Localization of neuregulin isoforms and erbB receptors in myelinating glial cells

Rare Deletions or Large Duplications Contribute to Genetic Variation in Patients with Severe Tinnitus and Meniere Disease

Meniere disease (MD) is a debilitating disorder of the inner ear defined by sensorineural hearing loss (SNHL) associated with episodes of vertigo and tinnitus. Severe tinnitus, which occurs in around 1% of patients, is a multiallelic disorder associated with a burden of rare missense single nucleotide variants in synaptic genes. Rare structural variants (SVs) may also contribute to MD and severe tinnitus. In this study, we analyzed exome sequencing data from 310 MD Spanish patients and selected 75 patients with severe tinnitus based on a Tinnitus Handicap Inventory (THI) score > 68. Three rare deletions were identified in two unrelated individuals overlapping the ERBB3 gene in the positions: NC_000012.12:g.56100028_56100172del, NC_000012.12:g.56100243_56101058del, and NC_000012.12:g.56101359_56101526del. Moreover, an ultra-rare large duplication was found covering the AP4M1, COPS6, MCM7, TAF6, MIR106B, MIR25, and MIR93 genes in another two patients in the NC_000007.14:g.100089053_100112257dup region. All the coding genes exhibited expression in brain and inner ear tissues. These results confirm the contribution of large SVs to severe tinnitus in MD and pinpoint new candidate genes to get a better molecular understanding of the disease.

Newly Identified Deficiencies in the Multiple Sclerosis Central Nervous System and Their Impact on the Remyelination Failure

The pathogenesis of multiple sclerosis (MS) remains enigmatic and controversial. Myelin sheaths in the central nervous system (CNS) insulate axons and allow saltatory nerve conduction. MS brings about the destruction of myelin sheaths and the myelin-producing oligodendrocytes (ODCs). The conundrum of remyelination failure is, therefore, crucial in MS. In this review, the roles of epidermal growth factor (EGF), normal prions, and cobalamin in CNS myelinogenesis are briefly summarized. Thereafter, some findings of other authors and ourselves on MS and MS-like models are recapitulated, because they have shown that: (a) EGF is significantly decreased in the CNS of living or deceased MS patients; (b) its repeated administration to mice in various MS-models prevents demyelination and inflammatory reaction; (c) as was the case for EGF, normal prion levels are decreased in the MS CNS, with a strong correspondence between liquid and tissue levels; and (d) MS cobalamin levels are increased in the cerebrospinal fluid, but decreased in the spinal cord. In fact, no remyelination can occur in MS if these molecules (essential for any form of CNS myelination) are lacking. Lastly, other non-immunological MS abnormalities are reviewed. Together, these results have led to a critical reassessment of MS pathogenesis, partly because EGF has little or no role in immunology.

ERBB3: A potential serum biomarker for early detection and therapeutic target for devil facial tumour 1 (DFT1)

Devil Facial Tumour 1 (DFT1) is one of two transmissible neoplasms of Tasmanian devils (Sarcophilus harrisii) predominantly affecting their facial regions. DFT1's cellular origin is that of Schwann cell lineage where lesions are evident macroscopically late in the disease. Conversely, the pre-clinical timeframe from cellular transmission to appearance of DFT1 remains uncertain demonstrating the importance of an effective pre-clinical biomarker. We show that ERBB3, a marker expressed normally by the developing neural crest and Schwann cells, is immunohistohemically expressed by DFT1, therefore the potential of ERBB3 as a biomarker was explored. Under the hypothesis that serum ERBB3 levels may increase as DFT1 invades local and distant tissues our pilot study determined serum ERBB3 levels in normal Tasmanian devils and Tasmanian devils with DFT1. Compared to the baseline serum ERBB3 levels in unaffected Tasmanian devils, Tasmanian devils with DFT1 showed significant elevation of serum ERBB3 levels. Interestingly Tasmanian devils with cutaneous lymphoma (CL) also showed elevation of serum ERBB3 levels when compared to the baseline serum levels of Tasmanian devils without DFT1. Thus, elevated serum ERBB3 levels in otherwise healthy looking devils could predict possible DFT1 or CL in captive or wild devil populations and would have implications on the management, welfare and survival of Tasmanian devils. ERBB3 is also a therapeutic target and therefore the potential exists to consider modes of administration that may eradicate DFT1 from the wild.

Activated ErbB3 Translocates to the Nucleus via Clathrin-independent Endocytosis, Which Is Associated with Proliferating Cells

Members of the receptor tyrosine kinase family (RTK) have been shown to be present in the nucleus of cells; however, the mechanisms underlying their trafficking to the nucleus, and their relevance once there are poorly understood. In the present study, we focus on the RTK ErbB3 and elucidate the mechanisms regulating its trafficking. We show that heregulin-stimulation induces trafficking of phosphorylated ErbB3 from the plasma membrane to the nucleus via a clathrin-independent mechanism. Nuclear import of ErbB3 occurs via importin β1, which drives the receptor through the nuclear pore complex. In the nucleus, ErbB3 interacts with transcription complexes, and thereby has a role in transcriptional regulation. Our results also demonstrate that ErbB3 nuclear localization is transient as it is exported out of the nucleus by the nuclear receptor protein crm-1. Analysis of normal, regenerating tissues, and tumors showed that ErbB3 nuclear translocation is a common event in proliferating tissues.

