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. SHP-11 is a nonreceptor protein-tyrosine phosphatase that contains tandem Src homology 2 (SH2) domains at its N terminus, enabling its association with tyrosine-phosphorylated proteins. It is expressed primarily in hematopoietic cells and epithelial cells and acts predominantly as a negative regulator of a broad spectrum of receptors, including receptor proteintyrosine kinases such as c-Kit (1), colony-stimulating factor (2), epidermal growth factor (3, 4), and platelet-derived growth factor (5, 6) receptors, cytokine receptors such as erythropoietin (7), interleukin-3 (8) and interferon (9) receptors, and immunoreceptors such as the B cell (10), T cell (11), and natural killer (NK) cell (12, 13) receptors. The importance of the inhibitory signals delivered by SHP-1 is highlighted by the motheaten (me) mouse, which has natural defect in SHP-1 expression (14). Mice with this deficiency display widespread autoimmune phenomena caused by an inability to negatively regulate immune responses (14). The inhibitory effect of SHP-1 appears to reflect its capacity to associate with and dephosphorylate the activated receptors and/or the signaling molecules in the receptor complexes such as receptor protein-tyrosine kinase in c-Kit signaling (1), Jak kinase in cytokine receptor signaling (7), and Lck, ZAP70, and Syk in antigen receptor signaling (10, 11).In addition to direct association with the activated receptor complexes and down-regulation of the signaling of the "growthpromoting" receptors, SHP-1 performs its inhibitory function in many hematopoietic cells by associating with inhibitory receptors that bear the immunoreceptor tyrosine-based inhibitory motifs (ITIMs) (reviewed in Refs. 10, 12, and 13). Among the ITIM-bearing proteins are sialic acid binding immunoglobulinlike lectins (siglecs), a recently designated superfamily of cell surface molecules. The human...

A single factorial experiment was conducted to test the effects of three dietary levels of energy on mRNA expression of fatty acid synthase (FAS-mRNA) and hormone-sensitive lipase (HSL-mRNA) and their association with intramuscular fat in finishing pigs. 72 crossbred (Large White×Rongchang) barrows with an average initial body weight of 20.71 (s.e. 0.1) kg, were randomly allotted to three dietary treatments (11.75, 13.05 and 14.36 MJ DE/kg) and fed until slaughtered at 100 or 101 kg. The diets were iso-nitrogenous and iso-essential amino acids. The growth performances including the duration of finishing were changed linearly (p<0.05) or quadratically (p<0.05) with increased dietary energy levels. The effects of dietary energy content on the percentage of external fat, intramuscular backfat and the fat thickness were linear (p<0.05). The content of dietary energy increased FAS-mRNA linearly or quadratically, while HSL-mRNA decreased linearly or quadratically in backfat and Longissmus dorsi muscle. Meanwhile, significant positive correlations (p<0.05) were found between energy level and intramuscular fat, FAS-mRNA or the ratio of FAS-mRNA to HSL-mRNA, between the ratio of FAS-mRNA to HSL-mRNA and intramuscular fat. However, the correlations between HSL mRNA and dietary energy or intramuscular fat were negative (p<0.05). The results indicated that dietary energy level regulates lipid accumulation, especially intramuscular fat, possibly by modulating the mRNA of FAS and HSL together rather than individually.

