Heregulin inhibits proliferation via ERKs and phosphatidyl-inositol 3-kinase activation but regulates urokinase plasminogen activator independently of these pathways in metastatic mammary tumor cells

The Yin and Yang of ERBB4: Tumor Suppressor and Oncoprotein

ERBB4 (HER4) is a member of the ERBB family of receptor tyrosine kinases, a family that includes the epidermal growth factor receptor (EGFR/ERBB1/HER1), ERBB2 (Neu/HER2), and ERBB3 (HER3). EGFR and ERBB2 are oncoproteins and validated targets for therapeutic intervention in a variety of solid tumors. In contrast, the role that ERBB4 plays in human malignancies is ambiguous. Thus, here we review the literature regarding ERBB4 function in human malignancies. We review the mechanisms of ERBB4 signaling with an emphasis on mechanisms of signaling specificity. In the context of this signaling specificity, we discuss the hypothesis that ERBB4 appears to function as a tumor suppressor protein and as an oncoprotein. Next, we review the literature that describes the role of ERBB4 in tumors of the bladder, liver, prostate, brain, colon, stomach, lung, bone, ovary, thyroid, hematopoietic tissues, pancreas, breast, skin, head, and neck. Whenever possible, we discuss the possibility that ERBB4 mutants function as biomarkers in these tumors. Finally, we discuss the potential roles of ERBB4 mutants in the staging of human tumors and how ERBB4 function may dictate the treatment of human tumors. SIGNIFICANCE STATEMENT: This articles reviews ERBB4 function in the context of the mechanistic model that ERBB4 homodimers function as tumor suppressors, whereas ERBB4-EGFR or ERBB4-ERBB2 heterodimers act as oncogenes. Thus, this review serves as a mechanistic framework for clinicians and scientists to consider the role of ERBB4 and ERBB4 mutants in staging and treating human tumors.

Neuregulins in Neurodegenerative Diseases

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), are typically characterized by progressive neuronal loss and neurological dysfunctions in the nervous system, affecting both memory and motor functions. Neuregulins (NRGs) belong to the epidermal growth factor (EGF)-like family of extracellular ligands and they play an important role in the development, maintenance, and repair of both the central nervous system (CNS) and peripheral nervous system (PNS) through the ErbB signaling pathway. They also regulate multiple intercellular signal transduction and participate in a wide range of biological processes, such as differentiation, migration, and myelination. In this review article, we summarized research on the changes and roles of NRGs in neurodegenerative diseases, especially in AD. We elaborated on the structural features of each NRG subtype and roles of NRG/ErbB signaling networks in neurodegenerative diseases. We also discussed the therapeutic potential of NRGs in the symptom remission of neurodegenerative diseases, which may offer hope for advancing related treatment.

Dysregulation of Neuregulin-1/ErbB signaling in the hippocampus of rats after administration of doxorubicin

Objective

Long-term use of doxorubicin (Dox) can cause neurobiological side effects associated with depression, but the underlying mechanisms remain equivocal. While recent evidence has indicated that Neuregulin-1 (NRG1) and its ErbB receptors play an essential role in neural function, much is still unknown concerning the biological link between the NRG1/ErbB pathway and the Dox-induced neurotoxicity. Therefore, we examined the protein expression of NRG1 and ErbB receptors in the hippocampus of rats following Dox treatment.

Materials and methods

The drug was administered every 2 days at a dose of 2.5 mg/kg, and the animals in different groups were treated with intraperitoneal injection for three or seven times, respectively.

Results

Our data showed that the rats treated with Dox for seven times (DoxL group) exhibited depression-like behaviors, whereas the short-term treatment (DoxS group) had no effect on the behavioral changes. Dox treatment also induced the neural apoptosis with more severe neurotoxicity. Intriguingly, the expression of NRG1 and the ratio of pErbB4/ErbB4 and pErbB2/ErbB2 were significantly decreased in the DoxL group, but enhanced activation of ErbB receptors was observed in the DoxS group. In parallel, administration of Dox for seven times suppressed the downstream Akt and ERK phosphorylation, while the Akt phosphorylation was enhanced with the administration of Dox for three times.

