The role of phosphatidylinositol 3-kinase and the mitogen-activated protein kinases in insulin-like growth factor-I-mediated effects in vascular endothelial cells

Linalool inhibits the angiogenic activity of endothelial cells by downregulating intracellular ATP levels and activating TRPM8

Angiogenesis crucially contributes to various diseases, such as cancer and diabetic retinopathy. Hence, anti-angiogenic therapy is considered as a powerful strategy against these diseases. Previous studies reported that the acyclic monoterpene linalool exhibits anticancer, anti-inflammatory and anti-oxidative activity. However, the effects of linalool on angiogenesis still remain elusive. Therefore, we investigated the action of (3R)-(-)-linalool, a main enantiomer of linalool, on the angiogenic activity of human dermal microvascular endothelial cells (HDMECs) by a panel of angiogenesis assays. Non-cytotoxic doses of linalool significantly inhibited HDMEC proliferation, migration, tube formation and spheroid sprouting. Linalool also suppressed the vascular sprouting from rat aortic rings. In addition, Matrigel plugs containing linalool exhibited a significantly reduced microvessel density 7 days after implantation into BALB/c mice. Mechanistic analyses revealed that linalool promotes the phosphorylation of extracellular signal-regulated kinase (ERK), downregulates the intracellular level of adenosine triphosphate (ATP) and activates the transient receptor potential cation channel subfamily M (melastatin) member (TRPM)8 in HDMECs. Inhibition of ERK signaling, supplementation of ATP and blockade of TRPM8 significantly counteracted linalool-suppressed HDMEC spheroid sprouting. Moreover, ATP supplementation completely reversed linalool-induced ERK phosphorylation. In addition, linalool-induced ERK phosphorylation inhibited the expression of bone morphogenetic protein (BMP)-2 and linalool-induced TRPM8 activation caused the inhibition of β1 integrin/focal adhesion kinase (FAK) signaling. These findings indicate an anti-angiogenic effect of linalool, which is mediated by downregulating intracellular ATP levels and activating TRPM8.

Emerging importance of molecular pathogenesis of vascular malformations in clinical practice and classifications

Vascular malformations occur during early vascular development resulting in abnormally formed vessels that can manifest as arterial, venous, capillary or lymphatic lesions, or in combination, and include local tissue overdevelopment. Vascular malformations are largely caused by sporadic somatic gene mutations. This article aims to review and discuss current molecular signaling pathways and therapeutic targets for vascular malformations and to classify vascular malformations according to the molecular pathways involved. A literature review was performed using Embase and Medline. Different MeSH terms were combined for the search strategy, with the aim of encompassing all studies describing the classification, pathogenesis, and treatment of vascular malformations. Major pathways involved in the pathogenesis of vascular malformations are vascular endothelial growth factor (VEGF), Ras/Raf/MEK/ERK, angiopoietin-TIE2, transforming growth factor beta (TGF-β), and PI3K/AKT/mTOR. These pathways are involved in controlling cellular growth, apoptosis, differentiation, and proliferation, and play a central role in endothelial cell signaling and angiogenesis. Many vascular malformations share similar aberrant molecular signaling pathways with cancers and inflammatory disorders. Therefore, selective anticancer agents and immunosuppressants may be beneficial in treating vascular malformations of specific mutations. The current classification systems of vascular malformations, including the International Society of the Study of Vascular Anomalies (ISSVA) classification, are primarily observational and clinical, and are not based on the molecular pathways involved in the pathogenesis of the condition. Several molecular pathways with potential therapeutic targets have been demonstrated to contribute to the development of various vascular anomalies. Classifying vascular malformations based on their molecular pathogenesis may improve treatment by determining the underlying nature of the condition and their potential therapeutic target.

ARK5 promotes invasion and migration in hepatocellular carcinoma cells by regulating epithelial-mesenchymal transition

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-associated mortality worldwide. The highly invasive nature of HCC leads to poor prognosis in patients with malignant HCC. AMPK-related protein kinase 5 (ARK5) is a key mediator of migratory activity in human cancer cells. However, the role of ARK5 in invasion and metastasis of HCC cells remains unclear. The present study attempted to determine whether ARK5 is involved in invasion and migration via regulation of epithelial-mesenchymal transition (EMT). Wound healing and Transwell Matrigel invasion assays were utilized to detect the ability of the epithelial Huh7 and mesenchymal SNU387 HCC cells to migrate and invade. Next, the expression of ARK5 and EMT markers, E-cadherin and vimentin, were examined by western blot analysis. Inhibition of ARK5 was able to significantly reduce the ability HCC cells to invade and metastasize. Furthermore, the knockdown of ARK5 was able to reverse the process of EMT in HCC cells. These data suggested that ARK5 may serve an important role in regulating EMT in HCC cells. Taken together, these findings indicate that ARK5 is a potential molecular target for the development of novel HCC therapeutics, which focus on cell invasion and EMT regulation.

Enhancing engineered vascular networks in vitro and in vivo: The effects of IGF1 on vascular development and durability

OBJECTIVES

Creation of functional, durable vasculature remains an important goal within the field of regenerative medicine. Engineered biological vasculature has the potential to restore or improve human tissue function. We hypothesized that the pleotropic effects of insulin-like growth factor 1 (IGF1) would enhance the engineering of capillary-like vasculature.

MATERIALS AND METHODS

The impact of IGF1 upon vasculogenesis was examined in in vitro cultures for a period of up to 40 days and as subcutaneous implants within immunodeficient mice. Co-cultures of human umbilical vein endothelial cells and human bone marrow-derived mesenchymal stem cells in collagen-fibronectin hydrogels were supplemented with either recombinant IGF1 protein or genetically engineered cells to provide sustained IGF1. Morphometric analysis was performed on the vascular networks that formed in four concentrations of IGF1.

RESULTS

IGF1 supplementation significantly enhanced de novo vasculogenesis both in vitro and in vivo. Effects were long-term as they lasted the duration of the study period, and included network density, vessel length, and diameter. Bifurcation density was not affected. However, the highest concentrations of IGF1 tested were either ineffective or even deleterious. Sustained IGF1 delivery was required in vivo as the inclusion of recombinant IGF1 protein had minimal impact.

CONCLUSION

IGF1 supplementation can be used to produce neovasculature with significantly enhanced network density and durability. Its use is a promising methodology for engineering de novo vasculature to support regeneration of functional tissue.

The role of insulin growth factor-1 on the vascular regenerative effect of MAA coated disks and macrophage-endothelial cell crosstalk

The IGF-1 signaling pathway and IGF-1-dependent macrophage/endothelial cell crosstalk was found to be critical features of the vascular regenerative effect displayed by implanted methacrylic acid -co-isodecyl acrylate (MAA-co-IDA; 40% MAA) coated disks in CD1 mice. Inhibition of IGF-1 signaling using AG1024 an IGF1-R tyrosine kinase inhibitor abrogated vessel formation 14 days after disk implantation in a subcutaneous pocket. Explanted tissue had increased arginase 1 expression and reduced iNOS expression consistent with the greater shift from "M1" ("pro-inflammatory") macrophages to "M2" ("pro-angiogenic") macrophages for MAA coated disks relative to control MM (methyl methacrylate-co-IDA) disks; the latter did not generate a vascular response and the polarization shift was muted with AG1024. In vitro, medium conditioned by macrophages (both human dTHP1 cells and mouse bone marrow derived macrophages) had elevated IGF-1 mRNA and protein levels, while the cells had reduced IGF1-R but elevated IGFBP-3 mRNA levels. These cells also had reduced iNOS and elevated Arg1 expression, consistent with the in vivo polarization results, including the inhibitory effects of AG1024. On the other hand, HUVEC exposed to dTHP1 conditioned medium migrated and proliferated faster suggesting that the primary target of the macrophage released IGF-1 was endothelial cells. Although further investigation is warranted, IGF-1 appears to be a key feature underpinning the observed vascularization. Why MAA based materials have this effect remains to be defined, however.

Melatonin and IL-25 modulate apoptosis and angiogenesis mediators in metastatic (CF-41) and non-metastatic (CMT-U229) canine mammary tumour cells

BACKGROUND

Melatonin has oncostatic actions and IL-25 is active in inflammatory processes that induce apoptosis in tumor cells AIM: The aim of this study was to evaluate melatonin and IL-25 in metastatic (CF-41) and non-metastatic (CMT-U229) canine mammary tumor cells cultured as monolayers and tridimensional structures.

MATERIALS AND METHODS

The cells were treated with melatonin, IL-25 and IL-17B silencing gene and performed cell viability, gene and protein expression of caspase-3 and VEGFA (Vascular endothelial growth factor A) and an apoptosis membrane protein array.

