• BMB Reports
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• v.40 no.6
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• pp.899-910
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• 2007

Extracellular Regulated Kinases (ERK) and Protein Kinase B (Akt) are intermediaries in relaying extracellular growth signals to intracellular targets. Each pathway can become activated upon stimulation of G protein-coupled receptors mediated by $G_q$ and $G_{i/o}$ proteins subjected to regulation by RGS proteins. The goal of the study was to delineate the specificity in which cardiac RGS proteins modulate $G_{q^-}$ and $G_{i/o}$-induced ERK and Akt phosphorylation. To isolate $G_{q^-}$ and $G_{i/o}$-mediated effects, we exclusively expressed muscarinic $M_2$ or $M_3$ receptors in COS-7 cells. Western blot analyses demonstrated increase of phosphorylation of ERK 1.7-/3.3-fold and Akt 2.4-/6-fold in $M_{2^-}/M_{3^-}$ expressing cells through carbachol stimulation. In co-expressions, $M_3/G_q$-induced activation of Akt was exclusively blunted through RGS3s/RGS3, whereas activation of ERK was inhibited additionally through RGS2/RGS5. $M_2/G_{i/o}$ induced Akt activation was inhibited by all RGS proteins tested. RGS2 had no effect on $M_2/G_{i/o}$-induced ERK activation. The high degree of specificity in RGS proteins-depending modulation of $G_{q^-}$ and $G_{i/o}$-mediated ERK and Akt activation in the muscarinic network cannot merely be attributed exclusively to RGS protein selectivity towards $G_q$ or $G_{i/o}$ proteins. Counter-regulatory mechanisms and inter-signaling cross-talk may alter the sensitivity of GPCR-induced ERK and Akt activation to RGS protein regulation.

• Molecules and Cells
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• v.38 no.6
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• pp.535-539
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• 2015

Olfactory stimulation activates multiple signaling cascades in order to mediate activity-driven changes in gene expression that promote neuronal survival. To date, the mechanisms involved in activity-dependent olfactory neuronal survival have yet to be fully elucidated. In the current study, we observed that olfactory sensory stimulation, which caused neuronal activation, promoted activation of the phosphatidylinositol 3'-kinase (PI3K)/Akt pathway and the expression of Bcl-2, which were responsible for olfactory receptor neuron (ORN) survival. We demonstrated that Bcl-2 expression increased after odorant stimulation both in vivo and in vitro. We also showed that odorant stimulation activated Akt, and that Akt activation was completely blocked by incubation with both a PI3K inhibitor (LY294002) and Akt1 small interfering RNA. Moreover, blocking the PI3K/Akt pathway diminished the odorantinduced Bcl-2 expression, as well as the effects on odorant-induced ORN survival. A temporal difference was noted between the activation of Akt1 and the expression of Bcl-2 following odorant stimulation. Blocking the PI3K/Akt pathway did not affect ORN survival in the time range prior to the increase in Bcl-2 expression, implying that these two events, activation of the PI3K pathway and Bcl-2 induction, were tightly connected to promote post-translational ORN survival. Collectively, our results indicated that olfactory activity activated PI3K/Akt, induced Bcl-2, and promoted long term ORN survival as a result.

• The Korean Journal of Physiology and Pharmacology
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• v.12 no.2
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• pp.37-41
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• 2008

Melatonin has been reported to protect neurons from a variety of neurotoxicity. However, the underlying mechanism by which melatonin exerts its neuroprotective property has not yet been clearly understood. We previously demonstrated that melatonin protected kainic acid-induced neuronal cell death in mouse hippocampus, accompanied by sustained activation of Akt, a critical mediator of neuronal survival. To further elucidate the neuroprotective action of melatonin, we examined in the present study the causal mechanism how Akt signaling pathway is regulated by melatonin in a rat primary astrocyte culture model. Melatonin resulted in increased astrocytic Akt phosphorylation, which was significantly decreased with wortmannin, a specific inhibitor of PI3K, suggesting that activation of Akt by melatonin is mediated through the PI3K-Akt signaling pathway. Furthermore, increased Akt activation was also significantly decreased with luzindole, a non-selective melatonin receptor antagonist. As downstream signaling pathway of Akt activation, increased levels of CREB phoshorylation and GDNF expression were observed, which were also attenuated with wortmannin and luzindole. These results strongly suggest that melatonin exerts its neuroprotective property in astrocytes through the activation of plasma membrane receptors and then PI3K-Akt signaling pathway.

