Cell death or survival promoted by alternative isoforms of ErbB4

Comprehensive analysis of hub genes associated with cisplatin-resistance in ovarian cancer and screening of therapeutic drugs through bioinformatics and experimental validation

BACKGROUND

To identify key genes associated with cisplatin resistance in ovarian cancer, a comprehensive analysis was conducted on three datasets from the GEO database and through experimental validation.

METHODS

Gene expression profiles were retrieved from the GEO database. DEGs were identified by comparing gene expression profiles between cisplatin-sensitive and resistant ovarian cancer cell lines. The identified genes were further subjected to GO, KEGG, and PPI network analysis. Potential inhibitors of key genes were identified through methods such as LibDock nuclear molecular docking. In vitro assays and RT-qPCR were performed to assess the expression levels of key genes in ovarian cancer cell lines. The sensitivity of cells to chemotherapy and proliferation of key gene knockout cells were evaluated through CCK8 and Clonogenic assays.

RESULTS

Results showed that 12 genes influenced the chemosensitivity of the ovarian cancer cell line SKOV3, and 9 genes were associated with the prognosis and survival outcomes of ovarian cancer patients. RT-qPCR results revealed NDRG1, CYBRD1, MT2A, CNIH3, DPYSL3, and CARMIL1 were upregulated, whereas ERBB4, ANK3, B2M, LRRTM4, EYA4, and SLIT2 were downregulated in cisplatin-resistant cell lines. NDRG1, CYBRD1, and DPYSL3 knock-down significantly inhibited the proliferation of cisplatin-resistant cell line SKOV3. Finally, photofrin, a small-molecule compound targeting CYBRD1, was identified.

CONCLUSION

This study reveals changes in the expression level of some genes associated with cisplatin-resistant ovarian cancer. In addition, a new small molecule compound was identified for the treatment of cisplatin-resistant ovarian cancer.

An extracellular receptor tyrosine kinase motif orchestrating intracellular STAT activation

The ErbB4 receptor isoforms JM-a and JM-b differ within their extracellular juxtamembrane (eJM) domains. Here, ErbB4 isoforms are used as a model to address the effect of structural variation in the eJM domain of receptor tyrosine kinases (RTK) on downstream signaling. A specific JM-a-like sequence motif is discovered, and its presence or absence (in JM-b-like RTKs) in the eJM domains of several RTKs is demonstrated to dictate selective STAT activation. STAT5a activation by RTKs including the JM-a like motif is shown to involve interaction with oligosaccharides of N-glycosylated cell surface proteins such as β1 integrin, whereas STAT5b activation by JM-b is dependent on TYK2. ErbB4 JM-a- and JM-b-like RTKs are shown to associate with specific signaling complexes at different cell surface compartments using analyses of RTK interactomes and super-resolution imaging. These findings provide evidence for a conserved mechanism linking a ubiquitous extracellular motif in RTKs with selective intracellular STAT signaling.

Tissue Specificity Based Isoform Function Prediction

Alternative splicing enables a gene spliced into different isoforms and hence protein variants. Identifying individual functions of these isoforms help deciphering the functional diversity of proteins. Although much efforts have been made for automatic gene function prediction, few efforts have been moved toward computational isoform function prediction, mainly due to the unavailable (or scanty) functional annotations of isoforms. Existing efforts directly combine multiple RNA-seq datasets without account of the important tissue specificity of alternative splicing. To bridge this gap, we introduce a novel approach called TS-Isofun to predict the functions of isoforms by integrating multiple functional association networks with respect to tissue specificity. TS-Isofun first constructs tissue-specific isoform functional association networks using multiple RNA-seq datasets from tissue-wise. Next, TS-Isofun assigns weights to these networks and models the tissue specificity by selectively integrating them with adaptive weights. It then introduces a joint matrix factorization-based data fusion model to leverage the integrated network, gene-level data and functional annotations of genes to infer the functions of isoforms. To achieve coherent weight assignment and isoform function prediction, TS-Isofun jointly optimizes the weights of individual networks and the isoform function prediction in a unified objective function. Experimental results show that TS-Isofun significantly outperforms state-of-the-art methods and the account of tissue specificity contributes to more accurate isoform function prediction.

Age-specific impacts of nicotine and withdrawal on hippocampal neuregulin signalling

Smoking remains the leading cause of preventable death in the United States, with 87% of smokers starting before the age of 18. Age of initiation is a major predictive factor for smoking frequency and successful smoking cessation. People who initiate smoking during adolescences are 2.33 times more likely to become heavy smokers and half as likely to quit compared with smokers who started during adulthood. Additionally, schizophrenia, a disease state linked to altered neurodevelopment during adolescence, is a major predictive factor for smoking status. Smoking rates among people suffering from schizophrenia are between 60% and 90%. Interestingly, the Neuregulin Signalling Pathway (NSP), which plays an important role in neurodevelopment, is implicated in both schizophrenia and nicotine use disorder. Specifically, SNPS in neuregulin 3 (Nrg3) and Erb-B2 Receptor Tyrosine Kinase 4 (ErbB4) have been associated with smoking cessation outcomes and schizophrenia. Here, we examine the effects of chronic nicotine (18 mg/kg/day) and 24-h withdrawal on NSP gene expression in the hippocampus of adult (20-week-old) and adolescent (4-week-old) mice. We show that withdrawal from chronic nicotine decreased the expression of Erbb4 mRNA in the hippocampus of the adult mice but increased the expression of cytosolic Erbb4 protein in adolescent mice. Nrg3 mRNA and protein expression was not altered by chronic nicotine or withdrawal in the adult or adolescent cohorts, but Nrg3 mRNA and synaptosomal protein expression was lower in the adult withdrawal group when compared with their adolescent counterparts. These results highlight the age-specific effects of nicotine withdrawal on the NSP and may contribute to the lower quit rate and higher cigarette consumption of smokers who initiation during adolescences.

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.

Stimulation of the four isoforms of receptor tyrosine kinase ErbB4, but not ErbB1, confers cardiomyocyte hypertrophy

Epidermal growth factor (EGF) receptors (ErbB1-ErbB4) promote cardiac development and growth, although the specific EGF ligands and receptor isoforms involved in growth/repair versus pathology remain undefined. We challenged ventricular cardiomyocytes with EGF-like ligands and observed that selective activation of ErbB4 (the receptor for neuregulin 1 [NRG1]), but not ErbB1 (the receptor for EGF, EGFR), stimulated hypertrophy. This lack of direct ErbB1-mediated hypertrophy occurred despite robust activation of extracellular-regulated kinase 1/2 (ERK) and protein kinase B. Hypertrophic responses to NRG1 were unaffected by the tyrosine kinase inhibitor (AG1478) at concentrations that are selective for ErbB1 over ErbB4. NRG1-induced cardiomyocyte enlargement was suppressed by small interfering RNA (siRNA) knockdown of ErbB4 and ErbB2, whereas ERK phosphorylation was only suppressed by ErbB4 siRNA. Four ErbB4 isoforms exist (JM-a/JM-b and CYT-1/CYT-2), generated by alternative splicing, and their expression declines postnatally and following cardiac hypertrophy. Silencing of all four isoforms in cardiomyocytes, using an ErbB4 siRNA, abrogated NRG1-induced hypertrophic promoter/reporter activity, which was rescued by coexpression of knockdown-resistant versions of the ErbB4 isoforms. Thus, ErbB4 confers cardiomyocyte hypertrophy to NRG1, and all four ErbB4 isoforms possess the capacity to mediate this effect.