RESULTS

Treatment with 1 mM of melatonin reduced cell viability of both tumor cell lines, all treatments alone and combined significantly increased caspase-3 cleaved and proteins involved in the apoptotic pathway and reduced pro-angiogenic VEGFA, confirming the effectiveness of these potential promising treatments.

CONCLUSION

This is the first study evaluating the potential use of these strategies in CF-41 and CMT-U229 cell lines and together encourages subsequent in vitro and in vivo studies for further exploration of clinical applications.

Effect of thymosin beta 4 in the presence of up-regulation of the insulin-like growth factor-1 signaling pathway on high-glucose-exposed vascular endothelial cells

Thymosin beta 4 (Tβ4), which regulates vascular cell growth, can ameliorate some of the problems associated with diabetes. However, the precise signaling mechanisms by which Tβ4 protects against hyperglycemia-induced damage to endothelial cells have not been investigated in detail. Thus, the aim of this study was to elucidate the role of Tβ4 in diabetes and the possible involvement of insulin-like growth factor-1 (IGF-1), which affects cellular survival, metabolism, and glucose homeostasis in high-glucose (HG)-injured human umbilical vein endothelial cells (HUVECs). Immunoblotting assays revealed that under HG blockade conditions, Tβ4 did not alter the insulin-signaling pathway, but induced overexpression of IGF-1 protein, leading to activation of factors in alternative signaling pathway. Small interfering RNA of Tβ4 and IGF-1 were studied to clarify relationship between Tβ4 and IGF-1. These findings suggest that IGF-1 induction by Tβ4 ameliorates the damage in HG-injured HUVECs which manifest as diabetic vascular disorder.

Combination of IGF‑1 gene manipulation and 5‑AZA treatment promotes differentiation of mesenchymal stem cells into cardiomyocyte‑like cells

Mesenchymal stem cell (MSC) transplantation has been proposed as a promising therapeutic strategy for ischemic myocardium repair following myocardial infarction. Differentiation of MSCs into cardiomyocyte-like cells prior to cell transplantation is advantageous in improving their potential clinical benefits for cardiac repair. In the present study, we isolated and cultured porcine MSCs and evaluated the synergistic effect of 5-azacytidine (5-AZA) treatment and insulin-like growth factor-1 (IGF-1) gene manipulation on MSC differentiation into cardiomyocyte-like cells. Our results demonstrated that 5-AZA treatment alone induced a limited cardiomyocyte-like differentiation effect in vitro. Overexpression of the IGF-1 gene in MSCs improved the induction effect of 5-AZA, while knockdown of the IGF-1 gene attenuated the differentiation. These results suggest that IGF-1 is a significant stimulus affecting the cardiomyocyte-like differentiation of porcine MSCs. In addition, the combination of IGF-1 gene manipulation and 5-AZA treatment provides a new strategy to obtain more committed differentiated cardiomyocyte-like cells from porcine MSCs prior to cell transplantation.

Insulin resistance is associated with significant clinical atherosclerosis in nondiabetic patients with acute myocardial infarction

OBJECTIVE

The prevalence of insulin resistance (IR) is increasing worldwide because of increasing age, obesity, and physical inactivity. Emerging evidence supports a direct proatherogenic effect of IR on the coronary vasculature, but the relation between IR and angiographic atherosclerosis in a real-world clinical setting is uncertain. In this work, we assessed whether IR is independently associated with clinically significant angiographic atherosclerosis in nondiabetic individuals.

APPROACH AND RESULTS

We examined the association between IR and the extent of coronary atherosclerosis determined by angiography in 1073 nondiabetic patients surviving acute myocardial infarction. Patients were divided into quartiles on the basis of the homeostasis model assessment grading of IR, and associations between IR and multivessel coronary artery disease, defined as ≥ 2 arteries with ≥ 70% stenosis (or ≥ 50% left main stenosis), were analyzed in bivariate and multivariable modeling. Overall, the cohort had a median age of 56 years; 28.9% women and 21.8% nonwhite. The crude prevalence of multivessel coronary artery disease was 37.8%, 42.3%, 47.2%, and 48.0% for homeostasis model assessment grading of IR quartiles 1, 2, 3, and 4, respectively (P(trend) = 0.009). In multivariable modeling, compared with quartile 1, both quartile 3 (relative risk [95% confidence interval], 1.31 [1.07-1.60]) and quartile 4 (1.29 [1.03-1.60]) were independently associated with multivessel coronary artery disease. Covariates in the model included patient demographic and clinical characteristics and metabolic factors (low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, triglyceride, glycosylated hemoglobin, and high-sensitivity C-reactive protein).

CONCLUSIONS

We demonstrate an independent association between IR and multivessel coronary artery disease in nondiabetic postmyocardial infarction patients. Our findings strengthen the experimental evidence for a direct atherogenic effect of IR independent of glucose control and other components of the metabolic syndrome.

MicroRNA 299-3p modulates replicative senescence in endothelial cells

MicroRNAs (miRNAs) regulate various cellular processes. While several genes associated with replicative senescence have been described in endothelial cells, miRNAs that regulate these genes remain largely unknown. The present study was designed to identify miRNAs associated with replicative senescence and their target genes in human umbilical vein endothelial cells (HUVECs). An integrated miRNA and gene profiling approach revealed that hsa-miR-299-3p is upregulated in senescent HUVECs compared with the young cells, and one of its target genes could be IGF1. IGF1 was upregulated in senescent compared with young HUVECs, and knockdown of hsa-miR-299-3p dose-dependently increased the mRNA expression of IGF1, more significantly observed in the presenescent cells (passage 19) compared with the senescent cells (passage 25). Knockdown of hsa-miR-299-3p also resulted in significant reduction in the percentage of cells positively stained for senescence-associated β-galactosidase and increases in cell viability measured by MTT assay but marginal increases in cell proliferation and cell migration capacity measured by real-time growth kinetics analysis. Moreover, knockdown of hsa-miR-299-3p also increased proliferation of cells treated with H2O2 to induce senescence. These findings suggest that hsa-miR-299-3p may delay or protect against replicative senescence by improving the metabolic activity of the senesced cells but does not stimulate growth of the remaining cells in senescent cultures. Hence, these findings provide an early insight into the role of hsa-miR-299-3p in the modulation of replicative senescence in HUVECs.

Insulin-like growth factor 1 activates methionine adenosyltransferase 2A transcription by multiple pathways in human colon cancer cells

We have previously reported that the expression of MAT2A (methionine adenosyltransferase 2A) is increased in human colon cancer and in colon cancer cells treated with IGF-1 (insulin-like growth factor-1), which was required for its mitogenic effect. The aim of the present study was to elucidate the molecular mechanisms of IGF-1-mediated MAT2A induction. Nuclear run-on analysis confirmed that the increase in MAT2A expression lies at the transcriptional level. DNase I footprinting of the MAT2A promoter region revealed a similar protein-binding pattern in colon cancer and IGF-1-treated RKO cells. IGF-1 induced MAT2A promoter activity and increased nuclear protein binding to USF (upstream stimulatory factor)/c-Myb, YY1 (Yin and Yang 1), E2F, AP-1 (activator protein 1) and NF-κB (nuclear factor κB) consensus elements. IGF-1 increased the expression of c-Jun, FosB, MafG, p65, c-Myb, E2F-1 and YY1 at the pre-translational level. Knockdown of p65, MafG, c-Myb or E2F-1 lowered basal MAT2A expression and blunted the inductive effect of IGF-1 on MAT2A, whereas knockdown of YY1 increased basal MAT2A expression and had no effect on IGF-1-mediated MAT2A induction. Consistently, mutation of AP-1, NF-κB, E2F and USF/c-Myb elements individually blunted the IGF-1-mediated increase in MAT2A promoter activity, and combined mutations completely prevented the increase. In conclusion, IGF-1 activates MAT2A transcription by both known and novel pathways. YY1 represses MAT2A expression.

The role of insulin resistance in the pathogenesis of atherosclerotic cardiovascular disease: an updated review

Insulin resistance is the main pathologic mechanism that links the constellation of clinical, metabolic and anthropometric traits with increased risk for cardiovascular disease and type II diabetes mellitus. These traits include hyperinsulinemia, impaired glucose intolerance, endothelial dysfunction, dyslipidemia, hypertension, and generalized and upper body fat redistribution. This cluster is often referred to as insulin resistance syndrome. The progression of insulin resistance to diabetes mellitus parallels the progression of endothelial dysfunction to atherosclerosis leading to cardiovascular disease and its complications. In fact, insulin resistance assessed by homeostasis model assessment (HOMA) has shown to be independently predictive of cardiovascular disease in several studies and one unit increase in insulin resistance is associated with a 5.4% increase in cardiovascular disease risk. This review article addresses the role of insulin resistance as a main causal factor in the development of metabolic syndrome and endothelial dysfunction, and its relationship with cardiovascular disease. In addition to this, we review the type of lifestyle modification and pharmacotherapy that could possibly ameliorate the effect of insulin resistance and reverse the disturbances in insulin, glucose and lipid metabolism.

