Cell Fusions (eBook)

Preface 5
Contents 7
Contributors 9
1 Regulation and Control of Cell--Cell Fusions 13
References 20
2 Retroviruses and Cell Fusions: Overview 22
2.1 Introduction 24
2.2 Basic Features of the Retroviral Fusion Machinery 26
2.2.1 Entry 26
2.2.2 Receptors 26
2.2.3 Interference 27
2.2.4 Membrane Fusion 28
2.2.5 Fusion Inhibitors 30
2.2.6 The Significance of the Coiled Coil Structures 30
2.2.7 Control Mechanism for Fusion Activation 31
2.2.8 Retroviral Fusion of Cells 32
2.3 Fusion Control in Different Groups of Retroviruses 33
2.4 Endogenous Retroviruses and Cell Fusion 37
2.4.1 Origin and Classification of Endogenous Retroviruses 37
2.4.2 Evolutionary View of HERV env Genes 38
2.4.3 Structural Composition of HERV Envelope Proteins 42
2.5 Conclusion 43
References 44
3 Retroviral Membrane Fusions: Regulation by Proteolytic Processing and Cellular Factors 51
3.1 Introduction 53
3.2 Membrane Fusion by Retroviral Env Protein 54
3.2.1 Cell Surface Receptor 54
3.2.2 Membrane Fusion Mechanism 56
3.3 Regulation of Retroviral Membrane Fusion by Proteolytic Processing 57
3.3.1 Processing of Precursor Env Polyprotein 57
3.3.2 R Peptide Cleavage 58
3.3.3 Syncytium Formation in XC Cells by MLV 59
3.3.4 Mechanism of R Peptide to Inhibit Membrane Fusion 59
3.3.5 Cleavage by Cathepsin Proteases 60
3.4 Regulation of Retroviral Membrane Fusion by Cellular Factors 62
3.4.1 Lipid Raft 62
3.4.2 Cell Adhesion Molecules 63
3.4.3 Cytoskeleton-Associated Molecules 64
3.5 Conclusion 65
References 65
4 A Comparative Portrait of Retroviral Fusogens and Syncytins 72
4.1 Introduction 75
4.2 Contribution of the Envelope to the Retroviral Life Cycle 77
4.2.1 Synthesis of Env Glycoprotein and Viral Assembly 78
4.2.1.1 Synthesis and Maturation of Env Glycoprotein 80
4.2.1.2 Cellular Localization of Env Glycoprotein and Viral Assembly 82
4.2.1.3 Fusion Competency 84
4.2.2 Virus-Host Cell Membrane Fusion: A Multistep Mechanism 84
4.2.2.1 Receptor Binding and Peptide Fusion Liberation 86
4.2.2.2 Pore Formation and Fusion of the Target Membranes 88
4.2.3 Rous Meets Mendel 89
4.3 Syncytins and CellCell Fusion 92
4.3.1 Integration, Domestication Steps and Biological Functions of Endogenous Viral Glycoproteins 94
4.3.1.1 Integration Dating and Orthologues 94
4.3.1.2 Endogenous Retrovirus Envelopes Are Expressed in the Placenta and in the Testis Suggesting a Direct Involvement in Developmental Process 96
4.3.1.3 Biological Function of ERVs Envelopes 96
4.3.2 Fusion Mechanism and Receptor Recognition 98
4.3.2.1 Maturation 98
4.3.2.2 Receptor Binding 101
4.3.2.3 Incorporation in Particles 102
4.3.3 Retroviral Envelopes Are Involved in the Placenta Development 103
4.3.3.1 Envelope and Receptor Localization Throughout Mammalian Gestation 103
4.3.3.2 Splicing Strategy, Transcription Factors and Epigenetic Control 106
4.3.3.3 Additional Factors 108
4.3.4 Syncytin-1 Expression Outside of Its Privileged Tissue 111
4.4 Conclusion 112
References 113
5 Syncytins: Molecular Aspects 125
5.1 Cell Fusion in the Placenta 127
5.1.1 Development of the Placenta 127
5.1.2 Human Syncytin-1 128
5.1.3 Human Syncytin-2 129
5.1.4 Mouse Syncytin-A and -B 130
5.2 Structure and Functional Studies of Syncytins 130
5.2.1 Biosynthesis of Syncytins 131
5.2.2 Functional Domains and Motifs in Syncytins 132
