GH modulates hepatic epidermal growth factor signaling in the mouse

Growth Hormone Action as a Target in Cancer: Significance, Mechanisms, and Possible Therapies

Growth hormone (GH) is a pituitary-derived endocrine hormone required for normal postnatal growth and development. Hypo- or hypersecretion of endocrine GH results in 2 pathologic conditions, namely GH deficiency (GHD) and acromegaly. Additionally, GH is also produced in nonpituitary and tumoral tissues, where it acts rather as a cellular growth factor with an autocrine/paracrine mode of action. An increasingly persuasive and large body of evidence over the last 70 years concurs that GH action is implicit in escalating several cancer-associated events, locally and systemically. This pleiotropy of GH's effects is puzzling, but the association with cancer risk automatically raises a concern for patients with acromegaly and for individuals treated with GH. By careful assessment of the available knowledge on the fundamental concepts of cancer, suggestions from epidemiological and clinical studies, and the evidence from specific reports, in this review we aimed to help clarify the distinction of endocrine vs autocrine/paracrine GH in promoting cancer and to reconcile the discrepancies between experimental and clinical data. Along this discourse, we critically weigh the targetability of GH action in cancer-first by detailing the molecular mechanisms which posit GH as a critical node in tumor circuitry; and second, by enumerating the currently available therapeutic options targeting GH action. On the basis of our discussion, we infer that a targeted intervention on GH action in the appropriate patient population can benefit a sizable subset of current cancer prognoses.

Liver impact of growth hormone (GH) intermittent treatment during the growth period in mice

Liver impact of prolonged GH-treatment given to non-GH-deficient growing mice between the third and eighth week of life was evaluated in both sexes. Tissues were collected 6 h after last dose or four weeks later. Somatometric, biochemical, histological, immunohistochemical, RT-qPCR and immunoblotting determinations were performed. Five-week GH intermittent administration induced body weight gain and body and bone length increase, augmented organ weight, higher hepatocellular size and proliferation, and increased liver IGF1 gene expression. Phosphorylation of signaling mediators and expression of GH-induced proliferation-related genes was decreased in GH-treated mice liver 6h after last injection, reflecting active sensitization/desensitization cycles. In females, GH elicited EGFR expression, associated to higher EGF-induced STAT3/5 phosphorylation. Four weeks after treatment, increased organ weight concomitant to body weight gain was still observed, whereas hepatocyte enlargement reverted. However, basal signaling for critical mediators was lower in GH-treated animals and in male controls compared to female ones, suggesting signaling declination.

Growth Hormone Modulation of Hepatic Epidermal Growth Factor Receptor Signaling

Epidermal growth factor receptor (EGFR) signaling has a central role in the regenerative response of the liver upon injury and is involved in cellular transformation linked to chronic damage. Hepatic EGFR expression, trafficking, and signaling are regulated by growth hormone (GH). Chronically elevated GH levels are associated with liver cancer development and progression in mice. Studies in different in vivo experimental models indicate that EGF and GH mutually crossregulate in a complex manner. Several factors, such as the extent of exposure to supraphysiological GH levels and the pattern of GH administration, are important variables to be considered in exploring the interplay between the two hormones in connection with the progression of hepatic tumors.

Opposing roles of E3 ligases TRIM23 and TRIM21 in regulation of ion channel ANO1 protein levels

Anoctamin-1 (ANO1) (TMEM16A) is a calcium-activated chloride channel that plays critical roles in diverse physiological processes, such as sensory transduction and epithelial secretion. ANO1 levels have been shown to be altered under physiological and pathological conditions, although the molecular mechanisms that control ANO1 protein levels remain unclear. The ubiquitin–proteasome system is known to regulate the levels of numerous ion channels, but little information is available regarding whether and how ubiquitination regulates levels of ANO1. Here, we showed that two E3 ligases, TRIM23 and TRIM21, physically interact with the C terminus of ANO1. In vitro and in vivo assays demonstrated that whereas TRIM23 ubiquitinated ANO1 leading to its stabilization, TRIM21 ubiquitinated ANO1 and induced its degradation. Notably, ANO1 regulation by TRIM23 and TRIM21 is involved in chemical-induced pain sensation, salivary secretion, and heart-rate control in mice, and TRIM23 also mediates ANO1 upregulation induced by epidermal growth factor treatment. Our results suggest that these two antagonistic E3 ligases act together to control ANO1 expression and function. Our findings reveal a previously unrecognized mechanism for regulating ANO1 protein levels and identify a potential molecular link between ANO1 regulation, epidermal growth factor, and other signaling pathways.

