A virally encoded GPCR drives glioblastoma through feed-forward activation of the SK1-S1P1 signaling axis

Signal termination of the chemokine receptor CCR9 is governed by an arrestin-independent phosphorylation mechanism

The C-C chemokine receptor type 9 (CCR9) coordinates immune cell migration from the thymus to the small intestine along gradients of the chemokine CCL25. Receptor dysregulation is associated with a variety of inflammatory bowel diseases such as Crohn's and ulcerative colitis, whereas aberrant CCR9 overexpression correlates with tumor metastasis. Despite being an attractive therapeutic target, attempts to clinically antagonize CCR9 have been unsuccessful. This highlights the need for a deeper understanding of its specific regulatory mechanisms and signaling pathways. CCR9 is a G protein-coupled receptor (GPCR) and activates Gi and Gq pathways. Unexpectedly, live-cell bioluminescence resonance energy transfer assays reveal only limited G protein activation, and signaling is rapidly terminated. Truncating the receptor C terminus significantly enhanced G protein coupling, highlighting a regulatory role of this domain. Signal suppression was not because of canonical arrestin-coordinated desensitization. Rather, removal of GPCR kinase phosphorylation led to sustained and robust G protein activation by CCR9. Using site-directed mutagenesis, we identified specific phosphorylation motifs that attenuate G protein coupling. Receptor internalization did not correlate with G protein activation capabilities. Instead, CCR9 phosphorylation disrupted the interaction of G protein heterotrimers with the receptor. This interference may lead to rapid loss of productive coupling and downstream signaling as phosphorylation would effectively render the receptor incapable of G protein coupling. An arrestin-independent, phosphorylation-driven deactivation mechanism could complement arrestin-dependent regulation of other GPCRs and have consequences for therapeutically targeting these receptors.

Pharmacological characterization of a clinical candidate, TG-0054, a small molecule inverse agonist targeting CXCR4

CXCR4 is an important therapeutic target for hematopoietic stem cell mobilization, which enhances the success of autologous stem cell transplantation for treating blood cancers such as lymphomas and myeloma. As CXCR4 has been shown to be involved in various inflammatory diseases, cancer progression, and cell entry by the human immunodeficiency virus, understanding the molecular mechanism of CXCR4 inhibitors has potential implications in a wide area of diseases. Here, we present an exploratory study which involves the molecular pharmacological characterization of TG-0054 (burixafor, GPC-100), a clinical candidate for hematopoietic stem cell mobilization. TG-0054 inhibited CXCL12 binding at CXCR4, and antagonized both Gαi and β-arrestin2 recruitment as well as the downstream Gαi-attenuation of cAMP signaling pathway, with pIC50 of 7.7, 8.0, and 7.9, respectively. Compared with the clinically used antagonist AMD3100 and the prototypical inverse agonist Isothiourea-1t (IT1t), TG-0054 displayed a unique pharmacological profile. Like IT1t, TG-0054 inhibited the constitutive Gαi signaling of CXCR4. However, in contrast to IT1t and other reported inverse agonists, TG-0054 was not able to induce monomerization of CXCR4 oligomeric complexes. Considering the unique properties of TG-0054 on CXCR4, TG-0054 is an interesting tool compound for studying the relevance of inverse agonism as well as CXCR4 monomerization in various pathologies. SIGNIFICANCE STATEMENT: CXCR4-targeted therapeutics hold important potential for the treatment of blood cancers. TG-0054 has inverse agonistic properties and is a non-CXCR4-monomerizing small molecule antagonist, unlike other well studied CXCR4 small molecule antagonists.

Why Are Cytomegalovirus-Encoded G-Protein-Coupled Receptors Essential for Infection but Only Variably Conserved?

Cytomegaloviruses (CMVs) encode viral G-protein-coupled receptors (vGPCRs) that have diverged from their cellular homologues to perform new functions. Human cytomegalovirus (HCMV) encodes four vGPCRs: UL33, UL78, US27, and US28, which contribute to viral pathogenesis, cellular signalling, and latency. While the role of US28 in chemokine signalling and viral latency is well characterised, the functions of other vGPCRs remain incompletely understood. Rodent cytomegaloviruses only have homologues to UL33 and UL78, while primates have two to five additional GPCRs which are homologues of US27 and US28. Different CMVs appear to have evolved vGPCRs with functions specific to infection of their respective host. As non-human CMVs are used as model organisms to understand clinical cytomegalovirus disease and develop vaccines and antivirals, understanding the differences between these vGPCRs helps researchers understand critical differences between their models. This review aims to address the differences between CMV vGPCRs, and how these differences may affect models of CMV disease to facilitate future research.

