Modulation of Erbb2 signaling during development: a threshold level of Erbb2 signaling is required for development

High-throughput sequencing reveals hub genes for human early embryonic development arrest in vitro fertilization: a pilot study

Many clinical studies have shown that embryos of in vitro fertilization (IVF) are often prone to developmental arrest, which leads to recurrent failure of IVF treatment. Early embryonic arrest has always been an urgent clinical problem in assisted reproduction centers. However, the molecular mechanisms underlying early embryonic development arrest remain largely unknown. The objective of this study is to investigate potential candidate hub genes and key signaling pathways involved in early stages of embryonic development. RNA-seq analysis was performed on normal and arrest embryos to study the changes of gene expression during early embryonic development. A total of 520 genes exhibiting differential expression were identified, with 174 genes being upregulated and 346 genes being downregulated. Upregulated genes show enrichment in biosynthesis, cellular proliferation and differentiation, and epigenetic regulation. While downregulated genes exhibit enrichment in transcriptional activity, epigenetic regulation, cell cycle progression, cellular proliferation and ubiquitination. The STRING (search tool for the retravel of interacting genes/proteins) database was utilized to analyze protein-protein interactions among these genes, aiming to enhance comprehension of the potential role of these differentially expressed genes (DEGs). A total of 22 hub genes (highly connected genes) were identified among the DEGs using Cytoscape software. Of these, ERBB2 and VEGFA were upregulated, while the remaining 20 genes (CCNB1, CCNA2, DICER1, NOTCH1, UBE2B, UBE2N, PRMT5, UBE2D1, MAPK3, SOX9, UBE2C, UB2D2, EGF, ACTB, UBA52, SHH, KRAS, UBE2E1, ADAM17 and BRCA2) were downregulated. These hub genes are associated with crucial biological processes such as ubiquitination, cellular senescence, cell proliferation and differentiation, and cell cycle. Among these hub genes, CCNA2 and CCNB1 may be involved in controlling cell cycle, which are critical process in early embryonic development.

Integrated multi-omics analysis of adverse cardiac remodeling and metabolic inflexibility upon ErbB2 and ERRα deficiency

Functional oncogenic links between ErbB2 and ERRα in HER2+ breast cancer patients support a therapeutic benefit of co-targeted therapies. However, ErbB2 and ERRα also play key roles in heart physiology, and this approach could pose a potential liability to cardiovascular health. Herein, using integrated phosphoproteomic, transcriptomic and metabolic profiling, we uncovered molecular mechanisms associated with the adverse remodeling of cardiac functions in mice with combined attenuation of ErbB2 and ERRα activity. Genetic disruption of both effectors results in profound effects on cardiomyocyte architecture, inflammatory response and metabolism, the latter leading to a decrease in fatty acyl-carnitine species further increasing the reliance on glucose as a metabolic fuel, a hallmark of failing hearts. Furthermore, integrated omics signatures of ERRα loss-of-function and doxorubicin treatment exhibit common features of chemotherapeutic cardiotoxicity. These findings thus reveal potential cardiovascular risks in discrete combination therapies in the treatment of breast and other cancers.

Murine hearts deficient in ErbB2 and/or ERRα are used to profile the adverse cardiac remodeling associated with potential targeted breast cancer treatments by phosphoproteomic, transcriptomic and metabolomic profiling.

Pulling back the curtain: The hidden functions of receptor tyrosine kinases in development

Receptor tyrosine kinases (RTKs) are a conserved superfamily of transmembrane growth factor receptors that drive numerous cellular processes during development and in the adult. Upon activation, multiple adaptors and signaling effector proteins are recruited to binding site motifs located within the intracellular domain of the RTK. These RTK-effector interactions drive subsequent intracellular signaling cascades involved in canonical RTK signaling. Genetic dissection has revealed that alleles of Fibroblast Growth Factor receptors (FGFRs) that lack all canonical RTK signaling still retain some kinase-dependent biological activity. Here we examine how genetic analysis can be used to understand the mechanism by which RTKs drive multiple developmental processes via canonical signaling while revealing noncanonical activities. Recent data from both FGFRs and other RTKs highlight potential noncanonical roles in cell adhesion and nuclear signaling. The data supporting such functions are discussed as are recent technologies that have the potential to provide valuable insight into the developmental significance of these noncanonical activities.

