Two EGF molecules contribute additively to stabilization of the EGFR dimer

Probing phosphorylation events in biological membranes: The transducer function

The extracellular environment is sensed by receptors in the plasma membrane. Some of these receptors initiate cytoplasmic signaling cascades involving phosphorylation: the addition of a phosphate group to a specific amino acid, such as tyrosine, in a protein. Receptor Tyrosine Kinases (RTKs) are one large class of membrane receptors that can directly initiate signaling cascades through their intracellular kinase domains, which both catalyze tyrosine phosphorylation and get phosphorylated. In the first step of signaling, the ligands stabilize phosphorylation-competent RTK dimers and oligomers, which leads to the phosphorylation of specific tyrosine residues in the activation loop of the kinases. Here we discuss quantitative measurements of tyrosine phosphorylation efficiencies for RTKs, described by the "transducer function". The transducer function links the phosphorylation (the response) and the binding of the activating ligand to the receptor (the stimulus). We overview a methodology that allows such measurements in direct response to ligand binding. We discuss experiments which demonstrate that EGF is a partial agonist, and that two tyrosines in the intracellular domain of EGFR, Y1068 and Y1173, are differentially phosphorylated in the EGF-bound EGFR dimers.

The impact of nitric oxide on HER family post-translational modification and downstream signaling in cancer

The human epidermal growth factor receptor (HER) family consists of four members, activated by two families of ligands. They are known for mediating cell-cell interactions in organogenesis, and their deregulation has been associated with various cancers, including breast and esophageal cancers. In particular, aberrant epidermal growth factor receptor (EGFR) and HER2 signaling drive disease progression and result in poorer patient outcomes. Nitric oxide (NO) has been proposed as an alternative activator of the HER family and may play a role in this aberrant activation due to its ability to induce s-nitrosation and phosphorylation of the EGFR. This review discusses the potential impact of NO on HER family activation and downstream signaling, along with its role in the efficacy of therapeutics targeting the family.

Molecular basis of VEGFR1 autoinhibition at the plasma membrane

Ligand-independent activation of VEGFRs is a hallmark of diabetes and several cancers. Like EGFR, VEGFR2 is activated spontaneously at high receptor concentrations. VEGFR1, on the other hand, remains constitutively inactive in the unligated state, making it an exception among VEGFRs. Ligand stimulation transiently phosphorylates VEGFR1 and induces weak kinase activation in endothelial cells. Recent studies, however, suggest that VEGFR1 signaling is indispensable in regulating various physiological or pathological events. The reason why VEGFR1 is regulated differently from other VEGFRs remains unknown. Here, we elucidate a mechanism of juxtamembrane inhibition that shifts the equilibrium of VEGFR1 towards the inactive state, rendering it an inefficient kinase. The juxtamembrane inhibition of VEGFR1 suppresses its basal phosphorylation even at high receptor concentrations and transiently stabilizes tyrosine phosphorylation after ligand stimulation. We conclude that a subtle imbalance in phosphatase activation or removing juxtamembrane inhibition is sufficient to induce ligand-independent activation of VEGFR1 and sustain tyrosine phosphorylation.

Distinct interactions stabilize EGFR dimers and higher-order oligomers in cell membranes

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase with important roles in many cellular processes as well as in cancer and other diseases. EGF binding promotes EGFR dimerization and autophosphorylation through interactions that are well understood structurally. How these dimers relate to higher-order EGFR oligomers seen in cell membranes, however, remains unclear. Here, we used single-particle tracking (SPT) and Förster resonance energy transfer imaging to examine how each domain of EGFR contributes to receptor oligomerization and the rate of receptor diffusion in the cell membrane. Although the extracellular region of EGFR is sufficient to drive receptor dimerization, we find that the EGF-induced EGFR slowdown seen by SPT requires higher-order oligomerization-mediated in part by the intracellular tyrosine kinase domain when it adopts an active conformation. Our data thus provide important insight into the interactions required for higher-order EGFR assemblies involved in EGF signaling.

Exploring the potential of biologically active phenolic acids from marine natural products as anticancer agents targeting the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) dimerizes upon ligand bindings to the extracellular domain that initiates the downstream signaling cascades and activates intracellular kinase domain. Thus, activation of autophosphorylation through kinase domain results in metastasis, cell proliferation, and angiogenesis. The main objective of this research is to discover more promising anti-cancer lead compound against EGRF from the phenolic acids of marine natural products using in-silico approaches. Phenolic compounds reported from marine sources are reviewed from previous literatures. Furthermore, molecular docking was carried out using the online tool CB-Dock. The molecules with good docking and binding energies scores were subjected to ADME, toxicity and drug-likeness analysis. Subsequently, molecules from the docking experiments were also evaluated using the acute toxicity and MD simulation studies. Fourteen phenolic compounds from the reported literatures were reviewed based on the findings, isolation, characterized and applications. Molecular docking studies proved that the phenolic acids have good binding fitting by forming hydrogen bonds with amino acid residues at the binding site of EGFR. Chlorogenic acid, Chicoric acid and Rosmarinic acid showed the best binding energies score and forming hydrogen bonds with amino acid residues compare to the reference drug Erlotinib. Among these compounds, Rosmarinic acid showed the good pharmacokinetics profiles as well as acute toxicity profile. The MD simulation study further revealed that the lead complex is stable and could be future drug to treat the cancer disease. Furthermore, in a wet lab environment, both in-vitro and in-vivo testing will be employed to validate the existing computational results.Communicated by Ramaswamy H. Sarma.

Structural basis for inactivation of PRC2 by G-quadruplex RNA

Polycomb repressive complex 2 (PRC2) silences genes through trimethylation of histone H3K27. PRC2 associates with numerous precursor messenger RNAs (pre-mRNAs) and long noncoding RNAs (lncRNAs) with a binding preference for G-quadruplex RNA. In this work, we present a 3.3-Å-resolution cryo-electron microscopy structure of PRC2 bound to a G-quadruplex RNA. Notably, RNA mediates the dimerization of PRC2 by binding both protomers and inducing a protein interface composed of two copies of the catalytic subunit EZH2, thereby blocking nucleosome DNA interaction and histone H3 tail accessibility. Furthermore, an RNA-binding loop of EZH2 facilitates the handoff between RNA and DNA, another activity implicated in PRC2 regulation by RNA. We identified a gain-of-function mutation in this loop that activates PRC2 in zebrafish. Our results reveal mechanisms for RNA-mediated regulation of a chromatin-modifying enzyme.

Combination immunochemotherapy for recurrent or metastatic head and neck squamous cell carcinoma: a systematic review and meta-analysis

OBJECTIVE

To evaluate the efficacy and safety of combination immunochemotherapy regimens for the treatment of recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC).

