Insulin signaling through insulin receptor substrate 1 and 2 in normal liver development

Monocarbonyl analogs of curcumin C66 and B2BrBC modulate oxidative stress, JNK activity, and pancreatic gene expression in rats with streptozotocin-induced diabetes

The pathogenesis of type 1 diabetes mellitus (T1DM) involves oxidative stress and inflammation. Curcumin, a natural polyphenolic compound found in turmeric, known to exhibit antioxidative and anti-inflammatory properties, is characterized by poor chemical stability, low bioavailability, and rapid metabolism. Monocarbonyl analogs of curcumin (MACs) with a structural absence of β-diketone and enhanced stability and bioavailability present a potential solution to the challenges associated with the use of curcumin. This study aimed to evaluate the effect of two MACs, C66 and B2BrBC, on oxidative stress markers, antioxidant enzyme activity, expression of diabetes-associated genes, and signaling pathway proteins in the context of T1DM. Streptozotocin (STZ)-induced male Wistar rats or rat pancreatic RIN-m cells were used for in vivo and in vitro experiments, respectively. C66 or B2BrBC were given either before or after STZ treatment. Oxidative stress markers and antioxidant enzyme activities were determined in various tissues. Expression of diabetes-associated genes was assessed using RT-qPCR, and the activity of signaling pathway proteins in the pancreas was determined through Western blot analysis. Treatment with C66 and B2BrBC significantly reduced oxidative stress markers and positively influenced antioxidant enzyme activities. Moreover, both compounds inhibited JNK activity in the pancreas while enhancing the expression of genes crucial for β-cell survival and glucose and redox homeostasis. The findings highlight the multifaceted potential of C66 and B2BrBC in ameliorating oxidative stress, influencing gene expression patterns linked to diabetes, and modulating key signaling pathways in the pancreas. The findings suggest that these compounds can potentially address diabetes-related pathological processes.

SLU7: A New Hub of Gene Expression Regulation—From Epigenetics to Protein Stability in Health and Disease

SLU7 (Splicing factor synergistic lethal with U5 snRNA 7) was first identified as a splicing factor necessary for the correct selection of 3′ splice sites, strongly impacting on the diversity of gene transcripts in a cell. More recent studies have uncovered new and non-redundant roles of SLU7 as an integrative hub of different levels of gene expression regulation, including epigenetic DNA remodeling, modulation of transcription and protein stability. Here we review those findings, the multiple factors and mechanisms implicated as well as the cellular functions affected. For instance, SLU7 is essential to secure liver differentiation, genome integrity acting at different levels and a correct cell cycle progression. Accordingly, the aberrant expression of SLU7 could be associated with human diseases including cancer, although strikingly, it is an essential survival factor for cancer cells. Finally, we discuss the implications of SLU7 in pathophysiology, with particular emphasis on the progression of liver disease and its possible role as a therapeutic target in human cancer.

Antioxidant Effects and Potential Molecular Mechanism of Action of Limonium aureum Extract Based on Systematic Network Pharmacology

Oxidative stress is the redox imbalance state of organisms that involves in a variety of biological processes of diseases. Limonium aureum (L.) Hill. is an excellent wild plant resource in northern China, which has potential application value for treating oxidative stress. However, there are few studies that focused on the antioxidant effect and related mechanism of L. aureum. Thus, the present study combining systematic network pharmacology and molecular biology aimed to investigate the antioxidant effects of L. aureum and explore its underlying anti-oxidation mechanisms. First, the antioxidant activity of L. aureum extracts was confirmed by in vitro and intracellular antioxidant assays. Then, a total of 11 bioactive compounds, 102 predicted targets, and 70 antioxidant-related targets were obtained from open source databases. For elucidating the molecular mechanisms of L. aureum, the PPI network and integrated visualization network based on bioinformatics assays were constructed to preliminarily understand the active compounds and related targets. The subsequent enrichment analysis results showed that L. aureum mainly affect the biological processes involving oxidation-reduction process, response to drug, etc., and the interference with these biological processes might be due to the simultaneous influence on multiple signaling pathways, including the HIF-1 and ERBB signaling pathways. Moreover, the mRNA levels of predicted hub genes were measured by qRT-PCR to verify the regulatory effect of L. aureum on them. Collectively, this finding lays a foundation for further elucidating the anti-oxidative damage mechanism of L. aureum and promotes the development of therapeutic drugs for oxidative stress.

