Role of epidermal growth factor receptor in vascular structure and function.

REVIEW URRENT C OPINION

Role of epidermal growth factor receptor in vascular structure and function Barbara Schreier, Michael Gekle, and Claudia Grossmann

Purpose of the review The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase with a wide implication in tumor biology, wound healing and development. Besides acting as a growth factor receptor activated by ligands such as EGF, the EGFR can also be transactivated and thereby mediate cross-talk with different signaling pathways. The aim of this review is to illustrate the Janus-faced function of the EGFR in the vasculature with its relevance for vascular biology and disease. Recent findings Over recent years, the number of identified signaling partners of the EGFR has steadily increased, as have the biological processes in which the EGFR is thought to be involved. Recently, new models have allowed investigation of EGFR effects in vivo, shedding some light on the overall function of the EGFR in the vasculature. At the same time, EGFR inhibitors and antibodies have become increasingly established in cancer therapy, providing potential therapeutic tools for decreasing EGFR signaling. Summary The EGFR is a versatile signaling pathway integrator associated with vascular homeostasis and disease. In addition to modulating basal vascular tone and tissue homeostasis, the EGFR also seems to be involved in proinflammatory, proliferative, migratory and remodeling processes, with enhanced deposition of extracellular matrix components, thereby promoting vascular diseases such as hypertension or atherosclerosis. Keywords atherosclerosis, diabetes, endothelial cells, hypertension, vascular smooth muscle cells

INTRODUCTION In humans, 58 receptor tyrosine kinases have so far been identified. Of those, the epidermal growth factor receptor (EGFR), also known as ErbB1, is a prominent member [1]. It belongs to the ErbB family and is composed of an N-terminal extracellular ligand-binding region, a single alpha helical transmembrane region, a juxtamembrane domain that is conserved between the family members and a c-terminal cytoplasmic region with tyrosine kinase activity and phosphorylation sites. Activation of EGFR occurs either by binding of ligands such as EGF (epidermal growth factor) and heparin boundEGF, or by transactivation. Upon binding of ligand to a single receptor, conformational changes occur that allow dimerization and allosteric activation of the tyrosine kinase domain in the cytoplasm [2], resulting in phosphorylation of tyrosine residues, enabling docking of different signaling components [3,4]. Transactivation may be mediated by activation of matrix metalloproteases (MMPs)/a

disintegrin and metalloproteases (ADAMS) and cleavage of membrane-bound ligand precursor molecules of the EGFR or by activation of the EGFR through intracellular protein kinases. This flexibility enables the EGFR to mediate the cross-talk between different signaling pathways and to act as an important signal integrator (Fig. 1). The EGFR is widely acknowledged for its influence in tumor biology and wound healing but an additional role in maintaining organ and cellular homeostasis in general is becoming more and more evident especially in the cardiovascular

Julius Bernstein Institute of Physiology, Martin Luther University HalleWittenberg, Halle, Germany Correspondence to Claudia Grossmann, Julius-Bernstein-Institut fu¨r Physiologie, Universita¨t Halle-Wittenberg, Magdeburger Strasse 6, 06097 Halle/Saale, Germany. Tel: 49 345 557 1886; fax: +49 345 557 4019; e-mail: [email protected] Curr Opin Nephrol Hypertens 2014, 23:113–121 DOI:10.1097/01.mnh.0000441152.62943.29

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Pathophysiology of hypertension

VASCULAR SMOOTH MUSCLE CELLS

KEY POINTS The EGFR is an important signaling pathway integrator of G-protein-coupled receptors, steroid receptors and (receptor) tyrosine kinases. It seems to be a Janus-faced receptor for vascular biology because it is involved in homeostatic and also pathological actions. Regarding vascular homeostasis, the EGFR supports basal vascular tone and enhances ROS defense capacity. During the pathogenesis of vascular disease, the EGFR enhances inflammation, proliferation, migration and extracellular matrix deposition, potentially promoting atherosclerotic processes, diabetic vascular complications and hypertension.

