Coordinate activation of intracellular signaling pathways by insulin-like growth factor-1 and platelet-derived growth factor in rat hepatic stellate cells

Metabolic aspects of hepatitis C virus

Many metabolic factors are associated with chronic hepatitis C virus (HCV) infection and can influence the course of the illness and impact the progression of liver and non-liver-related diseases through complex interactions. Several of these factors impact the course of chronic HCV (CHC) and result in the conceptual translation of CHC from a localized to systemic disease. Besides the traditional liver manifestations associated with CHC infection, such as cirrhosis and hepatocellular carcinoma, various extrahepatic disorders are associated with HCV infection, including atherosclerosis, glucose and lipid metabolic disturbances, alterations in the iron metabolic pathways, and lymphoproliferative diseases. The coexistence of metabolic disorders and CHC is known to influence the chronicity and virulence of HCV and accelerates the progression to liver fibrosis and hepatocellular carcinoma. Insulin resistance is one of the key factors that have a tremendous metabolic impact on CHC. Therefore, there is a great need to properly evaluate patients with CHC infection and correct the modifiable metabolic risk factors. Furthermore, patients with HCV who achieved a sustained virological response showed an overall improvement in glucose metabolism, but the exact evidence still requires further studies with long-term follow-up. This review delineates the most recent evidence on the main metabolic factors associated with CHC and the possible influence of chronic HCV infection on metabolic features.

Glycogen synthase kinase-3β: a promising candidate in the fight against fibrosis

Fibrosis exists in almost all organs/tissues of the human body, plays an important role in the occurrence and development of diseases and is also a hallmark of the aging process. However, there is no effective prevention or therapeutic method for fibrogenesis. As a serine/threonine (Ser/Thr)-protein kinase, glycogen synthase kinase-3β (GSK-3β) is a vital signaling mediator that participates in a variety of biological events and can inhibit extracellular matrix (ECM) accumulation and the epithelial-mesenchymal transition (EMT) process, thereby exerting its protective role against the fibrosis of various organs/tissues, including the heart, lung, liver, and kidney. Moreover, we further present the upstream regulators and downstream effectors of the GSK-3β pathway during fibrosis and comprehensively summarize the roles of GSK-3β in the regulation of fibrosis and provide several potential targets for research. Collectively, the information reviewed here highlights recent advances vital for experimental research and clinical development, illuminating the possibility of GSK-3β as a novel therapeutic target for the management of tissue fibrosis in the future.

Activation of Insulin-PI3K/Akt-p70S6K Pathway in Hepatic Stellate Cells Contributes to Fibrosis in Nonalcoholic Steatohepatitis

BACKGROUND AND AIMS

Hyperinsulinemia and insulin resistance are hallmark features of nonalcoholic fatty liver disease and steatohepatitis (NASH). It remains unclear whether and how insulin contributes to the development of fibrosis in NASH. In this study, we explored insulin signaling in the regulation of hepatic stellate cell (HSC) activation and the progression of NASH-fibrosis.

METHODS

Phosphorylation of Akt and p70S6K were examined in primary HSC and in a rat model of NASH-fibrosis induced by high-fat and high-cholesterol diet for 24 weeks. HSC activation was analyzed for the changes in cell morphology, intracellular lipid droplets, expression of α-SMA and cell proliferation. The serum markers and histology for NASH-fibrosis were also characterized in animals.

RESULTS

Insulin enhanced the expression of smooth muscle actin-α in quiescent but not in activated HSC in culture. Insulin-mediated activation of the PI3K/Akt-p70S6K pathway was involved in the regulation of profibrogenic effects of insulin. Although insulin did not stimulate HSC proliferation directly, the insulin-PI3K/Akt-p70S6K pathway was necessary for serum-enhanced cell proliferation during initial HSC activation. In a rat model of NASH-fibrosis induced by high-fat and high-cholesterol diet, hyperinsulinemia is associated with the activation of p70S6K and enhanced fibrosis.

CONCLUSION

The insulin-PI3K/Akt-p70S6K pathway plays an important role in the early activation of HSC. The profibrogenic effect of insulin is dependent on the activation stage of HSC. Dysregulation of the insulin pathway likely correlates with the development of fibrosis in NASH, suggesting a potentially novel antifibrotic target of inhibiting insulin signaling in HSC.