Conclusion

Our data first showed the Dox-induced alterations of the NRG1/ErbB system in the hippocampus, indicating the potential involvement of the NRG1/ErbB pathway in the Dox-induced nervous system dysfunction.

Identification of novel biomarkers for prediction of neurological prognosis following cardiac arrest

Background

Early prognostication of neurological outcome in comatose patients after cardiac arrest (CA) is important for devising patient treatment strategies. However, there is still a lack of sensitive and specific biomarkers for easy identification of these patients. We evaluated whether molecular signatures from blood of CA patients might help to improve the prediction of neurological outcome.

Methods

We examined 22 comatose patients resuscitated after CA and obtained peripheral blood samples 48 hours after CA. To identify novel blood biomarkers, we aimed to measure neurological outcomes according to the Cerebral Performance Category (CPC) score at 6 months after CA and to determine blood transcriptome-based molecular signature of poor neurological outcome group.

Results

According to the CPC score, 10 patients exhibited a CPC score of one and 12 patients, a CPC score four to five. Blood transcriptomics revealed differently expressed profiles between the good outcome group and poor outcome group. A total of 150 genes were down-regulated and 237 genes were up-regulated in the poor neurological outcome group compared with good outcome group. From the blood transcriptome-based signatures, we identified that MAPK3, BCL2 and AKT1 were more specific and sensitive diagnostic biomarkers in poor neurological outcome with an area under the curve of 0.867 (p<0.0001), 0.800 (p=0.003), and 0.767 (p=0.016) respectively.

Conclusions

We identify three biomarkers as potential predictors of neurological outcome following CA. Further assessment of the prognostic value of transcriptomic analysis in larger cohorts of CA patients is needed.

Antitumoral Effects of D-Fraction from Grifola Frondosa (Maitake) Mushroom in Breast Cancer

D-Fraction is protein-bound β-1,6 and β-1,3 glucans (proteoglucan) extracted from the edible and medicinal mushroom Grifola frondosa (Maitake). The antitumoral effect of D-Fraction has long been exclusively attributed to their immunostimulatory capacity. However, in recent years increasing evidence showed that D-Fraction directly affects the viability of canine and human tumor cells, independent of the immune system. Previously, we have reported that D-Fraction modulates the expression of genes associated with cell proliferation, cell death, migration, invasion, and metastasis in MCF7 human breast cancer cells. Therefore, the purpose of the current study is to investigate if this modulation of gene expression by Maitake D-Fraction really modulates tumor progression. In the present work, we demonstrate for the first time that Maitake D-Fraction is able to act directly on mammary tumor cells, modulating different cellular processes involved in the development and progression of cancer. We demonstrate that D-Fraction decreases cell viability, increases cell adhesion, and reduces the migration and invasion of mammary tumor cells, generating a less aggressive cell behavior. In concordance with these results, we also demonstrate that D-Fraction decreases tumor burden and the number of lung metastases in a murine model of breast cancer.

Neuregulin-1 (Nrg1) signaling has a preventive role and is altered in the frontal cortex under the pathological conditions of Alzheimer's disease

Alzheimer's disease (AD), one of the neurodegenerative disorders that may develop in the elderly, is characterized by the deposition of β‑amyloid protein (Aβ) and extensive neuronal cell death in the brain. Neuregulin‑1 (Nrg1)‑mediated intercellular and intracellular communication via binding to ErbB receptors regulates a diverse set of biological processes involved in the development of the nervous system. In the present study, a linear correlation was identified between Nrg1 and phosphorylated ErbB (pNeu and pErbB4) receptors in a human cortical tissue microarray. In addition, increased expression levels of Nrg1, but reduced pErbB receptor levels, were detected in the frontal lobe of a patient with AD. Western blotting and immunofluorescence staining were subsequently performed to uncover the potential preventive role of Nrg1 in cortical neurons affected by the neurodegenerative processes of AD. It was observed that the expression of Nrg1 increased as the culture time of the cortical neurons progressed. In addition, H2O2 and Aβ1‑42, two inducers of oxidative stress and neuronal damage, led to a dose‑dependent decrease in Nrg1 expression. Recombinant Nrg1β, however, was revealed to exert a pivotal role in preventing oxidative stress and neuronal damage from occurring in the mouse cortical neurons. Taken together, these results suggest that changes in Nrg1 signaling may influence the pathological development of AD, and exogenous Nrg1 may serve as a potential candidate for the prevention and treatment of AD.

Differential changes in Neuregulin-1 signaling in major brain regions in a lipopolysaccharide-induced neuroinflammation mouse model

Neuregulin 1 (Nrg1) is involved in multiple biological processes in the nervous system. The present study investigated changes in Nrg1 signaling in the major brain regions of mice subjected to lipopolysaccharide (LPS)-induced neuroinflammation. At 24 h post‑intraperitoneal injection of LPS, mouse brain tissues, including tissues from the cortex, striatum, hippocampus and hypothalamus, were collected. Reverse transcription‑polymerase chain reaction was used to determine the expression of Nrg1 and its receptors, Neu and ErbB4, at the mRNA level. Western blotting was performed to determine the levels of these proteins and the protein levels of phosphorylated extracellular signal-regulated kinases (Erk)1/2 and Akt1. Immunohistochemical staining was utilized to detect the levels of pNeu and pErbB4 in these regions. LPS successfully induced sites of neuroinflammation in these regions, in which changes in Nrg1, Neu and ErbB4 at the mRNA and protein levels were identified compared with controls. LPS induced a reduction in pNeu and pErbB4 in the striatum and hypothalamus, although marginally increased pErbB4 levels were found in the hippocampus. LPS increased the overall phosphorylation of Src but this effect was reduced in the hypothalamus. Moreover, increased phosphorylation of Akt1 was found in the striatum and hippocampus. These data suggest diverse roles for Nrg1 signaling in these regions during the process of neuroinflammation.

Stat3 regulates ErbB-2 expression and co-opts ErbB-2 nuclear function to induce miR-21 expression, PDCD4 downregulation and breast cancer metastasis

Membrane overexpression of the receptor tyrosine kinase ErbB-2 (MErbB-2) accounts for a clinically aggressive breast cancer (BC) subtype (ErbB-2-positive) with increased incidence of metastases. We and others demonstrated that nuclear ErbB-2 (NErbB-2) also plays a key role in BC and is a poor prognostic factor in ErbB-2-positive tumors. The signal transducer and activator of transcription 3 (Stat3), another player in BC, has been recognized as a downstream mediator of MErbB-2 action in BC metastasis. Here, we revealed an unanticipated novel direction of the ErbB-2 and Stat3 interaction underlying BC metastasis. We found that Stat3 binds to its response elements (GAS) at the ErbB-2 promoter to upregulate ErbB-2 transcription in metastatic, ErbB-2-positive BC. We validated these results in several BC subtypes displaying metastatic and non-metastatic ability, highlighting Stat3 general role as upstream regulator of ErbB-2 expression in BC. Moreover, we showed that Stat3 co-opts NErbB-2 function by recruiting ErbB-2 as its coactivator at the GAS sites in the promoter of microRNA-21 (miR-21), a metastasis-promoting microRNA (miRNA). Using an ErbB-2 nuclear localization domain mutant and a constitutively activated ErbB-2 variant, we found that NErbB-2 role as a Stat3 coactivator and also its direct role as transcription factor upregulate miR-21 in BC. This reveals a novel function of NErbB-2 as a regulator of miRNAs expression. Increased levels of miR-21, in turn, downregulate the expression of the metastasis-suppressor protein programmed cell death 4 (PDCD4), a validated miR-21 target. Using an in vivo model of metastatic ErbB-2-postive BC, in which we silenced Stat3 and reconstituted ErbB-2 or miR-21 expression, we showed that both are downstream mediators of Stat3-driven metastasis. Supporting the clinical relevance of our results, we found an inverse correlation between ErbB-2/Stat3 nuclear co-expression and PDCD4 expression in ErbB-2-positive primary invasive BCs. Our findings identify Stat3 and NErbB-2 as novel therapeutic targets to inhibit ErbB-2-positive BC metastasis.