A Novel PTP1B Inhibitor-Phosphate of Polymannuronic Acid Ameliorates Insulin Resistance by Regulating IRS-1/Akt Signaling

Protein tyrosine phosphatase 1B (PTP1B) is a critical negative modulator of insulin signaling and has attracted considerable attention in treating type 2 diabetes mellitus (T2DM). Low-molecular-weight polymannuronic acid phosphate (LPMP) was found to be a selective PTP1B inhibitor with an IC₅₀ of 1.02 ± 0.17 μM. Cellular glucose consumption was significantly elevated in insulin-resistant HepG2 cells after LPMP treatment. LPMP could alleviate oxidative stress and endoplasmic reticulum stress, which are associated with the development of insulin resistance. Western blot and polymerase chain reaction (PCR) analysis demonstrated that LPMP could enhance insulin sensitivity through the PTP1B/IRS/Akt transduction pathway. Furthermore, animal study confirmed that LPMP could decrease blood glucose, alleviate insulin resistance, and exert hepatoprotective effects in diabetic mice. Taken together, LPMP can effectively inhibit insulin resistance and has high potential as an anti-diabetic drug candidate to be further developed.

Long-Term Effects of Prenatal Severe Hypoxia on Central and Peripheral Components of the Glucocorticoid System in Rats

INTRODUCTION

Prenatal hypoxia is a risk factor for the development of numerous neurological disorders. It is known that the maternal stress response to hypoxia determines the epigenetic impairment of the perinatal expression of glucocorticoid receptors (GR) in the hippocampus of the progeny, but so far no detailed study of how this affects the functional state of the glucocorticoid system during further ontogenesis has been performed.

OBJECTIVE

The goal of the present study was to examine the long-term effects of the prenatal hypoxia on the functioning of the glucocorticoid system throughout life.

METHODS

Prenatal severe hypobaric hypoxia (PSH) was induced in the critical period of embryonic hippocampal formation on days 14-16 of gestation in a hypobaric chamber (180 Torr, 5% oxygen, 3 h). The activity of central (hippocampus) and peripheral (liver) components of the glucocorticoid system was assessed in 1-day-old (newborn), 2-week-old (juvenile), 3-month-old (adult), and 18-month-old (aged) male rats.

RESULTS

The PSH resulted in continuously elevated baseline corticosterone blood levels in the adult and aged rats. The chronic elevation of the corticosterone levels was accompanied by a progressive deficit of the GR expression in the liver, increased hepatic glycogen content, dysregulated glucose-6-phosphatase activity, and eventually hypoglycemia. Elevated corticosterone appears to result from the impairment of the mechanisms of glucocorticoid negative feedback since a substantial decrease in both the total number of GR and their nuclear localization was observed already in the hippocampus of newborn rat pups and persisted throughout life. Corresponding stable hippocampal downregulation of GR-dependent genes was observed as well. Suppression of the maternal glucocorticoid stress response to hypoxia by metyrapone injection to pregnant rats prior to each hypoxic challenge considerably reduced corticosterone over-response to hypoxia and prevented reduced hippocampal GR.

CONCLUSIONS

Our findings demonstrate that in progeny a deficit of hippocampal GR resulting from maternal glucocorticoid response to hypoxia remains stable throughout life and is accompanied by severe disturbances of baseline glucocorticoid levels and its peripheral reception. Negative consequences of PSH can be prevented by injection with an inhibitor of corticosterone synthesis (metyrapone) to pregnant females undergoing hypoxia.

Metabolic and Molecular Mechanisms of Macrophage Polarisation and Adipose Tissue Insulin Resistance

Inflammation plays a key role in the development and progression of type-2 diabetes (T2D), a disease characterised by peripheral insulin resistance and systemic glucolipotoxicity. Visceral adipose tissue (AT) is the main source of inflammation early in the disease course. Macrophages are innate immune cells that populate all peripheral tissues, including AT. Dysregulated AT macrophage (ATM) responses to microenvironmental changes are at the root of aberrant inflammation and development of insulin resistance, locally and systemically. The inflammatory activation of macrophages is regulated at multiple levels: cell surface receptor stimulation, intracellular signalling, transcriptional and metabolic levels. This review will cover the main mechanisms involved in AT inflammation and insulin resistance in T2D. First, we will describe the physiological and pathological changes in AT that lead to inflammation and insulin resistance. We will next focus on the transcriptional and metabolic mechanisms described that lead to the activation of ATMs. We will discuss more novel metabolic mechanisms that influence macrophage polarisation in other disease or tissue contexts that may be relevant to future work in insulin resistance and T2D.