Acute cytokine-mediated downregulation of the zinc transporter ZnT8 alters pancreatic beta-cell function

Genetic studies suggest that Zn transporters such as ZnT8 play a role in insulin secretion by pancreatic beta-cells; however, little is known about the dynamic roles of Zn trafficking pathways on beta-cell physiology. To test the acute effects of the inflammatory cytokines interleukin 1 beta (IL1 beta) and tumor necrosis factor alpha (TNFalpha) on Zn homeostasis, the mRNA expression profile of Zn transporters of the ZnT and ZIP families was examined. Exposure of MIN6 cells or primary murine islets to IL1 beta or TNFalpha altered the mRNA expression profile of Zn transporters; most notable was decreased ZnT8 mRNA levels. siRNA-mediated gene knockdown was used to examine the effects of decreased ZnT8 expression in primary dispersed murine islet cells from C57/BL6 mice and MIN6 cells. ZnT8 knockdown in these murine islets led to reduced glucose stimulated insulin secretion without altering the total cellular insulin content or cell viability at normal or supraphysiological Zn concentrations. The labile Zn content determined by flow cytometry after loading with the Zn-specific sensor FluoZin-3 AM was decreased in MIN6 cells following ZnT8 knockdown or IL1 beta treatment. These results suggest that an acute decrease in ZnT8 levels impairs beta-cell function and Zn homeostasis, and may contribute to inflammatory cytokine-induced alterations in beta-cell function.

Erk1 and Erk2 regulate endothelial cell proliferation and migration during mouse embryonic angiogenesis

Angiogenesis is a complex process orchestrated by both growth factors and cell adhesion and is initiated by focal degradation of the vascular basement membrane with subsequent migration and proliferation of endothelial cells. The Ras/Raf/MEK/ERK pathway is required for EC function during angiogenesis. Although in vitro studies implicate ERK1 and ERK2 in endothelial cell survival, their precise role in angiogenesis in vivo remains poorly defined. Cre/loxP technology was used to inactivate Erk1 and Erk2 in endothelial cells during murine development, resulting in embryonic lethality due to severely reduced angiogenesis. Deletion of Erk1 and Erk2 in primary endothelial cells resulted in decreased cell proliferation and migration, but not in increased apoptosis. Expression of key cell cycle regulators was diminished in the double knockout cells, and decreased DNA synthesis could be observed in endothelial cells during embryogenesis. Interestingly, both Paxillin and Focal Adhesion Kinase were expressed at lower levels in endothelial cells lacking Erk1 and Erk2 both in vivo and in vitro, leading to defects in the organization of the cytoskeleton and in cell motility. The regulation of Paxillin and Focal Adhesion Kinase expression occurred post-transcriptionally. These results demonstrate that ERK1 and ERK2 coordinate endothelial cell proliferation and migration during angiogenesis.

MEK5 and ERK5 are mediators of the pro-myogenic actions of IGF-2

During the differentiation of muscle satellite cells, committed myoblasts respond to specific signalling cues by exiting the cell cycle, migrating, aligning, expressing muscle-specific genes and finally fusing to form multinucleated myotubes. The predominant foetal growth factor, IGF-2, initiates important signals in myogenesis. The aim of this study was to investigate whether ERK5 and its upstream MKK activator, MEK5, were important in the pro-myogenic actions of IGF-2. ERK5 protein levels, specific phosphorylation and kinase activity increased in differentiating C2 myoblasts. ERK5-GFP translocated from the cytoplasm to the nucleus after activation by upstream MEK5, whereas phospho-acceptor site mutated (dominant-negative) ERK5AEF-GFP remained cytoplasmic. Exogenous IGF-2 increased MHC levels, myogenic E box promoter-reporter activity, ERK5 phosphorylation and kinase activity, and rapidly induced nuclear localisation of ERK5. Transfection with antisense Igf2 decreased markers of myogenesis, and reduced ERK5 phosphorylation, kinase and transactivation activity. These negative effects of antisense Igf2 were rescued by constitutively active MEK5, whereas transfection of myoblasts with dominant-negative MEK5 blocked the pro-myogenic action of IGF-2. Our findings suggest that the MEK5-ERK5 pathway is a novel key mediator of IGF-2 action in myoblast differentiation.

TNFalpha promotes osteogenic differentiation of human mesenchymal stem cells by triggering the NF-kappaB signaling pathway

Mesenchymal stem cells are multipotent cells able to differentiate into different mesenchymal lineages. Studies in the past had suggested that two of these mesenchymal differentiation directions, the chondrogenic and the myogenic differentiation, are negatively regulated by the transcription factor NF-kappaB. Although osteogenic differentiation has been extensively studied, the influence of NF-kappaB on this differentiation lineage was not subject of detailed analyses in the past. We have analyzed the consequences of TNF-alpha treatment and genetic manipulation of the NF-kappaB pathway for osteogenic differentiation of hMSCs. Treatment of hMSCs during differentiation with TNF-alpha activates NF-kappaB and this results in enhanced expression of osteogenetic proteins like bone morphogenetic protein2 (BMP-2) and alkaline phosphatase (ALP). In addition, enhanced matrix mineralization was observed. The direct contribution of the NF-kappaB pathway was confirmed in cells that express a constitutively active version of the NF-kappaB-inducing kinase IKK2 (CA-IKK2). The IKK2/NF-kappaB-induced BMP-2 up-regulation results in the enhancement of RUNX2 and Osterix expression, two critical regulators of the osteogenic differentiation program. Interestingly, a genetic block of the NF-kappaB pathway did not interfere with osteogenic differentiation. We conclude that TNFalpha mediated NF-kappaB activation, although not absolutely required for BMP-2 expression and matrix mineralization nevertheless supports osteogenic differentiation and matrix mineralization by increasing BMP-2 expression. Our results therefore suggest that NF-kappaB activation may function in lineage selection during differentiation of hMSCs by fostering osteogenic differentiation at the expense of other differentiation lineages.

Silencing TRPM7 promotes growth/proliferation and nitric oxide production of vascular endothelial cells via the ERK pathway

AIMS

The presence and potential function of transient receptor potential melastatin 7 (TRPM7), a Ca2+-permeable non-selective cation channel of the TRP channel superfamily in human vascular endothelial cells, were examined.

METHODS AND RESULTS

Whole-cell patch-clamp recordings showed outward-rectifying currents in human umbilical vein endothelial cells (HUVECs), which was potentiated by removing the extracellular Ca2+ and Mg2+, but inhibited by non-specific TRPM7 blocker Gd3+ or 2-aminoethoxydiphenyl borate (2-APB). TRPM7 mRNA was detected in HUVECs by RT-PCR, but TRPM6, its closest homologue, was not. Silencing TRPM7 by small interfering RNA (siRNA) decreased the level of TRPM7 mRNA and the TRPM7-like current. Interestingly, knockdown of TRPM7 with siRNA or inhibition of TRPM7 function with 2-APB increased the phosphorylation of extracellular signal-regulated kinase (ERK) and enhanced growth/proliferation of HUVECs. This enhanced cell growth/proliferation was abolished by an inhibitor of the ERK signalling pathway. In addition to cell growth/proliferation, silencing TRPM7 also increased expression of nitric oxide synthase and nitric oxide production in an ERK pathway-dependent manner.

CONCLUSION

These observations suggest that TRPM7 channels may play an important role in the function of vascular endothelial cells.