The effect of Zataria multiflora on inflammatory cytokine and respiratory symptoms in veterans exposed to sulfur mustard

The effect of Zataria multiflora (Z. multiflora) on serum cytokine, chemokines, and respiratory symptoms in the veterans exposed to sulfur mustard (SM) more than two decades (27-30 years) ago was conducted in 2018. Thirty-four patients were randomly assigned to the placebo group (P, mean age (54.40 ± 5.51)) and two treated groups with Z. multiflora extract 5 and 10 mg/kg/day (Z5 and 10; mean age, 58.50 ± 3.60 and 55.18 ± 4.11, respectively). Serum levels of tumor necrosis factor (TNF-α), monocyte chemotactic protein 1 (MCP-1), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), forced expiratory volume-one second (FEV₁), and respiratory symptoms including chest wheeze (CW), night wheeze (NW), night cough (NC), and cough and wheeze during exercise (ECW) were assessed at the baseline (phase 0), 1 and 2 months after starting treatment (phase I and II, respectively). The value of FEV₁ was significantly increased in Z10 in phase I and II compared with that in phase 0 (p < 0.01 for both) and in Z5 in phase II compared with phase I and 0 (p < 0.001for both). All respiratory symptoms significantly decreased in Z5 and 10 in phase I and II compared with those in phase 0 (p < 0.05 to p < 0.001). Serum levels of TNF-α and VEGF were decreased in Z5 and 10 in phase I and II compared with those in phase 0 (p < 0.05 to p < 0.001). Serum levels of MCP-1 and EGF were decreased in Z10 in phase I and II compared with those in phase 0 (p < 0.05 to p < 0.001). The percent change of respiratory symptoms, serum levels of cytokines during the treatment period, was significantly improved in the treated groups compared with that in the placebo group. Two months' of treatment with Z. multiflora improved cytokine levels, respiratory symptom, and FEV₁ values in SM-exposed patients.

Concentration-dependent effects of sodium cholate and deoxycholate bile salts on breast cancer cells proliferation and survival

Bile acids (BAs) are bioactive molecules that have potential therapeutic interest and their derived salts are used in several pharmaceutical systems. BAs have been associated with tumorigenesis of several tissues including the mammary tissue. Therefore, it is crucial to characterize their effects on cancer cells. The objective of this work was to analyse the molecular and cellular effects of the bile salts sodium cholate and sodium deoxycholate on epithelial breast cancer cell lines. Bile salts (BSs) effects over breast cancer cells viability and proliferation were assessed by MTS and BrdU assays, respectively. Activation of cell signaling mediators was determined by immunobloting. Microscopy was used to analyze cell migration, and cellular and nuclear morphology. Interference of membrane fluidity was studied by generalized polarization and fluorescence anisotropy. BSs preparations were characterized by transmission electron microscopy and dynamic light scattering. Sodium cholate and sodium deoxycholate had dual effects on cell viability, increasing it at the lower concentrations assessed and decreasing it at the highest ones. The increase of cell viability was associated with the promotion of AKT phosphorylation and cyclin D1 expression. High concentrations of bile salts induced apoptosis as well as sustained activation of p38 and AKT. In addition, they affected cell membrane fluidity but not significant effects on cell migration were observed. In conclusion, bile salts have concentration-dependent effects on breast cancer cells, promoting cell proliferation at physiological levels and being cytotoxic at supraphysiological ones. Their effects were associated with the activation of kinases involved in cell signalling.

Hepatic gene body hypermethylation is a shared epigenetic signature of murine longevity

Dietary, pharmacological and genetic interventions can extend health- and lifespan in diverse mammalian species. DNA methylation has been implicated in mediating the beneficial effects of these interventions; methylation patterns deteriorate during ageing, and this is prevented by lifespan-extending interventions. However, whether these interventions also actively shape the epigenome, and whether such epigenetic reprogramming contributes to improved health at old age, remains underexplored. We analysed published, whole-genome, BS-seq data sets from mouse liver to explore DNA methylation patterns in aged mice in response to three lifespan-extending interventions: dietary restriction (DR), reduced TOR signaling (rapamycin), and reduced growth (Ames dwarf mice). Dwarf mice show enhanced DNA hypermethylation in the body of key genes in lipid biosynthesis, cell proliferation and somatotropic signaling, which strongly correlates with the pattern of transcriptional repression. Remarkably, DR causes a similar hypermethylation in lipid biosynthesis genes, while rapamycin treatment increases methylation signatures in genes coding for growth factor and growth hormone receptors. Shared changes of DNA methylation were restricted to hypermethylated regions, and they were not merely a consequence of slowed ageing, thus suggesting an active mechanism driving their formation. By comparing the overlap in ageing-independent hypermethylated patterns between all three interventions, we identified four regions, which, independent of genetic background or gender, may serve as novel biomarkers for longevity-extending interventions. In summary, we identified gene body hypermethylation as a novel and partly conserved signature of lifespan-extending interventions in mouse, highlighting epigenetic reprogramming as a possible intervention to improve health at old age.

