ABSTRACT
Chemokines interact with glycosaminoglycans (GAGs) at the cellular surface and to specific cell-surface receptors to activate signaling pathways. The GAG interaction allows the formation of a chemotactic gradient of chemokine required for cell haptotaxis and chemokine oligomerization. Poxviruses encode secreted chemokine-binding proteins with no sequence similarity to their cellular counterparts to modulate the host immune system. The E163 protein from ectromelia virus, the causative agent of mousepox, binds chemokines through their GAG-binding domain. In addition, E163 interacts with GAGs to be anchored at the cell surface, but its ability to interfere with chemokine-GAG interactions has not been demonstrated. We report the identification of the GAG-binding regions in E163 and the generation of mutant forms deficient of GAG binding. Chemokine binding assays show that some of the E163 GAG-binding sites are also involved in the interaction with chemokines. By using recombinant GAG-binding mutant forms we demonstrate that E163 prevents the interaction of chemokines with cell-surface GAGs, providing mechanisms for the immunomodulatory activity of the viral chemokine-binding protein E163.
Subject(s)
Chemokines/chemistry , Ectromelia virus/chemistry , Glycosaminoglycans/chemistry , Viral Proteins/chemistry , Animals , CHO Cells , Chemokines/genetics , Chemokines/metabolism , Cricetulus , Ectromelia virus/genetics , Ectromelia virus/metabolism , Glycosaminoglycans/genetics , Glycosaminoglycans/metabolism , Mutation , Protein Binding , Protein Domains , Viral Proteins/genetics , Viral Proteins/metabolismABSTRACT
Modulating T cell activation is critical for treating autoimmune diseases but requires avoiding concomitant opportunistic infections. Antigen binding to the T cell receptor (TCR) triggers the recruitment of the cytosolic adaptor protein Nck to a proline-rich sequence in the cytoplasmic tail of the TCR's CD3ε subunit. Through virtual screening and using combinatorial chemistry, we have generated an orally available, low-molecular weight inhibitor of the TCR-Nck interaction that selectively inhibits TCR-triggered T cell activation with an IC50 (median inhibitory concentration) ~1 nM. By modulating TCR signaling, the inhibitor prevented the development of psoriasis and asthma and, furthermore, exerted a long-lasting therapeutic effect in a model of autoimmune encephalomyelitis. However, it did not prevent the generation of a protective memory response against a mouse pathogen, suggesting that the compound might not exert its effects through immunosuppression. These results suggest that inhibiting an immediate TCR signal has promise for treating a broad spectrum of human T cell-mediated autoimmune and inflammatory diseases.
Subject(s)
Autoimmune Diseases/drug therapy , Receptors, Antigen, T-Cell/antagonists & inhibitors , Administration, Oral , Animals , Anti-Inflammatory Agents/pharmacology , Autoimmune Diseases/immunology , Cell Proliferation , Cytokines/metabolism , Drug Design , Female , Healthy Volunteers , Humans , Immunosuppression Therapy , Inhibitory Concentration 50 , Ligands , Lymphocyte Activation , Magnetic Resonance Spectroscopy , Mice , Mice, Inbred C57BL , Protein Domains , Receptors, Antigen, T-Cell/immunology , Signal Transduction , Surface Plasmon Resonance , T-Lymphocytes/cytologyABSTRACT
Chemokines are chemoattractant cytokines that mediate the migration of immune cells to sites of infection which play an important role in innate and adaptive immunity. As an immune evasion strategy, large DNA viruses (herpesviruses and poxviruses) encode soluble chemokine binding proteins that bind chemokines with high affinity, even though they do not show sequence similarity to cellular chemokine receptors. This review summarizes the different secreted viral chemokine binding proteins described to date, with special emphasis on the diverse mechanisms of action they exhibit to interfere with chemokine function and their specific contribution to virus pathogenesis.