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system [1,5 ]. The EGFR is expressed in vascular smooth muscle cells (VSMC), endothelial cells, macrophages and regulatory T lymphocytes, and all of these cells also secrete EGFR ligands.

Dopamine

Aldosterone

Angiotensin II ATP

Thrombin

Opioids

EGFR ligands

15-HETE

Estrogen

Research so far has mainly focused on describing the effects of EGFR in VSMC, and evidence of an involvement in pathophysiology is beginning to emerge. The EGFR seems to mediate the generation of a proinflammatory phenotype, for example by promoting formation of inflammatory mediators, such as prostaglandins and sphingosin-1-phosphate via the protein kinase C (PKC) delta/c-Src/EGFR/ PI3K/Akt/Elk-1 pathway [6]. Vasoactive sphingosin-1-phosphate in turn can transactivate the EGFR to stimulate inflammatory signaling, a response enhanced in spontaneously hypertensive strokeprone rats, providing a novel link between hypertension and vascular inflammation [7]. Transactivation of the EGFR by renin-angiotensin-aldosterone system (RAAS) components leads to oxidative stress and also a proinflammatory phenotype [8]. Interestingly, attenuation of angiotensin II-induced inflammation and growth by the hepatocyte growth factor/c-Met system has been shown to rely on EGFR degradation, thereby preventing atherosclerotic changes [9]. During aging a shift to a

(EGF, TGF-α, amphiregulin, epigen, HB-EGF, betacellulin, epiregulin)

oxLDL

MMPs

Endothelin-1

ADAMs 9, 10, 12, 17

Norepinephrine Urokinase Thrombospondin

β

NOX γ

P P

Gα

P

Src

– Ca2+ – PI3K – Pyk2 – PKC ?

P P P P P P P P P P P EGFR

– Ras – ERK 1/2 – Src – PI3K

– mTOR – Akt – FAK – STAT ?

FIGURE 1. Model of the epidermal growth factor receptor (EGFR) transactivation signaling cascade. Transactivation of the EGFR occurs by binding of transactivating substances to their specific receptors. They can then induce phosphorylation of the EGFR either by intracellular signaling cascades or a triple-membrane-spanning mechanism involving shedding of EGFR-ligands by a disintegrin and metalloproteases/matrix metalloproteases (ADAMS/MMPs). Examples of the resulting different downstream signaling events are depicted in the figure. FAK, focal adhesion kinase; HB-EGF, heparin-binding epidermal growth factor-like growth factor; mTOR, mammalian target of rapamycin; oxLDL, oxidized low-density lipoproteins; PKC, protein kinase C; TGF, transforming growth factor. 114


