Control of immune cell trafficking through inter-organ communication

Regulation of CXCR4 function by S1P1 through heteromerization

BACKGROUND

The trafficking of immune cells between lymphoid organs and circulation depends on gradients of CXCL12 and sphingosine-1-phosphate (S1P), mediated through their cognate receptors C-X-C chemokine receptor type 4 (CXCR4) and S1P receptor type 1 (S1P1). S1P1 facilitates the egress of hematopoietic stem cells and lymphocytes by counteracting CXCR4-mediated retention signals. However, the molecular mechanisms underlying this interplay remain poorly understood. In this study, we uncover CXCR4-S1P1 heteromerization and explore their functional interactions.

METHODS

Bimolecular fluorescence complementation (BiFC) assay, proximity ligation assay (PLA), and quantitative bioluminescence resonance energy transfer (BRET) assay were employed to detect CXCR4-S1P1 heteromerization. Functional properties of the heteromers were assessed using cAMP assay, G protein activation, β-arrestin recruitment, ligand binding, calcium mobilization, and transwell migration assays. S1P1-overexpressing Jurkat T cells were generated via lentiviral transduction, while S1P1-deficient KARPAS299 cells and β-arrestin1/2-deficient HEK293A cells were constructed using the CRISPR/Cas9 system.

RESULTS

CXCR4-S1P1 heteromerization was observed in HEK293A cells overexpressing both receptors. The S1P/S1P1 axis interfered with CXCR4-mediated signaling, while CXCR4 did not affect S1P1-mediated signaling, indicating a unidirectional modulation of CXCR4 by S1P1. CXCL12 binding to CXCR4 remained unchanged in the presence of S1P1, and interference of CXCL12-induced Gαi activation by S1P1 was observed in β-arrestin1/2-deficient cells. BRET analysis revealed that S1P1 interfered with CXCR4-Gαi pre-association and CXCR4 oligomerization, both of which are critical for CXCR4 function. Domain-swapping experiments identified transmembrane domain 3 of S1P1 as essential for this modulation. In Jurkat T cells overexpressing S1P1, CXCR4-mediated signaling and cell migration were diminished, whereas these functions were enhanced in S1P1-deficient KARPAS299 cells. Co-activation of S1P1 attenuated CXCL12-induced migration, while pretreatment with S1P or FTY720-phosphate increased CXCR4-mediated migration by downregulating surface S1P1 in KARPAS299 cells. In primary T cells, PLA confirmed CXCR4-S1P1 heteromerization, and S1P interfered with CXCL12-induced migration.

CONCLUSIONS

This study identifies CXCR4-S1P1 heteromers and demonstrates a unidirectional modulation of CXCR4 by S1P1. S1P1 affects CXCR4 function by disrupting its G protein pre-association and oligomerization. These findings underscore the regulatory role of the S1P/S1P1 axis in CXCR4 signaling within the heteromeric context and provide novel insights into the intricate mechanisms governing immune cell trafficking.

Metalloproteins structural and functional insights into immunological patterns

Metalloproteins play a crucial role in regulating different aspects of the immune system in humans. They have various functions in immunity, including recognizing and presenting antigens, aiding in the movement and effectiveness of immune cells, and facilitating interactions between the host and pathogens. Understanding how these proteins work can help us develop new methods to control the immune response in different diseases. Metalloproteins contain metal ions in their structure, which allows them to perform these diverse functions. They encompass a wide range of enzymes, signaling molecules, and structural proteins that utilize metal ions as cofactors for their activities. Examples of metalloproteins include superoxide dismutase, catalase, and metalloproteases, which regulate oxidative stress, inflammation, and tissue remodelling processes associated with immune activation. By studying their functions and the effects of their dysfunction, researchers can develop strategies to improve immune function and combat various diseases. This review explores the diverse functions of metalloproteins in immune processes, highlighting their significance in both health and disease.

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

GPC-100, a novel CXCR4 antagonist, improves in vivo hematopoietic cell mobilization when combined with propranolol

Autologous Stem Cell Transplant (ASCT) is increasingly used to treat hematological malignancies. A key requisite for ASCT is mobilization of hematopoietic stem cells into peripheral blood, where they are collected by apheresis and stored for later transplantation. However, success is often hindered by poor mobilization due to factors including prior treatments. The combination of G-CSF and GPC-100, a small molecule antagonist of CXCR4, showed potential in a multiple myeloma clinical trial for sufficient and rapid collection of CD34+ stem cells, compared to the historical results from the standards of care, G-CSF alone or G-CSF with plerixafor, also a CXCR4 antagonist. In the present study, we show that GPC-100 has high affinity towards the chemokine receptor CXCR4, and it potently inhibits β-arrestin recruitment, calcium flux and cell migration mediated by its ligand CXCL12. Proximity Ligation Assay revealed that in native cell systems with endogenous receptor expression, CXCR4 co-localizes with the beta-2 adrenergic receptor (β2AR). Co-treatment with CXCL12 and the β2AR agonist epinephrine synergistically increases β-arrestin recruitment to CXCR4 and calcium flux. This increase is blocked by the co-treatment with GPC-100 and propranolol, a non-selective beta-adrenergic blocker, indicating a functional synergy. In mice, GPC-100 mobilized more white blood cells into peripheral blood compared to plerixafor. GPC-100 induced mobilization was further amplified by propranolol pretreatment and was comparable to mobilization by G-CSF. Addition of propranolol to the G-CSF and GPC-100 combination resulted in greater stem cell mobilization than the G-CSF and plerixafor combination. Together, our studies suggest that the combination of GPC-100 and propranolol is a novel strategy for stem cell mobilization and support the current clinical trial in multiple myeloma registered as NCT05561751 at www.clinicaltrials.gov.

Introduction: Electronic Medicine in Immunology Special Issue Part 1

Electronic Medicine in Immunology.