Epidermal Growth Factor Receptor Transactivation: Mechanisms, Pathophysiology, and Potential Therapies in the Cardiovascular System

Cardiac GPCR-Mediated EGFR Transactivation: Impact and Therapeutic Implications

G protein-coupled receptors (GPCRs) remain primary therapeutic targets for numerous cardiovascular disorders, including heart failure (HF), because of their influence on cardiac remodeling in response to elevated neurohormone signaling. GPCR blockers have proven to be beneficial in the treatment of HF by reducing chronic G protein activation and cardiac remodeling, thereby extending the lifespan of patients with HF. Unfortunately, this effect does not persist indefinitely, thus next-generation therapeutics aim to selectively block harmful GPCR-mediated pathways while simultaneously promoting beneficial signaling. Transactivation of epidermal growth factor receptor (EGFR) has been shown to be mediated by an expanding repertoire of GPCRs in the heart, and promotes cardiomyocyte survival, thus may offer a new avenue of HF therapeutics. However, GPCR-dependent EGFR transactivation has also been shown to regulate cardiac hypertrophy and fibrosis by different GPCRs and through distinct molecular mechanisms. Here, we discuss the mechanisms and impact of GPCR-mediated EGFR transactivation in the heart, focusing on angiotensin II, urotensin II, and β-adrenergic receptor systems, and highlight areas of research that will help us to determine whether this pathway can be engaged as future therapeutic strategy.

Novel mechanisms of G-protein-coupled receptors functions: AT1 angiotensin receptor acts as a signaling hub and focal point of receptor cross-talk

AT₁ angiotensin receptor (AT₁R), a prototypical G protein-coupled receptor (GPCR), is the main receptor, which mediates the effects of the renin-angiotensin system (RAS). AT₁R plays a crucial role in the regulation of blood pressure and salt-water homeostasis, and in the development of pathological conditions, such as hypertension, heart failure, cardiovascular remodeling, renal fibrosis, inflammation, and metabolic disorders. Stimulation of AT₁R leads to pleiotropic signal transduction pathways generating arrays of complex cellular responses. Growing amount of evidence shows that AT₁R is a versatile GPCR, which has multiple unique faces with distinct conformations and signaling properties providing new opportunities for functionally selective pharmacological targeting of the receptor. Biased ligands of AT₁R have been developed to selectively activate the β-arrestin pathway, which may have therapeutic benefits compared to the conventional angiotensin converting enzyme inhibitors and angiotensin receptor blockers. In this review, we provide a summary about the most recent findings and novel aspects of the AT₁R function, signaling, regulation, dimerization or oligomerization and its cross-talk with other receptors, including epidermal growth factor (EGF) receptor, adrenergic receptors and CB₁ cannabinoid receptor. Better understanding of the mechanisms and structural aspects of AT₁R activation and cross-talk can lead to the development of novel type of drugs for the treatment of cardiovascular and other diseases.

EGFR inhibition attenuates diabetic nephropathy through decreasing ROS and endoplasmic reticulum stress

Diabetic nephropathy (DN) is a progressive kidney disease due to glomerular capillary damage in diabetic patients. Endoplasmic reticulum (ER) stress caused by reactive oxygen species (ROS) is associated with DN progression. Epidermal growth factor receptor (EGFR) mediates oxidative stress and damage of cardiomyocytes in diabetic mice. Here we demonstrated that AG1478, a specific inhibitor of EGFR, blocked EGFR and AKT phosphorylation in diabetic mice. Oxidative stress and ER stress markers were eliminated after AG1478 administration. AG1478 decreased pro-fibrotic genes TGF-β and collagen IV. Furthermore, we found that high glucose (HG) induced oxidative stress and ER stress, and subsequently increased ATF4 and CHOP. These changes were eliminated by either AG1478 or ROS scavenger N-acetyl-L-cysteine (NAC) administration. These results were confirmed by knock-down approaches in renal mesangial SV40 cells. However, AG1478, not NAC, reversed HG induced EGFR and AKT phosphorylation. These results suggest that EGFR/AKT/ROS/ER stress signaling plays an essential role in DN development and inhibiting EGFR may serve as a potential therapeutic strategy in diabetic kidney diseases.