Rapamycin inhibits growth factor-induced cell cycle regulation in pancreatic beta cells

A progressive decline in islet function is a major obstacle to success of islet transplantation. The cause of this decline is islet function is unclear, but immunosuppressive agents may contribute. Insulin-like growth factor-I (IGF-I) and betacellulin are important for islet cell survival and/or proliferation. In the present study, we performed studies of IGF-I and betacellulin on progression of islet cells through the cell cycle and the impact of immunosuppressive agents. Treatment of INS-1 cells for 24 hours with 20 ng/mL betacellulin or 50 ng/mL IGF-1 increased cells in S phase by ~2-fold. Treatment of INS-1 cells with IGF-I or betacellulin also increased cyclin D1 expression and nuclear exclusion of the cyclindependent kinase inhibitors p21(Cip1) and p27(Kip1). In INS-1 cells and islets, betacellulin- and IGF-I increased the increase in p70(s6 kinase) phosphorylation stimulated by betacellulin- and IGF-I in INS-1 cells. Rapamycin also inhibited betacellulin- and IGF-I IN IGF-1 cells. Rapamycin also inhibited betacellulin- and IGF-I-induced entry of cells into S phase and 5'-Bromo-2'-deoxyuridine incorporation as well as the effect of betacellulin and IGF-I on cyclin D1 expression and nuclear exclusion of p21(Cip1) and p(27Kip1). Together, these data suggest that the effect of betacellulin and IGF-I on islet cell growth and proliferation is mediated, in part, via signaling through mammalian target of rapamycin. As rapamycin is used to treat islet transplant recipients, these results suggest that rapamycin could have deleterious effects on islet proliferation and function over time.

Stimulatory effects of insulin-like growth factor-I on growth plate chondrogenesis are mediated by nuclear factor-kappaB p65

Insulin-like growth factor-I (IGF-I) is an important regulator of endochondral ossification. However, little is known about the signaling pathways activated by IGF-I in growth plate chondrocytes. We have previously shown that NF-kappaB-p65 facilitates growth plate chondrogenesis. In this study, we first cultured rat metatarsal bones with IGF-I and/or pyrrolidine dithiocarbamate (PDTC), a known NF-kappaB inhibitor. The IGF-I-mediated stimulation of metatarsal growth and growth plate chondrogenesis was neutralized by PDTC. In rat growth plate chondrocytes, IGF-I induced NF-kappaB-p65 nuclear translocation. The inhibition of NF-kappaB-p65 expression and activity (by p65 short interfering RNA and PDTC, respectively) in chondrocytes reversed the IGF-I-mediated induction of cell proliferation and differentiation and the IGF-I-mediated prevention of cell apoptosis. Moreover, the inhibition of the phosphatidylinositol 3-kinase and Akt abolished the effects of IGF-I on NF-kappaB activation. In conclusion, our findings indicate that IGF-I stimulates growth plate chondrogenesis by activating NF-kappaB-p65 in chondrocytes.

Suppression of NFkappaB and its regulated gene products by oral administration of green tea polyphenols in an autochthonous mouse prostate cancer model

PURPOSE

This study examines the role of cell survival/apoptosis related proteins involved in NFkappaB signaling pathways and its associated events in GTP-induced chemoprevention of prostate cancer in TRAMP mice.

METHODS

Mice were given 0.1% GTP as drinking fluid. Western blot and immunohistochemical analysis performed to examine NFkappaB and its regulated pathway in response to GTP.

RESULTS

Our data demonstrated increased expression of NFkappaB, IKKalpha, IKKbeta, RANK, NIK and STAT-3 in dorso-lateral prostate of TRAMP mice as a function of age and tumor growth and continuous GTP infusion for 32 weeks resulted in substantial reduction in these proteins. The levels of transcription factor osteopontin, a non-collagenous extracellular matrix protein, were also downregulated. Inhibition of NFkappaB signaling is known to activate apoptotic and inhibit anti-apoptotic proteins. Therefore, we analyzed Bax and Bcl2 levels in the dorsolateral prostate of TRAMP mice fed GTP and observed a shift in balance between Bax and Bcl2 favoring apoptosis.

CONCLUSIONS

Based on the data we suggest that oral consumption of GTP might inhibit osteopontin and NFkappaB signaling that may contribute to induction of apoptosis observed in GTP fed TRAMP mice.

TGF-beta activates ERK5 in human renal epithelial cells

The role of the MAP kinase, extracellular signal-regulated kinase 5 (ERK5) remains unknown, however it is involved in cell differentiation and survival as highlighted by the embryonic lethality of the ERK5 knockout. ERK5 can be activated by growth factors and other extracellular signals. TGF-beta, a powerful controller of epithelial cell phenotype, is known to activate the MAP kinase, ERK1/2 however its effect on ERK5 remains unknown. This study demonstrates, fort the first time, ERK5 activation by TGF-beta, observed in both transformed and primary adult human PTEC; activation required ALK-5 receptor activity. In addition this work demonstrates expression of myocyte enhancer factor-2 (MEF2C) by PTEC and that TGF-beta increased the association of MEK5 with phospho-ERK5 and MEF2C. ERK5 activation by either TGF-beta or epidermal growth factor (EGF) was also inhibited by the p38 MAP kinase inhibitor, SB-202190.

Decorin regulates endothelial cell motility on collagen I through activation of insulin-like growth factor I receptor and modulation of alpha2beta1 integrin activity

The proteoglycan decorin is expressed by sprouting but not quiescent endothelial cells, and angiogenesis is dysregulated in its absence. Previously, we have shown that decorin core protein can bind to and activate insulin-like growth factor-I receptor (IGF-IR) in endothelial cells. In this study, we show that decorin promotes alpha2beta1 integrin-dependent endothelial cell adhesion and migration on fibrillar collagen type I. We provide evidence that decorin modulates cell-matrix interaction in this context by stimulating cytoskeletal and focal adhesion reorganization through activation of the IGF-IR and the small GTPase Rac. Further, the glycosaminoglycan moiety of decorin interacts with alpha2beta1, but not alpha1beta1 integrin, at a site distinct from the collagen I-binding A-domain, to allosterically modulate collagen I-binding activity of the integrin. We propose that induction of decorin expression in angiogenic, as opposed to quiescent, endothelial cells promotes a motile phenotype in an interstitial collagen I-rich environment by both signaling through IGF-IR and influencing alpha2beta1 integrin activity.

Precursor IGF-II (proIGF-II) and mature IGF-II (mIGF-II) induce Bcl-2 And Bcl-X L expression through different signaling pathways in breast cancer cells

IGF-II plays a crucial role in fetal and cancer development by signaling through the IGF-I receptor. We have shown that inhibition of IGF-II by resveratrol (RSV) induced apoptosis and that proIGF-II (highly expressed in cancer) was more potent than mIGF-II in inhibiting this effect. Thus, we hypothesized that IGF-II differentially regulates the signaling cascade of the IGF-I receptor to stimulate the anti-apoptotic proteins Bcl-2 and Bcl-X(L) to prevent apoptosis. RSV treatment to breast cancer cells inhibited Bcl-2 and Bcl-X(L) expression and induced mitochondrial membrane depolarization. ProIGF-II was more potent than mIGF-II in: (1) activating the PI3/Akt pathway, (2) regulating Bcl-2 and Bcl-X(L) expression, and (3) inducing phosphorylation/nuclear translocation of Cyclic AMP-responsive element binding protein. Furthermore, IGF-II differentially regulated the intracellular translocation of Bcl-2 and Bcl-X(L), a critical process in breast cancer progression to hormone-independence. Our study provides a novel mechanism of how proIGF-II promotes progression and chemoresistance in breast cancer development.

Insulin-like growth factor 1 enhances the migratory capacity of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are attractive candidates for cell based therapies. However, the mechanisms responsible for stem cell migration and homing after transplantation remain unknown. It has been shown that insulin-like growth factor-1 (IGF-1) induces proliferation and migration of some cell types, but its effects on stem cells have not been investigated. We isolated and cultured MSC from rat bone marrow, and found that IGF-1 increased the expression levels of the chemokine receptor CXCR4 (receptor for stromal cell-derived factor-1, SDF-1). Moreover, IGF-1 markedly increased the migratory response of MSC to SDF-1. The IGF-1-induced increase in MSC migration in response to SDF-1 was attenuated by PI3 kinase inhibitor (LY294002 and wortmannin) but not by mitogen-activated protein/ERK kinase inhibitor PD98059. Our data indicate that IGF-1 increases MSC migratory responses via CXCR4 chemokine receptor signaling which is PI3/Akt dependent. These findings provide a new paradigm for biological effects of IGF-1 on MSC and have implications for the development of novel stem cell therapeutic strategies.

Role of insulin resistance and hyperglycemia in the development of atherosclerosis

Insulin resistance (IR) is the underlying defect in >90% of patients with type 2 diabetes mellitus and the major pathologic mechanism for the associated susceptibility to premature cardiovascular disease (CVD). The progression of IR to diabetes parallels the progression of endothelial dysfunction to atherosclerosis. The downregulation of the antiatherogenic phosphatidylinositol-3-kinase-mediated insulin receptor-signaling pathway, and maintained activity of the proatherogenic mitogenic-activated protein kinase pathway in insulin-resistant states, leads to accelerated atherosclerosis. Efforts to prevent or slow the epidemic of atherothrombotic CVD must focus on the reversal of the disturbances in glucose and lipid homeostasis through the amelioration of IR.