Proteolytic cleavage, trafficking, and functions of nuclear receptor tyrosine kinases

Intracellular localization has been reported for over three-quarters of receptor tyrosine kinase (RTK) families in response to environmental stimuli. Internalized RTK may bind to non-canonical substrates and affect various cellular processes. Many of the intracellular RTKs exist as fragmented forms that are generated by γ-secretase cleavage of the full-length receptor, shedding, alternative splicing, or alternative translation initiation. Soluble RTK fragments are stabilized and intracellularly transported into subcellular compartments, such as the nucleus, by binding to chaperone or transcription factors, while membrane-bound RTKs (full-length or truncated) are transported from the plasma membrane to the ER through the well-established Rab- or clathrin adaptor protein-coated vesicle retrograde trafficking pathways. Subsequent nuclear transport of membrane-bound RTK may occur via two pathways, INFS or INTERNET, with the former characterized by release of receptors from the ER into the cytosol and the latter characterized by release of membrane-bound receptor from the ER into the nucleoplasm through the inner nuclear membrane. Although most non-canonical intracellular RTK signaling is related to transcriptional regulation, there may be other functions that have yet to be discovered. In this review, we summarize the proteolytic processing, intracellular trafficking and nuclear functions of RTKs, and discuss how they promote cancer progression, and their clinical implications.

The Soluble Heparin-Binding EGF-Like Growth Factor Stimulates EGF Receptor Trafficking to the Nucleus

Most ligands of epidermal growth factor receptor (EGFR) have the ability to induce EGFR translocation into the nucleus, where EGFR acts as an important transcriptional regulator. Soluble form of heparin-binding EGF-like growth factor (sHB-EGF) is one of the ligands for EGFR in many cell types; however, there is no evidence for the ability of sHB-EGF to induce EGFR nuclear importation. Here, we demonstrated that treatment of A431 cells with sHB-EGF resulted in nuclear localization of EGFR and such translocation occurs via retrograde pathway. It was shown by confocal microscopy and co-immunoprecipitation assay that the translocation complex consisted of both ligand and receptor. The chromatin immunoprecipitation assay showed the association of sHB-EGF–EGFR complex with promoter region of cyclin D1 in the cell nucleus and this association was prevented by application of EGFR kinase inhibitor AG-1478. The obtained data suggest that sHB-EGF acts similarly to other EGFR ligands and is capable to induce EGFR nuclear translocation as a part of ligand-receptor complex in a tyrosine phosphorylation-dependent manner.

Glial cells as key players in schizophrenia pathology: recent insights and concepts of therapy

The past decade has witnessed an explosion of knowledge on the impact of glia for the neurobiological foundation of schizophrenia. A plethora of studies have shown structural and functional abnormalities in all three types of glial cells. There is convincing evidence of reduced numbers of oligodendrocytes, impaired cell maturation and altered gene expression of myelin/oligodendrocyte-related genes that may in part explain white matter abnormalities and disturbed inter- and intra-hemispheric connectivity, which are characteristic signs of schizophrenia. Earlier reports of astrogliosis could not be confirmed by later studies, although the expression of a variety of astrocyte-related genes is abnormal in psychosis. Since astrocytes play a key role in the synaptic metabolism of glutamate, GABA, monoamines and purines, astrocyte dysfunction may contribute to certain aspects of disturbed neurotransmission in schizophrenia. Finally, increased densities of microglial cells and aberrant expression of microglia-related surface markers in schizophrenia suggest that immunological/inflammatory factors are of considerable relevance for the pathophysiology of psychosis. This review describes current evidence for the multifaceted role of glial cells in schizophrenia and discusses efforts to develop glia-directed therapies for the treatment of the disease.

GABA-B receptors in the PNS have a role in Schwann cells differentiation?

γ-aminobutyric acid type B (GABA-B) receptor mediates the inhibitory transmission of γ-aminobutyric acid in the mammalian nervous system, being present in neurons and also in glial cells. Recently the presence of GABA-B has been demonstrated in Schwann cells (SC) suggesting its contribution in regulating the cell fate, maturation, and plasticity. Here, we further support the functional presence of GABA-B receptor in SC plasma membrane. By confocal microscopy immunofluorescence we provide evidences that GABA-B localization on the cell elongated processes correlates with the morphological changes occurring in the differentiated SC. In vivo most of the GABA-B receptors seem to be present in non-myelinating SC, which are committed to ensheath the nociceptive fibers. Therefore, we argue that GABA-B receptors do not control exclusively the in vivo differentiation yielding the myelinating SC, but are also fundamental in regulating the SC plasticity versus the non-myelinating state. Data from the literature and our recent findings corroborate the role of the GABAergic system and GABA-B receptors in the peripheral nervous system, opening new perspectives on the mechanisms controlling the differentiation of SC.

Landscape of EGFR signaling network in human cancers: biology and therapeutic response in relation to receptor subcellular locations

The epidermal growth factor receptor (EGFR) pathway is one of the most dysregulated molecular pathways in human cancers. Despite its well-established importance in tumor growth, progression and drug-resistant phenotype over the past several decades, targeted therapy designed to circumvent EGFR has yielded only modest clinical success in cancer patients, except those with non-small cell lung cancer (NSCLC) carrying EGFR activation mutations. However, almost all of these NSCLC patients eventually developed resistance to small molecule EGFR kinase inhibitors. These disappointing outcomes are, in part, due to the high complexity and the interactive nature of the EGFR signaling network. More recent compelling evidence further indicates that EGFR functionality can be dependent on its subcellular location. In this regard, EGFR undergoes translocation into different organelles where it elicits distinctly different functions than its best known activity as a plasma membrane-bound receptor tyrosine kinase. EGFR can be shuttled into the cell nucleus and mitochondrion upon ligand binding, radiation, EGFR-targeted therapy and other stimuli. Nuclear EGFR behaves as transcriptional regulator, tyrosine kinase, and mediator of other physiological processes. The role of mitochondrial EGFR remains poorly understood but it appears to regulate apoptosis and autophagy. While studies using patient tumors have shown nuclear EGFR to be an indicator for poor clinical outcomes in cancer patients, the impact of mitochondrial EGFR on tumor behavior and patient prognosis remains to be defined. Most recently, several lines of evidence suggest that mislocated EGFR may regulate tumor response to therapy and that plasma membrane-bound EGFR elicits survival signals independent of its kinase activity. In light of these recent progresses and discoveries, we will outline in this minireview an emerging line of research that uncovers and functionally characterizes several novel modes of EGFR signaling that take center stage in the cell nucleus, mitochondrion and other subcellular compartments. We will also discuss the clinical implications of these findings in the rationale design for therapeutic strategy that overcomes tumor drug resistance.

