PI3K/Akt signaling is involved in the disruption of gap junctional communication caused by v-Src and TNF-α

Study on Active Components of Cuscuta chinensis Promoting Neural Stem Cells Proliferation: Bioassay-Guided Fractionation

Neural stem cells (NSCs) exist in the central nervous system of adult animals and capable of self-replication. NSCs have two basic functions, namely the proliferation ability and the potential for multi-directional differentiation. In this study, based on the bioassay-guided fractionation, we aim to screen active components in Cuscuta chinensis to promote the proliferation of NSCs. CCK-8 assays were used as an active detection method to track the active components. On the basis of isolating active fraction and monomer compounds, the structures of these were identified by LC-MS and (¹H, ¹³C) NMR. Moreover, active components were verified by pharmacodynamics and network pharmacology. The system solvent extraction method combined with the traditional isolation method were used to ensure that the fraction TSZE-EA-G6 of Cuscuta chinensis exhibited the highest activity. Seven chemical components were identified from the TSZE-EA-G6 fraction by UPLC-QE-Orbitrap-MS technology, which were 4-O-p-coumarinic acid, chlorogenic acid, 5-O-p-coumarinic acid, hyperoside, astragalin, isochlorogenic acid C, and quercetin-3-O-galactose-7-O-glucoside. Using different chromatographic techniques, five compounds were isolated in TSZE-EA-G6 and identified as kaempferol, kaempferol-3-O-glucoside (astragalin), quercetin-3-O-galactoside (hyperoside), chlorogenic acid, and sucrose. The activity study of these five compounds showed that the proliferation rate of kaempferol had the highest effects; at a certain concentration (25 μg/mL, 3.12 μg/mL), the proliferation rate could reach 87.44% and 59.59%, respectively. Furthermore, research results using network pharmacology techniques verified that kaempferol had an activity of promoting NSCs proliferation and the activity of flavonoid aglycones might be greater than that of flavonoid glycosides. In conclusion, this research shows that kaempferol is the active component in Cuscuta chinensis to promote the proliferation of NSCs.

Src Regulation of Cx43 Phosphorylation and Gap Junction Turnover

The gap junction protein Connexin43 (Cx43) is highly regulated by phosphorylation at over a dozen sites by probably at least as many kinases. This Cx43 “kinome” plays an important role in gap junction assembly and turnover. We sought to gain a better understanding of the interrelationship of these phosphorylation events particularly related to src activation and Cx43 turnover. Using state-of-the-art live imaging methods, specific inhibitors and many phosphorylation-status specific antibodies, we found phospho-specific domains in gap junction plaques and show evidence that multiple pathways of disassembly exist and can be regulated at the cellular and subcellular level. We found Src activation promotes formation of connexisomes (internalized gap junctions) in a process involving ERK-mediated phosphorylation of S279/282. Proteasome inhibition dramatically and rapidly restored gap junctions in the presence of Src and led to dramatic changes in the Cx43 phospho-profile including to increased Y247, Y265, S279/282, S365, and S373 phosphorylation. Lysosomal inhibition, on the other hand, nearly eliminated phosphorylation on Y247 and Y265 and reduced S368 and S373 while increasing S279/282 phosphorylation levels. We present a model of gap junction disassembly where multiple modes of disassembly are regulated by phosphorylation and can have differential effects on cellular signaling.

Silencing of SPP1 Suppresses Progression of Tongue Cancer by Mediating the PI3K/Akt Signaling Pathway

Background:

In the present study, we aimed to find an effective target for the treatment of tongue cancer using gene chip screening and signal pathway research.

Methods:

We used microarray screening and gene expression profile analyses to find important differentially expressed genes in tongue cancer. We constructed a protein-protein interaction network, and used enrichment analysis of the Kyoto Encyclopedia of Genes and Genomes to screen for important genes. We then silenced the genes of interest in SCC154 cells to study the relationship with the Phosphatidylinositol 3-kinase/Akt signal pathway. Western blot analyses, the 3-(4,5Dimethylthiazol-yl)-2,5Dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT) test, and immunofluorescence assays were used to compare the expression levels of Phosphatidylinositol 3-kinase/Akt signal pathway-related proteins, cell viability, and cell proliferation ability in normal SCC154 cells, Si-RNA SCC154 cells, and gene-silenced SCC154 cells. The scratch test, Transwell test, and western blotting were used to determine migration, invasion, and carcinogenesis.

