Early growth response factor-1 mediates insulin-inducible vascular endothelial cell proliferation and regrowth after injury

Serine 26 in Early Growth Response-1 Is Critical for Endothelial Proliferation, Migration, and Network Formation

Background

Vascular endothelial cell proliferation, migration, and network formation are key proangiogenic processes involving the prototypic immediate early gene product, Egr‐1 (early growth response‐1). Egr‐1 undergoes phosphorylation at a conserved Ser26 but its function is completely unknown in endothelial cells or any other cell type.

Methods and Results

A CRISPR/Cas9 strategy was used to introduce a homozygous Ser26>Ala mutation into endogenous Egr‐1 in human microvascular endothelial cells. In the course of generating mutant cells, we produced cells with homozygous deletion in Egr‐1 caused by frameshift and premature termination. We found that Ser26 mutation in Egr‐1, or Egr‐1 deletion, perturbed endothelial cell proliferation in models of cell counting or real‐time growth using the xCELLigence System. We found that Ser26 mutation or Egr‐1 deletion ameliorated endothelial cell migration toward VEGF‐A₁₆₅ (vascular endothelial growth factor‐A) in a dual‐chamber model. On solubilized basement membrane preparations, Ser26 mutation or Egr‐1 deletion prevented endothelial network (or tubule) formation, an in vitro model of angiogenesis. Flow cytometry further revealed that Ser26 mutation or Egr‐1 deletion elevated early and late apoptosis. Finally, we demonstrated that Ser26 mutation or Egr‐1 deletion increased VE‐cadherin (vascular endothelial cadherin) expression, a regulator of endothelial adhesion and signaling, permeability, and angiogenesis.

Conclusions

These findings not only indicate that Egr‐1 is essential for endothelial cell proliferation, migration, and network formation, but also show that point mutation in Ser26 is sufficient to impair each of these processes and trigger apoptosis as effectively as the absence of Egr‐1. This highlights the importance of Ser26 in Egr‐1 for a range of proangiogenic processes.

Insulin Treatment Forces Arteriogenesis in Diabetes Mellitus by Upregulation of the Early Growth Response-1 (Egr-1) Pathway in Mice

The process of arteriogenesis is severely compromised in patients with diabetes mellitus (DM). Earlier studies have reported the importance of Egr-1 in promoting collateral outward remodeling. However, the role of Egr-1 in the presence of DM in outward vessel remodeling was not studied. We hypothesized that Egr-1 expression may be compromised in DM which may lead to impaired collateral vessel growth. Here, we investigated the relevance of the transcription factor Egr-1 for the process of collateral artery growth in diabetic mice. Induction of arteriogenesis by femoral artery ligation resulted in an increased expression of Egr-1 on mRNA and protein level but was severely compromised in streptozotocin-induced diabetic mice. Diabetes mellitus mice showed a significantly reduced expression of Egr-1 endothelial downstream genes Intercellular Adhesion Molecule-1 (ICAM-1) and urokinase Plasminogen Activator (uPA), relevant for extravasation of leukocytes which promote arteriogenesis. Fluorescent-activated cell sorting analyses confirmed reduced leukocyte recruitment. Diabetes mellitus mice showed a reduced expression of the proliferation marker Ki-67 in growing collaterals whose luminal diameters were also reduced. The Splicing Factor-1 (SF-1), which is critical for smooth muscle cell proliferation and phenotype switch, was found to be elevated in collaterals of DM mice. Treatment of DM mice with insulin normalized the expression of Egr-1 and its downstream targets and restored leukocyte recruitment. SF-1 expression and the diameter of growing collaterals were normalized by insulin treatment as well. In summary, our results showed that Egr-1 signaling was impaired in DM mice; however, it can be rescued by insulin treatment.

Extracellular signal-regulated kinase-1 phosphorylates early growth response-1 at serine 26

Egr-1, an immediate-early gene product and master regulator was originally described as a phosphoprotein following its discovery in the 1980s. However specific residue(s) phosphorylated in Egr-1 remain elusive. Here we phosphorylated recombinant Egr-1 in vitro with ERK1 prior to mass spectrometry, which identified phosphorylation of Ser¹² and Ser²⁶ with the latter ∼12 times more abundant than Ser¹². Phosphorylation of wild-type recombinant Egr-1 (as compared with Ser²⁶>Ala²⁶ mutant Egr-1) revealed that Ser²⁶ accounts for the majority of phosphorylation of Egr-1 by ERK1. N-FGSFPH(pS)PTMDNYC-C was used as an antigen to generate mouse monoclonal antibodies (pS26 MAb). pS26 MAb recognised ERK1-phosphorylated Egr-1 but not Egr-1 bearing a point mutation at Ser²⁶. pS26 MAb recognised inducible ∼75 kDa and 100 kDa species in nuclear extracts of cells exposed to FGF-2. Peptide blocking revealed both inducible species were phosphosite-specific. Immunoprecipitation of nuclear extracts of cells exposed to FGF-2 with pS26 MAb followed by SDS-PAGE and mass spectrometry identified Egr-1 sequences corresponding to the ∼75 kDa species but not ∼100 kDa species. This study identifies a specific amino acid phosphorylated in endogenous Egr-1.

Role of early growth response 1 in liver metabolism and liver cancer

The liver is an essential organ for nutrient and drug metabolism - possessing the remarkable ability to sense environmental and metabolic stimuli and provide an optimally adaptive response. Early growth response 1 (Egr1), an immediate early transcriptional factor which acts as a coordinator of the complex response to stress, is induced during liver injury and controls the expression of a wide range of genes involved in metabolism, cell proliferation, and role of Egr1 in liver injury and repair, deficiency of Egr1 delays liver regeneration process. The known upstream regulators of Egr1 include, but are not limited to, growth factors (e.g. transforming growth factor β1, platelet-derived growth factor, epidermal growth factor, hepatocyte growth factor), nuclear receptors (e.g. hepatocyte nuclear factor 4α, small heterodimer partner, peroxisome proliferator-activated receptor-γ), and other transcription factors (e.g. Sp1, E2F transcription factor 1). Research efforts using various animal models such as fatty liver, liver injury, and liver fibrosis contribute greatly to the elucidation of Egr1 function in the liver. Hepatocellular carcinoma (HCC) represents the second leading cause of cancer mortality worldwide due to the heterogeneity and the late stage at which cancer is generally diagnosed. Recent studies highlight the involvement of Egr1 in HCC development. The purpose of this review is to summarize current studies pertaining to the role of Egr1 in liver metabolism and liver diseases including liver cancer.

