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Wang Q, Onuma K, Liu C, Wong H, Bloom MS, Elliott EE, Cao RR, Hu N, Lingampalli N, Sharpe O, Zhao X, Sohn DH, Lepus CM, Sokolove J, Mao R, Cisar CT, Raghu H, Chu CR, Giori NJ, Willingham SB, Prohaska SS, Cheng Z, Weissman IL, Robinson WH. Dysregulated integrin αVβ3 and CD47 signaling promotes joint inflammation, cartilage breakdown, and progression of osteoarthritis. JCI Insight 2019; 4:128616. [PMID: 31534047 PMCID: PMC6795293 DOI: 10.1172/jci.insight.128616] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 08/13/2019] [Indexed: 12/13/2022] Open
Abstract
Osteoarthritis (OA) is the leading cause of joint failure, yet the underlying mechanisms remain elusive, and no approved therapies that slow progression exist. Dysregulated integrin function was previously implicated in OA pathogenesis. However, the roles of integrin αVβ3 and the integrin-associated receptor CD47 in OA remain largely unknown. Here, transcriptomic and proteomic analyses of human and murine osteoarthritic tissues revealed dysregulated expression of αVβ3, CD47, and their ligands. Using genetically deficient mice and pharmacologic inhibitors, we showed that αVβ3, CD47, and the downstream signaling molecules Fyn and FAK are crucial to OA pathogenesis. MicroPET/CT imaging of a mouse model showed elevated ligand-binding capacities of integrin αVβ3 and CD47 in osteoarthritic joints. Further, our in vitro studies demonstrated that chondrocyte breakdown products, derived from articular cartilage of individuals with OA, induced αVβ3/CD47-dependent expression of inflammatory and degradative mediators, and revealed the downstream signaling network. Our findings identify a central role for dysregulated αVβ3 and CD47 signaling in OA pathogenesis and suggest that activation of αVβ3 and CD47 signaling in many articular cell types contributes to inflammation and joint destruction in OA. Thus, the data presented here provide a rationale for targeting αVβ3, CD47, and their signaling pathways as a disease-modifying therapy.
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Affiliation(s)
- Qian Wang
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Kazuhiro Onuma
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Changhao Liu
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, Stanford University School of Medicine, Stanford, California, USA
| | - Heidi Wong
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Michelle S. Bloom
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Eileen E. Elliott
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Richard R.L. Cao
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Nick Hu
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Nithya Lingampalli
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Orr Sharpe
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Xiaoyan Zhao
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Dong Hyun Sohn
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
- Department of Microbiology and Immunology, Pusan National University School of Medicine, Yangsan, Gyeongsangnam-do, South Korea
| | - Christin M. Lepus
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Jeremy Sokolove
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Rong Mao
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Cecilia T. Cisar
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Harini Raghu
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
| | - Constance R. Chu
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
- Department of Orthopedic Surgery
| | - Nicholas J. Giori
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
- Department of Orthopedic Surgery
| | - Stephen B. Willingham
- Institute for Stem Cell Biology and Regenerative Medicine and the Ludwig Cancer Center, and
- Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, California, USA
| | - Susan S. Prohaska
- Institute for Stem Cell Biology and Regenerative Medicine and the Ludwig Cancer Center, and
- Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, California, USA
| | - Zhen Cheng
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, Stanford University School of Medicine, Stanford, California, USA
| | - Irving L. Weissman
- Institute for Stem Cell Biology and Regenerative Medicine and the Ludwig Cancer Center, and
- Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, California, USA
| | - William H. Robinson
- Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, California, USA
- Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA
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Sikic BI, Lakhani N, Patnaik A, Shah SA, Chandana SR, Rasco D, Colevas AD, O'Rourke T, Narayanan S, Papadopoulos K, Fisher GA, Villalobos V, Prohaska SS, Howard M, Beeram M, Chao MP, Agoram B, Chen JY, Huang J, Axt M, Liu J, Volkmer JP, Majeti R, Weissman IL, Takimoto CH, Supan D, Wakelee HA, Aoki R, Pegram MD, Padda SK. First-in-Human, First-in-Class Phase I Trial of the Anti-CD47 Antibody Hu5F9-G4 in Patients With Advanced Cancers. J Clin Oncol 2019; 37:946-953. [PMID: 30811285 DOI: 10.1200/jco.18.02018] [Citation(s) in RCA: 350] [Impact Index Per Article: 70.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
PURPOSE To evaluate the safety, pharmacokinetics, and pharmacodynamics of Hu5F9-G4 (5F9), a humanized IgG4 antibody that targets CD47 to enable phagocytosis. PATIENTS AND METHODS Adult patients with solid tumors were treated in four cohorts: part A, to determine a priming dose; part B, to determine a weekly maintenance dose; part C, to study a loading dose in week 2; and a tumor biopsy cohort. RESULTS Sixty-two patients were treated: 11 in part A, 14 in B, 22 in C, and 15 in the biopsy cohort. Part A used doses that ranged from 0.1 to 3 mg/kg. On the basis of tolerability and receptor occupancy studies that showed 100% CD47 saturation on RBCs, 1 mg/kg was selected as the priming dose. In subsequent groups, patients were treated with maintenance doses that ranged from 3 to 45 mg/kg, and most toxicities were mild to moderate. These included transient anemia (57% of patients), hemagglutination on peripheral blood smear (36%), fatigue (64%), headaches (50%), fever (45%), chills (45%), hyperbilirubinemia (34%), lymphopenia (34%), infusion-related reactions (34%), and arthralgias (18%). No maximum tolerated dose was reached with maintenance doses up to 45 mg/kg. At doses of 10 mg/kg or more, the CD47 antigen sink was saturated by 5F9, and a 5F9 half-life of approximately 13 days was observed. Strong antibody staining of tumor tissue was observed in a patient at 30 mg/kg. Two patients with ovarian/fallopian tube cancers had partial remissions for 5.2 and 9.2 months. CONCLUSION 5F9 is well tolerated using a priming dose at 1 mg/kg on day 1 followed by maintenance doses of up to 45 mg/kg weekly.
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Affiliation(s)
| | - Nehal Lakhani
- 2 South Texas Accelerated Therapeutics Midwest, Grand Rapids, MI
| | - Amita Patnaik
- 3 South Texas Accelerated Therapeutics, San Antonio, TX
| | - Sumit A Shah
- 1 Stanford University School of Medicine, Stanford, CA
| | | | - Drew Rasco
- 3 South Texas Accelerated Therapeutics, San Antonio, TX
| | | | - Timothy O'Rourke
- 2 South Texas Accelerated Therapeutics Midwest, Grand Rapids, MI
| | | | | | | | | | | | | | | | | | | | | | | | | | - Jie Liu
- 5 Forty Seven, Menlo Park, CA
| | | | - Ravindra Majeti
- 1 Stanford University School of Medicine, Stanford, CA.,5 Forty Seven, Menlo Park, CA
| | | | | | - Dana Supan
- 1 Stanford University School of Medicine, Stanford, CA
| | | | - Rhonda Aoki
- 1 Stanford University School of Medicine, Stanford, CA
| | - Mark D Pegram
- 1 Stanford University School of Medicine, Stanford, CA
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Chang E, Forsberg EC, Wu J, Bingyin Wang, Prohaska SS, Allsopp R, Weissman IL, Cooke JP. Cholinergic activation of hematopoietic stem cells: role in tobacco-related disease? Vasc Med 2011; 15:375-85. [PMID: 20926497 DOI: 10.1177/1358863x10378377] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Tobacco use is associated with an increase in the white blood cell (WBC) count. This association has been attributed to bronchopulmonary inflammation and/or infection. It is not known if nicotine itself may play a role. The objective of this study was to determine whether nicotine itself could affect the WBC count, and to determine whether this was due to a direct effect on hematopoietic stem cells (HSC). C57Bl6J mice received nicotine orally, and measurements of the WBC count, bone marrow and spleen cellularity, and HSC count were made. To determine the functionality of HSCs, irradiated animals received bone marrow transplants from vehicle or nicotine-treated mice. Nicotine increased leukocytes in the peripheral blood, bone marrow and spleen. The peripheral red cell and platelet count were unaffected. Nicotine increased the frequency of HSC in the bone marrow. Isolated long-term HSCs from nicotine-treated mice transplanted into irradiated mice regenerated all hematopoietic cell lineages, demonstrating the functional competence of those HSCs. HSCs expressed nicotinic acetylcholine receptors (nAChRs), as documented by FITC-conjugated alpha-bungarotoxin binding. Nicotine increased soluble Kit ligand, consistent with stem cell activation. In conclusion, the data suggest a new mechanism for the increased WBC associated with tobacco use. The effect of nicotine to activate hematopoiesis may contribute to tobacco-related diseases.
