A novel juxtamembrane domain isoform of HER4/ErbB4. Isoform-specific tissue distribution and differential processing in response to phorbol ester

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.

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

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

Bergmann glia function in granule cell migration during cerebellum development

Granule cell migration influences the laminar structure of the cerebellum and thereby affects cerebellum function. Bergmann glia are derived from radial glial cells and aid in granule cell radial migration by providing a scaffold for migration and by mediating interactions between Bergmann glia and granule cells. In this review, we summarize Bergmann glia characteristics and the mechanisms underlying the effect of Bergmann glia on the radial migration of granule neurons in the cerebellum. Furthermore, we will focus our discussion on the important factors involved in glia-mediated radial migration so that we may elucidate the possible mechanistic pathways used by Bergmann glia to influence granule cell migration during cerebellum development.

Bergmann glia function in granule cell migration during cerebellum development

Granule cell migration influences the laminar structure of the cerebellum and thereby affects cerebellum function. Bergmann glia are derived from radial glial cells and aid in granule cell radial migration by providing a scaffold for migration and by mediating interactions between Bergmann glia and granule cells. In this review, we summarize Bergmann glia characteristics and the mechanisms underlying the effect of Bergmann glia on the radial migration of granule neurons in the cerebellum. Furthermore, we will focus our discussion on the important factors involved in glia-mediated radial migration so that we may elucidate the possible mechanistic pathways used by Bergmann glia to influence granule cell migration during cerebellum development.

Hypoxia changes the expression of the epidermal growth factor (EGF) system in human hearts and cultured cardiomyocytes

Background

The epidermal growth factor (EGF) receptors HER2 and HER4 and the ligands HB-EGF and NRG1 are crucial for heart development. The purpose of our study was to investigate the role of the complete EGF system in relation to hypoxia of the heart.

Methodology/Principal Findings

We examined the mRNA expression by real time PCR of the 4 receptors and 12 ligands from the EGF-system in paired normoxic and hypoxic biopsies isolated from human hearts during coronary artery bypass operation. Compared to normoxic biopsies, hypoxic samples showed down-regulation of HER2 (P = 0.0005) and NRG1 (both α (P = 0.02) and β (P = 0.03) isoforms). In contrast, HB-EGF (P = 0.0008), NRG2β (P = 0.01) and EGFR (P = 0.02) were up-regulated. As HER2 is essential for heart development and we find its expression reduced under hypoxia we investigated the effect of HER2 inhibition in hypoxic HL-1 cardiomyocytes by treatment with trastuzumab (20 nM). This resulted in inhibition of cardiomyocyte proliferation, but interestingly only in hypoxic cells. Co-treatment of HL-1 cells with HB-EGF (10 nM) but not with NRG-1 (5 ng/ml) rescued the cardiomyocytes from HER2 inhibition. HL-1 cardiomyocytes exposed to hypoxia revealed nuclear translocation of activated MAPK and the activity of this downstream signaling molecule was decreased by HER2 inhibition (20 nM trastuzumab), and re-established by HB-EGF (10 nM).

Conclusions/Significance

Hypoxia in the human heart alters the expression of the EGF system. Mimicking the HER2 down-regulation seen in the human heart in cultured cardiomyocytes inhibited their proliferation under hypoxic conditions. Interestingly, HB-EGF is induced in the hypoxic human hearts, and rescues hypoxic cardiomyocytes from the effect of HER2 inhibition in the in vitro model. The results have implications for future treatment strategies of patients with ischemic heart disease.

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.

Neuregulin 1-ErbB4-PI3K signaling in schizophrenia and phosphoinositide 3-kinase-p110δ inhibition as a potential therapeutic strategy

Neuregulin 1 (NRG1) and ErbB4, critical neurodevelopmental genes, are implicated in schizophrenia, but the mediating mechanisms are unknown. Here we identify a genetically regulated, pharmacologically targetable, risk pathway associated with schizophrenia and with ErbB4 genetic variation involving increased expression of a PI3K-linked ErbB4 receptor (CYT-1) and the phosphoinositide 3-kinase subunit, p110δ (PIK3CD). In human lymphoblasts, NRG1-mediated phosphatidyl-inositol,3,4,5 triphosphate [PI(3,4,5)P3] signaling is predicted by schizophrenia-associated ErbB4 genotype and PIK3CD levels and is impaired in patients with schizophrenia. In human brain, the same ErbB4 genotype again predicts increased PIK3CD expression. Pharmacological inhibition of p110δ using the small molecule inhibitor, IC87114, blocks the effects of amphetamine in a mouse pharmacological model of psychosis and reverses schizophrenia-related phenotypes in a rat neonatal ventral hippocampal lesion model. Consistent with these antipsychotic-like properties, IC87114 increases AKT phosphorylation in brains of treated mice, implicating a mechanism of action. Finally, in two family-based genetic studies, PIK3CD shows evidence of association with schizophrenia. Our data provide insight into a mechanism of ErbB4 association with schizophrenia; reveal a previously unidentified biological and disease link between NRG1-ErbB4, p110δ, and AKT; and suggest that p110δ is a previously undescribed therapeutic target for the treatment of psychiatric disorders.

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.

The role of neuregulin/ErbB2/ErbB4 signaling in the heart with special focus on effects on cardiomyocyte proliferation

The signaling complex consisting of the growth factor neuregulin-1 (NRG1) and its tyrosine kinase receptors ErbB2 and ErbB4 has a critical role in cardiac development and homeostasis of the structure and function of the adult heart. Recent research results suggest that targeting this signaling complex may provide a viable strategy for treating heart failure. Clinical trials are currently evaluating the effectiveness and safety of intravenous administration of recombinant NRG1 formulations in heart failure patients. Endogenous as well as administered NRG1 has multiple possible activities in the adult heart, but how these are related is unknown. It has recently been demonstrated that NRG1 administration can stimulate proliferation of cardiomyocytes, which may contribute to repair failing hearts. This review summarizes the current knowledge of how NRG1 and its receptors control cardiac physiology and biology, with special emphasis on its role in cardiomyocyte proliferation during myocardial growth and regeneration.

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.