Oncogenic ERG Represses PI3K Signaling through Downregulation of IRS2

Genomic rearrangements leading to the aberrant expression of ERG are the most common early events in prostate cancer and are significantly enriched for the concomitant loss of PTEN. Genetically engineered mouse models reveal that ERG overexpression alone is not sufficient to induce tumorigenesis, but combined loss of PTEN results in an aggressive invasive phenotype. Here, we show that oncogenic ERG repressed PI3K signaling through direct transcriptional suppression of IRS2, leading to reduced RTK levels and activity. In accordance with this finding, ERG-positive human prostate cancers had a repressed AKT gene signature and transcriptional downregulation of IRS2. Although overexpression of IRS2 activated PI3K signaling, promoting cell migration in a PI3K-dependent manner, this did not fully recapitulate the phenotype seen with loss of PTEN as PI3K signaling is not as robust as observed in the setting of loss of PTEN. Importantly, deletions of the PTEN locus, which promotes active PI3K signaling, were among the most significant copy-number alterations that co-occurred with ERG genomic rearrangements. This work provides insight on how initiating oncogenic events may directly influence the selection of secondary concomitant alterations to promote oncogenic signaling during tumor evolution. SIGNIFICANCE: This work provides insight on how initiating oncogenic events may directly influence the selection of secondary concomitant alterations to promote tumorigenesis.

Comparative study of testosterone and vitamin D analogue, elocalcitol, on insulin-controlled signal transduction pathway regulation in human skeletal muscle cells

PURPOSE

Skeletal muscle (Skm) plays a key role in regulating energetic metabolism through glucose homeostasis. Several hormones such as Testosterone (T) and Vitamin D (VD) have been shown to affect energy-dependent cell trafficking by determining Insulin (I)-like effects.

AIM

To elucidate possible hormone-related differences on muscular metabolic control, we analyzed and compared the effects of T and elocalcitol (elo), a VD analogue, on the activation of energy-dependent cell trafficking, metabolism-related-signal transduction pathways and transcription of gene downstream targets.

METHODS

Human fetal skeletal muscle cells (Hfsmc) treated with T or elo were analyzed for GLUT4 localization, phosphorylation/activation status of AKT, ERK1/2, IRS-1 signaling and c-MYC protein expression.

RESULTS

T, similar to elo, induced GLUT4 protein translocation likely in lipid raft microdomains. While both T and elo induced a rapid IRS-1 phosphorylation, the following dynamic in phosphorylation/activation of AKT and ERK1/2 signaling was different. Moreover, T but not elo increased c-MYC protein expression.

CONCLUSIONS

All together, our evidence indicates that whether both T and elo are able to affect upstream I-like pathway, they differently determine downstream effects in I-dependent cascade, suggesting diverse physiological roles in mediating I-like response in human skeletal muscle.

A hypothesis on paradoxical privileged portal vein metastasis of hepatocellular carcinoma. Can organ evolution shed light on patterns of human pathology, and vice versa?

