EGF stimulates proliferation of mouse embryonic stem cells: involvement of Ca2+influx and p44/42 MAPKs

Ras promotes germline stem cell division in Drosophila ovaries

The Ras family genes are proto-oncogenes that are highly conserved from Drosophila to humans. In Drosophila, RasV12 is a constitutively activated form of the Ras oncoprotein, and its function in cell-cycle progression is context dependent. However, how it influences the cell cycle of female germline stem cells (GSCs) still remains unknown. Using both wild-type GSCs and bam mutant GSC-like cells as model systems, here we determined that RasV12 overexpression promotes GSC division, not growth, opposite to that in somatic wing disc cells. Ras performs this function through activating the mitogen-activated protein kinase (MAPK) signaling. This signaling is activated specifically in the M phase of mitotic germ cells, including both wild-type GSCs and bam mutant GSC-like cells. Furthermore, RasV12 overexpression triggers polyploid nurse cells to die through inducing mitotic stress. Given the similarities between Drosophila and mammalian GSCs, we propose that the Ras/MAPK signaling also promotes mammalian GSC division.

Regulation of Embryonic Stem Cell Self-Renewal

Embryonic stem cells (ESCs) are a type of cells capable of self-renewal and multi-directional differentiation. The self-renewal of ESCs is regulated by factors including signaling pathway proteins, transcription factors, epigenetic regulators, cytokines, and small molecular compounds. Similarly, non-coding RNAs, small RNAs, and microRNAs (miRNAs) also play an important role in the process. Functionally, the core transcription factors interact with helper transcription factors to activate the expression of genes that contribute to maintaining pluripotency, while suppressing the expression of differentiation-related genes. Additionally, cytokines such as leukemia suppressor factor (LIF) stimulate downstream signaling pathways and promote self-renewal of ESCs. Particularly, LIF binds to its receptor (LIFR/gp130) to trigger the downstream Jak-Stat3 signaling pathway. BMP4 activates the downstream pathway and acts in combination with Jak-Stat3 to promote pluripotency of ESCs in the absence of serum. In addition, activation of the Wnt-FDZ signaling pathway has been observed to facilitate the self-renewal of ESCs. Small molecule modulator proteins of the pathway mentioned above are widely used in in vitro culture of stem cells. Multiple epigenetic regulators are involved in the maintenance of ESCs self-renewal, making the epigenetic status of ESCs a crucial factor in this process. Similarly, non-coding RNAs and cellular energetics have been described to promote the maintenance of the ESC's self-renewal. These factors regulate the self-renewal and differentiation of ESCs by forming signaling networks. This review focused on the role of major transcription factors, signaling pathways, small molecular compounds, epigenetic regulators, non-coding RNAs, and cellular energetics in ESC's self-renewal.

Immunomodulatory Effect of Epidermal Growth Factor Secreted by Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells on Atopic Dermatitis

Background and Objectives

Human mesenchymal stem cells (MSCs) are emerging as a treatment for atopic dermatitis (AD), a chronic inflammatory skin disorder that affects a large number of people across the world. Treatment of AD using human umbilical cord blood-derived MSCs (hUCB-MSCs) has recently been studied. However, the mechanism underlying their effect needs to be studied continuously. Thus, the objective of this study was to investigate the immunomodulatory effect of epidermal growth factor (EGF) secreted by hUCB-MSCs on AD.

Methods and Results

To explore the mechanism involved in the therapeutic effect of MSCs for AD, a secretome array was performed using culture medium of hUCB-MSCs. Among the list of genes common for epithelium development and skin diseases, we focused on the function of EGF. To elucidate the effect of EGF secreted by hUCB-MSCs, EGF was downregulated in hUCB-MSCs using EGF-targeting small interfering RNA. These cells were then co-cultured with keratinocytes, Th2 cells, and mast cells. Depletion of EGF disrupted immunomodulatory effects of hUCB-MSCs on these AD-related inflammatory cells. In a Dermatophagoides farinae-induced AD mouse model, subcutaneous injection of hUCB-MSCs ameliorated gross scoring, histopathologic damage, and mast cell infiltration. It also significantly reduced levels of inflammatory cytokines including interleukin (IL)-4, tumor necrosis factor (TNF)-α, thymus and activation-regulated chemokine (TARC), and IL-22, as well as IgE levels. These therapeutic effects were significantly attenuated at all evaluation points in mice injected with EGF-depleted hUCB-MSCs.

Conclusions

EGF secreted by hUCB-MSCs can improve AD by regulating inflammatory responses of keratinocytes, Th2 cells, and mast cells.

Small Molecules that Promote Self-Renewal of Stem Cells and Somatic Cell Reprogramming

The ground state of embryonic stem cells (ESCs) is closely related to the development of regenerative medicine. Particularly, long-term culture of ESCs in vitro, maintenance of their undifferentiated state, self-renewal and multi-directional differentiation ability is the premise of ESCs mechanism and application research. Induced pluripotent stem cells (iPSC) reprogrammed from mouse embryonic fibroblasts (MEF) cells into cells with most of the ESC characteristics show promise towards solving ethical problems currently facing stem cell research. However, integration into chromosomal DNA through viral-mediated genes may activate proto oncogenes and lead to risk of cancer of iPSC. At the same time, iPS induction efficiency needs to be further improved to reduce the use of transcription factors. In this review, we discuss small molecules that promote self-renewal and reprogramming, including growth factor receptor inhibitors, GSK-3β and histone deacetylase inhibitors, metabolic regulators, pathway modulators as well as EMT/MET regulation inhibitors to enhance maintenance of ESCs and enable reprogramming. Additionally, we summarize the mechanism of action of small molecules on ESC self-renewal and iPSC reprogramming. Finally, we will report on the progress in identification of novel and potentially effective agents as well as selected strategies that show promise in regenerative medicine. On this basis, development of more small molecule combinations and efficient induction of chemically induced pluripotent stem cell (CiPSC) is vital for stem cell therapy. This will significantly improve research in pathogenesis, individualized drug screening, stem cell transplantation, tissue engineering and many other aspects.

