Sphingolipids elicit a wide variety of eukaryotic cellular responses, most involving regulation of cell growth, differentiation, and apoptosis. Sphingosine 1-phosphate, a sphingolipid catabolite, is mitogenic in fibroblasts and inhibits the chemotactic mobility and invasiveness of human tumor cells. Sphingosine 1-phosphate degradation requires cleavage at the C2-3 carbon bond by sphingosine phosphate lyase. A yeast genetic approach was used to clone the first sphingosine phosphate lyase gene, BST1. BST1 overexpression conferred resistance to sphingosine in yeast. BST1 deletion produced sensitivity to exogenous D-erythro-sphingosine and phytosphingosine and intracellular accumulation of sphingosine 1-phosphate upon exposure to exogenous sphingosine. This study confirms that sphingoid base metabolism is similar in all eukaryotes and suggests that yeast genetics may be useful in the isolation and identification of other genes involved in sphingolipid signaling and metabolism.

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Expression of the ompF and ompC genes coding for major outer membrane proteins is osmoregulated by solutes, such as sucrose and NaCl, in the growth medium. The OmpR protein, a positive regulator of these genes, is involved in the osmoregulation (Dairi et al. 1985; Nara et al. 1984). In the present work, five mutant ompR genes exhibiting different phenotypes of osmoregulation were cloned and sequenced. Three of them, ompR1, ompR2 and ompR20, were previously isolated mutants. The others, ompR3 and ompR4, were isolated in the present work. The ompR1 mutation resulted in the deletion of 19 amino acids near the C-terminus of the OmpR protein. The ompR3 and ompR4 mutations resulted in Arg15 to Cys and Arg71 to Thr conversions, respectively, at the N-terminal portion, whereas the ompR20 and ompR2 mutations resulted in Arg150 to Cys and Val207 to Met conversions, respectively, at the C-terminal portion. Based on these results, the structure and function of the OmpR protein are discussed in relation to the mechanism of osmoregulation.

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Scyphostatin is a specific inhibitor for mammalianneutral magnesium-dependent sphingomyelinase with a fifty percent inhibition concentration (IC50) value of 1.0 fiM. When used to inhibit lysosomal acid sphingomyelinase, an approximately 50-fold greater concentration is required. In humanperipheral monocytes, the compoundinhibits bacterial lipopolysaccharide (LPS)-induced prostaglandin E2 production and LPS-induced

Weperformed experiments to screen for neutral sphingomyelinase inhibitors using rat brain microsomes as an enzyme source. Amongmore than 10,000 microbial extracts tested, a mycelial extract of Trichopeziza mollissima SANK 13892 exhibited potent inhibitory activity. The active compound, scyphostatin, was purified by a series of chromatographies. Scyphostatin inhibited the enzyme with an IC50 value of 1.0fiM.

Very little is known about the contribution of a low affinity neurotrophin receptor, p75, to neurotransmitter release. Here we show that nerve growth factor (NGF) induced a rapid release of glutamate and an increase of Ca 2؉ in cerebellar neurons through a p75-dependent pathway. The NGF-induced release occurred even in the presence of the Trk inhibitor K252a. The release caused by NGF but not brain-derived neurotrophic factor was enhanced in neurons overexpressing p75. Further, after transfection of p75-small interfering RNA, which downregulated the endogenous p75 expression, the NGF-induced release was inhibited, suggesting that the NGFinduced glutamate release was through p75. We found that the NGF-increased Ca 2؉ was derived from the ryanodine-sensitive Ca 2؉ receptor and that the NGF-increased Ca 2؉ was essential for the NGF-induced glutamate release. Furthermore, scyphostatin, a sphingomyelinase inhibitor, blocked the NGF-dependent Ca 2؉ increase and glutamate release, suggesting that a ceramide produced by sphingomyelinase was required for the NGF-stimulated Ca 2؉ increase and glutamate release. This action of NGF only occurred in developing neurons whereas the brain-derived neurotrophic factor-mediated Ca 2؉ increase and glutamate release was observed at the mature neuronal stage. Thus, we demonstrate that NGF-mediated neurotransmitter release via the p75-dependent pathway has an important role in developing neurons.

Mas-related G-protein coupled receptor member D (MRGPRD) is a G protein-coupled receptor (GPCR) which belongs to the Mas-related GPCRs expressed in the dorsal root ganglia (DRG). In this study, we investigated two novel ligands in addition to beta-alanine: (1) beta-aminoisobutyric acid, a physiologically active substance, with which possible relation to tumors has been seen together with beta-alanine; (2) diethylstilbestrol, a synthetic estrogen hormone. In addition to the novel ligands, we found that transfection of MRGPRD leads fibroblast cells to form spheroids, which would be related to oncogenicity. To understand the MRGPRD novel character, oncogenicity, a large chemical library was screened in order to obtain MRGPRD antagonists to utilize in exploring the character. The antagonist in turn inhibited the spheroid proliferation that is dependent on MRGPRD signaling as well as MRGPRD signals activated by beta-alanine. The antagonist, a small-molecule compound we found in this study, is a potential anticancer agent.