Human cytomegalovirus UL82 promotes cell cycle progression of colorectal cancer by upregulating AGR2

The correlation between persistent human cytomegalovirus (HCMV) infection and poor prognosis in colorectal cancer (CRC) patients has garnered increasing attention. UL82 is a tegument protein of HCMV, and our previous research indicated that the presence of UL82 is significantly associated with reduced overall survival in CRC patients. However, the mechanism by which UL82 affects the prognosis of CRC patients remains unclear. In this study, we investigated the role of UL82 in CRC progression through both in vitro and in vivo experiments, and revealed its downstream regulatory pathways by integrating transcriptomics, metabolomics, and proteomics. Our findings first revealed that UL82 significantly promoted CRC cell proliferation by increasing the proportion of cells in the S phase of the cell cycle. Additionally, UL82 enhanced the expression of the oncogene AGR2, while knockdown of AGR2 abolished the proliferative effect of UL82. Interestingly, UL82 interacted with the transcription factor DDX5, which transcriptionally inhibited AGR2 expression. Furthermore, this UL82-AGR2 axis promoted nucleotide metabolism in CRC cells by enhancing the levels of nucleotide synthesis enzymes DTYMK, RRM2, and TYMS. In conclusion, our study suggests that the UL82/DDX5 complex may promote nucleotide metabolism and cell cycle progression of CRC by upregulating AGR2 and UL82 may serve as a potential prognostic biomarker for CRC patients.

Clinical implications of cytomegalovirus in glioblastoma progression and therapy

Glioblastoma (GBM) is one of the deadliest brain cancers with a median survival of only 15 months. This poor prognosis has prompted exploration of novel therapeutic targets for GBM patients. Human cytomegalovirus (HCMV) has been implicated in GBM; however, its impact remains poorly defined, and there is conflicting data over the presence of HCMV in tumors. Nonetheless, clinical trials targeting HCMV have shown promising initial data, and evidence suggests that HCMV may negatively impact GBM patient survival by multiple mechanisms including changes in GBM cell behavior and the tumor microenvironment (TME) that potentiate tumor progression as well as therapy-induced virus reactivation. Moreover, HCMV has many effects on host immunity that could impact tumor behavior by altering the TME, which are largely unexplored. The goal of this review is to describe these potential interactions between HCMV and GBM. Better understanding of these processes may allow the development of new therapeutic modalities to improve GBM patient outcomes.

Multivalent CXCR4-targeting nanobody formats differently affect affinity, receptor clustering, and antagonism

The chemokine receptor CXCR4 is involved in the development and migration of stem and immune cells but is also implicated in tumor progression and metastasis for a variety of cancers. Antagonizing ligand (CXCL12)-induced CXCR4 signaling is, therefore, of therapeutic interest. Currently, there are two small-molecule CXCR4 antagonists on the market for the mobilization of hematopoietic stem cells. Other molecules with improved potencies and safety profiles are being developed for different indications, including cancer. Moreover, multiple antagonistic nanobodies targeting CXCR4 displayed similar or better potencies as compared to the CXCR4-targeting molecule AMD3100 (Plerixafor), which was further enhanced through avid binding of bivalent derivatives. In this study, we aimed to compare the affinities of various multivalent nanobody formats which might be differently impacted by avidity. By fusion to a flexible GS-linker, Fc-region of human IgG1, different C4bp/CLR multimerization domains, or via site-directed conjugation to a trivalent linker scaffold, we generated different types of multivalent nanobodies with varying valencies ranging from bivalent to decavalent. Of these, C-terminal fusion, especially to human Fc, was most advantageous with a 2-log-fold and 3-log-fold increased potency in inhibiting CXCL12-mediated Gαi- or β-arrestin recruitment, respectively. Overall, we describe strategies for generating multivalent and high-potency CXCR4 antagonistic nanobodies able to induce receptor clustering and conclude that fusion to an Fc-tail results in the highest avidity effect irrespective of the hinge linker.

Sphingolipid Signaling and Complement Activation in Glioblastoma: A Promising Avenue for Therapeutic Intervention

Glioblastoma is the most common and aggressive type of malignant brain tumor with a poor prognosis due to the lack of effective treatment options. Therefore, new treatment options are required. Sphingolipids are essential components of the cell membrane, while complement components are integral to innate immunity, and both play a critical role in regulating glioblastoma survival signaling. This review focuses on recent studies investigating the functional roles of sphingolipid metabolism and complement activation signaling in glioblastoma. It also discusses how targeting these two systems together may emerge as a novel therapeutic approach.

G protein-coupled receptors: a gateway to targeting oncogenic EVs?

Dysregulated intercellular communication is a key feature driving cancer progression. Recently, extracellular vesicles (EVs) have added a new channel to this dense communication network. Despite solid evidence that EVs are central mediators of dysregulated signaling in onco-pathological settings, this has yet to be translated into clinically actionable strategies. The heterogeneity of EV cargo molecules, plasticity of biogenesis routes, and large overlap with their role in physiological communication, complicate a potential targeting strategy. However, recent work has linked EV biology to perhaps the "most druggable" proteins - G protein-coupled receptors (GPCRs). GPCR targeting accounts for ~60% of drugs in development and more than a third of all currently approved drugs, spanning almost all areas of medicine. Although several GPCRs have been linked to cancer initiation and progression, relatively few agents have made it into oncological regimes, suggesting that their potential is underexploited. Herein, we examine the molecular mechanisms linking GPCRs to EV communication in cancer settings. We propose that GPCRs hold potential in the search for EV-targeting in oncology.