Citrus auraptene targets translation of MMP-7 (matrilysin) via ERK1/2-dependent and mTOR-independent mechanism

Matrix metalloproteinase (MMP)-7 is considered to play essential roles in cancer progression. We examined the efficacy of auraptene, a citrus coumarin derivative, for suppressing MMP-7 expression in the human colorectal adenocarcinoma cell line HT-29. Auraptene remarkably inhibited the production of proMMP-7 protein, without affecting its mRNA expression level. Rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), showed similar results, suggesting that auraptene suppresses mTOR-dependent proMMP-7 translation. Interestingly, however, auraptene showed no effects on the activation of Akt/mTOR signaling, whereas the phosphorylation levels of 4E binding protein (4EBP)1 and eukaryotic translation initiation factor (eIF)4B were substantially decreased. In addition, auraptene remarkably dephosphorylated constitutively activated extracellular signal-regulated kinase (ERK)1/2. Transfection of ERK1/2 siRNA led to a significant reduction of proMMP-7 protein production as well as of the phosphorylation of eIF4B. These results demonstrate that auraptene targets the translation step for proMMP-7 protein synthesis by disrupting ERK1/2-mediated phosphorylation of 4EBP1 and eIF4B.     

Ginsenoside Rg1 facilitates neural differentiation of mouse embryonic stem cells via GR-dependent signaling pathway

Ginsenoside Rg1, a steroidal saponin of high abundance in ginseng, possesses the neuroprotective effects. In this study, we tried to explore the effect of Rg1 on promoting differentiation of mouse embryonic stem (ES) cells towards the neuronal lineage and its potential role involved in glucocorticoid receptor (GR) activation. Rg1 treatment induced a remarkable increase in the population of neuron-like cells in a time-dependent manner. More than 80% of Rg1-treated embryoid bodies (EBs) differentiated into neuron-like cells on d 8 + 10. Furthermore, the gradually increased protein expression of neurofilament (NEFM) and β-tubulin III (a neuronal specific protein) was determined. GR expression gradually increased during the differentiation course. RU486, an antagonist of GR, could efficiently block the neurogenesis-promoting activity of Rg1. On the other side, Rg1 stimulated the phosphorylation of ERK1/2 and Akt at different time points through GR activation-dependent mechanisms. Treatment of both U0126 (an inhibitor of MEK) and LY294002 (an inhibitor of PI3 K), hampered the neuronal differentiation induced by Rg1. Meantime, U0126 further decreased Rg1-induced p-Akt expression. In conclusion, Rg1 possesses the effects on inducing differentiation of mouse ES cells into neurons in vitro via the GR-MEK-ERK1/2-PI3 K-Akt signaling pathway.     

Hypotonic stress induces E-cadherin expression in cultured human keratinocytes

Human epidermis marks the interface between internal and external environments with the major task being to maintain body hydration. Alternating exposure of skin to a dry or humid environment is likely to cause changes in the epidermal water gradient resulting in osmotic alterations of epidermal keratinocytes. The present in vitro approach studied the effect of hypotonicity on cell-cell contact. It was demonstrated that hypotonic stress applied to human epithelial cells (HaCaT, A-431) induced upregulation of E-cadherin at both, the protein and mRNA level. 5'-deletional mutants of the E-cadherin promoter identified an element ranging from -53 to +31 that conveyed strong transactivation under hypotonic stress. In order to define relevant upstream regulators members of the MAP kinase family, the epidermal growth factor receptor (EGFR) and protein kinase B/Akt (PKB/Akt) were investigated. Hypotonic conditions led to a fast activation of ERK1/2, SAPK/JNK, p38, EGFR and PKB/Akt with distinct activation patterns. Experiments using specific inhibitors showed that p38 contributes to the E-cadherin transactivation under hypotonic conditions. Further upstream, adhesion was found to be a prerequisite for E-cadherin transactivation in this model. In summary, the present study provides evidence that E-cadherin is an osmo-sensitive gene that responds to hypotonic stress. The function of this regulation may be found in morphological changes induced by cell swelling. It is likely that induction of E-cadherin contributes to the stabilization between adjacent cells in order to withstand the physical forces induced by hypotonicity.     