Deletion of the EGF receptor in vascular smooth muscle cells prevents chronic angiotensin II-induced arterial wall stiffening and media thickening

AIM

In vivo vascular smooth muscle cell (VSMC) EGF receptor (EGFR) contributes to acute angiotensin II (AII) effects on vascular tone and blood pressure. The ubiquitously expressed EGFR has been implicated in vascular remodelling preceding end-organ damage by pharmacological inhibition, and AII signalling in cultured vascular cells is partly EGFR-dependent. However, the role of VSMC-EGFR in vivo during AII-induced pathophysiological processes is not known.

METHODS

This study assesses the in vivo relevance of VSMC-EGFR during chronic AII challenge without further stressors, using a mouse model with inducible, VSMC-specific EGFR knock out (VSMC-EGFR-KO). In these mice functional and structural vascular, renal and cardiac effects or biomarkers were investigated in vivo and ex vivo.

RESULTS

Vascular smooth muscle cell-EGFR-KO prevented AII-induced media hypertrophy of mesenteric arteries, renal arterioles and the aorta, VSMC ERK1/2-phosphorylation as well as the impairment of vascular compliance. Furthermore, induction of vascular fibrosis, creatinineamia, renal interstitial fibrosis as well as the increase in fractional water excretion was prevented. AII-induced increase in systolic blood pressure was mitigated. By contrast, endothelial dysfunction, induction of vascular inflammatory marker mRNA and albuminuria were not inhibited. Cardiac and cardiomyocyte hypertrophy were also not prevented by VSMC-EGFR-KO.

CONCLUSION

Vascular smooth muscle cell-EGFRs are relevant for pathological AII action in vivo. Our data show in vivo and ex vivo the necessity of VSMC-EGFR for AII-induced structural and functional vascular remodelling, not including endothelial dysfunction. Hereby, VSMC-EGFR gains importance for complete AII-induced renal end-organ damage succeeding vascular remodelling.

The role of oxidative stress in the crosstalk between leptin and mineralocorticoid receptor in the cardiac fibrosis associated with obesity

We have investigated whether mineralocorticoid receptor activation can participate in the profibrotic effects of leptin in cardiac myofibroblasts, as well as the potential mechanisms involved. The presence of eplerenone reduced the leptin-induced increase in protein levels of collagen I, transforming growth factor β, connective tissue growth factor and galectin-3 and the levels of both total and mitochondrial of superoxide anion (O₂^.−) in cardiac myofibroblasts. Likewise, the MEK/ERK inhibitor, PD98059, and the PI3/Akt inhibitor, LY294002, showed a similar pattern. Mitochondrial reactive oxygen species (ROS) scavenger (MitoTempo) attenuated the increase in body weight observed in rats fed a high fat diet (HFD). No differences were found in cardiac function or blood pressure among any group. However, the cardiac fibrosis and enhanced O₂^.-levels observed in HFD rats were attenuated by MitoTempo, which also prevented the increased circulating leptin and aldosterone levels in HFD fed animals. This study supports a role of mineralocorticoid receptor in the cardiac fibrosis induced by leptin in the context of obesity and highlights the role of the mitochondrial ROS in this process.