GGF2 (Nrg1-β3) treatment enhances NG2+ cell response and improves functional recovery after spinal cord injury

The adult spinal cord contains a pool of endogenous glial precursor cells, which spontaneously respond to spinal cord injury (SCI) with increased proliferation. These include oligodendrocyte precursor cells that express the NG2 proteoglycan and can differentiate into mature oligodendrocytes. Thus, a potential approach for SCI treatment is to enhance the proliferation and differentiation of these cells to yield more functional mature glia and improve remyelination of surviving axons. We previously reported that soluble glial growth factor 2 (GGF2)- and basic fibroblast growth factor 2 (FGF2)-stimulated growth of NG2(+) cells purified from injured spinal cord in primary culture. This study examines the effects of systemic administration of GGF2 and/or FGF2 after standardized contusive SCI in vivo in both rat and mouse models. In Sprague-Dawley rats, 1 week of GGF2 administration, beginning 24 h after injury, enhanced NG2(+) cell proliferation, oligodendrogenesis, chronic white matter at the injury epicenter, and recovery of hind limb function. In 2',3'-cyclic-nucleotide 3'-phosphodiesterase-enhanced green fluorescent protein mice, GGF2 treatment resulted in increased oligodendrogenesis and improved functional recovery, as well as elevated expression of the stem cell transcription factor Sox2 by oligodendrocyte lineage cells. Although oligodendrocyte number was increased chronically after SCI in GGF2-treated mice, no evidence of increased white matter was detected. However, GGF2 treatment significantly increased levels of P0 protein-containing peripheral myelin, produced by Schwann cells that infiltrate the injured spinal cord. Our results suggest that GGF2 may have therapeutic potential for SCI by enhancing endogenous recovery processes in a clinically relevant time frame.

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.

Neuregulin-1/ErbB signaling and chronic heart failure

Neuregulin-1 (NRG-1), a cardioactive growth factor released from endothelial cells, is indispensable for cardiac development, structural maintenance, and functional integrity of the heart. In recent years, a growing number of studies have focused on NRG-1 and members of the ErbB family that serve as receptors for NRG-1 in order to better understand the role of this signaling pathway in physiology and pathophysiology of the heart. An essential role for NRG-1 and ErbB in heart development and functionality has been suggested by studies in conditional NRG-1/ErbB-deficient mice and by the cardiac-related side effects of anti-ErbB2 antibody therapies used for treatment of breast cancer. In vitro and in vivo studies using recombinant human neuregulin-1 (rhNRG-1), which contains the epidermal growth factor (EGF)-like domain (necessary for ErbB2/ErbB4 activation), have further supported the hypothesis that NRG-1 plays an important role in heart function. Consistent with other studies, expression of rhNRG-1 not only restored normal cardiomyocytic structure altered by nutritional deficiency in cell cultures, but also improved the pumping function of the heart in several animal models of chronic heart failure (CHF). As a result of these findings, proteins involved in the NRG-1/ErbB-signaling pathway have been explored as potential drug targets for treatment of heart failure. Clinical trials to evaluate the safety and efficacy of rhNRG-1 have been conducted in both China and Australia. As predicted, rhNRG-1 treatment improved both cardiac function and reversed remodeling of the heart. Therefore, rhNRG-1 may represent a new drug for treatment of CHF with a novel therapeutic mechanism.

Nuclear translocation of the epidermal growth factor receptor family membrane tyrosine kinase receptors

Integral membrane proteins contain a hydrophobic transmembrane domain and mainly locate in the plasma membrane lipid bilayer. The receptor tyrosine kinases (RTK) of the epidermal growth factor receptor (EGFR) superfamily, including ErbB-1, ErbB-2, ErbB-3, and ErbB-4, constitute an important group of such membrane proteins, which have a profound impact on cancer initiation, progression, and patient outcome. Although studies of their functions have conventionally focused on their membrane-associated forms, documented observations of the presence of these membrane receptors and their functioning partners in the nucleus have reshaped the intracellular geography and highlight the need to modify the central dogma. The ErbB proteins in the membrane can translocate to the nucleus through different mechanisms. Nuclear RTKs regulate a variety of cellular functions, such as cell proliferation, DNA damage repair, and signal transduction, both in normal tissues and in human cancer cell. In addition, they play important roles in determining cancer response to cancer therapy. Nuclear presence of these ErbB proteins is emerging as an important marker in human cancers. An integrated picture of the RTK-centered signaling transduction network extending from the membrane-cytoplasm boundary to the nuclear compartment is looming in the foreseeable horizon for clinical application.

