EGF and NRG induce phosphorylation of HER3/ERBB3 by EGFR using distinct oligomeric mechanisms

Neuregulin-induced HER3 activation drives migration in head and neck squamous cell carcinoma via HER2 and FAK signaling pathways

PURPOSE

To investigate the role of neuregulin (NRG) signaling in promoting head and neck squamous cell carcinoma (HNSCC) migration through HER3-dependent pathways and to assess the therapeutic potential of targeting the NRG/HER3 axis in mitigating perineural invasion.

METHODS

NRG-driven migration was studied using DRG co-culture, wound healing assays, and HER3 inhibition (shRNA, AV-203). The biological function and biochemical effects of the HER3/HER2/FAK axis in response to NRG were analyzed via phosphorylation assays, knockdown, western blotting, and cell staining for protein expression.

RESULTS

NRG promoted directional migration of FaDu and TU138 HNSCC cells through HER3/HER2 and HER3/PI3K interactions. HER3 inhibition (shRNA or AV-203) abolished HER3 phosphorylation, disrupted HER3-HER2 interactions, and suppressed AKT and ERK signaling. Wound healing assays confirmed that NRG enhances migration via HER3 activation. NRG also induced HER3-dependent FAK phosphorylation, and FAK knockdown or inhibition with PF228 significantly reduced NRG-driven migration, highlighting the critical role of HER3-FAK signaling.

CONCLUSION

NRG promotes HNSCC cell migration by activating HER3, forming HER3-HER2 and HER3-FAK complexes, and driving downstream AKT, ERK, and FAK signaling. Targeting the NRG/HER3 axis holds potential as a therapeutic strategy to address perineural invasion and associated clinical challenges in HNC.

Single-molecule localization microscopy as a tool to quantify di/oligomerization of receptor tyrosine kinases and G protein-coupled receptors

Dimerization and oligomerization of membrane receptors, including G protein-coupled receptors and receptor tyrosine kinases, are fundamental for regulating cell signaling and diversifying downstream responses to mediate a range of physiological processes. Receptor di/oligomers play roles in diverse facets of receptor function. Changes in receptor di/oligomers have been implicated in a range of diseases; therefore, better understanding of the specific composition and interactions between receptors in complexes is essential, especially for the development of di/oligomer-specific drugs. Previously, different optical microscopy approaches and proximity-based biophysical assays have been used to demonstrate di/oligomerization of membrane receptors. However, in recent years, single-molecule super-resolution microscopy techniques have allowed researchers to quantify and uncover the precise dynamics and stoichiometry of specific receptor complexes. This allows the organization of membrane protein receptors to be mapped across the plasma membrane to explore the effects of factors such as ligands, effectors, membrane environment, and therapeutic agents. Quantification of receptor complexes is required to better understand the intricate balance of distinct receptor complexes in cells. In this brief review, we provide an overview of single-molecule approaches for the quantification of receptor di/oligomerization. We will discuss the techniques commonly employed to study membrane receptor di/oligomerization and their relative advantages and limitations. SIGNIFICANCE STATEMENT: Receptor di/oligomerization plays an important role in their function. For some receptors, di/oligomerization is essential for functional signaling, whereas for others, it acts as a mechanism to achieve signaling pleiotropy. Aberrant receptor di/oligomerization has been implicated in a wide range of diseases. Single-molecule super-resolution microscopy techniques provide convincing methods to precisely quantify receptor complexes at the plasma membrane. Understanding receptor complex organization in disease models can also influence the targeting of specific monomeric or oligomeric complexes in therapeutic strategies.

PCSK9 Promotes the Malignancy of Triple-negative Breast Cancer Cells by Reducing Cholesterol Levels at the Plasma Membrane to Activate EGFR and HER3

Triple-negative breast cancer (TNBC) is a highly heterogeneous and clinically aggressive disease with the highest mortality rate among all subtypes of breast cancer. To discover new driver genes for metastatic TNBC, this work compares the transcription profiles of MDA-MB-231-GFP cells and 231-GFP-derived lung metastatic cells (4-11). Results reveal that proprotein convertase subtilisin/kexin type 9 (PCSK9) is highly upregulated in 4-11 cells. Knockdown of PCSK9 greatly decreases the tumorigenic and metastatic potential of 4-11 cells, whereas overexpression of PCSK9 significantly enhances tumor maliganancy. Mechanistically, the binding of PCSK9 to the low-density lipoprotein receptor (LDLR) results in decreased LDLR at the plasma membrane, which further decreases cholesterol and lipid raft in the plasma membrane and activates human epidermal growth factor receptor 1 and 3 (EGFR and HER3). Subsequently, phosphorylated EGFR and HER3 activate the Src/ERK/c-Jun to increase the levels of cyclin D3 and vimentin and thereby enhance cell growth and metastasis. Metadata analyses also reveal that TNBC patients with high PCSK9 expression exhibited worse clinical outcomes. Taken together, these findings not only reveal a novel mechanism by which PCSK9 promotes the malignant potential of TNBC but also indicate that PCSK9 is a potential therapeutic target for treating TNBC patients.

Hotspot mutations in HER2 interfaces destabilize structure, causing breast cancer treatment failure

Many HER2-positive breast cancer (BC) patients relapse within a year of trastuzumab or neratinib treatment. We identified specific pathogenic mutations in the dimerization domains II and IV of the HER2 receptor that contribute to treatment resistance. Mutations G309A, S310Y, and P523S induce significant structural alterations, disrupting crucial HER2:HER2 binding pockets. HER3-preferring mutants exhibited increased HER2:HER3 interactions, as confirmed by proximity ligation assay in HER2-low and HER2-high cell lines. G309A, S310Y, and P523S mutations induced a receptor switch, altering downstream signaling from ERK to AKT activation, leading to high insensitivity to trastuzumab or neratinib in cell survival and migration assays, which was further confirmed by bioluminescence imaging of orthotopic tumors expressing the P523S mutation. This study identifies new hotspot mutations in HER2 domains II and IV causing trastuzumab resistance. Notably, cells with either wild-type or the examined dimerization domain mutations retained sensitivity to the FDA-approved HER2 kinase inhibitor, tucatinib.

CRISPR-Cas12a-Assisted DNA Circuit for Nonmicroscopic Detection of Cell Surface Receptor Clustering

Protein-protein interactions (PPIs) on the cell surface have been of great interest due to their high clinical relevance and significance; however, the methods for detecting PPIs heavily rely on microscopic instruments. In this work, we designed a Cas12a-assisted DNA circuit for detecting cell surface receptor clustering events without a dependence on microscopy. This nonmicroscopic approach is based on the proximity principle, where localized protein-protein interactions such as receptor clustering are converted into DNA barcodes. These barcodes can then be identified by Cas12a for signal generation in the bulk. The compatibility of the circuit with Cas12a was first experimentally verified. Several leak reactions were identified and minimized. Lastly, we implemented this design in human breast cancer cell line models to distinguish the different levels of human epidermal growth factor receptor 2 (HER2) homodimers and heterodimers with HER1 and HER3 semiquantitatively without the use of a microscope. Overall, our proposed Cas12a-assisted DNA circuit for detecting cell surface receptor clustering shows the potential for fast screening in diagnostic applications and drug discovery, demonstrating the promising use of enzymatic DNA circuits in biological applications.

Method for Mapping the Membrane Protein Nanoenvironments Using DNA Nanostructures (NanoDeep)

The distribution of proteins at the plasma membrane is not uniform, but rather many proteins localize to dynamic nanodomains. To understand the functional importance of membrane protein nanodomains, it is necessary to be able to map their composition and spatial organization en masse in cell populations. Here, we present the protocol to implement a non-microscopy-based method called NanoDeep, which enables ensemble analysis of membrane protein nanodomains. NanoDeep utilizes DNA nanoassemblies to convert information about membrane protein organization into a DNA sequencing readout. By using NanoDeep, we have previously investigated the Her2 nanoenvironments, an important membrane receptor in cancer. NanoDeep has the potential to provide a new understanding of the effects of protein composition and spatial organization on the regulation of membrane protein function. In this chapter, we describe the NanoDeep protocol as applied to Her2 nanoenvironments.

