EGF-induced inhibition of glucose transport is mediated by PKC and MAPK signal pathways in primary cultured chicken hepatocytes

Inhibition of Glucose Transport by Tomatoside A, a Tomato Seed Steroidal Saponin, through the Suppression of GLUT2 Expression in Caco-2 Cells

We investigated whether tomatoside A (5α-furostane-3β,22,26-triol-3-[O-β-d-glucopyranosyl (1→2)-β-d-glucopyranosyl (1→4)-β-d-galactopyranoside] 26-O-β-d-glucopyranoside), a tomato seed saponin, may play a role in the regulation of intestinal glucose transport in human intestinal Caco-2 cells. Tomatoside A could not penetrate through Caco-2 cell monolayers, as observed in the transport experiments using liquid chromatography-mass spectrometry. The treatment of cells with 10 μM tomatoside A for 3 h resulted in a 46.0% reduction in glucose transport as compared to untreated cells. Western blotting analyses revealed that tomatoside A significantly (p < 0.05) suppressed the expression of glucose transporter 2 (GLUT2) in Caco-2 cells, while no change in the expression of sodium-dependent glucose transporter 1 was observed. In glucose transport experiments, the reduced glucose transport by tomatoside A was ameliorated by a protein kinase C (PKC) inhibitor and a multidrug resistance-associated protein 2 (MRP2) inhibitor. The tomatoside A-induced reduction in glucose transport was restored in cells treated with apical sodium-dependent bile acid transporter (ASBT) siRNA or an ASBT antagonist. These findings demonstrated for the first time that the nontransportable tomato seed steroidal saponin, tomatoside A, suppressed GLUT2 expression via PKC signaling pathway during the ASBT-influx/MRP2-efflux process in Caco-2 cells.

On the adhesion-cohesion balance and oxygen consumption characteristics of liver organoids

Liver organoids (LOs) are of interest in tissue replacement, hepatotoxicity and pathophysiological studies. However, it is still unclear what triggers LO self-assembly and what the optimal environment is for their culture. Hypothesizing that LO formation occurs as a result of a fine balance between cell-substrate adhesion and cell-cell cohesion, we used 3 cell types (hepatocytes, liver sinusoidal endothelial cells and mesenchymal stem cells) to investigate LO self-assembly on different substrates keeping the culture parameters (e.g. culture media, cell types/number) and substrate stiffness constant. As cellular spheroids may suffer from oxygen depletion in the core, we also sought to identify the optimal culture conditions for LOs in order to guarantee an adequate supply of oxygen during proliferation and differentiation. The oxygen consumption characteristics of LOs were measured using an O₂ sensor and used to model the O₂ concentration gradient in the organoids. We show that no LO formation occurs on highly adhesive hepatic extra-cellular matrix-based substrates, suggesting that cellular aggregation requires an optimal trade-off between the adhesiveness of a substrate and the cohesive forces between cells and that this balance is modulated by substrate mechanics. Thus, in addition to substrate stiffness, physicochemical properties, which are also critical for cell adhesion, play a role in LO self-assembly.

Transmissible Gastroenteritis Virus Infection Enhances SGLT1 and GLUT2 Expression to Increase Glucose Uptake

Transmissible gastroenteritis virus (TGEV) is a coronavirus that causes villus atrophy, followed by crypt hyperplasia, reduces the activities of intestinal digestive enzymes, and disrupts the absorption of intestinal nutrients. In vivo, TGEV primarily targets and infects intestinal epithelial cells, which play an important role in glucose absorption via the apical and basolateral transporters Na⁺-dependent glucose transporter 1 (SGLT1) and facilitative glucose transporter 2 (GLUT2), respectively. In this study, we therefore sought to evaluate the effects of TGEV infection on glucose uptake and SGLT1 and GLUT2 expression. Our data demonstrate that infection with TGEV resulted in increased glucose uptake and augmented expression of EGFR, SGLT1 and GLUT2. Moreover, inhibition studies showed that EGFR modulated glucose uptake in control and TGEV infected cells. Finally, high glucose absorption was subsequently found to promote TGEV replication.

