ErbB4 splice variants Cyt1 and Cyt2 differ by 16 amino acids and exert opposing effects on the mammary epithelium in vivo

Mechanisms and therapeutic targets of ErbB family receptors in hepatocellular carcinoma: a narrative review

Background and Objective

Hepatocellular carcinoma (HCC) is a highly heterogeneous and aggressive tumor. In recent years, the incidence of HCC has been increasing worldwide. Despite notable advancements in treatment methodologies, the prognosis of HCC patients remains unsatisfactory. ErbB family proteins play important roles in the occurrence, progression, and metastasis of HCC, and their abnormal expression is often closely associated with poor patient prognosis. This article sought to investigate the current status and research progress of ErbB family protein targeted therapy in HCC in recent years to provide a reference for basic research and clinical treatment.

Methods

We performed a comprehensive, narrative review of the latest literature to define the current progress of ErbB family receptors in HCC in both the pre-clinical and clinical arenas.

Key Content and Findings

The ErbB family belongs to the tyrosine kinase (TK) receptor family that comprises four members. These members are closely associated with proliferation, cell cycle regulation, and migration during HCC development through multiple signaling pathways. ErbB-targeted therapy has shown tremendous potential and prospects in the treatment of HCC.

Conclusions

Through in-depth research and the application of ErbB-targeted therapy, broader avenues will be opened for the treatment of HCC and other tumors, leading to more personalized and precise treatment approaches.

Cabergoline as a Novel Strategy for Post-Pregnancy Breast Cancer Prevention in Mice and Human

Post-pregnancy breast cancer often carries a poor prognosis, posing a major clinical challenge. The increasing trend of later-life pregnancies exacerbates this risk, highlighting the need for effective chemoprevention strategies. Current options, limited to selective estrogen receptor modulators, aromatase inhibitors, or surgical procedures, offer limited efficacy and considerable side effects. Here, we report that cabergoline, a dopaminergic agonist, reduces the risk of breast cancer post-pregnancy in a Brca1/P53-deficient mouse model, with implications for human breast cancer prevention. We show that a single dose of cabergoline administered post-pregnancy significantly delayed the onset and reduced the incidence of breast cancer in Brca1/P53-deficient mice. Histological analysis revealed a notable acceleration in post-lactational involution over the short term, characterized by increased apoptosis and altered gene expression related to ion transport. Over the long term, histological changes in the mammary gland included a reduction in the ductal component, decreased epithelial proliferation, and a lower presence of recombinant Brca1/P53 target cells, which are precursors of tumors. These changes serve as indicators of reduced breast cancer susceptibility. Additionally, RNA sequencing identified gene expression alterations associated with decreased proliferation and mammary gland branching. Our findings highlight a mechanism wherein cabergoline enhances the protective effect of pregnancy against breast cancer by potentiating postlactational involution. Notably, a retrospective cohort study in women demonstrated a markedly lower incidence of post-pregnancy breast cancer in those treated with cabergoline compared to a control group. Our work underscores the importance of enhancing postlactational involution as a strategy for breast cancer prevention, and identifies cabergoline as a promising, low-risk option in breast cancer chemoprevention. This strategy has the potential to revolutionize breast cancer prevention approaches, particularly for women at increased risk due to genetic factors or delayed childbirth, and has wider implications beyond hereditary breast cancer cases.

Molecular complexity of mammary glands development: a review of lactogenic differentiation in epithelial cells

The mammary gland is a dynamic organ with various physiological processes like cellular proliferation, differentiation, and apoptosis during the pregnancy-lactation-involution cycle. It is essential to understand the molecular changes during the lactogenic differentiation of mammary epithelial cells (MECs, the milk-synthesizing cells). The MECs are organized as luminal milk-secreting cells and basal myoepithelial cells (responsible for milk ejection by contraction) that form the alveoli. The branching morphogenesis and lactogenic differentiation of the MECs prepare the gland for lactation. This process is governed by many molecular mediators including hormones, growth factors, cytokines, miRNAs, regulatory proteins, etc. Interestingly, various signalling pathways guide lactation and understanding these molecular transitions from pregnancy to lactation will help researchers design further research. Manipulation of genes responsible for milk synthesis and secretion will promote augmentation of milk yield in dairy animals. Identifying protein signatures of lactation will help develop strategies for persistent lactation and shortening the dry period in farm animals. The present review article discusses in details the physiological and molecular changes occurring during lactogenic differentiation of MECs and the associated hormones, regulatory proteins, miRNAs, and signalling pathways. An in-depth knowledge of the molecular events will aid in developing engineered cellular models for studies related to mammary gland diseases of humans and animals.

ERBB Receptors and Their Ligands in the Developing Mammary Glands of Different Species: Fifteen Characters in Search of an Author

The ERBB tyrosine kinase receptors and their ligands belong to a complex family that has diverse biological effects and expression profiles in the developing mammary glands, where its members play an essential role in translating hormone signals into local effects. While our understanding of these processes stems mostly from mouse models, there is the potential for differences in how this family functions in the mammary glands of other species, particularly in light of their unique histomorphological features. Herein we review the postnatal distribution and function of ERBB receptors and their ligands in the mammary glands of rodents and humans, as well as for livestock and companion animals. Our analysis highlights the diverse biology for this family and its members across species, the regulation of their expression, and how their roles and functions might be modulated by varying stromal composition and hormone interactions. Given that ERBB receptors and their ligands have the potential to influence processes ranging from normal mammary development to diseased states such as cancer and/or mastitis, both in human and veterinary medicine, a more complete understanding of their biological functions should help to direct future research and the identification of new therapeutic targets.