HER3: Updates and current biology function, targeted therapy and pathologic detecting methods

Being a member of the EGFR tyrosine kinase family, HER3 has been shown to be overexpressed in a number of cancers, including breast cancer (BC). The kinase activity of HER3 is extremely low, and it forms heterodimers with partners, HER2 in particular, that promote biological processes like cell migration, survival, and proliferation by activating downstream carcinogenic signaling pathways. The overexpression of HER3 is also directly linked to tumor invasion, metastasis, and a poor prognosis. Despite the relatively low expression of HER3 compared to EGFR and HER2, a lot of targeted drugs are making their way into clinical trials and seem to have a bright further. This review aims to summarize the relationship between HER3 overexpression, mutations, and carcinogenicity and drug resistance, starting from the unique structure and kinase activity of HER3. Simultaneously, numerous approaches to HER3 targeted therapy are enumerated, and the clinical detection methods for HER3 that are commonly employed in pathology are sorted and contrasted to offer physicians a range of options. We think that a better knowledge of the mechanisms underlying HER3 in tumors and the advancement of targeted HER3 therapy will contribute to an improved prognosis for cancer patients and an increase in the efficacy of anticancer therapies.

HER4 is a high-affinity dimerization partner for all EGFR/HER/ErbB family proteins

Human epidermal growth factor receptors (HER)-also known as EGFR or ErbB receptors-are a subfamily of receptor tyrosine kinases (RTKs) that play crucial roles in cell growth, division, and differentiation. HER4 (ErbB4) is the least studied member of this family, partly because its expression is lower in later stages of development. Recent work has suggested that HER4 can play a role in metastasis by regulating cell migration and invasiveness; however, unlike EGFR and HER2, the precise role that HER4 plays in tumorigenesis is still unresolved. Early work on HER family proteins suggested that there are direct interactions between the four members, but to date, there has been no single study of all four receptors in the same cell line with the same biophysical method. Here, we quantitatively measure the degree of association between HER4 and the other HER family proteins in live cells with a time-resolved fluorescence technique called pulsed interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS). PIE-FCCS is sensitive to the oligomerization state of membrane proteins in live cells, while simultaneously measuring single-cell protein expression levels and diffusion coefficients. Our PIE-FCCS results demonstrate that HER4 interacts directly with all HER family members in the cell plasma membrane. The interaction between HER4 and other HER family members intensified in the presence of a HER4-specific ligand. Our work suggests that HER4 is a preferred dimerization partner for all HER family proteins, even in the absence of ligands.

Neuregulin 1 Signaling Attenuates Tumor Necrosis Factor α-Induced Female Rat Luteal Cell Death

The corpus luteum (CL) is a transient ovarian endocrine structure that maintains pregnancy in primates during the first trimester and in rodents during the entire pregnancy by producing steroid hormone progesterone (P4). CL lifespan, growth, and differentiation are tightly regulated by survival and cell death signals through luteotrophic and luteolytic factors, including the epidermal growth factor (EGF)-like factor family. Neuregulin 1 (NRG1), a member of the EGF family, mediates its effect through ErbB2/3 receptors. However, the functional role of NRG1 in luteal cells (LCs) is unknown. Thus, this study investigated the role of NRG1 and its molecular mechanism of action in rat LC. Our experimental results suggest a strong positive correlation between steroidogenic acute regulatory protein (StAR) and NRG1 expression in mid-CL and serum P4 and estrogen (E2) production. In contrast, there was a decrease in StAR and NRG1 expression and P4 and E2 production with an increase in tumor necrosis factor α (TNFα) expression in regressing CL. Further in vitro studies in LCs showed that the knockdown of endogenous Nrg1 promoted the expression of proinflammatory and proapoptotic factors and decreased prosurvival factor expression. Subsequently, treatment with exogenous TNFα under these experimental conditions profoundly elevated proinflammatory and proapoptotic factors. Further analysis demonstrated that the phosphorylation status of ErbB2/3, PI3K, Ak strain transforming or protein kinase B (Akt), and ErK1/2 was significantly inhibited under these experimental conditions, whereas the treatment of TNFα further inhibited the phosphorylation of ErbB2/3, PI3K, Akt, and ErK1/2. Collectively, these studies provide new insights into the NRG1-mediated immunomodulatory and prosurvival role in LCs, which may maintain the function of CL.

ESM1 facilitates the EGFR/HER3-triggered epithelial-to-mesenchymal transition and progression of gastric cancer via modulating interplay between Akt and angiopoietin-2 signaling

Gastric cancer (GC) poses global challenges due to its difficult early diagnosis and drug resistance, necessitating the identification of early detection markers and understanding of oncogenic pathways for effective GC therapy. Endothelial cell-specific molecule 1 (ESM1), a secreted glycoprotein, is elevated in various cancers, but its role in GC remains controversial. In our study, ESM1 was elevated in GC tissues, and its concentration was correlated with progression and poorer patient prognosis in independent cohorts. Functionally, ESM1 expression promoted proliferation, anoikis resistance, and motility of GC cells, as well as tumor growth in PDOs and in GC xenograft models. Mechanistically, ESM1 expression triggered the epithelial-to-mesenchymal transition (EMT) of GC cells by enhancing epidermal growth factor receptor (EGFR)/human EGFR 3 (HER3) association and activating the EGFR/HER3-Akt pathway. Additionally, angiopoietin-2 (ANGPT2) was found to be highly correlated with ESM1 and interplayed with Akt to induce the EMT and cancer progression. Use of a signal peptide deletion mutant (ESM1-19del) showed that the secreted form of ESM1 is crucial for its protumorigenic effects by activating the EGFR/HER3-Akt/ANGPT2 pathway to promote the EMT. Patients with high levels of both ESM1 and ANGPT2 had the poorest prognoses. Furthermore, therapeutic peptides successfully inhibited ESM1's induction of the aforementioned signals and motility of GC cells. ESM1's oncogenic role in GC involves activating the EGFR/HER3-Akt/ANGPT2 pathway, presenting a potential therapeutic target for GC.

Efficacy and safety of bispecific antibodies vs. immune checkpoint blockade combination therapy in cancer: a real-world comparison

Emerging tumor immunotherapy methods encompass bispecific antibodies (BSABs), immune checkpoint inhibitors (ICIs), and adoptive cell immunotherapy. BSABs belong to the antibody family that can specifically recognize two different antigens or epitopes on the same antigen. These antibodies demonstrate superior clinical efficacy than monoclonal antibodies, indicating their role as a promising tumor immunotherapy option. Immune checkpoints are also important in tumor immunotherapy. Programmed cell death protein-1 (PD-1) is a widely acknowledged immune checkpoint target with effective anti-tumor activity. PD-1 inhibitors have demonstrated notable therapeutic efficacy in treating hematological and solid tumors; however, more than 50% of patients undergoing this treatment exhibit a poor response. However, ICI-based combination therapies (ICI combination therapies) have been demonstrated to synergistically increase anti-tumor effects and immune response rates. In this review, we compare the clinical efficacy and side effects of BSABs and ICI combination therapies in real-world tumor immunotherapy, aiming to provide evidence-based approaches for clinical research and personalized tumor diagnosis and treatment.

SIBP-03, a novel anti-HER3 antibody, exerts antitumor effects and synergizes with EGFR- and HER2-targeted drugs

HER3 (human epidermal growth factor receptor 3) acts through heterodimerization with EGFR (epidermal growth factor receptor) or HER2 to play an essential role in activating phosphoinositide 3-kinase (PI3K) and AKT signaling-a crucial pathway that promotes tumor cell survival. HER3 is a promising target for cancer therapy, and several HER3-directed antibodies have already entered into clinical trials. In this study we characterized a novel anti-HER3 monoclonal antibody, SIBP-03. SIBP-03 (0.01-10 μg/mL) specifically and concentration-dependently blocked both neuregulin (NRG)-dependent and -independent HER3 activation, attenuated HER3-mediated downstream signaling and inhibited cell proliferation. This antitumor activity was dependent, at least in part, on SIBP-03-induced, cell-mediated cytotoxicity and cellular phagocytosis. Importantly, SIBP-03 enhanced the antitumor activity of EGFR- or HER2-targeted drugs (cetuximab or trastuzumab) in vitro and in vivo. The mechanisms underlying this synergy involve increased inhibition of HER3-mediated downstream signaling. Collectively, these results demonstrated that SIBP-03, which is currently undergoing a Phase I clinical trial in China, may offer a new treatment option for patients with cancers harboring activated HER3, particularly as part of a combinational therapeutic strategy.

