A potential role of connexin 43 in epidermal growth factor-induced proliferation of mouse embryonic stem cells: involvement of Ca2+/PKC, p44/42 and p38 MAPKs pathways

Betacellulin regulates gap junction intercellular communication by inducing the phosphorylation of connexin 43 in human granulosa-lutein cells

BACKGROUND

The gap junction protein, connexin 43 (Cx43) is highly expressed in human granulosa-lutein (hGL) cells. The phosphorylation of certain amino acid residues in the Cx43 protein has been shown to be related to a decline in gap junction intercellular communication (GJIC), which subsequently affects oocyte meiotic resumption. As a member of the epidermal growth factor (EGF) family, betacellulin (BTC) mediates luteinizing hormone (LH)-induced oocyte maturation and cumulus cell expansion in mammalian follicles. Whether BTC can regulate Cx43 phosphorylation, which further reduces Cx43-coupled GJIC activity in hGL cells remains to be determined.

METHODS

Immortalized human granulosa cells (SVOG cells) and primary human granulosa-lutein cells obtained from women undergoing in vitro fertilization in an academic research center were used as the study models. The expression levels of Cx43 and phosphorylated Cx43 were examined following cell incubation with BTC at different time points. Several kinase inhibitors (sotrastaurin, AG1478, and U0126) and small interfering RNAs targeting EGF receptor (EGFR) and receptor tyrosine-protein kinase 4 (ErbB4) were used to verify the specificity of the effects and to investigate the molecular mechanisms. Real-time-quantitative PCR and western blot analysis were used to detect the specific mRNA and protein levels, respectively. GJIC between SVOG cells were evaluated using a scrape loading and dye transfer assay. Results were analyzed by one-way analysis of variance.

RESULTS

The results showed that BTC induced the rapid phosphorylation of Cx43 at serine368 without altering the expression of Cx43 in primary and immortalized hGL cells. Additionally, using a dual inhibition approach (kinase inhibitors and siRNA-based expression knockdown), we demonstrated that this effect was mainly mediated by the EGFR but not the ErbB4 receptor. Furthermore, using a protein kinase C (PKC) kinase assay and a scrape-loading and dye transfer assay, we revealed that PKC signaling is the downstream signaling pathway that mediates the increase in Cx43 phosphorylation and subsequent decrease in GJIC activity in response to BTC treatment in hGL cells.

CONCLUSIONS

BTC promptly induced the phosphorylation of connexin 43 at Ser368, leading to decreased GJIC activity in hGL cells. The BTC-induced cellular activities were most likely driven by the EGFR-mediated PKC-dependent signaling pathway. Our findings shed light on the detailed molecular mechanisms by which BTC regulates the process of oocyte meiotic resumption.

Arteannuin B Enhances the Effectiveness of Cisplatin in Non-Small Cell Lung Cancer by Regulating Connexin 43 and MAPK Pathway

Cisplatin (DDP)-based chemotherapy is the first-line regimen for advanced non-small cell lung cancer (NSCLC) patients. However, advanced NSCLC patients may have innate resistance to DDP or develop resistance during DDP treatment. We investigated a natural compound, arteannuin B (Art B), for its potential effects on DDP resistance in NSCLC. Art B was isolated from Artemisia annua by chromatographic purification and spectral elucidation. The activities of Art B on DDP-mediated effects were examined using in vitro and in vivo assays. We observed significant correlations in T stage, clinical stage, chemotherapy resistance and poor survival of NSCLC patients with low Cx43 expression. Art B enhanced the effectiveness of cisplatin by increasing Cx43 expression in normal and DDP-resistant NSCLC cells. Art B also increased DDP uptake through up-regulating Cx43. The combination of DDP and Art B showed better therapeutic effect than individual treatments both in vitro and in vivo. Art B increased intracellular Fe[Formula: see text] level, promoted calcium influx, and activated gap junction and MAPK pathways, which might contribute to Art B-mediated effects. Art B may serve as a new drug candidate to enhance the antitumor effect of DDP on NSCLC.