Neuregulin 4 Boosts the Efficacy of Anti-ERBB2 Neutralizing Antibodies

ERBB4 is a tyrosine kinase receptor reported to exert both oncogenic and tumor suppressor activities. These paradoxical effects were suggested to stem from different ERBB4 homo-/hetero-dimers and/or isoforms. By stratifying breast cancer patients for clinical and molecular subtypes and ERBB4 mRNA abundance, we here report that higher ERBB4 levels correlate with longer relapse-free survival in breast cancer patients of HER2-enriched and luminal A molecular subtypes, proposing a cancer-protecting role for this receptor in these specific subgroups. We also observed that HER2-enriched breast cancers express intermediate ERBB4 mRNA levels compared to luminal and triple-negative/basal-like subgroups, which displayed the highest and the lowest levels, respectively. Inspired by these clinical data, we tested the activation of ERBB4 by Neuregulins as a potential anticancer strategy for HER2+ breast cancers. To this end, we employed two HER2+ breast cancer cellular models (BT474 and SKBR3), which express intermediate/high and low ERBB4 levels, respectively. Cell proliferation and motility were evaluated on these cellular models following treatments with Neuregulin 1 (NRG1), which activates both ERBB3 and ERBB4, or Neuregulin 4 (NRG4), which specifically activates ERBB4. Both NRG1 and NRG4 were used alone or in combination with anti-ERBB2 neutralizing antibodies, namely trastuzumab and pertuzumab. In vitro treatment with NRG1 on BT474 cells restrained cell growth and reduced the anti-proliferative efficacy of trastuzumab. In contrast, treatment with NRG1 on SKBR3 cells increased cell proliferation and migration, and partially or completely impaired the anti-proliferative/anti-migratory action of trastuzumab and/or pertuzumab. Importantly, in both the cell lines, treatment with NRG4 robustly potentiated the anti-proliferative action of trastuzumab and pertuzumab. Collectively, our data in HER2+ breast cancer cells highlight that NRG1 may exert both pro- and anti-proliferative effects, and may reduce the efficacy of anti-HER2 agents, whereas NRG4 may boost the anti-proliferative effects of anti-ERBB2 agents. We propose a provocative paradigm shift in the field of growth factors in cancer progression, suggesting the administration of ERBB4 ligands, such as Neuregulin 4, as a strategy to improve the efficacy of anti-ERBB2 agents.

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.

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.

Biasing human epidermal growth factor receptor 4 (HER4) tyrosine kinase signaling with antibodies: Induction of cell death by antibody-dependent HER4 intracellular domain trafficking

Human epidermal growth factor receptor 4 (HER4) isoforms have oncogenic or tumor suppressor functions depending on their susceptibility to proteolytic cleavage and HER4 intracellular domain (4ICD) translocation. Here, we report that the neuregulin 1 (NRG1) tumor suppressor mechanism through the HER4 JMa/CYT1 isoform can be mimicked by the agonist anti‐HER4 Ab C6. Neuregulin 1 induced cleavage of poly(ADP‐ribose) polymerase (PARP) and sub‐G₁ DNA fragmentation, and also reduced the metabolic activity of HER3⁻/HER4⁺ cervical (C‐33A) and ovarian (COV318) cancer cells. This effect was confirmed in HER4 JMa/CYT1‐, but not JMa/CYT2‐transfected BT549 triple‐negative breast cancer cells. Neuregulin 1 favored 4ICD cleavage and retention in mitochondria in JMa/CYT1‐transfected BT549 cells, leading to reactive oxygen species (ROS) production through mitochondrial depolarization. Similarly, the anti‐HER4 Ab C6, which binds to a conformational epitope located on a.a. 575‐592 and 605‐620 of HER4 domain IV, induced 4ICD cleavage and retention in mitochondria, and mimicked NRG1‐mediated effects on PARP cleavage, ROS production, and mitochondrial membrane depolarization in cancer cells. In vivo, C6 reduced growth of COV434 and HCC1187 tumor cell xenografts in nude mice. Biasing 4ICD trafficking to mitochondria with anti‐HER4 Abs to mimic NRG1 suppressor functions could be an alternative anticancer strategy.

Functional role of WW domain-containing proteins in tumor biology and diseases: Insight into the role in ubiquitin-proteasome system

The ubiquitin-proteasome system (UPS) governs the protein degradation process and balances proteostasis and cellular homeostasis. It is a well-controlled mechanism, in which removal of the damaged or excessive proteins is essential in driving signal pathways for cell survival or death. Accumulation of damaged proteins and failure in removal may contribute to disease initiation such as in cancers and neurodegenerative diseases. In this notion, specific protein-protein interaction is essential for the recognition of targeted proteins in UPS. WW domain plays an indispensable role in the protein-protein interactions during signaling. Among the 51 WW domain-containing proteins in the human proteomics, near one-quarter of them are involved in the UPS, suggesting that WW domains are crucial modules for driving the protein-protein binding and subsequent ubiquitination and degradation. In this review, we detail a broad spectrum of WW domains in protein-protein recognition, signal transduction, and relevance to diseases. New perspectives in dissecting the molecular interactions are provided.