Structural dynamics of the active HER4 and HER2/HER4 complexes is finely tuned by different growth factors and glycosylation

Human Epidermal growth factor Receptor 4 (HER4 or ERBB4) carries out essential functions in the development and maintenance of the cardiovascular and nervous systems. HER4 activation is regulated by a diverse group of extracellular ligands including the neuregulin (NRG) family and betacellulin (BTC), which promote HER4 homodimerization or heterodimerization with other HER receptors. Important cardiovascular functions of HER4 are exerted via heterodimerization with its close homolog and orphan receptor, HER2. To date structural insights into ligand-mediated HER4 activation have been limited to crystallographic studies of HER4 ectodomain homodimers in complex with NRG1β. Here, we report cryo-EM structures of near full-length HER2/HER4 heterodimers and full-length HER4 homodimers bound to NRG1β and BTC. We show that the structures of the heterodimers bound to either ligand are nearly identical and that in both cases the HER2/HER4 heterodimer interface is less dynamic than those observed in structures of HER2/EGFR and HER2/HER3 heterodimers. In contrast, structures of full-length HER4 homodimers bound to NRG1β and BTC display more large-scale dynamics mirroring states previously reported for EGFR homodimers. Our structures also reveal the presence of multiple glycan modifications within HER4 ectodomains, modeled for the first time in HER receptors, that distinctively contribute to the stabilization of HER4 homodimer interfaces over those of HER2/HER4 heterodimers.

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.

Structural dynamics of the active HER4 and HER2/HER4 complexes is finely tuned by different growth factors and glycosylation

Human Epidermal growth factor Receptor 4 (HER4 or ERBB4) carries out essential functions in the development and maintenance of the cardiovascular and nervous systems. HER4 activation is regulated by a diverse group of extracellular ligands including the neuregulin (NRG) family and betacellulin (BTC), which promote HER4 homodimerization or heterodimerization with other HER receptors. Important cardiovascular functions of HER4 are exerted via heterodimerization with its close homolog and orphan receptor, HER2. To date structural insights into ligand-mediated HER4 activation have been limited to crystallographic studies of HER4 ectodomain homodimers in complex with NRG1β. Here we report cryo-EM structures of near full-length HER2/HER4 heterodimers and full-length HER4 homodimers bound to NRG1β and BTC. We show that the structures of the heterodimers bound to either ligand are nearly identical and that in both cases the HER2/HER4 heterodimer interface is less dynamic than those observed in structures of HER2/EGFR and HER2/HER3 heterodimers. In contrast, structures of full-length HER4 homodimers bound to NRG1β and BTC display more large-scale dynamics mirroring states previously reported for EGFR homodimers. Our structures also reveal the presence of multiple glycan modifications within HER4 ectodomains, modeled for the first time in HER receptors, that distinctively contribute to the stabilization of HER4 homodimer interfaces over those of HER2/HER4 heterodimers.

HER4 and EGFR Activate Cell Signaling in NRG1 Fusion-Driven Cancers: Implications for HER2-HER3-specific Versus Pan-HER Targeting Strategies

INTRODUCTION

NRG1 gene fusions are clinically actionable alterations identified in NSCLC and other tumors. Previous studies have reported that NRG1 fusions signal through HER2 and HER3 but, thus far, strategies targeting HER3 specifically or HER2-HER3 signaling have exhibited modest activity in patients with NSCLC bearing NRG1 fusions. Although NRG1 fusion proteins can bind HER4 in addition to HER3, the contribution of HER4 and other HER family members in NRG1 fusion-positive cancers is not fully understood.

METHODS

We investigated the role of HER4 and EGFR-HER3 signaling in NRG1 fusion-positive cancers using Ba/F3 models engineered to express various HER family members in combination with NRG1 fusions and in vitro and in vivo models of NRG1 fusion-positive cancer.

RESULTS

We determined that NRG1 fusions can stimulate downstream signaling and tumor cell growth through HER4, independent of other HER family members. Moreover, EGFR-HER3 signaling is also activated in cells expressing NRG1 fusions, and inhibition of these receptors is also necessary to effectively inhibit tumor cell growth. We observed that cetuximab, an anti-EGFR antibody, in combination with anti-HER2 antibodies, trastuzumab and pertuzumab, yielded a synergistic effect. Furthermore, pan-HER tyrosine kinase inhibitors were more effective than tyrosine kinase inhibitors with greater specificity for EGFR, EGFR-HER2, or HER2-HER4, although the relative degree of dependence on EGFR or HER4 signaling varied between different NRG1 fusion-positive cancers.

CONCLUSIONS

Our findings indicate that pan-HER inhibition including HER4 and EGFR blockade is more effective than selectively targeting HER3 or HER2-HER3 in NRG1 fusion-positive cancers.

ULK1 forms distinct oligomeric states and nanoscopic structures during autophagy initiation

Autophagy induction involves extensive molecular and membrane reorganization. Despite substantial progress, the mechanism underlying autophagy initiation remains poorly understood. Here, we used quantitative photoactivated localization microscopy with single-molecule sensitivity to analyze the nanoscopic distribution of endogenous ULK1, the kinase that triggers autophagy. Under amino acid starvation, ULK1 formed large clusters containing up to 161 molecules at the endoplasmic reticulum. Cross-correlation analysis revealed that ULK1 clusters engaging in autophagosome formation require 30 or more molecules. The ULK1 structures with more than the threshold number contained varying levels of Atg13, Atg14, Atg16, LC3B, GEC1, and WIPI2. We found that ULK1 activity is dispensable for the initial clustering of ULK1, but necessary for the subsequent expansion of the clusters, which involves interaction with Atg14, Atg16, and LC3B and relies on Vps34 activity. This quantitative analysis at the single-molecule level has provided unprecedented insights into the behavior of ULK1 during autophagy initiation.

Pathogenic HER3 dimerization domain mutations create a structural bias towards un-conventional EGFR-HER3 signalling axis in breast cancer

Among the EGFR family of receptors, HER3 is considered as a pseudo-kinase which primarily interacts with HER2 in presence of heregulin-1β. We identified two hotspot mutations i.e. G284R and D297Y and one double mutant HER2-S310F/HER3-G284R in breast cancer patients. Long term MDS (7.5 μs) revealed that HER3-D297Y and HER2-S310F:HER3-G284R do not allow the interaction with HER2 as these mutations cause dramatic conformational changes in its flanking regions. This results in formation of an unstable HER2-WT:HER3-D297Y heterodimer, thereby abrogating the downstream signalling by AKT. We found that His228 and Ser300 of HER3-D297Y form stable interactions with Glu245 and Tyr270 of EGFR-WT, in the presence of either EGF or heregulin-1β. Applying TRIM-ing mediated direct knockdown of endogenous EGFR protein, specificity of the unconventional EGFR:HER3-D297Y interaction was validated. Due to this unusual ligand mediated interaction, cancer cells were found susceptible to EGFR targeted therapeutics i.e. Gefitinib and Erlotinib. Further, in TCGA analysis, BC patients harbouring HER3-D297Y mutation showed increased p-EGFR levels as compared to the patients harbouring HER3-WT and HER3-G284R mutations. For the first time, this comprehensive study showed the importance of specific hotspot mutations in HER3 dimerization domain can defy the Trastuzumab therapy, rather cells become susceptible to the EGFR inhibitors.