Hypoxia induces apoptosis of HUVECs in an in vitro capillary model by activating proapoptotic signal p38 through suppression of ERK1/2

We recently reported that hypoxia induces chromatin condensation and cell nuclear fragmentation, morphological markers of apoptosis, to tube-forming HUVECs in an in vitro blood vessel model by activating p38 MAPK. In this report, we further examined what role p38 plays and how it is activated during hypoxia-induced apoptosis. First, in order to confirm that p38 can indeed induce apoptosis, the cells were treated with anisomycin, a p38 activator, during normoxia. The activator treatment induced apoptosis and activation of p38 and caspase-3 in a very short time, which indicated that p38 activation alone was sufficient to trigger apoptosis in tube-forming HUVECs. We then observed hypoxia-induced changes in intracellular signals, ERK1/2 and Akt. ERK1/2 inactivation was shown to occur prior to p38 activation and caspase-3 cleavage during hypoxia. On the other hand, anisomycin had no inhibitory effect on ERK1/2 activation during normoxia. It was also shown that the amount of Akt protein slightly decreased by either hypoxia or anisomycin treatment. We then investigated how these two survival signals, ERK1/2 and Akt, are involved in p38 activation by using MEK inhibitor U0126 and PI3K inhibitor LY294002. When tube-forming HUVECs were treated with U0126 or LY294002 during normoxia, the two inhibitors were able to induce apoptosis and activation of p38 and caspase-3 in a relatively short time. U0126 was able to inhibit ERK1/2 activation, but had almost no effect on Akt activation. In contrast, LY294002 was able to inhibit Akt activation, but had very little effect on ERK1/2 activation. These results indicate that ERK1/2 inactivation, rather than Akt decrease, is responsible for hypoxia-induced p38 activation. Taken together, our results strongly suggest that hypoxia-induced apoptosis is regulated through signal transduction in which inactivation of ERK1/2 leads to activation of p38, which then triggers caspase cascade as an execution mechanism of apoptosis.

Differential growth factor regulation of aspartyl-(asparaginyl)-beta-hydroxylase family genes in SH-Sy5y human neuroblastoma cells

Background

Aspartyl (asparaginyl)-β-hydroxylase (AAH) hydroxylates Asp and Asn residues within EGF-like domains of Notch and Jagged, which mediate cell motility and differentiation. This study examines the expression, regulation and function of AAH, and its related transcripts, Humbug and Junctin, which lack catalytic domains, using SH-Sy5y neuroblastoma cells.

Results

Real time quantitative RT-PCR demonstrated 8- or 9-fold higher levels of Humbug than AAH and Junctin, and lower levels of all 3 transcripts in normal human brains compared with neuroblastic tumor cells. AAH and Humbug expression were significantly increased in response to insulin and IGF-I stimulation, and these effects were associated with increased directional motility. However, over-expression of AAH and not Humbug significantly increased motility. Treatment with chemical inhibitors of Akt, Erk MAPK, or cyclin-dependent kinase 5 (Cdk-5) significantly reduced IGF-I stimulated AAH and Humbug expression and motility relative to vehicle-treated control cells. In addition, significantly increased AAH and Humbug expression and directional motility were observed in cells co-transfected with Cdk-5 plus its p35 or p25 regulatory partner. Further studies demonstrated that activated Cdk-5 mediated its stimulatory effects on AAH through Erk MAPK and PI3 kinase.

Conclusion

AAH and Humbug are over-expressed in SH-Sy5y neuroblastoma cells, and their mRNAs are regulated by insulin/IGF-1 signaling through Erk MAPK, PI3 kinase-Akt, and Cdk-5, which are known mediators of cell migration. Although AAH and Humbug share regulatory signaling pathways, AAH and not Humbug mediates directional motility in SH-Sy5y neuroblastoma cells.

Insulin-like Growth Factor-I signaling mechanisms, type I collagen and alpha smooth muscle actin in human fetal lung fibroblasts

Bronchial wall remodeling is a major morbidity component in oxidant injury in bronchopulmonary dysplasia (BPD) and asthma.

HYPOTHESIS

IGF-1 enhances alpha smooth muscle expression and collagen synthesis in developing lung fibroblasts leading to fibrosis through nuclear NF-(k)B -dependent transcription. We studied NF-(k)B dependent transcription by transfecting HFLF with a NF-(k)B responsive promoter driving the luciferase gene and treating with IGF-1 (100 ng/mL) and measuring luciferase activity. We exposed cells to the PI-3 kinase inhibitor or the Erk1/2 inhibitor one hr before stimulating with IGF-1. We also used IGF-1 receptor antibody to inhibit the action of IGF-1 and studied its effect on alpha-sma and type I collagen. IGF-1 treatment significantly increased luciferase activity. This was attenuated by PI-3 kinase and MAP-Kinase inhibitors. Western blot analysis showed PI-3 kinase mediates IGF-1 activation of NF-(k)B independent of I(K)B phosphorylation. We found an up-regulation of phospho NF-kB in the nuclear extract compared with total NFKB showing that IGF-1 regulates NF-(k)B transcriptional activity downstream of NF-(k)B nuclear translocation. IGF-1-induced increase in alpha-sma expression and type-I collagen was significantly inhibited by pretreatment with LY294002 and IGF-1 receptor antibody. IGF-1 cell signaling leading to collagen synthesis in fetal lung fibroblasts is mediated by PI3 Kinase acting through NF-(k)B in HFLF.

Insulin resistance and atherosclerosis

The epidemic of obesity in the developed world over the last two decades is driving a large increase in type 2 diabetes and consequentially setting the scene for an impending wave of cardiovascular morbidity and mortality. It is only now being recognized that the major antecedent of type 2 diabetes, insulin resistance with its attendant syndrome, is the major underlying cause of the susceptibility to type 2 diabetes and cardiovascular disease. In metabolic tissues, insulin signaling via the phosphatidylinositol-3-kinase pathway leads to glucose uptake so that in insulin resistance a state of hyperglycemia occurs; other factors such as dyslipidemia and hypertension also arise. In cardiovascular tissues there are two pathways of insulin receptor signaling, one that is predominant in metabolic tissues (mediated by phosphatidylinositol-3-kinase) and another being a growth factor-like pathway (mediated by MAPK); the down-regulation of the former and continued activity of the latter pathway leads to atherosclerosis. This review addresses the metabolic consequences of the insulin resistance syndrome, its relationship with atherosclerosis, and the impact of insulin resistance on processes of atherosclerosis including insulin signaling in cells of the vasculature.

Role of the Mitogen-Activated Protein Kinases in Cytokine-Mediated Inhibition of Insulin Gene Expression

BACKGROUND

Following islet transplant, inflammatory cells in the vicinity of the transplant graft elaborate cytokines that contribute to islet graft dysfunction. To better understand the mechanism for this effect of cytokines on graft function, we examined the impact of cytokines on intracellular signaling and insulin promoter activity in pancreatic beta cells.

METHODS

Two pancreatic beta cell lines, RINm5F and MIN6 cells, were transfected with a rat insulin promoter (RIP) luciferase fusion gene and treated with a combination of cytokines, including 5 ng/mL interleukin-1beta + 10 ng/mL tumor necrosis factor alpha + 25 ng/mL interferon-gamma. The effect of cytokines on beta cell transcription factors and signaling pathways was analyzed by real-time reverse transcriptase polymerase chain reaction and Western blotting.

RESULTS

Treatment for 48 hours with the combination of cytokines decreased insulin 1 messenger ribonucleic acid (mRNA) levels to 51% and 38% and RIP1 activity to 16% and 30% of control levels in RINm5F and MIN6 cells, respectively. The level of mRNAs encoding transcription factors important for insulin gene expression and beta cell function, including MafA, PDX-1, Nkx6.1, and Pax6, was also decreased by cytokine treatment. Cytokines increased phosphorylation of ERK and c-Jun NH2-terminal kinase (JNK) in RINm5F and MIN6 cells but had no effect on p38 kinase phosphorylation. Neither JNK nor ERK inhibition had a significant effect on cytokine-mediated inhibition of RIP1 activity.

CONCLUSION

Beyond modulating beta cell survival, cytokines inhibit insulin promoter activity, which likely contributes to islet dysfunction following islet transplant. This effect appears to be mediated, in part, via altered expression of transcription factors important for insulin gene expression.