Weak power frequency magnetic fields induce microtubule cytoskeleton reorganization depending on the epidermal growth factor receptor and the calcium related signaling

We have shown previously that a weak 50 Hz magnetic field (MF) invoked the actin-cytoskeleton, and provoked cell migration at the cell level, probably through activating the epidermal growth factor receptor (EGFR) related motility pathways. However, whether the MF also affects the microtubule (MT)-cytoskeleton is still unknown. In this article, we continuously investigate the effects of 0.4 mT, 50 Hz MF on the MT, and try to understand if the MT effects are also associated with the EGFR pathway as the actin-cytoskeleton effects were. Our results strongly suggest that the MF effects are similar to that of EGF stimulation on the MT cytoskeleton, showing that 1) the MF suppressed MT in multiple cell types including PC12 and FL; 2) the MF promoted the clustering of the EGFR at the protein and the cell levels, in a similar way of that EGF did but with higher sensitivity to PD153035 inhibition, and triggered EGFR phosphorylation on sites of Y1173 and S1046/1047; 3) these effects were strongly depending on the Ca²⁺ signaling through the L-type calcium channel (LTCC) phosphorylation and elevation of the intracellular Ca²⁺ level. Strong associations were observed between EGFR and the Ca²⁺ signaling to regulate the MF-induced-reorganization of the cytoskeleton network, via phosphorylating the signaling proteins in the two pathways, including a significant MT protein, tau. These results strongly suggest that the MF activates the overall cytoskeleton in the absence of EGF, through a mechanism related to both the EGFR and the LTCC/Ca²⁺ signaling pathways.

Distinct requirements for the maintenance and establishment of mouse embryonic stem cells

Mouse embryonic stem cells (ESCs) that maintain a sustainable pluripotent state are derived from the inner cell mass (ICM) of blastocysts, in which pluripotency is lost during differentiation in vivo. It is unclear when and how the ability to maintain pluripotency is acquired during the derivation of ESCs. We analyzed the required culture condition for the maintenance and establishment of ESCs in detail. Even at low concentration of the GSK3β inhibitor and LIF (LowGiL), the expression levels of pluripotency markers and the chimera-producing ability of the cells were comparable with those of ESCs cultured in the presence of both inhibitors and LIF (2iL). However, blastocysts underwent spontaneous differentiation, and ESCs were not established under LowGiL condition. Time-course analysis showed that 2iL condition for three days from the initiation of culture was sufficient for the acquisition of permanent pluripotency. Although X chromosome-linked pluripotent genes were significantly up-regulated during the culture of both male and female blastocysts in 2iL condition, no such up-regulation was observed in LowGiL condition. In conclusion, 2iL-dependent activation of these X-linked genes at the earliest phase of ESC derivation is one of the molecular bases for the acquisition of permanent pluripotency.

Bioinformatics analysis to screen key genes implicated in the differentiation of induced pluripotent stem cells to hepatocytes

Due to the lack of potential organs, hepatocellular transplantation has been considered for treating end-stage liver disease. Induced pluripotent stem cells (iPSCs) are reverted from somatic cells and are able to differentiate into hepatocytes. The present study aimed to investigate the mechanisms underlying iPSC differentiation to hepatocytes. GSE66076 was downloaded from the Gene Expression Omnibus; this database includes data from 3 undifferentiated (T0), 3 definitive endoderm (T5), and 3 early hepatocyte (T24) samples across hepatic‑directed differentiation of iPSCs. Differentially expressed genes (DEGs) between T0 and T5 or T24 samples were identified using the linear models for microarray data package in Bioconductor, and enrichment analyses were performed. Using the weighted correlation network analysis package in R, clusters were identified for the merged DEGs. Cytoscape was used to construct protein‑protein interaction (PPI) networks for DEGs identified to belong to significant clusters. Using the ReactomeFI plugin in Cytoscape, functional interaction (FI) networks were constructed for the common genes. A total of 433 and 1,342 DEGs were identified in the T5 and T24 samples respectively, compared with the T0 samples. Blue and turquoise clusters were identified as significant gene clusters. In the PPI network for DEGs in the blue cluster, the key node fibroblast growth factor 2 (FGF2) could interact with bone morphogenetic protein 2 (BMP2). Cyclin‑dependent kinase 1 (CDK1) was demonstrated to have the highest degree (degree=71) in the PPI network for DEGs in the turquoise cluster. Enrichment analysis for the common genes, including hepatocyte nuclear factor 4α (HNF4A) and epidermal growth factor (EGF), in the FI network indicated that EGF and FGF2 were enriched in the Ras and Rap1 signaling pathways. The present results suggest that FGF2, BMP2, CDK1, HNF4A and EGF may participate in the differentiation of iPSCs into hepatocytes.

Epidermal growth factor (EGF) triggers the malignancy of hemangioma cells via activation of NF-κB signals

Hemangioma (HA) is tumor formed by hyper-proliferation of vascular endothelial cells. However, the role and mechanisms of epidermal growth factor (EGF) on the progression of HA are not well illustrated. Our present study revealed that EGF can significantly promote the in vitro proliferation and motility of HA cells, which was confirmed by the up regulation of Bcl-2, proliferating cell nuclear antigen (PCNA), and metalloproteinase-2 (MMP-2) and MMP-9. The pharmacological inhibition of NF-κB, while not ERK1/2 or PI3K/Akt, attenuated EGF induced cell proliferation and expression of MMP-2 and MMP-9. EGF treatment also increased the phosphorylation, nuclear translocation and transcriptional activities of NF-κB in HA cells. These data suggested that NF-κB plays an essential role in EGF induced malignancy of HA cells. Furthermore, EGF treatment also increased the phosphorylation of IκB and IKKα, while not IKKβ or IKKγ. The knockdown of IKKα reversed EGF induced activation of NF-κB. EGF treatment also decreased the phosphorylation of GSK-3β and increased its activities in both HDEC and CRL-2586 EOMA cells. LiCl, a potent GSK-3β inhibitor, can obviously reverse EGF induced up regulation of p65 phosphorylation. Collectively, our study revealed that EGF can trigger the malignancy of HA cells via induction of proliferation and invasion. The activation of NF-κB through IKKα/IκBα and GSK-3β signal is essential for this process. It suggested that EGF/NF-κB signal may represent a novel therapeutic target for the treatment of human HA.

Cell-cycle-dependent Ca2+ transients in human induced pluripotent stem cells revealed by a simultaneous imaging of cell nuclei and intracellular Ca2+ level

Simultaneous imaging of cell nuclei and intracellular Ca²⁺ level revealed that human iPS cells exhibited cell cycle-dependent Ca²⁺ transients.