To cut or not to cut: New rules for proteolytic shedding of membrane proteins

Sheddases are specialized proteases that control the abundance and function of membrane proteins by cleaving their substrate's extracellular domain (ectodomain), a process known as shedding. Hundreds of shedding substrates have been identified, but little is known about the mechanisms that govern ectodomain shedding. Iwagishi et al. now report that negatively charged amino acids in the membrane-proximal juxtamembrane domain of substrates make them resistant to shedding by the metalloprotease ADAM17. These findings will help researchers better understand the regulation of shedding and may aid in the development of drugs targeting sheddases.

Her4 promotes cancer metabolic reprogramming via the c-Myc-dependent signaling axis

Despite the growing recognition of metabolic reprogramming as an important hallmark of cancer in the past few years, the molecular mechanisms underlying metabolic alterations during tumorigenesis remain unclear. In this study, we identified a critical role of Her4 in rewiring cancer metabolism toward tumor-promoting metabolic processes, including increased glycolysis, glutaminolysis, mitochondrial biogenesis, and oxidative phosphorylation, which may in part cooperate to promote tumorigenesis. We found that overexpression of Her4 promoted the stabilization of c-Myc through a CIP2A-mediated increase in c-Myc^S62 phosphorylation and GSK3β-mediated decrease in c-Myc^T58 phosphorylation, both of which decreased c-Myc degradation. Furthermore, Her4 was found to increase glucose uptake and tumor growth in an osteosarcoma xenograft model. Overall, these findings provide a better understanding of the involvement of Her4 in tumorigenesis and document its potential role in metabolic reprogramming for the first time. We believe that our study might lead to promising opportunities for targeted metabolic therapy for cancer.

Chemerin isoform analysis in human biofluids using an LC/MRM-MS-based targeted proteomics approach with stable isotope-labeled standard

Targeted proteomics has advantages over earlier conventional technologies for protein detection. We developed and validated an LC/MRM-MS-based targeted proteomic method combined with immunoaffinity precipitation for the enrichment and detection of low abundance chemerin isoforms in human biofluids. After tryptic digestion, each chemerin isoform was characterized by isoform-specific peptides, and the absolute quantification was achieved by using stable isotope-labeled peptides as internal standards. In serum, follicular fluid and synovial fluid, a total of 6 chemerin isoforms were identified and quantified, among which a novel natural isoform 153Q was discovered for the first time. The relative content of the six chemerin isoforms in human serum was 157S ≫ 156F ≫ 158K > 154F ≥ 155A > 153Q in the ratio of 25:17:5:2.5:2.2:1, respectively. The absolute contents were in the range of 88-3.5 ng/mL. This distribution remained consistent among the 3 biofluids analyzed. Total chemerin were found to be increased in both polycystic ovary syndrome (serum and follicular fluid) and rheumatoid arthritis (serum) patients. However, chemerin isoform analysis revealed that only 156F & 157S were increased in the former, while 155A, 156F & 157S were increased in the latter. This demonstrates the potential of this method in detailed characterization of changes in chemerin isoforms that may be of clinical relevance.

Temporal Dynamics of the Neuregulin-ErbB Network in the Murine Prefrontal Cortex across the Lifespan

Neuregulin-ErbB signaling is essential for numerous functions in the developing, adult, and aging brain, particularly in the prefrontal cortex (PFC). Mouse models with disrupted Nrg and/or ErbB genes are relevant to psychiatric, developmental, and age-related disorders, displaying a range of abnormalities stemming from cortical circuitry impairment. Many of these models display nonoverlapping phenotypes dependent upon the gene target and timing of perturbation, suggesting that cortical expression of the Nrg-ErbB network undergoes temporal regulation across the lifespan. Here, we report a comprehensive temporal expression mapping study of the Nrg-ErbB signaling network in the mouse PFC across postnatal development through aging. We find that Nrg and ErbB genes display distinct expression profiles; moreover, splice isoforms of these genes are differentially expressed across the murine lifespan. We additionally find a developmental switch in ErbB4 splice isoform expression potentially mediated through coregulation of the lncRNA Miat expression. Our results are the first to comprehensively and quantitatively map the expression patterns of the Nrg-ErbB network in the mouse PFC across the postnatal lifespan and may help disentangle the pathway's involvement in normal cortical sequences of events across the lifespan, as well as shedding light on the pathophysiological mechanisms of abnormal Nrg-ErbB signaling in neurological disease.

Negative feedback regulation of ErbB4 tyrosine kinase activity by ERK-mediated non-canonical phosphorylation

ErbB4 receptor tyrosine kinase has four different isoforms that are classified based on variants in the extracellular juxtamembrane domain (JM-a and JM-b) and the C-terminal region (CYT-1 and CYT-2). Here, we used the JM-b/CYT-1 isoform to investigate the roles of serine/threonine phosphorylation in MEK-ERK-dependent feedback inhibition. TPA as an activator of the ERK pathway markedly induced ErbB4 phosphorylation at Thr-674, the conserved common feedback site in the intracellular JM domain, which resulted in the downregulation of tyrosine autophosphorylation. We also identified Ser-1026 as an ErbB4-specific ERK target site in the CYT-1 region. Moreover, double mutations (Thr-674/Ser-1026 to Ala) significantly upregulated ErbB4 activation, indicating that Thr-674 and Ser-1026 are cooperatively involved in negative feedback regulation. Given the fact that ErbB4 mutation is one of the most common genetic alterations in melanoma cells, we demonstrated that a typical oncogenic ErbB4 mutant was resistant to the negative feedback regulation to maintain a highly active status of tyrosine kinase activity. Together, these findings indicate that feedback mechanisms are key switches determining oncogenic potentials of ErbB receptor kinases.

Altered immunoreactivity of ErbB4, a causative gene product for ALS19, in the spinal cord of patients with sporadic ALS

ErbB4 is the protein implicated in familial amyotrophic lateral sclerosis (ALS), designated as ALS19. ErbB4 is a receptor tyrosine kinase activated by its ligands, neuregulins (NRG), and plays an essential role in the function and viability of motor neurons. Mutations in the ALS19 gene lead to the reduced autophosphorylation capacity of the ErbB4 protein upon stimulation with NRG‐1, suggesting that the disruption of the NRG–ErbB4 pathway causes motor neuron degeneration. We used immunohistochemistry to study ErbB4 in the spinal cord of patients with sporadic ALS (SALS) to test the hypothesis that ErbB4 may be involved in the pathogenesis of SALS. ErbB4 was specifically immunoreactive in the cytoplasm of motor neurons in the anterior horns of the spinal cord. In patients with SALS, some of the motor neurons lost immunoreactivity with ErbB4, with the proportion of motor neurons with a loss of immunoreactivity correlated with the severity of motor neuron loss. The subcellular localization was altered, demonstrating nucleolar or nuclear localization, threads/dots and spheroids. The ectopic glial immunoreactivity was observed, mainly in the oligodendrocytes of the lateral columns and anterior horns. The reduction in the ErbB4 immunoreactivity was significantly correlated with the cytoplasmic mislocalization of transactivation response DNA‐binding protein 43 kDa (TDP‐43) in the motor neurons. No alteration in immunoreactivity was observed in the motor neurons of mice carrying atransgene for mutant form of the superoxide dismutase 1 gene (SOD1). This study provided compelling evidence that ErbB4 is also involved in the pathophysiology of SALS, and that the disruption of the NRG–ErbB4 pathway may underlie the TDP‐43‐dependent motor neuron degeneration in ALS.

Target HER four in breast cancer?