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proinflammatory phenotype within the vessel wall occurs that resembles the beginning of vessel disease and leads to endothelial dysfunction, vascular stiffening and thickening of intima and media [10]. In parallel, aging increases EGFR expression and enhances the expression of proinflammatory markers such as transforming growth factor-beta (TGF-b) or intercellular adhesion molecule (ICAM) through an EGFR-dependent mechanism [11]. Conversely, reactive oxygen species (ROS)-defense capacity, measured as glucose-6-phosphate dehydrogenase activity, was reduced in VSMC from EGFR knockout mice [5 ]. EGFR-dependent VSMC proliferation and migration with enhanced deposition of extracellular matrix components may contribute to vascular remodeling, as has been suggested for vascular injury or disease [12]. Ligands such as EGF, heparin-binding epidermal growth factor-like growth factor (HB-EGF) [13,14 ,15,16] or other stimuli, such as angiotensin II [17–20], urokinase [16,21], thrombin [22], 15(S)hydroxyeicosatetraenic acid [23], adenosine triphophate [6], ROS [18,19,21,23,24] and oxidized lowdensity lipoproteins (oxLDL) [25,26], induce migration and proliferation of VSMC mediated by EGFR. Thrombin, for example, induces the activation of Gab1 via EGFR, with subsequent RhoA/cdc42/ Rac-1/PAK-1 activation, which causes stress fiber formation [22]. In the case of migration, the turnover of focal adhesions, mediated by focal adhesion kinase (FAK), plays a central role [14 ] and is supported by EGFR. Despite these examples, further investigations are required to elucidate the molecular mechanisms underlying EGFR-induced VSMC migration. There are several indications that EGFR mediates enhanced expression of matrix components when transactivated by members of the RAAS system such as angiotensin II and the mineralocorticoid receptor [27–30]. More recently, the importance of the ErbB-family members for the profibrotic TGF-b response in the vasculature has been recognized, for which a cross-talk with platelet-derived growth factor receptor (PDGFR) is required, and connective tissue growth factor (CTGF) has been suggested as a new EGFR ligand [31,32 ]. Consequently, combined inhibition of EGFR and PDGFR seems a promising approach to target organ fibrosis. Activated EGFR may contribute to fibrotic responses by supporting the induction of profibrotic mediators such as plasminogen activator inhibitor-1 (PAI-1) that also influences VSMC migration, proliferation and apoptosis [33]. In addition to inducing angiogenic effects in tumors and wounds [34–37], the EGFR contributes to the angiogenic effect of vasoactive petides such as angiotensin II, chemokines, and blood coagulation factor XII [38–41]. &&

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ENDOTHELIAL CELLS In endothelial cells, enhanced EGFR activation has been associated with nitric oxide (NO) homeostasis, which is important as an attenuator of endothelial activation and influences inflammation, migration, proliferation and angiogenesis [42]. On the one hand, EGFR has been shown to mediate vasoprotective antiatherosclerotic effects. In bovine aortic, human umbilicalvein,and humanmicrovascularendothelial cells, estradiol nongenomically can induce endothelial nitric oxide synthase (eNOS) via activation of estrogen receptor (ER)-a and b followed by rapid activation of c-Src, MMP and EGFR transactivation [43]. On the other hand, under conditions favoring eNOS uncoupling, activation of eNOS can stimulate O2 – generation that furthers endothelial dysfunction and atherosclerosis. Factors favoring uncoupling include angiotensin II, aldosterone and aging, and may involve EGFR as has been shown for angiotensin II [44–46]. Additionally, stimuli such as 5-HETE and aldosterone can enhance ACE expression via EGFR, which leads to enhanced angiotensin II generation and endothelial dysfunction, thereby imbedding a potential positive feedback loop [47 ,48]. &

IN-VIVO DATA First indications of an in-vivo relevance of the EGFR in vascular homeostasis and pathophysiology came from studies in spontaneously hypertensive rats (SHR) that displayed polygenetic hypertension with vascular remodeling. Their VSMCs showed enhanced EGFR phosphorylation and proliferated more rapidly [49]. This effect was attributed to elevated angiotensin II and endothelin I concentrations acting on angiotensin II-type 1, endothelin-A and endothelin-B receptors to induce ROS production, c-Src phosphorylation, EGFR transactivation and MAPK activation, potentially leading to Gi alpha overexpression [50,51]. The next step in deciphering the relevance of EGFR for vascular biology and disease were experiments in waved-2 mice, a spontaneous mutant with 90% reduced EGFR tyrosine kinase activity in all tissues. No difference in mean basal blood pressure was observed but the vasoconstrictor response to endothelin-1 was weaker in EGFR-deficient mice or after EGFR inhibition, suggesting that EGFR mediates endothelin-induced vasoconstriction. Additionally, endothelin-1 was able to activate the procollagen-2(I)-gene in freshly isolated aortas in an EGFR- and ERK1/2-dependent manner. EGFR therefore seems to support fibrogenesis and contraction of the vascular wall [52]. Recently, more detailed investigations regarding the vascular phenotype of the EGFR were performed in waved-2 mice [53]. No difference in arterial wall



