endothelin-1 and sphingosine-kinase

Preterm birth (PTB), defined as birth before 37 completed weeks of gestation, occurs in up to 18 percent of births worldwide and accounts for the majority of perinatal morbidity and mortality. While the single most common cause of PTB has been identified as inflammation, safe and effective pharmacotherapy to prevent PTB has yet to be developed.. Our group has used an in vivo model of inflammation-driven PTB, biochemical methods, pharmacological approaches, a novel endothelin receptor antagonist that we synthesized and RNA knockdown to help establish the role of endothelin-1 (ET-1) in inflammation-associated PTB. Further, we have used our in vivo model to test whether sphingosine kinase, which acts downstream of ET-1, plays a role in PTB.. We have shown that levels of endothelin converting enzyme-1 (ECE-1) and ET-1 are increased when PTB is induced in timed pregnant mice with lipopolysaccharide (LPS) and that blocking ET-1 action, pharmacologically or using ECE-1 RNA silencing, rescues LPS-induced mice from PTB. ET-1 activates the sphingosine kinase/sphingosine-1-phosphate (SphK/S1P) pathway. S1P, in turn, is an important signaling molecule in the proinflammatory response. Interestingly, we have shown that SphK inhibition also prevents LPS-induced PTB in timed pregnant mice. Further, we showed that SphK inhibition suppresses the ECE-1/ET-1 axis, implicating positive feedback regulation of the SphK/S1P/ECE-1/ET-1 axis.. The ET-1/SphK/SIP pathway is a potential pharmacotherapeutic target for the prevention of PTB.

Topics: Animals; Endothelin-1; Female; Humans; Inflammation; Lipopolysaccharides; Lysophospholipids; Mice; Phosphotransferases (Alcohol Group Acceptor); Pregnancy; Premature Birth; Sphingosine

Ceramide is important for water retention and permeability barrier functions in the stratum corneum, and plays a key role in the pathogenesis of atopic dermatitis (AD). A Pseudomonas aeruginosa-derived neutral ceramidase (PaCDase) isolated from a patient with AD was shown to effectively degrade ceramide in the presence of Staphylococcus aureus-derived lipids or neutral detergents. However, the effect of ceramide metabolites on the functions of differentiating keratinocytes is poorly understood. We found that the ceramide metabolite sphingosine-1-phosphate (S1P) stimulated the production of inflammatory mediators such as TNF-α and IL-8 from three-dimensionally cultured human primary keratinocytes (termed "3D keratinocytes"), which form a stratum corneum. PaCDase alone did not affect TNF-α gene expression in 3D keratinocytes. In the presence of the detergent Triton X-100, which damages stratum corneum structure, PaCDase, but not heat-inactivated PaCDase or PaCDase-inactive mutant, induced the production of TNF-α, endothelin-1, and IL-8, indicating that this production was dependent on ceramidase activity. Among various ceramide metabolites, sphingosine and S1P enhanced the gene expression of TNF-α, endothelin-1, and IL-8. The PaCDase-enhanced expression of these genes was inhibited by a sphingosine kinase inhibitor and by an S1P receptor antagonist VPC 23019. The TNF-α-binding antibody infliximab suppressed the PaCDase-induced upregulation of IL-8, but not TNF-α, mRNA. PaCDase induced NF-κB p65 phosphorylation. The NF-κB inhibitor curcumin significantly inhibited PaCDase-induced expression of IL-8 and endothelin-1. VPC 23019 and infliximab inhibited PaCDase-induced NF-κB p65 phosphorylation and reduction in the protein level of the NF-κB inhibitor IκBα. Collectively, these findings suggest that (i) 3D keratinocytes produce S1P from sphingosine, which is produced through the hydrolysis of ceramide by PaCDase, (ii) S1P induces the production of TNF-α via S1P receptors, and (iii) released TNF-α stimulates the production of inflammatory mediators such as IL-8.

Topics: Cells, Cultured; Endothelin-1; Humans; I-kappa B Proteins; Inflammation Mediators; Interleukin-8; Keratinocytes; Lysophospholipids; Neutral Ceramidase; NF-KappaB Inhibitor alpha; Phosphotransferases (Alcohol Group Acceptor); Pseudomonas; Receptors, Lysosphingolipid; Sphingosine; Transcription Factor RelA; Tumor Necrosis Factor-alpha

Sphingosine 1-phosphate (S1P), a bioactive sphingolipid involved in diverse biological processes, is generated by sphingosine kinase (SphK) and acts via intracellular and/or extracellular mechanisms. We used biochemical, pharmacological, and physiological approaches to investigate in rat myometrium the contractile effect of exogenous S1P and the possible contribution of SphK in endothelin-1 (ET-1)-mediated contraction. S1P stimulated uterine contractility (EC(50) = 1 microM and maximal response = 5 microM) by a pertussis toxin-insensitive and a phospholipse C (PLC)-independent pathway. Phosphorylated FTY720, which interacts with all S1P receptors, except S1P(2) receptors, failed to mimic S1P contractile response, indicating that the effects of S1P involved S1P(2) receptors that are expressed in myometrium. Contraction mediated by S1P and ET-1 required extracellular calcium and Rho kinase activation. Inhibition of SphK reduced ET-1-mediated contraction. ET-1, via ET(A) receptors coupled to pertussis toxin-insensitive G proteins, stimulated SphK1 activity and induced its translocation to the membranes. Myometrial contraction triggered by ET-1 is consecutive to the sequential activation of PLC, protein kinase C, SphK1 and Rho kinase. Prolonged exposure of the myometrium to S1P downregulated S1P(2) receptors and abolished the contraction induced by exogenous S1P. However, in these conditions, the tension triggered by ET-1 was not reduced, indicating that SphK activated by ET-1 contributed to its contractile effect via a S1P(2) receptor-independent process. Our findings demonstrated that exogenous S1P and SphK activity regulated myometrial contraction and may be of physiological relevance in the regulation of uterine motility during gestation and parturition.