DESIGN

Meta-analysis and systematic review.

DATA SOURCES

PubMed, Embase, Web of Science and Cochrane library and the Clinicaltrials.gov clinical trials registry were searched up to 14 March 2022.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

We included randomised controlled trials that compared combination immunochemotherapy with conventional chemotherapy for R/M HNSCC. Primary outcomes of interest were overall survival (OS), progression-free survival (PFS), objective response rate (ORR) and adverse effects (AEs).

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently extracted data and assessed the risk of bias of the included studies. The HR and its 95% CI were used as the effect analysis statistic for survival analysis, while the OR and its 95% CI were used as the effect analysis statistic for dichotomous variables. These statistics were extracted by the reviewers and aggregated using a fixed-effects model to synthesise the data.

RESULTS

A total of 1214 relevant papers were obtained after the initial search, and five papers that met the inclusion criteria were included; these studies included a total of 1856 patients with R/M HNSCC. Meta-analysis showed that the OS and PFS of patients with R/M HNSCC in the combination immunochemotherapy group were significantly longer than those in the conventional chemotherapy group (HR=0.84; 95% CI 0.76, 0.94; p=0.002; HR=0.67; 95% CI 0.61, 0.75; p<0.0001), and the ORR was significantly higher (OR=1.90; 95% CI 1.54, 2.34; p<0.00001). The analysis of AEs showed that there was no significant difference in the overall incidence rate of AEs between two groups (OR=0.80; 95% CI 0.18, 3.58; p=0.77), but the rate of grade III and IV AEs was significantly higher in patients in the combination immunochemotherapy group (OR=1.39; 95% CI 1.12, 1.73; p=0.003).

CONCLUSIONS

Combination immunochemotherapy prolonged OS and PFS in patients with R/M HNSCC and improved the ORR; while this approach did not increase the overall incidence of AEs in patients, it increased the rate of grade III and IV AEs.

PROSPERO REGISTRATION NUMBER

CRD42022344166.

Distinct interactions stabilize EGFR dimers and higher-order oligomers in cell membranes

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase (RTK) with important roles in many cellular processes as well as cancer and other diseases. EGF binding promotes EGFR dimerization and autophosphorylation through interactions that are well understood structurally. However, it is not clear how these dimers relate to higher-order EGFR oligomers detected at the cell surface. We used single-particle tracking (SPT) and Förster resonance energy transfer (FRET) imaging to examine how each domain within EGFR contributes to receptor dimerization and the rate of its diffusion in the cell membrane. We show that the EGFR extracellular region is sufficient to drive receptor dimerization, but that the EGF-induced EGFR slow-down seen by SPT requires formation of higher order oligomers, mediated in part by the intracellular tyrosine kinase domain - but only when in its active conformation. Our data thus provide important insight into higher-order EGFR interactions required for EGF signaling.

Structural basis for inactivation of PRC2 by G-quadruplex RNA

The histone methyltransferase PRC2 (Polycomb Repressive Complex 2) silences genes via successively attaching three methyl groups to lysine 27 of histone H3. PRC2 associates with numerous pre-mRNA and lncRNA transcripts with a binding preference for G-quadruplex RNA. Here, we present a 3.3Ã…-resolution cryo-EM structure of PRC2 bound to a G-quadruplex RNA. Notably, RNA mediates the dimerization of PRC2 by binding both protomers and inducing a protein interface comprised of two copies of the catalytic subunit EZH2, which limits nucleosome DNA interaction and occludes H3 tail accessibility to the active site. Our results reveal an unexpected mechanism for RNA-mediated inactivation of a chromatin-modifying enzyme. Furthermore, the flexible loop of EZH2 that helps stabilize RNA binding also facilitates the handoff between RNA and DNA, an activity implicated in PRC2 regulation by RNA.

One-Sentence Summary

Cryo-EM structure of RNA-bound PRC2 dimer elucidates an unexpected mechanism of PRC2 inhibition by RNA.

Targeting EGFR in melanoma - The sea of possibilities to overcome drug resistance

Melanoma is considered one of the most aggressive skin cancers. It spreads and metastasizes quickly and is intrinsically resistant to most conventional chemotherapeutics, thereby presenting a challenge to researchers and clinicians searching for effective therapeutic strategies to treat patients with melanoma. The use of inhibitors of mutated serine/threonine-protein kinase B-RAF (BRAF), e.g., vemurafenib and dabrafenib, has revolutionized melanoma chemotherapy. Unfortunately, the response to these drugs lasts a limited time due to the development of acquired resistance. One of the proteins responsible for this process is epidermal growth factor receptor (EGFR). In this review, we summarize the role of EGFR signaling in the multidrug resistance of melanomas and discuss possible applications of EGFR inhibitors to overcome the development of drug resistance in melanoma cells during therapy.

Interactions between EGFR and EphA2 promote tumorigenesis through the action of Ephexin1

The cell signaling factors EGFR, EphA2, and Ephexin1 are associated with lung and colorectal cancer and play an important role in tumorigenesis. Although the respective functional roles of EGFR and EphA2 are well known, interactions between these proteins and a functional role for the complex is not understood. Here, we showed that Ephexin1, EphA2, and EGFR are each expressed at higher levels in lung and colorectal cancer patient tissues, and binding of EGFR to EphA2 was associated with both increased tumor grade and metastatic cases in both cancer types. Treatment with Epidermal Growth Factor (EGF) induced binding of the RR domain of EGFR to the kinase domain of EphA2, and this binding was promoted by Ephexin1. Additionally, the AKT-mediated phosphorylation of EphA2 (at Ser897) promoted interactions with EGFR, pointing to the importance of this pathway. Two mutations in EGFR, L858R and T790M, that are frequently observed in lung cancer patients, promoted binding to EphA2, and this binding was dependent on Ephexin1. Our results indicate that the formation of a complex between EGFR, EphA2, and Ephexin1 plays an important role in lung and colorectal cancers, and that inhibition of this complex may be an effective target for cancer therapy.

Critical roles for EGFR and EGFR-HER2 clusters in EGF binding of SW620 human carcinoma cells

Epidermal growth factor (EGF) signalling regulates normal epithelial and other cell growth, with EGF receptor (EGFR) overexpression reported in many cancers. However, the role of EGFR clusters in cancer and their dependence on EGF binding is unclear. We present novel single-molecule total internal reflection fluorescence microscopy of (i) EGF and EGFR in living cancer cells, (ii) the action of anti-cancer drugs that separately target EGFR and human EGFR2 (HER2) on these cells and (iii) EGFR–HER2 interactions. We selected human epithelial SW620 carcinoma cells for their low level of native EGFR expression, for stable transfection with fluorescent protein labelled EGFR, and imaged these using single-molecule localization microscopy to quantify receptor architectures and dynamics upon EGF binding. Prior to EGF binding, we observe pre-formed EGFR clusters. Unexpectedly, clusters likely contain both EGFR and HER2, consistent with co-diffusion of EGFR and HER2 observed in a different model CHO-K1 cell line, whose stoichiometry increases following EGF binding. We observe a mean EGFR : EGF stoichiometry of approximately 4 : 1 for plasma membrane-colocalized EGFR–EGF that we can explain using novel time-dependent kinetics modelling, indicating preferential ligand binding to monomers. Our results may inform future cancer drug developments.