CAMK1 phosphoinositide signal-mediated protein sorting and transport network in human hepatocellular carcinoma (HCC) by biocomputation

We data-analyzed and constructed the high-expression CAMK1 phosphoinositide signal-mediated protein sorting and transport network in human hepatocellular carcinoma (HCC) compared with low-expression (fold change ≥ 2) no-tumor hepatitis/cirrhotic tissues (HBV or HCV infection) in GEO data set, using integration of gene regulatory network inference method with gene ontology (GO). Our result showed that CAMK1 transport subnetwork upstream KCNQ3, LCN2, NKX2_5, NUP62, SORT1, STX1A activated CAMK1, and downstream CAMK1-activated AFP, ENAH, KPNA2, SLC4A3; CAMK1 signal subnetwork upstream BRCA1, DKK1, GPSM2, LEF1, NR5A1, NUP62, SORT1, SSTR5, TBL3 activated CAMK1, and downstream CAMK1-activated MAP2K6, SFRP4, SSTR5, TSHB, UBE2C in HCC. We proposed that CAMK1 activated network enhanced endosome to lysosome transport, endosome transport via multivesicular body sorting pathway, Golgi to endosome transport, intracellular protein transmembrane transport, intracellular protein transport, ion transport, mRNA transport, plasma membrane to endosome transport, potassium ion transport, protein transport, vesicle-mediated transport, anion transport, intracellular transport, androgen receptor signaling pathway, cell surface receptor-linked signal transduction, hormone-mediated signaling, induction of apoptosis by extracellular signals, signal transduction by p53 class mediator resulting in transcription of p21 class mediator, signal transduction resulting in induction of apoptosis, phosphoinositide-mediated signaling, Wnt receptor signaling pathway, as a result of inducing phosphoinositide signal-mediated protein sorting, and transport in HCC. Our hypothesis was verified by CAMK1 functional regulation subnetwork containing positive regulation of calcium ion transport via voltage gated calcium channel, cell proliferation, DNA repair, exocytosis, I-kappaB kinase/NF-kappaB cascade, immunoglobulin-mediated immune response, mast cell activation, natural killer cell-mediated cytotoxicity directed against tumor cell target, protein ubiquitination, sodium ion transport, survival gene product activity, T cell-mediated cytotoxicity, transcription, transcription from RNA polymerase II promoter, transcription initiation from RNA polymerase II promoter, transcription via serum response element binding, exit from mitosis, ubiquitin ligase activity during mitotic cell cycle, regulation of angiogenesis, apoptosis, cell growth, cell proliferation, cyclin-dependent protein kinase activity, gene expression, insulin secretion, steroid biosynthesis, transcription from RNA polymerase II promoter, transcription from RNA polymerase III promoter, cell cycle, cell migration, DNA recombination, and protein metabolism; also by CAMK1 negative functional regulation subnetwork including negative regulation of apoptosis, cell proliferation, centriole replication, fatty acid biosynthesis, lipoprotein lipase activity, MAPK activity, progression through cell cycle, transcription, transcription from RNA polymerase II promoter, cell growth, phosphorylation, and ubiquitin ligase activity during mitotic cell cycle in HCC.

ERK1/2 and p38 MAPKs are complementarily involved in estradiol 17ß-D-glucuronide-induced cholestasis: crosstalk with cPKC and PI3K

Objective

The endogenous, cholestatic metabolite estradiol 17ß-d-glucuronide (E₂17G) induces endocytic internalization of the canalicular transporters relevant to bile formation, Bsep and Mrp2. We evaluated here whether MAPKs are involved in this effect.

Design

ERK1/2, JNK1/2, and p38 MAPK activation was assessed by the increase in their phosphorylation status. Hepatocanalicular function was evaluated in isolated rat hepatocyte couplets (IRHCs) by quantifying the apical secretion of fluorescent Bsep and Mrp2 substrates, and in isolated, perfused rat livers (IPRLs), using taurocholate and 2,4-dinitrophenyl-S-glutathione, respectively. Protein kinase participation in E₂17G-induced secretory failure was assessed by co-administering selective inhibitors. Internalization of Bsep/Mrp2 was assessed by confocal microscopy and image analysis.