Dopamine D₄ receptors inhibit proliferation and migration of vascular smooth muscle cells induced by insulin via down-regulation of insulin receptor expression

Vascular smooth muscle cells (VSMCs) proliferation and migration, which are central in the development of vascular diseases, are regulated by numerous hormones and humoral factors. Activation of the insulin receptor stimulates VSMCs proliferation while dopamine receptors, via D₁ and D₃ receptors, inhibit the stimulatory effects of norepinephrine on VSMCs proliferation. We hypothesize that activation of the D₄ dopamine receptor may also inhibit the proliferation and migration of VSMCs, therefore, inhibit atherosclerosis. Our current study found that insulin increased the proliferation and migration of A10 cells, an effect that was reduced in the presence of a D₄ receptor agonist, PD168077. The negative effect of the D₄ receptor on insulin’s action may be via decreasing insulin receptor expression, because activation of the D₄ receptor inhibited insulin receptor protein and mRNA expressions, indicating that the regulation occured at the transcriptional or post-transcriptional levels. To determine whether or not the inhibition of D₄ receptor on insulin-mediated proliferation and migration of VSMCs has physiological significance, hyper-insulinemic Sprague–Dawley rats with balloon-injured carotid artery were treated with a D₄ agonist, PD168077, (6 mg/kg/d) for 14 days. We found that PD168077 significantly inhibited neointimal formation by inhibition of VSMC proliferation. This study suggests that activation of the D₄ receptor suppresses the proliferation and migration of VSMCs, therefore, inhibit atherosclerosis. The D₄ receptor may be a potential therapeutic target to reduce the effects of insulin on artery remodeling.

Expression, signaling and function of Egr transcription factors in pancreatic β-cells and insulin-responsive tissues

Egr-1 and the related zinc finger transcription factors Egr-2, Egr-3, and Egr-4 are stimulated by many extracellular signaling molecules and represent a convergence point for intracellular signaling cascades. Egr-1 expression is induced in insulinoma cells and pancreatic β-cells following stimulation with either glucose, or pregnenolone sulfate. Moreover, stimulation of Gαq and Gαs-coupled receptors enhances EGR-1 gene transcription. Functional studies revealed that Egr transcription factors control insulin biosynthesis via regulation of Pdx-1 expression. Glucose homeostasis and pancreatic islet size are regulated by Egr transcription factors, indicating that these proteins control central physiological parameters regulated by pancreatic β-cells. In addition, Egr-1 is an integral part of the insulin receptor signaling cascade in insulin-responsive tissues and influences insulin resistance.

Control of adipose tissue expandability in response to high fat diet by the insulin-like growth factor-binding protein-4

Adipose tissue expansion requires growth and proliferation of adipocytes and the concomitant expansion of their stromovascular network. We have used an ex vivo angiogenesis assay to study the mechanisms involved in adipose tissue expansion. In this assay, adipose tissue fragments placed under pro-angiogenic conditions form sprouts composed of endothelial, perivascular, and other proliferative cells. We find that sprouting was directly stimulated by insulin and was enhanced by prior treatment of mice with the insulin sensitizer rosiglitazone. Moreover, basal and insulin-stimulated sprouting increased progressively over 30 weeks of high fat diet feeding, correlating with tissue expansion during this period. cDNA microarrays analyzed to identify genes correlating with insulin-stimulated sprouting surprisingly revealed only four positively correlating (Fads3, Tmsb10, Depdc6, and Rasl12) and four negatively correlating (Asph, IGFbp4, Ppm1b, and Adcyap1r1) genes. Among the proteins encoded by these genes, IGFbp4, which suppresses IGF-1 signaling, has been previously implicated in angiogenesis, suggesting a role for IGF-1 in adipose tissue expandability. Indeed, IGF-1 potently stimulated sprouting, and the presence of activated IGF-1 receptors in the vasculature was revealed by immunostaining. Recombinant IGFbp4 blocked the effects of insulin and IGF-1 on mouse adipose tissue sprouting and also suppressed sprouting from human subcutaneous adipose tissue. These results reveal an important role of IGF-1/IGFbp4 signaling in post-developmental adipose tissue expansion.

Aldose reductase drives hyperacetylation of Egr-1 in hyperglycemia and consequent upregulation of proinflammatory and prothrombotic signals

Sustained increases in glucose flux via the aldose reductase (AR) pathway have been linked to diabetic vascular complications. Previous studies revealed that glucose flux via AR mediates endothelial dysfunction and leads to lesional hemorrhage in diabetic human AR (hAR) expressing mice in an apoE(-/-) background. Our studies revealed sustained activation of Egr-1 with subsequent induction of its downstream target genes tissue factor (TF) and vascular cell adhesion molecule-1 (VCAM-1) in diabetic apoE(-/-)hAR mice aortas and in high glucose-treated primary murine aortic endothelial cells expressing hAR. Furthermore, we observed that flux via AR impaired NAD(+) homeostasis and reduced activity of NAD(+)-dependent deacetylase Sirt-1 leading to acetylation and prolonged expression of Egr-1 in hyperglycemic conditions. In conclusion, our data demonstrate a novel mechanism by which glucose flux via AR triggers activation, acetylation, and prolonged expression of Egr-1 leading to proinflammatory and prothrombotic responses in diabetic atherosclerosis.