Activation of diacylglycerol O-acyltransferase 1 gene results in increased tumor necrosis factor-alpha gene expression in 3T3-L1 adipocytes

The tumor necrosis factor-alpha (TNF-alpha) expression has been reported to be largely dependent on the size of adipocytes. We herein investigated the gene regulation of diacylglycerol O-acyltransferase (DGAT) in order to clarify the mechanism of TNF-alpha expression induced in large adipocytes. 3T3-L1 cells were cultured in the presence of 5 mM or 25 mM glucose to generate adipocytes from which the triglyceride content differs. The expression of TNF-alpha, DGAT1, and DGAT2 were upregulated in adipocytes cultured with 25 mM glucose. Furthermore, knockdown of DGAT1 gene significantly inhibited the TNF-alpha expression. Finally, the DGAT1 expression levels were closely related to the TNF-alpha level in 3T3-L1 adipocytes.     

ERK2 small interfering RNAs prevent epidural fibrosis via the efficient inhibition of collagen expression and inflammation in laminectomy rats

Laminectomy is a widely accepted treatment for lumbar disorders. Epidural Fibrosis (EF) is a common post-laminectomy or post-discectomy complication, which is thought to cause recurrent pain. RNA interference (RNAi) is a process by which double-stranded RNA triggers the destruction of mRNAs sharing the same sequence. Previously, extra-cellular signal-regulated kinase (ERK) 2 plays crucial roles in suppressing the collagen expression. To investigate the effects of lentiviral ERK2 siRNA on the prevention of post-laminectomy EF formation in a rat model, a controlled double-blinded study was conducted in 75 healthy adult Wistar rats that underwent laminectomy. They were divided randomly into 3 groups according to the treatment method: (1) control group; (2) ERK scrRNA group; (3) ERK siRNA group. All rats were euthanized humanely 4 weeks post-laminectomy. The hydroxyproline content, Rydell score, vimentin cells density, fibroblasts density, inflammatory cells density and inflammatory factors expressions were performed. The hydroxyproline content, Rydell score, vimentin cells density, fibroblasts density, inflammatory cells density and inflammatory factors expressions all suggested better results in ERK siRNA group than other two groups. None of the rats expired and no obvious adverse effects were observed. Local delivery of a lentiviral siRNA targeting ERK2 can prevent epidural scar adhesion in post-laminectomy rat via inhibiting collagen expression and inflammation.     

PI3K/Akt is involved in brown adipogenesis mediated by growth differentiation factor-5 in association with activation of the Smad pathway

We have previously demonstrated promotion by growth differentiation factor-5 (GDF5) of brown adipogenesis for systemic energy expenditure through a mechanism relevant to activating the bone morphological protein (BMP) receptor/mothers against decapentaplegic homolog (Smad)/peroxisome proliferator-activated receptor gamma co-activator 1α (PGC-1α) pathway. Here, we show the involvement of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in brown adipogenesis mediated by GDF5. Overexpression of GDF5 in cells expressing adipocyte protein-2 markedly accelerated the phosphorylation of Smad1/5/8 and Akt in white and brown adipose tissues. In brown adipose tissue from heterozygous GDF5^Rgsc451 mutant mice expressing a dominant-negative (DN) GDF5 under obesogenic conditions, the basal phosphorylation of Smad1/5/8 and Akt was significantly attenuated. Exposure to GDF5 not only promoted the phosphorylation of both Smad1/5/8 and Akt in cultured brown pre-adipocytes, but also up-regulated Pgc1a and uncoupling protein-1 expression in a manner sensitive to the PI3K/Akt inhibitor Ly294002 as well as retroviral infection with DN-Akt. GDF5 drastically promoted BMP-responsive luciferase reporter activity in a Ly294002-sensitive fashion. Both Ly294002 and DN-Akt markedly inhibited phosphorylation of Smad5 in the nuclei of brown pre-adipocytes. These results suggest that PI3K/Akt signals play a role in the GDF5-mediated brown adipogenesis through a mechanism related to activation of the Smad pathway.     