Nuclear expression of epidermal growth factor receptor is a novel prognostic value in patients with ovarian cancer

The epidermal growth factor receptor (EGFR) has previously been detected in the nucleus of cancer cells and primary tumors. We have reported that EGFR translocates from the plasma membrane to the nucleus. Accumulation of nuclear EGFR is linked to increased DNA synthesis and proliferation; however, the pathological significance of nuclear EGFR is not completely understood. Here, we sought to determine the predictive value of EGFR for the survival of ovarian cancer patients, through the examination of 221 cases of ovarian cancer tissues by immunohistochemical analysis to determine nuclear EGFR expression. In addition, we also examined cyclin D1 and Ki-67 through immunohistochemisty. Furthermore, we examined nuclear EGFR levels in ovarian cancer cell lines treated with EGF, and primary ovarian tumor tissue using immunofluorescence analysis. Nuclear fractions extracted from serum-starved cells treated with or without EGF were subjected to SDS-PAGE and Western blot analyses. We found that 28.3% of the cohort had high levels of nuclear EGFR, while 22.5% had low levels of nuclear EGFR, and 49.2% were negative for nuclear EGFR. Importantly, there was an inverse correlation between high nuclear EGFR, cyclin D1, and Ki-67 with overall survival (P < 0.01, P < 0.09, P < 0.041). Additionally, nuclear EGFR correlated positively with increased levels of cyclin D1 and Ki-67, both indicators for cell proliferation. Our findings indicate a pathological significance of nuclear EGFR that might be important for predicting clinical prognosis of ovarian cancer patients.

Induction of ERBB2 nuclear transport after radiation in breast cancer cells

The ERBB2 nuclear transport in breast cancer cell lines after radiation and its possible role in radiation tolerance were observed. Confocal microscopy and Western blotting were applied to detect the nuclear ERBB2 expression after radiation in breast carcinomas cells. And the effects of Herceptin, AG825 and Cisplatin on the expression of nuclear ERBB2 were investigated. Survival fractions were also observed. After radiation, compared with control group, confocal microscopy and Western blot revealed that the expression of nuclear ERBB2 was increased in breast cancer cells time-dependently. Herceptin, and AG825 could significantly inhibit the radiation-induced nuclear ERBB2 expression, and decrease survival fractions. Cisplatin also induced the nuclear ERBB2 expression in breast cancer cells with high ERBB2 expression. It was concluded that radiation could induce ERBB2 nuclear transport, and nuclear ERBB2 may correlate with radiation resistance in breast cancer cells with high ERBB2 expression.

In situ hybridization reveals developmental regulation of ErbB1-4 mRNA expression in mouse midbrain: implication of ErbB receptors for dopaminergic neurons

Although epidermal growth factor (EGF) and neuregulin-1 are neurotrophic factors for mesencephalic dopaminergic neurons and implicated in schizophrenia, the cellular localization and developmental regulation of their receptors (ErbB1-4) remain to be characterized. Here we investigated the distributions of mRNA for ErbB1-4 in the midbrain of the developing mouse with in situ hybridization and immunohistochemistry. The expression of ErbB1 and ErbB2 mRNAs was relatively high at the perinatal stage and frequently colocalized with mRNA for S100beta and Olig2, markers for immature astrocytes or oligodendrocyte precursors. Modest signal for ErbB1 mRNA was also detected in a subset of dopaminergic neurons. ErbB3 mRNA was detectable at postnatal day 10, peaked at postnatal day 18, and colocalized with 2',3'-cyclic nucleotide 3'-phosphodiesterase, a marker for oligodendrocytes. In contrast, ErbB4 mRNA was exclusively localized in neurons throughout development. Almost all of ErbB4 mRNA-expressing cells (94%-96%) were positive for tyrosine hydroxylase in the substantia nigra pars compacta but 66%-78% in the ventral tegmental area and substantia nigra pars lateralis. Conversely, 92%-99% of tyrosine hydroxylase-positive cells expressed ErbB4 mRNA. The robust and restricted expression of ErbB4 mRNA in the midbrain dopaminergic neurons suggests that ErbB4 ligands, neuregulin-1 and other EGF-related molecules, contribute to development or maintenance of this neuronal population.

Neuregulin-1/ErbB signaling: a druggable target for treating heart failure

Neuregulin-1s are widely expressed signaling molecules that are involved in cell differentiation, proliferation, growth, survival, and apoptosis. They transmit their signals by interacting with cell membrane receptors of the ErbB family, resulting in the activation of intracellular signaling cascades, which participate in various physiological and etiological processes. Besides their essential function in the development of the heart and the physiology of cardiac pumping, there is emerging evidence for the involvement of neuregulin-1/ErbB signals in human disease, including heart failure. These reasons prompt the development of new therapeutic agents based on neuregulin-1.

The ERBB3 receptor in cancer and cancer gene therapy

ERBB3, a member of the epidermal growth factor receptor (EGFR) family, is unique in that its tyrosine kinase domain is functionally defective. It is activated by neuregulins, by other ERBB and nonERBB receptors as well as by other kinases, and by novel mechanisms. Downstream it interacts prominently with the phosphoinositol 3-kinase/AKT survival/mitogenic pathway, but also with GRB, SHC, SRC, ABL, rasGAP, SYK and the transcription regulator EBP1. There are likely important but poorly understood roles for nuclear localization and for secreted isoforms. Studies of ERBB3 expression in primary cancers and of its mechanistic contributions in cultured cells have implicated it, with varying degrees of certainty, with causation or sustenance of cancers of the breast, ovary, prostate, certain brain cells, retina, melanocytes, colon, pancreas, stomach, oral cavity and lung. Recent results link high ERBB3 activity with escape from therapy targeting other ERBBs in lung and breast cancers. Thus a wide and centrally important role for ERBB3 in cancer is becoming increasingly apparent. Several approaches for targeting ERBB3 in cancers have been tested or proposed. Small inhibitory RNA (siRNA) to ERBB3 or AKT is showing promise as a therapeutic approach to treatment of lung adenocarcinoma.