Linoleic acid induces proinflammatory events in vascular endothelial cells via activation of PI3K/Akt and ERK1/2 signaling

Linoleic acid (18:2n-6), is a major unsaturated fatty acid in the American diet. Linoleic acid is considered to be atherogenic because of its pro-oxidative and proinflammatory properties. There is substantial evidence that linoleic acid (LA) can activate vascular endothelial cells and contribute to an inflammatory response. To explore the mechanisms of LA-induced proinflammatory signaling pathways, the present study addresses the role of the phosphatidylinositol 3-kinase/amino kinase terminal (PI3K/Akt), extracellular signal regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) pathways during vascular endothelial cell activation. After a 3- to 6-h exposure, LA significantly activated both Akt and ERK in endothelial cells, as assessed by western blot and immunofluorescence. In contrast, LA activated p38 MAPK already at 10 min, suggesting that p38 MAPK signaling occurred upstream of the ERK1/2 pathway. Furthermore, inhibition of ERK activity by PD98059 and PI3K/Akt activity by LY294002 or wortmannin significantly reduced the LA-induced activation of nuclear factor kappa B (NF-kappaB). These results suggest a contribution of both the ERK1/2 and PI3K/Akt pathways to the effect of LA on NF-kappaB-dependent transcription. Indeed, LA-mediated gene expression of the vascular cell adhesion molecule 1 was suppressed by PD98059, wortmannin and LY294002. These data indicate that both PI3K/Akt- and ERK1/2-mediated proinflammatory signaling events are critical in LA-induced endothelial cell activation and vascular inflammation.

Multiple signaling pathways are involved in endothelin-1-induced brain endothelial cell migration

We have observed that the vasoactive peptide endothelin-1 is a potent inducer of migration of primary human brain-derived microvascular endothelial cells. By blocking signal transduction pathways with specific inhibitors, and using dominant negative mutant infections, we have demonstrated that multiple pathways are involved in endothelin-1-induced migration. Absolutely required for migration are protein tyrosine kinase Src, Ras, protein kinase C (PKC), phosphatidylinositol 3-kinase, ERK, and JNK; partial requirements were exhibited by cAMP-activated protein kinase and p38 kinase. Partial elucidation of the signal transduction sequences showed that the MAPKs ERK, JNK, and p38 are positioned downstream of both PKC and cAMP-activated protein kinase in the signal transduction scheme. The results show that human brain endothelial cell migration has distinct characteristics, different from cells derived from other vascular beds, or from other species, often used as model systems. Furthermore, the results indicate that endothelin-1, secreted by many tumors, is an important contributor to tumor-produced proangiogenic microenvironment. This growth factor has been associated with increased microvessel density in tumors and is responsible for endothelial cell proliferation, migration, invasion, and tubule formation. Because many signal transduction pathways investigated in this study are potential or current targets for anti-angiogenesis therapy, these results are of critical importance for designing physiological antiangiogenic protocols.

IGF-II induces CREB phosphorylation and cell survival in human lung cancer cells

We have previously shown that lung tumors arising in MMTV-IGF-II transgenic mice displayed elevated levels of phosphorylated cAMP response element binding protein (CREB). To investigate the role that insulin-like growth factor II (IGF-II) and CREB play in human lung tumorigenesis, A549 and NCI-H358 cells were examined. In these cell lines, IGF-II administration enhances human tumor cell survival and CREB phosphorylation. Further, the effects of IGF-II on cell survival and CREB phosphorylation appeared to be mediated, at least in part, by activation of the Erk pathways, as inhibition of these signaling pathways reduced tumor cell survival and CREB phosphorylation. Specifically, Erk5 appeared as the predominant mediator of CREB phosporylation. To further verify the importance of CREB in human lung tumorigenesis, A549 and NCI-H358 cells were stably transfected with a vector containing a dominant negative CREB construct (KCREB). KCREB transfection significantly inhibited the soft agar growth of both human tumor cell lines. In contrast, overexpression of wild-type CREB in the normal human bronchial epithelial cell line, HBE135, enhanced soft agar growth. Therefore, our results indicate that CREB and its associated proteins play a significant role in lung adenocarcinoma and IGF-II induces CREB phosphorylation, at least in part, via the Erk5 signaling pathway.

Hepatocyte growth factor stimulates nitric oxide production through endothelial nitric oxide synthase activation by the phosphoinositide 3-kinase/Akt pathway and possibly by mitogen-activated protein kinase kinase in vascular endothelial cells

Hepatocyte growth factor (HGF) has recently been the focus of attention due to its angiogenic effects, which are similar to those of vascular endothelial growth factor (VEGF); because of these effects, HGF is considered to be a novel therapeutic agent against vascular disorders, including atherosclerotic angiopathies. Although nitric oxide (NO), which is derived from vascular endothelial cells (ECs), is also involved in angiogenesis, little is known regarding the interactions between HGF and NO. We therefore examined the effects of HGF on NO production as well as endothelial NO synthase (eNOS) phosphorylation, and investigated their mechanisms. In bovine aortic ECs, HGF induced a rapid (5 min) increase of NO production measured by diaminofluorescein-2 diacetate. Moreover, HGF rapidly (2.5 min) stimulated eNOS phosphorylation (Ser-1179) as determined by Western immunoblot analyses. Both of these effects were almost completely suppressed by the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, and were partially suppressed by the mitogen-activated protein kinase (MAPK) kinase 1/2 inhibitor U0126. HGF also stimulated Akt phosphorylation (Ser-473), which was completely suppressed by LY294002 and was partially suppressed by U0126. Moreover, HGF stimulated extracellular signal-regulated kinase 1/2 phosphorylation (Thr-202/Tyr-204), which was completely suppressed by U0126 and was partially suppressed by LY294002. Taken together, these results indicate that HGF not only phosphorylates eNOS through the PI3K/Akt pathway, but also partially through the MAPK pathway, and that these two pathways may interact. Compared with VEGF, HGF was more potent in both NO production and eNOS phosphorylation. Our study thus demonstrates a novel activity of HGF-the stimulation of NO production-which occurs via eNOS phosphorylation that may in turn be mediated by cross-talk between the PI3K/Akt and MAPK pathways.

Imatinib-induced regression of AIDS-related Kaposi's sarcoma

PURPOSE

Activation of the platelet-derived growth factor (PDGF) and c-kit receptors has been proposed as important in mediating the growth of AIDS-related Kaposi's sarcoma (KS). We investigated the response of KS to the PDGF receptor (PDGFR)/c-kit inhibitor, imatinib mesylate, and investigated the effect of this therapy on critical signal transduction intermediates.

PATIENTS AND METHODS

Ten male patients with AIDS-related cutaneous KS, which progressed despite chemotherapy and/or highly active antiretroviral therapy, received imatinib mesylate administered orally, 300 mg twice daily. Clinical response was determined by serial tumor measurements. To determine biologic and histologic response, skin lesion biopsies were obtained at baseline and following 4 weeks of therapy.

RESULTS

Five of 10 participants had a partial response by tumor measurements. Biopsies after 4 weeks of therapy demonstrated histologic regression in four of six patients. Four patients' tumor biopsies were assessable for immunohistochemistry end points pre- and post-therapy. These demonstrated inhibition of PDGFR and its downstream effector, extracellular receptor kinase, which is a member of the mitogen-activated protein kinase family. The most common adverse event was diarrhea, which led to dose reduction in six patients.

CONCLUSION

Imatinib mesylate administered orally twice daily for AIDS-related KS results in clinical and histologic regression of cutaneous KS lesions within 4 weeks. These promising results demonstrate that inhibition of the c-kit and/or PDGF receptors may represent an effective strategy for treating KS.

Insulin-like Growth Factor-1 Regulates Endogenous RUNX2 Activity in Endothelial Cells through a Phosphatidylinositol 3-Kinase/ERK-dependent and Akt-independent Signaling Pathway

Insulin-like growth factor-1 (IGF-1) is an angiogenic and oncogenic factor that activates signal transduction pathways involved in the expression of transcriptional regulators of tumorigenesis. RUNX2, a member of the Ig-loop family of transcription factors is expressed in vascular endothelial cells (EC) and regulates EC migration, invasion, and proliferation. Here we show that IGF-1 and its receptor regulate post-translational changes in RUNX2 to activate DNA binding in proliferating EC. The phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, reduced both basal and IGF-1-stimulated RUNX2 DNA binding activity in the absence of changes in RUNX2 protein as did the overexpression of the phosphatidylinositol 3-phosphate phosphatase, confirming that PI3K signaling mediates RUNX2 activation. IGF-1 increased ERK1/2 activation, which was abrogated by the inhibition of PI3K, thus linking these two pathways in EC. Treatment with U0126, which inhibits ERK1/2 activation, reduced IGF-1-stimulated RUNX2 DNA binding without affecting RUNX2 protein levels. Overexpression of constitutively active MKK1 increased RUNX2 DNA binding and phosphorylation. No additive effects of PI3K or ERK inhibitors on DNA binding were evident. Surprisingly, these IGF-1-mediated effects on RUNX2 were not regulated by Akt phosphorylation, a common downstream target of PI3K, as determined by pharmacological or genetic inhibition. However, an inhibitor of the p21-activated protein kinase-1, glutathione S-transferase-Pak1-(83-149), inhibited both basal and IGF-1-stimulated RUNX2 DNA binding, suggesting that Pak1 mediates IGF-1 signaling to increase RUNX2 activity. These results indicate that the angiogenic growth factor, IGF-1, can regulate RUNX2 DNA binding through sequential activation of the PI3K/Pak1 and ERK1/2 signaling cascade.