Vascular ADAM17 (a Disintegrin and Metalloproteinase Domain 17) Is Required for Angiotensin II/β-Aminopropionitrile-Induced Abdominal Aortic Aneurysm

Angiotensin II (AngII)-activated epidermal growth factor receptor has been implicated in abdominal aortic aneurysm (AAA) development. In vascular smooth muscle cells (VSMCs), AngII activates epidermal growth factor receptor via a metalloproteinase, ADAM17 (a disintegrin and metalloproteinase domain 17). We hypothesized that AngII-dependent AAA development would be prevented in mice lacking ADAM17 in VSMCs. To test this concept, control and VSMC ADAM17-deficient mice were cotreated with AngII and a lysyl oxidase inhibitor, β-aminopropionitrile, to induce AAA. We found that 52.4% of control mice did not survive because of aortic rupture. All other surviving control mice developed AAA and demonstrated enhanced expression of ADAM17 in the AAA lesions. In contrast, all AngII and β-aminopropionitrile-treated VSMC ADAM17-deficient mice survived and showed reduction in external/internal diameters (51%/28%, respectively). VSMC ADAM17 deficiency was associated with lack of epidermal growth factor receptor activation, interleukin-6 induction, endoplasmic reticulum/oxidative stress, and matrix deposition in the abdominal aorta of treated mice. However, both VSMC ADAM17-deficient and control mice treated with AngII and β-aminopropionitrile developed comparable levels of hypertension. Treatment of C57Bl/6 mice with an ADAM17 inhibitory antibody but not with control IgG also prevented AAA development. In conclusion, VSMC ADAM17 silencing or systemic ADAM17 inhibition seems to protect mice from AAA formation. The mechanism seems to involve suppression of epidermal growth factor receptor activation.

Epidermal growth factor receptor transactivation is involved in the induction of human hepatoma SMMC7721 cell proliferation by insufficient radiofrequency ablation

Our previous study revealed that insufficient radiofrequency ablation (RFA) promotes the malignancy of human hepatocellular carcinoma (HCC) SMMC7721 cells via the Ca²⁺/calmodulin-dependent protein kinase II (CaMKII)/extracellular signal-regulated kinase (ERK)-induced overexpression of vascular endothelial growth factor (VEGF). The aims of the present study were to address the involvement of epidermal growth factor receptor (EGFR) transactivation in the enhanced SMMC7721 cell proliferation induced by insufficient RFA, in addition to its association with the CaMKII/ERK/VEGF signaling cascade. SMMC7721 cells were subjected to a 47°C treatment regimen to simulate insufficient RFA. Cell proliferation was determined using MTT and colony formation assays. The expression levels of VEGF, CaMKII, phosphorylated (phospho)-CaMKII, ERK, phospho-ERK, EGFR and phospho-EGFR were analyzed using western blotting. The results demonstrated that the enhancement of SMMC7721 cell proliferation by the 47°C treatment regimen was significantly inhibited by exposure of the cells to AG178 (a specific inhibitor of EGFR). Furthermore, AG1478 exposure prevented the overexpression of VEGF and phosphorylation of ERK, but had no significant effects on CaMKII phosphorylation. By contrast, 47°C treatment-induced EGFR phosphorylation was inhibited by treatment with KN93 (a specific inhibitor of CaMKII). Overall, the results of the present study have suggested a role for EGFR transactivation in the RFA-promoted growth of residual HCC. Thus, targeting EGFR may represent a useful preventive and therapeutic strategy for RFA-induced HCC progression and recurrence.

AT1 receptor signaling pathways in the cardiovascular system

The importance of the renin angiotensin aldosterone system in cardiovascular physiology and pathophysiology has been well described whereas the detailed molecular mechanisms remain elusive. The angiotensin II type 1 receptor (AT1 receptor) is one of the key players in the renin angiotensin aldosterone system. The AT1 receptor promotes various intracellular signaling pathways resulting in hypertension, endothelial dysfunction, vascular remodeling and end organ damage. Accumulating evidence shows the complex picture of AT1 receptor-mediated signaling; AT1 receptor-mediated heterotrimeric G protein-dependent signaling, transactivation of growth factor receptors, NADPH oxidase and ROS signaling, G protein-independent signaling, including the β-arrestin signals and interaction with several AT1 receptor interacting proteins. In addition, there is functional cross-talk between the AT1 receptor signaling pathway and other signaling pathways. In this review, we will summarize an up to date overview of essential AT1 receptor signaling events and their functional significances in the cardiovascular system.