Glioblastoma mutations alter EGFR dimer structure to prevent ligand bias

The epidermal growth factor receptor (EGFR) is frequently mutated in human cancer^1,2, and is an important therapeutic target. EGFR inhibitors have been successful in lung cancer, where mutations in the intracellular tyrosine kinase domain activate the receptor¹, but not in glioblastoma multiforme (GBM)³, where mutations occur exclusively in the extracellular region. Here we show that common extracellular GBM mutations prevent EGFR from discriminating between its activating ligands⁴. Different growth factor ligands stabilize distinct EGFR dimer structures⁵ that signal with different kinetics to specify or bias outcome^5,6. EGF itself induces strong symmetric dimers that signal transiently to promote proliferation. Epiregulin (EREG) induces much weaker asymmetric dimers that drive sustained signalling and differentiation⁵. GBM mutations reduce the ability of EGFR to distinguish EREG from EGF in cellular assays, and allow EGFR to form strong (EGF-like) dimers in response to EREG and other low-affinity ligands. Using X-ray crystallography, we further show that the R84K GBM mutation symmetrizes EREG-driven extracellular dimers so that they resemble dimers normally seen with EGF. By contrast, a second GBM mutation, A265V, remodels key dimerization contacts to strengthen asymmetric EREG-driven dimers. Our results argue for an important role of altered ligand discrimination by EGFR in GBM, with potential implications for therapeutic targeting.

The Yin and Yang of ERBB4: Tumor Suppressor and Oncoprotein

ERBB4 (HER4) is a member of the ERBB family of receptor tyrosine kinases, a family that includes the epidermal growth factor receptor (EGFR/ERBB1/HER1), ERBB2 (Neu/HER2), and ERBB3 (HER3). EGFR and ERBB2 are oncoproteins and validated targets for therapeutic intervention in a variety of solid tumors. In contrast, the role that ERBB4 plays in human malignancies is ambiguous. Thus, here we review the literature regarding ERBB4 function in human malignancies. We review the mechanisms of ERBB4 signaling with an emphasis on mechanisms of signaling specificity. In the context of this signaling specificity, we discuss the hypothesis that ERBB4 appears to function as a tumor suppressor protein and as an oncoprotein. Next, we review the literature that describes the role of ERBB4 in tumors of the bladder, liver, prostate, brain, colon, stomach, lung, bone, ovary, thyroid, hematopoietic tissues, pancreas, breast, skin, head, and neck. Whenever possible, we discuss the possibility that ERBB4 mutants function as biomarkers in these tumors. Finally, we discuss the potential roles of ERBB4 mutants in the staging of human tumors and how ERBB4 function may dictate the treatment of human tumors. SIGNIFICANCE STATEMENT: This articles reviews ERBB4 function in the context of the mechanistic model that ERBB4 homodimers function as tumor suppressors, whereas ERBB4-EGFR or ERBB4-ERBB2 heterodimers act as oncogenes. Thus, this review serves as a mechanistic framework for clinicians and scientists to consider the role of ERBB4 and ERBB4 mutants in staging and treating human tumors.

A Review of HER4 (ErbB4) Kinase, Its Impact on Cancer, and Its Inhibitors

HER4 is a receptor tyrosine kinase that is required for the evolution of normal body systems such as cardiovascular, nervous, and endocrine systems, especially the mammary glands. It is activated through ligand binding and activates MAPKs and PI3K/AKT pathways. HER4 is commonly expressed in many human tissues, both adult and fetal. It is important to understand the role of HER4 in the treatment of many disorders. Many studies were also conducted on the role of HER4 in tumors and its tumor suppressor function. Mostly, overexpression of HER4 kinase results in cancer development. In the present article, we reviewed the structure, location, ligands, physiological functions of HER4, and its relationship to different cancer types. HER4 inhibitors reported mainly from 2016 to the present were reviewed as well.

Epitope Mapping of an Anti-Human Epidermal Growth Factor Receptor Monoclonal Antibody (EMab-51) Using the RIEDL Insertion for Epitope Mapping Method

The classic method for identifying the epitope that monoclonal antibodies (mAbs) bind uses deletion mutants and point mutants of the target protein. However, determining the epitope of mAbs-reactive membrane proteins is often challenging. We recently developed the RIEDL insertion for epitope mapping (REMAP) method to identify mAb-binding epitopes. Herein, we first checked the reactivity of an anti-epidermal growth factor receptor (EGFR) mAb (EMab-51) to several EGFR deletion mutants such as EGFR/dN152, EGFR/dN313, EGFR/dN370, EGFR/dN375, EGFR/dN380, and EGFR/dN482. We found the N-terminus of the EMab-51-binding epitope between residues 375 and 380 of EGFR. We next produced EGFR/dN313 mutants with the RIEDL peptide tag inserted at each possible position of ₃₇₅-AFRGDSFTHTPPLDP-₃₈₉. EMab-51 lost its reactivity with the mutants having a RIEDL tag inserted at each position of ₃₇₇-RGDSFTHTPP-₃₈₆, whereas LpMab-7 (an anti-RIEDL mAb) detected every mutant. Thus, using the REMAP method, we identified the EMab-51-binding epitope of EGFR as ₃₇₇-RGDSFTHTPP-₃₈₆.

Review on Epidermal Growth Factor Receptor (EGFR) Structure, Signaling Pathways, Interactions, and Recent Updates of EGFR Inhibitors

The epidermal growth factor receptor (EGFR) belongs to the ERBB family of tyrosine kinase receptors. EGFR signaling cascade is a key regulator in cell proliferation, differentiation, division, survival, and cancer development. In this review, the EGFR structure and its mutations, signaling pathway, ligand binding and EGFR dimerization, EGF/EGFR interaction, and the progress in the development of EGFR inhibitors have been explored.