Panax Quinquefolius Saponin of Stem and Leaf Attenuates Intermittent High Glucose-Induced Oxidative Stress Injury in Cultured Human Umbilical Vein Endothelial Cells via PI3K/Akt/GSK-3 β Pathway

Panax quinquefolius saponin of stem and leaf (PQS), the effective parts of American ginseng, is widely used in China as a folk medicine for diabetes and cardiovascular diseases treatment. In our previous studies, we have demonstrated that PQS could improve the endothelial function of type II diabetes mellitus (T2DM) rats with high glucose fluctuation. In the present study, we investigated the protective effects of PQS against intermittent high glucose-induced oxidative damage on human umbilical vein endothelial cells (HUVECs) and the role of phosphatidylinositol 3-kinase kinase (PI3K)/Akt/GSK-3 β pathway involved. Our results suggested that exposure of HUVECs to a high glucose concentration for 8 days showed a great decrease in cell viability accompanied by marked MDA content increase and SOD activity decrease. Moreover, high glucose significantly reduced the phosphorylation of Akt and GSK-3 β . More importantly, these effects were even more evident in intermittent high glucose condition. PQS treatment significantly attenuated intermittent high glucose-induced oxidative damage on HUVECs and meanwhile increased cell viability and phosphorylation of Akt and GSK-3 β of HUVECs. Interestingly, all these reverse effects of PQS on intermittent high glucose-cultured HUVECs were inhibited by PI3K inhibitor LY294002. These findings suggest that PQS attenuates intermittent-high-glucose-induced oxidative stress injury in HUVECs by PI3K/Akt/GSK-3 β pathway.

Effects of some anti-diabetic and cardioprotective agents on proliferation and apoptosis of human coronary artery endothelial cells

BACKGROUND

The leading cause of death for patients suffering from diabetes is macrovascular disease. Endothelial dysfunction is often observed in type 2 diabetic patients and it is considered to be an important early event in the pathogenesis of atherogenesis and cardiovascular disease. Many drugs are clinically applied to treat diabetic patients. However, little is known whether these agents directly interfere with endothelial cell proliferation and apoptosis. This study therefore aimed to investigate how anti-diabetic and cardioprotective agents affect human coronary artery endothelial cells (HCAECs).

METHODS

The effect of anti-diabetic and cardioprotective agents on HCAEC viability, proliferation and apoptosis was studied. Viability was assessed using Trypan blue exclusion; proliferation in 5 mM and 11 mM of glucose was analyzed using [3H]thymidine incorporation. Lipoapoptosis of the cells was investigated by determining caspase-3 activity and the subsequent DNA fragmentation after incubation with the free fatty acid palmitate, mimicking diabetic lipotoxicity.

RESULTS

Our data show that insulin, metformin, BLX-1002, and rosuvastatin improved HCAEC viability and they could also significantly increase cell proliferation in low glucose. The proliferative effect of insulin and BLX-1002 was also evident at 11 mM of glucose. In addition, insulin, metformin, BLX-1002, pioglitazone, and candesartan significantly decreased the caspase-3 activity and the subsequent DNA fragmentation evoked by palmitate, suggesting a protective effect of the drugs against lipoapoptosis.

CONCLUSION

Our results suggest that the anti-diabetic and cardioprotective agents mentioned above have direct and beneficial effects on endothelial cell viability, regeneration and apoptosis. This may add yet another valuable property to their therapeutic effect, increasing their clinical utility in type 2 diabetic patients in whom endothelial dysfunction is a prominent feature that adversely affect their survival.

Coordinated sumoylation and ubiquitination modulate EGF induced EGR1 expression and stability

Background

Human early growth response-1 (EGR1) is a member of the zing-finger family of transcription factors induced by a range of molecular and environmental stimuli including epidermal growth factor (EGF). In a recently published paper we demonstrated that integrin/EGFR cross-talk was required for Egr1 expression through activation of the Erk1/2 and PI3K/Akt/Forkhead pathways. EGR1 activity and stability can be influenced by many different post-translational modifications such as acetylation, phosphorylation, ubiquitination and the recently discovered sumoylation. The aim of this work was to assess the influence of sumoylation on EGF induced Egr1 expression and/or stability.

Methods

We modulated the expression of proteins involved in the sumoylation process in ECV304 cells by transient transfection and evaluated Egr1 expression in response to EGF treatment at mRNA and protein levels.

Results

We demonstrated that in ECV304 cells Egr1 was transiently induced upon EGF treatment and a fraction of the endogenous protein was sumoylated. Moreover, SUMO-1/Ubc9 over-expression stabilized EGF induced ERK1/2 phosphorylation and increased Egr1 gene transcription. Conversely, in SUMO-1/Ubc9 transfected cells, EGR1 protein levels were strongly reduced. Data obtained from protein expression and ubiquitination analysis, in the presence of the proteasome inhibitor MG132, suggested that upon EGF stimuli EGR1 sumoylation enhanced its turnover, increasing ubiquitination and proteasome mediated degradation.

Conclusions

Here we demonstrate that SUMO-1 modification improving EGR1 ubiquitination is involved in the modulation of its stability upon EGF mediated induction.

Inhibition of cell proliferation by CD44: Akt is inactivated and EGR-1 is down-regulated

OBJECTIVE

CD44 is a transmembrane glycoprotein and can facilitate signal transduction by serving as a platform for molecular recruitment and assembly. A number of studies have suggested that CD44 can either positively or negatively regulate cell proliferation. The purpose of this study was to investigate how CD44 can inhibit cell proliferation.

MATERIALS AND METHODS

We engineered E6.1 Jurkat cells to express CD44. Importantly, these cells lack endogenous CD44 expression. Molecular pathways involved with cell proliferation were studied using RT(2)-PCR array, siRNA, Western blotting and by employing pharmacological inhibitors of ERK1/2, p38 and the PI3K/Akt pathways.

RESULTS

We found that CD44 expression significantly inhibited cell proliferation and down-regulated EGR-1 expression and EGR-1 targets cyclin D1 and cyclin D2. Transfection of control E6.1 Jurkat cells with EGR-1 siRNA also inhibited cell proliferation, confirming its role. Disruption of the PI3K/Akt pathway with pharmacological inhibitors reduced both EGR-1 expression and cell proliferation, recapitulating the properties of CD44 expressing cells. Akt was hypophosphorylated in cells expressing CD44 showing its potential role in negatively regulating Akt activation. Strikingly, constitutively active Akt rescued the proliferation defect showing requirement for active Akt, in our system.

CONCLUSION

Our results suggest a novel pathway by which CD44 inactivates Akt, down-regulates EGR-1 expression and inhibits cell proliferation.

