doi: 10.1161/ATVBAHA.109.195552
© 2009 American Heart Association, Inc.
Editorials |
Tyrosine Sulfation of Leukocyte Adhesion Molecules and Chemokine Receptors Promotes Atherosclerosis
From the Division of Inflammation Biology, La Jolla Institute for Allergy & Immunology, Calif.
Correspondence to Klaus Ley, MD, Division of Inflammation Biology, La Jolla Institute for Allergy & Immunology, 9420 Athena Circle Drive, La Jolla, CA 92037. E-mail klaus{at}liai.org
In this issue of Arteriosclerosis, Thrombosis, and Vascular Biology, Westmuckett and Moore describe a prominent role of tyrosine sulfation in hematopoietic cells during atherosclerosis development.1 Atherosclerosis represents a major health problem in developed and developing countries and is the most common underlying process precipitating myocardial infarctions, limb ischemia, and stroke. In the United States alone, more than 60 million people have some form of atherosclerotic vascular disease.2 Atherosclerosis is a complex disease associated with lipid accumulation and formation of atherosclerotic plaque in the major arteries of the body, which can rupture or erode to cause acute thrombosis, arterial occlusion, and necrosis of the dependent tissue.
See accompanying article on page 1730
In a last two decades, it has become clear that immune processes play an important role in atherosclerosis development, plaque formation, and progression of the disease. Although all major types of immune cells are involved in atherosclerosis (reviewed in3), the exact molecular and cellular mechanisms of disease development and progression are not completely understood. Two commonly used mouse models of atherosclerosis are apolipoprotein E-deficient Apoe–/– or low-density lipoprotein (LDL) receptor-deficient Ldlr–/– mice. In both models, LDL cholesterol is elevated, which promotes atherosclerotic lesion formation in locations similar to those in the human disease. Ldlr–/– mice can be reconstituted with bone marrow from donor mice to produce chimeric mice lacking targeted molecules of interest in hematopoietic cells only.
Leukocyte recruitment is critical for chronic inflammation and progression of atherosclerosis. This process is regulated by adhesion molecules and chemoattractants such as chemokines and their receptors.4 One class of adhesion molecules required for recruitment of inflammatory the cells to sites of atherosclerotic lesion formation are selectins. P- E- and L-selectin all can bind P-selectin glycoprotein ligand-1 (PSGL-1).5
The expression and function of adhesion molecules and chemokine receptors is controlled at the transcriptional and translational levels as well as by posttranslational modifications. Many intracellular proteins are regulated by phosphorylation, but other types of covalent modifications exist. Sulfation of tyrosine residues turns out to be critical for the function of many secreted and transmembrane proteins, which are involved in both homeostasis and immune responses.6 Two broadly expressed enzymes catalyzing the transfer of the sulfoil group from 3'-phosphoadenosin 5'-phosphosulfate (PAPS) to the hydroxyl group of peptidyl-tyrosine within these proteins have been described in humans and mice, the tyrosylprotein sulfotransferases-1 and -2 (TPST-1, TPST-2). Disruption of Tpst genes by gene targeting and homologous recombination in mice demonstrates important roles for these enzymes in crucial biological functions, such as metabolism, reproduction, and cardiovascular development. For instance, Tpst1–/– mice have a significant decrease of postnatal body weight attributable to impaired digestion.7 Male Tpst2–/– mice have reduced fertility attributable to impaired sulfation of proteins responsible for male reproductive function.8 Although at least some Tpst1–/–Tpst2–/– double knockout animals were born alive, most of them died because of cardiopulmonary deficiency in the early postnatal period.9
Previous work has shown that sulfation of tyrosine residues in N-terminal regions of chemokine receptors plays an important role in interaction with their chemokine ligands. Intriguingly, O-sulfation was observed in a number of chemokine receptors. Some of these are implicated in atherosclerosis progression, including the chemokine receptors CCR2, CCR5, CX3CR1. Selective ablation of CCR2,10 CCR5,11 or CX3CR112,13 significantly decreases lesion formation in atherosclerosis-prone mice, likely because of impaired recruitment of mononuclear cells.
To study a functional role of tyrosine sulfation in chemokine receptors, several groups introduced point mutations to substitute Phe for Tyr. For example, cells bearing point mutations in tyrosine residues in CXCR3 were unable to migrate effectively toward the CXCR3 ligands CXCL9, CXCL10, and CXCL11.14 Mutation in one of two N-terminal tyrosine residues of CX3CR1 caused a 100-fold decrease of affinity for its ligand CX3CL1, whereas mutation in another tyrosine residue (Tyr 22) decreased cell adhesion.15 The function of both CCR5 and CXCR4 was also modified by tyrosine sulfation16,17 as shown by reduced migration to their cognate ligands when tyrosines were mutated to phenylalanines.