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structure and morphological parameters of the carotid artery was detected compared with controls and the maximal vascular contraction in response to KCl and phenylephrine was also comparable. However, eNOS expression was reduced in the aorta of waved-2 mice and was associated with an increase in oxidative stress. Moreover, aorta relaxation in response to acetylcholine was weaker in waved-2 mice, whereas the response to NO donors was similar, suggesting that EGFR activation may be beneficial under basal conditions. As expected, control animals responded to nephrectomy-aldosterone-salt treatment (NAS) with reduced eNOS expression and increased oxidative stress markers in the aorta, indicating endothelial dysfunction. Additionally, functional vasomotoric effects occurred, such as an impaired vasorelaxation in response to acetylcholine and a potentiation of the vasoconstrictive response to phenylephrine and angiotensin II. In waved-2 mice, no further changes in oxidative stress markers or eNOS expression were detected and the functional changes induced by NAS were blunted or unchanged compared to wildtype mice. These data suggest that EGFR is involved in NAS-induced functional changes in the vasculature without affecting remodeling. Nevertheless, EGFR deficiency resulted in increased collagen 1 and 3 mRNA in NAS-treated mice. As a more straightforward approach of testing the overall significance of the EGFR signaling pathway for vascular biology and disease, tissuespecific knockout mice were generated [5 ,54] as global EGFR knockout mice die during in-utero development or shortly after birth [55]. In an EGFR-SM22 VSMC knockout model, which allows differentiation between effects mediated by VSMC and endothelial cell EGFR, systolic blood pressure was not different between genotypes; however, total peripheral vascular resistance, diastolic blood pressure and mean blood pressure were reduced. Loss of VSMC-EGFR resulted in a dilated phenotype of small vessels with minor signs of fibrosis and inflammation, suggesting that in the vasculature EGFR contributes to the appropriate vascular wall architecture and vessel reactivity, thereby supporting a role in physiological vascular tone. No differences in NOX2 or NOX4 expression were detected, suggesting that changes in oxidative stress measured by Griol-Charhbili originate from the endothelium and not the VSMCs [5 ]. To summarize, the importance of EGFR for vascular tone and vascular remodeling can be deduced from the above studies. &&

inflammatory response and there are indications that EGFR transactivation contributes to this pathophysiology. The presence of HB-EGF and EGFR in atherosclerotic plaques from different species has been confirmed [15,22,56 ,57 ,58] and seem to be involved on multiple levels in plaque formation. In macrophages, the proinflammatory metalloprotease meprin-a induces the activation of EGFR [56 ]. In Ox-PAPC-stimulated human aortic endothelial cells, the expression of IL-8, inducing migration of macrophages into the vessel wall, is reduced if these cells are treated with siRNA against HB-EGF, EGFR or with AG1478, an EGFR inhibitor. It is reported that ox-PAPC can interact with ADAM 10, 19 and a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS) 4 by covalent binding, which would be an additional mechanism for EGFR receptor transactivation [59 ]. Furthermore, oxLDL-induced and angiotensin II-type 1 receptor-mediated transformation of macrophages into foam cells can be inhibited by AG1478 [60]. IL-8 in turn can activate CXCR2 (interleukin-8-receptor b) and thereby induces HB-EGF shedding and EGFR transactivation, resulting in migration of microvascular endothelial cells [61]. In contrast to the brief EGFR transactivation achieved by ROS, EGFR transactivation by oxLDL lasts several hours, suggesting a different mechanism and damaging potential [62,63]. Nevertheless, H2O2-induced Src, EGFR and JNK activation was also shown to potentially mediate oxidative stress response [64]. An increase in vasoactive peptides such as endothelin is typical for patients with cardiovascular disease. Hsieh et al. report that this increase leads to enhanced transactivation of the EGFR followed by PI3K, Akt and MAPK activation, resulting in AP1-induced enhancement of COX2 (cyclooxygenase-2) activity and prostaglandin-E2 biosynthesis. Thereby, a proinflammatory milieu enhancing remodeling processes is promoted [65]. Stimuli enhancing neointima formation by EGFR transactivation include thrombin [22,66], 15-HETE [23], angiotensin II [67], uremic toxins and oxLDL[25,68]. Recently, Wong et al. [69 ] demonstrated that inhibition of the mammalian target of rapamycin (mTOR) induces migration and differentiation of vascular progenitor cells (Sca-1þ) through a CXCR4/EGFR/b-catenin pathway, suggesting an involvement in restenosis and possibly atherosclerosis. &