• Journal of Physiology & Pathology in Korean Medicine
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• v.23 no.2
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• pp.416-425
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• 2009

Angiogenesis is important for promoting cardiovascular disease, wound healing, and tissue regeneration. We here investigated the pharmacological effects of Korea red ginseng water extract (KRGE) on angiogenesis and its underlying signal mechanism. This study showed that KRGE increased in vitro proliferation, migration, and tube formation of human umbilical endothelial cells, as well as stimulated in vivo angiogenesis. KRGE-induced angiogenesis was accompanied by phosphorylation of ERK1/2, Akt, and endothelial nitric oxide synthase (eNOS) as well as an increase in NO production. Inhibition of PI3K activity by wortmannin completely inhibited KRGE-induced angiogenesis and phosphorylation of Akt, ERK1/2, and eNOS, indicating that PI3K/Akt activation is an upstream event of KRGE-mediated angiogenic pathway. The MEK inhibitor PD98059 completely blocked KRGE-induced angiogenesis and ERK phosphorylation without affecting Akt and eNOS activation. However, the eNOS inhibitor NMA effectively inhibited tube formation, but partially blocked proliferation and migration as well as ERK phosphorylation without altering Akt and eNOS activation, revealing that eNOS/NO pathway is in part involved in ERK1/2 activation. This study first demonstrated the critical involvement of both ERK1/2 and eNOS activation in KRGE-induced angiogenesis, which lie on downstream of PI3K/Akt. Thus, these results indicate that KRGE requires activation of both the PI3K/Akt-dependent ERK1/2 and eNOS signal pathways and their cross-talk for its full angiogenic activity.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.3
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• pp.123-129
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• 2006

In several experimental models, estrogens protect neurons against ischemic insults. However, the recent clinical studies of hormone replacement showed negative results to prevent stroke. Therefore, optimal models to study estrogen replacement for neuroprotection are needed before its clinical ap-plication. Organotypic hippocampal slice under oxygen-glucose deprivation (OGD) has been established as a model of cerebral ischemia and has advantages to study drug effects. We investigated whether estrogen protected CAI neurons and affected activation of Akt (pAkt) in CAI region under OGD. Thus, rat hippocampal slices on day 7 of culture were treated with $17-{\beta}$ estradiol (E, 1 nM) for 7 days before 30 min OGD, and cell death of CAI neurons was quantified by propidium iodide (PI) staining and expression of pAkt was studied by Western blot and immunofluorescence. PI intensity in slices treated with E was significantly reduced 72 hour after OGD compared to that of non-treated slices (p < 0.05). E pretreatment also increased the expression of pAkt 72 hour after OGD compared to that of no treatment (p<0.01). These data suggest that estrogen pretreatment may rescue neurons from ischemic insults through the activation of Akt and also indicate that our model would be a useful alternative method to study the mechanisms and effects of estrogen replacement treatment for neuroprotection.

• The Korean Journal of Physiology and Pharmacology
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• v.27 no.5
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• pp.493-511
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• 2023

Hippo/YAP signaling hinders cancer progression. Inactivation of this pathway contributes to the development of esophageal cancer by activation of Akt. However, the possible interaction between Akt and Hippo/YAP pathways in esophageal cancer progression is unclear. In this study, we found that ursolic acid (UA) plus 3'3-diindolylmethane (DIM) efficiently suppressed the oncogenic Akt/Gsk-3β signaling pathway while activating the Hippo tumor suppressor pathway in esophageal cancer cells. Moreover, the addition of the Akt inhibitor LY294002 and the PI3K inhibitor 3-methyladenine enhanced the inhibitory effects of UA plus DIM on Akt pathway activation and further stimulated the Hippo pathway, including the suppression of YAP nuclear translocation in esophageal cancer cells. Silencing YAP under UA plus DIM conditions significantly increased the activation of the tumor suppressor PTEN in esophageal cancer cells, while decreasing p-Akt activation, indicating that the Akt signaling pathway could be down-regulated in esophageal cancer cells by targeting PTEN. Furthermore, in a xenograft nude mice model, UA plus DIM treatment effectively diminished esophageal tumors by inactivating the Akt pathway and stimulating the Hippo signaling pathway. Thus, our study highlights a feedback loop between the PI3K/Akt and Hippo signaling pathways in esophageal cancer cells, implying that a low dose of UA plus DIM could serve as a promising chemotherapeutic combination strategy in the treatment of esophageal cancer.

• Tuberculosis and Respiratory Diseases
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• v.54 no.5
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• pp.551-562
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• 2003