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Affiliation(s)
- Edwin Chang
- Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA
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4
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Abstract
Hematopoietic stem cells (HSCs) divide and give rise to more committed progenitors, which ultimately produce all lineages of blood cells. HSCs can be induced to enter the cell cycle in vitro and in vivo by stimulatory cytokines and in vivo by ablation of bone marrow (BM) cells with irradiation or chemotherapeutic agents. Although it has been postulated that rates of HSC proliferation increase with normal hematopoietic stresses, such as infection or hemorrhage, this hypothesis has never been directly tested. The ability to analyze HSCs prospectively by cell-surface phenotype c-kit(+), Thy1.1(lo), Sca-1(+), Linage(neg/lo) has allowed us to perform a detailed examination of the effects of bleeding on the cell cycle kinetics of HSCs. Our results demonstrate for the first time that HSCs in both the BM and the spleen proliferate and self-renew in response to tail-vein bleeding in mice. This response was suppressed when red blood cells, but not when white blood cells, were transferred after bleeding. Thus, regulators of HSC proliferation can sense and respond to red blood cell levels.
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Affiliation(s)
- Samuel H Cheshier
- Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA 94305, USA
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5
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Forsberg EC, Prohaska SS, Katzman S, Heffner GC, Stuart JM, Weissman IL. Differential expression of novel potential regulators in hematopoietic stem cells. PLoS Genet 2006; 1:e28. [PMID: 16151515 PMCID: PMC1200425 DOI: 10.1371/journal.pgen.0010028] [Citation(s) in RCA: 224] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2005] [Accepted: 07/14/2005] [Indexed: 12/12/2022] Open
Abstract
The hematopoietic system is an invaluable model both for understanding basic developmental biology and for developing clinically relevant cell therapies. Using highly purified cells and rigorous microarray analysis we have compared the expression pattern of three of the most primitive hematopoietic subpopulations in adult mouse bone marrow: long-term hematopoietic stem cells (HSC), short-term HSC, and multipotent progenitors. All three populations are capable of differentiating into a spectrum of mature blood cells, but differ in their self-renewal and proliferative capacity. We identified numerous novel potential regulators of HSC self-renewal and proliferation that were differentially expressed between these closely related cell populations. Many of the differentially expressed transcripts fit into pathways and protein complexes not previously identified in HSC, providing evidence for new HSC regulatory units. Extending these observations to the protein level, we demonstrate expression of several of the corresponding proteins, which provide novel surface markers for HSC. We discuss the implications of our findings for HSC biology. In particular, our data suggest that cell–cell and cell–matrix interactions are major regulators of long-term HSC, and that HSC themselves play important roles in regulating their immediate microenvironment. Hematopoietic, or blood-forming, stem cells (HSC) are responsible for the continual replenishment of all blood cells throughout life. This ability to both renew themselves and give rise to expanded populations of differentiating and mature cells is a hallmark of stem cells and is therefore an area of intense research. The rarity of HSC as well as their location in the bone marrow environment has made it difficult to identify the genes that regulate these properties. The earliest stages of blood development begins with the long-term (LT) repopulating HSC that then differentiate into short-term (ST) repopulating HSC and non-self renewing multipotent progenitors (MPP). The authors investigated the gene expression differences in these highly purified populations that differ mainly in their capacity to self renew, and identified a number of genes specific to each of these populations. Intriguingly, many of these genes code for proteins that are involved in cell–cell and cell–matrix interactions that were not previously identified on these populations. These novel discoveries will, together with future experiments, enhance our understanding of the basic biology of stem cells and their clinical uses.