Purinergic receptor X7 mediates leptin induced GLUT4 function in stellate cells in nonalcoholic steatohepatitis

Metabolic oxidative stress via CYP2E1 can act as a second hit in NASH progression. Our previous studies have shown that oxidative stress in NASH causes higher leptin levels and induces purinergic receptor X7 (P2X7r). We tested the hypothesis that higher circulating leptin due to CYP2E1-mediated oxidative stress induces P2X7r. P2X7r in turn activates stellate cells and causes increased proliferation via modulating Glut4, the glucose transporter, and increased intracellular glucose. Using a high fat diet-fed NAFLD model where bromodichloromethane (BDCM) was administered to induce CYP2E1-mediated oxidative stress, we show that P2X7r expression and protein levels were leptin and CYP2E1 dependent. P2X7r KO mice had significantly decreased stellate cell proliferation. Human NASH livers showed marked increase in P2X7r, and Glut4 in α-SMA positive cells. NASH livers had significant increase in Glut4 protein and phosphorylated AKT, needed for Glut4 translocation while leptin KO and P2X7r KO mice showed marked decrease in Glut4 levels primarily in stellate cells. Mechanistically stellate cells showed increase in phosphorylated AKT, Glut4 protein and localization in the membrane following administration of P2X7r agonist or leptin+P2X7r agonist, while use of P2X7r antagonist or AKT inhibitor attenuated the response suggesting that leptin-P2X7r axis in concert but not leptin alone is responsible for the Glut4 induction and translocation. Finally P2X7r-agonist and leptin caused an increase in intracellular glucose and consumption by increasing the activity of hexokinase. In conclusion, the study shows a novel role of leptin-induced P2X7r in modulating Glut4 induction and translocation in hepatic stellate cells, that are key to NASH progression.

Helicobacter pylori infection causes hepatic insulin resistance by the c-Jun/miR-203/SOCS3 signaling pathway

BACKGROUND

Epidemiological studies have indicated that patients with chronic Helicobacter pylori infection have an increased risk of developing type 2 diabetes mellitus, but the underlying mechanisms remain largely unknown. This study aimed to investigate whether H. pylori infection contributes to the development of insulin resistance, as well as the underlying mechanisms both in vivo and in vitro.

METHODS

The effect of H. pylori infection on glucose metabolism was evaluated in humans and mouse models. The role of the c-Jun/miR-203/suppressor of cytokine signaling 3 (SOCS3) pathway in H. pylori-induced insulin resistance was determined in vitro and was validated in vivo.

RESULTS

Average fasting glucose levels were increased in patients (P = 0.012) and mice (P = 0.004) with H. pylori infection. Diabetic mice with H. pylori infection showed impaired glucose metabolism and insulin tolerance and hyperinsulinemia. Furthermore, H. pylori infection impaired insulin signaling in primary hepatocytes. H. pylori infection could upregulate SOCS3, a well-known insulin signaling inhibitor, by downregulating miR-203. SOCS3 overexpression interfered with insulin signaling proteins, and knockdown of SOCS3 alleviated H. pylori-induced impairment of insulin signaling. The transcription factor c-Jun, which affects gene expression, was induced by H. pylori infection and suppressed miR-203 expression.

CONCLUSIONS

Our results demonstrated that H. pylori infection induced hepatic insulin resistance by the c-Jun/miR-203/SOCS3 signaling pathway and provide possible implications with regard to resolving insulin resistance.

Tetramethylpyrazine reduces glucose and insulin-induced activation of hepatic stellate cells by inhibiting insulin receptor-mediated PI3K/AKT and ERK pathways

Hepatic stellate cell (HSC) activation is the central event during liver fibrogenesis. Metabolic syndrome characterized by hyperglycemia and hyperinsulinemia contributes to nonalcoholic steatohepatitis-associated liver fibrosis. This study was to investigate the effects of tetramethylpyrazine (TMP) on HSC activation induced by glucose and insulin (Glu/Ins) and the underlying mechanisms. Results showed that Glu/Ins significantly stimulated proliferation, invasion, adhesion, and extracellular matrix (ECM) production in HSCs. TMP inhibited HSC proliferation, invasion and adhesion, and reduced the expression of marker genes related to HSC activation in Glu/Ins-activated HSCs. Mechanistic evidence revealed that TMP reduced insulin receptor (InsR) expression and blocked the downstream phosphatidylinositol-3-kinase (PI3K)/AKT and extracellular signal-regulated kinase (ERK) cascades, which was required for TMP attenuation of HSC activation. Moreover, TMP modulated the genes relevant to ECM homeostasis favoring ECM degradation. It could be concluded that TMP inhibited Glu/Ins-stimulated HSC activation and ECM production by inhibiting InsR-mediated PI3K/AKT and ERK pathways.