Inhibition of EGFR attenuates fibrosis and stellate cell activation in diet-induced model of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease. NAFLD begins with steatosis and advances to nonalcoholic steatohepatitis (NASH) and cirrhosis. The molecular mechanisms involved in NAFLD progression are not understood. Based on recent studies showing dysregulation of epidermal growth factor receptor (EGFR) in animal models of liver injury, we sought to determine if inhibition of EGFR mitigates liver fibrosis and HSC activation in NAFLD. We utilized the high fat diet (HFD)-induced murine model of liver injury to study the role of EGFR in NAFLD. The lipid accumulation, oxidative stress, hepatic stellate cell (HSC) activation and matrix deposition were examined in the liver tissues. We also evaluated the EGFR signaling pathway, ROS activation and pro-fibrogenic phenotype in oxidized low density lipoproteins (ox-LDL) challenged cultured HSCs. We demonstrate that EGFR was phosphorylated in liver tissues of HFD murine model of NAFLD. Inhibition of EGFR prevented diet-induced lipid accumulation, oxidative stress, and HSC activation and matrix deposition. In cultured HSCs, we show that ox-LDL caused rapid activation of the EGFR signaling pathway and induce the production of reactive oxygen species. EGFR also mediated HSC activation and promoted a pro-fibrogenic phenotype. In conclusion, our data demonstrate that EGFR plays an important role in NAFLD and is an attractive target for NAFLD therapy.

Attenuation of epidermal growth factor (EGF) signaling by growth hormone (GH)

Transgenic mice overexpressing growth hormone (GH) show increased hepatic protein content of the epidermal growth factor receptor (EGFR), which is broadly associated with cell proliferation and oncogenesis. However, chronically elevated levels of GH result in desensitization of STAT-mediated EGF signal and similar response of ERK1/2 and AKT signaling to EGF compared to normal mice. To ascertain the mechanisms involved in GH attenuation of EGF signaling and the consequences on cell cycle promotion, phosphorylation of signaling mediators was studied at different time points after EGF stimulation, and induction of proteins involved in cell cycle progression was assessed in normal and GH-overexpressing transgenic mice. Results from kinetic studies confirmed the absence of STAT3 and 5 activation and comparable levels of ERK1/2 phosphorylation upon EGF stimulation, which was associated with diminished or similar induction of c-MYC, c-FOS, c-JUN, CYCLIN D1 and CYCLIN E in transgenic compared to normal mice. Accordingly, kinetics of EGF-induced c-SRC and EGFR phosphorylation at activating residues demonstrated that activation of these proteins was lower in the transgenic mice with respect to normal animals. In turn, EGFR phosphorylation at serine 1046/1047, which is implicated in the negative regulation of the receptor, was increased in the liver of GH-overexpressing transgenic mice both in basal conditions and upon EGF stimulus. Increased basal phosphorylation and activation of the p38-mitogen-activated protein kinase might account for increased Ser 1046/1047 EGFR. Hyperphosphorylation of EGFR at serine residues would represent a compensatory mechanism triggered by chronically elevated levels of GH to mitigate the proliferative response induced by EGF.

