Separate elements are required for ligand-dependent and -independent internalization of metastatic potentiator CXCR4

WHIM Syndrome: from Pathogenesis Towards Personalized Medicine and Cure

WHIM syndrome is a rare combined primary immunodeficiency disease named by acronym for the diagnostic tetrad of warts, hypogammaglobulinemia, infections, and myelokathexis. Myelokathexis is a unique form of non-cyclic severe congenital neutropenia caused by accumulation of mature and degenerating neutrophils in the bone marrow; monocytopenia and lymphopenia, especially B lymphopenia, also commonly occur. WHIM syndrome is usually caused by autosomal dominant mutations in the G protein-coupled chemokine receptor CXCR4 that impair desensitization, resulting in enhanced and prolonged G protein- and β-arrestin-dependent responses. Accordingly, CXCR4 antagonists have shown promise as mechanism-based treatments in phase 1 clinical trials. This review is based on analysis of all 105 published cases of WHIM syndrome and covers current concepts, recent advances, unresolved enigmas and controversies, and promising future research directions.

M. de Rosales R. Exploiting the Metal-Chelating Properties of the Drug Cargo for In Vivo Positron Emission Tomography Imaging of Liposomal Nanomedicines

The clinical value of current and future nanomedicines can be improved by introducing patient selection strategies based on noninvasive sensitive whole-body imaging techniques such as positron emission tomography (PET). Thus, a broad method to radiolabel and track preformed nanomedicines such as liposomal drugs with PET radionuclides will have a wide impact in nanomedicine. Here, we introduce a simple and efficient PET radiolabeling method that exploits the metal-chelating properties of certain drugs (e.g., bisphosphonates such as alendronate and anthracyclines such as doxorubicin) and widely used ionophores to achieve excellent radiolabeling yields, purities, and stabilities with 89Zr, 52Mn, and 64Cu, and without the requirement of modification of the nanomedicine components. In a model of metastatic breast cancer, we demonstrate that this technique allows quantification of the biodistribution of a radiolabeled stealth liposomal nanomedicine containing alendronate that shows high uptake in primary tumors and metastatic organs. The versatility, efficiency, simplicity, and GMP compatibility of this method may enable submicrodosing imaging studies of liposomal nanomedicines containing chelating drugs in humans and may have clinical impact by facilitating the introduction of image-guided therapeutic strategies in current and future nanomedicine clinical studies.

Overview and potential unifying themes of the atypical chemokine receptor family

Chemokines modulate immune responses through their ability to orchestrate the migration of target cells. Chemokines directly induce cell migration through a distinct set of 7 transmembrane domain G protein-coupled receptors but are also recognized by a small subfamily of atypical chemokine receptors, characterized by their inability to support chemotactic activity. Atypical chemokine receptors are now emerging as crucial regulatory components of chemokine networks in a wide range of physiologic and pathologic contexts. Although a new nomenclature has been approved recently to reflect their functional distinction from their conventional counterparts, a systematic view of this subfamily is still missing. This review discusses their biochemical and immunologic properties to identify potential unifying themes in this emerging family.

CXCR4 WHIM-like frameshift and nonsense mutations promote ibrutinib resistance but do not supplant MYD88(L265P) -directed survival signalling in Waldenström macroglobulinaemia cells

CXCR4(WHIM) frameshift and nonsense mutations follow MYD88(L265P) as the most common somatic variants in Waldenström Macroglobulinaemia (WM), and impact clinical presentation and ibrutinib response. While the nonsense (CXCR4(S338X) ) mutation has been investigated, little is known about CXCR4 frameshift (CXCR4(FS) ) mutations. We engineered WM cells to express CXCR4(FS) mutations present in patients, and compared their CXCL12 (SDF-1a) induced signalling and ibrutinib sensitivity to CXCR4(wild-type (WT)) and CXCR4(S338X) cells. Following CXCL12 stimulation, CXCR4(FS) and CXCR4(S338X) WM cells showed impaired CXCR4 receptor internalization, and enhanced AKT1 (also termed AKT) and MAPK1 (also termed ERK) activation versus CXCR(WT) cells (P < 0·05), though MAPK1 activation was more prolonged in CXCR4(S338X) cells (P < 0·05). CXCR4(FS) and CXCR4(S338X) cells, but not CXCR4(WT) cells, were rescued from ibrutinib-triggered apoptosis by CXCL12 that was reversed by AKT1, MAPK1 or CXCR4 antagonists. Treatment with an inhibitor that blocks MYD88(L265P) signalling triggered similar levels of apoptosis that was not abrogated by CXCL12 treatment in CXCR4(WT) and CXCR4(WHIM) cells. These studies show a functional role for CXCR4(FS) mutations in WM, and provide a framework for the investigation of CXCR4 antagonists with ibrutinib in CXCR4(WHIM) -mutated WM patients. Direct inhibition of MYD88(L265P) signalling overcomes CXCL12 triggered survival effects in CXCR4(WHIM) -mutated cells supporting a primary role for this survival pathway in WM.