Tyrosine sulfation is also critical for PSGL-1 function, because mutation in N-terminal tyrosine residues dramatically reduced the affinity of PSGL-1 for P-selectin.18,19
Many of these studies addressing the role of tyrosine sulfation for the interaction of ligand-receptor pairs were performed in vitro, and the exact relevance of this process in vivo remained unclear. The global pathophysiological role of tyrosine sulfation in atherosclerosis has never been examined.
A study published in this issue1 uncovers an important role for tyrosine sulfation in the atherosclerosis development. The authors generated bone marrow chimeric mice using hematopoietic progenitors from tyrosylprotein sulfotransferase-deficient animals lacking both TPST-1 and -2 and studied the Tpst1–/–Tpst2–/– mutation in hematopoietic cells in the atherosclerosis-prone Ldlr–/– genetic background. TSPT-deficient (Tpst1–/–Tpst2–/– ->Ldlr–/–) and control (WT->Ldlr–/–) mice were fed a high-fat atherogenic diet and atherosclerosis development was analyzed. The authors found significantly reduced atherosclerotic plaques in mice with defective tyrosine sulfation in hematopoietic cells. Importantly, necrotic areas and macrophage numbers were significantly decreased in these mice compared with the control group. The authors also showed that murine PSGL-1 and CX3CR1 are tyrosine sulfated (Figure). Tyrosine sulfation is completely absent in Tpst1–/–Tpst2–/– mice, and therefore PSGL-1 and CX3CR1 are likely nonfunctional in the absence of sulfation in bone marrow chimeric mice (Tpst1–/– Tpst2–/– ->Ldlr–/–). Thus, their studies clearly establish that tyrosine sulfation in bone marrow-derived cells play a critical role in atherosclerotic plaque formation and growth. However, it remains unclear what type of hematopoietic cells play a major role in connecting tyrosine sulfation and atherosclerosis. It is tempting to speculate that both macrophages and T cells may be affected by the lack of tyrosine sulfation, because these cell types are the most important immune subsets enriched in the plaque. Although tyrosine sulfation was described for CCR2, CCR5, and CX3CR1, chemokine receptors involved in recruitment of inflammatory cells into atherosclerosis plaque, it remains to be investigated whether tyrosine sulfation of these (or possibly other) chemokine receptors plays a predominant role in atherosclerosis development. The role of PSGL-1 tyrosine sulfation also remains to be investigated in detail. From the Tpst1–/– Tpst2–/– mice described by Westmuckett and Moore,1 leukocytes could be isolated and tested in flow chambers for their ability to tether and roll on P-selectin, which is likely the PSGL-1 function most relevant for atherosclerosis.
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Tyrosylprotein sulfotransferases might also be a target for pharmacological intervention to prevent or treat atherosclerosis or other inflammatory diseases. Potential side effects must be expected because of the broad expression of these enzymes. Tyrosylprotein sulfotransferases may be inhibitable by small molecules targeting their catalytic center. Development of specific antibodies, which could distinguish between sulfated and nonsulfated proteins in vivo, may be another potential direction for creating an antiatherosclerosis therapy based on limiting immune cell recruitment into the area of inflammation. To be successful, the key receptors that require tyrosine sulfation and are indispensible for atherosclerosis development must be determined. The study by Westmuckett and Moore1 suggests that such targets exist and can be found.
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Acknowledgments |
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Disclosures
None.
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References |
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 Top References |
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1. Westmuckett AD, Moore KL. Lack of tyrosylprotein sulfotransferase activity in hematopoietic cells drastically attenuates atherosclerosis in Ldlr–/– mice. Arterioscler Thromb Vasc Biol. 2009; 29: 1730–1736.
2. Lloyd-Jones D, Adams R, Carnethon M, De Simone G, Ferguson TB, Flegal K, Ford E, Furie K, Go A, Greenlund K, Haase N, Hailpern S, Ho M, Howard V, Kissela B, Kittner S, Lackland D, Lisabeth L, Marelli A, McDermott M, Meigs J, Mozaffarian D, Nichol G, O'Donnell C, Roger V, Rosamond W, Sacco R, Sorlie P, Stafford R, Steinberger J, Thom T, Wasserthiel-Smoller S, Wong N, Wylie-Rosett J, Hong Y. Heart disease and stroke statistics-2009 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation. 2009; 119: e21–e181.