Comparison of tyrosine kinase domain properties for the neurotrophin receptors TrkA and TrkB

The tropomyosin-related kinase (Trk) family consists of three receptor tyrosine kinases (RTKs) called TrkA, TrkB, and TrkC. These RTKs are regulated by the neurotrophins, a class of secreted growth factors responsible for the development and function of neurons. The Trks share a high degree of homology and utilize overlapping signaling pathways, yet their signaling is associated with starkly different outcomes in certain cancers. For example, in neuroblastoma, TrkA expression and signaling correlates with a favorable prognosis, whereas TrkB is associated with poor prognoses. To begin to understand how activation of the different Trks can lead to such distinct cellular outcomes, we investigated differences in kinase activity and duration of autophosphorylation for the TrkA and TrkB tyrosine kinase domains (TKDs). We find that the TrkA TKD has a catalytic efficiency that is ∼2-fold higher than that of TrkB, and becomes autophosphorylated in vitro more rapidly than the TrkB TKD. Studies with mutated TKD variants suggest that a crystallographic dimer seen in many TrkA (but not TrkB) TKD crystal structures, which involves the kinase-insert domain, may contribute to this enhanced TrkA autophosphorylation. Consistent with previous studies showing that cellular context determines whether TrkB signaling is sustained (promoting differentiation) or transient (promoting proliferation), we also find that TrkB signaling can be made more transient in PC12 cells by suppressing levels of p75NTR. Our findings shed new light on potential differences between TrkA and TrkB signaling, and suggest that subtle differences in signaling dynamics can lead to substantial shifts in the cellular outcome.

Comprehensive Model for Epidermal Growth Factor Receptor Ligand Binding Involving Conformational States of the Extracellular and the Kinase Domains

The epidermal growth factor (EGF) receptor (EGFR) undergoes ligand-dependent dimerization to initiate transmembrane signaling. Although crystallographic structures of the extracellular and kinase domains are available, ligand binding has not been quantitatively analyzed taking the influence of both domains into account. Here, we developed a model explicitly accounting for conformational changes of the kinase and extracellular domains, their dimerizations and ligand binding to monomeric and dimeric receptor species. The model was fitted to ligand binding data of suspended cells expressing receptors with active or inactive kinase conformations. Receptor dimers with inactive, symmetric configuration of the kinase domains exhibit positive cooperativity and very weak binding affinity for the first ligand, whereas dimers with active, asymmetric kinase dimers are characterized by negative cooperativity and subnanomolar binding affinity for the first ligand. The homodimerization propensity of EGFR monomers with active kinase domains is ∼100-times higher than that of dimers with inactive kinase domains. Despite this fact, constitutive, ligand-independent dimers are mainly generated from monomers with inactive kinase domains due to the excess of such monomers in the membrane. The experimental finding of increased positive cooperativity at high expression levels of EGFR was recapitulated by the model. Quantitative prediction of ligand binding to different receptor species revealed that EGF binds to receptor monomers and dimers in an expression-level dependent manner without significant recruitment of monomers to dimers upon EGF stimulation below the phase transition temperature of the membrane. Results of the fitting offer unique insight into the workings of the EGFR.

Bacteria as a double-action sword in cancer

Bacteria have long been known as one of the primary causative agents of cancer, however, recent studies suggest that they can be used as a promising agent in cancer therapy. Because of the limitations that conventional treatment faces due to the specific pathophysiology and the tumor environment, there is a great need for the new anticancer therapeutic agents. Bacteriotherapy utilizes live, attenuated strains or toxins, peptides, bacteriocins of the bacteria in the treatment of cancer. Moreover, they are widely used as a vector for delivering genes, peptides, or drugs to the tumor target. Interestingly, it was found that their combination with the conventional therapeutic approaches may enhance the treatment outcome. In the genome editing era, it is feasible to develop a novel generation of therapeutic bacteria with fewer side effects and more efficacy for cancer therapy. Here we review the current knowledge on the dual role of bacteria in the development of cancer as well as cancer therapy.

Insulin and epidermal growth factor receptor family members share parallel activation mechanisms

Insulin receptor (IR) and the epidermal growth factor receptor (EGFR) were the first receptor tyrosine kinases (RTKs) to be studied in detail. Both are important clinical targets-in diabetes and cancer, respectively. They have unique extracellular domain compositions among RTKs, but share a common module with two ligand-binding leucine-rich-repeat (LRR)-like domains connected by a flexible cysteine-rich (CR) domain (L1-CR-L2 in IR/domain, I-II-III in EGFR). This module is linked to the transmembrane region by three fibronectin type III domains in IR, and by a second CR in EGFR. Despite sharing this conserved ligand-binding module, IR and EGFR family members are considered mechanistically distinct-in part because IR is a disulfide-linked (αβ)₂ dimer regardless of ligand binding, whereas EGFR is a monomer that undergoes ligand-induced dimerization. Recent cryo-electron microscopy (cryo-EM) structures suggest a way of unifying IR and EGFR activation mechanisms and origins of negative cooperativity. In EGFR, ligand engages both LRRs in the ligand-binding module, "closing" this module to break intramolecular autoinhibitory interactions and expose new dimerization sites for receptor activation. How insulin binds the activated IR was less clear until now. Insulin was known to associate with one LRR (L1), but recent cryo-EM structures suggest that it also engages the second LRR (albeit indirectly) to "close" the L1-CR-L2 module, paralleling EGFR. This transition simultaneously breaks autoinhibitory interactions and creates new receptor-receptor contacts-remodeling the IR dimer (rather than inducing dimerization per se) to activate it. Here, we develop this view in detail, drawing mechanistic links between IR and EGFR.

Bacteria and cancer: Different sides of the same coin

Conventional cancer therapies such as chemotherapy, radiation therapy, and immunotherapy due to the complexity of cancer have been unsuccessful in the complete eradication of tumor cells. Thus, there is a need for new therapeutic strategies toward cancer. Recently, the therapeutic role of bacteria in different fields of medicine and pharmaceutical research has attracted attention in recent decades. Although several bacteria are notorious as cancer-causing agents, recent research revealed intriguing results suggesting the bacterial potential in cancer therapy. Thus, bacterial cancer therapy is an alternative anticancer approach that has promising results on tumor cells in-vivo. Moreover, with the aid of genetic engineering, some natural or genetically modified bacterial strains can directly target hypoxic regions of tumors and secrete therapeutic molecules leading to cancer cell death. Additionally, stimulation of immune cells by bacteria, bacterial cancer DNA vaccine and antitumor bacterial metabolites are other therapeutic applications of bacteria in cancer therapy. The present study is a comprehensive review of different aspects of bacterial cancer therapy alone and in combination with conventional methods, for improving cancer therapy.