MicroRNA-221 is required for proliferation of mouse embryonic stem cells via P57 targeting

Factors responsible for the rapid proliferative properties of embryonic stem (ES) cells are largely unknown. MicroRNA-221/222 (miR-221/222) regulate proliferation in many somatic cells, however, their roles in proliferation of ES cells are unclear. In this study, E14 mouse ES cells proliferation was determined by total cell counting, Cell Counting Kit (CCK-8), size of colonies and cell cycle analysis, while apoptosis and necrosis using Annexin V and propidium iodide staining. miR-221 inhibitor decreased proliferation of ES cells without inducing apoptosis and necrosis. miR-221 mimic, miR-222 mimic and miR-222 inhibitor did not affect ES cells proliferation. The expression level of miR-221 remained unchanged upon embryoid body (EB) formation. ES cells with miR-221 inhibition maintained an undifferentiated state, as indicated by unchanged alkaline phosphatase enzyme activity and Sox2, Nanong, and Oct4 expressions. P57 was post-transcriptionally regulated by miR-221 in ES cells. P57 knockdown completely abolished the inhibition effects of ES cells proliferation observed in miR-221 reduction, further indicating that miR-221 inhibition is likely to mediate its antiproliferative effects via P57 expression. To exclude that the function of miR-221 in ES cells is E14 specific, the effects of miR-221 mimic and inhibitor in size of colonies and cell cycle of R1 mouse ES cells were also determined and similar effects in inhibiting proliferation were achieved with miR-221 inhibition. Therefore, miR-221 is required for mouse ES cells proliferation via P57 targeting. This study indicates that miR-221 is among the regulators that control ES cells proliferation and might be used to influence the fate of ES cells.

Protein kinases and associated pathways in pluripotent state and lineage differentiation

Protein kinases (PKs) mediate the reversible conversion of substrate proteins to phosphorylated forms, a key process in controlling intracellular signaling transduction cascades. Pluripotency is, among others, characterized by specifically expressed PKs forming a highly interconnected regulatory network that culminates in a finely-balanced molecular switch. Current high-throughput phosphoproteomic approaches have shed light on the specific regulatory PKs and their function in controlling pluripotent states. Pluripotent cell-derived endothelial and hematopoietic developments represent an example of the importance of pluripotency in cancer therapeutics and organ regeneration. This review attempts to provide the hitherto known kinome profile and the individual characterization of PK-related pathways that regulate pluripotency. Elucidating the underlying intrinsic and extrinsic signals may improve our understanding of the different pluripotent states, the maintenance or induction of pluripotency, and the ability to tailor lineage differentiation, with a particular focus on endothelial cell differentiation for anti-cancer treatment, cell-based tissue engineering, and regenerative medicine strategies.

ERK1/2 mediates sperm acrosome reaction through elevation of intracellular calcium concentration

Mammalian sperm acquire fertilization capacity after residing in the female reproductive tract for a few hours in a process called capacitation. Only capacitated sperm can bind the zona pellucida (ZP) of the egg and undergo the acrosome reaction, a process that allows penetration and fertilization. Extracellular signal regulated kinase (ERK1/2) mediates signalling in many cell types, however its role in sperm function is largely unknown. Here we show that ERK1/2 is highly phosphorylated/activated after a short incubation of mouse sperm under capacitation conditions and that this phosphorylation is reduced after longer incubation. Further phosphorylation was observed upon addition of crude extract of egg ZP or epidermal growth factor (EGF). The mitogen-activated ERK-kinase (MEK) inhibitor U0126 abolished ERK1/2 phosphorylation, in vitro fertilization rate and the acrosome reaction induced by ZP or EGF but not by the Ca2+-ionophore A23187. Moreover, inhibition of ERK1/2 along the capacitation process diminished almost completely the sperm's ability to go through the acrosome reaction, while inhibition at the end of capacitation attenuated the acrosome reaction rate by only 45%. The fact that the acrosome reaction, induced by the Ca2+ -ionophore A23187, was not inhibited by U0126 suggests that ERK1/2 mediates the acrosome reaction by activating Ca2+ transport into the cell. Direct determination of intracellular [Ca2+] revealed that Ca2+ influx induced by EGF or ZP was completely blocked by U0126. Thus, it has been established that the increase in ERK1/2 phosphorylation/activation in response to ZP or by activation of the EGF receptor (EGFR) by EGF, is a key event for intracellular Ca2+ elevation and the subsequent occurrence of the acrosome reaction.

Phospholipase D1 increases Bcl-2 expression during neuronal differentiation of rat neural stem cells

We studied the possible role of phospholipase D1 (PLD1) in the neuronal differentiation, including neurite formation of neural stem cells. PLD1 protein and PLD activity increased during neuronal differentiation. Bcl-2 also increased. Downregulation of PLD1 by transfection with PLD1 siRNA or a dominant-negative form of PLD1 (DN-PLD1) inhibited both neurite outgrowth and Bcl-2 expression. PLD activity was dramatically reduced by a PLCγ (phospholipase Cγ) inhibitor (U73122), a Ca(2+)chelator (BAPTA-AM), and a PKCα (protein kinase Cα) inhibitor (RO320432). Furthermore, treatment with arachidonic acid (AA) which is generated by the action of PLA2 (phospholipase A2) on phosphatidic acid (a PLD1 product), increased the phosphorylation of p38 MAPK and CREB, as well as Bcl-2 expression, indicating that PLA2 is involved in the differentiation process resulting from PLD1 activation. PGE2 (prostaglandin E2), a cyclooxygenase product of AA, also increased during neuronal differentiation. Moreover, treatment with PGE2 increased the phosphorylation of p38 MAPK and CREB, as well as Bcl-2 expression, and this effect was inhibited by a PKA inhibitor (Rp-cAMP). As expected, inhibition of p38 MAPK resulted in loss of CREB activity, and when CREB activity was blocked with CREB siRNA, Bcl-2 production also decreased. We also showed that the EP4 receptor was required for the PKA/p38MAPK/CREB/Bcl-2 pathway. Taken together, these observations indicate that PLD1 is activated by PLCγ/PKCα signaling and stimulate Bcl-2 expression through PLA2/Cox2/EP4/PKA/p38MAPK/CREB during neuronal differentiation of rat neural stem cells.

Melatonin enhances adult rat hippocampal progenitor cell proliferation via ERK signaling pathway through melatonin receptor

Melatonin, a neurohormone secreted mainly by the pineal gland, has a variety of physiological functions and neuroprotective effects. Previous studies have shown that melatonin could stimulate the proliferation of neural stem/progenitor cells (NS/PCs). Recent studies reported that the activities of mitogen-activated protein kinase (MAPK) of neural stem cells (NSCs) changed in response to the proliferative effect of melatonin. Therefore, the aim of the present study was to explore the proliferative mechanism mediated by melatonin on the adult rat hippocampal NS/PCs. Treatment with melatonin significantly increased the number of neurospheres in a concentration-dependent manner and up-regulated nestin protein. Pretreatment with luzindole, a melatonin receptor antagonist, and PD98059, a mitogen-activated protein kinase kinase (MEK) inhibitor, prevented the increase in the number of neurospheres formed by the activation of melatonin. The levels of phospho-c-Raf and phospho-extracellular signal-regulated kinase 1/2 (ERK1/2) increased when treated with melatonin. Pretreatment with luzindole or PD98059 prevented the melatonin-induced increase in these signaling molecules. The present results showed that melatonin could induce NS/PCs to proliferate by increasing phosphorylation of ERK1/2 and c-Raf through melatonin receptor. These results provide further evidence for a role of melatonin in promoting neurogenesis, adding to the remarkably pleiotropic nature of this neurohormone. This intrinsic modulator deserves further investigation to better understand its physiological and therapeutic implication.