Interaction with ErbB4 promotes hypoxia-inducible factor-1α signaling

The receptor-tyrosine kinase ErbB4 was identified as a direct regulator of hypoxia-inducible factor-1α (HIF-1α) signaling. Cleaved intracellular domain of ErbB4 directly interacted with HIF-1α in the nucleus, and stabilized HIF-1α protein in both normoxic and hypoxic conditions by blocking its proteasomal degradation. The mechanism of HIF stabilization was independent of VHL and proline hydroxylation but dependent on RACK1. ErbB4 activity was necessary for efficient HRE-driven promoter activity, transcription of known HIF-1α target genes, and survival of mammary carcinoma cells in vitro. In addition, mammary epithelial specific targeting of Erbb4 in the mouse significantly reduced the amount of HIF-1α protein in vivo. ERBB4 expression also correlated with the expression of HIF-regulated genes in a series of 4552 human normal and cancer tissue samples. These data demonstrate that soluble ErbB4 intracellular domain promotes HIF-1α stability and signaling via a novel mechanism.

Analysis of association between common SNPs in ErbB4 and bipolar affective disorder, major depressive disorder and schizophrenia in the Han Chinese population

Neuregulin-1 (NRG1) is associated with schizophrenia. As one of the receptors of NRG1, v-erb-a erythroblastic leukemia viral oncogene homolog 4 (ErbB4) has also been reported to be associated with schizophrenia. Since there can be shared genetic variants among bipolar affective disorder, major depressive disorder and schizophrenia, we tested the association between ErbB4 and these three major psychiatric disorders in the Han Chinese population. Five single nucleotide polymorphisms (SNPs) were selected based on previous positive reports and linkage disequilibrium information of the HapMap Han Chinese individuals from Beijing (CHB)+individuals from Tokyo, Japan (JPT) population. These SNPs were genotyped in 1140 bipolar affective disorder (BPAD) patients, 1140 schizophrenia (SCZ) patients, 1139 major depressive disorder (MDD) patients and 1140 normal controls. Two SNPs (rs707284 and rs839523) showed nominal significance in the BPAD patients but this was eliminated after permutation. No significant association between ErbB4 and the two other psychiatric disorders was observed, nor did haplotype analysis reveal any positive signal.

ErbB4 localization to cardiac myocyte nuclei, and its role in myocyte DNA damage response

The intracellular domain of ErbB4 receptor tyrosine kinase is known to translocate to the nucleus of cells where it can regulate p53 transcriptional activity. The purpose of this study was to examine whether ErbB4 can localize to the nucleus of adult rat ventricular myocytes (ARVM), and regulate p53 in these cells. We demonstrate that ErbB4 does locate to the nucleus of cardiac myocytes as a full-length protein, although nuclear location occurs as a full-length protein that does not require Protein Kinase C or γ-secretase activity. Consistent with this we found that only the non-cleavable JM-b isoform of ErbB4 is expressed in ARVM. Doxorubicin was used to examine ErbB4 role in regulation of a DNA damage response in ARVM. Doxorubicin induced p53 and p21 was suppressed by treatment with AG1478, an EGFR and ErbB4 kinase inhibitor, or suppression of ErbB4 expression with small interfering RNA. Thus ErbB4 localizes to the nucleus as a full-length protein, and plays a role in the DNA damage response induced by doxorubicin in cardiac myocytes.

ErbB4 modulates tubular cell polarity and lumen diameter during kidney development

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

Alternative splicing in oncogenic kinases: from physiological functions to cancer

Among the 518 protein kinases encoded by the human kinome, several of them act as oncoproteins in human cancers. Like other eukaryotic genes, oncogenes encoding protein kinases are frequently subjected to alternative splicing in coding as well as noncoding sequences. In the present paper, we will illustrate how alternative splicing can significantly impact on the physiological functions of oncogenic protein kinases, as demonstrated by mouse genetic model studies. This includes examples of membrane-bound tyrosine kinases receptors (FGFR2, Ret, TrkB, ErbB4, and VEGFR) as well as cytosolic protein kinases (B-Raf). We will further discuss how regular alternative splicing events of these kinases are in some instances implicated in oncogenic processes during tumor progression (FGFR, TrkB, ErbB2, Abl, and AuroraA). Finally, we will present typical examples of aberrant splicing responsible for the deregulation of oncogenic kinases activity in cancers (AuroraB, Jak2, Kit, Met, and Ron).

Conserved interneuron-specific ErbB4 expression in frontal cortex of rodents, monkeys, and humans: implications for schizophrenia

BACKGROUND

Neuregulin-1 and ErbB4 are genetically associated with schizophrenia, and detailed knowledge of the cellular and subcellular localization of ErbB4 is important for understanding how neuregulin-1 regulates neuronal network activity and behavior. Expression of ErbB4 is restricted to interneurons in the rodent hippocampus and cortex. However, controversy remains about the cellular expression pattern in primate brain and its subcellular distribution in postsynaptic somatodendritic locations versus presynaptic terminals.

METHODS

ErbB4 expression was analyzed in pyramidal cells and interneurons in the frontal cortex of five species: C57BL6 mice (n = 3), ErbB4⁻/⁻ mice (n = 2), Sprague-Dawley rats (n = 3), two macaque species (n = 3 + 2), and humans (normal control subjects, n = 2). We investigated 1) messenger RNA in mice, macaques, and humans; 2) protein expression in all species using highly specific monoclonal antibodies; and 3) specificity tests of several ErbB4 antibodies on brain samples (mouse, macaque, human).

RESULTS

ErbB4 RNA is restricted to interneurons in the frontal cortex of mice. ErbB4 protein is undetectable in pyramidal cells of rodents, macaques, and human frontal cortex, whereas most interneurons positive for parvalbumin, calretinin, or cholecystokinin, but only a minority of calbindin-positive cells, co-express ErbB4 in macaques. Importantly, no presynaptic ErbB4 expression was detected in any species.

CONCLUSIONS

The interneuron-selective somatodendritic expression of ErbB4 is consistent with a primary role of neuregulin-ErbB4 signaling in the postsynaptic modulation of gamma-aminobutyric acidergic function in rodents and primates. Our data validate the use of rodents to analyze effects of abnormal ErbB4 function as a means to model endophenotypes of psychiatric disorders.

Ligand activation leads to regulated intramembrane proteolysis of fibroblast growth factor receptor 3

FGFR3 is implicated in several human diseases. Following activation and endocytosis, FGFR3 undergoes sequential ectodomain and intramembrane cleavages to generate a soluble cytoplasmic fragment that can translocate to the nucleus.