Membrane receptor activation mechanisms and transmembrane peptide tools to elucidate them

Single-pass membrane receptors contain extracellular domains that respond to external stimuli and transmit information to intracellular domains through a single transmembrane (TM) α-helix. Because membrane receptors have various roles in homeostasis, signaling malfunctions of these receptors can cause disease. Despite their importance, there is still much to be understood mechanistically about how single-pass receptors are activated. In general, single-pass receptors respond to extracellular stimuli via alterations in their oligomeric state. The details of this process are still the focus of intense study, and several lines of evidence indicate that the TM domain (TMD) of the receptor plays a central role. We discuss three major mechanistic hypotheses for receptor activation: ligand-induced dimerization, ligand-induced rotation, and receptor clustering. Recent observations suggest that receptors can use a combination of these activation mechanisms and that technical limitations can bias interpretation. Short peptides derived from receptor TMDs, which can be identified by screening or rationally developed on the basis of the structure or sequence of their targets, have provided critical insights into receptor function. Here, we explore recent evidence that, depending on the target receptor, TMD peptides cannot only inhibit but also activate target receptors and can accommodate novel, bifunctional designs. Furthermore, we call for more sharing of negative results to inform the TMD peptide field, which is rapidly transforming into a suite of unique tools with the potential for future therapeutics.

Silencing of CD133 inhibits GLUT1-mediated glucose transport through downregulation of the HER3/Akt/mTOR pathway in colon cancer

Cluster of differentiation 133 (CD133) is a transmembrane glycoprotein that has been reported as a marker of cancer stem cells or cancer-initiating cells in various cancers. However, its contribution to tumorigenesis and differentiation remains to be elucidated. To determine the role of CD133 in colon cancer, we silenced CD133 in human colon cancer cells. Silencing of CD133 results in decreased cell proliferation, survival, migration, invasion, and glucose transport. These effects are mediated by downregulation of the human epidermal growth factor receptor 3 (HER3)/Akt/mTOR signaling pathway, culminating in reduced expression of the glucose transporter GLUT1. We also confirm that the cellular phenotypes of CD133-silenced cells are mediated by GLUT1 downregulation. We conclude that CD133 is a potential tumor initiator that positively regulates GLUT1 expression through modulation of HER3/Akt/mTOR signaling.

EGF Receptor Stalls upon Activation as Evidenced by Complementary Fluorescence Correlation Spectroscopy and Fluorescence Recovery after Photobleaching Measurements

To elucidate the molecular details of the activation-associated clustering of epidermal growth factor receptors (EGFRs), the time course of the mobility and aggregation states of eGFP tagged EGFR in the membranes of Chinese hamster ovary (CHO) cells was assessed by in situ mobility assays. Fluorescence correlation spectroscopy (FCS) was used to probe molecular movements of small ensembles of molecules over short distances and time scales, and to report on the state of aggregation. The diffusion of larger ensembles of molecules over longer distances (and time scales) was investigated by fluorescence recovery after photobleaching (FRAP). Autocorrelation functions could be best fitted by a two-component diffusion model corrected for triplet formation and blinking. The slow, 100–1000 ms component was attributed to membrane localized receptors moving with free Brownian diffusion, whereas the fast, ms component was assigned to cytosolic receptors or their fragments. Upon stimulation with 50 nM EGF, a significant decrease from 0.11 to 0.07 μm²/s in the diffusion coefficient of membrane-localized receptors was observed, followed by recovery to the original value in ~20 min. In contrast, the apparent brightness of diffusing species remained the same. Stripe FRAP experiments yielded a decrease in long-range molecular mobility directly after stimulation, evidenced by an increase in the recovery time of the slow component from 13 to 21.9 s. Our observations are best explained by the transient attachment of ligand-bound EGFRs to immobile or slowly moving structures such as the cytoskeleton or large, previously photobleached receptor aggregates.

Revisiting a controversy: The effect of EGF on EGFR dimer stability

EGFR is a receptor tyrosine kinase that plays a critical role in cell proliferation, differentiation, survival and migration. Its activating ligand, EGF, has long been believed to stabilize the EGFR dimer. Two research studies aimed at quantitative measurements of EGFR dimerization, however, have led to contradicting conclusions and have questioned this view. Given the controversy, here we sought to measure the dimerization of EGFR in the absence and in the presence of saturating EGF concentrations, and to tease out the effect of ligand on dimer stability, using a FRET-based quantitative method. Our measurements show that the dissociation constant is decreased ~150 times due to ligand binding, indicative of significant dimer stabilization. In addition, our measurements demonstrate that EGF binding induces a conformational change in the EGFR dimer.

Therapeutic bacteria to combat cancer; current advances, challenges, and opportunities

Successful treatment of cancer remains a challenge, due to the unique pathophysiology of solid tumors, and the predictable emergence of resistance. Traditional methods for cancer therapy including radiotherapy, chemotherapy, and immunotherapy all have their own limitations. A novel approach is bacteriotherapy, either used alone, or in combination with conventional methods, has shown a positive effect on regression of tumors and inhibition of metastasis. Bacteria-assisted tumor-targeted therapy used as therapeutic/gene/drug delivery vehicles has great promise in the treatment of tumors. The use of bacteria only, or in combination with conventional methods was found to be effective in some experimental models of cancer (tumor regression and increased survival rate). In this article, we reviewed the major advantages, challenges, and prospective directions for combinations of bacteria with conventional methods for tumor therapy.

Clinical development of targeted and immune based anti-cancer therapies

Cancer is currently the second leading cause of death globally and is expected to be responsible for approximately 9.6 million deaths in 2018. With an unprecedented understanding of the molecular pathways that drive the development and progression of human cancers, novel targeted therapies have become an exciting new development for anti-cancer medicine. These targeted therapies, also known as biologic therapies, have become a major modality of medical treatment, by acting to block the growth of cancer cells by specifically targeting molecules required for cell growth and tumorigenesis. Due to their specificity, these new therapies are expected to have better efficacy and limited adverse side effects when compared with other treatment options, including hormonal and cytotoxic therapies. In this review, we explore the clinical development, successes and challenges facing targeted anti-cancer therapies, including both small molecule inhibitors and antibody targeted therapies. Herein, we introduce targeted therapies to epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), human epidermal growth factor receptor 2 (HER2), anaplastic lymphoma kinase (ALK), BRAF, and the inhibitors of the T-cell mediated immune response, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein-1 (PD-1)/ PD-1 ligand (PD-1 L).