In vivo modeling of the EGFR family in breast cancer progression and therapeutic approaches

Modeling breast cancer through the generation of genetically engineered mouse models (GEMMs) has become the gold standard in the study of human breast cancer. Notably, the in vivo modeling of the epidermal growth factor receptor (EGFR) family has been key to the development of therapeutics and has helped better understand the signaling pathways involved in cancer initiation, progression and metastasis. The HER2/ErbB2 receptor is a member of the EGFR family and 20% of breast cancers are found to belong in the HER2-positive histological subtype. Historical and more recent advances in the field have shaped our understanding of HER2-positive breast cancer signaling and therapeutic approaches.

Receptor tyrosine kinase signaling: regulating neural crest development one phosphate at a time

Receptor tyrosine kinases (RTKs) bind to a subset of growth factors on the surface of cells and elicit responses with broad roles in developmental and postnatal cellular processes. Receptors in this subclass consist of an extracellular ligand-binding domain, a single transmembrane domain, and an intracellular domain harboring a catalytic tyrosine kinase and regulatory sequences that are phosphorylated either by the receptor itself or by various interacting proteins. Once activated, RTKs bind signaling molecules and recruit effector proteins to mediate downstream cellular responses through various intracellular signaling pathways. In this chapter, we highlight the role of a subset of RTK families in regulating the activity of neural crest cells (NCCs) and the development of their derivatives in mammalian systems. NCCs are migratory, multipotent cells that can be subdivided into four axial populations, cranial, cardiac, vagal, and trunk. These cells migrate throughout the vertebrate embryo along defined pathways and give rise to unique cell types and structures. Interestingly, individual RTK families often have specific functions in a subpopulation of NCCs that contribute to the diversity of these cells and their derivatives in the mammalian embryo. We additionally discuss current methods used to investigate RTK signaling, including genetic, biochemical, large-scale proteomic, and biosensor approaches, which can be applied to study intracellular signaling pathways active downstream of this receptor subclass during NCC development.

Erbb2 is required for cardiac atrial electrical activity during development

The heart is the first organ required to function during embryonic development and is absolutely necessary for embryo survival. Cardiac activity is dependent on both the sinoatrial node (SAN), which is the pacemaker of heart's electrical activity, and the cardiac conduction system which transduces the electrical signal though the heart tissue, leading to heart muscle contractions. Defects in the development of cardiac electrical function may lead to severe heart disorders. The Erbb2 (Epidermal Growth Factor Receptor 2) gene encodes a member of the EGF receptor family of receptor tyrosine kinases. The Erbb2 receptor lacks ligand-binding activity but forms heterodimers with other EGF receptors, stabilising their ligand binding and enhancing kinase-mediated activation of downstream signalling pathways. Erbb2 is absolutely necessary in normal embryonic development and homozygous mouse knock-out Erbb2 embryos die at embryonic day (E)10.5 due to severe cardiac defects. We have isolated a mouse line, l11Jus8, from a random chemical mutagenesis screen, which carries a hypomorphic missense mutation in the Erbb2 gene. Homozygous mutant embryos exhibit embryonic lethality by E12.5-13. The l11Jus8 mutants display cardiac haemorrhage and a failure of atrial function due to defects in atrial electrical signal propagation, leading to an atrial-specific conduction block, which does not affect ventricular conduction. The l11Jus8 mutant phenotype is distinct from those reported for Erbb2 knockout mouse mutants. Thus, the l11Jus8 mouse reveals a novel function of Erbb2 during atrial conduction system development, which when disrupted causes death at mid-gestation.

