title: Siglec-7 mediates nonapoptotic cell death independently of its immunoreceptor tyrosine-based inhibitory motifs in monocytic cell line U937.
abstract: Siglec-7, a sialic acid binding immunoglobulin-like lectin, predominantly transduces inhibitory signals through cytosolic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Here, we report that clustering of Siglec-7 with a specific F(ab')(2) elicited cell death. Interestingly, a truncated Siglec-7 lacking the cytosolic ITIM domain still induced the cell death, suggesting that the ITIMs are not essential for the death signaling. Further analyses of the death signaling revealed that an oxygen radical scavenger, N-acetyl cysteine, completely inhibited the cell death, whereas a pancaspase inhibitor did not. In addition, caspase-3 activation, DNA ladder formation, and nuclear condensation were not detected during the death process, suggesting that the cell death is nonapoptotic. To identify the critical region for the death signaling, we prepared a series of shuffling chimeras between Siglec-7 and Siglec-9, the latter of which did not transduce a death signal. The critical region was mapped to the middle of the membrane-proximal C2-set domain, which contained only six amino acid differences between Siglec-7 and Siglec-9. Point mutation analyses of each of these six amino acids revealed that four of the six amino acids were critical for the death signal. A computer-assisted 3D modeling revealed that these four amino acids were proximally located on the surface of the C2-set domain. In conclusion, Siglec-7 induces nonapoptotic cell death, the signal for which is transduced by an extracellular C2-set domain.
authors.affiliation: Glyco-chain Functions Laboratory, Supra-Biomolecule Research Group, RIKEN Frontier Research System, Saitama, Japan.
authors.forename: Motoaki
authors.initials: M
authors.lastname: Mitsuki
authors.forename: Kiyomitsu
authors.initials: K
authors.lastname: Nara
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yamaji
authors.forename: Ayako
authors.initials: A
authors.lastname: Enomoto
authors.forename: Mayumi
authors.initials: M
authors.lastname: Kanno
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Akane
authors.initials: A
authors.lastname: Yamada
authors.forename: Satoshi
authors.initials: S
authors.lastname: Waguri
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Hashimoto
mesh_terms: D020816:Amino Acid Motifs; D000911:Antibodies, Monoclonal / Q000276:immunology; D015214:Antigens, Differentiation, Myelomonocytic / Q000737:chemistry* / Q000276:immunology; D016923:Cell Death; D006801:Humans; D037102:Lectins / Q000737:chemistry* / Q000276:immunology; D009000:Monocytes / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism; D020298:U937 Cells
chemical_list: D000911:Antibodies, Monoclonal; D015214:Antigens, Differentiation, Myelomonocytic; D037102:Lectins; C402206:SIGLEC7 protein, human; D014443:Tyrosine