title: Characterization of inhibitory signaling motifs of the natural killer cell receptor Siglec-7: attenuated recruitment of phosphatases by the receptor is attributed to two amino acids in the motifs.
abstract: Siglec-7 (p75/AIRM1) is an inhibitory receptor on human natural killer cells (NK cells) and monocytes. The cytoplasmic domain of Siglec-7 contains two signaling motifs: a membrane-proximal immunoreceptor tyrosine-based inhibitory motif (ITIM) (Ile435-Gln-Tyr-Ala-Pro-Leu440) and a membrane-distal motif (Asn458-Glu-Tyr-Ser-Glu-Ile463). We report here that, upon pervanadate (PV) treatment, Siglec-7 recruited the protein tyrosine phosphatases Src homology-2 (SH2) domain-containing protein-tyrosine phosphatase-1 (SHP-1) and SHP-2 less efficiently than did other inhibitory receptors such as Siglec-9 and leukocyte-associated Ig-like receptor (LAIR-1). Alignment of the amino acid sequences of the two Siglecs revealed only three amino acids difference in these motifs. To identify the amino acid(s) critical to recruitment efficiency, we prepared a series of Siglec-7-based mutants in which each of the three amino acids were replaced with the corresponding one of Siglec-9 (I435L, P439S, and N458T mutants). P439S and N458T mutants showed pronounced enhancement of SHP recruitment, but I435L mutant had little effect. A double mutant (P439S, N458T) or triple mutant (I435L, P439S, N458T) recruited SHPs as much as did Siglec-9, indicating that Pro439 in the proximal motif and Asn458 in the distal motif of Siglec-7 attenuate its ability to recruit phosphatases. These amino acids appeared to affect not only phosphatase recruitment but also the subsequent attenuation of Syk phosphorylation.
authors.affiliation: Glyco-chain Functions Laboratory, Supra-biomolecular System Group, Frontier Research System, Institute of Physical and Chemical Research (RIKEN), Wako-shi, Saitama 351-0198, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yamaji
authors.forename: Motoaki
authors.initials: M
authors.lastname: Mitsuki
authors.forename: Takane
authors.initials: T
authors.lastname: Teranishi
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Hashimoto
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D015214:Antigens, Differentiation, Myelomonocytic / Q000737:chemistry* / Q000378:metabolism; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D005434:Flow Cytometry; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D037102:Lectins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D054645:Protein Phosphatase 1; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases; D015398:Signal Transduction
chemical_list: D015214:Antigens, Differentiation, Myelomonocytic; D017931:DNA Primers; D047908:Intracellular Signaling Peptides and Proteins; D037102:Lectins; C402206:SIGLEC7 protein, human; D054645:Protein Phosphatase 1; C516724:PTPN11 protein, human; C509249:PTPN6 protein, human; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases