Mechanism of attenuation of angiotensin-II-induced protein degradation by insulin-like growth factor-I (IGF-I)

Insulin-like growth factor-I (IGF-I) has been shown to attenuate protein degradation in murine myotubes induced by angiotensin II through downregulation of the ubiquitin-proteasome pathway, although the mechanism is not known. Angiotensin II is known to upregulate this pathway through a cellular signalling mechanism involving release of arachidonic acid, activation of protein kinase Cα (PKCα), degradation of inhibitor-κB (I-κB) and nuclear migration of nuclear factor-κB (NF-κB), and all of these events were attenuated by IGF-I (13.2 nM). Induction of the ubiquitin-proteasome pathway has been linked to activation of the RNA-activated protein kinase (PKR), since an inhibitor of PKR attenuated proteasome expression and activity in response to angiotensin II and prevented the decrease in the myofibrillar protein myosin. Angiotensin II induced phosphorylation of PKR and of the eukaryotic initiation factor-2 (eIF2) on the α-subunit, and this was attenuated by IGF-I, by induction of the expression of protein phosphatase 1, which dephosphorylates PKR. Release of arachidonic acid and activation of PKCα by angiotensin II were attenuated by an inhibitor of PKR and IGF-I, and the effect was reversed by Salubrinal (15 μM), an inhibitor of eIF2α dephosphorylation, as was activation of PKCα. In addition myotubes transfected with a dominant-negative PKR (PKRΔ6) showed no release of arachidonate in response to Ang II, and no activation of PKCα. These results suggest that phosphorylation of PKR by angiotensin II was responsible for the activation of the PLA2/PKC pathway leading to activation of NF-κB and that IGF-I attenuates protein degradation due to an inhibitory effect on activation of PKR. © 2007 Elsevier Inc. All rights reserved.

The regulation of AMP-activated protein kinase by vascular endothelial growth factor

The function of the vascular endothelium is to maintain vascular homeostasis, by providing an anti-thrombotic, anti-inflammatory and vasodilatory interface between circulating blood and the vessel wall, meanwhile facilitating the selective passage of blood components such as signaling molecules and immune cells. Dysfunction of the vascular endothelium is implicated in a number of pathological states including atherosclerosis and hypertension, and is thought to precede atherogenesis by a number of years. Vascular endothelial growth factor A (VEGF) is a crucial mitogenic signaling molecule, not only essential for embryonic development, but also in the adult for regulating both physiological and pathological angiogenesis. Previous studies by our laboratory have demonstrated that VEGF-A activates AMP-activated protein kinase (AMPK), the downstream component of a signaling cascade important in the regulation of whole body and cellular energy status. Furthermore, studies in our laboratory have indicated that AMPK is essential for VEGF-A-stimulated vascular endothelial cell proliferation. AMPK activation typically stimulates anabolic processes and inhibits catabolic processes including cell proliferation, with the ultimate aim of redressing energy imbalance, and as such is an attractive therapeutic target for the treatment of obesity, metabolic syndromes, and type 2 diabetes. Metabolic diseases are associated with adverse cardiovascular outcomes and AMPK activation is reported to have beneficial effects on the vascular endothelium. The mechanism by which VEGF-A stimulates AMPK, and the functional consequences of VEGF-A-stimulated AMPK activation remain uncertain. The present study therefore aimed to identify the specific mechanism(s) by which VEGF-A regulates the activity of AMPK in endothelial cells, and how this might differ from the activation of AMPK by other agents. Furthermore, the role of AMPK in the pro-proliferative actions of VEGF-A was further examined. Human aortic and umbilical vein endothelial cells were therefore used as a model system to characterise the specific effect(s) of VEGF-A stimulation on AMPK activation. The present study reports that AMPK α1 containing AMPK complexes account for the vast majority of both basal and VEGF-A-stimulated AMPK activity. Furthermore, AMPK α1 is localized to the endoplasmic reticulum when sub-confluent, but translocated to the Golgi apparatus when cells are cultured to confluence. AMPK α2 appears to be associated with a structural cellular component, but neither α1 nor α2 complexes appear to translocate in response to VEGF-A stimulation. The present study confirms previous reports that when measured using the MTS cell proliferation assay, AMPK is required for VEGF-A-stimulated endothelial cell proliferation. However, parallel experiments measuring cell proliferation using the Real-Time Cell Analyzer xCELLigence system, do not agree with these previous reports, suggesting that AMPK may in fact be required for an aspect of mitochondrial metabolism which is enhanced by VEGF-A. Studies into the mitochondrial activity of endothelial cells have proved inconclusive at this time, but further studies into this are warranted. During previous studies in our laboratory, it was suggested that VEGF-A-stimulated AMPK activation may be mediated via the diacylglycerol (DAG)-sensitive transient receptor potential cation channel (TRPCs -3, -6 or -7) family of ion channels. The present study can neither confirm, nor exclude the expression of TRPCs in vascular endothelial cells, nor rule out their involvement in VEGF-A-stimulated AMPK activation; more specific investigative tools are required in order to characterise their involvement. Furthermore, nicotinic acid adenine dinucleotide phosphate (NAADP)-stimulated Ca2+ release from acidic intracellular organelles is not required for AMPK activation by VEGF-A. Despite what is known about the mechanisms by which AMPK is activated, far less is known concerning the downregulation of AMPK activity, as observed in human and animal models of metabolic disease. Phosphorylation of AMPK α1 Ser485 (α2 Ser491) has recently been characterised as a mechanism by which the activity of AMPK is negatively regulated. We report here for the first time that VEGF-A stimulates AMPK α1 Ser485 phosphorylation independently of the previously reported AMPK α1 Ser485 kinases Akt (protein kinase B) and ERK1/2 (extracellular signal-regulated kinase 1/2). Furthermore, inhibition of protein kinase C (PKC), the activity of which is reported to be elevated in metabolic disease, attenuates VEGF-A- and phorbol 12-myristate 13-acetate (PMA)-stimulated AMPK α1 Ser485 phosphorylation, and increases basal AMPK activity. In contrast to this, PKC activation reduces AMPK activity in human vascular endothelial cells. Attempts to identify the PKC isoform responsible for inhibiting AMPK activity suggest that it is one (or more) of the Ca2+-regulated DAG-sensitive isoforms of PKC, however cross regulation of PKC isoform expression has limited the present study. Furthermore, AMPK α1 Ser485 phosphorylation was inversely correlated with human muscle insulin sensitivity. As such, enhanced AMPK α1 Ser485 phosphorylation, potentially mediated by increased PKC activation may help explain some of the reduced AMPK activity observed in metabolic disease.

Role of the 6-20 disulfide bridge in the structure and activity of epidermal growth factor

Two synthetic analogues of murine epidermal. growth factor, [Abu6, 20] mEGF4-48 (where Abu denotes amino-butyric acid) and [G1, M3, K21, H40] mEGF1-48, have been investigated by NMR spectroscopy. [Abu6, 20] mEGF4-48 was designed to determine the contribution of the 6-20 disulfide bridge to the structure and function of mEGF The overall structure of this analogue was similar to that of native mEGF, indicating that the loss of the 6-20 disulfide bridge did not affect the global fold of the molecule. Significant structural differences were observed near the N-terminus, however, with the direction of the polypeptide chain between residues four and nine being altered such that these residues were now located on the opposite face of the main beta-sheet from their position in native mEGF Thermal denaturation experiments also showed that the structure of [Abu6, 20] mEGF4-48 was less stable than that of mEGF. Removal of this disulfide bridge resulted in a significant loss of both mitogenic activity in Balb/c 3T3 cells and receptor binding on A431 cells compared with native mEGF and mEGF4-48, implying that the structural changes in [Abu6, 20] mEGF4-48, although limited to the N-terminus, were sufficient to interfere with receptor binding. The loss of binding affinity probably arose mainly from steric interactions of the dislocated N-terminal region with part of the receptor binding surface of EGF [G1, M3, K21, H40] mEGF1-48 was also synthesized in order to compare the synthetic polypeptide with the corresponding product of recombinant expression. Its mitogenic activity in Balb/c 3T3 cells was similar to that of native mEGF and analysis of its H-1 chemical shifts suggested that its structure was also very similar to native.

Growth hormone binding protein correlates strongly with leptin and percentage body fat in GH-deficient adults, is increased by GH replacement but does not predict IGF-I response

GH-binding protein (GHBP) corresponds to the extracellular domain of the GH receptor (GHR) and has been shown to be closely related to body fat. This study aimed to examine the inter-relationship between GHBP, leptin and body fat, and to test the hypothesis that GHBP is modified by GH replacement in GH-deficient adults and predicts IGF-I response. Twenty adults, mean age 47 years (range 20-69) with proven GH deficiency were randomly allocated to either GH (up to 0.25 U/kg/week in daily doses) or placebo for 3 months before cross-over to the opposite treatment. Plasma GHBP and leptin were measured at baseline and 2, 4, 8 and 12 weeks after each treatment. Whole body composition was measured at baseline by dual-energy X-ray absorptiometry (DEXA). There was a strong correlation between baseline leptin and GHBP (r = 0.88, P < 0.0001) and between baseline GHBP and percentage body fat, (r = 0.83, P < 0.0001). Mean GHBP levels were higher on GH compared with placebo, 1.53 +/- 0.28 vs 1.41 +/- 0.25 nM, P = 0.049. There was no correlation between baseline IGF-I and GHBP (r = -0.049, P = 0.84), and GHBP did not predict IGF-I response to GH replacement. The close inter-relationship between GHBP, leptin and body fat suggests a possible role for GHBP in the regulation of body composition. GHBP is increased by GH replacement in GH-deficient adults, but does not predict biochemical response to GH replacement. (C) 1999 Churchill Livingstone.

Cytokine-related genes identified from the RIKEN full-length mouse cDNA data set

To identify novel cytokine-related genes, we searched the set of 60,770 annotated RIKEN mouse cDNA clones (FANTOM2 clones), using keywords such as cytokine itself or cytokine names (such as interferon, interleukin, epidermal growth factor, fibroblast growth factor, and transforming growth factor). This search produced 108 known cytokines and cytokine-related products such as cytokine receptors, cytokine-associated genes, or their products (enhancers, accessory proteins, cytokine-induced genes). We found 15 clusters of FANTOM2 clones that are candidates for novel cytokine-related genes. These encoded products with strong sequence similarity to guanylate-binding protein (GBP-5), interleukin-1 receptor-associated kinase 2 (IRAK-2), interleukin 20 receptor alpha isoform 3, a member of the interferon-inducible proteins of the Ifi 200 cluster, four members of the membrane-associated family 1-8 of interferon-inducible proteins, one p27-like protein, and a hypothetical protein containing a Toll/Interleukin receptor domain. All four clones representing novel candidates of gene products from the family contain a novel highly conserved cross-species domain. Clones similar to growth factor-related products included transforming growth factor beta-inducible early growth response protein 2 (TIEG-2), TGFbeta-induced factor 2, integrin beta-like 1, latent TGF-binding protein 4S, and FGF receptor 4B. We performed a detailed sequence analysis of the candidate novel genes to elucidate their likely functional properties.

A proteome analysis of conditioned media from human neonatal fibroblasts used in the maintenance of human embryonic stem cells

The pathways involved in the maintenance of human embryonic stem (hES) cells remain largely unknown, although some signaling pathways have been identified in mouse embryonic stem (mES) cells. Fibroblast feeder layers are used to maintain the undifferentiated growth of hES cells and an examination of the conditioned media (CM) of human neonatal fibroblasts (HNFs) could provide insights into the maintenance of hES cells. The neonatal foreskin fibroblast line (HNF02) used in this study was shown to have a normal 2n = 46, XY chromosomal complement and to support the undifferentiated growth of the Embryonic Stem Cell International Pte. Ltd.-hES3 cell line. The CM of HNF02 was examined using two-dimensional liquid chromatography-tandem mass spectrometry (2-D LCMS) and two-dimensional electrophoresis (2-DE) followed by matrix-assisted laser desorption/ionization-time of flight tandem mass spectrometry (2-DE/MALDI). A total of 102 proteins were identified, 19 by 2-DE/MALDI, 53 by 2-D LCMS and 30 by both techniques. These proteins were classified into 15 functional groups. Proteins identified in the extracellular matrix and differentiation and growth factor functional categories were considered most likely to be involved in the maintenance of hES cell growth, differentiation and pluripotency as these groups contained proteins involved in a variety of events including cell adhesion, cell proliferation and inhibition of cell proliferation, Writ signaling and inhibition of bone morphogenetic proteins.