Stochasticity and robustness analysis of microRNA-mediated ERK signaling network

MicroRNAs (miRNAs) play a critical role in regulating the signaling network such as the extracellular signal regulated kinase (ERK) pathway. However, the mechanisms of miRNA-mediated posttranscriptional regulations with regard to their impacts on signaling require further investigation from a systematic level. Therefore, we develop a mathematical model by analyzing the precise dynamic mechanisms with a bevy of miRNAs involved in the Ras/Raf/MEK/ERK pathway. A systems-based analysis approach is introduced into this model and the dynamics have been implemented deterministically and stochastically. Our analysis reveals that miRNAs are key participants regulating the gene expression of ERK network, and the cooperative actions of miRNAs are important in keeping the normal biological characteristics and amplification effects of the system. Meanwhile, the appearance of system disorder in the absence of miRNAs suggests that miRNAs may play a role in the pathological processes, such as tumor and inflammation. The sensitivity analysis and the kinetic parameter perturbation show that the binding of receptor (EGFR) and adaptor protein (Shc, Grb2 and Sos) under normal physiological conditions is crucial for the robustness of the whole pathway. In addition, the stochastic dynamic patterns are in a good agreement with the deterministic results, further demonstrating that the variability of the system due to the presence of some stochastic noise is low. All these will be helpful for a deeper understanding of the dynamic mechanism of miRNA-mediated ERK signal network, which might present a rich area of future research with the relevant regulatory roles of miRNAs in cell signaling pathway.

Plasmodium vivax Merozoite Surface Protein 1 Paralog as a Mediator of Parasite Adherence to Reticulocytes

Plasmodium vivax parasites preferentially invade reticulocytes in human beings. P. vivax merozoite surface protein 1 (PvMSP1) and PvMSP1 paralog (PvMSP1P) may have important functions in reticulocyte adherence during invasion. These proteins share similar structures, including the presence of two epidermal growth factor (EGF)-like and glycosylphosphatidylinositol (GPI)-anchored domains at the C terminus. However, there have been no reports concerning the functional activity of PvMSP1P in reticulocyte adherence during P. vivax invasion. In this study, the ability of PvMSP1P-19 to bind to reticulocytes and normocytes was analyzed. The reticulocyte binding activity of PvMSP1P-19 was 4.0-fold higher than its normocyte binding activity. The binding of PvMSP1P-19 to reticulocytes and normocytes was inhibited in a dose-dependent manner by antibodies from immunized rabbits and by antibodies from vivax parasite-infected patients. Consistently, antibodies against PvMSP1P inhibited parasite invasion during short-term in vitro cultivation. Similar to the case for PvDBPII binding activity, PvMSP1P-19 binding activity was reduced in chymotrypsin-treated reticulocytes. However, no significant difference between the binding of PvMSP1P-19 to Duffy-positive and Duffy-negative erythrocytes was found. The minimal binding motif of PvMSP1P-19 was characterized using synthetic peptides. The results showed that the residues at amino acid positions 1791 to 1808 may have an important function in mediating merozoite adherence to reticulocytes. The positively charged residues within the EGF-like domain were shown to constitute a key binding motif. This work presents strong evidence supporting the role of PvMSP1P in host target cell selection and invasion of Duffy-independent pathway in P. vivax Moreover, PvMSP1P-19-specific antibodies may confer protection against P. vivax reinvasion.

Delivery of a Proapoptotic Peptide to EGFR-Positive Cancer Cells by a Cyclic Peptide Mimicking the Dimerization Arm Structure of EGFR

A cyclic decapeptide, CQTPYYMNTC (1), which mimics the dimerization arm of the EGF receptor (EGFR), was previously found to be captured into cells. We have sought to investigate the promising potential of this peptide as an intracellular delivery vehicle directed to EGFR-positive cells. The selectivity of peptide 1 to the EGFR was confirmed by a positive correlation between the expression level of the receptor and the cellular uptake of peptide 1 as shown by siRNA knockdown of the EGFR. The proapoptotic domain (PAD) peptide ([KLAKLAK]₂) has limited use due to a deficiency of cell membrane permeability resulting from cationic sequences and lack of specificity for cancer cells. As a proof-of-concept study, the cellular delivery of the PAD peptide was challenged by conjugation with peptide 1. The cellular uptake of a conjugated peptide 2, which was composed of peptide 1, the PAD peptide, and a linker cleavable with a protease, was evaluated by treatment of an EGFR-positive lung carcinoma cell line, A549. Significant suppression of proliferation by peptide 2 was shown in the results of a cell viability assay. The PAD peptide alone had no effect on the cells. The results suggest that peptide 1 is a promising lead compound as a new intracellular delivery vehicle for therapeutically effective peptides.

Nanoparticle-cell interactions induced apoptosis: a case study with nanoconjugated epidermal growth factor

In addition to the intrinsic toxicity associated with the chemical composition of nanoparticles (NP) and their ligands, biofunctionalized NP can perturb specific cellular processes through NP-cell interactions and induce programmed cell death (apoptosis). In the case of the epidermal growth factor (EGF), nanoconjugation has been shown to enhance the apoptotic efficacy of the ligand, but the critical aspects of the underlying mechanism and its dependence on the NP morphology remain unclear. In this manuscript we characterize the apoptotic efficacy of nanoconjugated EGF as a function of NP size (with sphere diameters in the range 20-80 nm), aspect ratio (A.R., in the range of 4.5 to 8.6), and EGF surface loading in EGFR overexpressing MDA-MB-468 cells. We demonstrate a significant size and morphology dependence in this relatively narrow parameter space with spherical NP with a diameter of approx. 80 nm being much more efficient in inducing apoptosis than smaller spherical NP or rod-shaped NP with comparable EGF loading. The nanoconjugated EGF is found to trigger an EGFR-dependent increase in cytoplasmic reactive oxygen species (ROS) levels but no indications of increased mitochondrial ROS levels or mitochondrial membrane damage are detected at early time points of the apoptosis induction. The increase in cytoplasmic ROS is accompanied by a perturbation of the intracellular glutathione homeostasis, which represents an important check-point for NP-EGF mediated apoptosis. Abrogation of the oxidative stress through the inhibition of EGFR signaling by the EGFR inhibitor AG1478 or addition of antioxidants N-acetyl cysteine (NAC) or tempol, but not trolox, successfully suppressed the apoptotic effect of nanoconjugated EGF. A model to account for the observed morphology dependence of EGF nanoconjugation enhanced apoptosis and the underlying NP-cell interactions is discussed.