Phosphoinositide 3-kinase signaling in the vertebrate retina

The phosphoinositide (PI) cycle, discovered over 50 years ago by Mabel and Lowell Hokin, describes a series of biochemical reactions that occur on the inner leaflet of the plasma membrane of cells in response to receptor activation by extracellular stimuli. Studies from our laboratory have shown that the retina and rod outer segments (ROSs) have active PI metabolism. Biochemical studies revealed that the ROSs contain the enzymes necessary for phosphorylation of phosphoinositides. We showed that light stimulates various components of the PI cycle in the vertebrate ROS, including diacylglycerol kinase, PI synthetase, phosphatidylinositol phosphate kinase, phospholipase C, and phosphoinositide 3-kinase (PI3K). This article describes recent studies on the PI3K-generated PI lipid second messengers in the control and regulation of PI-binding proteins in the vertebrate retina.

High ambient glucose augments angiotensin II-induced proinflammatory gene mRNA expression in human mesangial cells: effects of valsartan and simvastatin

BACKGROUND

Hyperglycemia may potentiate the adverse renal effects of angiotensin II (AII). In the kidney, the major target of AII action is the glomerular mesangial cell, where its hemodynamic and proinflammatory action contributes to renal injury. AII action is mediated by several types of cell receptors. Among those, the AT1 receptor has been best studied using specific AII receptor blockers (ARBs). These agents have emerged as major new modalities in the prevention and amelioration of renal disease where the ARB renoprotective anti-inflammatory properties could be more important than previously appreciated. Like the ARBs, statins may also modulate inflammatory responses that are renoprotective and complement their cholesterol-lowering effects.

AIM

The aim of this project was to (i) identify a repertoire of proinflammatory mesangial cell AII-inducible mRNAs; (ii) determine if the AII-induced proinflammatory mRNA responses depend on ambient glucose, and (iii) test the anti-inflammatory effectiveness of an ARB, valsartan, either alone or in combination with a statin, simvastatin.

RESULTS/CONCLUSIONS

Using high-density microarrays and real-time PCR we identified several AII-inducible proinflammatory mesangial genes that exhibited augmented mRNA responses in high-glucose milieu. Valsartan blocked the AII-induced mRNA expression of proinflammatory genes (i.e. MCP-1, LIF and COX-2) maintained in normal and high glucose. These observations add to the mounting evidence that ARBs have anti-inflammatory effects in the kidney, a beneficial effect that may be more important in protecting renal function in diabetic patients. While simvastatin inhibited expression of some mRNAs encoding chemokines/cytokines, it enhanced expression of mRNA encoding COX-2, a key mediator of inflammation. Thus, the non-cholesterol effects of statins on inflammatory responses appear complex.

Activation of the insulin receptor (IR) by insulin and a synthetic peptide has different effects on gene expression in IR-transfected L6 myoblasts

Single-chain peptides have been recently produced that display either mimetic or antagonistic properties against the insulin and IGF-1 (insulin-like growth factor 1) receptors. We have shown previously that the insulin mimetic peptide S597 leads to significant differences in receptor activation and initiation of downstream signalling cascades despite similar binding affinity and in vivo hypoglycaemic potency. It is still unclear how two ligands can initiate different signalling responses through the IR (insulin receptor). To investigate further how the activation of the IR by insulin and S597 differentially activates post-receptor signalling, we studied the gene expression profile in response to IR activation by either insulin or S597 using microarray technology. We found striking differences between the patterns induced by these two ligands. Most remarkable was that almost half of the genes differentially regulated by insulin and S597 were involved in cell proliferation and growth. Insulin either selectively regulated the expression of these genes or was a more potent regulator. Furthermore, we found that half of the differentially regulated genes interact with the genes involved with the MAPK (mitogen-activated protein kinase) pathway. These findings support our signalling results obtained previously and confirm that the main difference between S597 and insulin stimulation resides in the activation of the MAPK pathway. In conclusion, we show that insulin and S597 acting via the same receptor differentially affect gene expression in cells, resulting in a different mitogenicity of the two ligands, a finding which has critical therapeutic implications.

Mechanisms of glucose-induced expression of pancreatic-derived factor in pancreatic beta-cells

Pancreatic-derived factor (PANDER) is a cytokine-like peptide highly expressed in pancreatic beta-cells. PANDER was reported to promote apoptosis of pancreatic beta-cells and secrete in response to glucose. Here we explored the effects of glucose on PANDER expression, and the underlying mechanisms in murine pancreatic beta-cell line MIN6 and primary islets. Our results showed that glucose up-regulated PANDER mRNA and protein levels in a time- and dose-dependent manner in MIN6 cells and pancreatic islets. In cells expressing cAMP response element-binding protein (CREB) dominant-negative construct, glucose failed to induce PANDER gene expression and promoter activation. Treatment of the cells with calcium chelator [EGTA, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl)ester (BAPTA/AM)], the voltage-dependent Ca(2+) channel inhibitor (nifedipine), the protein kinase A (PKA) inhibitor (H89), the protein kinase C (PKC) inhibitor (Go6976), or the MAPK kinase 1/2 inhibitor (PD98059), all significantly inhibited glucose-induced PANDER gene expression and promoter activation. Further studies showed that glucose induced CREB phosphorylation through Ca(2+)-PKA-ERK1/2 and Ca(2+)-PKC pathways. Thus, the Ca(2+)-PKA-ERK1/2-CREB and Ca(2+)-PKC-CREB signaling pathways are involved in glucose-induced PANDER gene expression. Wortmannin (phosphatidylinositol 3-kinase inhibitor), ammonium pyrrolidinedithiocarbamate (nuclear factor-kappaB inhibitor and nonspecific antioxidant), and N-acetylcysteine (antioxidant) were also found to inhibit glucose-induced PANDER promoter activation and gene expression. Because there is no nuclear factor-kappaB binding site in the promoter region of PANDER gene, these results suggest that phosphatidylinositol 3-kinase and reactive oxygen species be involved in glucose-induced PANDER gene expression. In conclusion, glucose induces PANDER gene expression in pancreatic beta-cells through multiple signaling pathways. Because PANDER is expressed by pancreatic beta-cells and in response to glucose in a similar way to those of insulin, PANDER may be involved in glucose homeostasis.