Immortalization and characterization of lineage-restricted neuronal progenitor cells derived from the porcine olfactory bulb

Crucial aspects in the development of in vitro neuropathogenic disease model systems are the identification, characterization and continuous mitotic expansion of cultured neuronal cells. To facilitate long-term cultivation, we immortalized porcine olfactory neuronally restricted progenitor cells by genomic insertion of a cDNA encoding the catalytic subunit of the human telomerase reverse transcriptase (hTERT) yielding a stable neuroblast subclone (OBGF400). The altered cells exhibited progenitor-cell-like morphology and mitotic competency based on sustained subpassaging, prevalence in the cell cycle G0/G1 phase and an overall lack of cellular senescence as compared to primary cultures. An OBGF400 neuronal phenotype was indicated by the recognition of a transfected neuronal progenitor-cell-specific tubulin-alpha1 gene promoter, intracellular presence of early neuronal markers (TuJ1, neuregulin-1, doublecortin and SOX2) and enhanced expression of neuronal- and progenitor lineage-active genes (MAP2, nestin, ENO and Syn1) compared to that of porcine epithelial cells. These OBGF400 neuroblasts are likely dependent on telomerase to prevent terminal differentiation as subcultures with a predominance of neuronally differentiated members had less enzymatic activity. Based on its susceptibility to a porcine alphaherpesvirus infection, this novel neuroblast cell line may be useful for exploring neuronal cell-pathogen interactions in vitro.

Neuregulin-1: a potential endogenous protector in perinatal brain white matter damage

Brain white matter damage, an important antecedent of long-term disabilities among preterm infants, has both endogenous and exogenous components. One of the endogenous components is the paucity of developmentally regulated protectors. Here we expand on this component, discussing the potential roles of one putative protector, neuregulin (NRG)-1, in brain development and damage. We outline how NRG-1 might be involved in perinatal brain damage pathomechanisms and suggest that NRG-1 might be one target for intervention.

Increased expression of neuregulin-1 in differentiating muscle satellite cells and in motoneurons during muscle regeneration

Neuregulins belong to a family of multipotent growth-promoting proteins, and have been shown to have a crucial role in accumulating acetylcholine receptor at neuromuscular junctions. A functional role of neuregulins in muscle regeneration has not yet been identified. Using reverse transcription (RT)-PCR, Western blot and immunofluorescence analysis following bupivacaine injection into rat muscle, we investigated the expression pattern of neuregulin-1 (NRG-1) in normal and regenerating tibialis anterior (TA) muscle. In addition, we examined changes in NRG-1 expression in the spinal cord following muscle damage. Western blotting showed that muscle NRG-1 protein decreased soon after the damage, and increased gradually after the 4th day following the damage. The amount of NRG-1 mRNA in the muscle increased from the 2nd to 6th post-surgical day. The amount of NRG-1 protein, but not mRNA, increased gradually in the spinal cord after muscle damage. Immunofluorescence revealed NRG-1 protein in some quiescent satellite cells identified by c-Met. After 6 and 10 days, clear co-localization between NRG-1 and myogenin was noted in differentiating satellite cells. Thus, NRG-1 may play an important role in the differentiation of satellite cells in muscle regeneration, while increased NRG-1 expression in motoneurons may enhance the remodeling of partially damaged axons.

ErbB receptors in fetal endothelium--a potential linkage point for inflammation-associated neonatal disorders

OBJECTIVE

ErbB receptors and their ligands play crucial roles in development. During late gestation, they might also be involved in the pathogenesis of prematurity-associated disorders. ErbB receptor dimerization leads to a diversity of biologic signals. We studied the expression and localization patterns of erbB receptors in the developing human umbilical endothelial cell system. It is still unclear, whether expression patterns might be developmentally regulated and depend on the cell type studied.

METHODS

Primary human umbilical venous endothelial cells (HUVEC) and arterial endothelial cells (HUAEC) were isolated between 24 and 42 weeks of gestation and used for immunoprecipitation, Western blotting, and confocal microscopy.

RESULTS

All four erbB receptors were present in HUVEC and HUAEC. Expression patterns were similar for cell types at gestational ages examined. ErbB4 always co-precipitated with erbB1 in both cell types independent of the gestational age. Confocal microscopy revealed that all erbB receptors were localized in the nucleus, erbB1 and erbB3 in the nucleoli, while erbB2 and erbB4 spared the nucleolar region. All receptors showed a tendency to co-localize. Growth factor stimulation altered localization patterns. Cellular subfractionation experiments for erbB4 largely confirmed microscopy results. Pretreatment with lipopolysaccharide enhanced this nuclear localization of erbB4, particularly of its intracellular domain.

CONCLUSIONS

All erbB receptors are present in both HUVEC and HUAEC at all gestational ages tested. ErbB receptor expression patterns were independent of the developmental stage of the endothelial cell, at least in the third trimester. We speculate that endothelial erbB receptors might play a role in normal development in mid and late gestation. We also speculate that these findings, together with the known involvement of erbB receptors in development, inflammation, and angiogenesis, will open new avenues for erbB receptor-related research in the pathogenesis of fetal and neonatal inflammation-associated disorders.