The HER4 receptor tyrosine kinase is known to have promiscuous activity in malignant cells, last but not least in breast cancer. Evidently, the prognostic and predictive impact of HER4 expression depends on the expression of different receptor isotypes, the way of receptor activation (ligand dependent vs. independent), and on the complex interaction of the HER4 intracellular domain (4ICD) with intracellular regulative molecules which results in either oncogenic or rather tumor suppressive HER4 activity. Recent data suggest that HER4 unfavorably affects the endocrine treatment of postmenopausal breast cancer patients with tamoxifen and therefore might represent an additional therapeutic target in luminal breast cancer.

Toward the Language Oscillogenome

Language has been argued to arise, both ontogenetically and phylogenetically, from specific patterns of brain wiring. We argue that it can further be shown that core features of language processing emerge from particular phasal and cross-frequency coupling properties of neural oscillations; what has been referred to as the language ‘oscillome.’ It is expected that basic aspects of the language oscillome result from genetic guidance, what we will here call the language ‘oscillogenome,’ for which we will put forward a list of candidate genes. We have considered genes for altered brain rhythmicity in conditions involving language deficits: autism spectrum disorders, schizophrenia, specific language impairment and dyslexia. These selected genes map on to aspects of brain function, particularly on to neurotransmitter function. We stress that caution should be adopted in the construction of any oscillogenome, given the range of potential roles particular localized frequency bands have in cognition. Our aim is to propose a set of genome-to-language linking hypotheses that, given testing, would grant explanatory power to brain rhythms with respect to language processing and evolution.

Gamma-secretase-dependent signaling of receptor tyrosine kinases

Human genome harbors 55 receptor tyrosine kinases (RTK). At least half of the RTKs have been reported to be cleaved by gamma-secretase-mediated regulated intramembrane proteolysis. The two-step process involves releasing the RTK ectodomain to the extracellular space by proteolytic cleavage called shedding, followed by cleavage in the RTK transmembrane domain by the gamma-secretase complex resulting in release of a soluble RTK intracellular domain. This intracellular domain, including the tyrosine kinase domain, can in turn translocate to various cellular compartments, such as the nucleus or proteasome. The soluble intracellular domain may interact with transcriptional regulators and other proteins to induce specific effects on cell survival, proliferation, and differentiation, establishing an additional signaling mode for the cleavable RTKs. On the other hand, the same process can facilitate RTK turnover and proteasomal degradation. In this review we focus on the regulation of RTK shedding and gamma-secretase cleavage, as well as signaling promoted by the soluble RTK ICDs. In addition, therapeutic implications of increased knowledge on RTK cleavage on cancer drug development are discussed.

Activation of ERBB4 in Glioblastoma Can Contribute to Increased Tumorigenicity and Influence Therapeutic Response

Glioblastoma (GBM) is often resistant to conventional and targeted therapeutics. ErbB2 Receptor Tyrosine Kinase 4 (ERBB4) is expressed throughout normal brain and is an oncogene in several pediatric brain cancers; therefore, we investigated ERBB4 as a prognostic marker and therapeutic target in GBM. Using RT-qPCR, we quantified mRNA encoding total ERBB4 and known ERBB4 variants in GBM and non-neoplastic normal brain (NNB) samples. Using immunohistochemistry, we characterized the localization of total and phosphorylated ERBB4 (p-ERBB4) and EGFR protein in archived GBM samples and assessed their association with patient survival. Furthermore, we evaluated the effect of ERBB4 phosphorylation on angiogenesis and tumorigenicity in GBM xenograft models. Total ERBB4 mRNA was significantly lower in GBM than NNB samples, with the juxtamembrane JM-a and cytoplasmic CYT-2 variants predominating. ERBB4 protein was ubiquitously expressed in GBM but was not associated with patient survival. However, high p-ERBB4 in 11% of archived GBM samples, independent of p-EGFR, was associated with shorter patient survival (12.0 ± 3.2 months) than was no p-ERBB4 (22.5 ± 9.5 months). Increased ERBB4 activation was also associated with increased proliferation, angiogenesis, tumorigenicity and reduced sensitivity to anti-EGFR treatment in xenograft models. Despite low ERBB4 mRNA in GBM, the functional effects of increased ERBB4 activation identify ERBB4 as a potential prognostic and therapeutic target.

Antitumor efficacy of the heparan sulfate mimic roneparstat (SST0001) against sarcoma models involves multi-target inhibition of receptor tyrosine kinases

The heparan sulfate (HS) mimic/heparanase inhibitor roneparstat (SST0001) shows antitumor activity in preclinical sarcoma models. We hypothesized that this 100% N-acetylated and glycol-split heparin could interfere with the functions of several receptor tyrosine kinases (RTK) coexpressed in sarcomas and activated by heparin-binding growth factors. Using a phospho-proteomic approach, we investigated the drug effects on RTK activation in human cell lines representative of different sarcoma subtypes. Inhibition of FGF, IGF, ERBB and PDGF receptors by the drug was biochemically and functionally validated. Roneparstat counteracted the autocrine loop induced by the COL1A1/PDGFB fusion oncogene, expressed in a human dermatofibrosarcoma protuberans primary culture and in NIH3T3^COL1A1/PDGFB transfectants, inhibiting cell anchorage-independent growth and invasion. In addition, roneparstat inhibited the activation of cell surface PDGFR and PDGFR-associated FAK, likely contributing to the reversion of NIH3T3^COL1A1/PDGFB cell transformed and pro-invasive phenotype. Biochemical and histological/immunohistochemical ex vivo analyses confirmed a reduced activation of ERBB4, EGFR, INSR, IGF1R, associated with apoptosis induction and angiogenesis inhibition in a drug-treated Ewing's sarcoma family tumor xenograft. The combination of roneparstat with irinotecan significantly improved the antitumor effect against A204 rhabdoid xenografts resulting in a high rate of complete responses and cures. These findings reveal that roneparstat exerts a multi-target inhibition of RTKs relevant in the pathobiology of different sarcoma subtypes. These effects, likely cooperating with heparanase inhibition, contribute to the antitumor efficacy of the drug. The study supports heparanase/HS axis targeting as a valuable approach in combination therapies of different sarcoma subtypes providing a preclinical rationale for clinical investigation.

SUMOylation regulates nuclear accumulation and signaling activity of the soluble intracellular domain of the ErbB4 receptor tyrosine kinase

Erb-B2 receptor tyrosine kinase 4 (ErbB4) is a kinase that can signal via a proteolytically released intracellular domain (ICD) in addition to classical receptor tyrosine kinase-activated signaling cascades. Previously, we have demonstrated that ErbB4 ICD is posttranslationally modified by the small ubiquitin-like modifier (SUMO) and functionally interacts with the PIAS3 SUMO E3 ligase. However, direct evidence of SUMO modification in ErbB4 signaling has remained elusive. Here, we report that the conserved lysine residue 714 in the ErbB4 ICD undergoes SUMO modification, which was reversed by sentrin-specific proteases (SENPs) 1, 2, and 5. Although ErbB4 kinase activity was not necessary for the SUMOylation, the SUMOylated ErbB4 ICD was tyrosine phosphorylated to a higher extent than unmodified ErbB4 ICD. Mutation of the SUMOylation site compromised neither ErbB4-induced phosphorylation of the canonical signaling pathway effectors Erk1/2, Akt, or STAT5 nor ErbB4 stability. In contrast, SUMOylation was required for nuclear accumulation of the ErbB4 ICD. We also found that Lys-714 was located within a leucine-rich stretch, which resembles a nuclear export signal, and could be inactivated by site-directed mutagenesis. Furthermore, SUMOylation modulated the interaction of ErbB4 with chromosomal region maintenance 1 (CRM1), the major nuclear export receptor for proteins. Finally, the SUMO acceptor lysine was functionally required for ErbB4 ICD-mediated inhibition of mammary epithelial cell differentiation in a three-dimensional cell culture model. Our findings indicate that a SUMOylation-mediated mechanism regulates nuclear localization and function of the ICD of ErbB4 receptor tyrosine kinase.