PSM/SH2-B distributes selected mitogenic receptor signals to distinct components in the PI3-kinase and MAP kinase signaling pathways

The Pro-rich, PH, and SH2 domain containing mitogenic signaling adapter PSM/SH2-B has been implicated as a cellular partner of various mitogenic receptor tyrosine kinases and related signaling mechanisms. Here, we report in a direct comparison of three peptide hormones, that PSM participates in the assembly of distinct mitogenic signaling complexes in response to insulin or IGF-I when compared to PDGF in cultured normal fibroblasts. The complex formed in response to insulin or IGF-I involves the respective peptide hormone receptor and presumably the established components leading to MAP kinase activation. However, our data suggest an alternative link from the PDGF receptor via PSM directly to MEK1/2 and consequently also to p44/42 activation, possibly through a scaffold protein. At least two PSM domains participate, the SH2 domain anticipated to link PSM to the respective receptor and the Pro-rich region in an association with an unidentified downstream component resulting in direct MEK1/2 and p44/42 regulation. The PDGF receptor signaling complex formed in response to PDGF involves PI 3-kinase in addition to the same components and interactions as described for insulin or IGF-I. PSM associates with PI 3-kinase via p85 and in addition the PSM PH domain participates in the regulation of PI 3-kinase activity, presumably through membrane interaction. In contrast, the PSM Pro-rich region appears to participate only in the MAP kinase signal. Both pathways contribute to the mitogenic response as shown by cell proliferation, survival, and focus formation. PSM regulates p38 MAP kinase activity in a pathway unrelated to the mitogenic response.

Transcriptional regulation of IL-8 by iron chelator in human epithelial cells is independent from NF-κB but involves ERK1/2- and p38 kinase-dependent activation of AP-1

We have shown that the bacterial iron chelator, deferoxamine (DFO), triggers inflammatory signals including the production of CXC chemokine IL-8, in human intestinal epithelial cells (IECs) by activating the ERK1/2 and p38 kinase pathways. In this study we investigated the mechanisms involved in IL-8 generation by DFO, focusing on the transcription factors involved and the roles of both mitogen-activated protein kinases (MAPKs) in the transcription factor activation. Treatment of human epithelial HT-29 cells with DFO markedly up-regulated the expression of the essential components of the transcription factor AP-1 at a transcriptional level, while it minimally affected the expression of the NF-kappaB subunits. DFO also induced AP-1-dependent transcriptional activity in HT-29 cells, and this activity was further augmented by the wild-type c-Jun transfection. In contrast, the AP-1 activity by DFO was markedly decreased by the dominant-negative c-Jun transfection. Electrophoretic mobility shift assays revealed that DFO increases the specific binding of AP-1 but not of NF-kappaB. Such AP-1 binding and transcriptional activities were blocked by the inhibitors of the ERK1/2 and p38 kinase pathways, suggesting that both mitogen-activated protein kinases (MAPKs) lie upstream of AP-1. Besides its action on AP-1, DFO also induced the specific binding of other transcription factors such as CREB and Egr-1. In summary, our results indicate that iron chelator-induced IL-8 generation in IECs involves activation of ERK1/2 and p38 kinase and downstream activation of AP-1. A possible link between iron status and two additional transcription factors, that is, CREB and Egr-1, rather than NF-kappaB, was also suggested.

Regulation of pancreas duodenum homeobox-1 expression by early growth response-1

The homeodomain transcription factor pancreas duodenum homeobox-1 (PDX-1) is a key regulator of pancreatic beta-cell development, function, and survival. Deficits in PDX-1 expression result in insulin deficiency and hyperglycemia. We previously found that the glucose-responsive transcription factor early growth response-1 (Egr-1) activates the insulin promoter in part by increasing expression levels of PDX-1. We now report that Egr-1 binds and activates multiple regulatory sites within the pdx-1 promoter. We identified consensus Egr-1 recognition sequences within proximal and distal regions of the mouse pdx-1 promoter and demonstrated specific binding of Egr-1 by chromatin immunoprecipitation and electrophoretic mobility shift assays. Overexpression of Egr-1 increased transcriptional activation of the -4500 proximal pdx-1 promoter and of the highly conserved regulatory Areas I, II, and III. Mutagenesis of a specific Egr-1 binding site within Area III substantially decreased Egr-1-mediated activation. Egr-1 increased the transcriptional activation of Areas I and II, despite the absence of Egr-1 recognition sequences within this promoter segment, suggesting that Egr-1 also can regulate the pdx-1 promoter indirectly. Egr-1 increased, and a dominant-negative Egr-1 mutant repressed, the transcriptional activation of distal pdx-1 promoter sequences. Mutagenesis of a specific Egr-1 binding site within regulatory Area IV reduced basal and Egr-1-mediated transcriptional activation. Our data indicate that Egr-1 regulates expression of PDX-1 in pancreatic beta-cells by both direct and indirect activation of the pdx-1 promoter. We propose that Egr-1 expression levels may act as a sensor in pancreatic beta-cells to translate extracellular signals into changes in PDX-1 expression levels and pancreatic beta-cell function.

Association of insulin resistance and hematologic parameters: study of a middle-aged and elderly Chinese population in Taiwan

BACKGROUND

Chronic inflammation is a common feature related to changes in hematologic parameters in insulin resistance. The aims of this study were to explore the relationship between hematologic parameters and insulin resistance, and to establish a gerontologic profile for following studies.

METHODS

Residents aged over 40 years in 3 major townships in I-Lan County participating in the Adult Health Examination were invited for the study. Diagnosis of diabetes mellitus (DM) was done according to American Diabetes Association criteria. Insulin resistance was measured by homeostasis model assessment (HOMA-IR), and subjects with the highest tertile of HOMA-IR were defined as being insulin resistant. Hematologic parameters including white blood cell (WBC) count, red blood cell (RBC) count, hemoglobin, and platelet count were measured for comparisons.