An integrated view of liver injury and disease progression in nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is rapidly becoming the most common cause of chronic liver disease globally. NAFLD represents a host of pathophysiologic mechanisms that culminate in the accumulation of fat, in a predominantly macrovesicular pattern, in the liver along with varying degrees of inflammation, hepatocellular injury, apoptosis and fibrosis. The most common mechanism for the development of NAFLD is insulin resistance. Insulin resistance is commonly associated with obesity, although it can develop in individuals who do not have obesity. A consequence of insulin resistance is increased peripheral lipolysis and increased delivery of free fatty acids to the liver. The concept of lipotoxicity emerged as the mechanisms by which fatty acids produce cell injury, promote apoptosis and activate inflammatory pathways were elucidated. While much work has been done mainly in cell culture models, the free fatty acid concentration in the liver is not significantly changed in NAFLD. Recently, the focus has shifted to alterations in other lipid metabolic pathways that appear to play an important role in the genesis of nonalcoholic steatohepatitis, the aggressive form of NAFLD. The innate immune system and the intestinal microbiota have been implicated in the development of NAFLD. These mechanisms are reviewed in this article.

Heparin-binding EGF-like growth factor induces heart interstitial fibrosis via an Akt/mTor/p70s6k pathway

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is essential for maintaining normal function of the adult heart and is known to play an important role in myocardial remodeling. In the present study, we observed that heart-specific HB-EGF transgenic (TG) mice had systolic dysfunction with decreased fractional shortening (FS%), increased end-systolic diameter (LVIDs) at 5 months of age, increased heart fibrosis, and increased mRNA expression of Col1α1 and Col3α1 at 1, 3, 5 and 7 months of age compared to nontransgenic (NTG) littermates. However, the left ventricular anterior wall thickness at end-systole (LVAWs) of the TG mice was not different than the NTG mice. Phosphorylation levels of Akt, mTor and p70s6k were increased due to HB-EGF expression in TG mice compared with the NTG mice at 3 and 7 months of age. Additionally, activated Akt, mTor and p70s6k were co-localized with vimentin to cardiac fibroblasts isolated from TG mice. Furthermore, HB-EGF significantly increased phosphorylation levels of Akt, mTor and p70s6k and increased expression of type I collagen in cultured primary cardiac fibroblasts. Rapamycin (Rapa) and CRM197, inhibitors of mTor and HB-EGF respectively, could inhibit the expression of type I collagen in the cultured primary cardiac fibroblasts and Rapa suppressed interstitial fibrosis of the heart tissues in vivo. In addition, a BrdU assay showed that HB-EGF increased proliferation of cardiac fibroblasts by 30% compared with cells without HB-EGF treatment. HB-EGF-induced proliferation was completely diminished in the presence of Rapa. These results suggest that HB-EGF induced heart fibrosis and proliferation of cardiac fibroblasts occurs through activation of the Akt/mTor/p70s6k pathway.

Heparin-binding EGF-like growth factor induces heart interstitial fibrosis via an Akt/mTor/p70s6k pathway

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is essential for maintaining normal function of the adult heart and is known to play an important role in myocardial remodeling. In the present study, we observed that heart-specific HB-EGF transgenic (TG) mice had systolic dysfunction with decreased fractional shortening (FS%), increased end-systolic diameter (LVIDs) at 5 months of age, increased heart fibrosis, and increased mRNA expression of Col1α1 and Col3α1 at 1, 3, 5 and 7 months of age compared to nontransgenic (NTG) littermates. However, the left ventricular anterior wall thickness at end-systole (LVAWs) of the TG mice was not different than the NTG mice. Phosphorylation levels of Akt, mTor and p70s6k were increased due to HB-EGF expression in TG mice compared with the NTG mice at 3 and 7 months of age. Additionally, activated Akt, mTor and p70s6k were co-localized with vimentin to cardiac fibroblasts isolated from TG mice. Furthermore, HB-EGF significantly increased phosphorylation levels of Akt, mTor and p70s6k and increased expression of type I collagen in cultured primary cardiac fibroblasts. Rapamycin (Rapa) and CRM197, inhibitors of mTor and HB-EGF respectively, could inhibit the expression of type I collagen in the cultured primary cardiac fibroblasts and Rapa suppressed interstitial fibrosis of the heart tissues in vivo. In addition, a BrdU assay showed that HB-EGF increased proliferation of cardiac fibroblasts by 30% compared with cells without HB-EGF treatment. HB-EGF-induced proliferation was completely diminished in the presence of Rapa. These results suggest that HB-EGF induced heart fibrosis and proliferation of cardiac fibroblasts occurs through activation of the Akt/mTor/p70s6k pathway.