DNA binding-independent transcriptional activation of the vascular endothelial growth factor gene (VEGF) by the Myb oncoprotein

Myb is a key transcription factor that can regulate proliferation, differentiation, and apoptosis, predominantly in the haemopoietic system. Abnormal expression of Myb is associated with a number of cancers, both haemopoietic and non-haemopoietic. In order to better understand the role of Myb in normal and tumorigenic processes, we undertook a cDNA array screen to identify genes that are regulated by this factor. In this way, we identified the gene encoding vascular endothelial growth factor (VEGF) as being potentially regulated by the Myb oncoprotein in myeloid cells. To determine whether this was a direct effect on VEGF gene transcription, we examined the activity of the murine VEGF promoter in the presence of either wild-type (WT) or mutant forms of Myb. It was found that WT Myb was able to activate the VEGF promoter and that a minimal promoter region of 120 bp was sufficient to confer Myb responsiveness. Surprisingly, activation of the VEGF promoter was independent of DNA binding by Myb. This was shown by the use of DNA binding-defective Myb mutants and by mutagenesis of a potential Myb-binding site in the minimal promoter. Mutation of Sp1 sites within this region abolished Myb-mediated regulation of a reporter construct, suggesting that Myb DNA binding-independent activation of VEGF expression occurs via these Sp1 binding elements. Regulation of VEGF production by Myb has implications for the potential role of Myb in myeloid leukaemias and in solid tumours where VEGF may be functioning as an autocrine growth factor. (c) 2006 Elsevier Inc. All rights reserved.

Expression of insulin-like growth factor-II and its receptor in pediatric and adult adrenocortical tumors

Background: Adrenocortical tumors are heterogeneous neoplasms with incompletely understood pathogenesis. IGF-II overexpression has been consistently demonstrated in adult adrenocortical carcinomas. Objectives: The objective of the study was to analyze expression of IGF-II and its receptor (IGF-IR) in pediatric and adult adrenocortical tumors and the effects of a selective IGF-IR kinase inhibitor (NVP-AEW541) on adrenocortical tumor cells. Patients: Fifty-seven adrenocortical tumors (37 adenomas and 20 carcinomas) from 23 children and 34 adults were studied. Methods: Gene expression was determined by quantitative real-time PCR. Cell proliferation and apoptosis were analyzed in NCI H295 cells and a new cell line established from a pediatric adrenocortical adenoma. Results: IGF-II transcripts were overexpressed in both pediatric adrenocortical carcinomas and adenomas. Otherwise, IGF-II was mainly overexpressed in adult adrenocortical carcinomas (270.5 +/- 130.2 vs. 16.1 +/- 13.3; P = 0.0001). IGF-IR expression was significantly higher in pediatric adrenocortical carcinomas than adenomas (9.1 +/- 3.1 vs. 2.6 +/- 0.3; P = 0.0001), whereas its expression was similar in adult adrenocortical carcinomas and adenomas. IGF-IR expression was a predictor of metastases in pediatric adrenocortical tumors in univariate analysis (hazard ratio 1.84; 95% confidence interval 1.28 -2.66; P = 0.01). Furthermore, NVP-AEW541 blocked cell proliferation in a dose-and time-dependent manner in both cell lines through a significant increase of apoptosis. Conclusion: IGF-IR overexpression was a biomarker of pediatric adrenocortical carcinomas. Additionally, a selective IGF-IR kinase inhibitor had antitumor effects in adult and pediatric adrenocortical tumor cell lines, suggesting that IGF-IR inhibitors represent a promising therapy for human adrenocortical carcinoma.