The role of ErbB4 in cancer

BACKGROUND

The epidermal growth factor receptor family consists of four members, ErbB1 (epidermal growth factor receptor-1), ErbB2, ErbB3, and ErbB4, which all have been found to play important roles in tumor development. ErbB4 appears to be unique among these receptors, because it is the only member with growth inhibiting properties. ErbB4 plays well-defined roles in normal tissue development, in particular the heart, the nervous system, and the mammary gland system. In recent years, information on the role of ErbB4 in a number of tumors has emerged and its general direction points towards a tumor suppressor role for ErbB4. However, there are some controversies and conflicting data, warranting a review on this topic.

CONCLUSIONS

Here, we discuss the role of ErbB4 in normal physiology and in breast, lung, colorectal, gastric, pancreatic, prostate, bladder, and brain cancers, as well as in hepatocellular carcinoma, cholangiocarcinoma, and melanoma. Understanding the role of ErbB4 in cancer is not only important for the treatment of tumors, but also for the treatment of other disorders in which ErbB4 plays a major role, e.g. cardiovascular disease.

HER4 expression in estrogen receptor-positive breast cancer is associated with decreased sensitivity to tamoxifen treatment and reduced overall survival of postmenopausal women

BACKGROUND

The sensitivity of estrogen receptor-positive breast cancers to tamoxifen treatment varies considerably, and the molecular mechanisms affecting the response rates are manifold. The human epidermal growth factor receptor-related receptor HER2 is known to trigger intracellular signaling cascades that modulate the activity of coregulators of the estrogen receptor which, in turn, reduces the cell sensitivity to tamoxifen treatment. However, the impact of HER2-related receptor tyrosine kinases HER1, HER3, and, in particular, HER4 on endocrine treatment is largely unknown.

METHODS

Here, we retrospectively evaluated the importance of HER4 expression on the outcome of tamoxifen- and aromatase inhibitor-treated estrogen receptor-positive breast cancer patients (n = 258). In addition, we experimentally analyzed the efficiency of tamoxifen treatment as a function of HER4 co-expression in vitro.

RESULTS

We found a significantly improved survival in tamoxifen-treated postmenopausal breast cancer patients in the absence of HER4 compared with those with pronounced HER4 expression. In accordance with this finding, the sensitivity to tamoxifen treatment of estrogen and HER4 receptor-positive ZR-75-1 breast cancer cells can be significantly enhanced by HER4 knockdown.

CONCLUSION

We suggest an HER4/estrogen receptor interaction that impedes tamoxifen binding to the estrogen receptor and reduces treatment efficiency. Whether the sensitivity to tamoxifen treatment can be enhanced by anti-HER4 targeting needs to be prospectively evaluated.

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.

HER4 isoform CYT2 and its ligand NRG1III are expressed at high levels in human colorectal cancer

The present study aimed to evaluate the expression of human epidermal growth factor receptor (HER4) isoforms and their ligand neuregulin 1 (NRG1) isoforms in human primary colorectal cancer (CRC). The mRNA expression of HER4 isoforms JM-a, JM-b, CYT1 and CYT2, and their ligand isoforms NRG1 I, II and III in CRC tissues and adjacent normal tissues were quantified by reverse transcription-quantitative polymerase chain reaction analysis. Univariate analysis and logistic regression analysis were performed to analyze the association between HER4 and NRG1 expression and lymph node metastasis in CRC. The expression levels of CYT1 (P=0.002), CYT2 (P=0.002) and NRG1 type III (P<0.001) were significantly higher in the CRC tissues than in the adjacent normal tissues. The expression of CYT2 was correlated with tumor stage (P=0.018), lymph node status (P=0.015) and tumor-node-metastasis (P=0.038) in CRC. The expression of NRG1III was correlated with lymph node metastasis, and the expression of CYT2 was associated with the expression of NRG1III (r=0.691, P<0.01). The logistic regression analysis indicated that expression of CYT2 >50 was a risk factor for lymph node metastasis in CRC. In conclusion the expression levels of CYT1, CYT2 and NRG1III were upregulated in CRC. An expression of CYT-2 >50 was identified as a risk factor for lymph node metastasis in CRC. Therefore, CY-2 and NRG1III may be involved in the progression of CRC.

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.

ErbB3 drives mammary epithelial survival and differentiation during pregnancy and lactation

Background

During pregnancy, as the mammary gland prepares for synthesis and delivery of milk to newborns, a luminal mammary epithelial cell (MEC) subpopulation proliferates rapidly in response to systemic hormonal cues that activate STAT5A. While the receptor tyrosine kinase ErbB4 is required for STAT5A activation in MECs during pregnancy, it is unclear how ErbB3, a heterodimeric partner of ErbB4 and activator of phosphatidyl inositol-3 kinase (PI3K) signaling, contributes to lactogenic expansion of the mammary gland.

Methods

We assessed mRNA expression levels by expression microarray of mouse mammary glands harvested throughout pregnancy and lactation. To study the role of ErbB3 in mammary gland lactogenesis, we used transgenic mice expressing WAP-driven Cre recombinase to generate a mouse model in which conditional ErbB3 ablation occurred specifically in alveolar mammary epithelial cells (aMECs).