ARK5 expression in colorectal cancer and its implications for tumor progression

A novel member of the human AMPK family, ARK5, was recently discovered to be a key molecule in mediating cancer cell migration activity in human pancreas cancer cell line PANC-1, and its activation was found to be induced by Akt-dependent phosphorylation at Ser 600. DNA array analysis with 241 paired cDNAs from 13 different types of tumors and corresponding normal tissues derived from cancer patients revealed ARK5 overexpression in the samples of colorectal cancer. ARK5 expression was measured and an in vitro invasion assay was performed in six human colorectal cancer cell lines, WiDr, HCT-15, DLD-1, SW620, LoVo, and SW480, and since high invasion activity was concordant with higher ARK5 expression, ARK5 expression was examined in relation to tumor progression and metastatic activity in clinical samples. In 56 clinical samples of primary colorectal cancers and their liver metastases, higher ARK5 expression was observed in the samples from more advanced cases, and much higher expression was observed in the liver metastases. In situ hybridization analysis showed ARK5 overexpression in tumor cells. Based on these findings, we propose that ARK5 overexpression is involved in tumor progression of colon cancer clinically.

Activation of protein kinase B (Akt) signaling after electroconvulsive shock in the rat hippocampus

Akt (protein kinase B, PKB) is one of the major downstream pathways of neurotrophin signaling and plays important roles in the cell survival and synaptic plasticity of the central nervous system. Electroconvulsive shock (ECS) has neurotrophic effect and it affects the synaptic plasticity. It can activate another major pathway of neurotrophin signaling, i.e., Ras-Raf-MEK-Erk cascade. In this paper, the authors investigated whether ECS can activate Akt signaling in the rat hippocampus. After a single ECS, the phosphorylation of Akt was increased, as were the signals detected by phospho-PDK1 substrate antibody, which suggests the activation of PDK1, an upstream molecule of Akt. The phosphorylation of downstream molecules of Akt, forkhead transcription factors (FKHR), endothelial nitric oxide synthase (eNOS), and glycogen synthase kinase-3beta (GSK-3beta) was also increased. The increased phosphorylation of Akt appeared within 5 min of ECS and its time frame paralleled that of the phosphorylation of Erks. Taken together, these results suggest that ECS activates Akt signaling over a similar time scale to that of Erks in the rat hippocampus.

Extracellular signal-regulated kinase and phosphoinositol-3 kinase mediate IGF-1 induced proliferation of fetal sheep cardiomyocytes

Growth of the fetal heart involves cardiomyocyte enlargement, division, and maturation. Insulin-like growth factor-1 (IGF-1) is implicated in many aspects of growth and is likely to be important in developmental heart growth. IGF-1 stimulates the IGF-1 receptor (IGF1R) and downstream signaling pathways, including extracellular signal-regulated kinase (ERK) and phosphoinositol-3 kinase (PI3K). We hypothesized that IGF-1 stimulates cardiomyocyte proliferation and enlargement through stimulation of the ERK cascade and stimulates cardiomyocyte differentiation through the PI3K cascade. In vivo administration of Long R3 IGF-1 (LR3 IGF-1) did not stimulate cardiomyocyte hypertrophy but led to a decreased percentage of cells that were binucleated in vivo. In culture, LR3 IGF-1 increased myocyte bromodeoxyuridine (BrdU) uptake by three- to five-fold. The blockade of either ERK or PI3K signaling (by UO-126 or LY-294002, respectively) completely abolished BrdU uptake stimulated by LR3 IGF-1. LR3 IGF-1 did not increase footprint area, but as expected, phenylephrine stimulated an increase in binucleated cardiomyocyte size. We conclude that 1) IGF-1 through IGF1R stimulates cardiomyocyte division in vivo; hyperplastic growth is the most likely explanation of IGF-1 stimulated heart growth in vivo; 2) IGF-1 through IGF1R does not stimulate binucleation in vitro or in vivo; 3) IGF-1 through IGF1R does not stimulate hypertrophy either in vivo or in vitro; and 4) IGF-1 through IGF1R requires both ERK and PI3K signaling for proliferation of near-term fetal sheep cardiomyocytes in vitro.

Expression, regulation, and function of IGF-1, IGF-1R, and IGF-1 binding proteins in blood vessels

The vascular insulin-like growth factor (IGF)-1 system includes the IGFs, the IGF-1 receptor (IGF-1R), and multiple binding proteins. This growth factor system exerts multiple physiologic effects on the vasculature through both endocrine and autocrine/paracrine mechanisms. The effects of IGF-1 are mediated principally through the IGF-1R but are modulated by complex interactions with multiple IGF binding proteins that themselves are regulated by phosphorylation, proteolysis, polymerization, and cell or matrix association. During the last decade, a significant body of evidence has accumulated, indicating that expression of the components of the IGF system are regulated by multiple factors, including growth factors, cytokines, lipoproteins, reactive oxygen species, and hemodynamic forces. In addition, cross-talk between the IGF system and other growth factors and integrin receptors has been demonstrated. There is accumulating evidence of a role for IGF-1 in multiple vascular pathologies, including atherosclerosis, hypertension, restenosis, angiogenesis, and diabetic vascular disease. This review will discuss the regulation of expression of IGF-1, IGF-1R, and IGF binding proteins in the vasculature and summarize evidence implicating involvement of this system in vascular diseases.

Angiopoietin-1 activates both anti- and proapoptotic mitogen-activated protein kinases

In this study, we identified whether mitogen-activated protein kinases (MAPKs) mediate the effects of angiopoietin-1 (Ang-1) on endothelial cell apoptosis. Exposure of human umbilical vein endothelial cells to Ang-1 (300 ng/ml) evoked within 15-30 min a 15-fold and a 5-fold increase in phosphorylation of ERK1/2 and p38 MAPKs, respectively. Inhibitors of the PI-3 kinase pathway attenuated Ang-1-induced ERK1/2 phosphorylation at a level up-stream from Raf and MEK1/2, but these inhibitors augmented Ang-1-induced p38 phosphorylation. When serum and growth supplements were withdrawn, the percentage of endothelial apoptosis tripled over 24 h compared with control cells. The presence of Ang-1 (300 ng/ml) significantly attenuated endothelial cell apoptosis and inhibited caspase-9, -7, and -3 activation. These antiapoptotic effects were augmented when a p38 inhibitor was combined with Ang-1, whereas inhibition of ERK1/2 eliminated the antiapoptotic properties of Ang-1. We conclude that both anti- (ERK1/2) and pro- (p38) apoptotic members of MAPKs are simultaneously activated by Ang-1 in endothelial cells and that activation of ERK1/2 by Ang-1 is mediated through the PI-3 kinase pathway. The strong antiapoptotic effects of the ERK and the PI-3 kinase pathways mask the proapoptotic function of p38 MAPKs resulting in net attenuation of apoptosis by Ang-1.