Mitogenic signaling pathways in the liver of growth hormone (GH)-overexpressing mice during the growth period

Growth hormone (GH) is a pleiotropic hormone that triggers STATs, ERK1/2 and Akt signaling, related to cell growth and proliferation. Transgenic mice overexpressing GH present increased body size, with a disproportionate liver enlargement due to hypertrophy and hyperplasia of the hepatocytes. We had described enhanced mitogenic signaling in liver of young adult transgenic mice. We now evaluate the activation of these signaling cascades during the growth period and relate them to the morphological alterations found. Signaling mediators, cell cycle regulators and transcription factors involved in cellular growth in the liver of GH-overexpressing growing mice were assessed by immunoblotting, RT-qPCR and immunohistochemistry. Hepatocyte enlargement can be seen as early as 2-weeks of age in GH-overexpressing animals, although it is more pronounced in young adults. Levels of cell cycle mediators PCNA and cyclin D1, and transcription factor c-Jun increase with age in transgenic mice with no changes in normal mice, whereas c-Myc levels are higher in 2-week-old transgenic animals and cyclin E levels decline with age for both genotypes. STAT3, Akt and GSK3 present higher activation in the adult transgenic mice than in the growing animals, while for c-Src and mTOR, phosphorylation in GH-overexpressing mice is higher than in control siblings at 4 and 9 weeks of age. No significant changes are observed for ERK1/2, neither by age or genotype. Thus, the majority of the mitogenic signaling pathways are gradually up-regulated in the liver of GH-transgenic mice, giving rise to the hepatic morphological changes these mice exhibit.

EGFR Signaling in Liver Diseases

The epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase that is activated by several ligands leading to the activation of diverse signaling pathways controlling mainly proliferation, differentiation, and survival. The EGFR signaling axis has been shown to play a key role during liver regeneration following acute and chronic liver damage, as well as in cirrhosis and hepatocellular carcinoma (HCC) highlighting the importance of the EGFR in the development of liver diseases. Despite the frequent overexpression of EGFR in human HCC, clinical studies with EGFR inhibitors have so far shown only modest results. Interestingly, a recent study has shown that in human HCC and in mouse HCC models the EGFR is upregulated in liver macrophages where it plays a tumor-promoting function. Thus, the role of EGFR in liver diseases appears to be more complex than what anticipated. Further studies are needed to improve the molecular understanding of the cell-specific signaling pathways that control disease development and progression to be able to develop better therapies targeting major components of the EGFR signaling network in selected cell types. In this review, we compiled the current knowledge of EGFR signaling in different models of liver damage and diseases, mainly derived from the analysis of HCC cell lines and genetically engineered mouse models (GEMMs).

The long noncoding RNA, EGFR-AS1, a target of GHR, increases the expression of EGFR in hepatocellular carcinoma

LncRNA has provided an important new perspective regarding gene regulation. Both the expression and activation of EGFR have been proven to be under the tight control of the GHR pathway. EGFR-AS1 has been found to inhibit the expression of EGFR. GHR-siRNA and EGFR-AS1-siRNA were transfected into HCC cell lines, and a series of WB, q-PCR, and IF experiments was conducted to evaluate whether EGFR-AS1 participated in the regulation of GHR and EGFR. We found that impeded expression of GHR decreased the expression of EGFR and EGFR-AS1 in vivo and in vitro. Then, it was verified that EGFR and EGFR-AS1 were relatively upregulated in HCC tissue, and they were significantly related to some clinical characteristics and patient prognosis. Furthermore, EGFR-AS1 was determined to promote HCC development by improving the ability of invasion and proliferation of HCC cells in vitro, and it was also found to affect the cell cycle. Our study identified that EGFR-AS1 may promote HCC genesis and development. EGFR-AS1 may act as a prognostic factor in HCC. More importantly, we observed that the inhibition of EGFR-AS1 in HCC cells significantly impeded cell proliferation and invasion in vivo, which might provide a potential possibility for targeted therapy of HCC.

Growth hormone resistance exacerbates cholestasis-induced murine liver fibrosis

Growth hormone (GH) resistance has been associated with liver cirrhosis in humans but its contribution to the disease remains controversial. In order to elucidate whether GH resistance plays a causal role in the establishment and development of liver fibrosis, or rather represents a major consequence thereof, we challenged mice lacking the GH receptor gene (Ghr(-/-), a model for GH resistance) by crossing them with Mdr2 knockout mice (Mdr2(-/-)), a mouse model of inflammatory cholestasis and liver fibrosis. Ghr(-/-);Mdr2(-/-) mice showed elevated serum markers associated with liver damage and cholestasis, extensive bile duct proliferation, and increased collagen deposition relative to Mdr2(-/-) mice, thus suggesting a more severe liver fibrosis phenotype. Additionally, Ghr(-/-);Mdr2(-/-) mice had a pronounced down-regulation of hepatoprotective genes Hnf6, Egfr, and Igf-1, and significantly increased levels of reactive oxygen species (ROS) and apoptosis in hepatocytes, compared to control mice. Moreover, single knockout mice (Ghr(-/-)) fed with a diet containing 1% cholic acid displayed an increase in hepatocyte ROS production, hepatocyte apoptosis, and bile infarcts compared to their wild-type littermates, indicating that loss of Ghr renders hepatocytes more susceptible to toxic bile acid accumulation. Surprisingly, and despite their severe fibrotic phenotype, Ghr(-/-);Mdr2(-/-) mice displayed a significant decrease in tumor incidence compared to Mdr2(-/-) mice, indicating that loss of Ghr signaling may slow the progression from fibrosis/cirrhosis to cancer in the liver.