Gαs regulates the post-endocytic sorting of G protein-coupled receptors

The role of Gαs in G protein-coupled receptor (GPCR) signalling at the cell surface is well established. Recent evidence has revealed the presence of Gαs on endosomes and its capacity to elicit GPCR-promoted signalling from this intracellular compartment. Here, we report an unconventional role for Gαs in the endocytic sorting of GPCRs to lysosomes. Cellular depletion of Gαs specifically delays the lysosomal degradation of GPCRs by disrupting the transfer of GPCRs into the intraluminal vesicles (ILVs) of multivesicular bodies. We show that Gαs interacts with GPCR-associated binding protein-1 (GASP1) and dysbindin, two key proteins that serve as linkers between GPCRs and the endosomal-sorting complex required for transport (ESCRT) machinery involved in receptor sorting into ILVs. Our findings reveal that Gαs plays a role in both GPCR signalling and trafficking pathways, providing another piece in the intertwining molecular network between these processes.

A whole-body dual-modality radionuclide optical strategy for preclinical imaging of metastasis and heterogeneous treatment response in different microenvironments

Imaging spontaneous cancer cell metastasis or heterogeneous tumor responses to drug treatment in vivo is difficult to achieve. The goal was to develop a new highly sensitive and reliable preclinical longitudinal in vivo imaging model for this purpose, thereby facilitating discovery and validation of anticancer therapies or molecular imaging agents.

METHODS

The strategy is based on breast cancer cells stably expressing the human sodium iodide symporter (NIS) fused to a red fluorescent protein, thereby permitting radionuclide and fluorescence imaging. Using whole-body nano-SPECT/CT with (99m)TcO4(-), we followed primary tumor growth and spontaneous metastasis in the presence or absence of etoposide treatment. NIS imaging was used to classify organs as small as individual lymph nodes (LNs) to be positive or negative for metastasis, and results were confirmed by confocal fluorescence microscopy. Etoposide treatment efficacy was proven by ex vivo anticaspase 3 staining and fluorescence microscopy.

RESULTS

In this preclinical model, we found that the NIS imaging strategy outperformed state-of-the-art (18)F-FDG imaging in its ability to detect small tumors (18.5-fold-better tumor-to-blood ratio) and metastases (LN, 3.6-fold) because of improved contrast in organs close to metastatic sites (12- and 8.5-fold-lower standardized uptake value in the heart and kidney, respectively). We applied the model to assess the treatment response to the neoadjuvant etoposide and found a consistent and reliable improvement in spontaneous metastasis detection. Importantly, we also found that tumor cells in different microenvironments responded in a heterogeneous manner to etoposide treatment, which could be determined only by the NIS-based strategy and not by (18)F-FDG imaging.

CONCLUSION

We developed a new strategy for preclinical longitudinal in vivo cancer cell tracking with greater sensitivity and reliability than (18)F-FDG PET and applied it to track spontaneous and distant metastasis in the presence or absence of genotoxic stress therapy. Importantly, the model provides sufficient sensitivity and dynamic range to permit the reliable assessment of heterogeneous treatment responses in various microenvironments.

NMR metabolomics of MTLn3E breast cancer cells identifies a role for CXCR4 in lipid and choline regulation

The alpha chemokine receptor CXCR4 is up-regulated in certain types of breast cancer. Truncation of the C-terminus of this receptor alters cell morphology and increases invasiveness and metastatic potential. Here, to better understand the effects of CXCR4 expression and truncation in breast cancer cells, we have used high resolution magic angle spinning (HR-MAS) NMR studies of rat breast carcinoma MtLn3E cells to characterize the metabolite complement of cells heterologously expressing human CXCR4 or its C-terminal truncation mutant, Δ34-CXCR4. Notable reductions in choline levels were detected when either cells expressing wild-type CXCR4 or Δ34-CXCR4 were compared with cells containing an empty expression vector. Cells expressing CXCR4-Δ34 had reduced lipid content when compared with either the wild-type CXCR4 expressing cells or those containing the empty expression vector. Taken together, our results show that distinct effects on the metabolite complement can be linked to either CXCR4 expression or CXCR4 regulation. The metabolite markers for these two effects identified in the present study can, in turn, be used to further investigate the role of CXCR4 in metastasis.