Unlike other carcinomas, hepatocellular carcinoma (HCC) metastasizes to distant organs relatively rarely. In contrast, it routinely metastasizes to liver vasculature/liver, affecting portal veins 3-10 times more often than hepatic veins. This portal metastatic predominance is traditionally rationalized within the model of a reverse portal flow, due to accompanying liver cirrhosis. However, this intuitive model is not coherent with facts: 1) reverse portal flow occurs in fewer than 10% of cirrhotic patients, while portal metastasis occurs in 30-100% of HCC cases, and 2) portal vein prevalence of HCC metastasis is also characteristic of HCC in non-cirrhotic livers. Therefore, we must assume that the route for HCC metastatic dissemination is the same as for other carcinomas: systemic dissemination via the draining vessel, i.e., via the hepatic vein. In this light, portal prevalence versus hepatic vein of HCC metastasis appears as a puzzling pattern, particularly in cases when portal HCC metastases have appeared as the sole manifestation of HCC. Considering that other GI carcinomas (colorectal, pancreatic, gastric and small bowel) invariably disseminate via portal vein, but very rarely form portal metastasis, portal prevalence of HCC metastasis appears as a paradox. However, nature does not contradict itself; it is rather our wrong assumptions that create paradoxes. The 'portal paradox' becomes a logical event within the hypothesis that the formation of the unique portal venous system preceded the appearance of liver in evolution of chordates. The analysis suggests that the appearance of the portal venous system, supplying hormones and growth factors of pancreatic family, which includes insulin, glucagon, somatostatin, and pancreatic polypeptide (HGFPF) to midgut diverticulum in the early evolution of chordates (in an Amphioxus-like ancestral animal), promoted differentiation of enterocytes into hepatocytes and their further evolution to the liver of vertebrates. These promotional-dependent interactions are conserved in the vertebrate lineage. I hypothesize that selective homing and proliferation of malignant hepatocytes (i.e., HCC cells) in the portal vein environment are due to a uniquely high concentration of HGFPF in portal blood. HGFPF are also necessary for liver function and renewal and are significantly extracted by hepatocytes from passing blood, creating a concentration gradient of HGFPF between the portal blood and hepatic vein outflow, making post-liver vasculature and remote organs less favorable spaces for HCC growth. It also suggested that the portal vein environment (i.e., HGFPF) promotes the differentiation of more aggressive HCC clones from already-seeded portal metastases, explaining the worse outcome of HCC with the portal metastatic pattern. The analysis also offers new hypothesis on the phylogenetic origin of the hepatic diverticulum of cephalochordates, with certain implications for the modeling of the chordate phylogeny.

A novel recombinant peptide INSR-IgG4Fc (Yiminsu) restores insulin sensitivity in experimental insulin resistance models

Type 2 diabetes mellitus (T2DM) is a chronic degenerative endocrine and metabolic disease with high mortality and morbidity, yet lacks effective therapeutics. We recently generated a novel fusion peptide INSR-IgG4Fc, Yiminsu (YMS), to facilitate the high-affinity binding and transportation of insulin. Thus, the aim of the present study was to determine whether the novel recombinant peptide, YMS, could contribute to restoring insulin sensitivity and glycaemic control in insulin resistance models and revealing its underlying mechanism. Palmitic acid (PA)-treated LO2 cells and high fat diet (HFD)-fed mice were treated with YMS. Therapeutic effects of YMS were measured using Western blotting, ELISA, qPCR, Histology and transmission electron microscopy. We observed that YMS treatment effectively improved insulin signaling in PA-treated LO2 cells and HFD-fed mice. Notably, YMS could significantly reduce serum levels of glucose, triglycerides, fatty acids and cholesterol without affecting the serum insulin levels. Moreover, our data demonstrated that YMS could restore glucose and lipid homeostasis via facilitating insulin transportation and reactivating PI3K/Akt signaling in both PA-treated cells and liver, gastrocnemius and brown fat of HFD-fed mice. Additionally, we noticed that the therapeutic effects of YMS was similar as rosiglitazone, a well-recognized insulin sensitizer. Our findings suggested that YMS is a potentially candidate for pharmacotherapy for metabolic disorders associated with insulin resistance, particularly in T2DM.

Bone marrow infiltrated Lnc-INSR induced suppressive immune microenvironment in pediatric acute lymphoblastic leukemia

Immune escape due to immunosuppressive microenvironments, such as those associated with regulatory T (Treg) cells is highly associated with initial occurrence and development of solid tumors or hematologic malignancies. Here, we employed high-throughput transcriptome screening to demonstrate immunosuppression-associated increases in the long noncoding (lnc) RNA lnc-insulin receptor precursor (INSR), which was corrected with INSR expression in CD4+ T cells extracted from the bone marrow of patients with childhood acute T lymphoblastic leukemia. Loss-of-function and gain-of-function assays in vitro and in vivo revealed that membrane-localized and cytoplasm-localized lnc-INSR promoted Treg distribution and decreased the percentage of cytotoxic T lymphocytes, which induced tumor growth. Through direct binding with INSR, lnc-INSR blocked the INSR ubiquitination site, causing abnormal activation of INSR and the phosphatidylinositide 3-kinase/AKT-signaling pathway. These results indicated that lnc-INSR might promote immune suppression by enhancing Treg-cell differentiation and serve as valuable therapeutic targets in the immunosuppressive tumor microenvironment.