Immunohistochemical Evidence for Impaired Neuregulin-1 Signaling in the Prefrontal Cortex in Schizophrenia and in Unipolar Depression

In the central nervous system (CNS), neuregulin-1 (NRG-1) proteins function in neuronal migration, differentiation, and survival of oligodendrocytes. The NRG-1 gene codes for at least 15 different isoforms, which may be classified on the basis of their molecular structure. At least two different haplotypes of the NRG-1 gene may be associated with schizophrenia. An abnormal expression pattern of NRG-1 mRNA was found in the prefrontal cortex of schizophrenic patients in comparison to controls. We here show that the NRG-1alpha isoform is significantly reduced in white matter of the prefrontal cortex in schizophrenia but not in affective disorder. In the prefrontal gray matter, the density of NRG-1alpha expressing neurons was reduced in individuals with schizophrenia and in unipolar patients. We studied brains of 22 schizophrenics, 12 patients with affective disorders (7 unipolar and 5 bipolar), and 22 matched controls. NRG-1alpha immunoreactive material was detected with a polyclonal antiserum against the synthetic peptide from alpha-type EGF-like domain of human NRG. The demonstrated decreased number of NRG-1 immunoreactive neurons in the brains of schizophrenics and patients with unipolar depression points to an important role of this NRG-1alpha splice variant in neuropsychiatric disorders. Reduced NRG-1alpha protein concentrations were found in brains of schizophrenics after Western blot analysis. The diminished expression of NRG-1alpha strongly supports an early neurodevelopmental component to schizophrenia.

Comparison of fresh and predegenerated muscle-vein-combined guides for the repair of rat median nerve

Over the last 10 years, we have investigated a particular type of bioengineered nerve guide, the muscle-vein-combined tube, which is made by filling a vein with skeletal muscle. In our previous studies we have always used fresh skeletal muscle to fill vein conduits. In the present study we compared the use of fresh and predegenerated (freeze-thawed) skeletal muscle for muscle-vein-combined nerve guides. In this study, a 10-mm-long rat median nerve defect was repaired using either type of nerve guide. The samples were analyzed 5 and 30 days after surgery by light and electron microscopy. In addition, reverse transcription polymerase chain reaction (RT-PCR) was carried out to investigate the expression of mRNAs coding for glial markers, as well as glial growth factor (NRG1) and its receptors (erbB2 and erbB3). Results showed differences between the two types of nerve guides at postoperative day 5; however, no difference was detected at day 30 suggesting that both types of tissue-engineered conduit are effective for repairing peripheral nerve defects in this experimental model.

EGFR signaling pathway in breast cancers: from traditional signal transduction to direct nuclear translocalization

Aberrant epidermal growth factor receptor (EGFR) signaling is a major characteristic of many human malignancies including breast cancer. Since the discovery of EGF in 1960's and its receptor in 1980's, our understanding of the EGF/EGFR pathway has been significantly advanced and consequently, EGFR is considered as a major oncogenic factor and an attractive therapeutic target. The well-established traditional function of EGFR is known to transmit extra-cellular mitogenic signals, such as EGF and transforming growth factor-alpha (TGF-alpha), through activating a number of downstream signaling cascades. These include signaling modules that involve phospholipase C-gamma, Ras, and phosphatidylinositol-3 kinase (PI-3K). In cancer cells, the common outcomes following the activation of the EGFR-mediated downstream pathways are altered gene activities, leading to un-controlled tumor proliferation and apoptosis. Interestingly, emerging evidences suggest the existence of a direct mode of the EGFR pathway that is distinct from the traditional transduction pathway. This new mode of EGFR signaling involves cellular transport of EGFR from the cell-surface to the cell nucleus, association of nuclear EGFR complex with gene promoters, and transcriptional regulation of the target genes. Although the nature and pathological consequences of the nuclear EGFR pathway remain elusive, accumulating evidences suggest its association with increased tumor cell proliferation and poor survival rate in breast cancer patients. While several anti-EGFR agents are being tested in breast cancer patients clinically and others under pre-clinical development, a better understanding of the traditional and the nuclear EGFR pathways will facilitate the identification of patients that are likely to respond to these agents as well as future development of more effective anti-EGFR therapeutic interventions.

Expression and nuclear localization of ErbB3 in prostate cancer

PURPOSE

The ErbB1 and ErbB2 receptors have been implicated in prostate cancer progression, but less is known about the role and biology of other ErbB receptor family members in prostate cancer. The aim of this study was to analyze the expression and localization of ErbB3 in prostate tissues and prostate cancer cell lines.

EXPERIMENTAL DESIGN

Immunohistochemistry of ErbB3 was done on prostate cancer tissue sections from 143 patients and on a tissue microarray containing 390 cores of radical prostatectomy-derived specimens representing normal, prostatic intraepithelial neoplasia, and malignant tissues from 81 patients. ErbB3 subcellular localization was studied by Western blot analysis in LNCaP, 22Rv1, PC-3, and DU145 prostate cancer cell lines.

RESULTS

Immunohistochemistry analysis of prostate cancer tissues revealed that >90% of prostate cancer tissues displayed cytoplasmic ErbB3 staining. Minimal ErbB3 nuclear staining was observed in normal prostate tissues and benign prostatic hyperplasia tissues; in contrast, ErbB3 was frequently localized in the nucleus of cancerous tissues. This nuclear localization was more frequent (P < 0.001) in hormone-refractory tissues (17 of 17, 100%) compared with hormone-sensitive samples (37 of 92, 40.2%). Additionally, in the tissue microarray, increased nuclear ErbB3 was associated with increasing Gleason grade. Interestingly, Western blot analysis of cytoplasmic and nuclear subcellular fractions showed that ErbB3 nuclear localization was more prevalent in hormone-sensitive prostate cancer cell lines (LNCaP and 22Rv1) compared with hormone-insensitive cell lines (PC-3 and DU145).