Results

Profiling of RNA from mouse MECs isolated throughout pregnancy revealed robust Erbb3 induction during mid-to-late pregnancy, a time point when aMECs proliferate rapidly and undergo differentiation to support milk production. Litters nursed by ErbB3^KO dams weighed significantly less when compared to litters nursed by ErbB3^WT dams. Further analysis revealed substantially reduced epithelial content, decreased aMEC proliferation, and increased aMEC cell death during late pregnancy. Consistent with the potent ability of ErbB3 to activate cell survival through the PI3K/Akt pathway, we found impaired Akt phosphorylation in ErbB3^KO samples, as well as impaired expression of STAT5A, a master regulator of lactogenesis. Constitutively active Akt rescued cell survival in ErbB3-depleted aMECs, but failed to restore STAT5A expression or activity. Interestingly, defects in growth and survival of ErbB3^KO aMECs as well as Akt phosphorylation, STAT5A activity, and expression of milk-encoding genes observed in ErbB3^KO MECs progressively improved between late pregnancy and lactation day 5. We found a compensatory upregulation of ErbB4 activity in ErbB3^KO mammary glands. Enforced ErbB4 expression alleviated the consequences of ErbB3 ablation in aMECs, while combined ablation of both ErbB3 and ErbB4 exaggerated the phenotype.

Conclusions

These studies demonstrate that ErbB3, like ErbB4, enhances lactogenic expansion and differentiation of the mammary gland during pregnancy, through activation of Akt and STAT5A, two targets crucial for lactation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0893-7) contains supplementary material, which is available to authorized users.

Immunocompetent mouse allograft models for development of therapies to target breast cancer metastasis

Effective drug development to combat metastatic disease in breast cancer would be aided by the availability of well-characterized preclinical animal models that (a) metastasize with high efficiency, (b) metastasize in a reasonable time-frame, (c) have an intact immune system, and (d) capture some of the heterogeneity of the human disease. To address these issues, we have assembled a panel of twelve mouse mammary cancer cell lines that can metastasize efficiently on implantation into syngeneic immunocompetent hosts. Genomic characterization shows that more than half of the 30 most commonly mutated genes in human breast cancer are represented within the panel. Transcriptomically, most of the models fall into the luminal A or B intrinsic molecular subtypes, despite the predominance of an aggressive, poorly-differentiated or spindled histopathology in all models. Patterns of immune cell infiltration, proliferation rates, apoptosis and angiogenesis differed significantly among models. Inherent within-model variability of the metastatic phenotype mandates large cohort sizes for intervention studies but may also capture some relevant non-genetic sources of variability. The varied molecular and phenotypic characteristics of this expanded panel of models should aid in model selection for development of antimetastatic therapies in vivo, and serve as a useful platform for predictive biomarker identification.

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.

ErbB1 and ErbB4 generate opposing signals regulating mesenchymal cell proliferation during valvulogenesis

HB-EGF plays an indispensable role in suppression of cell proliferation during mouse valvulogenesis. However, ligands of the EGF receptor (EGFR/ErbB1), including HB-EGF, are generally considered as growth-promoting factors as shown in cancers. HB-EGF binds to and activates ErbB1 and ErbB4. We investigated the role of ErbB receptors in valvulogenesis in vivo using ErbB1- and ErbB4-deficient mice, and an ex vivo model of endocardial cushion explants. We show that HB-EGF suppresses valve mesenchymal cell proliferation through a heterodimer of ErbB1 and ErbB4, and an ErbB1 ligand(s) promotes cell proliferation through a homodimer of ErbB1. Moreover, a rescue experiment with cleavable or uncleavable isoforms of ErbB4 in ERBB4 null cells indicates that the cleavable JM-a-type, but not the uncleavable JM-b-type, of ErbB4 rescues the defect of the null cells. These data suggest that the cytoplasmic intracellular domain of ErbB4, rather than the membrane-anchored tyrosine kinase, achieves this suppression. Our study demonstrates that opposing signals generated by different ErbB dimer combinations function in the same cardiac cushion mesenchymal cells for proper cardiac valve formation.

Direct coupling of the HER4 intracellular domain (4ICD) and STAT5A signaling is required to induce mammary epithelial cell differentiation

The HER4 receptor tyrosine kinase and STAT5A cooperate to promote mammary luminal progenitor cell maturation and mammary epithelial cell differentiation. Coupled HER4 and STAT5A signaling is mediated, in part, through association of the HER4 intracellular domain (4ICD) with STAT5A at STAT5A target gene promoters where 4ICD functions as a STAT5A transcriptional coactivator. Despite an essential role for coupled 4ICD and STAT5A signaling in mammary gland development, the mechanistic basis of 4ICD and STAT5A cooperative signaling remains unexplored. Here we show for the first time that 4ICD and STAT5A directly interact through STAT5A recruitment and binding to HER4/4ICD residue Y984. Accordingly, altering the 4ICD Y984 to phenylalanine results in a dramatic reduction of STAT5A and 4ICD-Y984F interacting complexes coimmunoprecipitated with HER4 or STAT5A specific antibodies. We further show that disrupting the 4ICD and STAT5A interaction has an important physiological impact on mammary epithelial cell differentiation. HC11 mammary epithelial cells with stable expression of 4ICD undergo differentiation with significantly increased expression of the STAT5A target genes and differentiation markers β-casein and WAP. In contrast, HC11 cells stably expressing 4ICD-Y984F failed to undergo differentiation with basal expression levels of β-casein and WAP. Differentiation in this cell system was induced in the absence of exogenous prolactin indicating that 4ICD activity is sufficient to induce mammary epithelial cell differentiation. Finally, we show that suppression of STAT5A expression abolishes the ability of 4ICD to induce HC11 differentiation and activate β-casein or WAP expression. Taken together our results demonstrate for the first time that direct coupling of 4ICD and STAT5A is both necessary and sufficient to drive mammary epithelial differentiation. In conclusion, our findings that 4ICD and STAT5A directly interact to form a physiologically important transcriptional activation complex, provide a mechanistic basis for the in vivo observations that HER4/4ICD and STAT5A cooperate to promote mammary gland progenitor cell maturation and initiate lactation at parturition.