5.2.3 Syncytin Receptors 134
5.2.4 Mechanism of Membrane Fusion 135
5.3 Regulation of Syncytin Expression 136
5.3.1 GCM1 Regulation of Syncytin-1 and -2 Gene Expression 136
5.3.2 Regulation of GCM1 Activity 137
5.3.3 Epigenetic Regulation of Syncytin-1 and -2 Gene Expression 138
5.4 Syncytins and Disease 139
5.4.1 Syncytins in Placental Disorders 139
5.4.2 Syncytin-1 in Malignancies 140
5.4.3 Syncytin-1 in Neurological Diseases 141
5.5 Conclusion 142
References 143
6 Role of the Actin Cytoskeleton Within FuRMAS During Drosophila Myoblast Fusion and First Functionally Conserved Factors in Vertebrates 146
6.1 Introduction to the Cell Biology and Topology of Myoblast Fusion in Drosophila 148
6.1.1 Founder Cells, Fusion-Competent Myoblasts, Progenitors and Myofibres 149
6.1.2 Two Phases of Myoblast Fusion 150
6.2 Pre-fusion Complexes Form at Opposing Membranes, the Membranes Vesiculate, and FCMs Are Integrated into the Growing Myotube 152
6.2.1 Electron-Dense Vesicles and the Pre-fusion Complex 154
6.2.2 Electron-Dense Plaques and Vesiculating Membranes 154
6.3 Cell Adhesion and Signalling Cascades 155
6.3.1 Cell Adhesion 157
6.3.2 Duf/Kirre Very Likely Acts via Rolling Pebbles in FCs and Growing Myoblasts 158
6.3.3 Signalling on the FCM Side 159
6.4 Actin Regulation at the Site of Adhesion During Drosophila Myoblast Fusion 160
6.4.1 Molecular Mechanisms of F-Actin Regulation at the Site of Drosophila Myoblast Fusion 161
6.4.2 Possible Roles for Arp2/3-Based F-Actin Formation at the Site of Drosophila Myoblast Fusion 163
6.4.3 Actin Regulation During Vertebrate Myoblast Fusion 166
6.5 The FuRMAS Model and the Topology of Myoblast Fusion 168
6.5.1 Fusion Pores, Membrane Vesiculation and the Size of Cytoplasmic Continuities 169
6.5.2 FuRMAS as Signalling Centres 170
6.6 Outlook 172
References 172
7 Role of CD9 in Sperm-Egg Fusion and Its General Role in Fusion Phenomena 178
7.1 Introduction 179
7.2 Sperm-Egg Fusion in Fertilization 180
7.3 CD9 and Its Role in Cell Function 182
7.4 Tetraspanin 183
7.5 Tetraspanin as a Component of Exosomes 185
7.6 Lessons from Living Eggs 185
7.7 Membrane Fusion and Exosomes 186
References 189
8 Gamete Binding and Fusion 192
8.1 Introduction 194
8.2 Membrane Fusion Events During Acrosomal Exocytosis 195
8.3 Essential Role of CD9 in Sperm-Egg Binding 196
8.4 IZUMO-the Candidate Sperm Partner of Oolemma Tetraspanins 198
8.5 IntegrinDisintegrin Interactions in Sperm-Egg Binding 199
8.6 Eqatorin MN9 and other Sperm Surface Ligands Implicated in Sperm-Oolemma Fusion 201
8.7 Conclusions 202
References 204
9 Mechanisms Regulating Human Trophoblast Fusion 209
9.1 Introduction 211
9.2 Human Placenta and Villous Trophoblast 211
9.3 Regulators of Trophoblast Fusion 212
9.3.1 Cytokines, Growth Factors and Trophoblast Fusion 212
9.3.2 Protein Kinases, Transcription Factors and Trophoblast Fusion 212
9.3.3 The Phosphatidylserine Flip and Trophoblast Fusion 214
9.3.4 Caspase 8 Activity and Trophoblast Fusion 215
9.3.5 Fusogenic Proteins and Trophoblast Fusion 217
9.4 Pitfalls in Dealing with Trophoblast Fusion In Vitro 218
9.4.1 Phenotype of Isolated Primary Trophoblasts 218
9.4.2 The Use of ß-hCG to Determine the Extentof Trophoblast Fusion 219
9.5 Conclusions 220
References 220
10 Macrophage Fusion: The Making of a New Cell 224
10.1 Macrophage Multinucleation 226