Relaxin, a pregnancy hormone, is a functional endothelin-1 antagonist: attenuation of endothelin-1-mediated vasoconstriction by stimulation of endothelin type-B receptor expression via ERK-1/2 and nuclear factor-kappaB

We have recently demonstrated that relaxin (RLX) acts as compensatory mediator in human heart failure. RLX inhibits the stimulation of endothelin-1, the most potent vasoconstrictor in heart failure. Upregulation of the endothelin type-B receptor (ET(B)), which mediates endothelin-1 clearance and endothelial release of NO, represents a pivotal mode of RLX action. However, signal transduction and abundance of this phenomenon are unknown. Therefore, we investigated RLX-induced regulation of ET(B) in human umbilical vein endothelial, epithelial (HeLa), and vascular smooth muscle cells. In human umbilical vein endothelial cells and HeLa cells, but not in human vascular smooth muscle cells, RLX upregulated ET(B) expression and activated extracellular signal-regulated kinase-1/2 (ERK-1/2) and nuclear factor-kappaB (NF-kappaB), a transcription factor. PD-98059, a selective inhibitor of the mitogen-activated protein kinase kinase-1 (MEK-1)-ERK-1/2 pathway, abolished ERK-1/2 and NF-kappaB activation and ET(B) upregulation. NF-kappaB inhibition also prevented RLX-mediated ET(B) stimulation. In NF-kappaB-luciferase reporter assays, we demonstrated complete inhibition of RLX-induced NF-kappaB activation in cells transfected with dominant-negative Raf-1, MEK-1, or ERK-1/2 constructs, whereas dominant-negative Ras had no effect. In rat aorta and mesenteric artery, RLX pretreatment, in an ET(B)-dependent fashion, mitigated the maximum contractile response to endothelin-1, by 38+/-4% and 43+/-6%, and the endothelin-1 sensitivity (-log[EC(50)]: aorta, 8.2+/-0.2 for vehicle versus 7.2+/-0.2 for RLX; mesenteric artery, 8.0+/-0.2 for vehicle versus 7.1+/-0.1 for RLX). RLX pretreatment augmented the dilator effect of the ET(B) agonist endothelin-3 by 100+/-8% and 133+/-13%. In conclusion, RLX stimulates endothelial and epithelial ET(B) via a Ras-independent Raf-1-MEK-1-ERK-1/2 pathway that activates NF-kappaB. On vascular smooth muscle cells, ET(B), a contributor to endothelin-mediated vasoconstriction, remains unaffected. This renders RLX a functional endothelin-1 antagonist.

Epidermal growth factor-induced activation of the insulin-like growth factor I receptor in rat hepatocytes

Insulin-like growth factor I (IGF-I) plays a critical role in the induction of cell cycle progression and survival in many cell types. However, there is minimal IGF-I binding to hepatocytes, and a role for IGF-I in hepatocyte signaling has not been elucidated. The dynamics of IGF-I receptor (IGF-IR) activation were examined in freshly isolated rat hepatocytes. IGF-I did not activate the IGF-IR. However, des(1-3)IGF-I, which weakly binds IGF binding protein-3 (IGFBP-3), induced IGF-IR phosphorylation. IGFBP-3 surface coating was identified by confocal immunofluorescence microscopy. In contrast with the inactivity of IGF-I, epidermal growth factor (EGF) induced the tyrosine phosphorylation of the IGF-IR in parallel with EGF receptor phosphorylation. Transactivation of the IGF-IR by EGF was inhibited by tyrphostin I-Ome-AG538, a tyrosine kinase inhibitor with high specificity for the IGF-IR. Src kinase inhibitors pyrazolopyrimidine PP-1 and PP-2 inhibited transactivation of the IGF-IR by EGF. EGF stimulated the tyrosine phosphorylation of Src, and induced its association with the IGF-IR. EGF-induced phosphorylations of insulin-related substrate (IRS)-1, IRS-2, Akt, and p42/44 mitogen-activated protein kinases (MAPKs) were inhibited variably by I-Ome-AG538. In conclusion, the data show an EGF- and Src-mediated transactivation pathway for IGF-IR activation in hepatocytes, and indicate a role for the IGF-IR in hepatocyte intracellular signaling. The findings also show a role for IGFBP-3 in the inhibition of IGF-I signaling in hepatocytes.

The role of p42/44 MAPK and protein kinase B in connective tissue growth factor induced extracellular matrix protein production, cell migration, and actin cytoskeletal rearrangement in human mesangial cells

Connective tissue growth factor (CTGF) is a member of an emerging family of immediate-early gene products that coordinate complex biological processes during differentiation and tissue repair. Here we describe the role of CTGF in integrin-mediated adhesive signaling and the production of extracellular matrix components in human mesangial cells. The addition of CTGF to primary mesangial cells induced fibronectin production, cell migration, and cytoskeletal rearrangement. These functional responses were associated with recruitment of Src and phosphorylation of p42/44 MAPK and protein kinase B. The inhibition of CTGF-induced p42/44 MAPK or phosphatidylinositol 3-kinase (PI3K)/protein kinase B pathway activities abrogated the induction of fibronectin expression. In addition, anti-beta(3) integrin antibodies attenuated the activation of both the p42/44 MAPK and protein kinase B and the increase in fibronectin levels. CTGF also induced mesangial cell migration via a beta(3) integrin-dependent mechanism that was similarly sensitive to the inhibition of the p42/44 MAPK and PI3K pathways, and it promoted the adhesion of the mesangial cells to type I collagen via up-regulation of alpha(1) integrin. Transient actin cytoskeletal disassembly was observed following treatment with the ligand over the course of a 24-h period. CTGF induced the loss of focal adhesions from the mesangial cell as evidenced by the loss of punctate vinculin. However, these processes are p42/44 MAPK and PI3K pathway-independent. Our data support the hypothesis that CTGF mediates a number of its biological effects by the induction of signaling processes via beta(3) integrin. However, others such as actin cytoskeleton disassembly are modulated in a beta(3) integrin/MAPK/PI3K-independent manner, indicating that CTGF is a complex pleiotropic factor with the potential to amplify primary pathophysiological responses.

Molecular and cellular basis of pulmonary vascular remodeling in pulmonary hypertension

Clinical pulmonary hypertension is characterized by a sustained elevation in pulmonary arterial pressure. Pulmonary vascular remodeling involves structural changes in the normal architecture of the walls of pulmonary arteries. The process of vascular remodeling can occur as a primary response to injury, or stimulus such as hypoxia, within the resistance vessels of the lung. Alternatively, the changes seen in more proximal vessels may arise secondary to a sustained increase in intravascular pressure. To withstand the chronic increase in intraluminal pressure, the vessel wall becomes thickened and stronger. This "armouring" of the vessel wall with extra-smooth muscle and extracellular matrix leads to a decrease in lumen diameter and reduced capacity for vasodilatation. This maladaptive response results in increased pulmonary vascular resistance and consequently, sustained pulmonary hypertension. The process of pulmonary vascular remodeling involves all layers of the vessel wall and is complicated by the finding that cellular heterogeneity exists within the traditional compartments of the vascular wall: intima, media, and adventitia. In addition, the developmental stage of the organism greatly modifies the response of the pulmonary circulation to injury. This review focuses on the latest advances in our knowledge of these processes as they relate to specific forms of pulmonary hypertension and particularly in the light of recent genetic studies that have identified specific pathways involved in the pathogenesis of severe pulmonary hypertension.

Activation of phosphatidylinositol 3-kinase contributes to insulin-like growth factor I-mediated inhibition of pancreatic beta-cell death

To begin to determine whether IGF-I treatment represents a potential means of enhancing the survival of islet cell grafts after transplantation, the present studies established a model of beta-cell death secondary to loss of trophic support and examined the ability of IGF-I to prevent cell death. The studies were performed using the rat pancreatic beta-cell line, INS-1. Incubating INS-1 cells in RPMI 1640 and 0.25% BSA for 48 h increased cell death, as determined by lactate dehydrogenase release, compared with that of cells maintained in RPMI and 10% fetal calf serum. Addition of 100 ng/ml IGF-I to the serum-free medium decreased lactate dehydrogenase release to a level comparable to that found in cells maintained in fetal calf serum. Similar results were seen using a mouse beta-cell line, MIN6, infected with an adenovirus expressing IGF-I. Examination of IGF-I-stimulated signaling demonstrated that IGF-I increased the phosphorylation of protein kinase B in both cell lines, whereas IGF-I-induced phosphorylation of the MAPKs, ERK1 and -2, was observed only in INS-1 cells. The effect of IGF-I on phosphorylation of substrates of phosphatidylinositol 3-kinase (PI 3-kinase) or protein kinase B was also examined in INS-1 cells. IGF-I increased the phosphorylation of glycogen synthase kinase 3beta, BAD, FKHR, and p70(S6) kinase. Another pathway that has been shown to mediate the protective of IGF-I in some cell types is activation of cAMP response element-binding protein (CREB). IGF-I increased CREB phosphorylation at a concentration as low as 10 ng/ml, and this effect was inhibited by H89, a PKA inhibitor, and PD98059, a MAPK kinase inhibitor. Consistent with the effect of IGF-I on CREB phosphorylation, IGF-I increased the transcriptional activity of CREB, although it had no effect on CREB binding to DNA. Use of inhibitors of the PI 3-kinase (LY 294002) or ERK (PD98059) pathways or CREB phosphorylation (H89) in the cell death assay demonstrated partial abrogation of the protective effect of IGF-I with LY 294002. These data demonstrate that IGF-I protects pancreatic beta-cells from cell death secondary to loss of trophic support and that, although IGF-I activates several signaling pathways that contribute to its protective effect in other cell types, only activation of PI 3-kinase contributes to this effect in beta-cells.