Results:

Using GSE9844, GSE13601, and GSE31056 gene chips, we identified 93 upregulated genes and 76 downregulated genes in tongue cancer. Using the protein-protein interaction network and Kyoto Encyclopedia of Genes and Genomes enrichment analyses, we further identified 47 differentially expressed genes. Using Kaplan-Meier plotter online tools, we also identified 3 genes (SPP1, Recombinant Human Secreted Phosphoprotein 1; PLAU, plasminogen activator urinary; and APP, amyloid precursor protein). Compared with normal SCC154 cells and Si-RNA control SCC154 cells, the expressions of Phosphatidylinositol 3-kinase/Akt pathway proteins in si-SPP1 SCC154 cells were significantly decreased (*P < 0.05), and the protein activities and proliferation abilities were also significantly decreased (*P < 0.05), while the migration ability, invasion ability, and cancer forming ability were significantly increased (*P < 0.05).

Conclusion:

Inhibition of the SPP1 gene may have a therapeutic effect on tongue cancer, and could be an effective target for the treatment of this disorder.

PI3k and Stat3: Oncogenes that are Required for Gap Junctional, Intercellular Communication

Gap junctional, intercellular communication (GJIC) is interrupted in cells transformed by oncogenes such as activated Src. The Src effector, Ras, is required for this effect, so that Ras inhibition restores GJIC in Src-transformed cells. Interestingly, the inhibition of the Src effector phosphatidyl-inositol-3 kinase (PI3k) or Signal Transducer and Activator of Transcription-3 (Stat3) pathways does not restore GJIC. In the contrary, inhibition of PI3k or Stat3 in non-transformed rodent fibroblasts or epithelial cells or certain human lung carcinoma lines with extensive GJIC inhibits communication, while mutational activation of PI3k or Stat3 increases GJIC. Therefore, it appears that oncogenes such as activated Src have a dual role upon GJIC; acting as inhibitors of communication through the Ras pathway, and as activators through activation of PI3k or Stat3. In the presence of high Src activity the inhibitory functions prevail so that the net effect is gap junction closure. PI3k and Stat3 constitute potent survival signals, so that their inhibition in non-transformed cells triggers apoptosis which, in turn, has been independently demonstrated to suppress GJIC. The interruption of gap junctional communication would confine the apoptotic event to single cells and this might be essential for the maintenance of tissue integrity. We hypothesize that the GJIC activation by PI3k or Stat3 may be linked to their survival function.

Oncogenic extracellular HSP70 disrupts the gap-junctional coupling between capillary cells

High levels of circulating heat shock protein 70 (HSP70) are detected in many cancers. In order to explore the effects of extracellular HSP70 on human microvascular endothelial cells (HMEC), we initially used gap-FRAP technique. Extracellular human HSP70 (rhHSP70), but not rhHSP27, blocks the gap-junction intercellular communication (GJIC) between HMEC, disrupts the structural integrity of HMEC junction plaques, and decreases connexin43 (Cx43) expression, which correlates with the phosphorylation of Cx43 serine residues. Further exploration of these effects identified a rapid transactivation of the Epidermal Growth Factor Receptor in a Toll-Like Receptor 4-dependent manner, preceding its internalization. In turn, cytosolic Ca²⁺ oscillations are generated. Both GJIC blockade and Ca²⁺ mobilization partially depend on ATP release through Cx43 and pannexin (Panx-1) channels, as demonstrated by blocking activity or expression of channels, and inactivating extracellular ATP. By monitoring dye-spreading into adjacent cells, we show that HSP70 released from human monocytes in response to macrophage colony-stimulating factor, prevents the formation of GJIC between monocytes and HMEC. Therapeutic manipulation of this pathway could be of interest in inflammatory and tumor growth.

Differential effects of polyoma virus middle tumor antigen mutants upon gap junctional, intercellular communication