Results

E₂17G activated all kinds of MAPKs. The PI3K inhibitor wortmannin prevented ERK1/2 activation, whereas the cPKC inhibitor Gö6976 prevented p38 activation, suggesting that ERK1/2 and p38 are downstream of PI3K and cPKC, respectively. The p38 inhibitor SB203580 and the ERK1/2 inhibitor PD98059, but not the JNK1/2 inhibitor SP600125, partially prevented E₂17G-induced changes in transporter activity and localization in IRHCs. p38 and ERK1/2 co-inhibition resulted in additive protection, suggesting complementary involvement of these MAPKs. In IPRLs, E₂17G induced endocytosis of canalicular transporters and a rapid and sustained decrease in bile flow and biliary excretion of Bsep/Mrp2 substrates. p38 inhibition prevented this initial decay, and the internalization of Bsep/Mrp2. Contrarily, ERK1/2 inhibition accelerated the recovery of biliary secretion and the canalicular reinsertion of Bsep/Mrp2.

Conclusions

cPKC/p38 MAPK and PI3K/ERK1/2 signalling pathways participate complementarily in E₂17G-induced cholestasis, through internalization and sustained intracellular retention of canalicular transporters, respectively.

Activation of extracellular-signal regulated kinase by epidermal growth factor is potentiated by cAMP-elevating agents in primary cultures of adult rat hepatocytes

We investigated the effects of α- and β-adrenergic agonists on epidermal growth factor (EGF)-stimulated extracellular-signal regulated kinase (ERK) isoforms in primary cultures of adult rat hepatocytes. Hepatocytes were isolated and cultured with EGF (20 ng/ml) and/or α(1)-, α(2)- and β(2)-adrenergic agonists. Phosphorylated ERK isoforms (ERK1; p44 mitogen-activated protein kinase (MAPK) and ERK2; p42 MAPK) were detected by Western blotting analysis using anti-phospho-ERK1/2 antibody. The results show that EGF induced a 2.5-fold increase in ERK2-, but not ERK1-, phosphorylation within 3 min. This EGF-induced ERK2 activation was abolished by treatment with the EGF-receptor kinase inhibitor AG1478 (10(-7) M) or the MEK (MAPK kinase) inhibitor PD98059 (10(-6) M). The α(2)-adrenergic and β(2)-adrenergic agonists, UK14304 (10(-6) M) and metaproterenol (10(-6) M), respectively, had no effect in the absence of EGF, but metaproterenol significantly potentiated EGF-induced ERK2 phosphorylation. Moreover, the cell-permeable cAMP analog 8-bromo cAMP (10(-7) M), also potentiated EGF-induced ERK2 phosphorylation. The effects of these analogs were antagonized by the protein kinase A (PKA) inhibitor H-89 (10(-7) M). These results suggest that direct or indirect activation of PKA represents a positive regulatory mechanism for EGF stimulation of ERK2 induction.

Central role of the EGF receptor in neurometabolic aging

A strong connection between neuronal and metabolic health has been revealed in recent years. It appears that both normal and pathophysiological aging, as well as neurodegenerative disorders, are all profoundly influenced by this "neurometabolic" interface, that is, communication between the brain and metabolic organs. An important aspect of this "neurometabolic" axis that needs to be investigated involves an elucidation of molecular factors that knit these two functional signaling domains, neuronal and metabolic, together. This paper attempts to identify and discuss a potential keystone signaling factor in this "neurometabolic" axis, that is, the epidermal growth factor receptor (EGFR). The EGFR has been previously demonstrated to act as a signaling nexus for many ligand signaling modalities and cellular stressors, for example, radiation and oxidative radicals, linked to aging and degeneration. The EGFR is expressed in a wide variety of cells/tissues that pertain to the coordinated regulation of neurometabolic activity. EGFR signaling has been highlighted directly or indirectly in a spectrum of neurometabolic conditions, for example, metabolic syndrome, diabetes, Alzheimer's disease, cancer, and cardiorespiratory function. Understanding the positioning of the EGFR within the neurometabolic domain will enhance our appreciation of the ability of this receptor system to underpin highly complex physiological paradigms such as aging and neurodegeneration.