ErbB4 signaling stimulates pro-inflammatory macrophage apoptosis and limits colonic inflammation

Efficient clearance of pro-inflammatory macrophages from tissues after resolution of a challenge is critical to prevent prolonged inflammation. Defects in clearance can contribute to conditions such as inflammatory bowel disease, and thus may be therapeutically targetable. However, the signaling pathways that induce termination of pro-inflammatory macrophages are incompletely defined. We tested whether the ErbB4 receptor tyrosine kinase, previously not known to have role in macrophage biology, is involved in this process. In vitro, pro-inflammatory activation of cultured murine and human macrophages induced ErbB4 expression; in contrast, other ErbB family members were not induced in pro-inflammatory cells, and other innate immune lineages (dendritic cells, neutrophils) did not express detectable ErbB4 levels. Treatment of activated pro-inflammatory macrophages with the ErbB4 ligand neuregulin-4 (NRG4) induced apoptosis. ErbB4 localized to the mitochondria in these cells. Apoptosis was accompanied by loss of mitochondrial membrane potential, and was dependent upon the proteases that generate the cleaved ErbB4 intracellular domain fragment, suggesting a requirement for this fragment and mitochondrial pathway apoptosis. In vivo, ErbB4 was highly expressed on pro-inflammatory macrophages but not neutrophils during experimental DSS colitis in C57Bl/6 mice. Active inflammation in this model suppressed NRG4 expression, which may allow for macrophage persistence and ongoing inflammation. Consistent with this notion, NRG4 levels rebounded during the recovery phase, and administration of exogenous NRG4 during colitis reduced colonic macrophage numbers and ameliorated inflammation. These data define a novel role for ErbB4 in macrophage apoptosis, and outline a mechanism of feedback inhibition that may promote resolution of colitis.

ERBB4 Expression in Ovarian Serous Carcinoma Resistant to Platinum-Based Therapy

Few data exist on the prognostic and predictive impact of erb-b2 receptor tyrosine kinase 4 (ERBB4) in ovarian cancer. Thus, we evaluated ERBB4 expression by immunohistochemistry in a tumor microarray consisting of 100 ovarian serous carcinoma specimens (50 complete responses [CRs] and 50 incomplete responses [IRs] to platinum-based therapy), 51 normal tissue controls, and 16 ovarian cancer cell lines. H scores were used to evaluate expression and were semiquantitatively classified into low, intermediate, and high categories. Category frequencies were compared between tumor specimens vs controls using an unpaired t test. Among tumors, category frequencies were compared between CR and IR to chemotherapy. Overall survival (OS) was stratified by category. In total, 74 ovarian serous carcinoma samples (32 CRs and 42 IRs), 28 normal controls, and 16 ovarian cancer cell lines were evaluable. High-level ERBB4 expression was observed at a significantly higher frequency in ovarian serous carcinoma compared with normal control tissue. Among tumor specimens, ERBB4 expression was significantly higher for those with an IR to chemotherapy compared with CR (P = .033). OS was inversely correlated with ERBB4 expression levels. Median rates of OS were 18, 22, and 58 months among high-, intermediate-, and low-expression tumors, respectively. Our results indicate that ERBB4 expression by immunohistochemistry may correlate with chemotherapy-resistant ovarian serous carcinoma and shortened OS.

Parallel microarray profiling identifies ErbB4 as a determinant of cyst growth in ADPKD and a prognostic biomarker for disease progression

Autosomal dominant polycystic kidney disease (ADPKD) is the fourth most common cause of end-stage renal disease. The disease course can be highly variable and treatment options are limited. To identify new therapeutic targets and prognostic biomarkers of disease, we conducted parallel discovery microarray profiling in normal and diseased human PKD1 cystic kidney cells. A total of 1,515 genes and 5 miRNA were differentially expressed by more than twofold in PKD1 cells. Functional enrichment analysis identified 30 dysregulated signaling pathways including the epidermal growth factor (EGF) receptor pathway. In this paper, we report that the EGF/ErbB family receptor ErbB4 is a major factor driving cyst growth in ADPKD. Expression of ErbB4 in vivo was increased in human ADPKD and Pkd1 cystic kidneys, both transcriptionally and posttranscriptionally by mir-193b-3p. Ligand-induced activation of ErbB4 drives cystic proliferation and expansion suggesting a pathogenic role in cystogenesis. Our results implicate ErbB4 activation as functionally relevant in ADPKD, both as a marker of disease activity and as a new therapeutic target in this major kidney disease.

Developmental pruning of excitatory synaptic inputs to parvalbumin interneurons in monkey prefrontal cortex

Working memory requires efficient excitatory drive to parvalbumin-positive (PV) interneurons in the primate dorsolateral prefrontal cortex (DLPFC). Developmental pruning eliminates superfluous excitatory inputs, suggesting that working memory maturation during adolescence requires pruning of excitatory inputs to PV interneurons. Therefore, we tested the hypothesis that excitatory synapses on PV interneurons are pruned during adolescence. The density of excitatory synapses, defined by overlapping vesicular glutamate transporter 1-positive (VGlut1+) and postsynaptic density 95-positive (PSD95+) puncta, on PV interneurons was lower in postpubertal relative to prepubertal monkeys. In contrast, puncta levels of VGlut1 and PSD95 proteins were higher in postpubertal monkeys and positively predicted activity-dependent PV levels, suggesting a greater strength of the remaining synapses after pruning. Because excitatory synapse number on PV interneurons is regulated by erb-b2 receptor tyrosine kinase 4 (ErbB4), whose function is influenced by alternative splicing, we tested the hypothesis that pruning of excitatory synapses on PV interneurons is associated with developmental shifts in ErbB4 expression and/or splicing. Pan-ErbB4 expression did not change, whereas the minor-to-major splice variant ratios increased with age. In cell culture, the major, but not the minor, variant increased excitatory synapse number on PV interneurons and displayed greater kinase activity than the minor variant, suggesting that the effect of ErbB4 signaling in PV interneurons is mediated by alternative splicing. Supporting this interpretation, in monkey DLPFC, higher minor-to-major variant ratios predicted lower PSD95+ puncta density on PV interneurons. Together, our findings suggest that ErbB4 splicing may regulate the pruning of excitatory synapses on PV interneurons during adolescence.

ErbB Receptors and Cancer

The ErbB receptor family, also known as the EGF receptor family or type I receptor family, includes the epidermal growth factor (EGF) receptor (EGFR) or ErbB1/Her1, ErbB2/Her2, ErbB3/Her3, and ErbB4/Her4. Among all RTKs, EGFR was the first RTK identified and the first one linked to cancer. Thus, EGFR has also been the most intensively studied among all RTKs. ErbB receptors are activated after homodimerization or heterodimerization. The ErbB family is unique among the various groups of receptor tyrosine kinases (RTKs) in that ErbB3 has impaired kinase activity, while ErbB2 does not have a direct ligand. Therefore, heterodimerization is an important mechanism that allows the activation of all ErbB receptors in response to ligand stimulation. The activated ErbB receptors bind to many signaling proteins and stimulate the activation of many signaling pathways. The specificity and potency of intracellular signaling pathways are determined by positive and negative regulators, the specific composition of activating ligand(s), receptor dimer components, and the diverse range of proteins that associate with the tyrosine phosphorylated C-terminal domain of the ErbB receptors. ErbB receptors are overexpressed or mutated in many cancers, especially in breast cancer, ovarian cancer, and non-small cell lung cancer. The overexpression and overactivation of ErbB receptors are correlated with poor prognosis, drug resistance, cancer metastasis, and lower survival rate. ErbB receptors, especially EGFR and ErbB2 have been the primary choices as targets for developing cancer therapies.