3. Galkina E, Ley K. Immune and inflammatory mechanisms of atherosclerosis. Annu Rev Immunol. 2009; 27: 165–197.[CrossRef][Medline] [Order article via Infotrieve]
4. Zernecke A, Shagdarsuren E, Weber C. Chemokines in atherosclerosis: an update. Arterioscler Thromb Vasc Biol. 2008; 28: 1897–1908.
5. Galkina E, Ley K. Vascular adhesion molecules in atherosclerosis. Arterioscler Thromb Vasc Biol. 2007; 27: 2292–2301.
6. Stone MJ, Chuang S, Hou X, Shoham M, Zhu JZ. Tyrosine sulfation: an increasingly recognised post-translational modification of secreted proteins. N Biotechnol. 2009; 25: 299–317.[CrossRef][Medline] [Order article via Infotrieve]
7. Ouyang YB, Crawley JT, Aston CE, Moore KL. Reduced body weight and increased postimplantation fetal death in tyrosylprotein sulfotransferase-1-deficient mice. J Biol Chem. 2002; 277: 23781–23787.
8. Borghei A, Ouyang YB, Westmuckett AD, Marcello MR, Landel CP, Evans JP, Moore KL. Targeted disruption of tyrosylprotein sulfotransferase-2, an enzyme that catalyzes post-translational protein tyrosine O-sulfation, causes male infertility. J Biol Chem. 2006; 281: 9423–9431.
9. Westmuckett AD, Hoffhines AJ, Borghei A, Moore KL. Early postnatal pulmonary failure and primary hypothyroidism in mice with combined TPST-1 and TPST-2 deficiency. Gen Comp Endocrinol. 2008; 156: 145–153.[CrossRef][Medline] [Order article via Infotrieve]
10. Boring L, Gosling J, Cleary M, Charo IF. Decreased lesion formation in CCR2–/– mice reveals a role for chemokines in the initiation of atherosclerosis. Nature. 1998; 394: 894–897.[CrossRef][Medline] [Order article via Infotrieve]
11. Braunersreuther V, Zernecke A, Arnaud C, Liehn EA, Steffens S, Shagdarsuren E, Bidzhekov K, Burger F, Pelli G, Luckow B, Mach F, Weber C. Ccr5 but not Ccr1 deficiency reduces development of diet-induced atherosclerosis in mice. Arterioscler Thromb Vasc Biol. 2007; 27: 373–379.
12. Combadiere C, Potteaux S, Gao JL, Esposito B, Casanova S, Lee EJ, Debre P, Tedgui A, Murphy PM, Mallat Z. Decreased atherosclerotic lesion formation in CX3CR1/apolipoprotein E double knockout mice. Circulation. 2003; 107: 1009–1016.
13. Liu P, Yu YR, Spencer JA, Johnson AE, Vallanat CT, Fong AM, Patterson C, Patel DD. CX3CR1 deficiency impairs dendritic cell accumulation in arterial intima and reduces atherosclerotic burden. Arterioscler Thromb Vasc Biol. 2008; 28: 243–250.
14. Colvin RA, Campanella GS, Manice LA, Luster AD. CXCR3 requires tyrosine sulfation for ligand binding and a second extracellular loop arginine residue for ligand-induced chemotaxis. Mol Cell Biol. 2006; 26: 5838–5849.
15. Fong AM, Alam SM, Imai T, Haribabu B, Patel DD. CX3CR1 tyrosine sulfation enhances fractalkine-induced cell adhesion. J Biol Chem. 2002; 277: 19418–19423.
16. Farzan M, Choe H, Vaca L, Martin K, Sun Y, Desjardins E, Ruffing N, Wu L, Wyatt R, Gerard N, Gerard C, Sodroski J. A tyrosine-rich region in the N terminus of CCR5 is important for human immunodeficiency virus type 1 entry and mediates an association between gp120 and CCR5. J Virol. 1998; 72: 1160–1164.
17. Farzan M, Babcock GJ, Vasilieva N, Wright PL, Kiprilov E, Mirzabekov T, Choe H. The role of post-translational modifications of the CXCR4 amino terminus in stromal-derived factor 1 alpha association and HIV-1 entry. J Biol Chem. 2002; 277: 29484–29489.
18. Pouyani T, Seed B. PSGL-1 recognition of P-selectin is controlled by a tyrosine sulfation consensus at the PSGL-1 amino terminus. Cell. 1995; 83: 333–343.[CrossRef][Medline] [Order article via Infotrieve]
19. Sako D, Comess KM, Barone KM, Camphausen RT, Cumming DA, Shaw GD. A sulfated peptide segment at the amino terminus of PSGL-1 is critical for P-selectin binding. Cell. 1995; 83: 323–331.[CrossRef][Medline] [Order article via Infotrieve]
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Arterioscler Thromb Vasc Biol 2009 29: 1730-1736.
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