CONCLUSIONS

ErbB3 nuclear localization discriminates normal from malignant prostate tissues and between tumors from hormone-sensitive versus hormone-refractory prostate cancer. ErbB3 nuclear staining seems to be associated with risk of disease progression. The high frequency of ErbB3 nuclear localization in hormone-refractory tissues indicates that ErbB3 warrants further study to understand its association with prostate cancer disease progression.

Nuclear-cytoplasmic transport of EGFR involves receptor endocytosis, importin beta1 and CRM1

Many receptor tyrosine kinases (RTKs) can be detected in the cell nucleus, such as EGFR, HER-2, HER-3, HER-4, and fibroblast growth factor receptor. EGFR, HER-2 and HER-4 contain transactivational activity and function as transcription co-factors to activate gene promoters. High EGFR in tumor nuclei correlates with increased tumor proliferation and poor survival in cancer patients. However, the mechanism by which cell-surface EGFR translocates into the cell nucleus remains largely unknown. Here, we found that EGFR co-localizes and interacts with importins alpha1/beta1, carriers that are critical for macromolecules nuclear import. EGFR variant mutated at the nuclear localization signal (NLS) is defective in associating with importins and in entering the nuclei indicating that EGFR's NLS is critical for EGFR/importins interaction and EGFR nuclear import. Moreover, disruption of receptor internalization process using chemicals and forced expression of dominant-negative Dynamin II mutant suppressed nuclear entry of EGFR. Additional evidences suggest an involvement of endosomal sorting machinery in EGFR nuclear translocalization. Finally, we found that nuclear export of EGFR may involve CRM1 exportin as we detected EGFR/CRM1 interaction and markedly increased nuclear EGFR following exposure to leptomycin B, a CRM1 inhibitor. Collectively, these data suggest the importance of receptor endocytosis, endosomal sorting machinery, interaction with importins alpha1/beta1, and exportin CRM1 in EGFR nuclear-cytoplasmic trafficking. Together, our work sheds light into the nature and regulation of the nuclear EGFR pathway and provides a plausible mechanism by which cells shuttle cell-surface EGFR and potentially other RTKs through the nuclear pore complex and into the nuclear compartment.

Neuregulins: Versatile growth and differentiation factors in nervous system development and human disease

The neuregulins are a family of growth and differentiation factors with a wide range of functions in the nervous system. The power and diversity of the neuregulin signaling system comes in part from a large number of alternatively-spliced forms of the NRG1 gene that can produce both soluble and membrane-bound forms. The soluble forms of neuregulin are unique from other factors in that they have a structurally distinct heparin-binding domain that targets and potentiates its actions. In addition, a finely tuned, bidirectional mechanism regulates when and where neuregulin is released from neurons in response to neurotrophic factors produced by both neuronal targets and supporting glial cells. Together, this produces a balanced intercellular signaling system that can be localized to distinct regions for both normal development and maintenance of the mature nervous system. Recent evidence suggests that neuregulin signaling plays important roles in many neurological disorders including multiple sclerosis, traumatic brain and spinal cord injury, peripheral neuropathy, and schizophrenia. Here, we review the basic biology of neuregulins and relate this to research suggesting their involvement with and potential therapeutic uses for neurological disorders.

Tissue array analysis of expression microarray candidates identifies markers associated with tumor grade and outcome in serous epithelial ovarian cancer

Molecular profiling is a powerful approach to identify potential clinical markers for diagnosis and prognosis as well as providing a better understanding of the biology of epithelial ovarian cancer. On the basis of the analysis of HuFL expression data, we have previously identified genes that distinguish low malignant potential and invasive serous epithelial ovarian tumors. In this study, we used immunohistochemistry to monitor a subset of differently expressed candidates (Ahr, Paep, Madh3, Ran, Met, Mek1, Ccne1, Ccd20, Cks1 and Cas). A tissue array composed of 244 serous tumors of different grades (0-3) and stages (I-IV) was used in this analysis. All markers assayed presented differential protein expression between serous tumors of low and high grade. Significant differences in Ccne1 and Ran expression were observed in a comparison of low malignant potential and grade 1 tumor samples (p<0.01). In addition, irrespective of the grade, Ccne1, Ran, Cdc20 and Cks1 showed significant differences of expression in association with the clinical stage of disease. While high level of Ccne1 have previously been associated with poor outcomes, here we found that high level of either Ran or Cdc20 appear to be more tightly associated with a poor prognosis (p<0.001, 0.03, respectively). The application of these biomarkers in both the initial diagnosis and prognostic attributes of patients with epithelial ovarian tumors should prove to be useful in patient management.

Localization of neuregulin-1α (heregulin-α) and one of its receptors, ErbB-4 tyrosine kinase, in developing and adult human brain

Using immunohistochemistry, Western blot analysis, and RT-polymerase chain reaction, we studied the distribution of neuregulin-1 splice variant alpha (NRG-1alpha) and one of its putative receptors, ErbB-4 tyrosine kinase, in human brain. In the pre- and perinatal human brain immunoreactivity was confined to numerous neurons, with the highest cell density found in cortical gray matter, hypothalamus and cerebellum. In the adult brain, single cortical gray and white matter neurons showed NRG-1alpha immunoreactivity. Occasionally, immunoreactive oligodendrocytes were observed. NRG-1alpha-expressing neurons were also found in the hypothalamus, hippocampus, basal ganglia and brain stem. Application of two antibodies recognizing alpha and beta isoforms revealed a different distribution pattern in that many cortical and hippocampal pyramidal neurons were labeled. ErbB-4 immunoreactivity was expressed in both neurons and oligodendrocytes. Our data show that NRG-1alpha expression is lower in the adult human brain than in the developing brain, and, therefore, support a role for NRG-1alpha in brain development.

Co-regulation of B-Myb expression by E2F1 and EGF receptor

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is frequently over-expressed in human cancers and is associated with tumorigenesis, and increased tumor proliferation and progression. Also found in breast tumors with high levels is B-Myb, a transcription factor whose expression is activated by E2F1/3 at the late G1 phase and the level is sustained through the S phase. Recent reports suggest a casual correlation between EGFR and B-Myb expression in primary breast carcinomas. However, the mechanism for such co-expression remains un-investigated. Here, we report that EGFR is important for B-Myb expression and the underlying mechanism involves cooperated effects from EGFR and E2F1. EGF stimulation and forced expression of EGFR significantly increase B-Myb gene activity and such increase occurs in the G1 phase. EGF-induced B-Myb expression was not significantly suppressed following inhibition of PI-3K and ERK, two major EGFR downstream pathways. In contrast, we observed EGF-induced in vivo association of nuclear EGFR to the B-Myb promoter and the association is only detected at the G1/S phase and is abolished by EGFR kinase inhibitor. As EGFR lacks DNA-binding domain but contains transactivational activity and E2F1 activates B-Myb expression in the G1/S phase, we further reasoned that nuclear EGFR might cooperate with E2F1 leading to activation of B-Myb. Indeed, we found that EGFR co-immunoprecipitated with E2F1 in an EGF-dependent manner and that EGF activated in vivo binding of E2F1 to the B-Myb promoter. Consistently, forced expression of both EGFR and E2F1 in EGFR-null CHO cells greatly enhanced B-Myb promoter activity, compared to the vector control and expression of EGFR or E2F1 alone. Promoter mutagenesis studies showed that EGF-induced activation of B-Myb promoter required both E2F and EGFR target sites. In summary, our data suggest that deregulated EGFR signaling pathway facilitate tumor cell proliferation partly via EGFR interaction with E2F1 and subsequent activation of B-Myb gene expression.

The ErbB4 neuregulin receptor mediates suppression of oligodendrocyte maturation

Neuregulin is required for proper oligodendrocyte development, but which receptors are involved and whether neuregulin promotes or inhibits maturation remain controversial. To assess the roles of the neuregulin receptor ErbB4 in oligodendrocyte development, we examined oligodendrocyte initiation and maturation in cultures derived from erbB4 knock-out mice and rat spinal cord in the presence of neutralizing erbB4 antibodies. No differences in the development of O4+ oligodendrocytes were detected in the presence or absence of erbB4 signaling. All four epidermal growth factor receptor family members were detected in the ventral neural tube at approximately the time of initial oligodendrocyte development, consistent with redundancy in neuregulin receptor signaling at the onset of oligodendrocyte development. In contrast, greater numbers of differentiated (monoclonal antibody O1+) oligodendrocytes developed in neural tube explants from erbB4(-/-) mice than either erbB4(+/+) or erbB4(+/-) littermates as well as in cultures treated with anti-erbB4. These data indicate that ErbB4 is not required for oligodendrocyte development and, in fact, inhibits oligodendrocyte lineage maturation. Together with previous studies, these data suggest a model in which early oligodendrocyte lineage development is regulated by promiscuous neuregulin receptor signaling, but subsequent lineage progression occurs through a balance of receptor-specific promotion or inhibition of maturation.

Nuclear interaction of EGFR and STAT3 in the activation of the iNOS/NO pathway

Epidermal growth factor receptor (EGFR) exists in the nucleus of highly proliferative cells where it functions as a transcription factor. Although EGFR has transactivational activity, it lacks a DNA binding domain and, therefore, may require a DNA binding transcription cofactor for its transcriptional function. Here, we report that EGFR physically interacts with signal transducers and activators of transcription 3 (STAT3) in the nucleus, leading to transcriptional activation of inducible nitric oxide synthase (iNOS). In breast carcinomas, nuclear EGFR positively correlates with iNOS. This study describes a mode of transcriptional control involving cooperated efforts of STAT3 and nuclear EGFR. Our work suggests that the deregulated iNOS/NO pathway may partly contribute to the malignant biology of tumor cells with high levels of nuclear EGFR and STAT3.

Novel Prognostic Value of Nuclear Epidermal Growth Factor Receptor in Breast Cancer

Epidermal growth factor receptor (EGFR) has been detected in the nucleus of cancer cells and primary tumors for decades. While localized in the nucleus, EGFR functions as a transcriptional regulator resulting in the activation of the cyclin D1 gene. Despite nuclear accumulation of EGFR is linked to increased DNA synthesis and proliferative potential, the pathological significance of nuclear EGFR, however, remains uninvestigated. Furthermore, expression of EGFR has not provided a consistent predictive value for survival of breast cancer patients. Here, we analyzed 130 breast carcinomas via immunohistochemical analyses for the levels of nuclear and non-nuclear EGFR. We found 37.7% of the cohort immunostained positively for nuclear EGFR and 6.9% with high levels of expression. Importantly, Kaplan-Meier survival analysis and log-rank test revealed a significant inverse correlation between high nuclear EGFR and overall survival (P = 0.009). Expression of nuclear EGFR correlated positively with increased levels of cyclin D1 and Ki-67, both are indicators for cell proliferation. In contrast, expression of non-nuclear EGFR did not significantly correlate with those of cyclin D1 and Ki-67 or the overall survival rate. In addition, we analyzed 37 oral squamous carcinomas for EGFR expression and found 24.3% of the cases to contain moderate/high levels of nuclear EGFR. Taken together, our findings indicate pathological significance of nuclear EGFR and may have important clinical implication.