In vitro epithelial differentiation of human induced pluripotent stem cells for vocal fold tissue engineering

OBJECTIVES

We determined the feasibility and optimization of differentiating human induced pluripotent stem cells (hiPS) into nonkeratinized stratified squamous epithelial cells for vocal fold engineering.

METHODS

hiPS were cultured and assessed for differentiation in 3 conditions: a 3-dimensional (3D) hyaluronic acid (HA) hydrogel scaffold, a 3D HA hydrogel scaffold with epidermal growth factor (EGF), and a 3D HA hydrogel scaffold cocultured with human vocal fold fibroblasts (hVFF). After 1, 2, and 4 weeks of cultivation, hiPS were selected for histology, immunohistochemistry, and/or transcript expression analysis.

RESULTS

At 4 weeks, hiPS cultivated with hVFF or with EGF had significantly decreased levels of Oct 3/4, indicating loss of pluripotency. Immunofluorescence revealed the presence of pancytokeratin and of cytokeratin (CK) 13 and 14 epithelial-associated proteins at 4 weeks after cultivation in hiPS EGF and hiPS hVFF cultures. The transcript expression level of CK14 was significantly increased for hiPS hVFF cultures only and was measured concomitantly with cell morphology that was clearly cohesive and displayed a degree of nuclear polarity suggestive of epithelial differentiation.

CONCLUSIONS

We found that hiPS cultivated in 3D HA hydrogel with hVFF demonstrated the most robust conversion evidence to date of epithelial differentiation. Further work is necessary to focus on amplification of these progenitors for application in vocal fold regenerative biology.

Global meta-analysis of transcriptomics studies

Transcriptomics meta-analysis aims at re-using existing data to derive novel biological hypotheses, and is motivated by the public availability of a large number of independent studies. Current methods are based on breaking down studies into multiple comparisons between phenotypes (e.g. disease vs. healthy), based on the studies' experimental designs, followed by computing the overlap between the resulting differential expression signatures. While useful, in this methodology each study yields multiple independent phenotype comparisons, and connections are established not between studies, but rather between subsets of the studies corresponding to phenotype comparisons. We propose a rank-based statistical meta-analysis framework that establishes global connections between transcriptomics studies without breaking down studies into sets of phenotype comparisons. By using a rank product method, our framework extracts global features from each study, corresponding to genes that are consistently among the most expressed or differentially expressed genes in that study. Those features are then statistically modelled via a term-frequency inverse-document frequency (TF-IDF) model, which is then used for connecting studies. Our framework is fast and parameter-free; when applied to large collections of Homo sapiens and Streptococcus pneumoniae transcriptomics studies, it performs better than similarity-based approaches in retrieving related studies, using a Medical Subject Headings gold standard. Finally, we highlight via case studies how the framework can be used to derive novel biological hypotheses regarding related studies and the genes that drive those connections. Our proposed statistical framework shows that it is possible to perform a meta-analysis of transcriptomics studies with arbitrary experimental designs by deriving global expression features rather than decomposing studies into multiple phenotype comparisons.

Weak power frequency magnetic field acting similarly to EGF stimulation, induces acute activations of the EGFR sensitive actin cytoskeleton motility in human amniotic cells

In this article, we have examined the motility-related effects of weak power frequency magnetic fields (MFs) on the epidermal growth factor receptor (EGFR)-sensitive motility mechanism, including the F-actin cytoskeleton, growth of invasive protrusions and the levels of signal molecules in human amniotic epithelial (FL) cells. Without extracellular EGF stimulation, the field stimulated a large growth of new protrusions, especially filopodia and lamellipodia, an increased population of vinculin-associated focal adhesions. And, an obvious reduction of stress fiber content in cell centers was found, corresponding to larger cell surface areas and decreased efficiency of actin assembly of FL cells in vitro, which was associated with a decrease in overall F-actin content and special distributions. These effects were also associated with changes in protein content or distribution patterns of the EGFR downstream motility-related signaling molecules. All of these effects are similar to those following epidermal growth factor (EGF) stimulation of the cells and are time dependent. These results suggest that power frequency MF exposure acutely affects the migration/motility-related actin cytoskeleton reorganization that is regulated by the EGFR-cytoskeleton signaling pathway. Therefore, upon the MF exposure, cells are likely altered to be ready to transfer into a state of migration in response to the stimuli.

SPIN90 knockdown attenuates the formation and movement of endosomal vesicles in the early stages of epidermal growth factor receptor endocytosis

The finding that SPIN90 colocalizes with epidermal growth factor (EGF) in EEA1-positive endosomes prompted us to investigate the role of SPIN90 in endocytosis of the EGF receptor (EGFR). In the present study, we demonstrated that SPIN90 participates in the early stages of endocytosis, including vesicle formation and trafficking. Stable HeLa cells with knockdown of SPIN90 displayed significantly higher levels of surface EGFR than control cells. Analysis of the abundance and cellular distribution of EGFR via electron microscopy revealed that SPIN90 knockdown cells contain residual EGFR at cell membranes and fewer EGFR-containing endosomes, both features that reflect reduced endosome formation. The delayed early endosomal targeting capacity of SPIN90 knockdown cells led to increased EGFR stability, consistent with the observed accumulation of EGFR at the membrane. Small endosome sizes and reduced endosome formation in SPIN90 knockdown cells, observed using fluorescent confocal microscopy, strongly supported the involvement of SPIN90 in endocytosis of EGFR. Overexpression of SPIN90 variants, particularly the SH3, PRD, and CC (positions 643 - 722) domains, resulted in aberrant morphology of Rab5-positive endosomes (detected as small spots located near the cell membrane) and defects in endosomal movement. These findings clearly suggest that SPIN90 participates in the formation and movement of endosomes. Consistent with this, SPIN90 knockdown enhanced cell proliferation. The delay in EGFR endocytosis effectively increased the levels of endosomal EGFR, which triggered activation of ERK1/2 and cell proliferation via upregulation of cyclin D1. Collectively, our findings suggest that SPIN90 contributes to the formation and movement of endosomal vesicles, and modulates the stability of EGFR protein, which affects cell cycle progression via regulation of the activities of downstream proteins, such as ERK1/2, after EGF stimulation.