CXCR4/CXCL12 expression profile is associated with tumor microenvironment and clinical outcome of liver metastases of colorectal cancer

Interaction between CXCR4 and CXCL12 plays a role in tumor progression. The present study examined CXCR4, CXCL12 and CD133 expression in liver metastases of colorectal cancer (CLM) and determined whether the expression profiles affect the tumor microenvironment and thus progression, and whether they could serve as a prognostic marker for survival. Liver metastases of colorectal cancer collected from 92 patients were evaluated by CXCR4, CXCL12 and CD133 immunohistochemistry and clinicopathological data were analyzed. The expression profile of CXCR4 was determined in the colorectal cancer cell line, SW48. The expression of cytoplasmic CXCR4 was higher in 36 (39%) patients than that indicated by CXCR4 staining intensity of hepatocytes. High levels of nuclear CXCR4 expression in 23 (25%) patients significantly correlated with CXCL12 expression in hepatocytes. Nuclear CXCR4 expression was increased in the cancer cells after exposure to CXCL12. Univariate and multivariate analyses demonstrated that the high levels of nuclear CXCR4 and CXCL12 expression in hepatocytes were significantly better prognostic factors for overall and hepatic disease-free survival in patients with CLM. The expression of CXCR4 and CXCL12 in CLM may have an interactive effect that could alter the tumor microenvironment. CXCR4 expression in metastatic liver tumors together with the upregulation of CXCL12 in hepatocytes may help to predict the clinical outcomes of patients with CLM after hepatectomy.

Role for CD74 and CXCR4 in clathrin-dependent endocytosis of the cytokine MIF

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that plays a role in innate and adaptive immunity. Depending on the cellular context and disease state, MIF signaling is mediated by its receptors CXCR2, CXCR4 and/or CD74. Although it is known that MIF is endocytosed, the exact mechanism has remained unknown. In exploring the mechanism of MIF endocytosis with biologically active Alexa(546)MIF, pathway-specific inhibitors (monodansylcadaverine, MDC; chlorpromazine, CPZ; dynasore; dominant-negative dynamin, bafilomycin, nocodazole) and receptor overexpression and blockade approaches, we identified a clathrin/dynamin-dependent endocytosis pathway as the main track for MIF internalization. MIF endocytosis was rapid and colocalization with both early and late endosomal vesicles in a microtubule- and acidification-dependent manner was observed. LDL endocytosis (which is clathrin-mediated) served as a control and was similarly inhibited by MDC or dynasore. When MIF endocytosis was compared to that of transferrin, acetylated LDL, and choleratoxin B (the latter internalized by a clathrin-independent pathway) by colocalization studies, the MIF internalization pathway clearly resembled that of LDL but also shared early trafficking with transferrin, whereas no colocalization with choleratoxin was noted. To identify the receptors involved in MIF endocytosis, we focused on CD74 and CXCR4 which form a heteromeric complex. Ectopic overexpression of CD74 in HEK293 and HeLa cells, which do not endogenously express CD74, led to a marked acceleration of MIF endocytosis while pharmacological blockade of CXCR4, which is endogenously expressed on these cells, with AMD3100 led to a 20% reduction of MIF endocytosis in HEK293-CD74 transfectants, whereas in untransfected cells, a blockade of 40% was observed. Of note, both CD74 and CXCR4 strongly colocalize with Alexa(546)MIF both on the plasma membrane and in endosomal compartments. Moreover, MIF-stimulated AKT signaling, which was previously shown to involve both CD74 and CXCR4, was reduced by endocytosis inhibitors, indicating that MIF signaling is at least in part due to endosomal signaling mechanisms. Thus, MIF uptake follows a rapid LDL-like, clathrin- and dynamin-dependent endocytosis pathway, which is dependent on the receptors CD74 and CXCR4 and leads to the initiation of endosomal signaling responses.