Cisplatin-induced increase in heregulin 1 and its attenuation by the monoclonal ErbB3 antibody seribantumab in bladder cancer

Cisplatin-based combination chemotherapy is the foundation for treatment of advanced bladder cancer (BlCa), but many patients develop chemoresistance mediated by increased Akt and ERK phosphorylation. However, the mechanism by which cisplatin induces this increase has not been elucidated. Among six patient-derived xenograft (PDX) models of BlCa, we observed that the cisplatin-resistant BL0269 express high epidermal growth factor receptor, ErbB2/HER2 and ErbB3/HER3. Cisplatin treatment transiently increased phospho-ErbB3 (Y1328), phospho-ERK (T202/Y204) and phospho-Akt (S473), and analysis of radical cystectomy tissues from patients with BlCa showed correlation between ErbB3 and ERK phosphorylation, likely due to the activation of ERK via the ErbB3 pathway. In vitro analysis revealed a role for the ErbB3 ligand heregulin1-β1 (HRG1/NRG1), which is higher in chemoresistant lines compared to cisplatin-sensitive cells. Additionally, cisplatin treatment, both in PDX and cell models, increased HRG1 levels. The monoclonal antibody seribantumab, that obstructs ErbB3 ligand-binding, suppressed HRG1-induced ErbB3, Akt and ERK phosphorylation. Seribantumab also prevented tumor growth in both the chemosensitive BL0440 and chemoresistant BL0269 models. Our data demonstrate that cisplatin-associated increases in Akt and ERK phosphorylation is mediated by an elevation in HRG1, suggesting that inhibition of ErbB3 phosphorylation may be a useful therapeutic strategy in BlCa with high phospho-ErbB3 and HRG1 levels.

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.

ERBB3 mediates the PI3K/AKT/mTOR pathway to alter the epithelial‑mesenchymal transition in cervical cancer and predict immunity filtration outcome

Cervical cancer is the fourth most common cancer among women worldwide, and the prognosis of advanced/recurrent cervical cancer remains poor. Metastasis and invasion of this type of cancer are closely associated with the tumor microenvironment. Studying the complex interactions between tumor progression and immune cells or stromal cells can provide new insights into treatment for patients with aggressive tumor, recurrence and drug resistance. In the present study, a bioinformatics method (Gene Expression Profiling Interactive Analysis, differentially expressed genes, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, protein-protein interactions and survival analysis) was used to explore the mRNA and protein level discrepancy gene signature of ERBB3 via the PI3K/AKT/mTOR pathway from the speculation in immuno-oncology and experimental verification of different cervical cancer cell lines. The high expression of ERBB3 in cervical cancer tissues (especially HPV-positive and adenocarcinoma-related) promoted the activation of the PI3K/AKT/mTOR pathway. The increased expression of MMP9 changed the macrophage infiltration in the tumor microenvironment and affected prognosis of patients with cervical cancer. In conclusion, the present study identified 14 EMT-related genes and 30 genes involved in the PI3K/AKT/mTOR pathway in cervical cancer, and they might provide novel clues for future treatment. The MMP family may be a notable factor associated with tumor cells and immune cells.

Cryo-electron Microscopic Analysis of Single-Pass Transmembrane Receptors

Single-pass transmembrane receptors (SPTMRs) represent a diverse group of integral membrane proteins that are involved in many essential cellular processes, including signal transduction, cell adhesion, and transmembrane transport of materials. Dysregulation of the SPTMRs is linked with many human diseases. Despite extensive efforts in past decades, the mechanisms of action of the SPTMRs remain incompletely understood. One major hurdle is the lack of structures of the full-length SPTMRs in different functional states. Such structural information is difficult to obtain by traditional structural biology methods such as X-ray crystallography and nuclear magnetic resonance (NMR). The recent rapid development of single-particle cryo-electron microscopy (cryo-EM) has led to an exponential surge in the number of high-resolution structures of integral membrane proteins, including SPTMRs. Cryo-EM structures of SPTMRs solved in the past few years have tremendously improved our understanding of how SPTMRs function. In this review, we will highlight these progresses in the structural studies of SPTMRs by single-particle cryo-EM, analyze important structural details of each protein involved, and discuss their implications on the underlying mechanisms. Finally, we also briefly discuss remaining challenges and exciting opportunities in the field.

Neuregulin-1 signaling regulates cytokines and chemokines expression and secretion in granulosa cell

BACKGROUND

Granulosa cells (GCs) are multilayered somatic cells within the follicle that provide physical support and microenvironment for the developing oocyte. In recent years, the role of Neuregulin-1 (NRG1), a member of the EGF-like factor family, has received considerable attention due to its neurodevelopmental and cardiac function. However, the exact physiological role of NRG1 in GC is mainly unknown. In order to confirm that NRG1 plays a regulatory role in rat GC functions, endogenous NRG1-knockdown studies were carried out in GCs using RNA interference methodology.

RESULTS

Knockdown of NRG1 in GCs resulted in the enhanced expression and secretion of the cytokines and chemokines. In addition, the phosphorylation of PI3K/Akt/ERK1/2 was significantly low in GCs under these experimental conditions. Moreover, in vitro experimental studies suggest that tumor necrosis factor-α (TNFα) treatment causes the physical destruction of GCs by activating caspase-3/7 activity. In contrast, exogenous NRG1 co-treatment of GCs delayed the onset of TNFα-induced apoptosis and inhibited the activation of caspase-3/7 activity. Furthermore, current experimental studies suggest that gonadotropins promote differential expression of NRG1 and ErbB3 receptors in GCs of the antral follicle. Interestingly, NRG1 and ErbB3 were intensely co-localized in the mural and cumulus GCs and cumulus-oocyte complex of pre-ovulatory follicles in the estrus stage.

CONCLUSIONS

The present studies suggest that gonadotropins-dependent NRG1-signaling in GCs may require the balance of the cytokines and chemokines expression and secretion, ultimately which may be supporting the follicular maturation and oocyte competence for ovulation and preventing follicular atresia.

ErbB3-Targeting Oncolytic Adenovirus Causes Potent Tumor Suppression by Induction of Apoptosis in Cancer Cells

Cancer is a multifactorial and deadly disease. Despite major advancements in cancer therapy in the last two decades, cancer incidence is on the rise and disease prognosis still remains poor. Furthermore, molecular mechanisms of cancer invasiveness, metastasis, and drug resistance remain largely elusive. Targeted cancer therapy involving the silencing of specific cancer-enriched proteins by small interfering RNA (siRNA) offers a powerful tool. However, its application in clinic is limited by the short half-life of siRNA and warrants the development of efficient and stable siRNA delivery systems. Oncolytic adenovirus-mediated therapy offers an attractive alternative to the chemical drugs that often suffer from innate and acquired drug resistance. In continuation to our reports on the development of oncolytic adenovirus-mediated delivery of shRNA, we report here the replication-incompetent (dAd/shErbB3) and replication-competent (oAd/shErbB3) oncolytic adenovirus systems that caused efficient and persistent targeting of ErbB3. We demonstrate that the E1A coded by oAd/shErbB, in contrast to dAd/shErbB, caused downregulation of ErbB2 and ErbB3, yielding stronger downregulation of the ErbB3-oncogenic signaling axis in in vitro models of lung and breast cancer. These results were validated by in vivo antitumor efficacy of dAd/shErbB3 and oAd/shErbB3.

Zenocutuzumab, a HER2xHER3 Bispecific Antibody, Is Effective Therapy for Tumors Driven by NRG1 Gene Rearrangements

NRG1 rearrangements are recurrent oncogenic drivers in solid tumors. NRG1 binds to HER3, leading to heterodimerization with other HER/ERBB kinases, increased downstream signaling, and tumorigenesis. Targeting ERBBs, therefore, represents a therapeutic strategy for these cancers. We investigated zenocutuzumab (Zeno; MCLA-128), an antibody-dependent cellular cytotoxicity-enhanced anti-HER2xHER3 bispecific antibody, in NRG1 fusion-positive isogenic and patient-derived cell lines and xenograft models. Zeno inhibited HER3 and AKT phosphorylation, induced expression of apoptosis markers, and inhibited growth. Three patients with chemotherapy-resistant NRG1 fusion-positive metastatic cancer were treated with Zeno. Two patients with ATP1B1-NRG1-positive pancreatic cancer achieved rapid symptomatic, biomarker, and radiographic responses and remained on treatment for over 12 months. A patient with CD74-NRG1-positive non-small cell lung cancer who had progressed on six prior lines of systemic therapy, including afatinib, responded rapidly to treatment with a partial response. Targeting HER2 and HER3 simultaneously with Zeno is a novel therapeutic paradigm for patients with NRG1 fusion-positive cancers.