Hyperoxia-mediated oxidative stress increases expression of UCP3 mRNA and protein in skeletal muscle

The uncoupling protein-3 (UCP3) is a mitochondrial protein expressed mainly in skeletal muscle. Among several hypotheses for its physiological function, UCP3 has been proposed to prevent excessive production of reactive oxygen species. In the present study, we evaluated the effect of an oxidative stress induced by hyperoxia on UCP3 expression in mouse skeletal muscle and C2C12 myotubes. We found that the hyperoxia-mediated oxidative stress was associated with a 5-fold and 3-fold increase of UCP3 mRNA and protein levels, respectively, in mouse muscle. Hyperoxia also enhanced reactive oxygen species production and UCP3 mRNA expression in C2C12 myotubes. Our findings support the view that both in vivo and in vitro UCP3 may modulate reactive oxygen species production in response to an oxidative stress.     

Induction of ornithine decarboxylase in T/C-28a2 chondrocytes by lysophosphatidic acid: signaling pathway and inhibition of cell proliferation

Among several extracellular messengers tested, lysophosphatidic acid (LPA) was able to cause the most marked induction of ornithine decarboxylase (ODC) in serum-starved human T/C-28a2 chondrocytes. LPA also induced the activation/phosphorylation of Src, Akt and p44/42 MAPK, and the translocation of PKC-delta from cytosol to membrane coupled to its tyrosine phosphorylation. Experiments with selective signaling inhibitors indicate that LPA leads to Src activation through Gi protein-coupled receptors. In turn Src can activate PI3K and PKC-delta, and all these signaling proteins are required for ODC induction. In conclusion these results show that chondrocytes may be a novel target for LPA action. However, although LPA is considered a mitogen for several cell types and ODC induction is generally correlated to cell growth, LPA was not able to stimulate chondrocyte growth, but rather exerted an anti-proliferative effect.     

MicroRNA expression profiling of NGF-treated PC12 cells revealed a critical role for miR-221 in neuronal differentiation

MicroRNAs (miRNAs) are small non-coding RNAs that control protein expression through translational inhibition or mRNA degradation. MiRNAs have been implicated in diverse biological processes such as development, proliferation, apoptosis and differentiation. Upon treatment with nerve growth factor (NGF), rat pheochromocytoma PC12 cells elicit neurite outgrowth and differentiate into neuron-like cells. NGF plays a critical role not only in neuronal differentiation but also in protection against apoptosis. In an attempt to identify NGF-regulated miRNAs in PC12 cells, we performed miRNA microarray analysis using total RNA harvested from cells treated with NGF. In response to NGF treatment, expression of 8 and 12 miRNAs were up- and down-regulated, respectively. Quantitative RT-PCR analysis of 11 out of 20 miRNAs verified increased expression of miR-181a^∗, miR-221 and miR-326, and decreased expression of miR-106b^∗, miR-126, miR-139-3p, miR-143, miR-210 and miR-532-3p after NGF treatment, among which miR-221 was drastically up-regulated. Functional annotation analysis of potential target genes of 7 out of 9 miRNAs excluding the passenger strands (*) revealed that NGF may regulate expression of various genes by controlling miRNA expression, including those whose functions and processes are known to be related to NGF. Overexpression of miR-221 induced neuronal differentiation of PC12 cells in the absence of NGF treatment, and also enhanced neuronal differentiation caused by low-dose NGF. Furthermore, miR-221 potentiated formation of neurite network, which was associated with increased expression of synapsin I, a marker for synapse formation. More importantly, knockdown of miR-221 expression by antagomir attenuated NGF-mediated neuronal differentiation. Finally, miR-221 decreased expression of Foxo3a and Apaf-1, both of which are known to be involved in apoptosis in PC12 cells. Our results suggest that miR-221 plays a critical role in neuronal differentiation as well as protection against apoptosis in PC12 cells.     

EGFR is dispensable for c-Met-mediated proliferation and survival activities in mouse adult liver oval cells