Selecting Potential Targetable Biomarkers for Imaging Purposes in Colorectal Cancer Using TArget Selection Criteria (TASC): A Novel Target Identification Tool

Peritoneal carcinomatosis (PC) of colorectal origin is associated with a poor prognosis. However, cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy is available for a selected group of PC patients, which significantly increases overall survival rates up to 30%. As a consequence, there is substantial room for improvement. Tumor targeting is expected to improve the treatment efficacy of colorectal cancer (CRC) further through 1) more sensitive preoperative tumor detection, thus reducing overtreatment; 2) better intraoperative detection and surgical elimination of residual disease using tumor-specific intraoperative imaging; and 3) tumor-specific targeted therapeutics. This review focuses, in particular, on the development of tumor-targeted imaging agents. A large number of biomarkers are known to be upregulated in CRC. However, to date, no validated criteria have been described for the selection of the most promising biomarkers for tumor targeting. Such a scoring system might improve the selection of the correct biomarker for imaging purposes. In this review, we present the TArget Selection Criteria (TASC) scoring system for selection of potential biomarkers for tumor-targeted imaging. By applying TASC to biomarkers for CRC, we identified seven biomarkers (carcinoembryonic antigen, CXC chemokine receptor 4, epidermal growth factor receptor, epithelial cell adhesion molecule, matrix metalloproteinases, mucin 1, and vascular endothelial growth factor A) that seem most suitable for tumor-targeted imaging applications in colorectal cancer. Further cross-validation studies in CRC and other tumor types are necessary to establish its definitive value.

AMSH interacts with ESCRT-0 to regulate the stability and trafficking of CXCR4

Reversible ubiquitination is essential for the endocytic sorting and down-regulation of G protein-coupled receptors, such as the chemokine receptor CXCR4. The deubiquitinating enzyme AMSH has been implicated in the endocytic sorting of both G protein-coupled receptors and receptor-tyrosine kinases. Herein, we examine the role of AMSH in the regulation of CXCR4 stability and trafficking and characterize protein-protein interactions critical for this function. Loss of AMSH catalytic activity or depletion by RNAi results in increased steady-state levels of CXCR4 under basal conditions. Analysis of truncation and point mutation of AMSH reveal the importance of an RXXK motif for CXCR4 degradation. The RXXK motif of AMSH interacts with the SH3 domains of the STAM and Grb2 families of adaptor proteins with high affinity. Cells expressing a catalytically inactive mutant of AMSH show basal hyperubiquitination, but not increased degradation, of the ESCRT-0 components STAM1 and Hrs. This is dependent on the RXXK motif of AMSH. Ubiquitination of endocytic machinery modulates their activity, suggesting that AMSH may directly regulate endocytic adaptor protein function. This is reflected in CXCR4 trafficking and provides a mechanism by which AMSH specifies the fate of endocytosed receptors. Taken together, these studies implicate AMSH as a key modulator of receptor fate determination through its action on components of the endocytic machinery.

WHIM syndrome: congenital immune deficiency disease

PURPOSE OF REVIEW

Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is characterized by susceptibility to human papilloma virus infection-induced warts and carcinomas; neutropenia, B-cell lymphopenia and hypogammaglobulinema-related infections; and bone marrow myelokathexis (myeloid hyperplasia with apoptosis). The purpose of this report is to review new findings about WHIM.

RECENT FINDINGS

Most WHIM patients have heterozygous C-terminus deletion mutations of the intracellular carboxy terminus of the chemokine receptor CXCR4. WHIM leukocytes have enhanced responses to CXCL12, the cognate ligand of CXCR4. Enhanced activity of CXCR4 delays release of mature neutrophils from bone marrow, resulting in neutropenia and apoptosis of mature neutrophils retained in the marrow. Finding two patients with WHIM who do not have detectable mutations of CXCR4 but whose cells are hyperresponsive to CXCL12 raises the possibility that there is more than one genetic basis for WHIM. One patient had low levels of G-protein receptor kinase 3, and the functional hyperactivity response to CXCL12 was corrected by forced gene transfer-mediated overexpression of G-protein receptor kinase 3, implicating defects in function of this protein as a potential alternate genetic cause of WHIM.

SUMMARY

Subjects reviewed include clinical presentation, diagnosis, and treatment of WHIM and advances in understanding the genetic basis of WHIM.