Privileged portal metastasis of hepatocellular carcinoma in light of the coevolution of a visceral portal system and liver in the chordate lineage: a search for therapeutic targets

Hepatocellular carcinoma (HCC) disseminates systemically, but metastases occur in distant organs only in minority of patients, whereas HCC routinely metastasizes to liver and its vessels. HCC cells disseminate via hepatic veins, but portal veins are affected by metastasis more frequently than are hepatic veins, and correlates with poor prognosis. In this review, I suggest that privileged HCC portal metastasis occurs because of high levels of pancreatic family hormones and growth factors (PHGFs) in the portal blood. The analysis suggests that the appearance of the portal system carrying PHGFs in the evolution of invertebrate chordate (Amphioxus) led to the evolution of the liver in vertebrate; given that the portal pattern of HCC metastasis and selection of more-aggressive clones are PHGF dependent, PHGFs and their ligands constitute therapeutic targets.

Regulation of liver development: implications for liver biology across the lifespan

The liver serves a spectrum of essential metabolic and synthetic functions that are required for the transition from fetal to postnatal life. Processes essential to the attainment of adequate liver mass and function during fetal life include cell lineage specification early in development, enzymic and other functional modes of differentiation throughout gestation, and ongoing cell proliferation to achieve adequate liver mass. Available data in laboratory rodents indicate that the signaling networks governing these processes in the fetus differ from those that can sustain liver function and mass in the adult. More specifically, fetal hepatocytes may develop independent of key mitogenic signaling pathways, including those involving the Erk mitogen-activated protein kinases MAPK1/3 and the mechanistic target of rapamycin (mTOR). In addition, the fetal liver is subject to environmental influences that, through epigenetic mechanisms, can have sustained effects on function and, by extension, contribute to the developmental origin of adult metabolic disease. Finally, the mitogen-independent phenotype of rat fetal hepatocytes in late gestation makes these cells suitable for cell-based therapy of liver injury. In the aggregate, studies on the mechanisms governing fetal liver development have implications not only for the perinatal metabolic transition but also for the prevention and treatment of liver disorders throughout the lifespan.

Splicing regulator SLU7 is essential for maintaining liver homeostasis

A precise equilibrium between cellular differentiation and proliferation is fundamental for tissue homeostasis. Maintaining this balance is particularly important for the liver, a highly differentiated organ with systemic metabolic functions that is endowed with unparalleled regenerative potential. Carcinogenesis in the liver develops as the result of hepatocellular de-differentiation and uncontrolled proliferation. Here, we identified SLU7, which encodes a pre-mRNA splicing regulator that is inhibited in hepatocarcinoma, as a pivotal gene for hepatocellular homeostasis. SLU7 knockdown in human liver cells and mouse liver resulted in profound changes in pre-mRNA splicing and gene expression, leading to impaired glucose and lipid metabolism, refractoriness to key metabolic hormones, and reversion to a fetal-like gene expression pattern. Additionally, loss of SLU7 also increased hepatocellular proliferation and induced a switch to a tumor-like glycolytic phenotype. Slu7 governed the splicing and/or expression of multiple genes essential for hepatocellular differentiation, including serine/arginine-rich splicing factor 3 (Srsf3) and hepatocyte nuclear factor 4α (Hnf4α), and was critical for cAMP-regulated gene transcription. Together, out data indicate that SLU7 is central regulator of hepatocyte identity and quiescence.

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.

Comparing signaling networks between normal and transformed hepatocytes using discrete logical models

Substantial effort in recent years has been devoted to constructing and analyzing large-scale gene and protein networks on the basis of "omic" data and literature mining. These interaction graphs provide valuable insight into the topologies of complex biological networks but are rarely context specific and cannot be used to predict the responses of cell signaling proteins to specific ligands or drugs. Conversely, traditional approaches to analyzing cell signaling are narrow in scope and cannot easily make use of network-level data. Here, we combine network analysis and functional experimentation by using a hybrid approach in which graphs are converted into simple mathematical models that can be trained against biochemical data. Specifically, we created Boolean logic models of immediate-early signaling in liver cells by training a literature-based prior knowledge network against biochemical data obtained from primary human hepatocytes and 4 hepatocellular carcinoma cell lines exposed to combinations of cytokines and small-molecule kinase inhibitors. Distinct families of models were recovered for each cell type, and these families clustered topologically into normal and diseased sets.