10.1.1 What Are Macrophages? 226
10.1.2 Osteoclasts and Giant Cells 227
10.1.3 Cellular Fusogens 229
10.1.4 Macrophage Fusion Machinery 230
10.1.5 Recognition of Self 232
10.2 Conclusion 234
References 235
11 Molecules Regulating Macrophage Fusions 237
11.1 Overall 239
11.1.1 Cell--Cell Fusion in Macrophages and Osteoclasts 239
11.2 Macrophage and Osteoclast CellCell Fusion 240
11.2.1 MGCs 240
11.2.2 FBGCs as MGCs 240
11.2.3 Phagocytosis and ER-Mediated Cell--Cell Fusion 241
11.2.4 Osteoclasts 241
11.3 Differentiation of Osteoclasts 242
11.3.1 Differentiation of Osteoclasts and Cell--Cell Fusion Is Induced at the Last Stage of Differentiation 242
11.3.2 Anchorage-Dependent Osteoclast Cell--Cell Fusion 242
11.3.3 Molecular Understanding of Cell--Cell Fusion in Macrophages and Osteoclasts 243
11.3.4 The Role of Cell--Cell Fusion: Described in Gene Targeted and Transgenic Mice 245
11.3.5 Transcriptional Regulation of Cell--Cell Fusion in Osteoclasts and MGCs 246
11.4 Future Directions 247
11.4.1 Fusion of Macrophages with Cancer and Somatic Cells 247
11.5 Concluding Remarks 248
References 248
12 Current Progress Towards Understanding Mechanisms of Myoblast Fusion in Mammals 253
12.1 Introduction 254
12.2 Biochemical Requirements for Myoblast Fusion 254
12.3 Methodology for Studying Myoblast Fusion 255
12.3.1 In Vitro Models 255
12.3.2 In Vivo Studies 257
12.4 Current Areas of Research in Myoblast Fusion 257
12.4.1 Elongation and Membrane Alterations 258
12.4.2 Migration 259
12.4.3 Muscle Cell Recognition/Adhesion 260
12.4.4 Actin Dynamics and Integrin Function 261
12.4.5 Regulation of Cell Fusion with Nascent Myotubes 262
12.4.5.1 Nuclear Factor of Activated T Cells: Modulators and Effectors 263
12.4.5.2 Additional Molecules that Control Fusion with Nascent Myotubes 264
12.5 Future Prospects 265
References 266
13 The Endogenous Envelope Protein Syncytin Is Involved in Myoblast Fusion 270
13.1 Introduction 271
13.2 Syncytin-1 and Myoblast Fusion 272
13.3 How Does Syncytin-1 Mediate Fusion? 275
13.4 Conclusions and Perspectives 276
References 276
14 Cell Fusion and Stem Cells 279
14.1 Introduction 281
14.1.1 Understanding Stem Cell Biology for Therapeutic Applications 281
14.1.2 Fusogenicity as a Potential Property of Embryonic and Adult Stem Cells 282
14.2 Gamete Fusion 283
14.2.1 A Historic Perspective of Sperm-Egg Fusion 284
14.2.2 Gamete Cell Adhesion Is Facilitated by ADAM and Integrin Proteins 285
14.2.3 Tetraspanins as Oocyte Fusion Components 286
14.2.4 Sperm Membrane Fusion Proteins 287
14.2.5 Relevance of Gamete Fusion to Stem Cell Biology 287
14.3 Myoblast Fusion 288
14.3.1 A Brief History of Myoblast Fusion 289
14.3.2 Drosophila as a Model to Study Myoblast Fusion 289
14.3.3 Zebrafish as a Vertebrate Myoblast Fusion Model 290
14.3.4 Relevance of Myoblast Fusion Towards Understanding Other Stem Cell Fusion 290
14.4 Cell Fusion with Organ Stem Cells 291
14.4.1 Neural Stem Cell Fusion 291
14.4.2 Mesenchymal Stem Cell Fusion 293
14.4.3 Intestinal Stem Cell Fusion as a Regenerative Response to Injury 293
14.4.4 Relevance of Tissue Stem Cell Fusion to Tissue Physiology 297
14.5 Fusion of Hematopoietic Progenitors as a Source of Regenerative Repair 298
14.5.1 Evidence for Hematopoietic Fusion 298
14.5.2 Hematopoietic Regeneration of Liver Hepatocytes 299