Liver progenitor cells rise as potential critical players in hepatic regeneration but also carcinogenesis. It is therefore mandatory to define the signals controlling their activation and expansion. Recently, by using a novel in vitro model of oval cell lines expressing a mutant tyrosine kinase-inactive form of c-Met we demonstrated that autocrine c-Met signalling plays an essential role in promoting oval cell survival. Here, we investigated the significance of the epidermal growth factor receptor (EGFR) signalling in oval cell proliferation and survival, as well as a potential functional crosstalk between the c-Met and the EGFR pathways. We found an autocrine activation of the EGFR-triggered pathway in Met^flx/flx and Met^−/− oval cells as judged by constitutive expression of the EGFR ligands, transforming growth factor-alpha (TGF-α) and heparin-binding EGF like growth factor (HB-EGF), and activation of EGFR. On the other hand, treatment with AG1478, a specific inhibitor of EGFR, effectively blocked endogenous and EGF-induced proliferation, while increased serum withdrawal and transforming growth factor-beta (TGF-β)-induced apoptosis. These results suggest that constitutively activated EGFR might promote oval cell proliferation and survival. We found that hepatocyte growth factor (HGF) does not transactivate EGFR nor EGF transactivates c-Met. Furthermore, treatment with AG1478 or EGFR gene silencing did not interfere with HGF-mediated activation of target signals, such as protein kinase B (AKT/PKB), and extracellular signal-regulated kinases 1/2 (ERK 1/2), nor did it have any effect on HGF-induced proliferative and antiapoptotic activities in Met^flx/flx cells, showing that HGF does not require EGFR activation to mediate such responses. EGF induced proliferation and survival equally in Met^flx/flx and Met^−/− oval cells, proving that EGFR signalling does not depend on c-Met tyrosine kinase activity. Together, our results provide strong evidence that in normal, untransformed oval cells, c-Met and EGFR represent critical molecular players to control proliferation and survival that function independent of one another.     

Analysis of microRNA expression profile induced by AICAR in mouse hepatocytes

AMP-activated protein kinase (AMPK) has been proposed to act as a key energy sensor mediating the metabolism of glucose and lipids, and pharmacological activation of AMPK may provide a new strategy for the management of type 2 diabetes. MicroRNAs (miRNAs) are a group of endogenous noncoding RNA that play important roles in many biological processes including energy metabolism. Whether miRNAs mediate AMPK action in regulating metabolic process is not clear. In this study, 0.5 mM 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) was added to increase activation of AMPK in 8 week old C57BL/6 mice primary hepatocytes. MiRNA microarray was performed to compare the miRNA expression profiles of hepatocytes treated with or without AICAR. We discovered that 41 miRNAs were significantly altered in AICAR-treated sample (fold change: > 2) compared with untreated control sample. Among them, 19 miRNAs were upregulated. MiRNA targets were predicted by TargetScan. Further bioinformatic analysis indicated that these predicted targets might be mainly involved in pathways of cellular metabolism and tumor pathogenesis. FUNDO analysis suggested that these predicted targets were enriched in cancer, diabetes mellitus, hypertension, obesity and heart failure (P < 0.01). A series of miRNAs could be regulated by the activation of AMPK and might mediate the action of AMPK during metabolic processes and tumor pathogenesis. Predicted target genes discovered in this study and pathway analysis provide new insights into hepatic metabolism and tumor pathogenesis regulated by AMPK signaling and clues to the possible molecular mechanism underlying the effect of AMPK.     

Amyloid precursor protein regulates migration and metalloproteinase gene expression in prostate cancer cells

Amyloid precursor protein (APP) is a type I transmembrane protein, and one of its processed forms, β-amyloid, is considered to play a central role in the development of Alzheimer’s disease. We previously showed that APP is a primary androgen-responsive gene in prostate cancer and that its increased expression is correlated with poor prognosis for patients with prostate cancer. APP has also been implicated in several human malignancies. Nevertheless, the mechanism underlying the pro-proliferative effects of APP on cancers is still not well-understood. In the present study, we explored a pathophysiological role for APP in prostate cancer cells using siRNA targeting APP (siAPP). The proliferation and migration of LNCaP and DU145 prostate cancer cells were significantly suppressed by siAPP. Differentially expressed genes in siAPP-treated cells compared to control siRNA-treated cells were identified by microarray analysis. Notably, several metalloproteinase genes, such as ADAM10 and ADAM17, and epithelial–mesenchymal transition (EMT)-related genes, such as VIM, and SNAI2, were downregulated in siAPP-treated cells as compared to control cells. The expression of these genes was upregulated in LNCaP cells stably expressing APP when compared with control cells. APP-overexpressing LNCaP cells exhibited enhanced migration in comparison to control cells. These results suggest that APP may contribute to the proliferation and migration of prostate cancer cells by modulating the expression of metalloproteinase and EMT-related genes.