SIGNIFICANCE

NRG1 rearrangements encode chimeric ligands that activate the ERBB receptor tyrosine kinase family. Here we show that targeting HER2 and HER3 simultaneously with the bispecific antibody Zeno leads to durable clinical responses in patients with NRG1 fusion-positive cancers and is thus an effective therapeutic strategy. This article is highlighted in the In This Issue feature, p. 1171.

It Takes More than Two to Tango: Complex, Hierarchal, and Membrane-Modulated Interactions in the Regulation of Receptor Tyrosine Kinases

The search for an understanding of how cell fate and motility are regulated is not a purely scientific undertaking, but it can also lead to rationally designed therapies against cancer. The discovery of tyrosine kinases about half a century ago, the subsequent characterization of certain transmembrane receptors harboring tyrosine kinase activity, and their connection to the development of human cancer ushered in a new age with the hope of finding a treatment for malignant diseases in the foreseeable future. However, painstaking efforts were required to uncover the principles of how these receptors with intrinsic tyrosine kinase activity are regulated. Developments in molecular and structural biology and biophysical approaches paved the way towards better understanding of these pathways. Discoveries in the past twenty years first resulted in the formulation of textbook dogmas, such as dimerization-driven receptor association, which were followed by fine-tuning the model. In this review, the role of molecular interactions taking place during the activation of receptor tyrosine kinases, with special attention to the epidermal growth factor receptor family, will be discussed. The fact that these receptors are anchored in the membrane provides ample opportunities for modulatory lipid-protein interactions that will be considered in detail in the second part of the manuscript. Although qualitative and quantitative alterations in lipids in cancer are not sufficient in their own right to drive the malignant transformation, they both contribute to tumor formation and also provide ways to treat cancer. The review will be concluded with a summary of these medical aspects of lipid-protein interactions.

Origin of diverse phosphorylation patterns in the ERBB system

Intercellular signals induce various cellular responses, including growth, proliferation, and differentiation, via the dynamic processes of signal transduction pathways. For cell fate decisions, ligand-binding induces the phosphorylation of ERBB receptors, which in turn activate downstream molecules. The ERBB family includes four subtypes, which diverged through two gene duplications from a common ancestor. Differences in the expression patterns of the subtypes have been reported between different organs in the human body. However, how these different expression properties influence the diverse phosphorylation levels of ERBB proteins is not well understood. Here we study the origin of the phosphorylation responses by experimental and mathematical analyses. The experimental measurements clarified that the phosphorylation levels heavily depend on the ERBB expression profiles. We developed a mathematical model consisting of the four subtypes as monomers, homodimers, and heterodimers and estimated the rate constants governing the phosphorylation responses from the experimental data. To understand the origin of the diversity, we analyzed the effects of the expression levels and reaction rates of the ERBB subtypes on the diversity. The difference in phosphorylation rates between ERBB subtypes showed a much greater contribution to the diversity than did the dimerization rates. This result implies that divergent evolution in phosphorylation reactions rather than in dimerization reactions after whole genome duplications was essential for increasing the diversity of the phosphorylation responses.

Emerging immunological strategies: recent advances and future directions

Immunotherapy plays a compelling role in cancer treatment and has already made remarkable progress. However, many patients receiving immune checkpoint inhibitors fail to achieve clinical benefits, and the response rates vary among tumor types. New approaches that promote anti-tumor immunity have recently been developed, such as small molecules, bispecific antibodies, chimeric antigen receptor T cell products, and cancer vaccines. Small molecule drugs include agonists and inhibitors that can reach the intracellular or extracellular targets of immune cells participating in innate or adaptive immune pathways. Bispecific antibodies, which bind two different antigens or one antigen with two different epitopes, are of great interest. Chimeric antigen receptor T cell products and cancer vaccines have also been investigated. This review explores the recent progress and challenges of different forms of immunotherapy agents and provides an insight into future immunotherapeutic strategies.

EGFR transactivates RON to drive oncogenic crosstalk

Crosstalk between different receptor tyrosine kinases (RTKs) is thought to drive oncogenic signaling and allow therapeutic escape. EGFR and RON are two such RTKs from different subfamilies, which engage in crosstalk through unknown mechanisms. We combined high-resolution imaging with biochemical and mutational studies to ask how EGFR and RON communicate. EGF stimulation promotes EGFR-dependent phosphorylation of RON, but ligand stimulation of RON does not trigger EGFR phosphorylation – arguing that crosstalk is unidirectional. Nanoscale imaging reveals association of EGFR and RON in common plasma membrane microdomains. Two-color single particle tracking captured formation of complexes between RON and EGF-bound EGFR. Our results further show that RON is a substrate for EGFR kinase, and that transactivation of RON requires formation of a signaling competent EGFR dimer. These results support a role for direct EGFR/RON interactions in propagating crosstalk, such that EGF-stimulated EGFR phosphorylates RON to activate RON-directed signaling.

Efficient Cross-Correlation Filtering of One- and Two-Color Single Molecule Localization Microscopy Data

Single molecule localization microscopy has become a prominent technique to quantitatively study biological processes below the optical diffraction limit. By fitting the intensity profile of single sparsely activated fluorophores, which are often attached to a specific biomolecule within a cell, the locations of all imaged fluorophores are obtained with ∼20 nm resolution in the form of a coordinate table. While rendered super-resolution images reveal structural features of intracellular structures below the optical diffraction limit, the ability to further analyze the molecular coordinates presents opportunities to gain additional quantitative insights into the spatial distribution of a biomolecule of interest. For instance, pair-correlation or radial distribution functions are employed as a measure of clustering, and cross-correlation analysis reveals the colocalization of two biomolecules in two-color SMLM data. Here, we present an efficient filtering method for SMLM data sets based on pair- or cross-correlation to isolate localizations that are clustered or appear in proximity to a second set of localizations in two-color SMLM data. In this way, clustered or colocalized localizations can be separately rendered and analyzed to compare other molecular properties to the remaining localizations, such as their oligomeric state or mobility in live cell experiments. Current matrix-based cross-correlation analyses of large data sets quickly reach the limitations of computer memory due to the space complexity of constructing the distance matrices. Our approach leverages k-dimensional trees to efficiently perform range searches, which dramatically reduces memory needs and the time for the analysis. We demonstrate the versatile applications of this method with simulated data sets as well as examples of two-color SMLM data. The provided MATLAB code and its description can be integrated into existing localization analysis packages and provides a useful resource to analyze SMLM data with new detail.

Neu Perspectives, Therapies, and Challenges for Metastatic HER2-Positive Breast Cancer

Even though gene amplification or protein overexpression occurs in approximately one-fifth of all breast cancers, the discovery of HER2 has, nevertheless, had profound implications for the disease. Indeed, the characterization of the receptor resulted in a number of significant advances. Structurally, unique features provided avenues for the development of numerous compounds with target-specificity; molecularly, biological constructs revealed a highly complex, internal signal transduction pathway with regulatory effects on tumor proliferation, survival, and perhaps, even resistance; and clinically, disease outcomes manifested its predictive and prognostic value. Yet despite the receptor’s utility, the beneficial effects are diminished by tumor recurrence after neo- or adjuvant therapy as well as losses resulting from the inability to cure patients with metastatic disease. What these observations suggest is that while tumor response may be partially linked to uncoupling cell surface message reception and nuclear gene expression, as well as recruitment of the innate immune system, disease progression and/or resistance may involve a reprogrammable signaling mainframe that elicits alternative growth and survival signals. This review attempts to meld current perceptions related to HER2-positive metastatic breast cancer with particular attention to current biological insights and therapeutic challenges.

Oncogenic switch and single-agent MET inhibitor sensitivity in a subset of EGFR-mutant lung cancer

[Figure: see text].

