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Depletion of serotonin and selective inhibition of 2B receptor suppressed tumor angiogenesis by inhibiting endothelial nitric oxide synthase and extracellular signal-regulated kinase 1/2 phosphorylation.

ABSTRACT: The effects of serotonin (5-HT) on tumor growth are inconsistent. We investigated whether a decreased level of 5-HT affected tumor growth using 5-HT transporter knockout (5-HTT(-/-)) mice, which showed 5-HT depletion. When cancer cells were injected subcutaneously into both 5-HTT(-/-) and 5-HTT(+/+) mice, the tumor growth was markedly attenuated in 5-HTT(-/-) mice. Serotonin levels in the blood, forebrain, and tumors of 5-HTT(-/-) mice bearing tumors were significantly smaller than those of their 5-HTT(+/+) littermates. However, 5-HT did not increase cancer cells' proliferation in vitro. When we applied 5-HTT inhibitors to the wild mice bearing tumors, they did not inhibit tumor growth. The endothelial nitric oxide synthase (eNOS) expressions in tumors were reduced in 5-HTT(-/-) mice compared with 5-HTT(+/+) mice. Stimulations with 5-HT (1-50 microM) induced eNOS expressions in human umbilical vein endothelial cell (HUVEC) in a concentration-dependent manner. When we measured activations of multiple signaling pathways by using a high-throughput phosphospecific antibodies platform, 5-HT stimulated the extracellular signal-regulated kinase 1/2 (ERK1/2) in HUVEC. Moreover, we found that the physiological level of 5-HT induced phosphorylation of both ERK1/2 and eNOS in HUVEC. Human umbilical vein endothelial cell expressed both 5-HT(2B) and 5-HT(2C) receptors. SB204741, a specific 5-HT(2B) receptor inhibitor, blocked 5-HT-induced ERK1/2 and eNOS phosphorylations, whereas RS102221, a specific 5-HT(2C) receptor inhibitor, did not in HUVEC. SB204741 reduced microvessel density in tumors and inhibited the proliferation of HUVEC in vitro. These results suggest that regulation of 5-HT and 5-HT receptors, especially the 5-HT(2B) receptor, may serve as a therapeutic strategy in cancer therapy.

SUBMITTER: Asada M

PROVIDER: S-EPMC2657884 | biostudies-other | 2009 Apr

REPOSITORIES: biostudies-other

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Depletion of serotonin and selective inhibition of 2B receptor suppressed tumor angiogenesis by inhibiting endothelial nitric oxide synthase and extracellular signal-regulated kinase 1/2 phosphorylation.

Asada Masanori M Ebihara Satoru S Yamanda Shinsuke S Niu Kaijun K Okazaki Tatsuma T Sora Ichiro I Arai Hiroyuki H

Neoplasia (New York, N.Y.) 20090401 4

The effects of serotonin (5-HT) on tumor growth are inconsistent. We investigated whether a decreased level of 5-HT affected tumor growth using 5-HT transporter knockout (5-HTT(-/-)) mice, which showed 5-HT depletion. When cancer cells were injected subcutaneously into both 5-HTT(-/-) and 5-HTT(+/+) mice, the tumor growth was markedly attenuated in 5-HTT(-/-) mice. Serotonin levels in the blood, forebrain, and tumors of 5-HTT(-/-) mice bearing tumors were significantly smaller than those of thei ...[more]

PMID: 19308295

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Project description:Serotonin is a neurotransmitter involved in many psychiatric diseases. In humans, a lack of 5-HT2B receptors is associated with serotonin-dependent phenotypes, including impulsivity and suicidality. A lack of 5-HT2B receptors in mice eliminates the effects of molecules that directly target serotonergic neurons including amphetamine derivative serotonin releasers, and selective serotonin reuptake inhibitor antidepressants. In this work, we tested the hypothesis that 5-HT2B receptors directly and positively regulate raphe serotonin neuron activity. By ex vivo electrophysiological recordings, we report that stimulation by the 5-HT2B receptor agonist, BW723C86, increased the firing frequency of serotonin Pet1-positive neurons. Viral overexpression of 5-HT2B receptors in these neurons increased their excitability. Furthermore, in vivo 5-HT2B-receptor stimulation by BW723C86 counteracted 5-HT1A autoreceptor-dependent reduction in firing rate and hypothermic response in wild-type mice. By a conditional genetic ablation that eliminates 5-HT2B receptor expression specifically and exclusively from Pet1-positive serotonin neurons (Htr2b 5-HTKO mice), we demonstrated that behavioral and sensitizing effects of MDMA (3,4-methylenedioxy-methamphetamine), as well as acute behavioral and chronic neurogenic effects of the antidepressant fluoxetine, require 5-HT2B receptor expression in serotonergic neurons. In Htr2b 5-HTKO mice, dorsal raphe serotonin neurons displayed a lower firing frequency compared to control Htr2b lox/lox mice as assessed by in vivo extracellular recordings and a stronger hypothermic effect of 5-HT1A-autoreceptor stimulation was observed. The increase in head-twitch response to DOI (2,5-dimethoxy-4-iodoamphetamine) further confirmed the lower serotonergic tone resulting from the absence of 5-HT2B receptors in serotonin neurons. Together, these observations indicate that the 5-HT2B receptor acts as a direct positive modulator of serotonin Pet1-positive neurons in an opposite way as the known 5-HT1A-negative autoreceptor.

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Depletion of serotonin and selective inhibition of 2B receptor suppressed tumor angiogenesis by inhibiting endothelial nitric oxide synthase and extracellular signal-regulated kinase 1/2 phosphorylation.

Publications

Depletion of serotonin and selective inhibition of 2B receptor suppressed tumor angiogenesis by inhibiting endothelial nitric oxide synthase and extracellular signal-regulated kinase 1/2 phosphorylation.

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