Role of Raf Kinase Inhibitor Protein in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) accounts for 80-90% of primary liver tumors and is one of the most common and devastating malignant diseases worldwide. The MAPK signaling pathway is activated in over 90% of HCCs, and RKIP has been identified as an inhibitor of the MAPK pathway. It has been observed that downregulation of RKIP expression in HCC tumors contributes to constitutive activation of the ERK/MAPK pathway and promotes proliferation and migration of HCC cells. More important, activation of IGF-I/ERK/MAPK pathways can be blocked by restoration of RKIP levels. The protein levels of RKIP are significantly reduced in HCC, whereas mRNA levels only decreased in 41% of HCC samples studied, suggesting that the downregulation of RKIP in HCC may be influenced through multiple mechanisms both at the mRNA and protein levels. In this context, mTOR inhibitor, insulin, and proteasome inhibitors were found to modulate RKIP expression in FOCUS HCC cells. A better understating of mechanisms by which RKIP expression is downregulated in HCC may be critical to develop a possible target for therapeutic intervention of HCC.

Curcumin attenuates the effects of insulin on stimulating hepatic stellate cell activation by interrupting insulin signaling and attenuating oxidative stress

Hyperinsulinemia associated with type II diabetes mellitus (T2DM) is a risk factor for non-alcoholic steatohepatitis (NASH) and hepatic fibrosis. Hepatic stellate cells (HSCs) are the major effectors in collagen production during hepatic fibrogenesis. Elevated levels of insulin stimulate HSC activation. In addition to its anti-diabetic effects, the antioxidant curcumin, the yellow pigment in curry from turmeric, suppresses HSC activation and protects the liver from fibrogenesis in vitro and in vivo. This study aims at evaluating the effect of curcumin on insulin-induced HSC activation and further elucidating the underlying mechanisms. We report that curcumin dose-dependently eliminates insulin-induced HSC activation by suppressing expression of type I collagen gene and other key genes relevant to HSC activation. Additional experiments indicate that curcumin interrupts insulin signaling in HSCs by reducing the phosphorylation level of insulin receptor (InsR) and suppressing gene expression of InsR. Furthermore, curcumin attenuates insulin-induced oxidative stress in HSCs by inducing gene expression of glutamate-cysteine ligase (GCL), leading to de novo synthesis of glutathione and the suppression of gene expression of InsR. These results support our initial hypothesis that curcumin inhibits the effects of insulin on stimulating HSC activation by interrupting insulin signaling and attenuating oxidative stress. Our results provide novel insights into the mechanisms by which curcumin inhibits the insulin-induced HSC activation.

Synergistic premalignant effects of chronic ethanol exposure and insulin receptor substrate-1 overexpression in liver

AIM

Insulin receptor substrate, type 1 (IRS-1) transmits growth and survival signals, and is overexpressed in more than 90% of hepatocellular carcinomas (HCCs). However, experimental overexpression of IRS-1 in the liver was found not to be sufficient to cause HCC. Since chronic alcohol abuse is a risk factor for HCC, we evaluated potential interactions between IRS-1 overexpression and chronic ethanol exposure by assessing premalignant alterations in gene expression.

METHODS

Wild-type (wt) or IRS-1 transgenic (Tg) mice, constitutively overexpressing the human (h) transgene in the liver, were pair-fed isocaloric liquid diets containing 0% or 24% ethanol for 8 weeks. The livers were used for histopathologic study and gene expression analysis, focusing on insulin, insulin-like growth factor (IGF) and wingless (WNT)-Frizzled (FZD) pathways, given their known roles in HCC.

RESULTS

In wt mice, chronic ethanol exposure caused hepatocellular microsteatosis with focal chronic inflammation, reduced expression of proliferating cell nuclear antigen (PCNA) and increased expression of IGF-I and IGF-I receptor. In hIRS-1 Tg mice, chronic ethanol exposure caused hepatic micro- and macrosteatosis, focal chronic inflammation, apoptosis and disordered lobular architecture. These effects of ethanol in hIRS-1 Tg mice were associated with significantly increased expression of IGF-II, insulin, IRS-4, aspartyl-asparaginyl beta hydroxylase (AAH), WNT-1 and FZD 7, as occurs in HCC.

