in colorectal carcinoma and its correlation with prognosis Meng-Xian Zhang, Iqbal Kashif, Shi-Ying Yu

AIM: To investigate the expression of chemokine receptor CXCR4 in colorectal carcinoma and its correlation with the clinicopathologic characteristics and prognosis.

METHODS: Immunohistochemistry was used to detect the expression of CXCR4 and tumor microvessel density (MVD) in 67 tissue specimens of colorectal carcinoma, and the correlation between the CXCR4 expression and clinicopathologic factors was evaluated.

RESULTS: The positive rate of CXCR4 expression was 56.7% in colorectal carcinoma, which was correlated with lymph node metastasis, clinical staging and MVD as well as the survival of patients, but not with the sex and age of patients, tumor location, T staging, and pathological types. The expression of CXCR4 was 40.6%, 68.2% and 76.9% in cases of N0, N1 and N2 stage, 39.4% and 73.5% in cases of Ⅰ+Ⅱ and Ⅲ stage, respectively. The positive rate of CXCR4 expression was significantly lower in the case with low MVD than that with high MVD (36.4% vs 74.3%, P < 0.01), and the CXCR4-positive case had a higher recurrent or metastatic rate (47.4% vs 24.1%, P < 0.05) and a lower 3-year survival rate (32.6% vs 71.3%, P < 0.05) than the CXCR4-negative one.

CONCLUSION: Positive CXCR4 expression and high tumor MVD are associated with the poor prognosis of patients, and they can be used as potential predictive factors for the recurrence or metastasis of colorectal cancer.