CONCLUSION

GH resistance dramatically exacerbates liver fibrosis in a mouse model of inflammatory cholestasis, therefore suggesting that GH resistance plays a causal role in the disease and provides a novel target for the development of liver fibrosis treatments.

GH administration rescues fatty liver regeneration impairment by restoring GH/EGFR pathway deficiency

GH pathway has been shown to play a major role in liver regeneration through the control of epidermal growth factor receptor (EGFR) activation. This pathway is down-regulated in nonalcoholic fatty liver disease. Because regeneration is known to be impaired in fatty livers, we wondered whether a deregulation of the GH/EGFR pathway could explain this deficiency. Hepatic EGFR expression and triglyceride levels were quantified in liver biopsies of 32 obese patients with different degrees of steatosis. We showed a significant inverse correlation between liver EGFR expression and the level of hepatic steatosis. GH/EGFR down-regulation was also demonstrated in 2 steatosis mouse models, a genetic (ob/ob) and a methionine and choline-deficient diet mouse model, in correlation with liver regeneration defect. ob/ob mice exhibited a more severe liver regeneration defect after partial hepatectomy (PH) than methionine and choline-deficient diet-fed mice, a difference that could be explained by a decrease in signal transducer and activator of transcription 3 phosphorylation 32 hours after PH. Having checked that GH deficiency accounted for the GH signaling pathway down-regulation in the liver of ob/ob mice, we showed that GH administration in these mice led to a partial rescue in hepatocyte proliferation after PH associated with a concomitant restoration of liver EGFR expression and signal transducer and activator of trnascription 3 activation. In conclusion, we propose that the GH/EGFR pathway down-regulation is a general mechanism responsible for liver regeneration deficiency associated with steatosis, which could be partially rescued by GH administration.

GH administration patterns differently regulate epidermal growth factor signaling

Current GH administration protocols imply frequent s.c. injections, resulting in suboptimal compliance. Therefore, there is interest in developing delivery systems for sustained release of the hormone. However, GH has different actions depending on its continuous or pulsatile plasma concentration pattern. GH levels and circulating concentration patterns could be involved in the regulation of epidermal growth factor receptor (EGFR) expression in liver. Aberrant expression of this receptor and/or its hyperactivation has been associated with the pathogenesis of different types of carcinoma. Considering that one of the adverse effects associated with GH overexpression and chronic use of GH is the increased incidence of malignancies, the aim of this study was to analyze the effects of GH plasma concentration patterns on EGFR expression and signaling in livers of mice. For this purpose, GH was administered by s.c. daily injections to produce an intermittent plasma pattern or by osmotic pumps to provoke a continuously elevated GH concentration. Intermittent injections of GH induced upregulation of liver EGFR content, augmented the response to EGF, and the induction of proteins involved in promotion of cell proliferation in female mice. In contrast, continuous GH delivery in male mice was associated with diminished EGFR in liver and decreased EGF-induced signaling and expression of early genes. The results indicate that sustained delivery systems that allow continuous GH plasma patterns would be beneficial in terms of treatment safety with regard to the actions of GH on EGFR signaling and its promitogenic activity.

Mitogenic effects of phosphatidylcholine nanoparticles on MCF-7 breast cancer cells

Lecithins, mainly composed of the phospholipids phosphatidylcholines (PC), have many different uses in the pharmaceutical and clinical field. PC are involved in structural and biological functions as membrane trafficking processes and cellular signaling. Considering the increasing applications of lecithin-based nanosystems for the delivery of therapeutic agents, the aim of the present work was to determine the effects of phosphatidylcholine nanoparticles over breast cancer cellular proliferation and signaling. PC dispersions at 0.01 and 0.1% (w/v) prepared in buffer pH 7.0 and 5.0 were studied in the MCF-7 breast cancer cell line. Neutral 0.1% PC-derived nanoparticles induced the activation of the MEK-ERK1/2 pathway, increased cell viability and induced a 1.2 fold raise in proliferation. These biological effects correlated with the increase of epidermal growth factor receptor (EGFR) content and its altered cellular localization. Results suggest that nanoparticles derived from PC dispersion prepared in buffer pH 7.0 may induce physicochemical changes in the plasma membrane of cancer cells which may affect EGFR cellular localization and/or activity, increasing activation of the MEK-ERK1/2 pathway and inducing proliferation. Results from the present study suggest that possible biological effects of delivery systems based on lecithin nanoparticles should be taken into account in pharmaceutical formulation design.