A role for PDGF signaling in expansion of the extra-embryonic endoderm lineage of the mouse blastocyst

The inner cell mass (ICM) of the implanting mammalian blastocyst comprises two lineages: the pluripotent epiblast (EPI) and primitive endoderm (PrE). We have identified platelet-derived growth factor receptor alpha (PDGFRα) as an early marker of the PrE lineage and its derivatives in both mouse embryos and ex vivo paradigms of extra-embryonic endoderm (ExEn). By combining live imaging of embryos and embryo-derived stem cells expressing a histone H2B-GFP fusion reporter under the control of Pdgfra regulatory elements with the analysis of lineage-specific markers, we found that Pdgfra expression coincides with that of GATA6, the earliest expressed transcriptional regulator of the PrE lineage. We show that GATA6 is required for the activation of Pdgfra expression. Using pharmacological inhibition and genetic inactivation we addressed the role of the PDGF pathway in the PrE lineage. Our results demonstrate that PDGF signaling is essential for the establishment, and plays a role in the proliferation, of XEN cells, which are isolated from mouse blastocyst stage embryos and represent the PrE lineage. Implanting Pdgfra mutant blastocysts exhibited a reduced number of PrE cells, an effect that was exacerbated by delaying implantation. Surprisingly, we also noted an increase in the number of EPI cells in implantation-delayed Pdgfra-null mutants. Taken together, our data suggest a role for PDGF signaling in the expansion of the ExEn lineage. Our observations also uncover a possible role for the PrE in regulating the size of the pluripotent EPI compartment.

Identification of ERK and JNK as signaling mediators on protein kinase C activation in cultured granulosa cells

PKC signaling is critical for follicular development and the induction of ovulatory genes including Pgr, Prkg2, and Cyp11a1 (SCC). We investigated PKC signaling mechanisms in the JC-410 porcine granulosa cell line stably expressing an SCC-luciferase reporter gene containing 2kb of the porcine SCC promoter. Addition of phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C, induced the promoter approximately 6-fold over the basal levels in 4h. This effect was predominantly mediated by the PKC beta and delta isoforms. PMA-mediated induction of the SCC promoter was sensitive to inhibition of ERK1/2 or JNK. Inhibition of p38 MAP kinase or Src tyrosine kinase did not alter the PMA-mediated inducibility of the promoter. SCC promoter induction in response to PMA treatment required basal EGF-receptor activity, but did not involve ectodomain shedding. Western blot analyses using phospho-specific antibodies showed that PMA treatment of JC-410 cells induced phosphorylation of MEK1/2, ERK1/2, and its downstream target p90 RSK at 15min. We also documented the rapid phosphorylation of JNK1/2 in response to PMA treatment. Phosphorylation of ERK and JNK was robust and sustained in contrast to activation of PKA and EGF-receptor signaling in these cells. Pretreatment of JC-410 granulosa cells with IGF-1 had a synergistic effect on PMA-mediated induction of the SCC promoter. We demonstrated the importance of PMA activation of ERK signaling and the synergism with IGF-1 by showing similar responses for Prkg2 expression in primary granulosa cells. In conclusion, our studies demonstrated PMA activation of ERK and JNK signaling which is relevant in the regulation of gene expression during follicular development, ovulation, and luteinization.

In human entrocytes, GLN transport and ASCT2 surface expression induced by short-term EGF are MAPK, PI3K, and Rho-dependent

Glutamine, a key nutrient for the enterocyte, is transported among other proteins by ASCT2. Epidermal growth factor (EGF) augments intestinal adaptation. We hypothesized that short-term treatment of human enterocytes with EGF enhances glutamine transport by increasing membranal ASCT2. To elucidate EGF-induced mechanisms, monolayers of C2(BBe)1 w/wo siRho transfection were treated w/wo EGF and w/wo tyrphostin AG1478 (AG1478), wortmanin, or PD98059. Total and system-specific (3)H-glutamine transports were determined w/wo 5 mmol/l amino acid inhibitors. Total and membranal ASCT2 proteins were measured by Westerns. EGF doubled glutamine transport by increasing B(0)/ASCT2 and B(0,+) activities. Despite the doubling of membranal ASCT2 protein with EGF treatment, total ASCT2 did not change. The increases in B(0)/ASCT2 activity and ASCT2 protein were eliminated by AG1478, PD98059, wortmanin, and siRho, while transport by B(0,+) was inhibited only by PD98059 and siRho. Thus, differential pathways are involved in EGF-induced increase in B(0)/ASCT2 glutamine transport and membranal ASCT2 compared to those involved in B(0,+) activity.