14.5.3 Hematopoietic Regeneration of Heart Myocardium via Cell Fusion 300
14.6 Cancer Stem Cell Fusion 301
14.6.1 Cancer Stem Cell Hypothesis 301
14.6.2 Cell Fusion with Cancer Stem Cells 302
14.6.3 Genomic Instability in Cancer Stem Cell Fusion and Tumor Initiation 302
14.6.4 Fusion as a Mediator of Cancer Progression 303
14.7 Insight into the Physiologic Fate of Stem Cell Fusion 304
14.7.1 Nuclear Reprogramming Within Cell Fusion Hybrid Cells 304
14.7.2 Key Factors that Direct Nuclear Reprogramming 305
14.7.3 Directionality of Nuclear Reprogramming 306
14.7.4 Identification of Discrete Factors Important for Nuclear Reprogramming 307
14.7.5 Lessons from Stem Cell Fusion 307
14.8 Conclusion: The Biological Consequence for Stem Cell Fusigenicity 309
References 311
15 Cell Fusion and Dendritic Cell-Based Vaccines 317
15.1 Introduction 319
15.2 The Rationale for DC-Based Cell Fusion as Tumor Vaccine 320
15.3 Methods 323
15.3.1 Generation of DC from Murine Bone Marrow Cells 323
15.3.2 Preparation of Tumor Cells 325
15.3.3 Cell Fusion 325
15.4 Choice of Fusogen 326
15.4.1 PEG-Mediated Fusion 326
15.4.2 Electrofusion 327
15.4.3 Virus-Mediated Fusion 328
15.5 Selection of Fusion Cells 329
15.6 Modifications in Cell Fusion 330
15.6.1 Allogenic DC 330
15.6.2 Allogeneic Tumor Cells 331
15.6.3 Fusion Cells Expressing Cytokines 331
15.6.4 DC Maturation 332
15.7 Fusion Cell Vaccines and Antitumor Immunity 333
15.7.1 Animal Studies 334
15.7.2 Clinical Trials 338
15.8 Promotion of Antitumor Immunity 341
15.8.1 Using Adjuvant with Fusion Vaccine 341
15.8.2 Combined Approaches 342
15.9 Summary 343
References 344
16 Cancer Cell Fusion with Myeloid Cells: Implications for Energy Metabolism in Malignant Hybrids 353
16.1 Introduction 355
16.2 Cancer Cell Fusion In Vivo 357
16.3 Tumor Associated Macrophages as Candidates for Cancer Cell Fusion Partners 361
16.4 BMDCs in Human Cancer and Stem Cell-Like Distribution Patterns 365
16.5 Cancer Cell Fusion and the Hybrid Phenotype 367
16.6 Macrophage-Melanoma Fusion In Vitro Generates Altered Gene Expression and a Metastatic Phenotype In Vivo 367
16.6.1 SPARC 369
16.6.2 MCR1 and c-Met 370
16.6.3 GnT-V and 1,6-Branched Oligosaccharides 371
16.6.4 Motility-Associated Integrins 371
16.6.5 Cell Surface Expression of Lysosome Associated Protein-1 (LAMP-1) 372
16.6.6 Autophagy and Coarse Melanin 372
16.6.7 Autophagy in Cutaneous Malignant Melanoma 373
16.7 Conclusions 385
16.8 Considerations for Studying Fusion In Vivo 385
16.9 Implications 386
References 387
17 Cell--Cell Fusions and Human Endogenous Retroviruses in Cancer 397
17.1 Development and Polyploidy 398
17.1.1 Short History of Cell--Cell Fusions 400
17.1.2 Cell--Cell Fusions in Development, Differentiation and Viral-Induced 401
17.1.2.1 Cytotrophoblasts-Syncytiotrophoblasts 402
17.1.2.2 Myoblasts-Myotubes 402
17.1.2.3 Osteoclasts 403
17.1.2.4 Unique Cell--Cell Fusions 403
17.1.2.5 Experimental Stem Cell Fusions 403
17.1.2.6 Virus Induced Cell Fusions 404
17.1.2.7 Bone Marrow Derived Cells (BMDC) 404
17.1.3 Cell--Cell Fusions During Tumorigenesis 406
17.2 Human Endogenous Retroviruses (HERVs) 410
17.2.1 HERV Expression in Human Cancers 414
17.2.2 HERVs in Cancer Cell--Cell Fusions: Driver or Passenger 415
17.3 CellCell Fusions in Cancer: Functional Role or Dead-End 416
References 419
Index 429