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Affiliation(s)
- E Camilla Forsberg
- Department of Pathology, Institute of Cancer and Stem Cell Biology and Medicine, Stanford University Medical School, Stanford, California, USA.
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6
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Kondo M, Wagers AJ, Manz MG, Prohaska SS, Scherer DC, Beilhack GF, Shizuru JA, Weissman IL. Biology of hematopoietic stem cells and progenitors: implications for clinical application. Annu Rev Immunol 2003; 21:759-806. [PMID: 12615892 DOI: 10.1146/annurev.immunol.21.120601.141007] [Citation(s) in RCA: 674] [Impact Index Per Article: 32.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Stem cell biology is scientifically, clinically, and politically a current topic. The hematopoietic stem cell, the common ancestor of all types of blood cells, is one of the best-characterized stem cells in the body and the only stem cell that is clinically applied in the treatment of diseases such as breast cancer, leukemias, and congenital immunodeficiencies. Multicolor cell sorting enables the purification not only of hematopoietic stem cells, but also of their downstream progenitors such as common lymphoid progenitors and common myeloid progenitors. Recent genetic approaches including gene chip technology have been used to elucidate the gene expression profile of hematopoietic stem cells and other progenitors. Although the mechanisms that control self-renewal and lineage commitment of hematopoietic stem cells are still ambiguous, recent rapid advances in understanding the biological nature of hematopoietic stem and progenitor cells have broadened the potential application of these cells in the treatment of diseases.
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Affiliation(s)
- Motonari Kondo
- Department of Immunology, Duke University Medical Center, Durham, North Carolina 27710, USA.
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7
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Abstract
The identification of the common lymphoid progenitors in mouse bone marrow allows us to directly assess the regulatory mechanisms of lymphoid lineage commitment. The unexpected finding of a latent myeloid differentiation potential in lymphoid progenitors sheds light on the importance of cytokine receptor expression at this stage. We will discuss the biological nature of common lymphoid progenitors as a model of differentiation from multipotent to lineage committed progenitors. Elucidation of this hidden differentiation potential in progenitors will help further our understanding of the molecular mechanisms that control the cell fate determination of not only common lymphoid progenitors, but also their ancestors, hematopoietic stem cells, and their descendents such as committed T and B cell progenitors.