CONCLUSION

In otherwise normal liver, chronic ethanol exposure mainly causes liver injury and inflammation with impaired DNA synthesis. In contrast, in the context of hIRS-1 overexpression, chronic ethanol exposure may serve as a cofactor in the pathogenesis of HCC by promoting expression of growth factors, receptors and signaling molecules known to be associated with hepatocellular transformation.

Loss of Raf kinase inhibitor protein promotes cell proliferation and migration of human hepatoma cells

BACKGROUND & AIMS

The Raf kinase inhibitor protein (RKIP) has been identified as a suppressor of the mitogen-activated protein kinase (MAPK) pathway. Loss of RKIP function promotes tumor metastasis in prostate cancer and melanoma. The insulin-like growth factor I (IGF-I)-mediated MAPK cascade is often activated in hepatocellular carcinoma (HCC), but the role of RKIP in the molecular pathogenesis of these tumors is unknown. This study was performed to evaluate the role of RKIP in the development of HCC.

METHODS

The levels of RKIP expression in HCC tumor and corresponding peritumoral tissues were determined by immunohistochemistry and Western blot analysis. The underlying mechanisms of RKIP were assessed with immunoblot analysis, Raf kinase activity assay, cell proliferation, and migration assays after either overexpression or knockdown of RKIP expression in HCC cell lines.

RESULTS

RKIP expression is down-regulated in human HCC compared with adjacent peritumoral tissues. Low RKIP levels were correlated with enhanced extracellular signal-regulated-kinase (ERK)/MAPK pathway activation. Reconstitution experiments antagonized IGF-I-mediated MAPK pathway activation, resulting in reduced nuclear accumulation of phospho-ERK. In contrast, knockdown of RKIP expression using small interfering RNA induced activation of the ERK/MAPK pathway. Ectopic expression of RKIP altered HCC cell proliferation and migration.

CONCLUSIONS

Our findings indicate that down-regulation of RKIP expression is a major factor in activation of the IGF-I/ERK/MAPK pathway during human hepatocarcinogenesis.

Aspartyl-asparagyl beta hydroxylase over-expression in human hepatoma is linked to activation of insulin-like growth factor and notch signaling mechanisms

Aspartyl-(asparagyl)-beta-hydroxylase (AAH) is overexpressed in various malignant neoplasms, including hepatocellular carcinomas (HCCs). The upstream regulation of AAH and its functional role in Notch-mediated signaling and motility in HCC cells was accessed. The mRNA transcript levels of AAH, insulin receptor substrate (IRS), insulin and insulin-like growth factor (IGF) receptors and polypeptides, Notch, Jagged, and HES were measured in 15 paired samples of HCC and adjacent HCC-free human liver biopsy specimens using real-time quantitative RT-PCR and Western blot analysis. Overexpression of AAH was detected in 87% of the HCC relative to the paired HCC-free liver tissue. IRS-1, IRS-2, and IRS-4 were each overexpressed in 80% of the HCC samples, and IGF-I and IGF-2 receptors were overexpressed in 40% and 100% of the HCCs, respectively. All HCC samples had relatively increased levels of Notch-1 and HES-1 gene expression. Overexpression of AAH led to increased levels of Notch, and co-immunoprecipitation experiments demonstrated a direct interaction between AAH and Notch as well as its ligand Jagged. In conclusion, contributions to the malignant phenotype of HCC is due to activation of IGF-I and IGF-II signaling that results in over-expression of both AAH and Notch. The functional role of AAH in relation to cell motility has been linked to increased activation of the Notch signaling pathway.