The Role of Connexin in Ophthalmic Neovascularization and the Interaction between Connexin and Proangiogenic Factors

The formation of new blood vessels is an important physiological process that occurs during development. When the body is injured, new blood vessel formation helps the body recuperate by supplying more oxygen and nutrients. However, this mechanism can have a negative effect. In ophthalmologic diseases, such as corneal new blood vessels, neonatal vascular glaucoma, and diabetes retinopathy, the formation of new blood vessels has become a critical component in patient survival. Connexin is a protein that regulates the cellular and molecular material carried by cells. It has been demonstrated that it is widely expressed in vascular endothelial cells, where it forms a slit connection between adjacent cells to promote cell-cell communication via hemichannels, as well as substance exchange into intracellular environments. Numerous studies have demonstrated that connexin in vascular endothelial cells plays an important role in angiogenesis and vascular leakage. The purpose of this study was to investigate the effect between the angiogenesis-associated factor and the connexin. It also reveals the effect of connexin on ophthalmic neovascularization.

Cx43 overexpression is involved in the hyper-proliferation effect of trichloroethylene on human embryonic stem cells

Trichloroethylene (TCE) is a major environmental contaminant. Maternal exposure of TCE is linked to developmental defects, but the mechanisms remain to be elucidated. Along with a strategy of 3Rs principle, human embryonic stem cells (hESCs) are regarded as most promising in vitro models for developmental toxicity studies. TCE interfered with hESCs differentiation, but no report was available for TCE effects on hESCs proliferation. Here, we aimed to explore the toxic effects and mechanisms of TCE on hESCs proliferation. Treatment with TCE, did not affect the pluripotency genes expression. However, TCE enhanced hESCs proliferation, manifested by increased cell number, PCNA expression and EdU incorporation. Moreover, TCE exposure upregulated the protein expression levels of Cx43 and cyclin-dependent kinases. Knockdown of Cx43 attenuated the TCE-induced cell hyper-proliferation and CDK2 upregulation. Furthermore, TCE increased Akt phosphorylation, and the inhibition of Akt blocked the TCE-induced Cx43 overexpression and cell proliferation. In conclusion, TCE exposure resulted in upregulation of Cx43 via Akt phosphorylation, consequently stimulated CDK2 expression, contributing to hyper-proliferation in hESCs. Our study brings to light that TCE stimulated the proliferation of hESCs via Cx43, providing a new research avenue for the causes of TCE-induced developmental toxicity.

How does Helicobacter pylori cause gastric cancer through connexins: An opinion review

Helicobacter pylori (H. pylori) is a Gram-negative bacterium with a number of virulence factors, such as cytotoxin-associated gene A, vacuolating cytotoxin A, its pathogenicity island, and lipopolysaccharide, which cause gastrointestinal diseases. Connexins function in gap junctional homeostasis, and their downregulation is closely related to gastric carcinogenesis. Investigations into H. pylori infection and the fine-tuning of connexins in cells or tissues have been reported in previous studies. Therefore, in this review, the potential mechanisms of H. pylori-induced gastric cancer through connexins are summarized in detail.

Role of connexin 43 in cadmium-induced proliferation of human prostate epithelial cells

Connexins (Cxs), the subunits of gap junction channels, are involved in many physiological processes. Aberrant control of Cxs and gap junction intercellular communication may contribute to many diseases, including the promotion of cancer. Cd exposure is associated with increased risk of human prostate cancer and benign prostatic hyperplasia. The roles of Cxs in the effects of Cd on the prostate have, however, not been reported previously. In this study, the human prostate epithelial cell line RWPE-1 was exposed to Cd. A low dose of Cd stimulated cell proliferation along with a lower degree of gap junction intercellular communication and an elevated level of the protein Cx43. Cd exposure increased the levels of intracellular Ca²⁺ and phosphorylated Cx43 at the Ser368 site. Knockdown of Cx43 using siRNA blocked Cd-induced proliferation and interfered with the Cd-induced changes in the protein levels of cyclin D1, cyclin B1, p27^Kip1 (p27) and p21^Waf1/Cip1 (p21). The increase in Cx43 expression induced by Cd was presumably mediated by the androgen receptor, because it was abolished upon treatment with the androgen receptor antagonist, flutamide. Thus, a low dose of Cd promotes cell proliferation in RWPE-1, possibly mediated by Cx43 expression through an effect on cell cycle-associated proteins. Cx43 might be a target for prostatic diseases associated with Cd exposure. Copyright © 2017 John Wiley & Sons, Ltd.