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HER4/4ICD tyrosine 984 mediates a direct interaction with STAT5A.

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4ICD expression with an intact Y984 is sufficient to induce mammary differentiation.

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Mammary differentiation is abolished by disrupting the 4ICD and STAT5A interaction.

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STAT5 expression is required for 4ICD-induced mammary differentiation.

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.

Neuregulin-activated ERBB4 induces the SREBP-2 cholesterol biosynthetic pathway and increases low-density lipoprotein uptake

Cholesterol is a lipid that is critical for steroid hormone production and the integrity of cellular membranes, and, as such, it is essential for cell growth. The epidermal growth factor receptor (EGFR) family member ERBB4, which forms signaling complexes with other EGFR family members, can undergo ligand-induced proteolytic cleavage to release a soluble intracellular domain (ICD) that enters the nucleus to modify transcription. We found that ERBB4 activates sterol regulatory element binding protein-2 (SREBP-2) to enhance low-density lipoprotein (LDL) uptake and cholesterol biosynthesis. Expression of the ERBB4 ICD in mammary epithelial cells or activation of ERBB4 with the ligand neuregulin 1 (NRG1) induced the expression of SREBP target genes involved in cholesterol biosynthesis, including HMGCR and HMGCS1, and lipid uptake, LDLR, which encodes the LDL receptor. Addition of NRG1 increased the abundance of the cleaved, mature form of SREBP-2 through a pathway that was blocked by addition of inhibitors of PI3K (phosphatidylinositol 3-kinase) or dual inhibition of mammalian target of rapamycin complex 1 (mTORC1) and mTORC2, but not by inhibition of AKT or mTORC1. Pharmacological inhibition of the activity of SREBP site 1 protease or of all EGFR family members (with lapatinib), but not EGFR alone (with erlotinib), impaired NRG1-induced expression of cholesterol biosynthesis genes. Collectively, our findings indicated that activation of ERBB4 promotes SREBP-2-regulated cholesterol metabolism. The connections of EGFR and ERBB4 signaling with SREBP-2-regulated cholesterol metabolism are likely to be important in ERBB-regulated developmental processes and may contribute to metabolic remodeling in ERBB-driven cancers.

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.

The localization of HER4 intracellular domain and expression of its alternately-spliced isoforms have prognostic significance in ER+ HER2- breast cancer

Human epidermal growth factor receptors (HERs) are known to play a pivotal role in breast cancer, both as prognostic markers and as therapeutic targets. The importance of Her4 expression is, however, still controversially discussed; there are few reports on the clinical significance of HER4, its splice variants, and cleaved HER4 intracellular domains (4ICD) which function differently depending on their localization in breast cancer. In 238 primary invasive breast cancer patients, we analyzed the expression levels of HER4 extracellular (JM-a and JM-b) and intracellular (CYT-1 and CYT-2) domains as well as 4ICD localization, and tested the relationship with clinicopathological characteristics and prognosis. The predominantly-expressed extracellular domain was JM-a, and lower CYT-2 dominance was a factor related to better relapse-free survival. CYT-2-dominance with higher nuclear 4ICD expression was a favorable prognostic marker especially in patients with the ER+ HER2- subtype treated with endocrine therapy. The absence of cytoplasmic 4ICD staining was related to better prognosis in CYT-1-dominant patients. In conclusion, analysis of splicing variants and 4ICD localization should be considered when targeting HER4 as a novel ER+/HER2- breast cancer treatment.

Overexpression of ERBB4 JM-a CYT-1 and CYT-2 isoforms in transgenic mice reveals isoform-specific roles in mammary gland development and carcinogenesis

Introduction

Human Epidermal Growth Factor Receptor (ERBB4/HER4) belongs to the Epidermal Growth Factor receptor/ERBB family of receptor tyrosine kinases. While ERBB1, ERBB2 and ERBB3 are often overexpressed or activated in breast cancer, and are oncogenic, the role of ERBB4 in breast cancer is uncertain. Some studies suggest a tumor suppressor role of ERBB4, while other reports suggest an oncogenic potential. Alternative splicing of ERBB4 yields four major protein products, these spliced isoforms differ in the extracellular juxtamembrane domain (JM-a versus JM-b) and cytoplasmic domain (CYT-1 versus CYT-2). Two of these isoforms, JM-a CYT-1 and JM-a CYT-2, are expressed in the mammary gland. Failure to account for isoform-specific functions in previous studies may account for conflicting reports on the role of ERBB4 in breast cancer.

Methods

We have produced mouse mammary tumour virus (MMTV) -ERBB4 transgenic mice to evaluate potential developmental and carcinogenic changes associated with full length (FL) JM-a ERBB4 CYT-1 versus ERBB4 CYT-2. Mammary tissue was isolated from transgenic mice and sibling controls at various developmental stages for whole mount analysis, RNA extraction, and immunohistochemistry. To maintain maximal ERBB4 expression, transgenic mice were bred continuously for a year after which mammary glands were isolated and analyzed.