Magnolol inhibits angiogenesis by regulating ROS-mediated apoptosis and the PI3K/AKT/mTOR signaling pathway in mES/EB-derived endothelial-like cells

Magnolol, a neolignan from the traditional medicinal plant Magnolia obovata, has been shown to possess neuroprotective, anti-inflammatory, anticancer and anti-angiogenic activities. However, the precise mechanism of the anti-angiogenic activity of magnolol remains to be elucidated. In the present study, the anti-angiogenic effect of magnolol was evaluated in mouse embryonic stem (mES)/embryoid body (EB)-derived endothelial-like cells. The endothelial-like cells were obtained by differentiation from mES/EB cells. Magnolol (20 µM) significantly suppressed the transcriptional and translational expression of platelet endothelial cell adhesion molecule (PECAM), an endothelial biomarker, in mES/EB-derived endothelial-like cells. To further understand the molecular mechanism of the suppression of PECAM expression, signaling pathways were analyzed in the mES/EB-derived endothelial-like cells. Magnolol induced the generation of reactive oxygen species (ROS) by mitochondria, a process that was associated with the induction of apoptosis as determined by positive Annexin V staining and the activation of cleaved caspase-3. The involvement of ROS generation by magnolol was confirmed by treatment with an antioxidant, N-acetyl-cysteine (NAC). NAC inhibited the magnolol-mediated induction of ROS generation and suppression of PECAM expression. In addition, magnolol suppressed the activation of MAPKs (ERK, JNK and p38) and the PI3K/AKT/mTOR signaling pathway in mES/EB-derived endothelial-like cells. Taken together, these findings demonstrate for the first time that the anti-angiogenic activity of magnolol may be associated with ROS-mediated apoptosis and the suppression of the PI3K/AKT/mTOR signaling pathway in mES/EB-derived endothelial-like cells.

CoCl2 induces apoptosis through the mitochondria- and death receptor-mediated pathway in the mouse embryonic stem cells

Embryonic hypoxia/ischemia is a major cause of a poor fetal outcome and future neonatal and adult handicaps. However, biochemical cellular events in mouse embryonic stem (mES) cells during hypoxia remains unclear. This study investigated the underlying mechanism of apoptosis in mES cells under CoCl2-induced hypoxic/ischemic conditions. CoCl2 enhanced the expression of hypoxia-inducible factor-1α (HIF-1α) and the accumulation of reactive oxygen species in mES cells. The CoCl2-treated mES cells showed a decrease in cell viability as well as typical apoptotic changes, cell shrinkage, chromatin condensation, and nuclear fragmentation and an extended G2/M phase of the cell cycle. CoCl2 augmented the release of cytochrome c into the cytosol from the mitochondria with a concomitant loss of the mitochondrial transmembrane potential (ΔΨm) and upregulated the voltage-dependent anion channel. In addition, CoCl2-induced caspase-3, -8, and -9 activation and upregulation of p53 level, whereas downregulated Bcl-2 and Bcl-xL, a member of the anti-apoptotic Bcl-2 family in mES cells. Furthermore, CoCl2 led to the upregulation of Fas and Fas-ligand, which are the death receptor assemblies, as well as the cleavage of Bid in mES cells. These results suggest that CoCl2 induces apoptosis through both mitochondria- and death receptor-mediated pathways that are regulated by the Bcl-2 family in mES cells.

Cellular retinoic acid binding protein I mediates rapid non-canonical activation of ERK1/2 by all-trans retinoic acid

All-trans retinoic acid (atRA), one of the active ingredients of vitamin A, exerts canonical activities to regulate gene expression mediated by nuclear RA receptors (RARs). AtRA could also elicit certain non-canonical activities including, mostly, rapid activation of extracellular signal regulated kinase 1/2 (ERK1/2); but the mechanism was unclear. In this study, we have found that cellular retinoic acid binding protein I (CRABPI) mediates the non-canonical, RAR- and membrane signal-independent activation of ERK1/2 by atRA in various cellular backgrounds. In the context of embryonic stem cells (ESCs), atRA/CRABPI-dependent ERK1/2 activation rapidly affects ESC cell cycle, specifically to expand the G1 phase. This is mediated by ERK stimulation resulting in dephosphorylation of nuclear p27, which elevates nuclear p27 protein levels to block G1 progression to S phase. This is the first study to identify CRABPI as the mediator for non-canonical activation of ERK1/2 by atRA, and demonstrate a new functional role for CRABPI in modulating ESC cell cycle progression.

Regulatory roles of ganglioside GQ1b in neuronal cell differentiation of mouse embryonic stem cells

Gangliosides play an important role in neuronal differentiation processes. The regulation of ganglioside levels is related to the induction of neuronal cell differentiation. In this study, the ST8Sia5 gene was transfected into mESCs and then differentiated into neuronal cells. Interestingly, ST8Sia5 gene transfected mESCs expressed GQ1b by HPTLC and immunofluorescence analysis. To investigate the effects of GQ1b over-expression in neurogenesis, neuronal cells were differentiated from GQ1b expressing mESCs in the presence of retinoic acid. In GQ1b expressing mESCs, increased EBs formation was observed. After 4 days, EBs were co-localized with GQ1b and nestin, and GFAP. Moreover, GQ1b co-localized with MAP-2 expressing cells in GQ1b expressing mESCs in 7-day-old EBs. Furthermore, GQ1b expressing mESCs increased the ERK1/2 MAP kinase pathway. These results suggest that the ST8Sia5 gene increases ganglioside GQ1b and improves neuronal differentiation via the ERK1/2 MAP kinase pathway.

