Sphingosine 1-phosphate protects primary human keratinocytes from apoptosis via nitric oxide formation through the receptor subtype S1P3.

Although the lipid mediator sphingosine 1-phosphate (S1P) has been identified to induce cell growth arrest of human keratinocytes, the sphingolipid effectively protects these epidermal cells from apoptosis. The molecular mechanism of the anti-apoptotic action induced by S1P is less characterized. Apart from S1P, endogenously produced nitric oxide (NO•) has been recognized as a potent modulator of apoptosis in keratinocytes. Therefore, it was of great interest to elucidate whether S1P protects human keratinocytes via a NO•-dependent signalling pathway. Indeed, S1P induced an activation of endothelial nitric oxide synthase (eNOS) in human keratinocytes leading to an enhanced formation of NO•. Most interestingly, the cell protective effect of S1P was almost completely abolished in the presence of the eNOS inhibitor L-NAME as well as in eNOS-deficient keratinocytes indicating that the sphingolipid metabolite S1P protects human keratinocytes from apoptosis via eNOS activation and subsequent production of protective amounts of NO•. It is well established that most of the known actions of S1P are mediated by a family of five specific G protein-coupled receptors. Therefore, the involvement of S1P-receptor subtypes in S1P-mediated eNOS activation has been examined. Indeed, this study clearly shows that the S1P(3) is the exclusive receptor subtype in human keratinocytes which mediates eNOS activation and NO• formation in response to S1P. In congruence, when the S1P(3) receptor subtype is abrogated, S1P almost completely lost its ability to protect human keratinocytes from apoptosis.

Phosphorylation of the immunomodulator FTY720 inhibits programmed cell death of fibroblasts via the S1P3 receptor subtype and Bcl-2 activation.

BACKGROUND: FTY720, a synthetic compound produced by modification of a metabolite from Isaria sinclairii, is known as a unique immunosuppressive agent that exerts its activity by inhibiting lymphocyte egress from secondary lymphoid tissues. FTY720 is phosphorylated in vivo by sphingosine kinase 2 to FTY720-phosphate (FTY720-P), which acts as a potent sphingosine-1-phosphate (S1P) receptor agonist. Despite its homology to S1P, which exerts antiapoptotic actions in different cells, FTY720 has also been reported to be able to induce apoptosis in a variety of cells. METHODS: Therefore, we investigated the action of both, FTY720 and its phosphorylated version FTY720-P, on apoptosis. Moreover, signalling pathways of apoptosis in response to FTY720 and FTY720-P were examined. RESULTS AND CONCLUSIONS: Although FTY720 acts apoptotic at micromolar concentrations in human fibroblasts the phosphorylated compound FTY720-P possesses a pronounced antiapoptotic effect counteracting FTY720-induced programmed cell death. Interestingly, none of the classical antiapoptotic pathways like MAP kinases, Akt or mTOR play a role in the protective role of FTY720-P. Most important, we identified that the S1P(3) receptor subtype is involved in the antiapoptotic action of FTY720-P leading to an increased phosphorylation of Bcl-2 and changes in the mitochondrial membrane potential.

Functional characterisation of hemokinin-1 in mouse uterus.

The preprotachykinin gene Tac4 expressed in murine uterus and placenta is thought to encode a peptide RSRTRQFYGLM-NH(2), mouse hemokinin 1. We have examined the uterotonic effects of mouse hemokinin 1 and its N-terminally truncated analogue, mouse hemokinin 1(2-11) on mouse uterus. Mouse hemokinin 1(2-11) was equieffective with but slightly less potent than substance P in tissues from non-pregnant Swiss mice. On myometrium from Balb C mice primed with oestrogen the positions of concentration-response curves to substance P and the mouse hemokinins were similar to those of neurokinin A, but the maximum responses were lower. The tachykinin NK(1) receptor antagonist, 1-{2-(3, 4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl) piperidin-3-yl]ethyl}-4phenyl-1-azonia-bicyclo[2.2.2]octane (SR 140333), reduced the effects of the agonists in tissues from both groups of mice. In myometria from late pregnant (Days 17-18) Balb C mice the responses to mouse hemokinin 1(2-11) were less potent than in those from oestrogen-primed mice. Human hemokinin 1, the human orthologue of mouse hemokinin 1, was more effective than mouse hemokinin 1(2-11), while endokinin D was inactive. Mouse hemokinin 1 effects were blocked by SR 140333 alone and in combination with ((S)-N-methyl-N[4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl]benzamide (SR 48968) but not by SR 48968 alone. Thus the mouse hemokinins are tachykinin NK(1) receptor-preferring uterotonic agonists in non-pregnant mice but lack action at the myometrial tachykinin NK(2) receptors present in late pregnant mice.

17-Beta-estradiol inhibits transforming growth factor-beta signaling and function in breast cancer cells via activation of extracellular signal-regulated kinase through the G protein-coupled receptor 30.

Breast cancer development and breast cancer progression involves the deregulation of growth factors leading to uncontrolled cellular proliferation, invasion and metastasis. Transforming growth factor (TGF)-beta plays a crucial role in breast cancer because it has the potential to act as either a tumor suppressor or a pro-oncogenic chemokine. A cross-communication between the TGF-beta signaling network and estrogens has been postulated, which is important for breast tumorigenesis. Here, we provide evidence that inhibition of TGF-beta signaling is associated with a rapid estrogen-dependent nongenomic action. Moreover, we were able to demonstrate that estrogens disrupt the TGF-beta signaling network as well as TGF-beta functions in breast cancer cells via the G protein-coupled receptor 30 (GPR30). Silencing of GPR30 in MCF-7 cells completely reduced the ability of 17-beta-estradiol (E2) to inhibit the TGF-beta pathway. Likewise, in GPR30-deficient MDA-MB-231 breast cancer cells, E2 achieved the ability to suppress TGF-beta signaling only after transfection with GPR30-encoding plasmids. It is most interesting that the antiestrogen fulvestrant (ICI 182,780), which possesses agonistic activity at the GPR30, also diminished TGF-beta signaling. Further experiments attempted to characterize the molecular mechanism by which activated GPR30 inhibits the TGF-beta pathway. Our results indicate that GPR30 induces the stimulation of the mitogen-activated protein kinases (MAPKs), which interferes with the activation of Smad proteins. Inhibition of MAPK activity prevented the ability of E2 from suppressing TGF-beta signaling. These findings are of great clinical relevance, because down-regulation of TGF-beta signaling is associated with the development of breast cancer resistance in response to antiestrogens.