Results

Overexpressing FL CYT-1 isoform resulted in suppression of mammary ductal morphogenesis which was accompanied by decreased number of mammary terminal end buds (TEBs) and Ki-67 positive cells within TEBs, while FL CYT-2 isoform had no effect on ductal growth in pubescent mice. The suppressive ductal phenotype in CYT-1 mice disappeared after mid-pregnancy, and subsequent developmental stages showed no abnormality in mammary gland morphology or function in CYT-1 or CYT-2 transgenic mice. However, sustained expression of FL CYT-1 isoform resulted in formation of neoplastic mammary lesions, suggesting a potential oncogenic function for this isoform.

Conclusions

Together, we present isoform-specific roles of ERBB4 during puberty and early pregnancy, and reveal a novel oncogenic property of CYT-1 ERBB4. The results may be exploited to develop better therapeutic strategies in breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0501-z) contains supplementary material, which is available to authorized users.

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.

Developmental pathways hijacked by osteosarcoma

Cancer of any type often can be described by an arrest, alteration or disruption in the normal development of a tissue or organ, and understanding of the normal counterpart's development can aid in understanding the malignant state. This is certainly true for osteosarcoma and the normal developmental pathways that guide osteoblast development that are changed in the genesis of osteogenic sarcoma. A carefully regulated crescendo-decrescendo expression of RUNX2 accompanies the transition from mesenchymal stem cell to immature osteoblast to mature osteoblast. This pivotal role is controlled by several pathways, including bone morphogenic protein (BMP), Wnt/β-catenin, fibroblast growth factor (FGF), and protein kinase C (PKC). The HIPPO pathway and its downstream target YAP help to regulate proliferation of immature osteoblasts and their maturation into non-proliferating mature osteoblasts. This pathway also helps regulate expression of the mature osteoblast protein osteocalcin. YAP also regulates expression of MT1-MMP, a membrane-bound matrix metalloprotease responsible for remodeling the extracellular matrix surrounding the osteoblasts. YAP, in turn, can be regulated by the ERBB family protein Her-4. Osteosarcoma may be thought of as a cell held at the immature osteoblast stage, retaining some of the characteristics of that developmental stage. Disruptions of several of these pathways have been described in osteosarcoma, including BMP, Wnt/b-catenin, RUNX2, HIPPO/YAP, and Her-4. Further, PKC can be activated by several receptor tyrosine kinases implicated in osteosarcoma, including the ERBB family (EGFR, Her-2 and Her-4 in osteosarcoma), IGF1R, FGF, and others. Understanding these functions may aid in the understanding the mechanisms underpinning clinical observations in osteosarcoma, including both the lytic and blastic phenotypes of tumors, the invasiveness of the disease, and the tendency for treated tumors to ossify rather than shrink. Through a better understanding of the relationship between normal osteoblast development and osteosarcoma, we may gain insights into novel therapeutic avenues and improved outcomes.

Neuregulin-3 regulates epithelial progenitor cell positioning and specifies mammary phenotype

Mutation of Neuregulin-3 (Nrg3) results in defective embryonic mammary gland development. Here, we investigate functions of Nrg3 signaling in embryonic mammary morphogenesis. Nrg3 regulates the distribution of epithelial progenitor cells within the presumptive mammary-forming region during early mammary morphogenesis. Basal and suprabasal epithelial cells are significantly smaller within the hypoplastic mammary primordium (MP) that forms in Nrg3 mutants, indicative of failure to acquire mammary epithelial cell (MEC) morphological phenotype. Activation of Erbb4 JM-a CYT-1, an Erbb4 isoform expressed in the developing MP, leads to MEC spreading and migration. Nrg3 promotes the accumulation of epithelial progenitor cells at the MP site in embryo explant cultures. Our results implicate Nrg3 signaling in mediating key events of mammary mesenchyme specification, including mesenchymal condensation, mitosis, and induction of mammary marker expression. Taken together, our results show Nrg3 has a major role in conferring specification of the mammary phenotype to both epithelial and mesenchymal progenitor cells.

Neuregulin-1/erbB activities with focus on the susceptibility of the heart to anthracyclines

Neuregulin-1 (NRG1) signaling through the tyrosine kinase receptors erbB2 and erbB4 is required for cardiac morphogenesis, and it plays an essential role in maintaining the myocardial architecture during adulthood. The tyrosine kinase receptor erbB2 was first linked to the amplification and overexpression of erbb2 gene in a subtype of breast tumor cells, which is indicative of highly proliferative cells and likely a poor prognosis following conventional chemotherapy. The development of targeted therapies to block the survival of erbB2-positive cancer cells revealed that impaired NRG1 signaling through erbB2/erbB4 heterodimers combined with anthracycline chemotherapy may lead to dilated cardiomyopathy in a subpopulation of treated patients. The ventricular-specific deletion of either erbb2 or erbb4 manifested dilated cardiomyopathy, which is aggravated by the administration of doxorubicin. Based on the exacerbated toxicity displayed by the combined treatment, it is expected that the relevant pathways would be affected in a synergistic manner. This review examines the NRG1 activities that were monitored in different model systems, focusing on the emerging pathways and molecular targets, which may aid in understanding the acquired dilated cardiomyopathy that occurs under the conditions of NRG1-deficient signaling.