This article is available online at http://www.jlr.org hydrolyze two principal lipid substrates associated with lipoprotein particles, triglycerides (TGs), and phospholipids. The released fatty acids (FAs) resulting from lipase hydrolysis are taken up by subjacent tissue and used for energy storage (adipose), oxidation, and energy production (skeletal muscle and heart) and the synthesis of bioactive metabolites (variety of tissues).LPL is principally a TG lipase involved in the metabolism of TG-rich lipoproteins (chylomicrons and very-lowdensity lipoproteins) in adipose and muscle and heart tissues ( 1 ). Its defi ciency and overexpression have been linked to metabolic abnormalities such as hypertriglyceridemia, insulin resistance, and cardiomyopathy, indicating the critical role of this enzyme in TG metabolism ( 4-10 ). Unlike LPL, HL has comparable TG lipase and phospholipase activities and is involved in the hepatic metabolism of high-density lipoprotein (HDL) as well as apolipoprotein B (apoB)-containing lipoproteins (LpBs) ( 11,12 ). Overexpression of HL reduces plasma levels of HDL and LpBs, whereas HL defi ciency has the opposite effect ( 13-16 ). EL is predominantly a phospholipase affecting HDL metabolism, but it also shares a redundant role with HL in the metabolism of LpBs ( 11,17 ). Indeed, modulation of EL activity in mice leads to changes in plasma HDL levels similar to those of HL (18)(19)(20), refl ecting their related substrate specifi cities. Consistent with their multifaceted involvement in lipoprotein metabolism, LPL, HL, and EL are strongly associated with plasma lipid levels in the general population ( 21 ). Abstract Lipase maturation factor 1 (Lmf1) is an endoplasmic reticulum (ER) membrane protein involved in the posttranslational folding and/or assembly of lipoprotein lipase (LPL) and hepatic lipase (HL) into active enzymes.Mutations in Lmf1 are associated with diminished LPL and HL activities ("combined lipase defi ciency") and result in severe hypertriglyceridemia in mice as well as in human subjects. Here, we investigate whether endothelial lipase (EL) also requires Lmf1 to attain enzymatic activity. We demonstrate that cells harboring a ( cld ) loss-of-function mutation in the Lmf1 gene are unable to generate active EL, but they regain this capacity after reconstitution with the Lmf1 wild type. Furthermore, we show that cellular EL copurifi es with Lmf1, indicating their physical interaction in the ER. Finally , we determined that post-heparin phospholipase activity in a patient with the LMF1 W464X mutation is reduced by more than 95% compared with that in controls. Thus, our study indicates that EL is critically dependent on Lmf1 for its maturation in the ER and demonstrates that Lmf1 is a required factor for all three vascular lipases, LPL, HL, and EL. The vascular lipase family is composed of three evolutionarily related enzymes, lipoprotein lipase (LPL), hepatic lipase (HL), and endothelial lipase (EL) ( 1-3 ). Localized to the luminal face of tissue capillaries, lipases

Objective Lipoprotein lipase (LPL) is a principal enzyme in lipoprotein metabolism, tissue lipid utilization and energy metabolism. LPL is synthesized by parenchymal cells in adipose, heart and muscle tissues followed by secretion to extracellular sites, where lipolyic function is exerted. The catalytic activity of LPL is attained during post-translational maturation, which involves glycosylation, folding and subunit assembly within the endoplasmic reticulum (ER). A lipase-chaperone, lipase maturation factor 1 (Lmf1), has recently emerged as a critical factor in this process. Previous studies demonstrated that loss-of-function mutations of Lmf1 result in diminished lipase activity and severe hypertriglyceridemia in mice and human subjects. The objective of this study is to investigate whether, beyond its role as a required factor in lipase maturation, variation in Lmf1 expression is sufficient to modulate LPL activity in vivo. Methods and Results To assess the effects of Lmf1 overexpression in adipose and muscle tissues, we generated aP2-Lmf1 and Mck-Lmf1 transgenic mice. Characterization of relevant tissues revealed increased LPL activity in both mouse strains. In the omental and subcutaneous adipose depots, Lmf1 overexpression was associated with increased LPL specific activity without changes in LPL mass. In contrast, increased LPL activity was due to elevated LPL protein level in heart and gonadal adipose tissue. To extend these studies to humans, we detected association between LMF1 gene variants and post-heparin LPL activity in a dyslipidemic cohort. Conclusions Our results suggest that variation in Lmf1 expression is a post-translational determinant of LPL activity.