Background : NF-${\kappa}B$ is a characteristic transcriptional factor which has been shown to regulate production of acute inflammatory mediators and to be involved in the pathogenesis of many inflammatory lung diseases. There has been some evidence that PI3K/Akt pathway could activate NF-${\kappa}B$ in human cell lines. However, the effect of PI3K/Akt pathway on the activation of NF-${\kappa}B$ varied depending on the cell lines used in the experiments. In this study we evaluated the effect of PI3K/Akt pathway on the activation of NF-${\kappa}B$ in human respiratory epithelial cell lines. Methods : BEAS-2B, A549 and NCI-H157 cell lines were used in this experiment. To evaluate the activation of Akt activation and I${\kappa}B$ degradation, cells were analysed by western blot assay using phospho-specific Akt Ab and $I{\kappa}B$ Ab. To block PI3K/Akt pathway, cells were pretreated with wortmannin or LY294002 and transfected with dominant negative Akt (DN-Akt). For IKK activity, immune complex kinase assay was performed. To evaluate the DNA binding affinity and transcriptional activity of NF-${\kappa}B$, electrophoretic mobility shift assay (EMSA) and luciferase assay were performed, respectively. Results : In BEAS-2B, A549 and NCI-H157 cell lines, Akt was activated by TNF-$\alpha$ and insulin. Activation of Akt by insulin did not induce $I{\kappa}B{\alpha}$ degradation. Blocking of PI3K/Akt pathway via wortmannin/LY294002 or DN-Akt did not inhibit TNF-$\alpha$-induced $I{\kappa}B{\alpha}$ degradation or IKK activation. Inhibition of PI3K/Akt did not affect TNF-$\alpha$-induced NF-${\kappa}B$ activation. Overexpression of DN-Akt did not block TNF-$\alpha$-induced transcriptional activation of NF-${\kappa}B$, but wortmannin enhanced TNF-$\alpha$-induced in NF-${\kappa}B$ transcriptional activity. Conclusion : PI3K/Akt was not involved in TNF-$\alpha$-induced $I{\kappa}B{\alpha}$ degradation or transcriptional activity of NF-${\kappa}B$ in human respiratory epithelial cell lines.

• Journal of Microbiology and Biotechnology
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• v.18 no.12
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• pp.1997-2003
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• 2008

Cordyceps militaris is well known as a traditional medicinal mushroom and has been shown to exhibit immunostimulatory and anticancer activities. In this study, we investigated the apoptosis induced by an aqueous extract of C. militaris (AECM) via the activation of caspases and altered mitochondrial membrane permeability in human breast cancer MDA-MB-231 cells. Exposure to AECM induced apoptosis, as demonstrated by a quantitative analysis of nuclear morphological change and a flow cytometric analysis. AECM increased hyperpolarization of mitochondrial membrane potential and promoted the activation of caspases. Both the cytotoxic effect and apoptotic characteristics induced by AECM treatment were significantly inhibited by z-DEVD-fmk, a caspase-3 inhibitor, which demonstrates the important role of caspase-3 in the observed cytotoxic effect. AECM-induced apoptosis was associated with the inhibition of Akt activation in a time-dependent manner, and pretreatment with LY294002, a PI3K/Akt inhibitor, significantly increased AECM-induced apoptosis. The results indicated that AECM-induced apoptosis may relate to the activation of caspase-3 and mitochondria dysfunctions that correlate with the inactivation of Akt.

• IMMUNE NETWORK
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• v.11 no.6
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• pp.420-423
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• 2011

Since CKD-712 has been developed as an anti-inflammatory agent, we examined the effect of CKD-712 during TLR4 signaling. Using HEK293 cells expressing TLR4, CKD-712 was pre-treated 1 hr before LPS stimulation. Activation of NF-${\kappa}B$ was assessed by promoter assay. The activation of ERK, JNK, p38, IRF3 and Akt was measured by western blotting. CKD-712 inhibited the NF-${\kappa}B$ signaling triggered by LPS. The activation of ERK, JNK, p38 or IRF3 was not inhibited by CKD-712. On the contrary the activation of these molecules was augmented slightly. The activation of Akt with stimulation of LPS was also enhanced with CKD-712 pre-treatment at lower concentration, but was inhibited at higher concentration. We suggest that during TLR4 signaling CKD-712 inhibits NF-${\kappa}B$ activation. However, CKD-712 augmented the activation of Akt as well as Map kinases. Therefore, we suggest that CKD-712 might have a role as an immunomodulator.

• Journal of Life Science
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• v.18 no.12
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• pp.1651-1656
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• 2008

Redox factor-1 (Ref-1) is essential for repair of oxidatively damaged DNA and also govern the reductive activation of many transcription factors. In this study, we examined the effect of overexpressed Ref-1 on AKT activation for nitric oxide (NO) production in mouse aortic endothelial (MAE) cells. Adenoviral-mediated overexpression of Ref-1 enhanced NO production in unstimulated- as well as bradykinin-stimulated MAE cells. Importantly, forced overexpression of Ref-1 induced direct phosphorylation of AKT in cells. And, a PI3K inhibitor wortmannin completely abolished the increase in AKT phosphorylation by stimulation of bradykinin and/or overexpressed Ref-1. In addition, inhibition of AKT activity with HA-tagged activation-deficient AKT suppressed Ref-1-induced endothelial NO synthase (eNOS) phosphorylation and resulted in a corresponding inhibition of unstimulated- and bradykinin-stimulated NO production. These results suggest that Ref-1 stimulates direct phosphorylation of AKT for eNOS enzyme activity in murine endothelial cells.