EGFRvIII expression triggers a metabolic dependency and therapeutic vulnerability sensitive to autophagy inhibition

Expression of EGFRvIII is frequently observed in glioblastoma and is associated with increased cellular proliferation, enhanced tolerance to metabolic stresses, accelerated tumor growth, therapy resistance and poor prognosis. We observed that expression of EGFRvIII elevates the activation of macroautophagy/autophagy during starvation and hypoxia and explored the underlying mechanism and consequence. Autophagy was inhibited (genetically or pharmacologically) and its consequence for tolerance to metabolic stress and its therapeutic potential in (EGFRvIII+) glioblastoma was assessed in cellular systems, (patient derived) tumor xenopgrafts and glioblastoma patients. Autophagy inhibition abrogated the enhanced proliferation and survival advantage of EGFRvIII+ cells during stress conditions, decreased tumor hypoxia and delayed tumor growth in EGFRvIII+ tumors. These effects can be attributed to the supporting role of autophagy in meeting the high metabolic demand of EGFRvIII+ cells. As hypoxic tumor cells greatly contribute to therapy resistance, autophagy inhibition revokes the radioresistant phenotype of EGFRvIII+ tumors in (patient derived) xenograft tumors. In line with these findings, retrospective analysis of glioblastoma patients indicated that chloroquine treatment improves survival of all glioblastoma patients, but patients with EGFRvIII+ glioblastoma benefited most. Our findings disclose the unique autophagy dependency of EGFRvIII+ glioblastoma as a therapeutic opportunity. Chloroquine treatment may therefore be considered as an additional treatment strategy for glioblastoma patients and can reverse the worse prognosis of patients with EGFRvIII+ glioblastoma.

A novel recombinant anti-epidermal growth factor receptor peptide vaccine capable of active immunization and reduction of tumor volume in a mouse model

Over-expression of epidermal growth factor receptor (EGFR) has been reported in a number of human malignancies. Strong expression of this receptor has been associated with poor survival in many such patients. Active immunizations that elicit antibodies of the desired type could be an appealing alternative to conventional passive immunization. In this regard, a novel recombinant peptide vaccine capable of prophylactic and therapeutic effects was constructed. A novel fusion recombinant peptide base vaccine consisting of L2 domain of murine extra-cellular domain-EGFR and EGFR mimotope (EM-L2) was constructed and its prophylactic and therapeutic effects in a Lewis lung carcinoma mouse (C57/BL6) model evaluated. Constructed recombinant peptide vaccine is capable of reacting with anti-EGFR antibodies. Immunization of mice with EM-L2 peptide resulted in antibody production against EM-L2. The constructed recombinant peptide vaccine reduced tumor growth and increased the survival rate. Designing effective peptide vaccines could be an encouraging strategy in contemporary cancer immunotherapy. Investigating the efficacy of such cancer immunotherapy approaches may open exciting possibilities concerning hyperimmunization, leading to more promising effects on tumor regression and proliferation.

EGFR Ligands Differentially Stabilize Receptor Dimers to Specify Signaling Kinetics

Epidermal growth factor receptor (EGFR) regulates many crucial cellular programs, with seven different activating ligands shaping cell signaling in distinct ways. Using crystallography and other approaches, we show how the EGFR ligands epiregulin (EREG) and epigen (EPGN) stabilize different dimeric conformations of the EGFR extracellular region. As a consequence, EREG or EPGN induce less stable EGFR dimers than EGF-making them partial agonists of EGFR dimerization. Unexpectedly, this weakened dimerization elicits more sustained EGFR signaling than seen with EGF, provoking responses in breast cancer cells associated with differentiation rather than proliferation. Our results reveal how responses to different EGFR ligands are defined by receptor dimerization strength and signaling dynamics. These findings have broad implications for understanding receptor tyrosine kinase (RTK) signaling specificity. Our results also suggest parallels between partial and/or biased agonism in RTKs and G-protein-coupled receptors, as well as new therapeutic opportunities for correcting RTK signaling output.

Preclinical efficacy of Sym004, novel anti-EGFR antibody mixture, in esophageal squamous cell carcinoma cell lines

Epidermal growth factor receptor (EGFR) is a well-validated oncological target molecule for monoclonal antibody therapies and Sym004 is a novel anti-EGFR antibody mixture comprising two recombinant chimeric IgG1 antibodies against non-overlapping epitopes of EGFR. Because EGFR is highly expressed in the majority of esophageal squamous cell carcinomas (ESCCs), we investigated the efficacy of Sym004 in human ESCC cell lines. Forty eight ESCC cell lines were treated with three kinds of anti-EGFR antibodies (Sym004, cetuximab, and panitumumab). Genetic background was investigated by next generation sequencing. The internalization of anti-EGFR antibodies into ESCC cells and inhibition of the EGFR signaling cascade by anti-EGFR antibodies were investigated in vitro. Furthermore, growth inhibition by anti-EGFR antibody treatment was investigated in vitro and in vivo. Sym004 treatments were more effective at inducing EGFR internalization and degradation than the two other anti-EGFR antibodies. Sym004 was more sensitive significantly to cell lines with EGFR gene amplification than those without amplification (P = 0.002). Growth inhibition of Sym004 was greater than in that of cetuximab or panitumumab in vitro and in vivo. These studies showed that Sym004 exhibited antitumor activity in some ESCC cell lines in preclinical settings and warrant a clinical evaluation in patients with ESCC. EGFR amplification is a potential biomarker of response to Sym004.

High Density or Urban Sprawl: What Works Best in Biology?

With new approaches in imaging-from new tools or reagents to processing algorithms-come unique opportunities and challenges to our understanding of biological processes, structures, and dynamics. Although innovations in super-resolution imaging are affording novel perspectives into how molecules structurally associate and localize in response to, or in order to initiate, specific signaling events in the cell, questions arise as to how to interpret these observations in the context of biological function. Just as each neighborhood in a city has its own unique vibe, culture, and indeed density, recent work has shown that membrane receptor behavior and action is governed by their localization and association state. There is tremendous potential in developing strategies for tracking how the populations of these molecular neighborhoods change dynamically.

Piecing it together: Unraveling the elusive structure-function relationship in single-pass membrane receptors

The challenge of crystallizing single-pass plasma membrane receptors has remained an obstacle to understanding the structural mechanisms that connect extracellular ligand binding to cytosolic activation. For example, the complex interplay between receptor oligomerization and conformational dynamics has been, historically, only inferred from static structures of isolated receptor domains. A fundamental challenge in the field of membrane receptor biology, then, has been to integrate experimentally observable dynamics of full-length receptors (e.g. diffusion and conformational flexibility) into static structural models of the disparate domains. In certain receptor families, e.g. the ErbB receptors, structures have led somewhat linearly to a putative model of activation. In other families, e.g. the tumor necrosis factor (TNF) receptors, structures have produced divergent hypothetical mechanisms of activation and transduction. Here, we discuss in detail these and other related receptors, with the goal of illuminating the current challenges and opportunities in building comprehensive models of single-pass receptor activation. The deepening understanding of these receptors has recently been accelerated by new experimental and computational tools that offer orthogonal perspectives on both structure and dynamics. As such, this review aims to contextualize those technological developments as we highlight the elegant and complex conformational communication between receptor domains. This article is part of a Special Issue entitled: Interactions between membrane receptors in cellular membranes edited by Kalina Hristova.

