Phosphorylation and subcellular localization of human phospholipase A1, DDHD1/PA-PLA1.

Protein phosphorylation is the most common post-translational modification of proteins and functions as a molecular switch for their regulation. This modification is reversibly regulated by protein kinases and phosphatases. In most cases, the phosphorylation of enzymes positively or negatively regulates enzyme activity.

Lysophosphatidylinositol Induced Morphological Changes and Stress Fiber Formation through the GPR55-RhoA-ROCK Pathway.

We previously reported that lysophosphatidylinositol (LPI) functions as an endogenous agonist of GPR55, a novel cannabinoid receptor. However, the physiological roles of LPI-GPR55 have not yet been elucidated in detail. In the present study, we found that LPI induced morphological changes in GPR55-expressing HEK293 cells.

-(4-Hydroxyphenyl) Retinamide Suppresses SARS-CoV-2 Spike Protein-Mediated Cell-Cell Fusion by a Dihydroceramide Δ4-Desaturase 1-Independent Mechanism.

The membrane fusion between the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and host cells is essential for the initial step of infection; therefore, the host cell membrane components, including sphingolipids, influence the viral infection. We assessed several inhibitors of the enzymes pertaining to sphingolipid metabolism, against SARS-CoV-2 spike protein (S)-mediated cell-cell fusion and viral infection. -(4-Hydroxyphenyl) retinamide (4-HPR), an inhibitor of dihydroceramide Δ4-desaturase 1 (DES1), suppressed cell-cell fusion and viral infection.

Phosphorylation of human phospholipase A1 DDHD1 at newly identified phosphosites affects its subcellular localization.

Phospholipase A1 (PLA1) hydrolyzes the fatty acids of glycerophospholipids, which are structural components of the cellular membrane. Genetic mutations in DDHD1, an intracellular PLA1, result in hereditary spastic paraplegia (HSP) in humans. However, the regulation of DDHD1 activity has not yet been elucidated in detail.

Complex formation of sphingomyelin synthase 1 with glucosylceramide synthase increases sphingomyelin and decreases glucosylceramide levels.

Sphingolipids, including sphingomyelin (SM) and glucosylceramide (GlcCer), are generated by the addition of a polar head group to ceramide (Cer). Sphingomyelin synthase 1 (SMS1) and glucosylceramide synthase (GCS) are key enzymes that catalyze the conversion of Cer to SM and GlcCer, respectively. GlcCer synthesis has been postulated to occur mainly in -Golgi, and SM synthesis is thought to occur in /-Golgi; however, SMS1 and GCS are known to partially co-localize in cisternae, especially in -Golgi.

Coenzyme-A-Independent Transacylation System; Possible Involvement of Phospholipase A2 in Transacylation.

The coenzyme A (CoA)-independent transacylation system catalyzes fatty acid transfer from phospholipids to lysophospholipids in the absence of cofactors such as CoA. It prefers to use C20 and C22 polyunsaturated fatty acids such as arachidonic acid, which are esterified in the glycerophospholipid at the -2 position. This system can also acylate alkyl ether-linked lysophospholipids, is involved in the enrichment of arachidonic acid in alkyl ether-linked glycerophospholipids, and is critical for the metabolism of eicosanoids and platelet-activating factor.

Carboxyl-terminal Tail-mediated Homodimerizations of Sphingomyelin Synthases Are Responsible for Efficient Export from the Endoplasmic Reticulum.

Sphingomyelin synthase (SMS) is the key enzyme for cross-talk between bioactive sphingolipids and glycerolipids. In mammals, SMS consists of two isoforms: SMS1 is localized in the Golgi apparatus, whereas SMS2 is localized in both the Golgi and plasma membranes. SMS2 seems to exert cellular functions through protein-protein interactions; however, the existence and functions of quaternary structures of SMS1 and SMS2 remain unclear.

Glycerophosphate/Acylglycerophosphate acyltransferases.

Acyl-CoA:glycerol-3-phosphate acyltransferase (GPAT) and acyl-CoA: 1-acyl-glycerol-3-phosphate acyltransferase (AGPAT) are involved in the de novo synthesis of triacylglycerol (TAG) and glycerophospholipids. Many enzymes belonging to the GPAT/AGPAT family have recently been identified and their physiological or pathophysiological roles have been proposed. The roles of GPAT/AGPAT in the synthesis of TAG and obesity-related diseases were revealed through the identification of causative genes of these diseases or analyses of genetically manipulated animals.

Sphingomyelin synthase 2, but not sphingomyelin synthase 1, is involved in HIV-1 envelope-mediated membrane fusion.

Membrane fusion between the viral envelope and plasma membranes of target cells has previously been correlated with HIV-1 infection. Lipids in the plasma membrane, including sphingomyelin, may be crucially involved in HIV-1 infection; however, the role of lipid-metabolic enzymes in membrane fusion remains unclear. In this study, we examined the roles of sphingomyelin synthase (SMS) in HIV-1 Env-mediated membrane fusion using a cell-cell fusion assay with HIV-1 mimetics and their target cells.

Acyltransferases and transacylases that determine the fatty acid composition of glycerolipids and the metabolism of bioactive lipid mediators in mammalian cells and model organisms.

Over one hundred different phospholipid molecular species are known to be present in mammalian cells and tissues. Fatty acid remodeling systems for phospholipids including acyl-CoA:lysophospholipid acyltransferases, CoA-dependent and CoA-independent transacylation systems, are involved in the biosynthesis of these molecular species. Acyl-CoA:lysophospholipid acyltransferase system is involved in the synthesis of phospholipid molecular species containing sn-1 saturated and sn-2 unsaturated fatty acids.