ERBB2 deficiency alters an E2F-1-dependent adaptive stress response and leads to cardiac dysfunction

The tyrosine kinase receptor ERBB2 is required for normal development of the heart and is a potent oncogene in breast epithelium. Trastuzumab, a monoclonal antibody targeting ERBB2, improves the survival of breast cancer patients, but cardiac dysfunction is a major side effect of the drug. The molecular mechanisms underlying how ERBB2 regulates cardiac function and why trastuzumab is cardiotoxic remain poorly understood. We show here that ERBB2 hypomorphic mice develop cardiac dysfunction that mimics the side effects observed in patients treated with trastuzumab. We demonstrate that this phenotype is related to the critical role played by ERBB2 in cardiac homeostasis and physiological hypertrophy. Importantly, genetic and therapeutic reduction of ERBB2 activity in mice, as well as ablation of ERBB2 signaling by trastuzumab or siRNAs in human cardiomyocytes, led to the identification of an impaired E2F-1-dependent genetic program critical for the cardiac adaptive stress response. These findings demonstrate the existence of a previously unknown mechanistic link between ERBB2 and E2F-1 transcriptional activity in heart physiology and trastuzumab-induced cardiac dysfunction.

ErbB2 dephosphorylation and anti-proliferative effects of neuregulin-1 in ErbB2-overexpressing cells; re-evaluation of their low-affinity interaction

Neuregulin-1 binds to ErbB3 and ErbB4 and regulates cancer proliferation and differentiation. Neuregulin-1 had been suggested to also react with ErbB2, but this argument becomes controversial. Here, we re-evaluated the cellular responses and ErbB2 interaction of neuregulin-1 in ErbB2 overexpressing cell lines. In a competitive ligand-binding assay, we detected significant replacement of [³⁵S]-labeled neuregulin-1 with nano molar ranges of cold neuregulin-1 in L929 cells expressing ErbB2 alone and SKOV3 cells carrying sulf-1 cDNA but not in these parental cells. The concentration of neuregulin-1 significantly decreased thymidine incorporation and phosphorylation of ErbB2 (Tyr877, Tyr1396, and Tyr1121) in ErbB2-overexpressing cancer cells as well as in L929 cells expressing ErbB2. A crosslinking assay ascertained the presence of neuregulin-1 immunoreactivity in the ErbB2 immune complexes of L929 expressing ErbB2 alone. These results suggest that the higher concentrations of neuregulin-1 exert an anti-oncogenic activity to attenuate ErbB2 auto-phosphorylation potentially through its low-affinity interaction with ErbB2.

Yy1 as a molecular link between neuregulin and transcriptional modulation of peripheral myelination

Fast axonal conduction depends on myelin, which is formed by Schwann cells in the PNS. We found that the transcription factor Yin Yang 1 (YY1) is crucial for peripheral myelination. Conditional ablation of Yy1 in the Schwann cell lineage resulted in severe hypomyelination, which occurred independently of altered Schwann cell proliferation or apoptosis. In Yy1 mutant mice, Schwann cells established a 1:1 relationship with axons but were unable to myelinate them. The Schwann cells expressed low levels of myelin proteins and of Egr2 (also called Krox20), which is an important regulator of peripheral myelination. In vitro, Schwann cells that lacked Yy1 did not upregulate Egr2 in response to neuregulin1 and did not express myelin protein zero. This phenotype was rescued by overexpression of Egr2. In addition, neuregulin-induced phosphorylation of YY1 was required for transcriptional activation of Egr2. Thus, YY1 emerges as an important activator of peripheral myelination that links neuregulin signaling with Egr2 expression.

Endocytosis and intracellular trafficking of ErbBs

This review article describes the pathways and mechanisms of endocytosis and post-endocytic sorting of the EGF receptor (EGFR/ErbB1) and other members of the ErbB family. Growth factor binding to EGFR accelerates its internalization through clathrin-coated pits which is followed by the efficient lysosomal targeting of internalized receptors and results in receptor down-regulation. The role of EGFR interaction with the Grb2 adaptor protein and Cbl ubiquitin ligase, and receptor ubiquitination in the clathrin-dependent internalization and sorting of EGFR in multivesicular endosomes is discussed. Activation and phosphorylation of ErbB2, ErbB3 and ErbB4 also results in their ubiquitination. However, these ErbBs are internalized and targeted to lysosomes less efficiently than EGFR. When overexpressed endocytosis-impaired ErbBs may inhibit the internalization and degradation of EGFR.