Cancer-associated mutations in the p85α N-terminal SH2 domain activate a spectrum of receptor tyrosine kinases

Phosphoinositide 3-kinase activation typically occurs following stimulation by upstream receptor tyrosine kinases (RTKs), which alleviate p110α inhibition by p85α. p85α and p110α driver mutations have been reported to activate p110α by disrupting the inhibitory interface between p85α and p110α. This study revealed that driver mutations in the p85α N-terminal SH2 domain can enhance p110α activity by inducing the activation of multiple RTKs. Furthermore, combination treatment with RTK and AKT inhibitors provides synergistic therapeutic efficacy. This previously uncharacterized oncogenic mechanism presents the exploitable vulnerability of a class of p85α mutant tumors.

The phosphoinositide 3-kinase regulatory subunit p85α is a key regulator of kinase signaling and is frequently mutated in cancers. In the present study, we showed that in addition to weakening the inhibitory interaction between p85α and p110α, a group of driver mutations in the p85α N-terminal SH2 domain activated EGFR, HER2, HER3, c-Met, and IGF-1R in a p110α-independent manner. Cancer cells expressing these mutations exhibited the activation of p110α and the AKT pathway. Interestingly, the activation of EGFR, HER2, and c-Met was attributed to the ability of driver mutations to inhibit HER3 ubiquitination and degradation. The resulting increase in HER3 protein levels promoted its heterodimerization with EGFR, HER2, and c-Met, as well as the allosteric activation of these dimerized partners; however, HER3 silencing abolished this transactivation. Accordingly, inhibitors of either AKT or the HER family reduced the oncogenicity of driver mutations. The combination of these inhibitors resulted in marked synergy. Taken together, our findings provide mechanistic insights and suggest therapeutic strategies targeting a class of recurrent p85α mutations.

MicroRNAs in blood act as biomarkers of colorectal cancer and indicate potential therapeutic targets

Association studies have linked alterations of blood-derived microRNAs (miRNAs) with colorectal cancer (CRC). Here, we performed a microarray-based comparison of the profiles of 2549 miRNAs in 80 blood samples from healthy donors and patients with colorectal adenomas, colorectal diverticulitis and CRC at different stages. Confirmation by quantitative real-time PCR (RT-PCR) was complemented by validation of identified molecules in another 36 blood samples. No variations in miRNA levels were observed in samples from patients with colorectal adenomas and diverticulitis or from healthy donors. However, there were 179 CRC-associated miRNAs of differential abundance compared to healthy controls. Only three - miR-1225-5p, miR-1207-5p and miR-4459 - exhibited increased levels at all CRC stages. Most deregulated miRNAs (128/179, 71%) specifically predicted metastatic CRC. Pathway analysis found several cancer-related pathways to which the miRNAs contribute in various ways. In conclusion, miRNA levels in blood vary throughout CRC progression and affect cellular functions relevant to haematogenous CRC progression and dissemination. The identified biomarker and therapeutic candidates require further confirmation of their clinical relevance.

NOTCH1 signaling promotes protein stability of HER3 through the AKT pathway in squamous cell carcinoma of head and neck

Epidermal growth factor receptor (EGFR) remains the sole druggable molecular target other than the PD1/PD-L1 pathway with meaningful clinical benefit in squamous cell carcinoma of head and neck (SCCHN). Human epidermal growth factor receptor 3 (HER3) confers the resistance to EGFR-targeted treatment in SCCHN. Thus, it is essential to determine the distribution and regulatory mechanisms of HER3 in SCCHN. We explored the prevalence of HER3 expression and its distribution within SCCHN by immunohistochemical staining and clinicopathological correlations were analyzed. The regulatory mechanism of HER3 expression was then dissected in vitro, using RT-PCR, Western blotting, and immunoprecipitation in a set of SCCHN cell lines. Subsequent in vivo validation in the murine model was also performed. We found that concomitant high expression of HER3 and its ligand NRG1 in SCCHN is associated with the increased presence of regional lymphatic metastasis and the majority of HER3 is located on the differentiated tumor cells. Further investigation revealed that HER3 is under positive control of NOTCH1 through transcriptional activation and inhibition of protein degradation through the polyubiquitination machinery via AKT pathway and USP8 deubiquitinating enzyme. In addition, loss of function of NOTCH1 suppresses HER3 expression through increased phosphorylation of serine 473 of AKT in SCCHN cells, and promotes the aggressiveness of the tumor cells. These data indicated that the level of HER3 is regulated by NOTCH1 in SCCHN both transcriptionally and post-translationally, and NOTCH1 is in a higher hierarchy in the regulatory system of the AKT pathway. Since NOTCH1 is inactivated in approximately 10% of SCCHN cases and this aberration strongly impacts the AKT pathway and diminishes HER3, exclusion of patients with NOTCH1-inactivated SCCHN may be beneficial for future clinical trials of HER3-targeting antibodies.

A Phase I, First-in-Human Study of GSK2849330, an Anti-HER3 Monoclonal Antibody, in HER3-Expressing Solid Tumors

BACKGROUND

GSK2849330, an anti-HER3 monoclonal antibody that blocks HER3/Neuregulin 1 (NRG1) signaling in cancer cells, is engineered for enhanced antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. This phase I, first-in-human, open-label study assessed the safety, pharmacokinetics (PK), pharmacodynamics, and preliminary activity of GSK2849330 in patients with HER3-expressing advanced solid tumors.

PATIENTS AND METHODS

Patients with various tumor types were prospectively selected for HER3 expression by immunohistochemistry; a subset was also screened for NRG1 mRNA expression. In the dose-escalation phase, patients received GSK2849330 1.4-30 mg/kg every 2 weeks, or 3 mg/kg or 30 mg/kg weekly, intravenously (IV). In the dose-expansion phase, patients received 30 mg/kg GSK2849330 IV weekly.

RESULTS

Twenty-nine patients with HER3-expressing cancers, of whom two expressed NRG1, received GSK2849330 (dose escalation: n = 18, dose expansion: n = 11). GSK2849330 was well tolerated. No dose-limiting toxicities were observed. The highest dose, of 30 mg/kg weekly, expected to provide full target engagement, was selected for dose expansion. Treatment-emergent adverse events (AEs) were mostly grade 1 or 2. The most common AEs were diarrhea (66%), fatigue (62%), and decreased appetite (31%). Dose-proportional plasma exposures were achieved, with evidence of HER3 inhibition in paired tissue biopsies. Of 29 patients, only 1 confirmed partial response, lasting 19 months, was noted in a patient with CD74-NRG1-rearranged non-small cell lung cancer (NSCLC).

CONCLUSION

GSK2849330 demonstrated a favorable safety profile, dose-proportional PK, and evidence of target engagement, but limited antitumor activity in HER3-expressing cancers. The exceptional response seen in a patient with CD74-NRG1-rearranged NSCLC suggests further exploration in NRG1-fusion-positive cancers.

IMPLICATIONS FOR PRACTICE

This first-in-human study confirms that GSK2849330 is well tolerated. Importantly, across a variety of HER3-expressing advanced tumors, prospective selection by HER3/NRG1 expression alone was insufficient to identify patients who could benefit from treatment with this antibody-dependent cell-mediated cytotoxicity- and complement-dependent cytotoxicity-enhanced anti-HER3 antibody. The only confirmed durable response achieved was in a patient with CD74-NRG1-rearranged lung cancer. This highlights the potential utility of screening for NRG1 fusions prospectively across tumor types to enrich potential responders to anti-HER3 agents in ongoing trials.

Growth factor-dependent ErbB vesicular dynamics couple receptor signaling to spatially and functionally distinct Erk pools

Growth factor-dependent vesicular dynamics allow cells to regulate the spatial distribution of growth factor receptors and thereby their coupling to downstream signaling effectors that guide cellular responses. We found that the ErbB ligands epidermal growth factor (EGF) and heregulin (HRG) generated distinct spatiotemporal patterns of cognate receptor activities to activate distinct subcellular pools of the extracellular signal-regulated kinase (Erk). Sustained plasma membrane activity of the receptor tyrosine kinases ErbB2/ErbB3 signaled to Erk complexed with the scaffold protein KSR to promote promigratory EphA2 phosphorylation and cellular motility upon HRG stimulation. In contrast, receptor-saturating EGF stimuli caused proliferation-inducing transient activation of cytoplasmic Erk due to the rapid internalization of EGF receptors (EGFR or ErbB1) toward endosomes. Paradoxically, promigratory signaling mediated by Erk complexed to KSR was sustained at low EGF concentrations by vesicular recycling that maintained steady-state amounts of active, phosphorylated EGFR at the plasma membrane. Thus, the effect of ligand identity and concentration on determining ErbB vesicular dynamics constitutes a mechanism by which cells can transduce growth factor composition through spatially distinct Erk pools to enable functionally diverse cellular responses.

