The KDR polymorphisms may serve as novel genetic markers for the risk of coronary heart disease.

Neuronal activity greatly influences the formation and stabilization of synapses. Although receptors for sphingosine-1-phosphate (S1P), a lipid mediator regulating diverse cellular processes, are abundant in the central nervous system, neuron-specific functions of S1P remain largely undefined. Here, we report two novel actions of S1P using primary hippocampal neurons as a model system: (i) as a secretagogue where S1P triggers glutamate secretion and (ii) as an enhancer where S1P potentiates depolarization-evoked glutamate secretion. Sphingosine kinase 1 (SK1), a key enzyme for S1P production, was enriched in functional puncta of hippocampal neurons. Silencing SK1 expression by small interfering RNA as well as SK1 inhibition by dimethylsphingosine resulted in a strong inhibition of depolarization-evoked glutamate secretion. Fluorescence recovery after photobleaching analysis showed translocation of SK1 from cytosol to membranes at the puncta during depolarization, which resulted in subsequent accumulation of S1P within cells. Fluorescent resonance energy transfer analysis demonstrated that the S1P 1 receptor at the puncta was activated during depolarization and that depolarization-induced S1P 1 receptor activation was inhibited in SK1-knock-down cells. Importantly, exogenously added S1P at a nanomolar concentration by itself elicited glutamate secretion from hippocampal cells even when the Na ؉ -channel was blocked by tetrodotoxin, suggesting that S1P acts on presynaptic membranes. Furthermore, exogenous S1P at a picomolar level potentiated depolarization-evoked secretion in the neurons. These findings indicate that S1P, through its autocrine action, facilitates glutamate secretion in hippocampal neurons both by secretagogue and enhancer actions and may be involved in mechanisms underlying regulation of synaptic transmission.One of the remarkable features of the central nervous system (CNS) is its ability to integrate and store enormous information. Neuronal information is rapidly transferred through the chemical synapse to specialized regions of the postsynaptic plasma membrane, where neurotransmitter receptors are concentrated. Neurotransmitter secretion in the CNS shares many features with constitutive membrane trafficking (4, 19); however, it also exhibits several unique features, including storage of enormous amounts of information and plasticity, that indicate the presence of additional regulators. There is considerable interest in identifying such regulators that modulate the speed and potency of neurotransmitter release. Among various regulators sphingolipid metabolites such as sphingosine-1-phosphate (S1P) have recently attracted attention for their role in the regulation of neuronal function (9). S1P, a phosphorylated product of sphingosine catalyzed by sphingosine kinase (SK), has been implicated as an important lipid mediator acting both inside and outside the cells (26,33). Extracellular S1P binds to members of GTP-binding protein (G-protein)-coupled S1P receptor family (S1P 1-5 ), triggering diverse...

Sphingosine kinase (SPHK) is a key enzyme producing important messenger sphingosine 1-phosphate and is implicated in cell proliferation and suppression of apoptosis. Because the extent of agonist-induced activation of SPHK is modest, signaling via SPHK may be regulated through its localization at specific intracellular sites. Although the SPHK1 isoform has been extensively studied and characterized, the regulation of expression and function of the other isoform, SPHK2, remain largely unexplored. Here we describe an important post-translational modification, namely, phosphorylation of SPHK2 catalyzed by protein kinase D (PKD), which regulates its localization. Upon stimulation of HeLa cells by tumor promoter phorbol 12-myristate 13-acetate, a serine residue in a novel and putative nuclear export signal, identified for the first time, in SPHK2 was phosphorylated followed by SPHK2 export from the nucleus. Constitutively active PKD phosphorylated this serine residue in the nuclear export signal both in vivo and in vitro. Moreover, downregulation of PKDs through RNA interference resulted in the attenuation of both basal and phorbol 12-myristate 13-acetateinduced phosphorylation, which was followed by the accumulation of SPHK2 in the nucleus in a manner rescued by PKD overexpression. These results indicate that PKD is a physiologically relevant enzyme for SPHK2 phosphorylation, which leads to its nuclear export for subsequent cellular signaling. Sphingosine kinases (SPHKs)3 catalyze the formation of sphingosine 1-phosphate, a bioactive lipid that regulates a diverse range of cellular processes, including cell growth, survival, differentiation, motility, and cytoskeletal organization (1, 2). Some of these cellular processes are mediated by five sphingosine 1-phosphatespecific G protein-coupled receptors, whereas others appear to be controlled by intracellular sphingosine 1-phosphate through as yet unidentified intracellular targets (2, 3).Two distinct SPHK isoforms, SPHK1 and SPHK2, have been cloned and characterized (4, 5). Diverse external stimuli, particularly growth and survival factors, stimulate SPHK1, and intracellularly generated sphingosine 1-phosphate has been implicated in their mitogenic and anti-apoptotic effects (6 -15). Expression of SPHK1 enhanced proliferation, promoted the G 1 /S transition, protected cells from apoptosis (6,8,16), and induced tumor formation in mice (8, 9).In contrast to SPHK1 much less is known about SPHK2. Although highly similar in amino acid sequence and possessing five evolutionarily conserved domains found in all SPHKs (17), SPHK2 diverges in its N terminus and central regions. These two isoforms have different kinetic properties and differ in developmental and tissue expression (5) implying that they may have distinct physiological functions. In fact, studies from our laboratory have demonstrated that, in contrast to cytosolic distribution of SPHK1, SPHK2 enters nuclei and inhibits DNA synthesis or induces apoptosis under stressful conditions such as serum deprivation (18,19)....

Background: The role of the unspliced XBP1 remains unclear.Results: Disturbed flow concomitantly up-regulates XBP1u and HDAC3, which form a complex with Akt1 and mTOR, leading to Nrf2-mediated HO-1 expression.Conclusion: XBP1u and HDAC3 synergistically exert a protective effect on disturbed flow-induced oxidative stress via regulation of HO-1 expression.Significance: This study provides new insights into the physiological roles of XBP1u and HDAC3.