Growth hormone modulation of EGF-induced PI3K-Akt pathway in mice liver

The epidermal growth factor (EGF) activates the phosphatidylinositol 3-kinase (PI3K)-Akt cascade among other signaling pathways. This route is involved in cell proliferation and survival, therefore, its dysregulation can promote cancer. Considering the relevance of the PI3K-Akt signaling in cell survival and in the pathogenesis of cancer, and that GH was reported to modulate EGFR expression and signaling, the objective of this study was to analyze the effects of increased GH levels on EGF-induced PI3K-Akt signaling. EGF-induced signaling was evaluated in the liver of GH-overexpressing transgenic mice and in their normal siblings. While Akt expression was increased in GH-overexpressing mice, EGF-induced phosphorylation of Akt, relative to its protein content, was diminished at Ser473 and inhibited at Thr308; consequently, mTOR, which is a substrate of Akt, was not activated by EGF. However, the activation of PDK1, a kinase involved in Akt phosphorylation at Thr308, was not reduced in transgenic mice. Kinetics studies of EGF-induced Akt phosphorylation showed that it is rapidly and transiently induced in GH-overexpressing mice compared with normal siblings. Thus, the expression and activity of phosphatases involved in the termination of the PI3K-Akt signaling were studied. In transgenic mice, neither PTEN nor PP2A were hyperactivated; however, EGF induced the rapid and transient association of SHP-2 to Gab1, which mediates association to EGFR and activation of PI3K. Rapid recruitment of SHP2, which would accelerate the termination of the proliferative signal induced, could be therefore contributing to the diminished EGF-induced activity of Akt in GH-overexpressing mice.

GH receptor plays a major role in liver regeneration through the control of EGFR and ERK1/2 activation

GH is a pleiotropic hormone that plays a major role in proliferation, differentiation, and metabolism via its specific receptor. It has been previously suggested that GH signaling pathways are required for normal liver regeneration but the molecular mechanisms involved have yet to be determined. The aim of this study was to identify the mechanisms by which GH controls liver regeneration. We performed two thirds partial hepatectomies in GH receptor (GHR)-deficient mice and wild-type littermates and showed a blunted progression in the G(1)/S transition phase of the mutant hepatocytes. This impaired liver regeneration was not corrected by reestablishing IGF-1 expression. Although the initial response to partial hepatectomy at the priming phase appeared to be similar between mutant and wild-type mice, cell cycle progression was significantly blunted in mutant mice. The main defect in GHR-deficient mice was the deficiency of the epidermal growth factor receptor activation during the process of liver regeneration. Finally, among the pathways activated downstream of GHR during G(1) phase progression, namely Erk1/2, Akt, and signal transducer and activator of transcription 3, we only found a reduced Erk1/2 phosphorylation in mutant mice. In conclusion, our results demonstrate that GH signaling plays a major role in liver regeneration and strongly suggest that it acts through the activation of both epidermal growth factor receptor and Erk1/2 pathways.

Epidermal Growth Factor Receptor (EGFR) Crosstalks in Liver Cancer

Hepatocarcinogenesis is a complex multistep process in which many different molecular pathways have been implicated. Hepatocellular carcinoma (HCC) is refractory to conventional chemotherapeutic agents, and the new targeted therapies are meeting with limited success. Interreceptor crosstalk and the positive feedback between different signaling systems are emerging as mechanisms of targeted therapy resistance. The identification of such interactions is therefore of particular relevance to improve therapeutic efficacy. Among the different signaling pathways activated in hepatocarcinogenesis the epidermal growth factor receptor (EGFR) system plays a prominent role, being recognized as a “signaling hub” where different extracellular growth and survival signals converge. EGFR can be transactivated in response to multiple heterologous ligands through the physical interaction with multiple receptors, the activity of intracellular kinases or the shedding of EGFR-ligands. In this article we review the crosstalk between the EGFR and other signaling pathways that could be relevant to liver cancer development and treatment.