Gap junctions are channels that connect the cytoplasm of adjacent cells. Oncogenes such as the middle Tumor antigen of polyoma virus (mT) are known to suppress gap junctional, intercellular communication (GJIC). mT associates with and is tyrosine-phosphorylated by cSrc family members. Specific mT phosphotyrosines provide docking sites for the phosphotyrosine binding domain of Shc (mT-tyr250) or the SH2 domain of the regulatory subunit of the phosphatidylinositol-3 kinase (PI3k, mT-tyr315). Binding results in the activation of their downstream signaling cascades, Ras/Raf/Erk and PI3 kinase/Akt, respectively, both of which are needed for full neoplastic transformation. To examine the effect of mT-initiated pathways upon gap junctional communication, GJIC was quantitated in rat liver epithelial T51B cells expressing mT-mutants, using a novel technique of in situ electroporation. The results demonstrate for the first time that, although even low levels of wild-type mT are sufficient to interrupt gap junctional communication, GJIC suppression still requires an intact tyr-250 site, that is activation of the Ras pathway. In sharp contrast, activation of the PI3k pathway is not required for GJIC suppression, indicating that GJIC suppression is independent of full neoplastic conversion and the concomitant morphological changes. Interestingly, expression of a constitutively active, myristylated form of the catalytic subunit of PI3k, p110, or the constitutively active mutants E545K and H1047R increased GJIC, while pharmacological inhibition of PI3k eliminated communication. Therefore, although PI3k is growth promoting and in an activated form it can act as an oncogene, it actually plays a positive role upon gap junctional, intercellular communication.

Managing the complexity of communication: regulation of gap junctions by post-translational modification

Gap junctions are comprised of connexins that form cell-to-cell channels which couple neighboring cells to accommodate the exchange of information. The need for communication does, however, change over time and therefore must be tightly controlled. Although the regulation of connexin protein expression by transcription and translation is of great importance, the trafficking, channel activity and degradation are also under tight control. The function of connexins can be regulated by several post translational modifications, which affect numerous parameters; including number of channels, open probability, single channel conductance or selectivity. The most extensively investigated post translational modifications are phosphorylations, which have been documented in all mammalian connexins. Besides phosphorylations, some connexins are known to be ubiquitinated, SUMOylated, nitrosylated, hydroxylated, acetylated, methylated, and γ-carboxyglutamated. The aim of the present review is to summarize our current knowledge of post translational regulation of the connexin family of proteins.

Polycyclic aromatic hydrocarbon-induced signaling events relevant to inflammation and tumorigenesis in lung cells are dependent on molecular structure

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental and occupational toxicants, which are a major human health concern in the U.S. and abroad. Previous research has focused on the genotoxic events caused by high molecular weight PAHs, but not on non-genotoxic events elicited by low molecular weight PAHs. We used an isomeric pair of low molecular weight PAHs, namely 1-Methylanthracene (1-MeA) and 2-Methylanthracene (2-MeA), in which only 1-MeA possessed a bay-like region, and hypothesized that 1-MeA, but not 2-MeA, would affect non-genotoxic endpoints relevant to tumor promotion in murine C10 lung cells, a non-tumorigenic type II alveolar pneumocyte and progenitor cell type of lung adenocarcinoma. The non-genotoxic endpoints assessed were dysregulation of gap junction intercellular communication function and changes in the major pulmonary connexin protein, connexin 43, using fluorescent redistribution and immunoblots, activation of mitogen activated protein kinases (MAPK) using phosphospecific MAPK antibodies for immunoblots, and induction of inflammatory genes using quantitative RT-PCR. 2-MeA had no effect on any of the endpoints, but 1-MeA dysregulated gap junctional communication in a dose and time dependent manner, reduced connexin 43 protein expression, and altered membrane localization. 1-MeA also activated ERK1/2 and p38 MAP kinases. Inflammatory genes, such as cyclooxygenase 2, and chemokine ligand 2 (macrophage chemoattractant 2), were also upregulated in response to 1-MeA only. These results indicate a possible structure-activity relationship of these low molecular weight PAHs relevant to non-genotoxic endpoints of the promoting aspects of cancer. Therefore, our novel findings may improve the ability to predict outcomes for future studies with additional toxicants and mixtures, identify novel targets for biomarkers and chemotherapeutics, and have possible implications for future risk assessment for these PAHs.

A contemporary review of molecular candidates for the development and treatment of childhood medulloblastoma

INTRODUCTION

Medulloblastoma is the most common pediatric central nervous system tumor; however, the causes are not well established. There has been some emphasis on mutations in developmental pathways and their impact on tumor pathology in hereditary diseases, but, in order to better understand the nature of diseases like medulloblastoma, other mechanisms also require attention.