ERBB4 promoter polymorphism is associated with poor distant disease-free survival in high-risk early breast cancer

A number of genetic variants have been linked to increased risk of breast cancer. Little is, however, known about the prognostic significance of hereditary factors. Here, we investigated the frequency and prognostic significance of two ERBB4 promoter region variants, -782G>T (rs62626348) and -815A>T (rs62626347), in a cohort of 1010 breast cancer patients. The frequency of nine previously described somatic ERBB4 kinase domain mutations was also analyzed. Clinical material used in the study consisted of samples from the phase III, adjuvant, FinHer breast cancer trial involving 1010 women. Tumor DNA samples were genotyped for ERBB4 variants and somatic mutations using matrix-assisted laser desorption ionization/time of flight mass spectrometry. Paraffin-embedded tumor sections from all patients were immunohistochemically stained for ErbB4 expression. Association of ERBB4 genotype to distant disease-free survival (DDFS) was assessed using Kaplan-Meier and Cox regression analyses. Genotyping was successful for 91-93% of the 1010 samples. Frequencies observed for the ERBB4 variants were 2.5% and 1.3% for -782G>T and -815A>T, respectively. Variant -815A>T was significantly associated with poor survival (HR  = 2.86 [95% CI 1.15-6.67], P = 0.017). In contrast, variant -782G>T was associated with well-differentiated cancer (P = 0.019). Two (0.2%) ERBB4 kinase domain mutations were found, both of which have previously been shown to be functional and promote cancer cell growth in vitro. These data present the germ-line ERBB4 variant -815A>T as a novel prognostic marker in high-risk early breast cancer and indicate the presence of rare but potentially oncogenic somatic ERBB4 mutations in breast cancer.

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.

Deletion of ErbB4 accelerates polycystic kidney disease progression in cpk mice

ErbB4 is highly expressed in the cystic kidneys with polycystic kidney diseases. To investigate its potential role in cystogenesis, cpk mice carrying a heart-rescued ErbB4 deletion were generated. Accelerated cyst progression and renal function deterioration were noted as early as 10 days postnatally in cpk mice with ErbB4 deletion compared to cpk mice, as indicated by increased cystic index, higher kidney weight to body weight ratios and elevated BUN levels. No apparent defects in renal development were noted with ErbB4 deletion itself. Increased cell proliferation was predominately seen in the cortex of cystic kidneys with or without ErbB4 deletion. However, there was significantly more cell proliferation in the cyst-lining epithelial cells in cpk mice with ErbB4 deletion. TUNEL staining localized apoptotic cells mainly to the renal medulla. There were significantly more apoptotic cells in the cyst-lining epithelial cells in ErbB4-deleted cpk kidneys, with decreased levels of cyclin D1, increased levels of p21, p27 and cleaved caspase 3. Thus, lack of ErbB4 may contribute to elevated cell proliferation and unbalanced cell apoptosis, resulting in accelerated cyst formation and early renal function deterioration. These studies suggest that the high level of ErbB4 expression seen in cpk mice may exert relative cytoprotective effects in renal epithelia.

The prognostic value of Her4 receptor isoform expression in triple-negative and Her2 positive breast cancer patients

BACKGROUND

Not only four but rather seven different human epidermal growth factor receptor related (Her) receptor tyrosine kinases (RTKs) have been described to be expressed in a variety of normal and neoplastic tissues: Her1, Her2, Her3, and additionally four Her4 isoforms have been identified. A differential expression of Her4 isoforms does not, however, play any role in either the molecular diagnostics or treatment decision for breast cancer patients. The prognostic and predictive impact of Her4 expression in breast cancer is basically unclear.

METHODS

We quantified the Her4 variants JM-a/CYT1, JM-a/CYT2, JM-b/CYT1, and JM-b/CYT2 by isoform-specific polymerase chain reaction (qPCR) in (i) triple-negative, (ii) Her2 positive breast cancer tissues and (iii) in benign breast tissues.

RESULTS

In all three tissue collectives we never found the JM-b/CYT1 or the JM-b/CYT2 isoform expressed. In contrast, the two JM-a/CYT1 and JM-a/CYT2 isoforms were always simultaneously expressed but at different ratios. We identified a positive prognostic impact on overall survival (OS) in triple-negative and event-free survival (EFS) in Her2 positive patients. This finding is independent of the absolute JM-a/CYT1 to JM-a/CYT2 expression ratio. In Her2 positive patients, Her4 expression only has a favorable effect in estrogen-receptor (ER)-positive but not in ER-negative individuals.

CONCLUSION

In summary, JM-a/CYT1 and JM-a/CYT2 but not JM-b isoforms of the Her4 receptor are simultaneously expressed in both triple-negative and Her2 positive breast cancer tissues. Although different expression ratios of the two JM-a isoforms did not reveal any additional information, Her4 expression basically indicates a prolonged EFS and OFS. An extended expression analysis that takes all Her receptor homologs, including the Her4 isoforms, into account might render more precisely the molecular diagnostics required for the development of optimized targeted therapies.