Proximal Tubulopathy: Prime Mover and Key Therapeutic Target in Diabetic Kidney Disease

The current view of diabetic kidney disease, based on meticulously acquired ultrastructural morphometry and the utility of measuring plasma creatinine and urinary albumin, has been almost entirely focused on the glomerulus. While clearly of great importance, changes in the glomerulus are not the major determinant of renal prognosis in diabetes and may not be the primary event in the development of diabetic kidney disease either. Indeed, advances in biomarker discovery and a greater appreciation of tubulointerstitial histopathology and the role of tubular hypoxia in the pathogenesis of chronic kidney disease have given us pause to reconsider the current "glomerulocentric" paradigm and focus attention on the proximal tubule that by virtue of the high energy requirements and reliance on aerobic metabolism render it particularly susceptible to the derangements of the diabetic state. Such findings raise important issues for therapeutic advances specifically targeting the pathophysiological perturbations that develop in this part of the nephron.

Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke

The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.

Developmental programming: Interaction between prenatal BPA and postnatal overfeeding on cardiac tissue gene expression in female sheep

Epidemiologic studies and studies in rodents point to potential risks from developmental exposure to BPA on cardiometabolic diseases. Furthermore, it is becoming increasingly evident that the manifestation and severity of adverse outcomes is the result of interaction between developmental insults and the prevailing environment. Consistent with this premise, recent studies in sheep found prenatal BPA treatment prevented the adverse effects of postnatal obesity in inducing hypertension. The gene networks underlying these complex interactions are not known. mRNA-seq of myocardium was performed on four groups of four female sheep to assess the effects of prenatal BPA exposure, postnatal overfeeding and their interaction on gene transcription, pathway perturbations and functional effects. The effects of prenatal exposure to BPA, postnatal overfeeding, and prenatal BPA with postnatal overfeeding all resulted in transcriptional changes (85-141 significant differentially expressed genes). Although the effects of prenatal BPA and postnatal overfeeding did not involve dysregulation of many of the same genes, they affected a remarkably similar set of biological pathways. Furthermore, an additive or synergistic effect was not found in the combined treatment group, but rather prenatal BPA treatment led to a partial reversal of the effects of overfeeding alone. Many genes previously known to be affected by BPA and involved in obesity, hypertension, or heart disease were altered following these treatments, and AP-1, EGR1, and EGFR were key hubs affected by BPA and/or overfeeding. Environ. Mol. Mutagen. 58:4-18, 2017. © 2016 Wiley Periodicals, Inc.

Developmental programming: Interaction between prenatal BPA and postnatal overfeeding on cardiac tissue gene expression in female sheep

Epidemiologic studies and studies in rodents point to potential risks from developmental exposure to BPA on cardiometabolic diseases. Furthermore, it is becoming increasingly evident that the manifestation and severity of adverse outcomes is the result of interaction between developmental insults and the prevailing environment. Consistent with this premise, recent studies in sheep found prenatal BPA treatment prevented the adverse effects of postnatal obesity in inducing hypertension. The gene networks underlying these complex interactions are not known. mRNA-seq of myocardium was performed on four groups of four female sheep to assess the effects of prenatal BPA exposure, postnatal overfeeding and their interaction on gene transcription, pathway perturbations and functional effects. The effects of prenatal exposure to BPA, postnatal overfeeding, and prenatal BPA with postnatal overfeeding all resulted in transcriptional changes (85-141 significant differentially expressed genes). Although the effects of prenatal BPA and postnatal overfeeding did not involve dysregulation of many of the same genes, they affected a remarkably similar set of biological pathways. Furthermore, an additive or synergistic effect was not found in the combined treatment group, but rather prenatal BPA treatment led to a partial reversal of the effects of overfeeding alone. Many genes previously known to be affected by BPA and involved in obesity, hypertension, or heart disease were altered following these treatments, and AP-1, EGR1, and EGFR were key hubs affected by BPA and/or overfeeding. Environ. Mol. Mutagen. 58:4-18, 2017. © 2016 Wiley Periodicals, Inc.