The role of Ca(2+) signaling on the self-renewal and neural differentiation of embryonic stem cells (ESCs)

Embryonic stem cells (ESCs) are promising resources for both scientific research and clinical regenerative medicine. With regards to the latter, ESCs are especially useful for treating several neurodegenerative disorders. Two significant characteristics of ESCs, which make them so valuable, are their capacity for self-renewal and their pluripotency, both of which are regulated by the integration of various signaling pathways. Intracellular Ca(2+) signaling is involved in several of these pathways. It is known to be precisely controlled by different Ca(2+) channels and pumps, which play an important role in a variety of cellular activities, including proliferation, differentiation and apoptosis. Here, we provide a review of the recent work conducted to investigate the function of Ca(2+) signaling in the self-renewal and the neural differentiation of ESCs. Specifically, we describe the role of intracellular Ca(2+) mobilization mediated by RyRs (ryanodine receptors); by cADPR (cyclic adenosine 5'-diphosphate ribose) and CD38 (cluster of differentiation 38/cADPR hydrolase); and by NAADP (nicotinic acid adenine dinucleotide phosphate) and TPC2 (two pore channel 2). We also discuss the Ca(2+) influx mediated by SOCs (store-operated Ca(2+) channels), TRPCs (transient receptor potential cation channels) and LTCC (L-type Ca(2+) channels) in the pluripotent ESCs as well as in neural differentiation of ESCs. Moreover, we describe the integration of Ca(2+) signaling in the other signaling pathways that are known to regulate the fate of ESCs.

The Roles of p21(Waf1/CIP1) and Hus1 in Generation and Transmission of Damage Signals Stimulated by Low-Dose Alpha-Particle Irradiation

Previously reported studies have demonstrated the involvement of p21(Waf1/CIP1) in radiation-induced bystander effects (RIBE). Mouse embryonic fibroblasts (MEFs) lacking Hus1 fail to proliferate in vitro, but inactivation of p21 allows for the continued growth of Hus1-deficient cells, indicating the close connection between p21 and Hus1 cells. In this study, wild-type MEFs, Hus1(+/+)p21(-/-) MEFs and p21(-/-)Hus1(-/-) MEFs were used in a series of radiation-induced bystander effect experiments, the roles of p21 and Hus1 in the induction and transmission of radiation-induced damage signals were investigated. Our results showed that after 5 cGy α particle irradiation, wild-type MEFs induced significant increases in γ-H2AX foci and micronuclei formation in bystander cells, whereas the bystander effects were not detectable in p21(-/-)Hus1(+/+) MEFs and were restored again in p21(-/-)Hus1(-/-) MEFs. Media transfer experiments showed that p21(-/-)Hus1(+/+) MEFs were deficient in the production bystander signals, but could respond to bystander signals. We further investigated the mitogen-activated protein kinases (MAPKs) that might be involved in the bystander effects. It was found that although knocking out p21 did not affect the expression of connexin43 and its phosphorylation, it did result in inactivation of some MAPK signal pathway kinases, including JNK1/2, ERK1/2 and p38, as well as a decrease in reactive oxygen species (ROS) levels in irradiated cells. However, the activation of MAPK kinases and the ROS levels in irradiated cells were restored in the cell line by knocking out Hus1. These results suggest that p21(Waf1/CIP1) and Hus1 play crucial roles in the generation and transmission of bystander damage signals after low-dose α-particle irradiation.

Temozolomide resistance in glioblastoma cells occurs partly through epidermal growth factor receptor-mediated induction of connexin 43

Glioblastoma Multiforme (GBM) is an aggressive adult primary brain tumor with poor prognosis. GBM patients develop resistance to the frontline chemotherapy, temozolomide (TMZ). As the connexins (Cx) have been shown to have a complex role in GBM, we investigated the role of Cx43 in TMZ resistance. Cx43 was increased in the TMZ-resistant low passage and cell lines. This correlated with the data in The Cancer Genome Atlas. Cx43 knockdown, reporter gene assays, chromatin immunoprecipitation assay, real-time PCR and western blots verified a role for Cx43 in TMZ resistance. This occurred by TMZ-resistant GBM cells being able to activate epidermal growth factor receptor (EGFR). In turn, EGFR activated the JNK-ERK1/2-AP-1 axis to induce Cx43. The increased Cx43 was functional as indicated by gap junctional intercellular communication among the resistant GBM cells. Cell therapy could be a potential method to deliver drugs, such as anti-EGF to tumor cells. Similar strategies could be used to reverse the expression of Cx43 to sensitize GBM cells to TMZ. The studies showed the potential for targeting EGF in immune therapy. These agents can be used in conjunction with stem cell therapy to treat GBM.