MEK Inhibition Reverses Aberrant Signaling in Melanoma Cells through Reorganization of NRas and BRAF in Self Nanoclusters

Hotspot mutations of the oncogenes BRAF and NRas are the most common genetic alterations in cutaneous melanoma. Still, the nanoscale organization and signal coupling of these proteins remain incompletely understood, particularly upon expression of oncogenic NRas mutants. Here we employed single-molecule localization microscopy to study the nanoscale organization of NRas and BRAF at the plasma membrane (PM) of melanoma cells. NRas and BRAF resided in self-clusters that did not associate well in resting cells. In EGF-activated cells, NRas clusters became more diffused while overall protein levels at the PM increased; thus allowing enhanced association of NRas and BRAF and downstream signaling. In multiple melanoma cell lines, mutant NRas resided in more pronounced self-clusters relative to wild-type (WT) NRas yet associated more with the clustered and more abundant BRAF. In cells resistant to trametinib, a clinical MEK inhibitor (MEKi), a similar coclustering of NRas and BRAF was observed upon EGF activation. Strikingly, treatment of cells expressing mutant NRas with trametinib reversed the effect of mutant NRas expression by restoring the nonoverlapping self-clusters of NRas and BRAF and by reducing their PM levels and elevated pERK levels caused by mutant NRas. Our results indicate a new mechanism for signal regulation of NRas in melanoma through its nanoscale dynamic organization and a new mechanism for MEKi function in melanoma cells carrying NRas mutations but lacking MEK mutations. SIGNIFICANCE: Nanoscale dynamic organization of WT and mutant NRas relative to BRAF serves as a regulatory mechanism for NRas signaling and may be a viable therapeutic target for its sensitivity to MEKi.

Expression and purification of active human kinases using Pichia pastoris as a general-purpose host

BACKGROUND

The heterologous expression of human kinases in good purity and in a monomeric, soluble and active form can be challenging. Most of the reported successful attempts are carried out in insect cells as a host. The use of E. coli for expression is limited to a few kinases and usually is facilitated by large solubility tags that can limit biophysical studies and affect protein-protein interactions. In this report, we evaluate the methylotrophic yeast Pichia pastoris (P. pastoris) as a general-purpose host for expression of human kinases.

METHODS

Six diverse kinases were chosen due to their therapeutic importance in human cancers. Tested proteins include serine/threonine kinases cyclin-dependent kinases 4 and 6 (CDK4 and 6) and aurora kinase A (AurKA), receptor tyrosine kinase erbB-2 (HER2), and dual specificity kinase mitogen-activated protein kinase kinase 3 (MKK3b). Noting that positively charged kinases expressed with higher yield, we sought to improve expression of two challenging targets, CDK6 and HER2, by fusing the highly basic, N-terminal domain of the secreted tyrosine-protein kinase VLK. The standard expression procedure for P. pastoris was adopted, followed by purification using affinity chromatography. Purity and activity of the proteins were confirmed and compared to published values.

RESULTS

Some kinases were purified with good yield and purity and with comparable activity to commercially available versions. Addition of the VLK domain improved expression and decreased aggregation of CDK6 and HER2.

Membrane therapy using DHA suppresses epidermal growth factor receptor signaling by disrupting nanocluster formation

Epidermal growth factor receptor (EGFR) signaling drives the formation of many types of cancer, including colon cancer. Docosahexaenoic acid (DHA, 22∶6Δ4,7,10,13,16,19), a chemoprotective long-chain n-3 polyunsaturated fatty acid suppresses EGFR signaling. However, the mechanism underlying this phenotype remains unclear. Therefore, we used super-resolution microscopy techniques to investigate the mechanistic link between EGFR function and DHA-induced alterations to plasma membrane nanodomains. Using isogenic in vitro (YAMC and IMCE mouse colonic cell lines) and in vivo (Drosophila, wild type and Fat-1 mice) models, cellular DHA enrichment via therapeutic nanoparticle delivery, endogenous synthesis, or dietary supplementation reduced EGFR-mediated cell proliferation and downstream Ras/ERK signaling. Phospholipid incorporation of DHA reduced membrane rigidity and the size of EGFR nanoclusters. Similarly, pharmacological reduction of plasma membrane phosphatidic acid (PA), phosphatidylinositol-4,5-bisphosphate (PIP2) or cholesterol was associated with a decrease in EGFR nanocluster size. Furthermore, in DHA-treated cells only the addition of cholesterol, unlike PA or PIP2, restored EGFR nanoscale clustering. These findings reveal that DHA reduces EGFR signaling in part by reshaping EGFR proteolipid nanodomains, supporting the feasibility of using membrane therapy, i.e., dietary/drug-related strategies to target plasma membrane organization, to reduce EGFR signaling and cancer risk.

Neuregulin Signaling in the Tumor Microenvironment

Neuregulins, members of the largest subclass of growth factors of the epidermal growth factor family, mediate a myriad of cellular functions including survival, proliferation, and differentiation in normal tissues through binding to receptor tyrosine kinases of the ErbB family. However, aberrant neuregulin signaling in the tumor microenvironment is increasingly recognized as a key player in initiation and malignant progression of human cancers. In this chapter, we focus on the role of neuregulin signaling in the hallmarks of cancer, including cancer initiation and development, metastasis, as well as therapeutic resistance. Moreover, role of neuregulin signaling in the regulation of tumor microenvironment and targeting of neuregulin signaling in cancer from the therapeutic perspective are also briefly discussed.

A DNA-nanoassembly-based approach to map membrane protein nanoenvironments

Most proteins at the plasma membrane are not uniformly distributed but localize to dynamic domains of nanoscale dimensions. To investigate their functional relevance, there is a need for methods that enable comprehensive analysis of the compositions and spatial organizations of membrane protein nanodomains in cell populations. Here we describe the development of a non-microscopy-based method for ensemble analysis of membrane protein nanodomains. The method, termed nanoscale deciphering of membrane protein nanodomains (NanoDeep), is based on the use of DNA nanoassemblies to translate membrane protein organization information into a DNA sequencing readout. Using NanoDeep, we characterized the nanoenvironments of Her2, a membrane receptor of critical relevance in cancer. Importantly, we were able to modulate by design the inventory of proteins analysed by NanoDeep. NanoDeep has the potential to provide new insights into the roles of the composition and spatial organization of protein nanoenvironments in the regulation of membrane protein function.

Regulation of the EGFR/ErbB signalling by clathrin in response to various ligands in hepatocellular carcinoma cell lines

Membrane receptor intracellular trafficking and signalling are frequently altered in cancers. Our aim was to investigate whether clathrin‐dependent trafficking modulates signalling of the ErbB receptor family in response to amphiregulin (AR), EGF, heparin‐binding EGF‐like growth factor (HB‐EGF) and heregulin‐1β (HRG). Experiments were performed using three hepatocellular carcinoma (HCC) cell lines, Hep3B, HepG2 and PLC/PRF/5, expressing various levels of EGFR, ErbB2 and ErbB3. Inhibition of clathrin‐mediated endocytosis (CME), by down‐regulating clathrin heavy chain expression, resulted in a cell‐ and ligand‐specific pattern of phosphorylation of the ErbB receptors and their downstream effectors. Clathrin down‐regulation significantly decreased the ratio between phosphorylated EGFR (pEGFR) and total EGFR in all cell lines when stimulated with AR, EGF, HB‐EGF or HRG, except in HRG‐stimulated Hep3B cells in which pEGFR was not detectable. The ratio between phosphorylated ErbB2 and total ErbB2 was significantly decreased in clathrin down‐regulated Hep3B cells stimulated with any of the ligands, and in HRG‐stimulated PLC/PRF/5 cells. The ratio between phosphorylated ErbB3 and total ErbB3 significantly decreased in clathrin down‐regulated cell lines upon stimulation with EGF or HB‐EGF. STAT3 phosphorylation levels significantly increased in all cell lines irrespective of stimulation, while that of AKT remained unchanged, except in AR‐stimulated Hep3B and HepG2 cells in which pAKT was significantly decreased. Finally, ERK phosphorylation was insensitive to clathrin inhibition. Altogether, our observations indicate that clathrin regulation of ErbB signalling in HCC is a complex process that likely depends on the expression of ErbB family members and on the autocrine/paracrine secretion of their ligands in the tumour environment.