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Affiliation(s)
- Susan S Prohaska
- Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305, USA
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8
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Robinson WH, Prohaska SS, Santoro JC, Robinson HL, Parnes JR. Identification of a mouse protein homologous to the human CD6 T cell surface protein and sequence of the corresponding cDNA. J Immunol 1995; 155:4739-48. [PMID: 7594475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
CD6 is a 105/130 kDa monomeric T cell surface glycoprotein that has been shown to play a role in human T cell activation. Recently a partial mouse CD6 cDNA sequence was described. We have isolated full-length cDNA clones including the initiation codon and sequence encoding the full signal peptide, as well as an additional 39 amino acids within the cytoplasmic domain as compared to the previously reported clone. The predicted full-length mouse CD6 protein contains 665 amino acids and has the features of a type I integral membrane protein. The extracellular domain of mouse CD6 is composed of three repeated cysteine-rich domains similar to those in human CD6, mouse and human CD5, and other members of a family of proteins whose prototype is the type I macrophage scavenger receptor. In marked contrast to the previously published human CD6 sequence, the mouse sequence predicts a long cytoplasmic tail that is not closely related to other proteins and possesses two proline-rich motifs containing the SH3-domain binding consensus sequence, three protein kinase C phosphorylation site motifs, nine casein kinase-2 phosphorylation site motifs, and a serine-threonine-rich motif repeated three times. Northern blot analysis revealed that mouse CD6 mRNA is expressed predominantly in thymus, lymph node, and spleen. A polyclonal antiserum was raised against mouse CD6 by gene gun plasmid DNA immunization of rabbits with the mouse CD6 cDNA in an expression vector. In immunofluorescence analysis this polyclonal antiserum positively stained the surface of cells transfected with the mouse CD6 cDNA in an expression vector, as well as most normal mouse thymocytes and peripheral T cells. CD6 protein is expressed on most CD4+CD8+ double-positive and CD4+ or CD8+ single-positive thymocytes, and is expressed at highest levels on mature CD3high thymocytes. The expression of mouse CD6 in thymocytes and peripheral T cells correlates closely with the expression of the related CD5 molecule. The polyclonal rabbit anti-mouse CD6 Abs immunoprecipitated a major polypeptide of 128 kDa from resting and 130 kDa from PMA- and FCS-activated mouse thymocytes and lymph node cells; it is likely that this increase in size upon activation is due to phosphorylation of mouse CD6 as has been described for human CD6. These data demonstrate that mouse thymocytes and T cells express a 130-kDa cell surface protein homologous to human CD6.
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MESH Headings
- Amino Acid Sequence
- Animals
- Antigens, CD/analysis
- Antigens, CD/genetics
- Antigens, CD/isolation & purification
- Antigens, Differentiation, T-Lymphocyte/analysis
- Antigens, Differentiation, T-Lymphocyte/genetics
- Antigens, Differentiation, T-Lymphocyte/isolation & purification
- Antigens, Surface/analysis
- Antigens, Surface/genetics
- Antigens, Surface/isolation & purification
- Base Sequence
- DNA, Complementary/genetics
- DNA, Complementary/isolation & purification
- Humans
- Lymphoid Tissue/metabolism
- Mice
- Molecular Sequence Data
- Sequence Alignment
- Sequence Homology, Amino Acid
- T-Lymphocytes/metabolism
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Affiliation(s)
- W H Robinson
- Department of Medicine, Stanford University School of Medicine, CA 94305, USA
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9
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Robinson WH, Prohaska SS, Santoro JC, Robinson HL, Parnes JR. Identification of a mouse protein homologous to the human CD6 T cell surface protein and sequence of the corresponding cDNA. The Journal of Immunology 1995. [DOI: 10.4049/jimmunol.155.10.4739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Abstract