EGF induces efficient Cx43 gap junction endocytosis in mouse embryonic stem cell colonies via phosphorylation of Ser262, Ser279/282, and Ser368

Gap junctions (GJs) traverse apposing membranes of neighboring cells to mediate intercellular communication by passive diffusion of signaling molecules. We have shown previously that cells endocytose GJs utilizing the clathrin machinery. Endocytosis generates cytoplasmic double-membrane vesicles termed annular gap junctions or connexosomes. However, the signaling pathways and protein modifications that trigger GJ endocytosis are largely unknown. Treating mouse embryonic stem cell colonies - endogenously expressing the GJ protein connexin43 (Cx43) - with epidermal growth factor (EGF) inhibited intercellular communication by 64% and activated both, MAPK and PKC signaling cascades to phosphorylate Cx43 on serines 262, 279/282, and 368. Upon EGF treatment Cx43 phosphorylation transiently increased up to 4-fold and induced efficient (66.4%) GJ endocytosis as evidenced by a 5.9-fold increase in Cx43/clathrin co-precipitation.

Electric stimulus opens intercellular spaces in skin

Iontophoresis is a technology for transdermal delivery of ionic small medicines by faint electricity. Since iontophoresis can noninvasively deliver charged molecules into the skin, this technology could be a useful administration method that may enhance patient comfort. Previously, we succeeded in the transdermal penetration of positively charged liposomes (diameters: 200-400 nm) encapsulating insulin by iontophoresis (Kajimoto, K., Yamamoto, M., Watanabe, M., Kigasawa, K., Kanamura, K., Harashima, H., and Kogure, K. (2011) Int. J. Pharm. 403, 57-65). However, the mechanism by which these liposomes penetrated the skin was difficult to define based on general knowledge of principles such as electro-repulsion and electro-osmosis. In the present study, we confirmed that rigid nanoparticles could penetrate into the epidermis by iontophoresis. We further found that levels of the gap junction protein connexin 43 protein significantly decreased after faint electric stimulus (ES) treatment, although occludin, CLD-4, and ZO-1 levels were unchanged. Moreover, connexin 43 phosphorylation and filamentous actin depolymerization in vivo and in vitro were observed when permeation of charged liposomes through intercellular spaces was induced by ES. Ca(2+) inflow into cells was promoted by ES with charged liposomes, while a protein kinase C inhibitor prevented ES-induced permeation of macromolecules. Consequently, we demonstrate that ES treatment with charged liposomes induced dissociation of intercellular junctions via cell signaling pathways. These findings suggest that ES could be used to regulate skin physiology.

Ca²⁺-dependent nitric oxide release in the injured endothelium of excised rat aorta: a promising mechanism applying in vascular prosthetic devices in aging patients

Background

Nitric oxide is key to endothelial regeneration, but it is still unknown whether endothelial cell (EC) loss results in an increase in NO levels at the wound edge. We have already shown that endothelial damage induces a long-lasting Ca²⁺ entry into surviving cells though connexin hemichannels (CxHcs) uncoupled from their counterparts on ruptured cells. The physiological outcome of injury-induced Ca²⁺ inflow is, however, unknown.

Methods

In this study, we sought to determine whether and how endothelial scraping induces NO production (NOP) in the endothelium of excised rat aorta by exploiting the NO-sensitive fluorochrome, DAF-FM diacetate and the Ca²⁺-sensitive fluorescent dye, Fura-2/AM.

Results

We demonstrated that injury-induced NOP at the lesion site is prevented in presence of the endothelial NO synthase inhibitor, L-NAME, and in absence of extracellular Ca²⁺. Unlike ATP-dependent NO liberation, the NO response to injury is insensitive to BTP-2, which selectively blocks store-operated Ca²⁺ inflow. However, injury-induced NOP is significantly reduced by classic gap junction blockers, and by connexin mimetic peptides specifically targeting Cx37Hcs, Cx40HCs, and Cx43Hcs. Moreover, disruption of caveolar integrity prevents injury-elicited NO signaling, but not the accompanying Ca²⁺ response.