Expression of platelet-derived growth factor-C and insulin-like growth factor I in hepatic stellate cells is inhibited by miR-29

MicroRNAs are short noncoding, endogenous RNA species that posttranscriptionally inhibit gene expression by targeting the untranslated region (UTR) of mRNAs. Recently, it was shown that miR-29 inhibits expression of extracellular matrix proteins such as collagens, suggesting an antifibrotic function of miR-29. In the present study, we now investigated the role of miR-29 in profibrogenic growth factor expression as a further central mechanism of fibrosis. Screening of databases revealed putative miR-29 target sequences in the mRNA of platelet-derived growth factor (PDGF)-B, PDGF-B receptor, PDGF-C, vascular endothelial growth factor-A, and insulin-like growth factor (IGF)-I. To analyze miR-29 interaction with the predicted binding sites, we cloned the 3'-UTR sequences of the putative targets in fusion to the luciferase-reporter coding sequence. Functional miR-29 binding to PDGF-C and IGF-I mRNA sequences, but not to the corresponding mutants, was then proven by reporter assays. Hepatic stellate cells (HSC) that transdifferentiate into myofibroblasts, producing extracellular matrix proteins and profibrogenic growth factors, for example, the members of the PDGF family, are crucial for liver fibrosis. Myofibroblastic transition of primary HSC resulted in the loss of miR-29, but in a significant increase of PDGF-C and IGF-I. Compensation of reduced miR-29 levels by miR-29 overexpression in myofibroblastic HSC was followed by a definitive repression of IGF-I and PDGF-C synthesis. After experimental fibrosis, induced by bile-duct occlusion, miR-29 expression was shown to be reduced, but IGF-I and PDGF-C expression was upregulated, correlating inversely to the miR-29 pattern. Thus, we conclude that miR-29, downregulated during fibrosis, acts as an antifibrogenic mediator not only by targeting collagen biosynthesis, but also by interfering with profibrogenic cell communication via PDGF-C and IGF-I.

Prevention of in vitro hepatic stellate cells activation by the adenosine derivative compound IFC305

We have previously shown that adenosine and the aspartate salt of adenosine (IFC305) reverse pre-established CCl(4)-induced cirrhosis in rats. However, their molecular mechanism of action is not clearly understood. Hepatic stellate cells (HSC) play a pivotal role in liver fibrogenesis leading to cirrhosis, mainly through their activation, changing from a quiescent adipogenic state to a proliferative myofibrogenic condition. Therefore, we decided to investigate the effect of IFC305 on primary cultured rat HSC. Our results reveal that this compound suppressed the activation of HSC, as demonstrated by the maintenance of a quiescent cell morphology, including lipid droplets content, inhibition of α-smooth muscle actin (α-SMA) and collagen α1(I) expression, and up-regulation of MMP-13, Smad7, and PPARγ expression, three key antifibrogenic genes. Furthermore, IFC305 was able to repress the platelet-derived growth factor (PDGF)-induced proliferation of HSC. This inhibition was independent of adenosine receptors stimulation; instead, IFC305 was incorporated into cells by adenosine transporters and converted to AMP by adenosine kinase. On the other hand, addition of pyrimidine ribonucleoside as uridine reversed the suppressive effect of IFC305 on the proliferation and activation of HSC, suggesting that intracellular pyrimidine starvation would be involved in the molecular mechanism of action of IFC305. In conclusion, IFC305 inhibits HSC activation and maintains their quiescence in vitro; these results could explain in part the antifibrotic liver beneficial effect previously described for this compound on the animal model.