Differential Expression Patterns of EGF, EGFR, and ERBB4 in Nasal Polyp Epithelium

Epidermal growth factor receptors play an important role in airway epithelial cell growth and differentiation. The current study investigates the expression profiles of EGF, EGFR and ERBB4 in patients with nasal polyps (NP), and their response to glucocorticosteroid (GC) treatment. Fifty patients with NP (40 without GC treatment and 10 with oral GC) and 20 control subjects with septal deviation were recruited into the study. Protein levels of EGF, EGFR, and ERBB4 were evaluated by immune-staining. In healthy nasal epithelium, EGF and EGFR localized within p63⁺ basal cells, while ERBB4 localized within ciliated cells. GC-naïve NP epithelium showed weak expression of EGF in 90% of samples versus 5% of controls. EGFR was significantly increased in the epithelium with basal cell hyperplasia from GC-naïve NPs (78%, 31/40) compared to controls (23%, 4/17). EGFR was also found in some degranulating goblet cells. ERBB4 expression was significantly higher in hyperplastic epithelium from GC-naïve NPs (65%, 26/40) than in controls (6%, 1/17). GC treatment restored the EGF expression and normalized the EGFR and ERBB4 expression in NPs. Differential expression patterns of EGF, EGFR, and ERBB4 are essential in epithelial restitution and remodeling in nasal epithelium.

Prognostic value of ERBB4 expression in patients with triple negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is known for aggressive biologic features and poor prognosis. Epidermal growth factor receptor (EGFR) overexpression in TNBC indicates poor prognosis. However, there is no previous study of the relationship between expression of the entire human epidermal growth factor receptor (HER) family genes and patient prognosis in TNBC. Accordingly, we investigated the expression profiles of HER family genes in patients with TNBC to determine the prognostic value and clinical implications of HER family expression.

METHODS

We used the nCounter expression assay (NanoString®) to measure the expression of EGFR, erb-B2 receptor tyrosine kinase 2 (ERBB2), ERBB3, ERBB4, and estrogen receptor 1 (ESR1) genes using mRNA extracted from paraffin-embedded tumor tissues from 203 patients diagnosed with TNBC. Our data were validated using a separate cohort of 84 TNBC patients.

RESULTS

A total of 203 TNBC patients who received adjuvant chemotherapy after curative surgery from 2000 to 2004 formed the training set. The 84 TNBC patients in the validation consort were selected from breast cancer patients who received curative surgery since 2005 to 2010. Analysis of the expression profiles of the HER family genes in TNBC tissue specimens revealed that increased expression of ERBB4 was associated with poor prognosis according to survival analysis (5-year distant relapse free survival [5Y DRFS], low vs. high expression [cut-off: median]: 90.1% vs. 80.2%; p = 0.022). This trend was also observed in the validation set of TNBC patients (5Y DRFS, low vs. high: 69.4% vs. 44.7%; p = 0.053). In a multivariate Cox regression model, ERBB4 expression was identified as a indicator of long-term prognosis in patients with TNBC.

CONCLUSIONS

The expression profile of ERBB4, a member of the HER family, might serve as a prognostic marker in patients with TNBC.

Nuclear HER4 mediates acquired resistance to trastuzumab and is associated with poor outcome in HER2 positive breast cancer

The role of HER4 in breast cancer is controversial and its role in relation to trastuzumab resistance remains unclear. We showed that trastuzumab treatment and its acquired resistance induced HER4 upregulation, cleavage and nuclear translocation. However, knockdown of HER4 by specific siRNAs increased trastuzumab sensitivity and reversed its resistance in HER2 positive breast cancer cells. Preventing HER4 cleavage by a γ-secretase inhibitor and inhibiting HER4 tyrosine kinase activity by neratinib decreased trastuzumab-induced HER4 nuclear translocation and enhanced trastuzumab response. There was also increased nuclear HER4 staining in the tumours from BT474 xenograft mice and human patients treated with trastuzumab. Furthermore, nuclear HER4 predicted poor clinical response to trastuzumab monotherapy in patients undergoing a window study and was shown to be an independent poor prognostic factor in HER2 positive breast cancer. Our data suggest that HER4 plays a key role in relation to trastuzumab resistance in HER2 positive breast cancer. Therefore, our study provides novel findings that HER4 activation, cleavage and nuclear translocation influence trastuzumab sensitivity and resistance in HER2 positive breast cancer. Nuclear HER4 could be a potential prognostic and predictive biomarker and understanding the role of HER4 may provide strategies to overcome trastuzumab resistance in HER2 positive breast cancer.

Role of the Neuregulin Signaling Pathway in Nicotine Dependence and Co-morbid Disorders

Smoking is currently the leading cause of preventable death in the United States and is responsible for over four million deaths annually worldwide. Therefore, there is a vast clinical unmet need with regards to therapeutics targeting smoking cessation. This is even more apparent when examining smokers co-morbid with psychiatric illness, as rates of smoking in this population are ~4× higher than in the general population. Examining common genetic and molecular signaling pathways impinging upon both smoking behavior and psychiatric illness will lead to a better understanding of co-morbid disorders and potential development of novel therapeutics. Studies have implicated the Neuregulin Signaling Pathway in the pathophysiology of a number of psychiatric illnesses. Additionally, recent studies have also shown an association between the Neuregulin Signaling Pathway and smoking behaviors. This review outlines basic mechanisms of the Neuregulin Signaling Pathway and how it may be exploited for precision medicine approaches in treating nicotine dependence and mental illness.

HER4 tumor expression in breast cancer patients randomized to treatment with or without tamoxifen

The human epidermal growth factor receptor (HER) 4 is a relative of HER2 and has been associated to endocrine breast cancer and prediction of tamoxifen response. In addition to PI3K/Akt and MAPK pathway activation, ligand binding to HER4 triggers proteolytic cleavage and release of an intracellular receptor domain (4ICD) with signaling properties. The aim of the present study was to analyze HER4 protein expression and intracellular localization in breast cancer tissue from patients randomized to treatment with or without adjuvant tamoxifen. To investigate HER4 expression and localization in response to estradiol (E2) and 4-hydroxytamoxifen (4-OHT) exposure, we also performed in vitro studies. Cytoplasmic, nuclear and membrane expression of HER4 protein was evaluated by immunohistochemical staining in tumor tissue from 912 breast cancer patients. Three different breast epithelia cancer cell lines were exposed to E2 and 4-OHT and mRNA expression was analyzed using qPCR. Further, nuclear and cytoplasmic proteins were separated and analyzed with western blotting. We found an association between nuclear HER4 protein expression and ER-positivity (P=0.004). Furthermore, significant association was found between cytoplasmic HER4 and ER-negativity (P<0.0005), PgR-negativity (P<0.0005), tumor size >20 mm (P=0.001) and HER2-negativity (P=0.008). However, no overall significance of HER4 on recurrence-free survival was found. After E2 exposure, HER4 mRNA and protein expression had decreased in two cell lines in vitro yet no changes in nuclear or cytoplasmic protein fractions were seen. In conclusion, nuclear HER4 seem to be co-located with ER, however, we did not find support for overall HER4 expression in independently predicting response of tamoxifen treatment. The possible influence of separate isoforms was not tested and future studies may further evaluate HER4 significance.