HER Specific TKIs Exert Their Antineoplastic Effects on Breast Cancer Cell Lines through the Involvement of STAT5 and JNK

Background

HER-targeted tyrosine kinase inhibitors (TKIs) have demonstrated pro-apoptotic and antiproliferative effects in vitro and in vivo. The exact pathways through which TKIs exert their antineoplastic effects are, however, still not completely understood.

Methods

Using Milliplex assays, we have investigated the effects of the three panHER-TKIs lapatinib, canertinib and afatinib on signal transduction cascade activation in SKBR3, T47D and Jurkat neoplastic cell lines. The growth-inhibitory effect of blockade of HER and of JNK and STAT5 signaling was measured by proliferation- and apoptosis-assays using formazan dye labeling of viable cells, Western blotting for cleaved PARP-1 and immunolabeling for active caspase 3, respectively.

Results

All three HER-TKIs clearly inhibited proliferation and increased apoptosis in HER2 overexpressing SKBR3 cells, while their effect was less pronounced on HER2 moderately expressing T47D cells where they exerted only a weak antiproliferative and essentially no pro-apoptotic effect. Remarkably, phosphorylation/activation of JNK and STAT5A/B were inhibited by HER-TKIs only in the sensitive, but not in the resistant cells. In contrast, phosphorylation/activation of ERK/MAPK, STAT3, CREB, p70 S6 kinase, IkBa, and p38 were equally affected by HER-TKIs in both cell lines. Moreover, we demonstrated that direct pharmacological blockade of JNK and STAT5 abrogates cell growth in both HER-TKI-sensitive as well as -resistant breast cancer cells, respectively.

Conclusion

We have shown that HER-TKIs exert a HER2 expression-dependent anti-cancer effect in breast cancer cell lines. This involves blockade of JNK and STAT5A/B signaling, which have been found to be required for in vitro growth of these cell lines.

Neurohypophyseal Neuregulin 1 Is Derived from the Hypothalamus as a Potential Prolactin Modulator

Although neuregulin 1 (Nrg1) has been identified in the rat hypothalamus, the localisation of Nrg1 in the hypothalamus-hypophyseal structure and its functions remain unclear and require further elucidation. In this study, we identified the existence of Nrg1β types I-III in the rat hypothalamus. We demonstrated that Nrg1 was partially localised in somatostatin-positive cells in the periventricular nucleus. It was also co-localised with arginine vasopressin in the supraoptic nucleus, median eminence and pituitary stalk. Nrg1 was also extensively distributed in the posterior pituitary (PP), including the projected neuronal fibres that surround the vascular structure and Herring bodies. Western blotting confirmed that these signals were primarily produced by soluble Nrg1 derived from a 45-kDa Nrg1 precursor mainly identified in the hypothalamus. Similar to Nrg1α, Nrg1β increased the prolactin (PRL) expression in rat pituitary RC-4B/C cells, which can be inhibited by an Akt inhibitor. In addition, Nrg1β had no apparent effect on growth hormone expression at the mRNA or protein levels. Collectively, we conclude that hypothalamic Nrg1 may be transported to the PP as the β form. We further hypothesise that Nrg1β may function via the regulation of PRL expression through a paracrine mechanism.

Involvement of protein kinase C α and δ activities on the induction of the retinoic acid system in mammary cancer cells

It has been established that retinoids exert some of their effects on cell differentiation and malignant phenotype reversion through the interaction with different members of the protein kinase C (PKC) family. Till nowadays the nature and extension of this interaction is not well understood. Due to the cytostatic and differentiating effects of retinoids, in the present study we propose to evaluate whether the crosstalk between the retinoid system and the PKC pathway could become a possible target for breast cancer treatment. We could determine that ATRA (all-trans retinoic) treatment showed a significant growth inhibition due to (G1 or G2) cell cycle arrest both in LM3 and SKBR3, a murine and human mammary cell line respectively. ATRA also induced a remarkable increase in PKCα and PKCδ expression and activity. Interestingly, the pharmacological inhibition of these two PKC isoforms prevented the activation of retinoic acid receptors (RARs) by ATRA, indicating that both PKC isoforms are required for RARs activation. Moreover, PKCδ inhibition also impaired ATRA-induced RARα translocation to the nucleus. In vivo assays revealed that a combined treatment using ATRA and PKCα inhibitors prevented lung metastatic dissemination in an additive way. Our results clearly indicate that ATRA modulates the expression and activity of different PKCs. Besides inducing cell arrest, the activity of both PKC is necessary for the induction of the retinoic acid system. The combined ATRA and PKCα inhibitors could be an option for the hormone-independent breast cancer treatment.