Conclusions

The data presented provide the first evidence that endothelial scraping stimulates NO synthesis at the wound edge, which might both exert an immediate anti-thrombotic and anti-inflammatory action and promote the subsequent re-endothelialization.

Store-operated Ca2+ entry is remodelled and controls in vitro angiogenesis in endothelial progenitor cells isolated from tumoral patients

BACKGROUND

Endothelial progenitor cells (EPCs) may be recruited from bone marrow to sustain tumor vascularisation and promote the metastatic switch. Understanding the molecular mechanisms driving EPC proliferation and tubulogenesis could outline novel targets for alternative anti-angiogenic treatments. Store-operated Ca(2+) entry (SOCE), which is activated by a depletion of the intracellular Ca(2+) pool, regulates the growth of human EPCs, where is mediated by the interaction between the endoplasmic reticulum Ca(2+)-sensor, Stim1, and the plasmalemmal Ca(2+) channel, Orai1. As oncogenesis may be associated to the capability of tumor cells to grow independently on Ca(2+) influx, it is important to assess whether SOCE regulates EPC-dependent angiogenesis also in tumor patients.

METHODOLOGY/PRINCIPAL FINDINGS

The present study employed Ca(2+) imaging, recombinant sub-membranal and mitochondrial aequorin, real-time polymerase chain reaction, gene silencing techniques and western blot analysis to investigate the expression and the role of SOCE in EPCs isolated from peripheral blood of patients affected by renal cellular carcinoma (RCC; RCC-EPCs) as compared to control EPCs (N-EPCs). SOCE, activated by either pharmacological (i.e. cyclopiazonic acid) or physiological (i.e. ATP) stimulation, was significantly higher in RCC-EPCs and was selectively sensitive to BTP-2, and to the trivalent cations, La(3+) and Gd(3+). Furthermore, 2-APB enhanced thapsigargin-evoked SOCE at low concentrations, whereas higher doses caused SOCE inhibition. Conversely, the anti-angiogenic drug, carboxyamidotriazole (CAI), blocked both SOCE and the intracellular Ca(2+) release. SOCE was associated to the over-expression of Orai1, Stim1, and transient receptor potential channel 1 (TRPC1) at both mRNA and protein level The intracellular Ca(2+) buffer, BAPTA, BTP-2, and CAI inhibited RCC-EPC proliferation and tubulogenesis. The genetic suppression of Stim1, Orai1, and TRPC1 blocked CPA-evoked SOCE in RCC-EPCs.

CONCLUSIONS

SOCE is remodelled in EPCs from RCC patients and stands out as a novel molecular target to interfere with RCC vascularisation due to its ability to control proliferation and tubulogenesis.

Cell-based therapy for prevention and reversal of myocardial remodeling

Although pharmacological and interventional advances have reduced the morbidity and mortality of ischemic heart disease, there is an ongoing need for novel therapeutic strategies that prevent or reverse progressive ventricular remodeling following myocardial infarction, the process that forms the substrate for ventricular failure. The development of cell-based therapy as a strategy to repair or regenerate injured tissue offers extraordinary promise for a powerful anti-remodeling therapy. In this regard, the field of cell therapy has made major advancements in the past decade. Accumulating data from preclinical studies have provided novel insights into stem cell engraftment, differentiation, and interactions with host cellular elements, as well as the effectiveness of various methods of cell delivery and accuracy of diverse imaging modalities to assess therapeutic efficacy. These findings have in turn guided rationally designed translational clinical investigations. Collectively, there is a growing understanding of the parameters that underlie successful cell-based approaches for improving heart structure and function in ischemic and other cardiomyopathies.