Activating ERBB4 mutations in non-small cell lung cancer

Recent efforts to comprehensively characterize the mutational landscape of non-small cell lung cancer have identified frequent mutations in the receptor tyrosine kinase ERBB4. However, the significance of mutated ERBB4 in non-small cell lung cancer remains elusive. Here, we have functionally characterized nine ERBB4 mutations previously identified in lung adenocarcinoma. Four out of the nine mutations, Y285C, D595V, D931Y and K935I, were found to be activating, increasing both basal and ligand-induced ErbB4 phosphorylation. According to structural analysis, the four activating mutations were located at critical positions at the dimerization interfaces of the ErbB4 extracellular (Y285C and D595V) and kinase (D931Y and K935I) domains. Consistently, the mutations enhanced ErbB4 dimerization and increased the trans activation in ErbB4 homodimers and ErbB4-ErbB2 heterodimers. The expression of the activating ERBB4 mutants promoted survival of NIH 3T3 cells in the absence of serum. Interestingly, serum starvation of NIH 3T3 cells expressing the ERBB4 mutants only moderately increased the phosphorylation of canonical ErbB signaling pathway effectors Erk1/2 and Akt as compared with wild-type ERBB4. In contrast, the mutations clearly enhanced the proteolytic release of signaling-competent ErbB4 intracellular domain. These results suggest the presence of activating driver mutations of ERBB4 in non-small cell lung cancer.

Combining lapatinib and pertuzumab to overcome lapatinib resistance due to NRG1-mediated signalling in HER2-amplified breast cancer

Acquired resistance to lapatinib, an inhibitor of EGFR and HER2 kinases, is common. We found that reactivation of EGFR, HER2 and HER3 occurred within 24 hours of lapatinib treatment after their initial dephosphorylation. This was associated with increased expression of NRG1 in cells treated with lapatinib. Exogenous NRG1 partially rescued breast cancer cells from growth inhibition by lapatinib. In addition, both parental and lapatinib-resistant breast cancer cells were sensitive to SGP1, which inhibits binding of NRG1 and other HER3 ligands. Addition of pertuzumab to lapatinib further inhibited NRG1-induced signalling, which was not fully inhibited by either drug alone. In animal model, a combination of pertuzumab to lapatinib induced a greater tumor regression than either lapatinib or pertuzumab monotherapy. This novel combination treatment may provide a promising strategy in clinical HER2-targeted therapy and may inhibit a subset of lapatinib-resistant breast cancer, although the group of patients that will respond to this therapy requires further stratification.

Neuregulin 1-activated ERBB4 interacts with YAP to induce Hippo pathway target genes and promote cell migration

The receptor tyrosine kinase ERBB4, a member of the epidermal growth factor receptor (EGFR) family, is unusual in that ERBB4 can undergo intramembrane proteolysis, releasing a soluble intracellular domain (ICD) that modulates transcription in the nucleus. We found that ERBB4 activated the transcriptional coactivator YAP, which promotes organ and tissue growth and is inhibited by the Hippo tumor-suppressor pathway. Overexpressing ERBB4 in cultured mammary epithelial cells or adding the ERBB4 ligand neuregulin 1 (NRG1) to breast cancer cell cultures promoted the expression of genes regulated by YAP, such as CTGF. Knocking down YAP or ERBB4 prevented the induction of CTGF expression by NRG1, as did treating cells with the ERBB inhibitors lapatinib or erlotinib, which reduced ERBB4 cleavage. NRG1 stimulated YAP activity to an extent comparable to that of EGF (epidermal growth factor) or LPA (lysophosphatidic acid), known activators of YAP. NRG1 stimulated YAP-dependent cell migration in breast cancer cell lines. These observations connect the unusual nuclear function of a growth factor receptor with a mechanosensory pathway and suggest that NRG1-ERBB4-YAP signaling contributes to the aggressive behavior of tumor cells.

Hypoxia-inducible factor-1α induces ErbB4 signaling in the differentiating mammary gland

Conditional knock-out of Hif1a in the mouse mammary gland impairs lobuloalveolar differentiation during lactation. Here, we demonstrate that expression of ErbB4 was reduced in the lobulalveoli of mice with mammary gland-specific deletion of Hif1a. Erbb4 was not, however, a direct target gene for transcriptional regulation by HIF-1α in vitro. HIF-1α overexpression or HIF accumulating prolyl hydroxylase inhibitors reduced ErbB4 endocytosis, promoted transcriptional co-regulatory activity of ErbB4, and stimulated ErbB4-induced differentiation of mammary carcinoma cells. Consistently, RNA interference-mediated down-regulation of HIF-1α resulted in reduced ErbB4 protein amount and reduced mammary carcinoma cell differentiation. These findings indicate that HIF-1α is a physiologically relevant regulator of ErbB4 and that ErbB4 is involved in HIF-regulated differentiation of the mammary gland.

The interaction of the ErbB4 intracellular domain p80 with α-enolase in the nuclei is associated with the inhibition of the neuregulin1-dependent cell proliferation

We have shown that the receptor tyrosine kinase ErbB4 signals neuregulin1-stimulated proliferation of human cells. Some isoforms of ErbB4 are cleaved to release the soluble intracellular domain p80; however, the function of p80 in cell proliferation remained unclear. Here we propose the possibility for p80 as a negative feedback modulator of ErbB4-mediated cell proliferation. Cells exposed to lower doses of neuregulin1 displayed a stimulated proliferation and contained ErbB4 but barely p80. By contrast, cells exposed to its higher doses displayed a suppressed proliferation and contained p80 but barely ErbB4. Analyses with cells overexpressing the p80 wild type and mutants indicated that nuclear p80 inhibits cell proliferation independently of the tyrosine kinase activity. A screen for a novel protein that interacts with p80 identified α-enolase, which is reported as a transcriptional inhibitor for the proliferation-associated c-myc gene. The c-myc mRNA expression was induced by lower doses of neuregulin1 but was suppressed by its higher doses. Subcellular fractionation demonstrated the localization of not only p80 and α-enolase but also the decrease of the functional c-myc amount in the nuclei of cells exposed to higher doses of neuregulin1. These results suggested that p80, which is generated from ErbB4 and translocates to the nuclei, interacts with α-enolase and inhibits neuregulin1-dependent ErbB4-mediated cell proliferation by impairing the c-myc gene transcription.

Convergent and divergent cellular responses by ErbB4 isoforms in mammary epithelial cells

Associations of ErbB4 (ERBB4/HER4), the fourth member of the EGFR family, with cancer are variable, possibly as a result of structural diversity of this receptor. There are multiple structural isoforms of ERBB4 arising by alternative mRNA splicing, and a subset undergo proteolysis that releases membrane-anchored and soluble isoforms that associate with transcription factors and coregulators to modulate transcription. To compare the differential and common signaling activities of full-length (FL) and soluble intracellular isoforms of ERBB4, four JM-a isoforms (FL and soluble intracellular domain (ICD) CYT-1 and CYT-2) were expressed in isogenic MCF10A cells and their biologic activities were analyzed. Both FL and ICD CYT-2 promoted cell proliferation and invasion, and CYT-1 suppressed cell growth. Transcriptional profiling revealed several new and underexplored ERBB4-regulated transcripts, including: proteases/protease inhibitors (MMP3 and SERPINE2), the YAP/Hippo pathway (CTGF, CYR61, and SPARC), the mevalonate/cholesterol pathway (HMGCR, HMGCS1, LDLR, and DHCR7), and cytokines (IL8, CCL20, and CXCL1). Many of these transcripts were subsequently validated in a luminal breast cancer cell line that normally expresses ERBB4. Furthermore, ChIP-seq experiments identified ADAP1, APOE, SPARC, STMN1, and MXD1 as novel molecular targets of ERBB4. These findings clarify the diverse biologic activities of ERBB4 isoforms, and reveal new and divergent functions.