Mineralocorticoid regulation of cell function: the role of rapid signalling and gene transcription pathways

The mineralocorticoid receptor (MR) and mineralocorticoids regulate epithelial handling of electrolytes, and induces diverse effects on other tissues. Traditionally, the effects of MR were ascribed to ligand-receptor binding and activation of gene transcription. However, the MR also utilises a number of intracellular signalling cascades, often by transactivating unrelated receptors, to change cell function more rapidly. Although aldosterone is the physiological mineralocorticoid, it is not the sole ligand for MR. Tissue-selective and mineralocorticoid-specific effects are conferred through the enzyme 11β-hydroxysteroid dehydrogenase 2, cellular redox status and properties of the MR itself. Furthermore, not all aldosterone effects are mediated via MR, with implication of the involvement of other membrane-bound receptors such as GPER. This review will describe the ligands, receptors and intracellular mechanisms available for mineralocorticoid hormone and receptor signalling and illustrate their complex interactions in physiology and disease.

Rapid Renal Regulation of Peroxisome Proliferator-activated Receptor γ Coactivator-1α by Extracellular Signal-Regulated Kinase 1/2 in Physiological and Pathological Conditions

Previous studies have shown that extracellular signal-regulated kinase 1/2 (ERK1/2) directly inhibits mitochondrial function during cellular injury. We evaluated the role of ERK1/2 on the expression of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) gene, a master regulator of mitochondrial function. The potent and specific MEK1/2 inhibitor trametinib rapidly blocked ERK1/2 phosphorylation, decreased cytosolic and nuclear FOXO3a/1 phosphorylation, and increased PGC-1α gene expression and its downstream mitochondrial biogenesis (MB) targets under physiological conditions in the kidney cortex and in primary renal cell cultures. The epidermal growth factor receptor (EGFR) inhibitor erlotinib blocked ERK1/2 phosphorylation and increased PGC-1α gene expression similar to treatment with trametinib, linking EGFR activation and FOXO3a/1 inactivation to the down-regulation of PGC-1α and MB through ERK1/2. Pretreatment with trametinib blocked early ERK1/2 phosphorylation following ischemia/reperfusion kidney injury and attenuated the down-regulation of PGC-1α and downstream target genes. These results demonstrate that ERK1/2 rapidly regulates mitochondrial function through a novel pathway, EGFR/ERK1/2/FOXO3a/1/PGC-1α, under physiological and pathological conditions. As such, ERK1/2 down-regulates mitochondrial function directly by phosphorylation of upstream regulators of PGC-1α and subsequently decreasing MB.

Caveolin-1 Deletion Prevents Hypertensive Vascular Remodeling Induced by Angiotensin II

It has been proposed that membrane microdomains, caveolae, in vascular cells are critical for signal transduction and downstream functions induced by angiotensin II (AngII). We have tested our hypothesis that caveolin-1 (Cav1), a major structural protein of vascular caveolae, plays a critical role in the development of vascular remodeling by AngII via regulation of epidermal growth factor receptor and vascular endothelial adhesion molecule-1. Cav1^-/- and control Cav^+/+ mice were infused with AngII for 2 weeks to induce vascular remodeling and hypertension. On AngII infusion, histological assessments demonstrated medial hypertrophy and perivascular fibrosis of aorta and coronary and renal arteries in Cav1^+/+ mice compared with sham-operated Cav1^+/+ mice. AngII-infused Cav1^+/+ mice also showed a phenotype of cardiac hypertrophy with increased heart weight to body weight ratio compared with control Cav1^+/+ mice. In contrast, Cav1^-/- mice infused with AngII showed attenuation of vascular remodeling but not cardiac hypertrophy. Similar levels of AngII-induced hypertension were found in both Cav1^+/+ and Cav1^-/- mice as assessed by telemetry. In Cav1^+/+ mice, AngII enhanced tyrosine-phosphorylated epidermal growth factor receptor staining in the aorta, which was attenuated in Cav1^-/- mice infused with AngII. Enhanced Cav1 and vascular endothelial adhesion molecule-1 expression was also observed in aorta from AngII-infused Cav1^+/+ mice but not in Cav1^-/- aorta. Experiments with vascular cells further provided a potential mechanism for our in vivo findings. These data suggest that Cav1, and presumably caveolae, in vascular smooth muscle and the endothelium plays a critical role in vascular remodeling and inflammation independent of blood pressure or cardiac hypertrophy regulation.