The E2F6 repressor activates gene expression in myocardium resulting in dilated cardiomyopathy

The E2F/Rb pathway regulates cardiac growth and development and holds great potential as a therapeutic target. The E2F6 repressor is a unique E2F member that acts independently of pocket proteins. Forced expression of E2F6 in mouse myocardium induced heart failure and mortality, with severity of symptoms correlating to E2F6 levels. Echocardiography demonstrated a 37% increase (P<0.05) in left ventricular end-diastolic diameter and reduced ejection fraction (<40%, P<0.05) in young transgenic (Tg) mice. Microarray and qPCR analysis revealed a paradoxical increase in E2F-responsive genes, which regulate the cell cycle, without changes in cardiomyocyte cell number or size in Tg mice. Young adult Tg mice displayed a 75% (P<0.01) decrease in gap junction protein connexin-43, resulting in abnormal electrocardiogram including a 24% (P<0.05) increase in PR interval. Further, mir-206, which targets connexin-43, was up-regulated 10-fold (P<0.05) in Tg myocardium. The mitogen-activated protein kinase pathway, which regulates the levels of miR-206 and connexin-43, was activated in Tg hearts. Thus, deregulated E2F6 levels evoked abnormal gene expression at transcriptional and post-transcriptional levels, leading to cardiac remodeling and dilated cardiomyopathy. The data highlight an unprecedented role for the strict regulation of the E2F pathway in normal postnatal cardiac function.

Laminin-111 stimulates proliferation of mouse embryonic stem cells through a reduction of gap junctional intercellular communication via RhoA-mediated Cx43 phosphorylation and dissociation of Cx43/ZO-1/drebrin complex

Gap junctions within extracellular matrix (ECM)-defined boundaries ensure synchronous activity between cells destined to become functional mediators that regulate cell behavior. However, the role of ECM in connexin (Cx) function in mouse embryonic stem cells (mESCs) has not been elucidated. Therefore, we examined the role of laminin-111 in the control of Cx43 functions and related signal pathways in mESCs. ECM components (laminin-111, fibronectin, and collagen I) increased Cx43 phosphorylation and decreased Lucifer yellow (Ly) diffusion. In addition, laminin-111 increased the proliferation index through reduction of gap junctional intercellular communication (GJIC), which was confirmed by 18α-glycyrrhetinic acid (18α-GA). Laminin-111 increased phosphorylation of focal adhesion kinase (FAK)/Src and protein kinase C (PKC), which were inhibited by integrin β1 antibody (Ab) and laminin receptor-1 (LR-1) Ab, respectively. In addition, inhibition of both FAK/Src and PKC blocked Cx43 phosphorylation. Laminin-111 increased the Ras homolog gene family, member A (RhoA) activation, which was blocked by FAK/Src and PKC inhibitors, suggesting the existence of parallel pathways that merge at RhoA. Inhibition of RhoA reversed the laminin-111-induced increase of Cx43 phosphorylation and reduction of GJIC. Laminin-111 also stimulated the dissociation of Cx43/ZO-1 complex followed by disruption of Cx43/drebrin and Cx43/F-actin complexes, which were reversed by C3 (RhoA inhibitor). ZO-1 small interfering (si) RNA significantly decreased Ly diffusion. Moreover, laminin-111 decreased Cx43 labeling at the intercellular junction, whereas pretreatment with degradation inhibitors (lysosomal protease inhibitor, chloroquine; proteasome inhibitor, lactacystin) increased Cx43 expression, reversely. In conclusion, laminin-111 stimulated mESC proliferation through a reduction of GJIC via RhoA-mediated Cx43 phosphorylation and Cx43/ZO-1/drebrin complex instability-mediated Cx43 degradation.

Adhesive forces in embryonic stem cell cultures

Most cell culture systems grow and spread as contact-inhibited monolayers on flat culture dishes, but the embryonic stem cell (ESC) is one of the cell phenotypes that prefer to self-organize as tightly packed three-dimensional (3D) colonies. ESC also readily form 3D cell aggregates, called embryoid bodies (EB) that partially mimic the spatial and temporal processes of the developing embryo. Here, the rationale for ESC aggregatation, rather than "spreading" on gelatin-coated or mouse embryonic fibroblast (MEF)-coated dishes, is examined through the quantification of the expression levels of adhesion molecules on ESC and the calculation of the adhesive forces on ESC. Modeling each ESC as a dodecahedron, the adhesive force for each ESC-ESC binding was found to be 9.1 x 10(5) pN, whereas, the adhesive force for ESC-MEF binding was found to be an order of magnitude smaller at 7.9 x 10(4) pN. We also show that E-cadherin is the dominating molecule in the ESC-ESC adhesion and blocking E-cadherin leads to a significant reduction in colony formation. Here, we mathematically describe the preference for ESC to self-assemble into ESC-ESC aggregates and 3D colonies, rather than to bind and spread on gelatin or MEF-coated dishes, and have shown that these interactions are predominantly due to E-cadherin expression on ESC.