Galectin LEC-1 plays a defensive role against damage due to oxidative stress in Caenorhabditis elegans.

LEC-1 is a major galectin in Caenorhabditis elegans and contains two carbohydrate recognition domains (CRDs), N-CRD and C-CRD. To determine the role of LEC-1, we examined the phenotypes of a mutant C. elegans strain lacking lec-1.

The actions and metabolism of lysophosphatidylinositol, an endogenous agonist for GPR55.

Lysophosphatidylinositol (LPI) is a subspecies of lysophospholipid and is assumed to be not only a degradation product of phosphatidylinositol (PI), but also a bioactive lysophospholipid mediator. However, not much attention has been directed toward LPI compared to lysophosphatidic acid (LPA), since the receptor for LPI has not been identified. During screening for an agonist for the orphan G protein coupled receptor GPR55, we identified LPI, 2-arachidonoyl LPI in particular, as an agonist for GPR55.

The DC2.3 gene in Caenorhabditis elegans encodes a galectin that recognizes the galactoseβ1→4fucose disaccharide unit.

Galectins comprise a large family of β-galactoside-binding proteins in animals and fungi. We previously isolated cDNAs of 10 galectin and galectin-like genes (lec-1 to lec-6 and lec-8 to lec-11) from Caenorhabditis elegans and characterized the carbohydrate-binding properties of their recombinant proteins. In the present study, we isolated cDNA corresponding to an open reading frame of the DC2.

Galectin LEC-6 interacts with glycoprotein F57F4.4 to cooperatively regulate the growth of Caenorhabditis elegans.

To study the endogenous counterpart of LEC-6, a major galectin in Caenorhabditis elegans, the proteomic analysis of glycoproteins captured by an immobilized LEC-6 column was performed using the nano liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique. A protein recovered in a significant amount was determined to be either F57F4.3 or F57F4.

Loss of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase 3 and reduced O-glycosylation in colon carcinoma cells selected for hepatic metastasis.

O-glycosylation of mucin is initiated by the attachment of N-acetyl-D-galactosamine (GalNAc) to serine or threonine residues in mucin core polypeptides by UDPGalNAc:polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts). It is not well understood how GalNAc attachment is regulated by multiple ppGalNAc-Ts in each cell. In the present study, the expression levels of murine ppGalNAc-Ts (mGalNAc-Ts), T1, T2, T3, T4, T6, and T7 were compared between mouse colon carcinoma colon 38 cells and variant SL4 cells, selected for their metastatic potentials, by using the competitive RT-PCR method.

Deletion of lec-10, a galectin-encoding gene, increases susceptibility to oxidative stress in Caenorhabditis elegans.

Galectins are a family of beta-galactoside-binding lectins. They are involved in the regulation of a variety of biological phenomena in mammals. However, little is known about their roles in invertebrates.

Caenorhabditis elegans galectins LEC-1-LEC-11: structural features and sugar-binding properties.

Galectins form a large family of beta-galactoside-binding proteins in metazoa and fungi. This report presents a comparative study of the functions of potential galectin genes found in the genome database of Caenorhabditis elegans. We isolated full-length cDNAs of eight potential galectin genes (lec-2-5 and 8-11) from a lambdaZAP cDNA library.

Spontaneous regression of lung metastasis in the absence of tumor necrosis factor receptor p55.

In order to clarify the roles of tumor necrosis factor (TNF)-alpha in lung metastasis, we injected Renca cells intravenously into TNF receptor p55-deficient (TNF-Rp55 KO) and wild-type (WT) mice. Microscopic and macroscopic metastasis foci appeared in lungs at 7 and 14 days after the tumor injection, respectively. Moreover, metastasis foci expanded at similar rates in both WT and TNF-Rp55 KO mice until 21 days, and lungs were occupied with metastasis foci.

Potential involvement of monocyte chemoattractant protein (MCP)-1/CCL2 in IL-4-mediated tumor immunity through inducing dendritic cell migration into the draining lymph nodes.

We previously observed that IL-4 gene transduction into a mouse colon 26 adenocarcinoma cell line abrogated its tumorigenicity due to the generation of anti-tumor CTL. DEC-205- and CD11c-double positive cells were increased in the lymph nodes of mice injected with IL-4-transfected cells between 2 and 3 days after the tumor injection, compared with those injected with parental cells. Most of these double positive cells expressed CD86 antigen.

Potential interaction between CCR1 and its ligand, CCL3, induced by endogenously produced interleukin-1 in human hepatomas.

Hepatoma cell lines can produce a massive amount of chemokines in response to various stimuli including hepatitis viruses and their products. However, it remains elusive on the types of chemokine receptor(s) expressed in the hepatoma tissues and its roles in hepatoma development. To clarify these points, we examined the chemokine receptor expression in six human hepatoma cell lines.

Essential roles of tumor necrosis factor receptor p55 in liver metastasis of intrasplenic administration of colon 26 cells.

Intrasplenic administration of a colon adenocarcinoma cell line, colon 26, induced tumor necrosis factor (TNF) alpha protein expression around the central and portal veins of the liver at 3 days, and liver metastases by 24 days after the tumor injection, in 90% of wild-type (WT) mice. To explore the roles of TNF-alpha in the process, we administered colon 26 cells into tumor necrosis factor receptor p55 (TNF-Rp55) knockout (KO) mice. Less than 50% of TNF-Rp55 KO mice developed liver metastasis with significantly lower liver weights and the volumes of metastatic foci.