Overexpression of insulin receptor substrate-2 in human and murine hepatocellular carcinoma

De-regulations in insulin and insulin-like growth factor (IGF) pathways may contribute to hepatocellular carcinoma. Although intracellular insulin receptor substrate-2 (IRS-2) is the main effector of insulin signaling in the liver, its role in hepatocarcinogenesis is unknown. Here, we show that IRS-2 was overexpressed in two murine models of hepatocarcinogenesis: administration of diethylnitrosamine and hepatic overexpression of SV40 large T antigen. In both models, IRS-2 overexpression was detected in preneoplastic lesions and at higher levels in tumoral nodules. IRS-2 overexpression associated with IGF-2 and IRS-1 overexpression and with GSK-3beta inhibition. Increased expression of IRS-2 was also detected in human hepatocellular carcinoma specimens and hepatoma cell lines. In murine and human hepatoma cells, IRS-2 protein induction associated with increased IRS-2 mRNA levels. The functionality of IRS-2 was demonstrated in Hep 3 B cells, in which IRS-2 tyrosine phosphorylation and its association with phosphatidylinositol-3 kinase were induced by IGF-2. Moreover, down-regulation of IRS-2 expression increased apoptosis in these cells. In conclusion, we demonstrate that IRS-2 is overexpressed in human and murine hepatocellular carcinoma. The emergence of IRS-2 overexpression at preneoplastic stages during experimental hepatocarcinogenesis and its protective effect against apoptosis suggest that IRS-2 contributes to liver tumor progression.

Effects of maternal starvation on hepatocyte proliferation in the late gestation fetal rat

Fetal growth retardation, a common end point for a variety of conditions affecting mother and fetus, is associated with reduced liver mass. We have performed studies to determine the mechanism for decreased liver mass in a maternal starvation model of fetal growth restriction in the rat. Pregnant dams were deprived of food for 48 h before delivery on embryonic day 19 (E19). Fetal body weight was not affected. However, fetal liver weight was reduced by approximately 15%. Immunostaining of fetal liver for proliferating cell nuclear antigen and flow cytometry on isolated fetal hepatocytes showed G1 cell cycle arrest in samples from starved dams. Based on our prior studies showing attenuated hepatic insulin signaling in the late gestation fetal rat, we tested the hypothesis that G1 arrest in our model might be due to altered nutrient signaling. Fetal plasma amino acid analyses showed no decrease in branched-chain amino acids, but arginine concentrations were decreased in fetuses of fasted mothers. Reduced arginine in E19 fetal hepatocyte culture media was associated with decreased DNA synthesis. Whereas levels of cyclins D and E were unchanged in fetal hepatocytes exposed to low arginine, cyclin E-dependent kinase activity was reduced. Low arginine also induced changes in the translational machinery, indicative of impaired signaling through the nutrient sensing kinase mammalian target of rapamycin. Our results are consistent with the hypothesis that restricted nutrient availability signals to the hepatocyte cell cycle in fetuses of fasted mothers, thereby accounting for decreased hepatocyte proliferation and liver mass.

Targeted hepatic overexpression of human IRS-1: postnatal effects in the developing mouse

Insulin receptor substrate-1 (IRS-1) is an intracellular docking protein involved in insulin and insulin-like growth factor (IGF) signaling. The present studies examine postnatal liver development in transgenic mice with targeted hepatic overexpression of human insulin receptor substrate-1 (hIRS-1). In mature animals, hIRS-1 overexpression augments liver growth. Based on our previous studies that have shown markedly attenuated insulin signaling in the late-gestation and early-postnatal rat, we hypothesized that the liver growth effect of overexpressed hIRS-1 would be attenuated in the neonatal period. Wild-type and heterozygous transgenic mice were studied at 1, 2, 4 or 8 weeks of age. Transgene expression was seen at all ages, albeit at a lower level in the youngest animals. Liver-to-carcass weight ratios were similar in hIRS-1 and wild-type mice at 1 and 2 weeks of age. At 4 and 8 weeks, transgenic mice had larger livers accounted for by increased hepatocyte number, not size. In addition, the transgenic mice had increased liver glycogen content at 8 weeks but not at 1 week. Relative to transgene mRNA expression, hIRS-1 protein levels were restricted in the younger animals. However, IRS-1-associated phosphatidylinositol-3 kinase (PI3K) activity was not similarly suppressed. Downstream from IRS-1, we found activation of the signaling kinase Akt in 8-week-old but not in 1-week-old animals. Our findings indicate that hepatic IRS-1-mediated signaling may be limited in neonatal mice at two levels, post-transcriptional down-regulation of IRS-1 content and attenuated signaling beyond the level of PI3K activation.