P2Y1 and P2Y13 purinergic receptors mediate Ca2+ signaling and proliferative responses in pulmonary artery vasa vasorum endothelial cells

Extracellular ATP and ADP have been shown to exhibit potent angiogenic effects on pulmonary artery adventitial vasa vasorum endothelial cells (VVEC). However, the molecular signaling mechanisms of extracellular nucleotide-mediated angiogenesis remain not fully elucidated. Since elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) is required for cell proliferation and occurs in response to extracellular nucleotides, this study was undertaken to delineate the purinergic receptor subtypes involved in Ca(2+) signaling and extracellular nucleotide-mediated mitogenic responses in VVEC. Our data indicate that stimulation of VVEC with extracellular ATP resulted in the elevation of [Ca(2+)](i) via Ca(2+) influx through plasma membrane channels as well as Ca(2+) mobilization from intracellular stores. Moreover, extracellular ATP induced simultaneous Ca(2+) responses in both cytosolic and nuclear compartments. An increase in [Ca(2+)](i) was observed in response to a wide range of purinergic receptor agonists, including ATP, ADP, ATPγS, ADPβS, UTP, UDP, 2-methylthio-ATP (MeSATP), 2-methylthio-ADP (MeSADP), and BzATP, but not adenosine, AMP, diadenosine tetraphosphate, αβMeATP, and βγMeATP. Using RT-PCR, we identified mRNA for the P2Y1, P2Y2, P2Y4, P2Y13, P2Y14, P2X2, P2X5, P2X7, A1, A2b, and A3 purinergic receptors in VVEC. Preincubation of VVEC with the P2Y1 selective antagonist MRS2179 and the P2Y13 selective antagonist MRS2211, as well as with pertussis toxin, attenuated at varying degrees agonist-induced intracellular Ca(2+) responses and activation of ERK1/2, Akt, and S6 ribosomal protein, indicating that P2Y1 and P2Y13 receptors play a major role in VVEC growth responses. Considering the broad physiological implications of purinergic signaling in the regulation of angiogenesis and vascular homeostasis, our findings suggest that P2Y1 and P2Y13 receptors may represent novel and specific targets for treatment of pathological vascular remodeling involving vasa vasorum expansion.

Nonmitogenic survival-enhancing autocrine factors including cyclophilin A contribute to density-dependent mouse embryonic stem cell growth

An improved understanding of the role of extracellular factors in controlling the embryonic stem cell (ESC) phenotype will aid the development of cell-based therapies. While the role of extracellular factors in controlling the pluripotency and differentiation of embryonic stem cells (ESCs) has been the subject of much investigation, the identity and role of extrinsic factors in modulating ESC growth under conditions supporting self-renewal remain largely unknown. We demonstrate that mouse ESC (mESC) growth is density dependent and that one of the mechanisms underlying this phenomenon is the action of survival-enhancing autocrine factors. Proteomic analysis of proteins secreted by mouse ESCs demonstrates significant levels of cyclophilin A which increases the growth rate of mouse ESCs in a dose-dependent manner. Additionally, inhibition of the cyclophilin A receptor CD147 decreases the growth rate of mESCs. These findings identify cyclophilin A as a novel survival-enhancing autocrine factor in mouse ESC cultures.

Ginsenosides promote proliferation of granulosa cells from chicken prehierarchical follicles through PKC activation and up-regulated cyclin gene expression

The effect of GS (ginsenosides) on proliferation of chicken GCs (granulosa cells) from prehierarchical SYF (small yellow follicles) was evaluated, and involvement of the PKC (protein kinase C) signalling pathway as well as mRNA expression of cyclins and CDK (cyclin-dependent kinase) were investigated. Whole SYF or GCs isolated from SYF were cultured in Medium 199 supplemented with 0.5% FCS (fetal calf serum). After 16 h, the cells were challenged with GS alone or in combination with PKC inhibitor H7 or activator PMA (phorbol 12-myristate 13-acetate) for 24 h in serum-free medium. Results showed that in both whole follicles and pure GCs monolayer culture system, GS (0.1-10 microg/ml) significantly increased the number of GCs in SYF in a dose-dependent manner, and this stimulatory effect was inhibited by H7, but enhanced by PMA. Meanwhile, the PCNA-LI (proliferating cell nuclear antigen labelling index) of GCs displayed similar changes with the cell number. Mechanism of GS action was further evaluated in cultured GCs separated from SYF. Western blot analysis showed that 10 microg/ml GS increased PKC translocation from cytoplasm to the plasma membrane of the GCs to become the active state. This effect was blocked by H7. Furthermore, GS up-regulated the expression of cyclin D1/CDK6 and cyclin E/CDK2 mRNAs in GCs; however, inhibition of PKC with H7 attenuated this stimulatory effect. These results indicated that GS could stimulate proliferation of chicken GCs through activated PKC-involved up-regulation of cyclin D1/CDK6 and cyclin E/CDK2 genes, subsequently promoting development of the chicken prehierarchical follicles.

The roles of glycosphingolipids in the proliferation and neural differentiation of mouse embryonic stem cells

Glycosphingolipids including gangliosides play important regulatory roles in cell proliferation and differentiation. UDP-glucose:ceramide glucosyltransferase (Ugcg) catalyze the initial step in glycosphingolipids biosynthesis pathway. In this study, Ugcg expression was reduced to approximately 80% by short hairpin RNAs (shRNAs) to evaluate the roles of glycosphingolipids in proliferation and neural differentiation of mouse embryonic stem cells (mESCs). HPTLC/immunofluorescence analyses of shRNA- transfected mESCs revealed that treatment with Ugcg-shRNA decreased expression of major gangliosides, GM3 and GD3. Furthermore, MTT and Western blot/immunofluorescence analyses demonstrated that inhibition of the Ugcg expression in mESCs resulted in decrease of cell proliferation (P<0.05) and decrease of activation of the ERK1/2 (P<0.05), respectively. To further investigate the role of glycosphingolipids in neural differentiation, the embryoid bodies formed from Ugcg-shRNA transfected mESCs were differentiated into neural cells by treatment with retinoic acid. We found that inhibition of Ugcg expression did not affect embryoid body (EB) differentiation, as judged by morphological comparison and expression of early neural precursor cell marker, nestin, in differentiated EBs. However, RT-PCR/immunofluorescence analyses showed that expression of microtubule-associated protein 2 (MAP-2) for neurons and glial fibrillary acidic protein (GFAP) for glial cells was decreased in neural cells differentiated from the shRNA-transfected mESCs. These results suggest that glycosphingolipids are involved in the proliferation of mESCs through ERK1/2 activation, and that glycosphingolipids play roles in differentiation of neural precursor cells derived from mESCs.

Influence of spontaneous calcium events on cell-cycle progression in embryonal carcinoma and adult stem cells

Spontaneous Ca(2+) events have been observed in diverse stem cell lines, including carcinoma and mesenchymal stem cells. Interestingly, during cell cycle progression, cells exhibit Ca(2+) transients during the G(1) to S transition, suggesting that these oscillations may play a role in cell cycle progression. We aimed to study the influence of promoting and blocking calcium oscillations in cell proliferation and cell cycle progression, both in neural progenitor and undifferentiated cells. We also identified which calcium stores are required for maintaining these oscillations. Both in neural progenitor and undifferentiated cells calcium oscillations were restricted to the G1/S transition, suggesting a role for these events in progression of the cell cycle. Maintenance of the oscillations required calcium influx only through inositol 1,4,5-triphosphate receptors (IP(3)Rs) and L-type channels in undifferentiated cells, while neural progenitor cells also utilized ryanodine-sensitive stores. Interestingly, promoting calcium oscillations through IP(3)R agonists increased both proliferation and levels of cell cycle regulators such as cyclins A and E. Conversely, blocking calcium events with IP(3)R antagonists had the opposite effect in both undifferentiated and neural progenitor cells. This suggests that calcium events created by IP(3)Rs may be involved in cell cycle progression and proliferation, possibly due to regulation of cyclin levels, both in undifferentiated cells and in neural progenitor cells.