IMPLICATIONS

ErbB4 as a regulator of Hippo and mevalonate pathways provides new insight into milk production and anabolic processes in normal mammary epithelia and cancer.

Submicroscopic genomic rearrangements change gene expression in T-cell large granular lymphocyte leukemia

OBJECTIVES

To better understand the molecular pathogenesis of T-cell large granular lymphocyte leukemia (T-LGL), we decided to search for those genetic alterations in T-LGL patients and MOTN-1 cell line (established from T-LGL patient) that have an impact on gene expression and as a result can influence cell biology.

METHODS

Multicolor fluorescence in situ hybridization (mFISH) analysis of the MOTN-1 cell line was performed as well as paired-end next-generation sequencing (NGS; Illumina HiSeq2000) of this cell line and one T-LGL patient. In addition, chosen 6q region was characterized in three T-LGL patients using high-resolution comparative genomic hybridization (FT-CGH) and LM-PCR. Gene expression was studied by RNA sequencing (RNAseq; SOLID5500).

RESULTS

Rearrangements were detected within 1p and 2q in MOTN-1 affecting expression of FGR, ZEB2, and CASP8, and within 6q in MOTN-1 and one T-LGL patient affecting MAP3K5 and IFNGR1. Nineteen genes, among them FOXN3, RIN3, AKT1, PPP2R5C, were overexpressed as a result of an amplification in 14q in one T-LGL patient. Two novel fusion transcripts were identified: CASP8-ERBB4 in MOTN-1 and SBF1-PKHD1L1 in T-LGL patient.

CONCLUSIONS

This study showed that submicroscopic genomic rearrangements change gene expression in T-LGL. Several genes involved in rearrangements were previously linked to cancer and survival pattern that characterizes T-LGL cells.

Molecular basis of the binding of YAP transcriptional regulator to the ErbB4 receptor tyrosine kinase

The newly discovered transactivation function of ErbB4 receptor tyrosine kinase is believed to be mediated by virtue of the ability of its proteolytically-cleaved intracellular domain (ICD) to physically associate with YAP2 transcriptional regulator. In an effort to unearth the molecular basis of YAP2-ErbB4 interaction, we have conducted a detailed biophysical analysis of the binding of WW domains of YAP2 to PPXY motifs located within the ICD of ErbB4. Our data show that the WW1 domain of YAP2 binds to PPXY motifs within the ICD in a differential manner and that this behavior is by and large replicated by the WW2 domain. Remarkably, while both WW domains absolutely require the integrity of the PPXY consensus sequence, non-consensus residues within and flanking this motif do not appear to be critical for binding. In spite of this shared mode of binding, the WW domains of YAP2 display distinct conformational dynamics in complex with PPXY motifs derived from ErbB4. Collectively, our study lends new insights into the molecular basis of a key protein-protein interaction involved in a diverse array of cellular processes.

Molecular origin of the binding of WWOX tumor suppressor to ErbB4 receptor tyrosine kinase

The ability of WWOX tumor suppressor to physically associate with the intracellular domain (ICD) of ErbB4 receptor tyrosine kinase is believed to play a central role in downregulating the transcriptional function of the latter. Herein, using various biophysical methods, we show that while the WW1 domain of WWOX binds to PPXY motifs located within the ICD of ErbB4 in a physiologically relevant manner, the WW2 domain does not. Importantly, while the WW1 domain absolutely requires the integrity of the PPXY consensus sequence, nonconsensus residues within and flanking this motif do not appear to be critical for binding. This strongly suggests that the WW1 domain of WWOX is rather promiscuous toward its cellular partners. We also provide evidence that the lack of binding of the WW2 domain of WWOX to PPXY motifs is due to the replacement of a signature tryptophan, lining the hydrophobic ligand binding groove, with tyrosine (Y85). Consistent with this notion, the Y85W substitution within the WW2 domain exquisitely restores its binding to PPXY motifs in a manner akin to the binding of the WW1 domain of WWOX. Of particular significance is the observation that the WW2 domain augments the binding of the WW1 domain to ErbB4, implying that the former serves as a chaperone within the context of the WW1-WW2 tandem module of WWOX in agreement with our findings reported previously. Altogether, our study sheds new light on the molecular basis of an important WW-ligand interaction involved in mediating a plethora of cellular processes.

Regulation of the Ras-MAPK and PI3K-mTOR Signalling Pathways by Alternative Splicing in Cancer

Alternative splicing is a fundamental step in regulation of gene expression of many tumor suppressors and oncogenes in cancer. Signalling through the Ras-MAPK and PI3K-mTOR pathways is misregulated and hyperactivated in most types of cancer. However, the regulation of the Ras-MAPK and PI3K-mTOR signalling pathways by alternative splicing is less well established. Recent studies have shown the contribution of alternative splicing regulation of these signalling pathways which can lead to cellular transformation, cancer development, and tumor maintenance. This review will discuss findings in the literature which describe new modes of regulation of components of the Ras-MAPK and PI3K-mTOR signalling pathways by alternative splicing. We will also describe the mechanisms by which signals from extracellular stimuli can be communicated to the splicing machinery and to specific RNA-binding proteins that ultimately control exon definition events.

ErbB1-4-dependent EGF/neuregulin signals and their cross talk in the central nervous system: pathological implications in schizophrenia and Parkinson's disease

Ligands for ErbB1-4 receptor tyrosine kinases, such as epidermal growth factor (EGF) and neuregulins, regulate brain development and function. Thus, abnormalities in their signaling are implicated in the etiology or pathology of schizophrenia and Parkinson's disease. Among the ErbB receptors, ErbB1, and ErbB4 are expressed in dopamine and GABA neurons, while ErbB1, 2, and/or 3 are mainly present in oligodendrocytes, astrocytes, and their precursors. Thus, deficits in ErbB signaling might contribute to the neurological and psychiatric diseases stemming from these cell types. By incorporating the latest cancer molecular biology as well as our recent progress, we discuss signal cross talk between the ErbB1-4 subunits and their neurobiological functions in each cell type. The potential contribution of virus-derived cytokines (virokines) that mimic EGF and neuregulin-1 in brain diseases are also discussed.

Comprehensive binary interaction mapping of SH2 domains via fluorescence polarization reveals novel functional diversification of ErbB receptors

First-generation interaction maps of Src homology 2 (SH2) domains with receptor tyrosine kinase (RTK) phosphosites have previously been generated using protein microarray (PM) technologies. Here, we developed a large-scale fluorescence polarization (FP) methodology that was able to characterize interactions between SH2 domains and ErbB receptor phosphosites with higher fidelity and sensitivity than was previously achieved with PMs. We used the FP assay to query the interaction of synthetic phosphopeptides corresponding to 89 ErbB receptor intracellular tyrosine sites against 93 human SH2 domains and 2 phosphotyrosine binding (PTB) domains. From 358,944 polarization measurements, the affinities for 1,405 unique biological interactions were determined, 83% of which are novel. In contrast to data from previous reports, our analyses suggested that ErbB2 was not more promiscuous than the other ErbB receptors. Our results showed that each receptor displays unique preferences in the affinity and location of recruited SH2 domains that may contribute to differences in downstream signaling potential. ErbB1 was enriched versus the other receptors for recruitment of domains from RAS GEFs whereas ErbB2 was enriched for recruitment of domains from tyrosine and phosphatidyl inositol phosphatases. ErbB3, the kinase inactive ErbB receptor family member, was predictably enriched for recruitment of domains from phosphatidyl inositol kinases and surprisingly, was enriched for recruitment of domains from tyrosine kinases, cytoskeletal regulatory proteins, and RHO GEFs but depleted for recruitment of domains from phosphatidyl inositol phosphatases. Many novel interactions were also observed with phosphopeptides corresponding to ErbB receptor tyrosines not previously reported to be phosphorylated by mass spectrometry, suggesting the existence of many biologically relevant RTK sites that may be phosphorylated but below the detection threshold of standard mass spectrometry procedures. This dataset represents a rich source of testable hypotheses regarding the biological mechanisms of ErbB receptors.