Endocytosis and intracellular trafficking of ErbBs

This review article describes the pathways and mechanisms of endocytosis and post-endocytic sorting of the EGF receptor (EGFR/ErbB1) and other members of the ErbB family. Growth factor binding to EGFR accelerates its internalization through clathrin-coated pits which is followed by the efficient lysosomal targeting of internalized receptors and results in receptor down-regulation. The role of EGFR interaction with the Grb2 adaptor protein and Cbl ubiquitin ligase, and receptor ubiquitination in the clathrin-dependent internalization and sorting of EGFR in multivesicular endosomes is discussed. Activation and phosphorylation of ErbB2, ErbB3 and ErbB4 also results in their ubiquitination. However, these ErbBs are internalized and targeted to lysosomes less efficiently than EGFR. When overexpressed endocytosis-impaired ErbBs may inhibit the internalization and degradation of EGFR.

Endocytic downregulation of ErbB receptors: mechanisms and relevance in cancer

ErbB receptors (EGFR (ErbB1), ErbB2, ErbB3, and ErbB4) are important regulators of normal growth and differentiation, and they are involved in the pathogenesis of cancer. Following ligand binding and receptor activation, EGFR is endocytosed and transported to lysosomes where the receptor is degraded. This downregulation of EGFR is a complex and tightly regulated process. The functions of ErbB2, ErbB3, and ErbB4 are also regulated by endocytosis to some extent, although the current knowledge of these processes is sparse. Impaired endocytic downregulation of signaling receptors is frequently associated with cancer, since it can lead to increased and uncontrolled receptor signaling. In this review we describe the current knowledge of ErbB receptor endocytic downregulation. In addition, we outline how ErbB receptors can escape endocytic downregulation in cancer, and we discuss how targeted anti-cancer therapy may induce endocytic downregulation of ErbB receptors.

Distinct ErbB-2 coupled signaling pathways promote mammary tumors with unique pathologic and transcriptional profiles

ErbB-2 overexpression and amplification occurs in 15% to 30% of human invasive breast carcinomas associated with poor clinical prognosis. Previously, we have shown that four ErbB-2/Neu tyrosine-autophosphorylation sites within the cytoplasmic tail of the receptor recruit distinct adaptor proteins and are sufficient to mediate transforming signals in vitro. Two of these sites, representing the growth factor receptor binding protein 2 (Grb2; Neu-YB) and the Src homology and collagen (Shc; Neu-YD) binding sites, can induce mammary tumorigenesis and metastasis. Here, we show that transgenic mice bearing the two other ErbB-2 autophosphorylation sites (Neu-YC and Neu-YE) develop metastatic mammary tumors. A detailed comparison of biological profiles among all Neu mutant mouse models revealed that Neu-YC, Neu-YD, and Neu-YE mammary tumors shared similar pathologic and transcriptional features. By contrast, the Neu-YB mouse model displayed a unique pathology with a high metastatic potential that correlates with a distinct transcriptional profile, including genes that promote malignant tumor progression such as metalloproteinases and chemokines. Furthermore, Neu-YB tumor epithelial cells showed abundant intracellular protein level of the chemokine CXCL12/SDF-1alpha, which may reflect the aggressive nature of this Neu mutant mouse model. Taken together, these findings indicate that activation of distinct Neu-coupled signaling pathways has an important impact on the biological behavior of Neu-induced tumors.

ErbB2 signaling in Schwann cells is mostly dispensable for maintenance of myelinated peripheral nerves and proliferation of adult Schwann cells after injury

Neuregulin/erbB signaling is critically required for survival and proliferation of Schwann cells as well as for establishing correct myelin thickness of peripheral nerves during development. In this study, we investigated whether erbB2 signaling in Schwann cells is also essential for the maintenance of myelinated peripheral nerves and for Schwann cell proliferation and survival after nerve injury. To this end, we used inducible Cre-loxP technology using a PLP-CreERT2 allele to ablate erbB2 in adult Schwann cells. ErbB2 expression was markedly reduced after induction of erbB2 gene disruption with no apparent effect on the maintenance of already established myelinated peripheral nerves. In contrast to development, Schwann cell proliferation and survival were not impaired in mutant animals after nerve injury, despite reduced levels of MAPK-P (phosphorylated mitogen-activated protein kinase) and cyclin D1. ErbB1 and erbB4 do not compensate for the loss of erbB2. We conclude that adult Schwann cells do not require major neuregulin signaling through erbB2 for proliferation and survival after nerve injury, in contrast to development and in cell culture.