High glucose induced translocation of Aquaporin8 to chicken hepatocyte plasma membrane: involvement of cAMP, PI3K/Akt, PKC, MAPKs, and microtubule

Aquaporin8 (AQP8) is a transmembrane water channel that is found mainly in hepatocytes. The direct involvement of AQP8 in high glucose condition has not been established. Therefore, this study examined the effects of high glucose on AQP8 and its related signal pathways in primary cultured chicken hepatocytes. High glucose increased the movement of AQP8 from the intracellular membrane to plasma membrane in a 30 mM glucose concentration and in a time- (> or =10 min) dependent manner. On the other hand, 30 mM mannitol did not affect the translocation of AQP8, which suggested the absence of osmotic effect. Thirty millimolar glucose increased intracellular cyclic adenosine 3, 5-monophosphate (cAMP) level. Moreover, high glucose level induced Akt phosphorylation, protein kinase C (PKC) activation, p44/42 mitogen-activated protein kinases (MAPKs), p38 MAPK, and c-jun NH2-terminal kinase (JNK) phosphorylation. On the other hand, inhibition of each pathway by SQ 22536 (adenylate cyclase inhibitor), LY 294002 (PI3-K phosphatidylinositol 3-kinase inhibitor), Akt inhibitor, staurosporine (PKC inhibitor), PD 98059 (MEK inhibitor), SB 203580 (p38 MAPK inhibitor), or SP 600125 (JNK inhibitor) blocked 30 mM glucose-induced AQP8 translocation, respectively. In addition, inhibition of microtubule movement with nocodazole blocked high glucose-induced AQP8 translocation. High glucose level also increased the level of kinesin light chain and dynein protein expression. In conclusion, high glucose level stimulates AQP8 via cAMP, PI3-K/Akt, PKC, and MAPKs pathways in primary cultured chicken hepatocytes.

Oxygen deprivation triggers upregulation of early growth response-1 by the receptor for advanced glycation end products

Myocardial infarction, stroke, and venous thromboembolism are characterized by oxygen deprivation. In hypoxia, biological responses are activated that evoke tissue damage. Rapid activation of early growth response-1 in hypoxia upregulates fundamental inflammatory and prothrombotic stress genes. We probed the mechanisms mediating regulation of early growth response-1 and demonstrate that hypoxia stimulates brisk generation of advanced glycation end products (AGEs) by endothelial cells. Via AGE interaction with their chief signaling receptor, RAGE, membrane translocation of protein kinase C-betaII occurs, provoking phosphorylation of c-Jun NH(2)-terminal kinase and increased transcription of early growth response-1 and its downstream target genes. These findings identify RAGE as a master regulator of tissue stress elicited by hypoxia and highlight this receptor as a central therapeutic target to suppress the tissue injury-provoking effects of oxygen deprivation.

Estradiol-17beta protects against hypoxia-induced hepatocyte injury through ER-mediated upregulation of Bcl-2 as well as ER-independent antioxidant effects

Although many previous studies have suggested that estrogen functions as a cytoprotective agent under oxidative stress conditions, the underlying mechanism by which this effect is exerted remains to be elucidated. This study assessed the effects of estradiol-17beta (E(2)) (10(-8) M) on hypoxia-induced cell injury and its related signaling in primary cultured chicken hepatocytes. Hypoxic conditions were found to augment the level of DNA damage and to reduce cell viability and the level of [(3)H]-thymidine incorporation, and these phenomena were prevented through treatment with E(2). Hypoxia also increased caspase-3 expression, but showed no evidence of an influence on the expression of Bcl-2. However, E(2) induced an increase in the level of Bcl-2 expression under hypoxic conditions and reduced the level of caspase-3 expression. The effects of E(2) on Bcl-2 and caspase expression were blocked by ICI 182780 (E(2) receptor (ER) antagonist, 10(-7) M). In addition, hypoxia resulted in an increase in the intracellular reactive oxygen species (ROS) generated. These effects were blocked by E(2), but not by E(2)-BSA and ICI 182780. Hypoxia also activated p38 mitogen-activated protein kinase (MAPK), c-JUN N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and nuclear factor-kappaB (NF-kappaB). These effects were blocked by E(2), but not by ICI 182780. The inhibition of p38 MAPK and JNK/SAPK blocked NF-kappaB activation. In conclusion, E(2) was found to protect against hypoxia-induced cell injury in chicken hepatocytes through ER-mediated upregulation of Bcl-2 expression and through reducing the activity of ROS-dependent p38 MAPK, JNK/SAPK and NF-kappaB.