CD6 is a 105/130 kDa monomeric T cell surface glycoprotein that has been shown to play a role in human T cell activation. Recently a partial mouse CD6 cDNA sequence was described. We have isolated full-length cDNA clones including the initiation codon and sequence encoding the full signal peptide, as well as an additional 39 amino acids within the cytoplasmic domain as compared to the previously reported clone. The predicted full-length mouse CD6 protein contains 665 amino acids and has the features of a type I integral membrane protein. The extracellular domain of mouse CD6 is composed of three repeated cysteine-rich domains similar to those in human CD6, mouse and human CD5, and other members of a family of proteins whose prototype is the type I macrophage scavenger receptor. In marked contrast to the previously published human CD6 sequence, the mouse sequence predicts a long cytoplasmic tail that is not closely related to other proteins and possesses two proline-rich motifs containing the SH3-domain binding consensus sequence, three protein kinase C phosphorylation site motifs, nine casein kinase-2 phosphorylation site motifs, and a serine-threonine-rich motif repeated three times. Northern blot analysis revealed that mouse CD6 mRNA is expressed predominantly in thymus, lymph node, and spleen. A polyclonal antiserum was raised against mouse CD6 by gene gun plasmid DNA immunization of rabbits with the mouse CD6 cDNA in an expression vector. In immunofluorescence analysis this polyclonal antiserum positively stained the surface of cells transfected with the mouse CD6 cDNA in an expression vector, as well as most normal mouse thymocytes and peripheral T cells. CD6 protein is expressed on most CD4+CD8+ double-positive and CD4+ or CD8+ single-positive thymocytes, and is expressed at highest levels on mature CD3high thymocytes. The expression of mouse CD6 in thymocytes and peripheral T cells correlates closely with the expression of the related CD5 molecule. The polyclonal rabbit anti-mouse CD6 Abs immunoprecipitated a major polypeptide of 128 kDa from resting and 130 kDa from PMA- and FCS-activated mouse thymocytes and lymph node cells; it is likely that this increase in size upon activation is due to phosphorylation of mouse CD6 as has been described for human CD6. These data demonstrate that mouse thymocytes and T cells express a 130-kDa cell surface protein homologous to human CD6.
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Affiliation(s)
- W H Robinson
- Department of Medicine, Stanford University School of Medicine, CA 94305, USA
| | - S S Prohaska
- Department of Medicine, Stanford University School of Medicine, CA 94305, USA
| | - J C Santoro
- Department of Medicine, Stanford University School of Medicine, CA 94305, USA
| | - H L Robinson
- Department of Medicine, Stanford University School of Medicine, CA 94305, USA
| | - J R Parnes
- Department of Medicine, Stanford University School of Medicine, CA 94305, USA
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10
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Abstract
Human CD6 is a monomeric 105/130-kDa T cell surface glycoprotein that is involved in T cell activation. The apparent discrepancy between the size of the cytoplasmic domain in human (44 amino acids) and mouse (243 amino acids) CD6, led us to use reverse transcriptase-polymerase chain reaction of human peripheral blood lymphocyte mRNA to isolate cDNA clones that include the carboxyl-terminal coding region of human CD6. The nucleotide sequence of the longest human cDNA clone, CD6-PB1, predicts a protein of 668 amino acids with a 244-amino acid cytoplasmic domain similar in size to and possessing 71.5% amino acid sequence identity with the cytoplasmic domain of mouse CD6. This previously unrecognized 244-amino acid cytoplasmic domain does not have significant homology to any other known protein (except mouse CD6), but does possess two proline-rich motifs containing the SH3 domain-binding consensus sequence, a serine-threonine-rich motif repeated three times, three protein kinase C phosphorylation-site motifs, and 10 casein kinase-2 phosphorylation-site motifs. These sequences are likely to play a role in the ability of CD6-specific monoclonal antibodies to stimulate T cell proliferation. Full-length CD6 cDNA containing this cytoplasmic domain sequence encodes a monomeric 105/130-kDa protein that can be immunoprecipitated from the surface of transfected cells and comigrates upon SDS-PAGE with wild-type CD6 immunoprecipitated from PBL. We also isolated two alternatively spliced forms of human CD6 cDNA lacking sequences encoding membrane-proximal regions of the cytoplasmic domain which maintain the same reading frame as CD6-PB1. The short cytoplasmic domain of the previously reported human CD6-15 cDNA clone results from a deletion of a 20-bp segment through use of an alternative 3' splice site, resulting in a frame shift and premature termination of translation relative to the clones we have isolated. These data demonstrate that human CD6 possesses a large cytoplasmic domain containing sequence motifs that are likely to be involved in signal transduction upon stimulation of T cells through CD6 ligation.
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Affiliation(s)
- W H Robinson
- Department of Medicine, Stanford University School of Medicine, CA 94305-5487, USA
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