Single-molecule functional anatomy of endogenous HER2-HER3 heterodimers

Human epidermal growth factor receptors (HERs) are the primary targets of many directed cancer therapies. However, the reason a specific dimer of HERs generates a stronger proliferative signal than other permutations remains unclear. Here, we used single-molecule immunoprecipitation to develop a biochemical assay for endogenously-formed, entire HER2-HER3 heterodimers. We observed unexpected, large conformational fluctuations in juxta-membrane and kinase domains of the HER2-HER3 heterodimer. Nevertheless, the individual HER2-HER3 heterodimers catalyze tyrosine phosphorylation at an unusually high rate, while simultaneously interacting with multiple copies of downstream signaling effectors. Our results suggest that the high catalytic rate and multi-tasking capability make a concerted contribution to the strong signaling potency of the HER2-HER3 heterodimers.

High ErbB3 activating activity in human blood is not due to circulating neuregulin-1 beta

Neuregulin-1β (NRG-1) is a membrane-bound or secreted growth and differentiation factor that mediates its action by binding to ErbB receptors. Circulating levels of NRG-1 are characterized by large inter-individual variability with the range of absolute values covering two orders of magnitude, from hundreds to tens of thousands of picograms per milliliter of blood. NRG-1 signaling via ErbB receptors contributes to the cell survival and downregulation of the inflammatory response. A higher level of circulating NRG-1 may indicate increased shedding of membrane-bound NRG-1, which in turn can contribute to better protection against cardiovascular stress or injury. However, it is unknown whether circulating NRG-1 can induce activation of ErbB receptors. In the current study, we performed an analysis of circulating NRG-1 functional activity using a cell-based ELISA measuring phosphorylation of ErbB3 induced by blood plasma obtained from healthy donors. We found high levels of ErbB3 activating activity in human plasma. No correlations were found between the levels of circulating NRG-1 and plasma ErbB3 activating activity. To determine the direct effect of circulating NRG-1, we incubated plasma with neutralizing antibody, which prevented the stimulatory effect of recombinant NRG-1 on activation of ErbB3. No effect of the neutralizing antibody was found on plasma-induced phosphorylation of ErbB3. We also found that a significant portion of circulating NRG-1 is comprised of full-length NRG-1 associated with large extracellular vesicles. Our results demonstrate that circulating NRG-1 does not contribute to plasma-induced ErbB3 activating activity and emphasizes the importance of functional testing of NRG-1 proteins in biological samples.

Receptor tyrosine kinase activation: From the ligand perspective

Receptor tyrosine kinases (RTKs) are single-span transmembrane receptors in which relatively conserved intracellular kinase domains are coupled to divergent extracellular modules. The extracellular domains initiate receptor signaling upon binding to either soluble or membrane-embedded ligands. The diversity of extracellular domain structures allows for coupling of many unique signaling inputs to intracellular tyrosine phosphorylation. The combinatorial power of this receptor system is further increased by the fact that multiple ligands can typically interact with the same receptor. Such ligands often act as biased agonists and initiate distinct signaling responses via activation of the same receptor. Mechanisms behind such biased agonism are largely unknown for RTKs, especially at the level of receptor-ligand complex structure. Using recent progress in understanding the structures of active RTK signaling units, we discuss selected mechanisms by which ligands couple receptor activation to distinct signaling outputs.

Development of bispecific antibodies in China: overview and prospects

A bispecific antibody (bsAb) can simultaneously bind two different epitopes or antigens, allowing for multiple mechanistic functions with synergistic effects. BsAbs have attracted significant scientific attentions and efforts towards their development as drugs for cancers. There are 21 bsAbs currently undergoing clinical trials in China. Here, we review their platform technologies, expression and production, and biological activities and bioassay of these bsAbs, and summarize their structural formats and mechanisms of actions. T-cell redirection and checkpoint inhibition are two main mechanisms of the bsAbs that we discuss in detail. Furthermore, we provide our perspective on the future of bsAb development in China, including CD3-bsAbs for solid tumors and related cytokine release syndromes, expression and chemistry, manufacturing and controls, clinical development, and immunogenicity.

Neuropeptide bombesin receptor activation stimulates growth of lung cancer cells through HER3 with a MAPK-dependent mechanism

Despite recent advances in treatment of non-small cell lung cancer (NSCLC), prognosis still remains poor and new therapeutic approaches are needed. Studies demonstrate the importance of the EGFR/HER-receptor family in NSCLC growth, as well as that of other tumors. Recently, HER3 is receiving increased attention because of its role in drug resistance and aggressive growth. Activation of overexpressed G-protein-coupled receptors (GPCR) can also initiate growth by transactivating EGFR/HER-family members. GPCR transactivation of EGFR has been extensively studied, but little is known of its ability to transactivate other EGFR/HER-members, especially HER3. To address this, we studied the ability of bombesin receptor (BnR) activation to transactivate all EGFR/HER-family members and their principal downstream signaling cascades, the PI3K/Akt- and MAPK/ERK-pathways, in human NSCLC cell-lines. In all three cell-lines studied, which possessed EGFR, HER2 and HER3, Bn rapidly transactivated EGFR, HER2 and HER3, as well as Akt and ERK. Immunoprecipitation studies revealed Bn-induced formation of both HER3/EGFR- and HER3/HER2-heterodimers. Specific EGFR/HER3 antibodies or siRNA-knockdown of EGFR and HER3, demonstrated Bn-stimulated activation of EGFR/HER members is initially through HER3, not EGFR. In addition, specific inhibition of HER3, HER2 or MAPK, abolished Bn-stimulated cell-growth, while neither EGFR nor Akt inhibition had an effect. These results show HER3 transactivation mediates all growth effects of BnR activation through MAPK. These results raise the possibility that targeting HER3 alone or with GPCR activation and its signal cascades, may be a novel therapeutic approach in NSCLC. This is especially relevant with the recent development of HER3-blocking antibodies.

Kinase activity of ERBB3 contributes to intestinal organoids growth and intestinal tumorigenesis

As a member of the epidermal growth factor receptor (EGFR) family, ERBB3 plays an essential role in development and disease independent of inherently inactive kinase domain. Recently, ERBB3 has been found to bind to ATP and has catalytic activity in vitro. However, the biological function of ERBB3 kinase activity remains elusive in vivo. Here we have identified the physiological function of inactivated ERBB3 kinase activity by creating Erbb3‐K740M knockin mice in which ATP cannot bind to ERBB3. Unlike Erbb3 knockout mice, kinase‐inactive Erbb3^K740M homozygous mice were born in Mendelian ratios and showed normal development. After dextran sulfate sodium‐induced colitis, the kinase‐inactive Erbb3 mutant mice showed normal recovery. However, the outgrowth of ileal organoids by neuregulin‐1 treatment was more attenuated in Erbb3 mutant mice than in WT mice. Moreover, in combination with the Apc^Min mouse, the proportion of polyps less than 1 mm in diameter in mutant mice was higher than in control mice and an increase in the number of apoptotic cells was observed in polyps from mutant mice compared with polyps from control mice. Taken together, the ERBB3 kinase activity contributes to the outgrowth of ileal organoids and intestinal tumorigenesis, and the development of ERBB3 kinase inhibitors, including epidermal growth factor receptor family members, can be a potential way to target colorectal cancer.