Proteolytic processing of ErbB4 in breast cancer

ErbB4 is a receptor tyrosine kinase that can signal by a mechanism involving proteolytic release of intracellular and extracellular receptor fragments. Proteolysis-dependent signaling of ErbB4 has been proposed to be enhanced in breast cancer, mainly based on immunohistochemical localization of intracellular epitopes in the nuclei. To more directly address the processing of ErbB4 in vivo, an ELISA was developed to quantify cleaved ErbB4 ectodomain from serum samples. Analysis of 238 breast cancer patients demonstrated elevated quantities of ErbB4 ectodomain in the serum (≥40 ng/mL) in 21% of the patients, as compared to 0% of 30 healthy controls (P = 0.002). Significantly, the elevated serum ectodomain concentration did not correlate with the presence of nuclear ErbB4 immunoreactivity in matched breast cancer tissue samples. However, elevated serum ectodomain concentration was associated with the premenopausal status at diagnosis (P = 0.04), and estradiol enhanced ErbB4 cleavage in vitro. A 3.4 Å X-ray crystal structure of a complex of ErbB4 ectodomain and the Fab fragment of anti-ErbB4 mAb 1479 localized the binding site of mAb 1479 on ErbB4 to a region on subdomain IV encompassing the residues necessary for ErbB4 cleavage. mAb 1479 also significantly blocked ErbB4 cleavage in breast cancer cell xenografts in vivo, and the inhibition of cleavage was associated with suppression of xenograft growth. These data indicate that ErbB4 processing is enhanced in breast cancer tissue in vivo, and that ErbB4 cleavage can be stimulated by estradiol and targeted with mAb 1479.

Linear motifs: lost in (pre)translation

Pretranslational modification by alternative splicing, alternative promoter usage and RNA editing enables the production of multiple protein isoforms from a single gene. A large quantity of data now supports the notion that short linear motifs (SLiMs), which are protein interaction modules enriched within intrinsically disordered regions, are key for the functional diversification of these isoforms. The inclusion or removal of these SLiMs can switch the subcellular localisation of an isoform, promote cooperative associations, refine the affinity of an interaction, coordinate phase transitions within the cell, and even create isoforms of opposing function. This article discusses the novel functionality enabled by the addition or removal of SLiM-containing exons by pretranslational modifications, such as alternative splicing and alternative promoter usage, and how these alterations enable the creation and modulation of complex regulatory and signalling pathways.

Protein inhibitor of activated STAT3 (PIAS3) protein promotes SUMOylation and nuclear sequestration of the intracellular domain of ErbB4 protein

ErbB4 is a receptor tyrosine kinase implicated in the development and homeostasis of the heart, central nervous system, and mammary gland. Cleavable isoforms of ErbB4 release a soluble intracellular domain (ICD) that can translocate to the nucleus and function as a transcriptional coregulator. In search of regulatory mechanisms of ErbB4 ICD function, we identified PIAS3 as a novel interaction partner of ErbB4 ICD. In keeping with the small ubiquitin-like modifier (SUMO) E3 ligase function of protein inhibitor of activated STAT (PIAS) proteins, we showed that the ErbB4 ICD is modified by SUMO, and that PIAS3 stimulates the SUMOylation. Upon overexpression of PIAS3, the ErbB4 ICD generated from the full-length receptor accumulated into the nucleus in a manner that was dependent on the functional nuclear localization signal of ErbB4. In the nucleus, ErbB4 colocalized with PIAS3 and SUMO-1 in promyelocytic leukemia nuclear bodies, nuclear domains involved in regulation of transcription. Accordingly, PIAS3 overexpression had an effect on the transcriptional coregulatory activity of ErbB4, repressing its ability to coactivate transcription with Yes-associated protein. Finally, knockdown of PIAS3 with siRNA partially rescued the inhibitory effect of the ErbB4 ICD on differentiation of MDA-MB-468 breast cancer and HC11 mammary epithelial cells. Our findings illustrate that PIAS3 is a novel regulator of ErbB4 receptor tyrosine kinase, controlling its nuclear sequestration and function.

Slow down to stay alive: HER4 protects against cellular stress and confers chemoresistance in neuroblastoma

BACKGROUND

Neuroblastoma (NBL) is a common pediatric solid tumor, and outcomes for patients with advanced neuroblastoma remain poor despite extremely aggressive treatment. Chemotherapy resistance at relapse contributes heavily to treatment failure. The poor survival of patients with high-risk NBL prompted this investigation into novel treatment options with the objective of gaining a better understanding of resistance mechanisms. On the basis of previous work and on data from publicly available studies, the authors hypothesized that human epidermal growth factor receptor 4 (Her4) contributes to resistance.

METHODS

Her4 expression was reduced with small-hairpin RNA (shRNA) to over express intracellular HER4, and the authors tested its impact on tumor cell survival under various culture conditions. The resulting changes in gene expression after HER4 knockdown were measured by using a messenger RNA (mRNA) array.

RESULTS

HER4 expression was up-regulated in tumor spheres compared with the expression in monolayer culture. With HER4 knockdown, NBL cells became less resistant to anoikis and serum starvation. Moreover, HER4 knockdown increased the chemosensitivity of NBL cells to cisplatin, doxorubicin, etoposide, and activated ifosfamide. In mRNA array analysis, HER4 knockdown predominately altered genes related to cell cycle regulation. In NBL spheres compared with monolayers, cell proliferation was decreased, and cyclin D expression was reduced. HER4 knockdown reversed cyclin D suppression. Overexpressed intracellular HER4 slowed the cell cycle and induced chemoresistance.

CONCLUSIONS

The current results indicated that HER4 protects NBL cells from multiple exogenous apoptotic stimuli, including anoikis, nutrient deficiency, and cytotoxic chemotherapy. The intracellular fragment of HER4 was sufficient to confer this phenotype. HER4 functions as a cell cycle suppressor, maintaining resistance to cellular stress. The current findings indicate that HER4 overexpression may be associated with refractory disease, and HER4 may be an important therapeutic target.

ErbB4 modulates tubular cell polarity and lumen diameter during kidney development

ErbB4 receptor tyrosine kinase contributes to the development of the heart, the central nervous system, and the lactating mammary gland, but whether it has a role in the development of the kidney epithelium is unknown. Here, we found that expression of Erbb4 isoforms JM-a CYT-1 and JM-a CYT-2 was first detectable around embryonic day 13 in the mouse, mainly in the collecting ducts and both the proximal and distal tubules. In vitro, overexpression of a relevant ErbB4 isoform promoted proliferation and disturbed polarization of kidney epithelial cells when cultured as three-dimensional structures. We examined ErbB4 function in developing kidney tubules in vivo with Pax8-Cre-mediated conditional overexpression of Rosa26 locus-targeted ERBB4 and with conditional Erbb4 knock-out mice. The Pax8-Cre-driven ERBB4 overexpression enhanced proliferation in the collecting ducts, reduced the size of epithelial duct lumens, and promoted formation of cortical tubular cysts. These defects were associated with changes in the subcellular distribution of markers of epithelial cell polarity. Similarly, the Pax8-Cre-mediated Erbb4 knock-out mice manifested dysfunctional kidneys with larger duct lumens and epithelial cell mispolarization. Taken together, these data suggest that ErbB4 signaling modulates proliferation and polarization, cellular functions critical for the development of epithelial ducts in the kidney.