Functional evaluation of fluorescein-labeled derivatives of a peptide inhibitor of the EGF receptor dimerization

A cyclic decapeptide (1, ), which acts on the extracellular region of the EGF receptor, preventing it from dimerizing, has been developed. Peptide 2, which was labeled with fluorescein at the N-terminus of peptide 1, was synthesized based on structure-activity relationship studies. Peptide 2 essentially retained the inhibitory activity of peptide 1 against the receptor autophosphorylation. Confocal microscopy studies revealed that in carcinoma cells, the fluorescence of peptide 2 was localized inside some vesicles. Treatment of intact cells by peptide 1 in combination with peptide 2 decreased the fluorescence intensity significantly compared to treatment with only peptide 2. These results indicate that peptide 2 competes with peptide 1 for binding to the cellular surface. Six derivatives of peptide 2, in which constituent amino acids, with the exception of two cysteines and proline were randomized, were synthesized and used to treat the cells. Peptides 6 and 9 showed the highest fluorescence intensity in cells. From the results of the EGF receptor autophosphorylation assay, these two derivatives were proven to have higher inhibitory activity than peptide 2, which would therefore be a useful delivery peptide and fluorescent probe to find new inhibitors against the EGF receptor. Peptides 6 and 9 are promising leads for EGF receptor inhibitors.

Identifying activating mutations in the EGFR gene: prognostic and therapeutic implications in non-small cell lung cancer

Lung cancer is the leading cause of cancer-related deaths worldwide. Promising new therapies have recently emerged from the development of molecular targeted drugs; particularly promising are those blocking the signal transduction machinery of cancer cells. One of the most widely studied cell signaling pathways is that of EGFR, which leads to uncontrolled cell proliferation, increased cell angiogenesis, and greater cell invasiveness. Activating mutations in the EGFR gene (deletions in exon 19 and mutation L858R in exon 21), first described in 2004, have been detected in approximately 10% of all non-squamous non-small cell lung cancer (NSCLC) patients in Western countries and are the most important predictors of a response to EGFR tyrosine-kinase inhibitors (EGFR-TKIs). Studies of the EGFR-TKIs gefitinib, erlotinib, and afatinib, in comparison with platinum-based regimens, as first-line treatments in chemotherapy-naïve patients have shown that the EGFR-TKIs produce gains in progression-free survival and overall response rates, although only in patients whose tumors harbor activating mutations in the EGFR gene. Clinical trials have also shown EGFR-TKIs to be effective as second- and third-line therapies in advanced NSCLC. Here, we review the main aspects of EGFR pathway activation in NSCLC, underscore the importance of correctly identifying activating mutations in the EGFR gene, and discuss the main outcomes of EGFR-TKI treatment in NSCLC.

Molecular basis for multimerization in the activation of the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is activated by dimerization, but activation also generates higher-order multimers, whose nature and function are poorly understood. We have characterized ligand-induced dimerization and multimerization of EGFR using single-molecule analysis, and show that multimerization can be blocked by mutations in a specific region of Domain IV of the extracellular module. These mutations reduce autophosphorylation of the C-terminal tail of EGFR and attenuate phosphorylation of phosphatidyl inositol 3-kinase, which is recruited by EGFR. The catalytic activity of EGFR is switched on through allosteric activation of one kinase domain by another, and we show that if this is restricted to dimers, then sites in the tail that are proximal to the kinase domain are phosphorylated in only one subunit. We propose a structural model for EGFR multimerization through self-association of ligand-bound dimers, in which the majority of kinase domains are activated cooperatively, thereby boosting tail phosphorylation.

DOI:http://dx.doi.org/10.7554/eLife.14107.001

Determining the geometry of oligomers of the human epidermal growth factor family on cells with <10 nm resolution

There is a limited range of methods available to characterize macromolecular organization in cells on length scales from 5-50 nm. We review methods currently available and show the latest results from a new single-molecule localization-based method, fluorophore localization imaging with photobleaching (FLImP), using the epidermal growth factor (EGF) receptor (EGFR) as an example system. Our measurements show that FLImP is capable of achieving spatial resolution in the order of 6 nm.

Resistance to Therapy

Identification of driver mutations in adenocarcinoma of the lung has revolutionized the treatment of this disease. It is now standard of care to look for activating mutations in epidermal growth factor receptor (EGFR), and translocations in anaplastic lymphoma kinase (ALK) or ROS1 in all newly diagnosed adenocarcinoma of the lung, and in many patients with squamous cell carcinoma as well. Recognition of multiple other lung cancer driver mutations has also expanded treatment options. Targeted treatments of these mutations lead to rapid and prolonged responses, but resistance inevitably develops. Until recently, traditional chemotherapy was the only alternative at that time, but better understanding of resistance mechanisms has lead to additional therapeutic options. These mechanisms of resistance and treatments are the focus of this chapter. Understanding of mechanisms of chemotherapy resistance is touched upon, along with a brief discussion of immune checkpoint inhibitors.

Two-Dimensional Trap for Ultrasensitive Quantification of Transient Protein Interactions

We present an ultrasensitive technique for quantitative protein-protein interaction analysis in a two-dimensional format based on phase-separated, micropatterned membranes. Interactions between proteins captured to lipid probes via an affinity tag trigger partitioning into the liquid-ordered phase, which is readily quantified by fluorescence imaging. Based on a calibration with well-defined low-affinity protein-protein interactions, equilibrium dissociation constants >1 mM were quantified. Direct capturing of proteins from mammalian cell lysates enabled us to detect homo- and heterodimerization of signal transducer and activator of transcription proteins. Using the epidermal growth factor receptor (EGFR) as a model system, quantification of low-affinity interactions between different receptor domains contributing to EGFR dimerization was achieved. By exploitation of specific features of the membrane-based assay, the regulation of EGFR dimerization by lipids was demonstrated.

A tale of the epidermal growth factor receptor: The quest for structural resolution on cells

The challenge of determining the architecture and geometry of oligomers of the epidermal growth factor receptor (EGFR) on the cell surface has been approached using a variety of biochemical and biophysical methods. This review is intended to provide a narrative of how key concepts in the field of EGFR research have evolved over the years, from the origins of the prevalent EGFR signalling dimer hypothesis through to the development and implementation of methods that are now challenging the conventional view. The synergy between X-ray crystallography and cellular fluorescence microscopy has become particularly important, precisely because the results from these two methods diverged and highlighted the complexity of the challenge. We illustrate how developments in super-resolution microscopy are now bridging this gap. Exciting times lie ahead where knowledge of the nature of the complexes can assist with the development of a new generation of anti-cancer drugs.