Vasopressin V1A receptor mediates cell proliferation through GRK2-EGFR-ERK1/2 pathway in A7r5 cells

Abnormal proliferation and hypertrophy of vascular smooth muscle (VSMC), as the main structural component of the vasculature, is an important pathological mechanism of hypertension. Recently, increased levels of arginine vasopressin (AVP) and copeptin, the C-terminal fragment of provasopressin, have been shown to correlate with the development of preeclampsia. AVP targets on the G_q-coupled vasopressin V_1A receptor and the G_s-coupled V₂ receptor in VSMC and the kidneys to regulate vascular tone and water homeostasis. However, the role of the vasopressin receptor on VSM cell proliferation during vascular remodeling is unclear. Here, we studied the effects of AVP on the proliferation of the rat VSMC-derived A7r5 cells. AVP, in a time- and concentration-dependent manner, promoted A7r5 cell proliferation as indicated by the induction of proliferating cell nuclear antigen expression, methylthiazolyldiphenyl-tetrazolium reduction and incorporation of 5'-bromodeoxyuridine into cellular DNA. These effects, coupled with the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK_1/2), were blocked by a V_1A receptor antagonist SR45059 but not by a V₂ receptor antagonist lixivaptan. Although acute activation of V_1A receptor induced ERK_1/2 phosphorylation via a protein kinase C-dependent pathway, this effect was not involved in cell proliferation. Cell proliferation and ERK_1/2 phosphorylation in response to prolonged stimulation with AVP were abolished by inhibition of G protein-coupled receptor kinase 2 (GRK2) and epidermal growth factor receptor (EGFR) using specific inhibitors or small hairpin RNA knock-down. These results suggest that activation of V_1A, but not V₂ receptor, produces a cell proliferative signal in A7r5 cells via a GRK2/EGFR/ERK_1/2-dependent mechanism.

Epidermal Growth Factor Receptor Silencing Blunts the Slow Force Response to Myocardial Stretch

Background

Myocardial stretch increases force biphasically: the Frank‐Starling mechanism followed by the slow force response (SFR). Based on pharmacological strategies, we proposed that epidermal growth factor (EGF) receptor (EGFR or ErbB1) activation is crucial for SFR development. Pharmacological inhibitors could block ErbB4, a member of the ErbB family present in the adult heart. We aimed to specifically test the role of EGFR activation after stretch, with an interference RNA incorporated into a lentiviral vector (small hairpin RNA [shRNA]‐EGFR).