RESULTS

A total of 857 subjects (mean age, 64.6 +/- 11.2 years; male/female, 373/484) participated in this study. Their mean body mass index (BMI) was 24.5 +/- 3.7 kg/m2, and 42.4% of them were obese and 21.8% were overweight. The overall prevalence of DM was 15.4% (7.7% were previously diagnosed and 7.7% were newly diagnosed), and impaired fasting glucose was 7.2%. Trend analyses confirmed that age, BMI, HOMA-IR, WBC and platelet counts were significantly increased as glycemic metabolism exacerbated (p = 0.007, < 0.001, < 0.001, < 0.001 and 0.025, respectively). Compared with insulin-sensitive subjects, insulin-resistant subjects were more likely to be females (70.2% vs. 49.7%, p < 0.001), and had significantly higher BMI (26.2 +/- 3.9 kg/m2 vs. 23.7 +/- 3.3 kg/m2, p < 0.001), HOMA-IR (3.6 +/- 3.5 vs. 0.7 +/- 0.3, p < 0.001), WBC count (6686.9 +/- 1889.2/mm3 vs. 5942.9 +/- 1740.4/mm3, p < 0.001), and platelet count (243.5 +/- 70.9 x 10(3)/mm3 vs. 231.0 +/- 62.2 x 10(3)/mm3, p = 0.011), but not age (64.5 +/- 11.0 years vs. 64.6 +/- 11.4 years, p = 0.93) or RBC count (4.6 +/- 0.6 M/mm3 vs. 4.6 +/- 0.6 M/mm3, p = 0.76). When age and sex were controlled, HOMA-IR significantly correlated with WBC count (gamma = 0.23, p < 0.001) and platelet count (gamma = 0.09, p = 0.007). However, by multiple logistic regression, female gender, overweight and obesity, and elevated WBC count were all found to be independent risk factors of insulin resistance, but age, RBC and platelet counts were not.

CONCLUSION

Elevated WBC count but not RBC count was significantly associated with insulin resistance and glycemic metabolism. The relationship between platelet count and insulin resistance deserves further investigations.

Regulation of insulin gene transcription by the immediate-early growth response gene Egr-1

Changes in extracellular glucose levels regulate the expression of the immediate-early response gene and zinc finger transcription factor early growth response-1 (Egr-1) in insulin-producing pancreatic beta-cells, but key target genes of Egr-1 in the endocrine pancreas have not been identified. We found that overexpression of Egr-1 in clonal (INS-1) beta-cells increased transcriptional activation of the rat insulin I promoter. In contrast, reductions in Egr-1 expression levels or function with the introduction of either small interfering RNA targeted to Egr-1 (siEgr-1) or a dominant-negative form of Egr-1 decreased insulin promoter activation, and siEgr-1 suppressed insulin gene expression. Egr-1 did not directly interact with insulin promoter sequences, and mutagenesis of a potential G box recognition sequence for Egr-1 did not impair the Egr-1 responsiveness of the insulin promoter, suggesting that regulation of insulin gene expression by Egr-1 is probably mediated through additional transcription factors. Overexpression of Egr-1 increased, and reduction of Egr-1 expression decreased, transcriptional activation of the glucose-responsive FarFlat minienhancer within the rat insulin I promoter despite the absence of demonstrable Egr-1-binding activity to FarFlat sequences. Notably, augmenting Egr-1 expression levels in insulin-producing cells increased the mRNA and protein expression levels of pancreas duodenum homeobox-1 (PDX-1), a major transcriptional regulator of glucose-responsive activation of the insulin gene. Increasing Egr-1 expression levels enhanced PDX-1 binding to insulin promoter sequences, whereas mutagenesis of PDX-1-binding sites reduced the capacity of Egr-1 to activate the insulin promoter. We propose that changes in Egr-1 expression levels in response to extracellular signals, including glucose, can regulate PDX-1 expression and insulin production in pancreatic beta-cells.

Hyperglycemia alters PI3k and Akt signaling and leads to endothelial cell proliferative dysfunction

Diabetes mellitus is a major risk factor for the development of vascular complications. We hypothesized that hyperglycemia decreases endothelial cell (EC) proliferation and survival via phosphatidylinositol 3-kinase (PI3k) and Akt signaling pathways. We cultured human umbilical vein ECs (HUVEC) in 5, 20, or 40 mM d-glucose. Cells grown in 5, 20, and 40 mM mannitol served as a control for osmotic effects. We measured EC proliferation for up to 15 days. We assessed apoptosis by annexin V and propidium iodide staining and flow cytometry, analyzed cell lysates obtained on culture day 8 for total and phosphorylated PI3k and Akt by Western blot analysis, and measured Akt kinase activity using a GSK fusion protein. HUVEC proliferation was also tested in the presence of pharmacological inhibitors of PI3k-Akt (wortmannin and LY294002) and after transfection with a constitutively active Akt mutant. ECs in media containing 5 mM d-glucose (control) exhibited log-phase growth on days 7-10. d-Glucose at 20 and 40 mM significantly decreased proliferation versus control (P < 0.05 for both), whereas mannitol did not impair EC proliferation. Apoptosis increased significantly in HUVEC exposed to 40 mM d-glucose. d-Glucose at 40 mM significantly decreased tyrosine-phosphorylated PI3k, threonine 308-phosphorylated-Akt, and Akt activity relative to control 5 mM d-glucose. Pharmacological inhibition of PI3k-Akt resulted in a dose-dependent decrease in EC proliferation. Transfection with a constitutively active Akt mutant protected ECs by enhancing proliferation when grown in 20 and 40 mM d-glucose. We conclude that d-glucose regulates Akt signaling through threonine phosphorylation of Akt and that hyperglycemia-impaired PI3k-Akt signaling may promote EC proliferative dysfunction in diabetes.