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&

&

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ATHEROSCLEROSIS During the pathogenesis of atherosclerosis, oxLDL and fatty acids play a major role in initiating an 116


DIABETES There is accumulating evidence that EGFR signaling participates in the pathogenesis of diabetic vascular complications. Case reports of patients receiving receptor tyrosine kinase inhibitors for the treatment of malignancies demonstrate an improvement of Volume 23 Number 2 March 2014


Epidermal growth factor receptor in vasculature Schreier et al.

preexisting type 2 diabetes [70–72]. In mesenteric vessels of diabetic rats, the EGFR was significantly overexpressed and EGFR inhibition attenuated the majority of gene expression changes detected in these rats compared with control animals [73]. Incubation of endothelial cells or VSMC with high glucose levels can lead to increased EGFR phosphorylation [74,75] via ROS-dependent c-Src phosphorylation, resulting in enhanced MAPK and PI3K activity as well as enhanced Gq/11 alpha expression [74,76,77]. In addition to glucose, fatty acids, advanced glycation end products (AGEs) and ROS are also elevated during diabetes and seem to participate in the pathogenesis of vascular complications in an EGFR-dependent fashion. Notably, glucose tolerance, insulin resistance and signaling were improved after long-term EGFR inhibition and subclinical inflammation was attenuated [78]. Additionally, AGEs stimulated NADPH oxidase with subsequent EGFR-dependent PKC-delta and ERK1/2 activation and enhanced proinflammatory NF-KB signaling in endothelial cells [79,80]. Similarly, leptin, known to be elevated in patients with metabolic disorders, can enhance EGFR signaling via ROS and c-Src as well as ErbB2 activity, providing another link between metabolic and cardiovascular disease [81]. In coronary and mesenteric arteries of diabetic mice, EGFR phosphorylation and pressure-induced myogenic tone were increased and endothelial function measured as eNOS expression and phosphorylation in response to shear stress and acetylcholine was impaired [75]. Perfused mesenteric beds and isolated renal artery ring segments of diabetic rats showed an EGFR-dependent increased response to vasoconstrictors and a decreased response to vasodilators [73,82]. In addition, mesenteric resistance arteries of diabetic mice showed increased NADPH oxidase activity and ER stress marker expression leading to impaired endothelium-dependent and independent relaxation [83 ]. In a fructose-induced insulin resistance rat model, the MMP-EGFR-ERK1/2 signaling pathway was activated and phosphorylation of the contractile protein myosin light chain II (MLCII) and the corresponding regulatory proteins P90RSK and SRF was enhanced, coinciding with hypertension that could be prevented by EGFR inhibition [74]. Vasoactive substances further enhanced expression of MLCII and myosin light chain kinase in insulin-resistant VSMC and may thereby aggravate the pathological effects induced by diabetes [74]. EGFR has also been suggested as mediating vascular dysfunction in diabetes as a heterodimer with ErbB2, as hyperreactivity to vasoconstrictors and reduced responsiveness to vasodilators in diabetic rats could be attenuated by EGFR or ErbB2 inhibitors [82,84,85]. &