Rapamycin inhibits hepatic fibrosis in rats by attenuating multiple profibrogenic pathways

Hepatic stellate cell transdifferentiation, epithelial-mesenchymal cell transition, and the ductular reaction each contribute to the development of hepatic fibrosis in cholestatic liver diseases. Inhibitors of mammalian target of rapamycin have antifibrotic properties. We evaluated the hypothesis that the antifibrotic action of rapamycin is due to attenuated myofibroblast proliferation in addition to an inhibitory effect on epithelial-mesenchymal transition and the ductular reaction. Hepatic fibrosis was induced by bile duct ligation, and rodents received 1.5 mg/kg/day rapamycin by subcutaneous infusion for 21 days. The expression of various markers of hepatic fibrosis, stellate cell transactivation, epithelial-mesenchymal transition, and the ductular reaction was compared between treated and untreated animals. Hepatic fibrosis, hepatic procollagen type 1 messenger RNA, and alpha-smooth muscle actin expression were significantly reduced in treated animals. Hepatic stellate cell procollagen expression and proliferation were also reduced by rapamycin. The following markers of epithelial-mesenchymal transition--vimentin protein expression, S100 calcium binding protein A4 and transforming growth factor beta 1 messenger RNA, and the mothers against decapentaplegic homolog signaling pathway--were all reduced after rapamycin treatment. The intensity of the ductular reaction was reduced by rapamycin as assessed by histopathological scoring and by reduced cytokeratin 19 expression. Rapamycin caused a reduction in hepatic progenitor cell proliferation. Together, these data show that multiple profibrogenic pathways are activated in an animal model of cholestasis and that rapamycin attenuates epithelial-mesenchymal transition and the ductular reaction as well as hepatic stellate cell activation.

Recent advances in nonalcoholic fatty liver disease

PURPOSE OF REVIEW

This review focuses on recent advances in the study of the epidemiology, pathogenesis, natural history and treatment of nonalcoholic fatty liver disease (NAFLD).

RECENT FINDINGS

Study of hepatic lipid metabolism with respect to the contribution of de-novo lipogenesis to hepatic steatosis and insulin resistance and the dysregulation of cellular adaptive response to stress, that is, the unfolded protein response has added to our current understanding of NAFLD. microRNA has recently emerged and has been shown to be differentially expressed in patients with nonalcoholic steatohepatitis. Its mechanism of action remains to be further explored. There is no proven pharmacotherapy for the treatment of NAFLD. Lifestyle intervention to achieve weight loss and increase exercise is persistently associated with improved liver histology. The diagnostic utility of noninvasive markers and imaging modalities in assessing fibrosis remains to be elucidated.

SUMMARY

The underlying mechanism and pathogenesis of NAFLD remain elusive. Although research effort has advanced the understanding of the natural history, pathogenesis and management of the disease, there is no proven therapy for this medical condition. At present, treatment concentrates on managing underlying metabolic risk factors.

Growth factor receptors signaling in glioblastoma cells: therapeutic implications

In this study, we investigated the protein expression of platelet-derived growth factor receptor (PDGFR), insulin like growth factor-1 receptor (IGF-1R), phosphatidylinositol 3-kinase (PI3-K) and extracellular signal-regulated kinase (ERK1/2) in five primary glioblastoma (GB), with a view to their possible use as therapeutic targets. Our results demonstrated that appreciable levels of these proteins could be detected in the analysed GB cell lines, except for a low level of PDGFR and ERK1/2 expression in one GB cell line. The small molecule inhibitors towards IGF-1R, PDGFR, PI3-K and ERK1/2 respectively, have only modest or no anti-tumour activity on GB cells and therefore their combination with other therapy modalities was analysed. The interaction between small inhibitors and radiation was mostly additive or sub-additive; synergistic interaction was found in five of forty analysed combinations. Our results showed that GB cells are in general resistant to treatment and illustrate the difficulties in predicting the treatment response in malignant gliomas.

Recent advances in nonalcholic fatty liver disease

PURPOSE OF REVIEW

The purpose of this review is to summarize recent advances in defining the clinical features, pathophysiology, natural history, and treatment of nonalcoholic fatty liver disease.

