Shi-hsiang Shen

Identification and Characterization of S2V, a Novel Putative Siglec That Contains Two V Set Ig-like Domains and Recruits Protein-tyrosine Phosphatases SHPs

We describe the molecular cloning and characterization of S2V, a novel sialic acid binding immunoglobulin-like lectin. The cDNA of S2V encodes a type 1 transmembrane protein with four extracellular immunoglobulin-like (Ig-like) domains and a cytoplasmic tail bearing a typical immunoreceptor tyrosine-based inhibitory motif (ITIM) and an ITIM-like motif. A unique feature of S2V is the presence of two V-set Ig-like domains responsible for the binding to sialic acid, whereas all other known siglecs possess only one. S2V is predominantly expressed in macrophage. In vivo S2V was tyrosine-phosphorylated when co-expressed with exogenous c-Src kinase. Upon tyrosine phosphorylation, S2V recruits both Src homology 2 (SH2) domain-containing protein-tyrosine phosphatases SHP-1 and SHP-2, two important inhibitory regulators of immunoreceptor signal transduction. These findings suggest that S2V is involved in the negative regulation of the signaling in macrophage by functioning as an inhibitory receptor. When expressed in COS-7 cells, S2V was able to mediate sialic acid-dependent binding to human red blood cells, suggesting that S2V may function through cell-cell interaction.

Cloning and evaluation of the role of rat GALR-2, a novel subtype of galanin receptor, in the control of pain perception.

Abstract: We have identified a novel subtype of galanin receptor (GALR‐2) in rat dorsal root ganglia and spinal cord. The open reading frame of GALR‐2 is 1116 nucleotides long, encoding a protein of 372 amino acids with a theoretical molecular mass of 40.7 kD. Membranes prepared from stable pools of 293 cells expressing GALR‐2, but not wild‐type 293 cells, demonstrated high affinity galanin binding sites. Rat galanin and galanin‐related peptides M40, C7, M15, and galanin1–16 effectively competed for binding; peptide C7 demonstrated a lower affinity for rGALR‐2, and all these peptides were agonists at rGALR‐2 when assessed on a microphysiometer. Studies on the expression of GALR‐2 in various tissues by Northern and in situ hybridization analyses suggest a low abundance but wide distribution of GALR‐2 mRNA, including several discrete areas in brain and spinal cord and a high abundance in the dorsal root ganglia.

Characterization of beta adrenoceptors on cultured endothelial cells by radioligand binding

The properties of beta-adrenoceptors present on the cultured bovine pulmonary artery endothelial cells were studied by radioligand binding. These cell contain a high density of beta-adrenoceptors (approximately 16,000 receptors/cell) having high affinity (Kd 18 pM) for 125I-iodocyanopindolol (ICYP). Competition binding experiments suggested the presence of more than two subtype of beta-adrenoceptors. 25% of the total population of receptors was found to be of beta 1-type. The remaining 75% represented a mixed population containing what is suggested to be a mixture of beta 2- and atypical beta-adrenoceptors.

Protein Tyrosine Phosphatases in Signal Transduction

The phosphorylation of proteins at tyrosine residues is implicated in numerous cellular processes such as signal transduction, neoplastic transformation and the mitotic cycle. These processes are regulated by the activities of both protein-tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). PTPs represent a highly diversified and rapidly expanding family of enzymes (Fischer et al., 1991, Walton and Dixon, 1993). Indeed, since the identification of PTP1B six years ago (Tonks et al., 1988), more than 40 PTPs, excluding species homologies, have been identified. This is in striking contrast to the relatively small number of serine/threonine phosphatases identified over the past forty years. As with protein tyrosine kinases (PTK), there are two classes of PTPs: transmembrane (receptor-type) and intracellular enzymes. Most transmembrane PTPs have two conserved tandem intracellular catalytic domains with diversified receptor-like extracellular sequences. All the intracellular enzymes contain only one conserved catalytic domain with widely diversified non-catalytic amino or carboxyl termini.