Fibroblast growth factor receptor 3 (FGFR3) is a major negative regulator of bone growth that inhibits the proliferation and differentiation of growth plate chondrocytes. Activating mutations of its c isoform cause dwarfism in humans; somatic mutations can drive oncogenic transformation in multiple myeloma and bladder cancer. How these distinct activities arise is not clear. FGFR3 was previously shown to undergo proteolytic cleavage in the bovine rib growth plate, but this was not explored further. Here, we show that FGF1 induces regulated intramembrane proteolysis (RIP) of FGFR3. The ectodomain is proteolytically cleaved (S1) in response to ligand-induced receptor activation, but unlike most RIP target proteins, it requires endocytosis and does not involve a metalloproteinase. S1 cleavage generates a C-terminal domain fragment that initially remains anchored in the membrane, is phosphorylated, and is spatially distinct from the intact receptor. Ectodomain cleavage is followed by intramembrane cleavage (S2) to generate a soluble intracellular domain that is released into the cytosol and can translocate to the nucleus. We identify the S1 cleavage site and show that γ-secretase mediates the S2 cleavage event. In this way we demonstrate a mechanism for the nuclear localization of FGFR3 in response to ligand activation, which may occur in both development and disease.

SynCAM1, a synaptic adhesion molecule, is expressed in astrocytes and contributes to erbB4 receptor-mediated control of female sexual development

Female sexual maturation requires erythroblastosis B (erbB)4 signaling in hypothalamic astrocytes; however, the mechanisms by which erbB4 contributes to this process are incompletely understood. Here we show that SynCAM1, a synaptic adhesion molecule with signaling capabilities, is not only expressed highly in neurons, but also in hypothalamic astrocytes and is functionally associated with erbB4 receptor activity. Whereas SynCAM1 expression is diminished in astrocytes with impaired erbB4 signaling, ligand-dependent activation of astroglial erbB4 receptors results in rapid association of erbB4 with SynCAM1 and activation of SynCAM1 gene transcription. To determine whether astrocytic SynCAM1-dependent intracellular signaling is required for normal female reproductive function, we generated transgenic mice that express in an astrocyte-specific manner a dominant-negative form of SynCAM1 lacking the intracellular domain. The mutant protein was correctly targeted to the cell membrane and was functionally viable as shown by its ability to block intracellular calcium/calmodulin-dependent serine protein kinase redistribution, a major SynCAM1-mediated event. Dominant-negative-SynCAM1 female mice had a delayed onset of puberty, disrupted estrous cyclicity, and reduced fecundity. These deficits were associated with a reduced capacity of neuregulin-dependent erbB4 receptor activation to elicit prostaglandin E2 release from astrocytes and GnRH release from the hypothalamus. We conclude that one of the mechanisms underlying erbB4 receptor-mediated facilitation of glial-neuronal interactions in the neuroendocrine brain involves SynCAM1-dependent signaling and that this interaction is required for normal female reproductive function.

A nuclear variant of ErbB3 receptor tyrosine kinase regulates ezrin distribution and Schwann cell myelination

Reciprocal interactions between glia and neurons are essential for the proper organization and function of the nervous system. Recently, the interaction between ErbB receptors (ErbB2 and ErbB3) on the surface of Schwann cells and neuronal Neuregulin-1 (NRG1) has emerged as the pivotal signal that controls Schwann cell development, association with axons, and myelination. To understand the function of NRG1-ErbB2/3 signaling axis in adult Schwann cell biology, we are studying the specific role of ErbB3 receptor tyrosine kinase (RTK) since it is the receptor for NRG1 on the surface of Schwann cells. Here, we show that alternative transcription initiation results in the formation of a nuclear variant of ErbB3 (nuc-ErbB3) in rat primary Schwann cells. nuc-ErbB3 possesses a functional nuclear localization signal sequence and binds to chromatin. Using chromatin immunoprecipitation (ChIP)-chip arrays, we identified the promoters that associate with nuc-ErbB3 and clustered the active promoters in Schwann cell gene expression. nuc-ErbB3 regulates the transcriptional activity of ezrin and HMGB1 promoters, whereas inhibition of nuc-ErbB3 expression results in reduced myelination and altered distribution of ezrin in the nodes of Ranvier. Finally, we reveal that NRG1 regulates the translation of nuc-ErbB3 in rat Schwann cells. For the first time, to our knowledge, we show that alternative transcription initiation from a gene that encodes a RTK is capable to generate a protein variant of the receptor with a distinct role in molecular and cellular regulation. We propose a new concept for the molecular regulation of myelination through the expression and distinct role of nuc-ErbB3.

Molecular and cellular mechanisms of ectodomain shedding

The extracellular domain of several membrane-anchored proteins is released from the cell surface as soluble proteins through a regulated proteolytic mechanism called ectodomain shedding. Cells use ectodomain shedding to actively regulate the expression and function of surface molecules, and modulate a wide variety of cellular and physiological processes. Ectodomain shedding rapidly converts membrane-associated proteins into soluble effectors and, at the same time, rapidly reduces the level of cell surface expression. For some proteins, ectodomain shedding is also a prerequisite for intramembrane proteolysis, which liberates the cytoplasmic domain of the affected molecule and associated signaling factors to regulate transcription. Ectodomain shedding is a process that is highly regulated by specific agonists, antagonists, and intracellular signaling pathways. Moreover, only about 2% of cell surface proteins are released from the surface by ectodomain shedding, indicating that cells selectively shed their protein ectodomains. This review will describe the molecular and cellular mechanisms of ectodomain shedding, and discuss its major functions in lung development and disease.

Cell death or survival promoted by alternative isoforms of ErbB4

The report demonstrates that two distinct isoforms of the ErbB4 receptor tyrosine kinase stimulate either proliferation or apoptosis by mechanisms involving differential transcriptional regulation of the PDGFRA gene. These data have implications for developing approaches to target ErbB4 signaling in cancer.