Topics: Animals; Biological Transport; Calcium; Cytosol; Endothelin-1; Enzyme Activation; Extracellular Fluid; Female; GTP-Binding Proteins; Intracellular Signaling Peptides and Proteins; Lysophospholipids; Myometrium; Pertussis Toxin; Phosphotransferases (Alcohol Group Acceptor); Protein Kinase C; Protein Serine-Threonine Kinases; Rats; Rats, Wistar; Receptors, Cell Surface; Receptors, Lysosphingolipid; rho GTP-Binding Proteins; rho-Associated Kinases; Sphingosine; Type C Phospholipases; Uterine Contraction

Sphingosine kinase-1 (SK1) is a key enzyme catalyzing the phosphorylation of sphingosine to sphingosine-1-phosphate (S1P). Recent studies suggest that SK1, and its product S1P, regulate diverse biological functions, including cell growth, differentiation, proliferation, and apoptosis. S1P may also play an important role in cardiac development and ischemic preconditioning, but the mechanism underlying these effects is not known. Using a yeast 2-hybrid screen with SK1 as bait and a cardiac cDNA library to identify novel proteins involved in regulating SK1 activity in cardiomyocytes, we identified the LIM-only factor FHL2 (SLIM3) as a SK1-interacting protein in both yeast and mammalian cells. FHL2, but not FHL1 or FHL3, interacted with SK1, and FHL2 colocalized with SK1 in the cytoplasm. The interaction sites with SK1 consisted of at least 4 LIM domains in FHL2, whereas the C-terminal portion of SK1 mediates the binding of FHL2 in SK1. Overexpression of FHL2 attenuated the activity and antiapoptotic effects of SK1. Indeed, endothelin-1, which is a potent survival factor in cardiomyocytes, inhibited FHL2-SK1 association and increased SK1 activity. These findings indicate that FHL2 is a novel inhibitor of SK1 activity in cardiomyocytes and suggest that targeting FHL2 for inhibition may prevent myocardial apoptosis through activation of SK1.

Topics: Animals; Apoptosis; Cell Line; Cell Survival; Endothelin-1; Homeodomain Proteins; Humans; LIM-Homeodomain Proteins; Male; Mice; Mice, Inbred C57BL; Muscle Proteins; Myocytes, Cardiac; Phosphotransferases (Alcohol Group Acceptor); Protein Structure, Tertiary; Rats; Rats, Sprague-Dawley; RNA, Small Interfering; Tissue Distribution; Transcription Factors

Uterine leiomyomas, or fibroids, are the most common tumors of the myometrium. The ELT3 cell line, derived from Eker rat leiomyoma, has been successfully used as a model for the study of leiomyomas. We have demonstrated previously the potent mitogenic properties of the peptidic hormone endothelin (ET)-1 in this cell line. Here we investigated the antiapoptotic effect of ET-1 in ELT3 cells. We found that 1) serum starvation of ELT3 cells induced an apoptotic process characterized by cytochrome c release from mitochondria, caspase-3/7 activation, nuclei condensation and DNA fragmentation; 2) ET-1 prevented the apoptotic process; and 3) this effect of ET-1 was fully reproduced by ETB agonists. In contrast, no antiapoptotic effect of ET-1 was observed in normal myometrial cells. A pharmacological approach showed that the effect of ET-1 on caspase-3/7 activation in ELT3 cells was not dependent on phosphatidylinositol 3-kinase, ERK1/2, or phospholipase D activities. However, inhibitors of sphingosine kinase-1 (SphK1), dimethylsphingosine and threo-dihydrosphingosine, reduced the effect of ET-1 by about 50%. Identical results were obtained when SphK1 expression was down-regulated in ELT3 cells transfected with SphK1 small interfering RNA. Furthermore, serum starvation induced a decrease in SphK1 activity that was prevented by ET-1 without affecting the level of SphK1 protein expression. Finally, sphingosine 1-phosphate, the product of SphK activity, was as efficient as ET-1 in inhibiting serum starvation-induced caspase-3/7 activation. Together, these results demonstrate that ET-1 possesses a potent antiapoptotic effect in ELT3 cells that involves sphingolipid metabolism through the activation of SphK1.

Topics: Animals; Apoptosis; Culture Media, Serum-Free; Cytoprotection; Endothelin-1; Female; Leiomyoma; Myometrium; Phosphotransferases (Alcohol Group Acceptor); Rats; Tumor Cells, Cultured; Uterine Neoplasms

Topics: Cell Division; Cyclooxygenase Inhibitors; Endothelin-1; Enzyme Activation; Humans; Liver; Lysophospholipids; Phosphotransferases (Alcohol Group Acceptor); Sphingosine