Substitution of the myristoylation signal of human immunodeficiency virus type 1 Pr55Gag with the phospholipase C-delta1 pleckstrin homology domain results in infectious pseudovirion production

The matrix domain (MA) of human immunodeficiency virus type 1 Pr55Gag is covalently modified with a myristoyl group that mediates efficient viral production. However, the role of myristoylation, particularly in the viral entry process, remains uninvestigated. This study replaced the myristoylation signal of MA with a well-studied phosphatidylinositol 4,5-biphosphate-binding plasma membrane (PM) targeting motif, the phospholipase C-delta1 pleckstrin homology (PH) domain. PH-Gag-Pol PM targeting and viral production efficiencies were improved compared with Gag-Pol, consistent with the estimated increases in Gag-PM affinity. Both virions were recovered in similar sucrose density-gradient fractions and had similar mature virion morphologies. Importantly, PH-Gag-Pol and Gag-Pol pseudovirions had almost identical infectivity, suggesting a dispensable role for myristoylation in the virus life cycle. PH-Gag-Pol might be useful in separating the myristoylation-dependent processes from the myristoylation-independent processes. This the first report demonstrating infectious pseudovirion production without myristoylated Pr55Gag.

Ligand-independent higher-order multimerization of CXCR4, a G-protein-coupled chemokine receptor involved in targeted metastasis

CXCR4, a G-protein-coupled receptor of CXCL12/stromal cell-derived factor-1alpha, mediates a wide range of physiological and pathological processes, including the targeted metastasis of cancer cells. CXCR4 has been shown to homo-oligomerize in several experimental systems. However, it remains unclear with which domains CXCR4 interacts homotypically, and whether it dimerizes or forms a higher-order complex. To address these issues, we used bioluminescent resonance energy transfer and bimolecular fluorescence complementation analyses to measure the homotypic interactions of CXCR4 in living cells. Both assays indicated that CXCR4 interacts homotypically, which is consistent with previous studies. By studying CXCR4 mutants lacking various domains, we found that multiple transmembrane domains probably serve as potential molecular interaction surfaces for oligomerization. The relative contribution of the amino- or carboxy-termini to oligomerization was small. To differentiate between a dimer and a multimer consisting of more than two molecules, bioluminescent resonance energy transfer-bimolecular fluorescence complementation analysis was conducted. It revealed that CXCR4 engages in higher-order oligomerization in a ligand-independent fashion. This is the first report providing direct experimental evidence for the higher-order multimerization of CXCR4 in vivo. We hypothesize that CXCR4 distributes to the cell surface as a multimer, in order to effectively sense, with increased avidity, the chemotaxis-inducing ligand in the microenvironment. Studying the structure and function of the oligomeric state of CXCR4 may lead us to develop novel CXCR4 inhibitors that disassemble the molecular cluster of CXCR4.

CCL2 increases X4-tropic HIV-1 entry into resting CD4+ T cells

During human immunodeficiency virus type 1 (HIV-1) infection, there is a strong positive correlation between CCL2 levels and HIV viral load. To determine whether CCL2 alters HIV-1 infection of resting CD4(+) T cells, we infected purified resting CD4(+) T cells after incubation with CCL2. We show that CCL2 up-regulates CXCR4 on resting CD4(+) T cells in a CCR2-dependent mechanism, and that this augmentation of CXCR4 expression by CCL2 increases the ability of these cells to be chemoattracted to CXCR4 using gp120 and renders them more permissive to X4-tropic HIV-1 infection. Thus, CCL2 has the capacity to render a large population of lymphocytes more susceptible to HIV-1 late in the course of infection.

Fluorophore labeling enables imaging and evaluation of specific CXCR4-ligand interaction at the cell membrane for fluorescence-based screening

Development of CXCR4-specific ligands is an important issue in chemotherapy of HIV infection, cancer metastasis, and rheumatoid arthritis, and numerous potential ligands have been developed to date. However, it is difficult to assess their binding mode and specificity because of uncertainties in the structure of the CXCR4-ligand complexes. To address this problem, we have synthesized fluorophore labeled Ac-TZ14011, which is derived from T140, a powerful CXCR4 antagonist. Binding of Ac-TZ14011 to CXCR4 on the cell membrane was observed by fluorescence microscope, and analysis of the binding data produced IC 50 values of several ligands comparable to those obtained in RI-based assays. This fluorescence-based assay is applicable to explore new pharmacophores of CXCR4-specific ligands with high-throughput screening and also to screening of the other GPCR binding ligands.