Caveolin-1 plays important role in EGF-induced migration and proliferation of mouse embryonic stem cells: involvement of PI3K/Akt and ERK

The involvement of caveolin-1 in the regulation of embryonic stem (ES) cell growth by epidermal growth factor (EGF) is by no means clear cut. Thus we examined the relationship between EGF and caveolin-1 in mouse ES cell migration and proliferation. The results revealed that EGF increased Src, caveolin-1, focal adhesion kinase (FAK), Akt, and extracellular signal-regulated kinase-1/2 (ERK) phosphorylation levels. Especially, phosphorylation of caveolin-1 is attenuated by AG1478, herbimycin A (tyrosine kinase inhibitors), and pyrazolopyrimidine 2 (PP2, Src inhibitor) and EGF-induced ERK activation was blocked by PP2, methyl-β-cyclodextrin (MβCD), caveolin-1 small interfering RNA (siRNA), LY-294002 [phosphoinositol-3 kinase inhibitor (PI3K)], and Akt inhibitor. In addition, EGF promoted the cell migration, which was attenuated by PP2, caveolin-1 siRNA, FAK siRNA, LY-294002, Akt inhibitor, and PD-98059. EGF also increased matrix metalloproteinase (MMP-2) expression levels and EGF-induced MMP2 expression was inhibited by caveolin-1 siRNA, FAK siRNA, LY-294002, Akt inhibitor, and PD-98059. Furthermore, EGF-induced increase of cell cycle proteins expression level and [3H]thymidine incorporation was blocked by MMP inhibitor. EGF also significantly increases [3H]thymidine incorporation and cell number, which were significantly blocked by AG 1478, PP2, MβCD, caveolin-1 siRNA, FAK siRNA, LY-294002, and PD-98059 (ERK inhibitor). EGF-induced increase of protooncogenes (c- fos, c- myc, and c- Jun) and cell cycle regulatory proteins (cyclin D1, CDK4, cyclin E, and CDK2) expression levels were also attenuated by caveolin-1 siRNA and FAK siRNA. In conclusion, these results demonstrated that EGF-induced DNA synthesis and cell migration are mediated by caveolin-1, which is activated by Src, FAK, PI3K/Akt, ERK, and MMP-2 signals in mouse ES cells.

BNP signaling is crucial for embryonic stem cell proliferation

Background

Embryonic stem (ES) cells have unlimited proliferation potential, and can differentiate into several cell types, which represent ideal sources for cell-based therapy. This high-level proliferative ability is attributed to an unusual type of cell cycle. The Signaling pathways that regulate the proliferation of ES cells are of great interest.

Methodology/Principal Findings

In this study, we show that murine ES cells specifically express brain natriuretic peptide (BNP), and its signaling is essential for ES cell proliferation. We found that BNP and its receptor (NPR-A, natriuretic peptide receptor-A) were highly expressed in self-renewing murine ES cells, whereas the levels were markedly reduced after ES cell differentiation by the withdrawal of LIF. Targeting of BNP with short interfering RNA (siRNA) resulted in the inhibition of ES cell proliferation, as indicated by a marked reduction in the cell number and colony size, a significant reduction in DNA synthesis, and decreased numbers of cells in S phase. BNP knockdown in ES cells led to the up-regulation of gamma-aminobutyric acid receptor A (GABA_AR) genes, and activation of phosphorylated histone (γ-H2AX), which negatively affects ES cell proliferation. In addition, knockdown of BNP increased the rate of apoptosis and reduced the expression of the transcription factor Ets-1.

Conclusions/Significance

Appropriate BNP expression is essential for the maintenance of ES cell propagation. These findings establish BNP as a novel endogenous regulator of ES cell proliferation.

Effect of low-level laser irradiation and epidermal growth factor on adult human adipose-derived stem cells

The study investigated the effects of low-level laser radiation and epidermal growth factor (EGF) on adult adipose-derived stem cells (ADSCs) isolated from human adipose tissue. Isolated cells were cultured to semi-confluence, and the monolayers of ADSCs were exposed to low-level laser at 5 J/cm(2) using 636 nm diode laser. Cell viability and proliferation were monitored using adenosine triphosphate (ATP) luminescence and optical density at 0 h, 24 h and 48 h after irradiation. Application of low-level laser irradiation at 5 J/cm(2) on human ADSCs cultured with EGF increased the viability and proliferation of these cells. The results indicate that low-level laser irradiation in combination with EGF enhances the proliferation and maintenance of ADSCs in vitro.

Induction of pluripotent stem cells from mouse embryonic fibroblasts by Oct4 and Klf4 with small-molecule compounds

Somatic cells can be induced into pluripotent stem cells (iPSCs) with a combination of four transcription factors, Oct4/Sox2/Klf4/c-Myc or Oct4/Sox2/Nanog/LIN28. This provides an enabling platform to obtain patient-specific cells for various therapeutic and research applications. However, several problems remain for this approach to be therapeutically relevant due to drawbacks associated with efficiency and viral genome integration. Recently, it was shown that neural progenitor cells (NPCs) transduced with Oct4/Klf4 can be reprogrammed into iPSCs. However, NPCs express Sox2 endogenously, possibly facilitating reprogramming in the absence of exogenous Sox2. In this study, we identified a small-molecule combination, BIX-01294 and BayK8644, that enables reprogramming of Oct4/Klf4-transduced mouse embryonic fibroblasts, which do not endogenously express the factors essential for reprogramming. This study demonstrates that small molecules identified through a phenotypic screen can compensate for viral transduction of critical factors, such as Sox2, and improve reprogramming efficiency.