Methods and Results

Silencing capability of p‐shEGFR was assessed in EGFR‐GFP transiently transfected HEK293T cells. Four weeks after lentivirus injection into the left ventricular wall of Wistar rats, shRNA‐EGFR–injected hearts showed ≈60% reduction of EGFR protein expression compared with shRNA‐SCR–injected hearts. ErbB2 and ErbB4 expression did not change. The SFR to stretch evaluated in isolated papillary muscles was ≈130% of initial rapid phase in the shRNA‐SCR group, while it was blunted in shRNA‐EGFR–expressing muscles. Angiotensin II (Ang II)‐dependent Na+/H+ exchanger 1 activation was indirectly evaluated by intracellular pH measurements in bicarbonate‐free medium, demonstrating an increase in shRNA‐SCR–injected myocardium, an effect not observed in the silenced group. Ang II‐ or EGF‐triggered reactive oxygen species production was significantly reduced in shRNA‐EGFR–injected hearts compared with that in the shRNA‐SCR group. Chronic lentivirus treatment affected neither the myocardial basal redox state (thiobarbituric acid reactive substances) nor NADPH oxidase activity or expression. Finally, Ang II or EGF triggered a redox‐sensitive pathway, leading to p90RSK activation in shRNA‐SCR‐injected myocardium, an effect that was absent in the shRNA‐EGFR group.

Conclusions

Our results provide evidence that specific EGFR activation after myocardial stretch is a key factor in promoting the redox‐sensitive kinase activation pathway, leading to SFR development.

Vascular ADAM17 as a Novel Therapeutic Target in Mediating Cardiovascular Hypertrophy and Perivascular Fibrosis Induced by Angiotensin II

Angiotensin II (AngII) has been strongly implicated in hypertension and its complications. Evidence suggests the mechanisms by which AngII elevates blood pressure and enhances cardiovascular remodeling and damage may be distinct. However, the signal transduction cascade by which AngII specifically initiates cardiovascular remodeling, such as hypertrophy and fibrosis, remains insufficiently understood. In vascular smooth muscle cells, a metalloproteinase ADAM17 mediates epidermal growth factor receptor transactivation, which may be responsible for cardiovascular remodeling but not hypertension induced by AngII. Thus, the objective of this study was to test the hypothesis that activation of vascular ADAM17 is indispensable for vascular remodeling but not for hypertension induced by AngII. Vascular ADAM17-deficient mice and control mice were infused with AngII for 2 weeks. Control mice infused with AngII showed cardiac hypertrophy, vascular medial hypertrophy, and perivascular fibrosis. These phenotypes were prevented in vascular ADAM17-deficient mice independent of blood pressure alteration. AngII infusion enhanced ADAM17 expression, epidermal growth factor receptor activation, and endoplasmic reticulum stress in the vasculature, which were diminished in ADAM17-deficient mice. Treatment with a human cross-reactive ADAM17 inhibitory antibody also prevented cardiovascular remodeling and endoplasmic reticulum stress but not hypertension in C57Bl/6 mice infused with AngII. In vitro data further supported these findings. In conclusion, vascular ADAM17 mediates AngII-induced cardiovascular remodeling via epidermal growth factor receptor activation independent of blood pressure regulation. ADAM17 seems to be a unique therapeutic target for the prevention of hypertensive complications.

Epidermal growth factor receptor signaling mediates aldosterone-induced profibrotic responses in kidney

Aldosterone has been recognized as a risk factor for the development of chronic kidney disease (CKD). Studies have indicated that enhanced activation of epidermal growth factor receptor (EGFR) is associated with the development and progression of renal fibrosis. But if EGFR is involved in aldosterone-induced renal fibrosis is less investigated. In the present study, we examined the effect of erlotinib, an inhibitor of EGFR tyrosine kinase activity, on the progression of aldosterone-induced renal profibrotic responses in a murine model underwent uninephrectomy. Erlotinib-treated rats exhibited relieved structural lesion comparing with rats treated with aldosterone alone, as characterized by glomerular hypertrophy, mesangial cell proliferation and expansion. Also, erlotinib inhibited the expression of TGF-β, α-SMA and mesangial matrix proteins such as collagen Ⅳ and fibronectin. In cultured mesangial cells, inhibition of EGFR also abrogated aldosterone-induced expression of extracellular matrix proteins, cell proliferation and migration. We also demonstrated that aldosterone induced the phosphorylation of EGFR through generation of ROS. And the activation of EGFR resulted in the phosphorylation of ERK1/2, leading to the activation of profibrotic pathways. Taken together, we concluded that aldosterone-mediated tissue fibrosis relies on ROS induced EGFR/ERK activation, highlighting EGFR as a potential therapeutic target for modulating renal fibrosis.