Adenovirus-mediated anti-sense ERK2 gene therapy inhibits tubular epithelial-mesenchymal transition and ameliorates renal allograft fibrosis

PURPOSE

Epithelial-mesenchymal transition (EMT) plays an important role in progress of renal allograft fibrosis. The adenovirus-mediated anti-sense extracellular signal-regulated kinase 2 (Adanti-ERK2) gene therapy was used to block ERK signaling pathway, and its effect on EMT and renal allograft fibrosis both in vivo and in vitro was explored.

METHODS

We first generated an in vitro EMT model by connective tissue growth factor (CTGF) stimulation in a HK-2 cell culture system, and then applied Adanti-ERK2 gene therapy on it. The transition of epithelial marker (E-cadherin) to mesenchymal markers (α-SMA, Vimentin) and the cell mobility function alteration were monitored for the observation of EMT progress. In vivo, a rat renal transplant model with Fisher-Lewis combination was employed and the Adanti-ERK2 gene therapy was given. The tubular EMT changes and pathology of allograft fibrosis were examined.

RESULTS

In vitro, Adanti-ERK2 gene therapy inhibited CTGF-induced tubular EMT and attenuated the cell motility function induced by CTGF. In vivo, Adanti-ERK2 gene therapy attenuated tubular EMT, modulated the infiltration of macrophages and CD8(+), CD4(+)T lymphocytes, and ameliorated fibrosis effectively in the renal allografts 24weeks after transplantation.

CONCLUSIONS

Adanti-ERK2 gene therapy inhibits tubular EMT and attenuates renal allograft fibrosis. It is possible to develop promising molecular drug(s) in the future based on ERK signaling pathway.

Functional interaction between TRPC1 channel and connexin-43 protein: a novel pathway underlying S1P action on skeletal myogenesis

We recently demonstrated that skeletal muscle differentiation induced by sphingosine 1-phosphate (S1P) requires gap junctions and transient receptor potential canonical 1 (TRPC1) channels. Here, we searched for the signaling pathway linking the channel activity with Cx43 expression/function, investigating the involvement of the Ca(2+)-sensitive protease, m-calpain, and its targets in S1P-induced C2C12 myoblast differentiation. Gene silencing and pharmacological inhibition of TRPC1 significantly reduced Cx43 up-regulation and Cx43/cytoskeletal interaction elicited by S1P. TRPC1-dependent functions were also required for the transient increase of m-calpain activity/expression and the subsequent decrease of PKCα levels. Remarkably, Cx43 expression in S1P-treated myoblasts was reduced by m-calpain-siRNA and enhanced by pharmacological inhibition of classical PKCs, stressing the relevance for calpain/PKCα axis in Cx43 protein remodeling. The contribution of this pathway in myogenesis was also investigated. In conclusion, these findings provide novel mechanisms by which S1P regulates myoblast differentiation and offer interesting therapeutic options to improve skeletal muscle regeneration.

Connexins: sensors and regulators of cell cycling

It is nowadays well established that gap junctions are critical gatekeepers of cell proliferation, by controlling the intercellular exchange of essential growth regulators. In recent years, however, it has become clear that the picture is not as simple as originally anticipated, as structural precursors of gap junctions can affect cell cycling by performing actions not related to gap junctional intercellular communication. Indeed, connexin hemichannels also foresee a pathway for cell growth communication, albeit between the intracellular compartment and the extracellular environment, while connexin proteins as such can directly or indirectly influence the production of cell cycle regulators independently of their channel activities. Furthermore, a novel set of connexin-like proteins, the pannexins, have lately joined in as regulators of the cell proliferation process, which they can affect as either single units or as channel entities. In the current paper, these multifaceted aspects of connexin-related signalling in cell cycling are reviewed.