Virulence factors of Staphylococcus aureus induce Erk-MAP kinase activation and c-Fos expression in S9 and 16HBE14o- human airway epithelial cells

Part of the innate defense of bronchial epithelia against bacterial colonization is regulated secretion of salt, water, and mucus as well as defensins and cytokines involving MAP kinase activation and alterations in early gene expression. We tested two different types of immortalized human airway epithelial cells (S9, 16HBE14o-) for activation of Erk-type MAP kinases and for expression of c-Fos on treatment with Staphylococcus aureus culture supernatants from the stationary growth phase [optical density (OD)(540 nm) = 10] or with recombinant S. aureus hemolysins A and B (Hla, Hlb). OD10 supernatants activated Erk-type MAP kinases and c-Fos expression in a concentration-dependent manner. Hla induced Erk-type kinase phosphorylation in S9 but not in 16HBE14o- cells. Hlb induced Erk activation in either cell type. Basal and stimulated levels of Erk-type MAP kinase phosphorylation were sensitive to the Mek1 inhibitor PD-98059, indicating that the bacterial products activated the entire signaling cascade that coregulates IL-8 induction and secretion. While c-Fos expression was enhanced by OD10 supernatants, Hla, and Hlb in S9 cells, 16HBE14o- cells responded to OD10 supernatant and Hlb but not to Hla. In S9 cells, PD-98059 suppressed c-Fos upregulation by OD10 supernatant, Hla, or Hlb, indicating that c-Fos expression requires activation of Erk-type MAP kinases. In 16HBE14o- cells, however, c-Fos expression by OD10 supernatant was sensitive to PD-98059, while that induced by Hlb was not. This indicates that ingredients of OD10 supernatants other than Hla or Hlb are activating Erk-type MAP kinases in 16HBE14o- cells and that other intracellular signaling systems apart from Erk-type MAP kinases contribute to Hlb-mediated regulation of c-Fos. Thus interaction of bacterial factors with airway epithelial cells may be highly cell type specific.

Effect of dihydrotestosterone on mouse embryonic stem cells exposed to H2O2-induced oxidative stress

Oxidative stresses induced by reactive oxygen species (ROS) have been shown to be involved in several physiological and pathophysiological processes, such as cell proliferation and differentiation. Steroid hormones can protect cells against apoptosis or induce cell proliferation by several mechanisms. Among androgenic hormones, dihydrotestosterone (DHT) is generated by a 5alpha- reduction of testosterone. Unlike testosterone, DHT cannot be aromatized to estradiol, therefore DHT is considered a pure androgenic steroid. This study was conducted to examine the effect of DHT (10(-7) M) on H2O2 (10(-3) M) -induced injuries in mouse embryonic stem (ES) cells. H2O2 induced ROS generation and increased lipid peroxide formation and DNA fragmentation. These effects of H2O2 were inhibited by pretreatment with DHT. H2O2 also increased the phosphorylation of p38 MAPK, SAPK/JNK and nuclear factor kappa B (NF-kappaB), but DHT blocked these effects. Moreover, H2O2 decreased DNA synthesis and the levels of cell cycle regulatory proteins [cyclin D1, cyclin E, cyclin-dependent kinase (CDK) 2, and CDK 4]. These effects of H2O2 were inhibited by pretreatment with DHT. In conclusion, DHT may partially prevent H2O2-induced cell injury through inhibition of ROS and ROS-induced activation of p38 MAPK, SAPK/JNK and NF-kappaB in mouse ES cells.

Epidermal growth factor-induced proliferation of chicken primordial germ cells: involvement of calcium/protein kinase C and NFKB1

Epidermal growth factor (EGF) has been shown to stimulate survival in diverse cells in vitro. In the present study, the effects of EGF and the EGF-related signaling pathway on proliferation of chicken primordial germ cells (PGCs) were investigated. Results showed that EGF (10-100 ng/ml) increased the number and area of PGC colonies in a time- and dose-dependent manner. EGF also activated PKC, a process that was inhibited by AG1478 (an EGFR tyrosine kinase inhibitor) and ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA; an intracellular Ca(2+) chelator). In addition, the degradation of NFKBIA and NFKB1 (p65) translocation was observed after EGF treatment, which was significantly blocked by pretreatment with AG1478, EGTA, H(7), or SN50 (NFKB1-specific inhibitor). Furthermore, we found that EGF-induced cell proliferation was significantly attenuated by AG1478, EGTA, H(7), and SN50, respectively. On the other hand, inhibition of EGFR, Ca(2+)/PKC, or NFKB1 abolished the EGF-stimulated increase in the expression of cyclins CCND1 and CCNE1, cyclin-dependent kinase 6 (CDK6), CDK2, and BCL2, and restored the EGF-induced inhibition of BAX expression and caspase 3/9 activity, indicating that EGFR, PKC, and NFKB1 signaling cascades were involved in EGF-stimulated DNA synthesis and antiapoptosis action. In conclusion, EGF stimulated proliferation of chicken PGCs via activation of Ca(2+)/PKC involving NFKB1 signaling pathway. These observations suggest that EGF signaling is important in regulating germ cell proliferation in the chicken embryonic gonad.

Role of HIF-1alpha and VEGF in human mesenchymal stem cell proliferation by 17beta-estradiol: involvement of PKC, PI3K/Akt, and MAPKs

17beta-Estradiol (E(2)) is a steroid hormone well known for its roles in the regulation of various cell functions. However, the precise role that E(2) plays in the proliferation of human mesenchymal stem cells (hMSCs) has not been completely elucidated. In the present study, we examined the effects of E(2) on cell proliferation and the related signaling pathways using hMSCs. We showed that E(2), at > or =10(-9) M, significantly increased [3H]thymidine incorporation after 24 h of incubation, and E(2) also increased [3H]thymidine incorporation at >6 h. Also, E(2) significantly increased the percentage of the cell population in the S phase based on FACS analysis. Moreover, E(2) increased estrogen receptor (ER), PKC, phosphatidylinositol 3-kinase (PI3K)/Akt, and MAPK phosphorylation. Subsequently, these signaling molecules were involved in an E(2)-induced increase of [3H]thymidine incorporation. E(2) also increased hypoxia-inducible factor (HIF)-1alpha and VEGF protein levels. These levels of protein expression were inhibited by ICI-182,780 (10(-6) M, an ER antagonist), staurosporine and bisindolylmaleimide I (10(-6) M, a PKC inhibitor), LY-294002 (10(-6) M, a PI3K inhibitor), Akt inhibitor (10(-5) M), SP-600125 (10(-6) M, a SAPK/JNK inhibitor), and PD-98059 (10(-5) M, a p44/42 MAPKs inhibitor). In addition, HIF-1alpha small interfering (si)RNA and ICI-182,780 inhibited E(2)-induced VEGF expression and cell proliferation. VEGF siRNA also significantly inhibited E(2)-induced cell proliferation. In conclusion, E(2) partially stimulated hMSC proliferation via HIF-1alpha activation and VEGF expression through PKC, PI3K/Akt, and MAPK pathways.