Soluble Epidermal Growth Factor Receptors (sEGFRs) in Cancer: Biological Aspects and Clinical Relevance

The identification of molecules that can reliably detect the presence of a tumor or predict its behavior is one of the biggest challenges of research in cancer biology. Biological fluids are intriguing mediums, containing many molecules that express the individual health status and, accordingly, may be useful in establishing the potential risk of cancer, defining differential diagnosis and prognosis, predicting the response to treatment, and monitoring the disease progression. The existence of circulating soluble growth factor receptors (sGFRs) deriving from their membrane counterparts has stimulated the interest of researchers to investigate the use of such molecules as potential cancer biomarkers. But what are the origins of circulating sGFRs? Are they naturally occurring molecules or tumor-derived products? Among these, the epidermal growth factor receptor (EGFR) is a cell-surface molecule significantly involved in cancer development and progression; it can be processed into biological active soluble isoforms (sEGFR). We have carried out an extensive review of the currently available literature on the sEGFRs and their mechanisms of regulation and biological function, with the intent to clarify the role of these molecules in cancer (and other pathological conditions) and, on the basis of the retrieved evidences, speculate about their potential use in the clinical setting.

Impact of PAMAM delivery systems on signal transduction pathways in vivo: Modulation of ERK1/2 and p38 MAP kinase signaling in the normal and diabetic kidney

The in vivo impact of two generation 6 cationic polyamidoamine (PAMAM) dendrimers on cellular signaling via extracellular-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (p38 MAPK), as well as their relationship to epidermal growth factor receptor (EGFR), were studied in the normal and/or diabetic rat kidney. A single 10mg/kg/i.p administration of Polyfect (PF; with an intact branching architecture) or Superfect (SF; with a fragmented branching architecture) modulated renal ERK1/2 and p38 MAPK phosphorylation in a dendrimer-specific and animal model-dependent manner. AG1478 treatment (a selective EGFR inhibitor) confirmed that renal ERK1/2 and p38 MAPK signaling was downstream of EGFR. Surprisingly, both PAMAMs induced hyperphosphorylation of ERK1/2 and p38 MAPK (at 1 or 5mg/kg) despite inhibiting EGFR phosphorylation in the diabetic kidney. PAMAMs did not alter renal morphology but their effects on p38 MAPK and EGFR phosphorylation were reversed by ex vivo treatment of kidneys with the anti-oxidant, Tempol. Thus, PAMAMs can intrinsically modulate signaling of mitogen-activated protein kinases (MAPKs) depending on the type of dendrimer (fragmented vs intact branching architecture) and animal model (normal vs diabetic) used and likely occurs via an EGFR-independent and oxidative-stress dependent mechanism. These findings might have important toxicological implications for PAMAM-based delivery systems.

Transactivation of Epidermal Growth Factor Receptor by G Protein-Coupled Receptors: Recent Progress, Challenges and Future Research

Both G protein-coupled receptors (GPCRs) and receptor-tyrosine kinases (RTKs) regulate large signaling networks, control multiple cell functions and are implicated in many diseases including various cancers. Both of them are also the top therapeutic targets for disease treatment. The discovery of the cross-talk between GPCRs and RTKs connects these two vast signaling networks and complicates the already complicated signaling networks that regulate cell signaling and function. In this review, we focus on the transactivation of epidermal growth factor receptor (EGFR), a subfamily of RTKs, by GPCRs. Since the first report of EGFR transactivation by GPCR, significant progress has been made including the elucidation of the mechanisms underlying the transactivation. Here, we first provide a basic picture for GPCR, EGFR and EGFR transactivation by GPCR. We then discuss the progress made in the last five years and finally provided our view of the future challenge and future researches needed to overcome these challenges.