PURPOSE

The purpose of this review is to provide an overview of the main genes involved in neurodevelopment, their downstream targets, and modulatory links by growth factors. Occurrence of pediatric brain tumors including medulloblastoma are mostly sporadic, but some hereditary diseases like Li-Fraumeni syndrome, Gorlin's syndrome, Turcot's syndrome, and Rubenstein-Tarbi syndrome are known to contribute their development as consequences of germline mutations at specific points: DNA-repairing gene Tp53 for Li-Fraumeni syndrome or Patch for Gorlin's, and apoptosis-related gene product adenomatous polyposis coli for Turcot's disease.

CONCLUSION

Intracellular relations at molecular level and future therapeutics that specifically target the corresponding pathways should be well understood in order to prevent and cure childhood medulloblastoma.

Coregulation of multiple signaling mechanisms in pp60v-Src-induced closure of Cx43 gap junction channels

Attenuation in gap junctional coupling has consistently been associated with induction of rapid or synchronous cell division in normal and pathological conditions. In the case of the v-src oncogene, gating of Cx43 gap junction channels has been linked to both direct phosphorylation of tyrosines (Y247 and 265) and phosphorylation of the serine targets of Erk1/2 (S255, 279 and 282) on the cytoplasmic C-terminal domain of Cx43. However, only the latter has been associated with acute, rather than chronic, gating of the channels immediately after v-src expression, a process that is mediated through a "ball-and-chain" mechanism. In this study we show that, while ERK1/2 is necessary for acute closure of gap junction channels, it is not sufficient. Rather, multiple pathways converge to regulate Cx43 coupling in response to expression of v-src, including parallel signaling through PKC and MEK1/2, with additional positive and negative regulatory effects mediated by PI3 kinase, distinguished by the involvement of Akt.

Prostaglandin E₂ maintains mouse ESC undifferentiated state through regulation of connexin31, connexin43 and connexin45 expression: involvement of glycogen synthase kinase 3β/β-catenin

BACKGROUND INFORMATION

Although previous reports have examined the function of prostaglandin E₂ (PGE₂) on gap junctions and undifferentiated stem cells, its effects on the reciprocal action of connexin (Cx) isoforms and undifferentiation in embryonic stem cells (ESCs) are unclear. Therefore, we investigated the role of PGE₂ on Cx isoforms and maintenance of mouse ESC undifferentiated state.

RESULTS

We have analysed 10 Cx genes, but found nine of them. PGE₂ (50 μM) stimulated Cx31, Cx32, Cx40, Cx43 and Cx45 mRNA expression. Amongst them, PGE₂ maximally stimulated the Cx43 mRNA expression and gap junction inter-cellular coupling. Therefore, we investigated the effect of PGE₂ on Cx43 expression. PGE₂ activated cAMP/protein kinase A (PKA) and phosphatidylinositol 3-kinase (PI3K)/Akt phosphorylation. In addition, treatments of adenylate cyclase activators increased Cx43 expression, but not PI3K/Akt phosphorylation. PGE₂ also inactivated GSK-3β and stimulated active-β-catenin. Furthermore, a ChiP assay demonstrated the association of β-catenin with the Cx26 (as control) and Cx43 promoter. Finally, down-regulation of PGE₂-induced Cx isoforms by AH 6809, Cx31-, Cx43-, Cx45 small interfering (si)RNA and 18α-glycyrrhetinic acid decreased levels of undifferentiated markers of ESCs, including Oct4, FoxD3, Sox2 and SSEA-1, but Nanog did not be down-regulated by Cx43 siRNA.

CONCLUSIONS

PGE₂ stimulates Cx isoforms via GSK-3β/β-catenin via EP2-receptor-dependent cAMP/PKA and PI3K/Akt in mouse ESCs, thereby partially contributing to the maintenance of their undifferentiated state.

Signalling of DNA damage and cytokines across cell barriers exposed to nanoparticles depends on barrier thickness

The use of nanoparticles in medicine is ever increasing, and it is important to understand their targeted and non-targeted effects. We have previously shown that nanoparticles can cause DNA damage to cells cultured below a cellular barrier without crossing this barrier. Here, we show that this indirect DNA damage depends on the thickness of the cellular barrier, and it is mediated by signalling through gap junction proteins following the generation of mitochondrial free radicals. Indirect damage was seen across both trophoblast and corneal barriers. Signalling, including cytokine release, occurred only across bilayer and multilayer barriers, but not across monolayer barriers. Indirect toxicity was also observed in mice and using ex vivo explants of the human placenta. If the importance of barrier thickness in signalling is a general feature for all types of barriers, our results may offer a principle with which to limit the adverse effects of nanoparticle exposure and offer new therapeutic approaches.