Another consequence of elevated EGFR signaling in diabetes seems to be vascular remodeling, leading to smaller passive diameters of resistance arteries, higher wall thickness to lumen diameter ratios and an increased stiffness with elevated collagen type 1 content. Treatment with AG1478 attenuated the morphological alterations [86]. Impaired blood flow recovery, vascular and capillary density and endothelial nitric oxide synthase activity after unilateral femoral artery ligation in diabetic db-db- mice could be significantly normalized by inhibition of EGFR and ERK1/2 activity, suggesting that EGFR und ERK1/2 inhibitors may be a therapeutic option in ischemia-induced vascular pathology in diabetes type 2 [87 ]. &&

SYSTEMIC HYPERTENSION The effect of EGF and HB-EGF on blood pressure seems to be primarily vasoconstrictive but vasodilator effects have been reported as well [88–91]. Under physiological conditions, EGFR shows little influence on systolic blood pressure [53,74,92,93]. However, in VSMC-specific knockout mice, a reduction in diastolic blood pressure without alteration in systolic blood pressure was demonstrated [5 ]. EGFR-induced vasoconstriction was observed in diseased vessels and different settings of experimental hypertension such as an infusion of angiotensin II, endothelin-1, aldosterone and phenylephrine [53,73,94–96]. Under these pathophysiological conditions, EGFR receptor tyrosine kinase blockade attenuated elevated blood pressure. The EGFR may also affect blood pressure through its actions on vessel remodeling as indicated above. &&

PULMONARY HYPERTENSION Pulmonary arterial hypertension (PAH) is elicited by a disequilibrium between vasoconstrictors and vasodilators and a chronic-proliferative component leading to vascular remodeling of small lung vessels. Different receptor tyrosine kinases have been suggested as important signal mediators and promising therapeutic targets, among them the EGFR [97,98 ,99]. In rats with monocrotaline-induced PAH, some EGFR/HER2 inhibitors led to an increased survival with a decrease in muscularization of small arteries and a reduction in pulmonary pressure and right ventricular hypertrophy, whereas others showed no beneficial effect [100]. EGFR inhibitors such as erlotinib and gefitinib reduced PASMC proliferation but showed no, or only slight, reduction in vascular remodeling measured as medial wall thickness and muscularization of pulmonary arteries [101]. Hypoxia, another inductor of PAH, has been identified as a trigger for EGFR activation and


&


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Vascular homeostasis • Vascular tone • ROS defense • NO balance

Endothelial cells • NO homeostasis • Endothelial dysfunction • Inflammation • Angiogenesis? VSMC • Vascular tone • ROS homeostasis • Inflammation • Migration • Proliferation • Fibrosis

Impact of EGFR

Atherosclerosis • Transactivation: oxLDL/fatty acids • IL-8 expression h • Migration: macrophages, VSMC, vascular progenitor cells • Macrophages g foam cells • Neointima formation h Diabetes (vessels) • Transactivation: glucose, fatty acids, AGEs, ROS • Proinflammatory • Endothelial dysfunction • Myogenic tone h • Vascular remodeling h

• Vascular tone • Oxidative stress • Vascular remodeling • Endothelial dysfunction • Fibrosis • Systemic hypertension

Pulmonary hypertension • Transactivation: hypoxia • Vascular remodeling h • Vasoconstrictor response h • NO availability i • Proinflammatory

FIGURE 2. Summary of the impact of the epidermal growth factor receptor on the vasculature. AGEs, advanced glycation end products; EGFR, epidermal growth factor receptor; NO, nitric oxide; oxLDL, oxidized low-density lipoproteins; ROS, reactive oxygen species; VSMC, vascular smooth muscle cells.