Cellular insulin resistance in Epstein-Barr virus-transformed lymphoblasts from young insulin-resistant Japanese men

The metabolic syndrome is characterized by a blunted insulin-mediated glucose uptake in various cell types. We compared the glucose uptake characteristics of Epstein-Barr virus (EBV)-transformed lymphoblasts obtained from young men with vs without metabolic and cardiovascular evidence of metabolic syndrome. From a population of 218 men, 20- to 25-year-old, 10 men with a systolic blood pressure (BP) > or =130 mm Hg and family history of hypertension were assigned to a high BP (HBP) group, and 10 with a BP < or =110 mm Hg, and no family history of hypertension was assigned to a low BP (LBP) group. Multiple clinical and metabolic characteristics were examined in both groups and compared. Peripheral lymphocytes from HBP and LBP subjects were EBV-transformed, and the glucose transporter (Glut)-mediated glucose uptake from each group was compared in lymphoblasts. Body mass index, fasting glucose, immunoreactive insulin, insulin resistance index based on a homeostasis model assessment (HOMA-R), and total and low-density lipoprotein cholesterol were significantly higher in the HBP than the LBP subgroup (whole-body insulin resistance). Baseline Glut-mediated and Glut-mediated insulin-stimulated glucose uptake by lymphoblasts from the HBP group were significantly lower than by lymphoblasts from the LBP group (cellular insulin resistance). The net increment in Glut-mediated glucose uptake by insulin was inversely correlated with HOMA-R. In conclusion, cellular insulin resistance in EBV-transformed lymphoblasts is associated with young Japanese subjects with HBP. The net increment in Glut-mediated glucose uptake by insulin in lymphoblasts may be a useful intermediate phenotype to study genetic aspects of the metabolic syndrome.

Peripheral nerve endoneurial microangiopathy and necrosis in rats with insulinoma

Peripheral nerve pathology related to chronic hyperinsulinemia and hypoglycemia has yet to be fully explored. Here we conducted a systematic quantitative analysis of morphological alterations in peripheral sensory and motor nerve fibers and endoneurial microvasculature in longstanding insulinoma-carrying rats (I-rats; n=12). Age-matched normal rats (n=6) served as controls. Over the 15-month observation period, two of I-rats developed paresis of the hind limbs when their blood glucose level fell below 1.7 mmol/l. These animals showed a massive myelinated fiber loss associated with active degeneration of residual myelinated fibers and multiple endoneurial microvascular occlusions at the sciatic nerve level. The rest of the non-paretic I-rats showed a decreased density of large myelinated fibers with axonal degeneration in the peroneal nerve and an increased density of small myelinated fibers with preserved morphology in the sural nerve. This was associated with endoneurial microangiopathic changes indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and an increase in endoneurial microvascular density in the sciatic and sural nerves. In conjunction with previous data, these findings suggest that the observed increase in endoneurial microvascular density may be a compensatory response to endoneurial ischemia/hypoxia induced by chronic hyperinsulinemia in I-rats without paresis. In conclusion, the present study showed characteristic morphological alterations in peripheral sensory and motor nerve fibers associated with microangiopathy indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and provides the first evidence for the occurrence of endoneurial necrosis in the sciatic nerve, to which the hind limb paresis can be ascribed in I-rats.

Inhibition of Egr-1 expression reverses transformation of prostate cancer cells in vitro and in vivo

Transcription factor early growth response-1 (Egr-1) is a crucial regulator of cell growth, differentiation and survival. Several observations suggest that Egr-1 is growth promoting in prostate cancer cells and that blocking its function may impede cancer progression. To test this hypothesis, we developed phosphorothioate antisense oligonucleotides that efficiently inhibit Egr-1 expression without altering the expression of other family members Egr-2, Egr-3 and Egr-4. In TRAMP mouse-derived prostate cancer cell lines, our optimal antisense oligonucleotide decreased the expression of the Egr-1 target gene transforming growth factor-beta1 whereas a control oligonucleotide had no effect, indicating that the antisense blocked Egr-1 function as a transcription factor. The antisense oligonucleotide deregulated cell cycle progression and decreased proliferation of the three TRAMP cell lines by an average of 54+/-3%. Both colony formation and growth in soft agar were inhibited by the antisense oligonucleotide. When TRAMP mice were treated systemically for 10 weeks, the incidence of palpable tumors at 32 weeks of age in untreated mice or mice injected with the control scramble oligonucleotide was 87%, whereas incidence of tumors in antisense-Egr-1-treated mice was significantly reduced to 37% (P=0.026). Thus, Egr-1 plays a functional role in the transformed phenotype and may represent a valid target for prostate cancer therapy.

High-glucose enhances a thromboxane A2-induced aortic contraction mediated by an alteration of phosphatidylinositol turnover

The effect of the thromboxane A(2) analogue U46619 (9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2)(alpha)) on sustained contraction in the mouse aorta was investigated. U46619 induced concentration-dependent (1 - 100 nM) increases in contraction. These contractile responses were enhanced significantly under high-glucose-physiological salt solution (HG-PSS) (2-fold greater than normal-PSS) conditions. This hyperactivation may be associated with aortic dysfunction in diabetes. However, the mechanisms remain unclear. HG-PSS enhanced U46619-induced accumulation of endogenous diacylglycerol (DG). Phospholipase C inhibitor (U73122) suppressed DG accumulation under normal conditions; however, suppression was not observed under high-glucose conditions. The HG-PSS-induced enhancement of contraction was inhibited by protein kinase C (PKC) inhibitor (calphostin C). This result indicated that accumulated DG might increase PKC activity, which then stimulates DG kinase activation as a feedback mechanism. DG kinase inhibition also suppressed HG-PSS-induced enhancement of contraction. Increased myo-inositol incorporation was detected under high-glucose conditions, indicating an acceleration of phosphatidylinositol (PI)-turnover. Moreover, rho kinase inhibitor (Y27632) suppressed U46619-induced contraction exclusively in normal-PSS. These findings indicated that HG-PSS treatment increases DG synthesis derived from incorporated glucose, PKC and DG kinase activation, and enhances the U46619-induced contraction via acceleration of PI-turnover. This series of responses may be involved in the dysfunction of aorta under high-glucose conditions occurring in association with diabetes.