Enhanced connexin 43 expression delays intra-mitotic duration and cell cycle traverse independently of gap junction channel function

Connexins (Cxs) and gap junction (GJ)-mediated communication have been linked with the regulation of cell cycle traverse. However, it is not clear whether Cx expression or GJ channel function are the key mediators in this process or at what stage this regulation may occur. We therefore tested the hypothesis that enhanced Cx expression could alter the rate of cell cycle traverse independently of GJ channel function. Sodium butyrate (NaBu) or anti-arrhythmic peptide (AAP10) were used to enhance Cx expression in HeLa cells stably expressing Cx43 (HeLa-43) and primary cultures of human fibroblasts (HFF) that predominantly express Cx43. To reduce GJ-mediated communication, 18-alpha-glycyrrhetinic acid (GA) was used. In HeLa-43 and HFF cells, NaBu and AAP10 enhanced Cx43 expression and increased channel function, while GA reduced GJ-mediated communication but did not significantly alter Cx43 expression levels. Timelapse microscopy and flow cytometry of HeLa-WT (wild-type, Cx deficient) and HeLa-43 cells dissected cell cycle traverse and enabled measurements of intra-mitotic time and determined levels of G1 arrest. Enhanced Cx43 expression increased mitotic durations corresponding with a G1 delay in cell cycle, which was linked to an increase in expression of the cell cycle inhibitor p21(waf1/cip1) in both HeLa-43 and HFF cells. Reductions in Cx43 channel function did not abrogate these responses, indicating that GJ channel function was not a critical factor in reducing cell proliferation in either cell type. We conclude that enhanced Cx43 expression and not GJ-mediated communication, is involved in regulating cell cycle traverse.

Involvement of Cx43 phosphorylation in 5'-N-ethylcarboxamide-induced migration and proliferation of mouse embryonic stem cells

Despite a lot of gap junction research, the complex connection between gap junction and cell proliferation remains an exciting area of investigation. Thus, we examined the effect of connexin 43 (Cx43) on the migration and proliferation of embryonic stem (ES) cells and its related signaling pathways following stimulation with the adenosine analogue 5'-N-ethylcarboxamide (NECA). NECA increased phosphorylation of Cx43 which was blocked by caffeine, a non-selective adenosine receptor antagonist. In experiment to measure the gap junctional intercellular communication, NECA blocked transfer of Lucifer yellow to neighboring cells in a scrape loading/dye transfer (SL/DT) assay. In addition, NECA-induced phosphorylation of phosphoinositide 3-kinase (PI3K)/Akt, protein kinase C (PKC), mitogen-activated protein kinases (MAPKs), and nuclear factor-kappa B (NF-kappaB) signal pathways. Inhibition of these signaling pathways reduced NECA-induced phosphorylation of Cx43. Moreover, NECA-treated cells demonstrated phosphorylation of Src, which was blocked by caffeine. In this experiment, a disruption of Cx43 using Cx43-specific small interfering RNA (siRNA) also enhanced Src phosphorylation. In a further study, phosphorylations of integrin beta1, focal adhesion kinase (FAK), and paxillin by NECA were restrained by caffeine as well as the Src blocker, PP2. Finally, we identified that NECA-stimulated cell migration and expressions of cell-cycle regulatory proteins [cyclin D1, cyclin-dependent kinase (CDK) 4, cyclin E, and CDK2]; these increases were inhibited by caffeine, or PP2. We conclude that NECA-stimulated Cx43 phosphorylation mediated by PI3K/Akt, PKC, MAPKs, and NF-kappaB, which subsequently stimulated cell migration and proliferation through Src, integrin beta1, FAK, and paxillin signal pathways.

FIP-fve stimulates interferon-gamma production via modulation of calcium release and PKC-alpha activation

Fungal immunomodulatory protein, FIP-fve, has been isolated from Flammulina velutipes, and its immunomodulatory effects are believed to be associated with the enhanced activation of IFN-gamma-releasing Th1 cells. However, the mechanisms of FIP-fve-mediated signal transduction in the regulation of interferon-gamma (IFN-gamma) gene expression in human peripheral blood mononuclear cells (PBMCs) are still poorly understood. Using fluo-3 AM, we found that FIP-fve induces a rapid elevation in calcium concentration. ELISA, RT-PCR and Western blot assays demonstrated significant increases in the production and mRNA expression of IFN-gamma and protein kinase C-alpha (PKC-alpha) activation in activated PBMCs, which were abolished by EGTA, nifedipine and GO6976. In conclusion, Ca2+ release and PKC-alpha activation are required for IFN-gamma production induced by FIP-fve in PBMCs.