Non-expression of insulin-like growth factor-I receptor is associated with apoptosis: an ultrastructural study on rat ameloblasts

Insulin-like growth factor-I (IGF-I) is a preiotrophic polypeptide which appears to have roles both as a circulating endocrine hormone and as a locally synthesized paracrine or autocrine tissue factor. IGF-I plays a major role in regulating the growth of cells in vivo and in vitro and initiates metabolic and mitogenic processes in a wide variety of cell types by binding to specific type I receptors in the plasma membrane, In this study, we report the distribution of IGF-I receptors in odontogenic cells at the ultrastructural level using the high resolution protein A-gold technique, In the pre-secretory stage, very little gold label was visible over the ameloblasts and odontoblasts, During the secretory stage the label was mostly seen in association with the cell membranes and endoplasmic reticulum of the ameloblasts. Lysosome-like elements in the post-secretory stage were labelled as well as multivesicular dense bodies, Very little labelling was encountered in the ameloblasts in the transitional stage, where apoptotic bodies were clearly visible, The maturation stage also exhibited labelling of the secretory-like granules in the distal surface. The presence of gold particles over the plasma membrane is an indication that IGF-I receptor is a membrane-bound receptor. Furthermore, the intracellular distribution of the label over the endoplasmic reticulum supports the local synthesis of the IGF-I receptor. The absence of labelling over the transitional ameloblasts suggests that the transitional stage may require the non-expression of IGF-I as a prerequiste or even a trigger for apoptosis.

Novel gene containing multiple epidermal growth factor-like motifs transiently expressed in the papillae of the ascidian tadpole larvae

We have investigated molecular mechanisms of the embryonic development of an ascidian, a primitive chordate which shares features of both invertebrates and vertebrates, with a view to identifying genes involved in development and metamorphosis, We isolated 12 partial cDNA sequences which were expressed in a stage-specific manner using differential display, We report here the isolation of a full-length cDNA sequence for one of these genes which was specifically expressed during the tailbud and larval stages of ascidian development, This cDNA, 1213 bp in length, is predicted to encode a protein of 337 amino acids containing four epidermal growth factor (EGF)-like repeats and three novel cysteine-rich repeats, Characterization of its spatial expression pattern by in situ hybridisation in late tailbud and larval embryos demonstrated strong expression localised throughout the papillae and anteriormost trunk and weaker expression in the epidermis of the remainder of the embryo, As recent evidence indicates that the signal for metamorphosis originates in the anterior trunk region, these results suggest that this gene may have a role in signalling the initiation of metamorphosis. (C) 1997 Wiley-Liss, Inc.

Adrenalectomy counteracts the local modulation of astroglial fibroblast growth factor system without interfering with the pattern of 6-OHDA-induced dopamine degeneration in regions of the ventral midbrain

The present study investigated the effects of bilateral adrenalectomy (ADX) on the synthesis of basic fibroblast growth factor (bFGF, FGF-2) mRNA and on the expression of its FGF receptor subtype-2 (FGFR2) mRNA after a 6-hydroxydopamine (6-OHDA)-induced lesion of nigrostriatal dopamine system. In previous papers we have demonstrated that corticosterone increases FGF-2 immunoreactivity mainly in the astrocytes of the substantia nigra [Chadi, G., Rosen, L., Cintra, A., Tinner, B., Zoli, M., Pettersson, R.F., Fuxe, K., 1993b. Corticosterone increases FGF-2 (bFGF) immunoreactivity in the substantia nigra of the rat. Neuroreport 4, 783-786.] and that 6-OHDA injected in the ventral midbrain upregulates FGF-2 synthesis in reactive astrocytes in the ascending dopamine pathways [Chadi, G., Cao, Y., Pettersson, R.F., Fuxe, K., 1994. Temporal and spatial increase of astroglial basic fibroblast growth factor synthesis after 6-hydroxydopamine-induced degeneration of the nigrostriatal dopamine neurons. Neuroscience 61, 891-910.]. Rats were adrenalectomized and received a 6-OHDA stereotaxical injection in the ventral midbrain 2 days later. Seven days after the dopamine lesion, Western blot analysis showed a decreased level of tyrosine hydroxylase in the lesioned side of the midbrain, an event that was not altered by ADX or corticosterone replacement. Moreover, the degeneration of nigral dopamine neurons, which was confirmed by the disappearance of acidic FGF (FGF-1) mRNA and the decrement of tyrosine hydroxylase mRNA labeled nigral neurons, was not altered by ADX. The FGF-2 protein (23 kDa isoform but not 21 kDa fraction) levels increased in the lesioned side of the ventral midbrain. This elevation was counteracted by ADX, an effect that was fully reversed by corticosterone replacement. In situ hybridization revealed that ADX counteracted the elevated FGF-2 mRNA levels in putative glial cells of the ipsilateral pars compacta of the substantia nigra and in the ventral tegmental area. The ADX also counteracted the increased density and intensity of the astroglial FGF-2 immunoreactive profiles within the lesioned pars compacta of the substantia nigra and the ventral tegmental area as determined by stereology. The stereotaxical mechanical needle insertion triggered the expression of FGFR2 mRNA in putative glial cells, spreading to the entire ipsilateral ventral midbrain from the region of needle track, an occurrence that was partially reversed by ADX. In conclusion, bilateral ADX counteracted the increased astroglial FGF-2 synthesis in the dopamine regions of the ventral midbrain following a 6-OHDA-induced local lesion and interfered with FGF receptor regulation around injury. These findings give further evidence that adrenocortical hormones may regulate the astroglial FGF-2-mediated trophic mechanisms and wound repair events in the lesioned central nervous system. (c) 2007 Elsevier B.V. All rights reserved.