The significance of ErbB4 in tumor biology is poorly understood. The ERBB4 gene is alternatively spliced producing juxtamembrane (JM-a and JM-b) and cytoplasmic (CYT-1 and CYT-2) isoforms. Here, signaling via the two alternative ErbB4 JM isoforms (JM-a CYT-2 and JM-b CYT-2) was compared. Fibroblasts expressing ErbB4 JM-a demonstrated enhanced ErbB4 autophosphorylation, growth, and survival. In contrast, cells overexpressing ErbB4 JM-b underwent starvation-induced death. Both pro- and antisurvival responses to the two ErbB4 isoforms were sensitive to an ErbB kinase inhibitor. Platelet-derived growth factor receptor-alpha (PDGFRA) was identified as an ErbB4 target gene that was differentially regulated by the two ErbB4 isoforms. The soluble intracellular domain of ErbB4, released from the JM-a but not from the JM-b isoform, associated with the transcription factor AP-2 and promoted its potential to enhance PDGFRA transcription. Survival of cells expressing JM-a was suppressed by targeting either PDGFR-α or AP-2, whereas cells expressing JM-b were rescued from cell death by the PDGFR-α agonist, PDGF-BB. These findings indicate that two alternative ErbB4 isoforms may promote antagonistic cellular responses and suggest that pharmacological inhibition of ErbB4 kinase activity may lead to either suppression or promotion of cellular growth.

Molecular cloning and characterization of the human ErbB4 gene: identification of novel splice isoforms in the developing and adult brain

ErbB4 is a growth factor receptor tyrosine kinase essential for neurodevelopment. Genetic variation in ErbB4 is associated with schizophrenia and risk-associated polymorphisms predict overexpression of ErbB4 CYT-1 isoforms in the brain in the disorder. The molecular mechanism of association is unclear because the polymorphisms flank exon 3 of the gene and reside 700 kb distal to the CYT-1 defining exon. We hypothesized that the polymorphisms are indirectly associated with ErbB4 CYT-1 via splicing of exon 3 on the CYT-1 background. We report via cloning and sequencing of adult and fetal human brain cDNA libraries the identification of novel splice isoforms of ErbB4, whereby exon 3 is skipped (del.3). ErbB4 del.3 transcripts exist as CYT-2 isoforms and are predicted to produce truncated proteins. Furthermore, our data refine the structure of the human ErbB4 gene, clarify that juxtamembrane (JM) splice variants of ErbB4, JM-a and JM-b respectively, are characterized by the replacement of a 75 nucleotide (nt) sequence with a 45-nt insertion, and demonstrate that there are four alternative exons in the gene. Our analyses reveal that novel splice variants of ErbB4 exist in the developing and adult human brain and, given the failure to identify ErbB4 del.3 CYT-1 transcripts, suggest that the association of risk polymorphisms in the ErbB4 gene with CYT-1 transcript levels is not mediated via an exon 3 splicing event.

Intramembranous valine linked to schizophrenia is required for neuregulin 1 regulation of the morphological development of cortical neurons

Neuregulin 1 (NRG1) signaling is critical to various aspects of neuronal development and function. Among different NRG1 isoforms, the type III isoforms of NRG1 are unique in their ability to signal via the intracellular domain after gamma-secretase-dependent intramembranous processing. However, the functional consequences of type III NRG1 signaling via its intracellular domain are mostly unknown. In this study, we have identified mutations within type III NRG1 that disrupt intramembranous proteolytic processing and abolish intracellular domain signaling. In particular, substitutions at valine 321, previously linked to schizophrenia risks, result in NRG1 proteins that fail to undergo gamma-secretase-mediated nuclear localization and transcriptional activation. Using processing-defective mutants of type III NRG1, we demonstrate that the intracellular domain signaling is specifically required for NRG1 regulation of the growth and branching of cortical dendrites but not axons. Consistent with the role of type III NRG1 signaling via the intracellular domain in the initial patterning of cortical dendrites, our findings from pharmacological and genetic studies indicate that type III NRG1 functions in dendritic development independent of ERBB kinase activity. Together, these results support the proposal that aberrant intramembranous processing and defective signaling via the intracellular domain of type III NRG1 impair a subset of NRG1 functions in cortical development and contribute to abnormal neuroconnectivity implicated in schizophrenia.

Common genetic variation in Neuregulin 3 (NRG3) influences risk for schizophrenia and impacts NRG3 expression in human brain

Structural and polymorphic variations in Neuregulin 3 (NRG3), 10q22-23 are associated with a broad spectrum of neurodevelopmental disorders including developmental delay, cognitive impairment, autism, and schizophrenia. NRG3 is a member of the neuregulin family of EGF proteins and a ligand for the ErbB4 receptor tyrosine kinase that plays pleotropic roles in neurodevelopment. Several genes in the NRG-ErbB signaling pathway including NRG1 and ErbB4 have been implicated in genetic predisposition to schizophrenia. Previous fine mapping of the 10q22-23 locus in schizophrenia identified genome-wide significant association between delusion severity and polymorphisms in intron 1 of NRG3 (rs10883866, rs10748842, and rs6584400). The biological mechanisms remain unknown. We identified significant association of these SNPs with increased risk for schizophrenia in 350 families with an affected offspring and confirmed association to patient delusion and positive symptom severity. Molecular cloning and cDNA sequencing in human brain revealed that NRG3 undergoes complex splicing, giving rise to multiple structurally distinct isoforms. RNA expression profiling of these isoforms in the prefrontal cortex of 400 individuals revealed that NRG3 expression is developmentally regulated and pathologically increased in schizophrenia. Moreover, we show that rs10748842 lies within a DNA ultraconserved element and homedomain and strongly predicts brain expression of NRG3 isoforms that contain a unique developmentally regulated 5' exon (P = 1.097E(-12) to 1.445E(-15)). Our observations strengthen the evidence that NRG3 is a schizophrenia susceptibility gene, provide quantitative insight into NRG3 transcription traits in the human brain, and reveal a probable mechanistic basis for disease association.

Understanding the HER family in breast cancer: interaction with ligands, dimerization and treatments

Breast carcinoma is the most frequent type of cancer affecting women. Among the recently described molecular and phenotypic classes of breast cancer, human epidermal growth factor receptor 2 (HER2)-positive tumours are associated with a poor prognosis. HER2 plays an important role in cancer progression being targeted to provide predictive and prognostic information. Moreover, HER2 is related to cancer resistance against a variety of therapies; however, trastuzumab (herceptin) has proved successful in treatment of this subgroup. Nevertheless, resistance to this drug may be acquired by patients after a period of treatment, which indicates that other molecular mechanisms might influence success of this therapy. Dimerization between members of the HER family may contribute to resistance against treatments due to different combinations that trigger different downstream pathways. This is promoted by ligands, which are expressed as transmembrane precursor protein molecules and have a conserved epidermal growth factor-like domain. Through resistance to trastuzumab, other drugs are being developed to interact in different domains of HER2 protein. It might be a good strategy to apply new drugs simultaneously to trastuzumab due to act in different domains of HER2. The study of interaction between receptors/ligands will characterize specifically their signalling pathway and understand which strategy to acquire.

Potential of ErbB4 antibodies for cancer therapy

Antibodies targeting the extracellular domains of ErbB receptors have been extensively studied for cancer drug development. This work has led to clinical approval of monoclonal antibodies against the well-known oncogenes EGFR and ErbB2. Here we discuss the biological activities of ErbB4, a less-studied member of the EGFR/ErbB growth factor receptor family and speculate on the potential clinical relevance of antibodies targeting ErbB4. In addition to their significance as therapeutics, the role of ErbB4 antibodies in prognostic and predictive applications is surveyed.

It's all in for the HER family in tumorigenesis

The EGF receptor family is a group of receptor tyrosine kinases that have been implicated in the development of a variety of malignancies. As such, they have been targeted in the generation of pharmacologic agents, several of which have been approved as anti-tumor therapeutics. The lone exception is ERBB4, for which the function and relationship to cancer are not yet clear and no targeted therapies exist. The paper under evaluation demonstrates a role for ERBB4 mutations in the development of melanoma. It identifies ERBB4 mutations present in melanomas that augment proliferation and cell survival and thus contribute to dysregulated growth. Furthermore, it shows that agents targeting the EGF receptor family can reduce the proliferation of melanoma cells harboring these mutations. These findings further emphasize the role of the ERBB subfamily in tumorigenesis and establish ERBB4 as a new target in the development of anti-tumor strategies.

Chemical genetics identifies small-molecule modulators of neuritogenesis involving neuregulin-1/ErbB4 signaling

Genetic findings have suggested that neuregulin-1 (Nrg1) and its receptor v-erb-a erythroblastic leukemia viral oncogene homolog 4 (ErbB4) may play a role in neuropsychiatric diseases. However, the downstream signaling events and relevant phenotypic consequences of altered Nrg1 signaling in the nervous system remain poorly understood. To identify small molecules for probing Nrg1-ErbB4 signaling, a PC12-cell model was developed and used to perform a live-cell, image-based screen of the effects of small molecules on Nrg1-induced neuritogenesis. By comparing the resulting phenotypic data to that of a similar screening performed with nerve growth factor (NGF), this multidimensional screen identified compounds that directly inhibit Nrg1-ErbB4 signaling, such as the 4-anilino-quinazoline Iressa (gefitinib), as well as compounds that potentiate Nrg1-ErbB4 signaling, such as the indolocarbazole K-252a. These findings provide new insights into the regulation of Nrg1-ErbB4 signaling events and demonstrate the feasibility of using such a multidimensional, chemical-genetic approach for discovering probes of pathways implicated in neuropsychiatric diseases.

Selective expression of ErbB4 in interneurons, but not pyramidal cells, of the rodent hippocampus

NRG1 and ERBB4 have emerged as some of the most reproducible schizophrenia risk genes. Moreover, the Neuregulin (NRG)/ErbB4 signaling pathway has been implicated in dendritic spine morphogenesis, glutamatergic synaptic plasticity, and neural network control. However, despite much attention this pathway and its effects on pyramidal cells have received recently, the presence of ErbB4 in these cells is still controversial. As knowledge of the precise locus of receptor expression is crucial to delineating the mechanisms by which NRG signaling elicits its diverse physiological effects, we have undertaken a thorough analysis of ErbB4 distribution in the CA1 area of the rodent hippocampus using newly generated rabbit monoclonal antibodies and ErbB4-mutant mice as negative controls. We detected ErbB4 immunoreactivity in GABAergic interneurons but not in pyramidal neurons, a finding that was further corroborated by the lack of ErbB4 mRNA in electrophysiologically identified pyramidal neurons as determined by single-cell reverse transcription-PCR. Contrary to some previous reports, we also did not detect processed ErbB4 fragments or nuclear ErbB4 immunoreactivity. Ultrastructural analysis in CA1 interneurons using immunoelectron microscopy revealed abundant ErbB4 expression in the somatodendritic compartment in which it accumulates at, and adjacent to, glutamatergic postsynaptic sites. In contrast, we found no evidence for presynaptic expression in cultured GAD67-positive hippocampal interneurons and in CA1 basket cell terminals. Our findings identify ErbB4-expressing interneurons, but not pyramidal neurons, as a primary target of NRG signaling in the hippocampus and, furthermore, implicate ErbB4 as a selective marker for glutamatergic synapses on inhibitory interneurons.

Growth factors and corneal epithelial wound healing

In this article, we briefly review recent findings in the effects of growth factors including the EGF family, KGF, HGF, IGF, insulin, and TGF-beta on corneal epithelial wound healing. We discuss the essential role of EGFR in inter-receptor cross-talk in response to wounding in corneal epithelium and bring forward a concept of "alarmins" to the field of wound healing research.

Presence of HER4 associates with increased sensitivity to Herceptin in patients with metastatic breast cancer

INTRODUCTION

HER2 overexpression, or rather HER2 gene amplification, is indicative for Herceptin therapy in both metastatic and pre-metastatic breast cancer patients. Patient's individual sensitivity to Herceptin treatment, however, varies enormously and spans from effectual responsiveness over acquired insensitivity to complete resistance from the outset. Thus no predictive information can be deduced from HER2 determination so that molecular biomarkers indicative for Herceptin sensitivity or resistance need to be identified. Both ErbB receptor-dependent signalling molecules as well as HER2-related ErbB receptor tyrosine kinases, known to mutually interact and to cross-regulate each other are prime candidates to be involved in cellular susceptibility to Herceptin.

METHODS

Using immunohistochemistry and fluorescence in situ hybridisation, we retrospectively investigated primary breast cancer tissues from 48 patients who were under Herceptin treatment. We quantified the gene copy numbers of all HER receptors and evaluated their coexpression profile. Moreover the HER2 phosphorylation state, the ratio of native to truncated HER2, p27(kip1) and PTEN expression were objects of this study.

RESULTS

Above all markers investigated in this study Kaplan-Meier and Cox regression analysis revealed a significant positive impact of HER4 (co-)expression on overall survival from beginning of antibody therapy. Both HER4 expression and HER4 gene amplification emerged as independent prognostic markers in Herceptin-treated breast cancer patients and responsiveness to Herceptin turned out to be more efficient if tumour cells show HER4 expression.

CONCLUSIONS

Although HER4 is known to potentially exert a tumour cell killing activity and in turn to have a favourable impact in breast cancer patients we demonstrate here the first time that HER4 expression prolongs overall survival in Herceptin-treated patients. Elucidating HER4 receptor function in the context of Herceptin treatment will advance the design of highly efficient receptor targeting. By then we need to extend the analysis of breast cancer by allowing for HER2/HER4 coexpression by which valuable additional prognostic and predictive information might possibly be revealed.

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

Data concerning the prognostic value of ErbB4 in breast cancer and effects on cell growth have varied in published reports, perhaps due to the unknown signaling consequences of expression of the intracellular proteolytic ErbB4 s80(HER4) fragment or due to differing signaling capabilities of alternatively spliced ErbB4 isoforms. One isoform (Cyt1) contains a 16-residue intracellular sequence that is absent from the other (Cyt2). We expressed s80(Cyt1) and s80(Cyt2) in HC11 mammary epithelial cells, finding diametrically opposed effects on the growth and organization of colonies in three-dimensional matrices. Whereas expression of s80(Cyt1) decreased growth and increased the rate of three-dimensional lumen formation, that of s80(Cyt2) increased proliferation without promoting lumen formation. These results were recapitulated in vivo, using doxycycline-inducible, mouse breast-transgenic expression of s80(Cyt1) amd s80(Cyt2). Expression of s80(Cyt1) decreased growth of the mammary ductal epithelium, caused precocious STAT5a activation and lactogenic differentiation, and increased cell surface E-cadherin levels. Remarkably, ductal growth inhibition by s80(Cyt1) occurred simultaneously with lobuloalveolar growth that was unimpeded by s80(Cyt1), suggesting that the response to ErbB4 may be influenced by the epithelial subtype. In contrast, expression of s80(Cyt2) caused epithelial hyperplasia, increased Wnt and nuclear beta-catenin expression, and elevated expression of c-myc and cyclin D1 in the mammary epithelium. These results demonstrate that the Cyt1 and Cyt2 ErbB4 isoforms, differing by only 16 amino acids, exhibit markedly opposing effects on mammary epithelium growth and differentiation.

The role of protease activity in ErbB biology

Proteases are now recognized as having an active role in a variety of processes aside from their recognized metabolic role in protein degradation. Within the ErbB system of ligands and receptors, proteases are known to be necessary for the generation of soluble ligands from transmembrane precursors and for the processing of the ErbB4 receptor, such that its intracellular domain is translocated to the nucleus. There are two protease activities involved in the events: proteases that cleave within the ectodomain of ligand (or receptor) and proteases that cleave the substrate within the transmembrane domain. The former are the ADAM proteases and the latter are the gamma-secretase complex and the rhomboid proteases. This review discusses the roles of each of these protease systems within the ErbB system.

Removal of cell surface heparan sulfate increases TACE activity and cleavage of ErbB4 receptor

Background

Nuclear localization of proteolytically formed intracellular fragment of ErbB4 receptor tyrosine kinase has been shown to promote cell survival, and nuclear localization of ErbB4 receptor has been described in human breast cancer. Tumor necrosis factor alpha converting enzyme (TACE) initiates the proteolytic cascade leading to ErbB4 intracellular domain formation. Interactions between matrix metalloproteases and heparan sulfate have been described, but the effect of cell surface heparan sulfate on TACE activity has not been previously described.

Results

As indicated by immunodetection of increased ErbB4 intracellular domain formation and direct enzyme activity analysis, TACE activity was substantially amplified by enzymatic removal of cell surface heparan sulfate but not chondroitin sulfate.

Conclusion

In this communication, we suggest a novel role for cell surface heparan sulfate. Removal of cell surface heparan sulfate led to increased formation of ErbB4 intracellular domain. As ErbB4 intracellular domain has previously been shown to promote cell survival this finding may indicate a novel mechanism how HS degradation active in tumor tissue may favor cell survival.

Suppression of breast cancer cell growth by a monoclonal antibody targeting cleavable ErbB4 isoforms

ErbB4 isoforms mediate different cellular activities depending on their susceptibility to proteolytic cleavage. The biological significance of ErbB4 cleavage in tumorigenesis, however, remains poorly understood. Here, we describe characterization of a monoclonal antibody (mAb 1479) that selectively recognizes the ectodomain of cleavable ErbB4 JM-a isoforms both in vitro and in vivo. mAb 1479 was used to analyse ErbB4 JM-a expression and ectodomain shedding in a series of 17 matched breast cancer/histologically normal peripheral breast tissue pairs. ErbB4 ectodomain was observed in 75% of tumors expressing ErbB4 but only in 18% of normal breast tissue samples expressing ErbB4. Difference in the relative quantity of ErbB4 ectodomain between normal and tumor tissue pairs was statistically significant (P=0.015). Treatment with mAb 1479 suppressed ErbB4 function by inhibiting ErbB4 tyrosine phosphorylation and ectodomain shedding, and by stimulating ErbB4 downregulation and ubiquitination. mAb 1479 suppressed both anchorage-dependent and -independent growth of human breast cancer cell lines that naturally express cleavable ErbB4 JM-a. These findings indicate that ErbB4 ectodomain shedding is enhanced in breast cancer tissue in vivo, and that mAb 1479 represents a potential drug candidate that suppresses breast cancer cell growth by selectively binding cleavable ErbB4 isoforms.

The ErbB4 growth factor receptor is required for colon epithelial cell survival in the presence of TNF

BACKGROUND & AIMS

The ErbB4 receptor tyrosine kinase regulates cell growth, survival, and differentiation in several tissues, but its role in the gastrointestinal tract has not been reported. We tested the hypothesis that ErbB4 promotes intestinal cell survival and restitution following injury or inflammation.

METHODS

ErbB4 expression in human inflammatory bowel disease was determined by immunohistochemistry. Mice were subjected to dextran sulfate sodium (DSS, 3%) colitis or injected with tumor necrosis factor (TNF), and ErbB4 expression was quantified by immunohistochemistry and Western blot. Cultured young adult mouse colon (YAMC) cells were exposed to TNF, and ErbB4 messenger RNA, protein, and phosphorylation levels were measured. Cells transfected with ErbB4 small interfering RNA (siRNA), or over expressing ErbB4, were subjected to wound healing and apoptosis assays.

RESULTS

ErbB4 levels increased in Crohn's colitis and the colon epithelium of mice with DSS colitis or injected with TNF. In YAMC cells, TNF induced ErbB4 messenger RNA, protein, and phosphorylation; nuclear factor kappaB activation also stimulated ErbB4 accumulation. ErbB4 siRNA sensitized cells to TNF-stimulated apoptosis, while over expression blocked apoptosis induced by TNF plus cycloheximide. Additionally, ErbB4 siRNA decreased YAMC cell wound healing. ErbB4 knockdown attenuated, while over expression elevated, phosphorylation of Akt in response to TNF. Inhibition of the phosphatidylinositol 3-kinase/Akt signaling cascade reversed the ability of ErbB4 over expression to protect from cytokine-induced apoptosis.

CONCLUSIONS

ErbB4 expression and signaling are key elements for TNF responses in vivo and in cell culture, protecting intestinal epithelial cells from apoptosis in the inflammatory environment, possibly through Akt activation.

The E3 ubiquitin ligase WWP1 selectively targets HER4 and its proteolytically derived signaling isoforms for degradation

In general, epidermal growth factor receptor family members stimulate cell proliferation. In contrast, at least one HER4 isoform, JM-a/Cyt1, inhibits cell growth after undergoing a two-step proteolytic cleavage that first produces a membrane-anchored 80-kDa fragment (m80(HER4)) and subsequently liberates a soluble 80-kDa fragment, s80(HER4). Here we report that s80(HER4) Cyt1 action increased the expression of WWP1 (for WW domain-containing protein 1), an E3 ubiquitin ligase, but not other members of the Nedd4 E3 ligase family. The HER4 Cyt1 isoform contains three proline-rich tyrosine (PY) WW binding motifs, while Cyt2 has only two. WWP1 binds to all three Cyt1 PY motifs; the interaction with PY2 found exclusively in Cyt1 was strongest. WWP1 ubiquitinated and caused the degradation of HER4 but not of EGFR, HER2, or HER3. The HER4-WWP1 interaction also accelerated WWP1 degradation. Membrane HER4 (full length and m80(HER4), the product of the first proteolytic cleavage) were the preferred targets of WWP1, correlating with the membrane localization of WWP1. Conversely s80(HER4), a poorer WWP1 substrate, was found in the cell nucleus, while WWP1 was not. Deletion of the C2 membrane association domain of WWP1 allowed more efficient s80(HER4) degradation, suggesting that WWP1 is normally part of a membrane complex that regulates HER4 membrane species levels, with a predilection for the growth-inhibitory Cyt1 isoform. Finally, WWP1 expression diminished HER4 biologic activity in MCF-7 cells. We previously showed that nuclear s80(HER4) is ubiquitinated and degraded by the anaphase-promoting complex, suggesting that HER4 ubiquitination within specific cellular compartments helps regulate the unique HER4 signaling capabilities.

HB-EGF stimulates eNOS expression and nitric oxide production and promotes eNOS dependent angiogenesis

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the epidermal growth factor (EGF) family of ligands that is expressed by many cell types including endothelial cells. We have previously shown that HB-EGF stimulates angiogenesis in vitro in human umbilical vein endothelial cells (HUVEC). Nitric oxide (NO) derived from endothelial nitric oxide synthase (eNOS) is an important regulator of angiogenesis. However, the role of HB-EGF in regulation of eNOS has not yet been investigated. Whether HB-EGF-induced endothelial cell migration and vascular network formation are mediated via production of NO from eNOS is also unknown. To address these questions, we stimulated HUVEC with HB-EGF and evaluated the expression of eNOS at the mRNA and protein levels. HB-EGF significantly upregulated expression of eNOS mRNA, stimulated eNOS protein production, and increased NO release from HUVEC. HB-EGF phosphorylated eNOS in a phosphatidylinositol 3-kinase (PI3K) dependent fashion, and stimulated in vitro angiogenesis. eNOS siRNA inhibited HB-EGF-stimulated HUVEC migration in a scratch assay. NG-nitro-L-arginine-methyl-ester (L-NAME) and L-N5-(1-lminoethyl)ornithine,dihydochloride (L-NIO) (specific inhibitors of eNOS) also abolished HB-EGF-induced HUVEC migration and angiogenesis. More importantly, we found that HB-EGF also promotes angiogenesis in vivo in the Marigel plug assay. Lastly, inhibition of the p38 MAPK pathway enhanced HB-EGF-induced EC migration and angiogenesis. We conclude that HB-EGF, through its interaction with EGF receptors (EGFR), stimulates eNOS activation and NO production via a PI3K-dependent pathway. Thus, activation of eNOS appears to be one of the key signaling pathways necessary for HB-EGF mediated angiogenesis. These novel findings highlight an important role for HB-EGF as a regulator of endothelial cell function.

Presenilin: RIP and beyond

Over the years the presenilins (PSENs), a family of multi-transmembrane domain proteins, have been ascribed a number of diverse potential functions. Recent in vivo evidence has supported the existence of PSEN functions beyond its well-established role in regulated intramembrane proteolysis. In this review, we will briefly discuss the ability of PSEN to modulate cellular signaling pathways through gamma-secretase cleavage of transmembrane proteins. Additionally, we will critically examine the proposed roles of PSEN in the regulation of beta-catenin function, protein trafficking, calcium regulation, and apoptosis.

Real-time quantitative polymerase chain reaction (qPCR) analysis with fluorescence resonance energy transfer (FRET) probes reveals differential expression of the four ERBB4 juxtamembrane region variants between medulloblastoma and pilocytic astrocytoma

AIMS

We report a comparative study on the mRNA expression of ErbB receptor tyrosine kinases, and in particular ERBB4 transcript variants, in two common paediatric brain tumours: medulloblastoma (MB) and pilocytic astrocytoma (PA).