Relation between insulin resistance and hematological parameters in elderly Koreans-Southwest Seoul (SWS) Study

In this study, we investigated the relation between insulin resistance and hematological parameters in elderly Koreans. This study included 1314 non-diabetic subjects over the age of 60, selected from a cross-sectional study, which was conducted in 1999 in Seoul, Korea. We measured fasting and post-load 2 h plasma glucose, insulin levels, lipid profiles, anthropometric measures, and hematological parameters. The degree of insulin resistance was assessed using the homeostasis model assessment (HOMA). We found a correlation between insulin resistance and hemoglobin concentrations in non-smoking men (r=0.20, P=0.0186). In non-smoking women, insulin resistance correlated with hemoglobin (r=0.10, P=0.0017) and with white blood cell (WBC) count (r=0.15, P=0.001). Hemoglobin concentrations and WBC counts were also associated with other components of the insulin resistance syndrome such as body mass index, blood pressure, lipid profiles and fasting plasma insulin levels (surrogate for insulin resistance). Furthermore, the group in the upper quartile for insulin resistance showed higher hemoglobin concentrations and WBC counts than the lower quartile, independent of smoking status and serum iron concentrations. Using HOMA-IR as a dependent variable in a multiple regression analysis, age, body mass index (BMI), waist-to-hip ratio (WHR), systolic blood pressure, HDL cholesterol, triglyceride, WBC count, hemoglobin, hematocrit and serum TIBC were significant. Our results provide support for a relation between insulin resistance/hyperinsulinemia and hematological parameters such as hemoglobin concentrations and WBC counts in elderly Koreans. This suggests that increased erythropoiesis and subclinical inflammation could be part of the metabolic syndrome in elderly Koreans.

Differential regulation of early growth response gene-1 expression by insulin and glucose in vascular endothelial cells

OBJECTIVE

Early growth response gene (Egr)-1 is a key transcription factor involved in vascular pathophysiology. Its role in diabetic vascular complications, however, remains unclear. Because hyperinsulinemia and hyperglycemia are major risk factors leading to diabetic vascular complications, we examined the effect of insulin and glucose on Egr-1 expression in murine glomerular vascular endothelial cells.

METHODS AND RESULTS

Insulin or glucose, when added separately, increased egr-1 mRNA levels and promoter activity, as well as Egr-1 protein levels in nuclear extracts. When insulin was added to cells preincubated with glucose, the two had an additive effect on Egr-1 expression. Furthermore, vascular endothelial growth factor receptor-1 (flt-1) and plasminogen activator inhibitor-1, two known Egr-1-responsive genes, were also upregulated in the presence of insulin or glucose. An investigation into the underlying molecular mechanisms demonstrated that insulin, but not glucose, increased Egr-1 expression through extracellular signal-regulated kinase 1/2 activation, which is consistent with our previous reports. In contrast, inhibition of protein kinase C by phorbol ester or by the specific protein kinase C inhibitor chelerythrine chloride downregulated glucose-induced, but not insulin-induced, Egr-1 expression.

CONCLUSIONS

Differential regulation of Egr-1 expression by insulin and glucose in vascular cells may be one of the initial key events that plays a crucial role in the development of diabetic vascular complications.

Specific inhibition of Egr-1 prevents mesangial cell hypercellularity in experimental nephritis

BACKGROUND

Mesangial cell proliferation is a frequent finding in glomerulonephritis. In cultured mesangial cells, we demonstrated that inhibition of the zinc finger transcription factor, early growth response gene-1 (Egr-1), by specific antisense oligonucleotides (AS ODN) blocks mesangial cell proliferation. Therefore, we here investigated the effect of Egr-1 inhibition on the course of an experimental mesangioproliferative glomerulonephritis in vivo.

METHODS

On day 3 after induction of anti-Thy-1.1 nephritis, specific glomerular oligonucleotide transfer was achieved by injection of an oligonucleotide/hemagglutinating virus of Japan/liposome mixture into the left renal artery. The right kidney was left untreated.

RESULTS

Induction of nephritis led to a sixfold induction of Egr-1 protein on day 6 of disease. This increase in Egr-1 expression was reduced by 48% in the left kidney by transfer of specific AS ODN. In parallel, the increases in glomerular cellularity, number of mitoses, and glomerular tuft area observed in day 6 nephritic animals were inhibited in the left kidney by 60%, 53%, and 50%, respectively. Changes in the right kidney were not significantly influenced. Likewise, control oligonucleotides showed no effect. Finally, the expression of platelet-derived growth factor-B (PDGF-B), a known target gene of Egr-1, was repressed by transfer of specific AS ODN against Egr-1.

CONCLUSION

We conclude that the transcription factor Egr-1 plays a critical role for mesangial cell proliferation in vivo. Interfering with the induction of Egr-1 or with its target genes could give rise to novel therapeutic principles in mesangioproliferative glomerulonephritis.

Coordinated patterns of gene expression for substrate and energy metabolism in skeletal muscle of diabetic mice

Metabolic abnormalities underlying diabetes are primarily the result of the lack of adequate insulin action and the associated changes in protein phosphorylation and gene expression. To define the full set of alterations in gene expression in skeletal muscle caused by diabetes and the loss of insulin action, we have used Affymetrix oligonucleotide microarrays and streptozotocin-diabetic mice. Of the genes studied, 235 were identified as changed in diabetes, with 129 genes up-regulated and 106 down-regulated. Analysis revealed a coordinated regulation at key steps in glucose and lipid metabolism, mitochondrial electron transport, transcriptional regulation, and protein trafficking. mRNAs for all of the enzymes of the fatty acid beta-oxidation pathway were increased, whereas those for GLUT4, hexokinase II, the E1 component of the pyruvate dehydrogenase complex, and subunits of all four complexes of the mitochondrial electron transport chain were all coordinately down-regulated. Only about half of the alterations in gene expression in diabetic mice could be corrected toward normal after 3 days of insulin treatment and euglycemia. These data point to as of yet undefined mechanisms for highly coordinated regulation of gene expression by insulin and potential new targets for therapy of diabetes mellitus.

Trends in genomic analysis of the cardiovascular system

OBJECTIVE

To evaluate the opportunities afforded cardiovascular medicine by the comprehensive and integrative approaches of genomics in cellular physiology. We present a meta-analysis of recently reported results obtained by means of high-throughput technologies (complementary DNA and oligonucleotide arrays, serial analysis of gene expression [SAGE]), as well as more traditional molecular biology approaches (real-time polymerase chain reaction, differential display, and others).

DATA SOURCES

Newly published articles identified on PubMed and additional data provided by authors on-line (where available).

CONCLUSIONS

The impact of genomic analysis on cardiovascular research is already visible. New genes of cardiovascular interest have been discovered, while a number of known genes have been found to be changed in unexpected contexts. The patterns in the variation of expression of many genes correlate well with the models currently used to explain the pathogenesis of cardiovascular diseases. Much more work has yet to be done, however, for the full exploitation of the immense informative potential still dormant in the genomic technologies.