High-throughput screening for identification of inhibitors of EpCAM-dependent growth of hepatocellular carcinoma cells

The cancer stem cell marker, EpCAM, is an important indicator of Wnt/β-catenin signaling activation and a functional component of hepatocellular tumor-initiating cells. A high-throughput screening assay was developed to identify inhibitors of EpCAM-dependent growth of hepatocellular carcinoma (HCC) cells. EpCAM(+) and EpCAM(-) HCC cell lines were assessed for differential sensitivity to a Wnt/β-catenin pathway inhibitor. Libraries comprising 22 668 pure compounds and 107 741 crude or partially purified natural product extracts were tested, and 12 pure compounds and 67 natural product extracts were identified for further study. Three active compounds and the positive control were further characterized in terms of effects on EpCAM expression. Treatment of EpCAM(+) Hep3B cells resulted in loss of EpCAM expression as assessed by flow cytometry. This reduction was incomplete (most cells continued to express EpCAM), but resulted in generation of cell populations expressing lower levels of EpCAM. Sublethal concentrations (~IC50 ) reduced median EpCAM expression to 28% of control after 1 day and 19% of control after 2 days. Reduction in EpCAM expression preceded growth inhibition suggesting that a threshold of EpCAM expression may be required for growth of EpCAM-dependent cells. The identification of compounds with a variety of possible molecular targets suggests a likelihood of multiple mechanisms for modulation of EpCAM-dependent cell growth.

Neuregulin 3 and erbb signalling networks in embryonic mammary gland development

We review the role of Neuregulin 3 (Nrg3) and Erbb receptor signalling in embryonic mammary gland development. Neuregulins are growth factors that bind and activate its cognate Erbb receptor tyrosine kinases, which form a signalling network with established roles in breast development and breast cancer. Studies have shown that Nrg3 expression profoundly impacts early stages of embryonic mammary development. Network analysis shows how Nrg/Erbb signals could integrate with other major regulators of embryonic mammary development to elicit the morphogenetic processes and cell fate decisions that occur as the mammary lineage is established.

Directing HER4 mRNA expression towards the CYT2 isoform by antisense oligonucleotide decreases growth of breast cancer cells in vitro and in vivo

Background:

The tyrosine kinase receptor HER4 is a member of the epidermal growth factor receptor (EGFR) family. It plays diverse roles in cancer development and cancer progression and can both exert oncogenic and tumour-suppressive activities. Alternatively spliced isoforms of HER4 are critical to the different signalling possibilities of HER4.

Methods:

We use a splice-switching oligonucleotide (SSO) to direct the alternative splicing of HER4 from the CYT1 to the CYT2 isoform in HER4-expressing breast cancer cells.

Results:

Treatment with a target-specific SSO was accompanied by a decreased growth of the cells (P<0.0001). In addition, the SSO treatment induced a decreased activity of Akt. We confirmed the SSO-dependent switching of the HER4 isoform CYT1 to CYT2 expression in a xenografted mouse tumour model driven by subcutaneously injected MCF7 cells. We hence demonstrated the feasibility of SSO-directed splice-switching activity in vivo. Furthermore, the SSO treatment efficiently decreased the growth of the xenografted tumour (P=0.0014).

Conclusion:

An SSO directing the splicing of HER4 towards the CYT2 isoform has an inhibitory effect of cancer cell growth in vitro and in vivo. These results may pave the way for the development of new anticancer drugs in HER4-deregulated cancers in humans.

Function of alternative splicing

Almost all polymerase II transcripts undergo alternative pre-mRNA splicing. Here, we review the functions of alternative splicing events that have been experimentally determined. The overall function of alternative splicing is to increase the diversity of mRNAs expressed from the genome. Alternative splicing changes proteins encoded by mRNAs, which has profound functional effects. Experimental analysis of these protein isoforms showed that alternative splicing regulates binding between proteins, between proteins and nucleic acids as well as between proteins and membranes. Alternative splicing regulates the localization of proteins, their enzymatic properties and their interaction with ligands. In most cases, changes caused by individual splicing isoforms are small. However, cells typically coordinate numerous changes in 'splicing programs', which can have strong effects on cell proliferation, cell survival and properties of the nervous system. Due to its widespread usage and molecular versatility, alternative splicing emerges as a central element in gene regulation that interferes with almost every biological function analyzed.

DiffSplice: the genome-wide detection of differential splicing events with RNA-seq

The RNA transcriptome varies in response to cellular differentiation as well as environmental factors, and can be characterized by the diversity and abundance of transcript isoforms. Differential transcription analysis, the detection of differences between the transcriptomes of different cells, may improve understanding of cell differentiation and development and enable the identification of biomarkers that classify disease types. The availability of high-throughput short-read RNA sequencing technologies provides in-depth sampling of the transcriptome, making it possible to accurately detect the differences between transcriptomes. In this article, we present a new method for the detection and visualization of differential transcription. Our approach does not depend on transcript or gene annotations. It also circumvents the need for full transcript inference and quantification, which is a challenging problem because of short read lengths, as well as various sampling biases. Instead, our method takes a divide-and-conquer approach to localize the difference between transcriptomes in the form of alternative splicing modules (ASMs), where transcript isoforms diverge. Our approach starts with the identification of ASMs from the splice graph, constructed directly from the exons and introns predicted from RNA-seq read alignments. The abundance of alternative splicing isoforms residing in each ASM is estimated for each sample and is compared across sample groups. A non-parametric statistical test is applied to each ASM to detect significant differential transcription with a controlled false discovery rate. The sensitivity and specificity of the method have been assessed using simulated data sets and compared with other state-of-the-art approaches. Experimental validation using qRT-PCR confirmed a selected set of genes that are differentially expressed in a lung differentiation study and a breast cancer data set, demonstrating the utility of the approach applied on experimental biological data sets. The software of DiffSplice is available at http://www.netlab.uky.edu/p/bioinfo/DiffSplice.

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.