METHODS

While the conventional real-time quantitative polymerase chain reaction was used to measure the expression of ERRBs and ErbB4-processing protease genes, the LightCycler fluorescence resonance energy transfer probes were specifically designed to investigate all of the known ERBB4 juxtamembrane (JM) and cytoplasmic transcript variants.

RESULTS

The overall expression of ERBBs suggests that ErbB2/ErbB4 heterodimers and ErbB4 homodimers may be major functional units of the ErbBs in MB, while ErbB2/ErbB3 heterodimers may play a more prominent role in addition to ErbB4-containing dimers in PA. Different expression patterns of ERBB4 JM transcripts in MB, PA and normal brain were observed. The JM-d variant was only detected in MBs, while JM-c was present in MB and PA but was not identified in normal brain. The expression of cleavable ERBB4 transcript variants was elevated in PAs and MBs compared with normal brain, while mRNA levels of ErbB4-processing proteases were similar in both tumour types and normal brain. This suggests that proteolytic cleavage of ErbB4 may be more common in MB and PA, which leads to signalling events divergent from those in normal brain.

CONCLUSION

Taken together, these results suggest that ErbB4 processing and function may be altered in brain tumours, such as MB and PA, via differential expression of JM transcript variants.

Trafficking of receptor tyrosine kinases to the nucleus

It has been known for at least 20 years that growth factors induce the internalization of cognate receptor tyrosine kinases (RTKs). The internalized receptors are then sorted to lysosomes or recycled to the cell surface. More recently, data have been published to indicate other intracellular destinations for the internalized RTKs. These include the nucleus, mitochondria, and cytoplasm. Also, it is recognized that trafficking to these novel destinations involves new biochemical mechanisms, such as proteolytic processing or interaction with translocons, and that these trafficking events have a function in signal transduction, implicating the receptor itself as a signaling element between the cell surface and the nucleus.

The role of Neuregulin-1beta/ErbB signaling in the heart

Products of the Neuregulin-1 (Nrg-1) gene, along with the ErbB family of receptor tyrosine kinases through which Nrg-1 ligands signal, play a critical role during cardiovascular development. Through studies of genetically manipulated mice, as well as studies in cells isolated from adult hearts, it appears that Nrg-1/ErbB signaling is an essential paracrine mediator of cell-cell interactions that not only regulates tissue organization during development, but also helps to maintain cardiac function throughout an organism's life. Studies in cells isolated from the heart demonstrate that Nrg-1 can activate a number of signaling pathways, which mediate cellular adaptations to stress in the myocardium. These observations provide insight as to why ErbB2-targeted cancer treatments have deleterious effects on cardiac function in some cancer patients. Moreover emerging data suggest that Nrg-1 ligands might be useful clinically to restore cardiac function after cardiac injury. In this review we will attempt to synthesize the literature behind this rapidly growing and exciting area of research.

HB-EGF but not amphiregulin or their receptors HER1 and HER4 is altered in endometrium of women with unexplained infertility

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) and its receptors (HER1 and HER4) play a role in the human implantation process. Amphiregulin is a member of the EGF family but with unknown function in human fertility. It has been suggested that some women with unexplained infertility have defective endometrial development. The aim of this study is to determine the presence of amphiregulin and the receptors HER1 and HER4 in normal human endometrium throughout the menstrual cycle. In addition, the present study aims to compare endometrium from women with unexplained infertility with endometrium from women with male factor infertility and healthy fertile controls. Immunohistochemistry and real-time polymerase chain reaction were used to determine the expression of HB-EGF, HER1, HER4, and amphiregulin. The stromal staining of HER1 and the epithelial staining of HER4 were most intense in the mid- and late-secretory-phase endometrium. Amphiregulin did not vary during the menstrual cycle. In the mid-secretory phase, the protein expression of HB-EGF was lower in endometrium from women with unexplained infertility versus normal endometrium and endometrium from women with male factor infertility. HB-EGF and HER4 mRNA expression in mid-secretory endometrium of women with unexplained and male factor infertility were increased compared with normal controls. Impaired endometrial expression of certain members of the EGF family may contribute to infertility in some women with unexplained infertility.

HER4 intracellular domain (4ICD) activity in the developing mammary gland and breast cancer

The HER4 receptor tyrosine kinase was the final member of the EGFR-family to be discovered. In contrast to the other three members of this receptor family which function primarily as mitogenic effectors in the breast, HER4 appears to have multiple divergent functions in the normal and malignant breast. Interestingly, the majority of HER4 activities in the breast including pregnancy induced differentiation and lactation initiation, transcriptional activation, tumor cell proliferation, growth suppression, and induction of apoptosis appear to be mediated by an independently signaling soluble HER4 intracellular domain (4ICD). The 4ICD can accumulate within the nucleus or mitochondria and subcellular localization of 4ICD in part determines the physiological response of breast cells to 4ICD action. Here I will discuss the evidence supporting the role of 4ICD as the critical effector of HER4 signaling in the breast. In addition a developmental and temporal model of 4ICD action in the normal breast and during the progression of breast cancer will be presented to explain the paradox of divergent HER4 and 4ICD activities.

ErbB4/HER4: role in mammary gland development, differentiation and growth inhibition

The ErbB receptor tyrosine kinase family has often been associated with increased growth of breast epithelial cells, as well as malignant transformation and progression. In contrast, ErbB4/HER4 exhibits unique attributes from a two step proteolytic cleavage which releases an 80 kilodalton, nuclear localizing, tyrosine kinase to a signal transduction mechanism that slows growth and stimulates differentiation of breast cells. This review provides an overview of ErbB4/HER4 in growth and differentiation of the mammary epithelium, including its physiologic role in development, the contrasting growth inhibition/tumor suppression and growth acceleration of distinct ErbB4/HER4 isoforms and a description of the unique cell cycle regulated pattern of nuclear HER4 ubiquitination and destruction.

Role of ErbB4 in breast cancer

Members of the ErbB subfamily of receptor tyrosine kinases are important regulators of normal mammary gland physiology, and aberrations in their signaling have been associated with breast tumorigenesis. Therapeutics targeting epidermal growth factor receptor (EGFR = ErbB1) or ErbB2 in breast cancer have been approved for clinical use. In contrast, relatively little is known about the biological significance of ErbB4 signaling in breast cancer. This review focuses on recent advances in our understanding about the role of ErbB4 in breast carcinogenesis, as well as in the potential clinical relevance of ErbB4 in breast cancer prognostics and therapy.