expression, leading to an increased vasoconstrictor response in pulmonary arteries by EGFR-dependent activation of Rac1 and NOX2 and subsequent calcium sensitization of myofilaments [98 ]. Hypoxia also induced EGFR-dependent proliferation of pulmonary endothelial cells and VSMCs, leading to wall thickening and distal muscularization in fetal pulmonary arteries, possibly by enhancing the proliferative response of SMC to such mitogens as PDGF, FGF-2 and EGF [102,103]. EGFR also mediated inflammation-dependent arginase activation, thereby reducing arginin and therefore NO availability [103,104]. In addition, EGFR has also been shown to interact with cytokine secretion, chemokine receptor activation, NFKB-/STAT3, PAF and PDGFR signaling during inflammation [105–107]. Furthermore, thrombospondin 1 can activate EGFR/HER2 and thereby cause phosphorylation of zonula adherens proteins and opening of the paracellular pathway in pulmonary microvascular endothelial cells [108]. Overall, EGFR is involved in the signaling events leading to pulmonary hypertension and therefore multireceptor tyrosine kinase inhibitors seem to be a promising therapeutic target for pulmonary hypertension. &

CONCLUSION The EGFR participates in a cross-talk with the signaling of G-protein-coupled receptors, steroid receptors 118


and other (receptor) tyrosine kinases. In the vasculature, the EGFR is essential for adequate basal vascular tone and tissue homeostasis (Fig. 2). In contrast, the EGFR may also be involved in induction of proinflammatory mediators, altered secretion of matrix components, enhanced proliferation, and migration of cells and vessel remodeling, thereby promoting vascular diseases such as atherosclerosis and hypertension. Overall, the EGFR is a versatile signaling pathway integrator that is required for basal vascular homeostasis and function but that may also be involved in pathophysiological actions. Acknowledgements None. Conflicts of interest This work was funded by the DFG grant GE 905/19–1. There are no conflicts of interest.

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Monoclonal antibodies to epidermal growth factor receptors in studies of receptor structure and function.

Gastric carcinoma, epidermal growth factor, and epidermal growth factor receptor.

Epidermal growth factor receptor mutation enhances expression of vascular endothelial growth factor in lung cancer.

Structure-function relationships in epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha).

Viruses exploit the function of epidermal growth factor receptor.

Expression and localization of epidermal growth factor, transforming growth factor-α and epidermal growth factor receptor in the canine testis.

Role of epidermal growth factor receptor and endoplasmic reticulum stress in vascular remodeling induced by angiotensin II.

Epidermal growth factor receptor inhibition by erlotinib prevents vascular smooth muscle cell and monocyte-macrophage function in vitro.

Expression of epidermal growth factor receptor and human epidermal growth factor receptor 2 in periocular squamous cell carcinomas of horses.

Epidermal growth factor receptor in pancreatic cancer.

Epidermal growth factor receptor in glioblastoma.

Diagnostic values of vascular endothelial growth factor and epidermal growth factor receptor for benign and malignant hydrothorax.

Oncogenic fingerprint of epidermal growth factor receptor pathway and emerging epidermal growth factor receptor blockade resistance in colorectal cancer.

The role of epidermal growth factor receptor mutations and epidermal growth factor receptor-tyrosine kinase inhibitors in the treatment of lung cancer.

Epidermal growth factor and transforming growth factor-alpha induce differential processing of the epidermal growth factor receptor.

Cytokine regulation by epidermal growth factor receptor inhibitors and epidermal growth factor receptor inhibitor associated skin toxicity in cancer patients.

Structure-function relationships and supramolecular organization of the EGFR (epidermal growth factor receptor) on the cell surface.

The role of epidermal growth factor receptor in prognosis and treatment of gastric cancer.

Epidermal Growth Factor and Epidermal Growth Factor Receptor: The Yin and Yang in the Treatment of Cutaneous Wounds and Cancer.

Role of human epidermal growth factor receptor 2 in gastric cancer: biological and pharmacological aspects.

The Role of MicroRNAs and Human Epidermal Growth Factor Receptor 2 in Proliferative Lupus Nephritis.

Structure-function analysis of epidermal growth factor: site directed mutagenesis and nuclear magnetic resonance.

The Prognostic and Predictive Role of Epidermal Growth Factor Receptor in Surgical Resected Pancreatic Cancer.

Is there a role for epidermal growth factor receptor tyrosine kinase inhibitors in epidermal growth factor receptor wild-type non-small cell lung cancer?