Biological activity of soluble CD100. I. The extracellular region of CD100 is released from the surface of T lymphocytes by regulated proteolysis.
CD100 is the first semaphorin described in lymphoid tissues, where it has been shown to be associated with a serine kinase activity. Semaphorins are molecules involved in axon pathfinding during nerve development and act as repellent guidance cues. In the nervous system semaphorins exist as either membrane-bound or secreted forms. We report here a spontaneous processing of membrane CD100, suggesting that it is also produced as a diffusable semaphorin from lymphoid cells. Monomeric and homodimeric forms of CD100 are expressed by T lymphocytes and CD100-transfected fibroblasts. We demonstrate that CD100 is released through a proteolytic process blocked by metalloprotease inhibitors. In T cells, only soluble CD100 dimers are produced, suggesting that CD100 dimerization is required for proteolysis. In agreement, we observe that increasing membrane dimers strongly favors shedding of the molecule. By expressing a CD100 molecule mutated at cysteine 674 into a COS cell system, we additionally demonstrate that this particular residue in the extracellular domain of the molecule is required for dimerization. Finally, we show that staurosporine, a serine kinase inhibitor, enhances the membrane cleavage of CD100. Together these results demonstrate that membrane CD100 is cleaved by a metalloprotease-dependent process, which is probably regulated by phosphorylation. Mainly, these findings shed light on a possible function for the semaphorin region of CD100 as a long range guidance cue in the immune system.
Institut National de la Santé et de la Recherche Médicale, Unité 448, Faculté de Médecine de Créteil, Créteil, France.
A
A
Elhabazi
S
S
Delaire
A
A
Bensussan
L
L
Boumsell
G
G
Bismuth
D016475:3T3 Cells; D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000818:Animals; D015703:Antigens, CD; D019556:COS Cells; D002462:Cell Membrane / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D003545:Cysteine / Q000235:genetics / Q000502:physiology; D019281:Dimerization; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D007460:Iodoacetamide / Q000494:pharmacology; D019169:Jurkat Cells; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors; D051379:Mice; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary / Q000235:genetics; D039961:Semaphorins; D012995:Solubility; D019311:Staurosporine / Q000494:pharmacology; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology / Q000378:metabolism*; D014162:Transfection
D000276:Adjuvants, Immunologic; D015703:Antigens, CD; C093224:CD100 antigen; D004791:Enzyme Inhibitors; D008562:Membrane Glycoproteins; D039961:Semaphorins; D004533:Egtazic Acid; D004492:Edetic Acid; D010450:Endopeptidases; D008666:Metalloendopeptidases; D019311:Staurosporine; D003545:Cysteine; D007460:Iodoacetamide