Down-regulation of expression of osteoblast and osteocyte markers in periodontal tissues associated with the spontaneous alveolar bone loss of interleukin-10 knockout mice

The aim of this study was to unravel the mechanisms by which interleukin (IL)-10, a potent pleiotropic cytokine, modulates alveolar bone homeostasis in C57BL/6 wild-type (WT) and IL-10 knockout (IL-10 KO) mice, evaluated at 8, 24, and 48 wk of age. Interleukin-10 KO mice presented significant alveolar bone loss when compared with WT mice, and this was not associated with changes in leukocyte counts or bacterial load. The levels of expression of messenger RNA (mRNA) for tumor necrosis factor-alpha (TNF-alpha), IL-1 beta, IL-6, transforming growth factor-beta (TGF-beta), receptor activator of nuclear factor kappa B ligand (RANKL), osteoprotegerin (OPG), and matrix metalloproteinase 13 (MMP13) were similar between both strains, whereas a significant decrease of tissue inhibitor of metalloproteinase 1 (TIMP1) mRNA expression was found at 48 wk in IL-10 KO mice. The osteoblast markers core binding factor alpha1 (CBFA1) and type I collagen (COL-I) were expressed at similar levels in both strains, whereas the levels of alkaline phosphatase (ALP) and osteocalcin (OCN), and those of the osteocyte markers phosphate-regulating gene endopeptidases (PHEX) and dentin matrix protein 1 (DMP1) were significantly lower in IL-10 KO mice. Our results demonstrate that the alveolar bone loss in the absence of IL-10 was associated with a reduced expression of osteoblast and osteocyte markers, an effect independent of microbial, inflammatory or bone-resorptive pathways.

Fibrinolytic activity is associated with presence of cystic medial degeneration in aneurysms of the ascending aorta

Fibrinolytic activity is associated with presence of cystic medial degeneration in aneurysms of the ascending aorta Aims: Thoracic ascending aortic aneurysms (TAA) are characterized by elastic fibre breakdown and cystic medial degeneration within the aortic media, associated with progressive smooth muscle cell (SMC) rarefaction. The transforming growth factor (TGF)-beta/Smad2 signalling pathway is involved in this process. Because the pericellular fibrinolytic system activation is able to degrade adhesive proteins, activate matrix metalloproteinase (MMP), induce SMC disappearance and increase the bioavailability of TGF-beta, the aim was to investigate the plasminergic system in TAA. Methods and results: Ascending aortas [21 controls and 19 TAAs (of three different aetiologies)] were analysed. Immunohistochemistry showed accumulation of t-PA, u-PA and plasmin in TAAs, associated with residual SMCs. Overexpression of t-PA and u-PA was confirmed by reverse transcription-polymerase chain reaction (RT-PCR), immunoblotting and zymography on TAA extracts and culture medium conditioned by TAA. Plasminogen was present on the SMC surface and inside cytoplasmic vesicles, but plasminogen mRNA was undetectable in the TAA medial layer. Plasmin-antiplasmin complexes were detected in TAA-conditioned medium and activation of the fibrinolytic system was associated with increased fibronectin turnover. Fibronectin-related material was detected immunohistochamically in dense clumps around SMCs and colocalized with latent TGF-beta binding protein-1. Conclusions: The fibrinolytic pathway could play a critical role in TAA progression, via direct or indirect impact on ECM and consecutive modulation of TGF-beta bioavailability.