RECENT FINDINGS

Nonalcoholic fatty liver disease is present in approximately 30% of the US population. A histologic grading and staging system has been developed and validated. Nonalcoholic fatty liver disease increases the risk of developing the metabolic syndrome. The presence and severity of nonalcoholic fatty liver disease correlates with the severity of obesity, fat distribution, age, and presence of other features of the metabolic syndrome. Fifteen to 20% of subjects with nonalcoholic steatohepatitis develop cirrhosis. Hepatic steatosis is associated with an increase in both free fatty acid delivery to the liver for re-esterification and increased de-novo lipogenesis. Several mechanisms of hepatocyte injury and death including free fatty acid toxicity, increased free cholesterol, cytokine-mediated injury and activation of the unfolded protein response have been defined. While many therapeutic targets have been identified and pilot studies performed, a definitive treatment for nonalcoholic steatohepatitis remains to be established.

SUMMARY

Nonalcoholic fatty liver disease is a widely prevalent disease that is critically linked to insulin resistance and the metabolic syndrome. While much new information on the pathogenesis and natural history of nonalcoholic steatohepatitis is available, an effective therapy remains to be established.

The insulin-like growth factor axis and risk of liver disease in hepatitis C virus/HIV-co-infected women

OBJECTIVE

Insulin-like growth factor (IGF) I stimulates the proliferation of hepatic stellate cells (HSC), the primary source of extracellular matrix accumulation in liver fibrosis. In contrast, insulin-like growth factor binding protein (IGFBP) 3, the most abundant IGFBP in circulation, negatively modulates HSC mitogenesis. To investigate the role of the IGF axis in hepatitis C virus (HCV)-related liver disease among high-risk patients, we prospectively evaluated HCV-viremic/HIV-positive women.

DESIGN

A cohort investigation.

METHODS

Total IGF-I and IGFBP-3 were measured in baseline serum specimens obtained from 472 HCV-viremic/HIV-positive subjects enrolled in the Women's Interagency HIV Study, a large multi-institutional cohort. The aspartate aminotransferase to platelet ratio index (APRI), a marker of liver fibrosis, was assessed annually.

RESULTS

Normal APRI levels (< 1.0) at baseline were detected in 374 of the 472 HCV-viremic/HIV-positive subjects tested, of whom 302 had complete liver function test data and were studied. IGF-I was positively associated [adjusted odds ratio comparing the highest and lowest quartiles (AORq4-q1), 5.83; 95% confidence interval (CI) 1.17-29.1; Ptrend = 0.03], and IGFBP-3 was inversely associated (AORq4-q1, 0.13; 95% CI 0.02-0.76; Ptrend = 0.04), with subsequent (incident) detection of an elevated APRI level (> 1.5), after adjustment for the CD4 T-cell count, alcohol consumption, and other risk factors.

CONCLUSION

High IGF-I may be associated with increased risk and high IGFBP-3 with reduced risk of liver disease among HCV-viremic/HIV-positive women.

Dual targeting of IGF-1R and PDGFR inhibits proliferation in high-grade gliomas cells and induces radiosensitivity in JNK-1 expressing cells

Increased expression and activation of receptor tyrosine kinases frequently occur in human brain tumors, mediating a variety of growth-promoting pathways and leading to radioresistance; however, little is known about their motogenic potency relative to one another. In this study, we found co-expression of Insulin like growth factor-1 receptor (IGF-1R) and platelet derived growth factor receptor (PDGFR) in two high-grade gliomas (HGG) cell lines 18 and 38. Dual targeting of IGF-1R and PDGFR increased cell death in both 18 and 38 cell lines in comparison to inhibition of either receptor alone. In addition, co-inhibition of IGF-1R and PDGFR increased radiosensitivity in 18 cells but failed to intensify the effect of radiation in 38 cells. In HGG cells, radiation-induced cell death has been connected to the activation of c-Jun-NH2-terminal kinase-1 (JNK1). We found that JNK1 was weakly expressed in 38 cells while it had an elevated expression in 18 cells. Exposure to ionizing radiation induced JNK1 activation only in 18 cells without affecting the protein activity in 38 cells. These results suggest that in 18 cell line radiation-activated JNK1 may provide an anti-proliferative signaling, parallel to receptors co-targeting. To test this hypothesis, HGG cells were treated with dominant negative JNK1 (dnJNK1) and the response to radiation was assayed in presence or absence of receptors co-inhibition. Indeed dnJNK protected 18 cells against gamma-irradiation-induced cell death. dnJNK treatment did not influence radiation response of the 38 cell line, which expressed low levels of JNK1. In conclusion we found that IGF-1R and PDGFR co-inhibition caused an increased cell death in two HGG cell line and induced the radiosensitization of the JNK1 expressing cell line.