Neuregulin-1 (Nrg1) is mainly expressed in rat pituitary gonadotroph cells and possibly regulates prolactin (PRL) secretion in a juxtacrine manner

The binding of Neuregulin-1 (Nrg1) to its cognate receptors ErbB-3 and -4 mediates intercellular and intracellular communication. In vitro, this interaction has been shown to control prolactin (PRL) secretion from pituitary tumour cells. However, Nrg1/ErbB signalling and its function in vivo are not well understood. In the present study, we demonstrated that type I and III Nrg1 isoforms were expressed in the rat anterior pituitary. We observed that Nrg1 positive gonadotrophs can form contacts with lactotrophs, which are positive for ErbB-3 receptor. In addition, we show that gonadotroph cell-derived Nrg1 regulates the secretion of an 18 kDa form of PRL from pituitary lactosomatotroph GH3 cells in vitro. The results obtained strongly suggest that gonadotrophs are the major source of Nrg1 in the normal anterior pituitary and that Nrg1 may function as a paracrine/juxtacrine regulator of PRL secretion.

Endogenous expression of Neuregulin-1 (Nrg1) as a potential modulator of prolactin (PRL) secretion in GH3 cells

The binding of Neuregulin-1 (Nrg1) to the epidermal growth factor family of receptor tyrosine kinases (ErbB) mediates intercellular and intracellular communication and regulates a broad spectrum of biological processes, such as tumorigenesis and myelination. Recombinant Nrg1 has been shown to control prolactin (PRL) secretion from rat prolactinoma GH3 cells. However, the endogenous expression of Nrg1 and its role in PRL secretion in GH3 cells are not known. In this study, we demonstrate that type III Nrg1 isoforms are endogenously expressed in GH3 cells. An in vitro functional analysis by using short interfering RNA against Nrg1 has revealed that endogenous Nrg1 regulates PRL secretion from GH3 cells in part in an ErbB-3-receptor-dependent manner, with no significant effects on growth hormone secretion. Therefore, Nrg1 is a specific modulator of PRL secretion in GH3 cells. Additionally, the co-localization of Nrg1 and ErbB-2 receptor, which is shared by both ErbB-3 and ErbB-4 receptors in the formation of heterodimers, has been detected in one out of five human prolactinoma tissues. Our findings suggest that GH3 cells intrinsically express a group of type III Nrg1 isoforms that regulate PRL secretion through an autocrine/paracrine mechanism. Further investigation into the role of Nrg1 on PRL secretion should provide clues to advance the clinical management of prolactinoma.

Decorin, erythroblastic leukaemia viral oncogene homologue B4 and signal transducer and activator of transcription 3 regulation of semaphorin 3A in central nervous system scar tissue

Scar tissue at sites of traumatic injury in the adult central nervous system presents a combined physical and molecular impediment to axon regeneration. Of multiple known central nervous system scar associated axon growth inhibitors, semaphorin 3A has been shown to be strongly expressed by invading leptomeningeal fibroblasts. We have previously demonstrated that infusion of the small leucine-rich proteoglycan decorin results in major suppression of several growth inhibitory chondroitin sulphate proteoglycans and growth of adult sensory axons across acute spinal cord injuries. Furthermore, decorin treatment of leptomeningeal fibroblasts significantly increases their ability to support neurite growth of co-cultured adult dorsal root ganglion neurons. In the present study we show that decorin has the ability to suppress semaphorin 3A expression within adult rat cerebral cortex scar tissue and in primary leptomeningeal fibroblasts in vitro. Infusion of decorin core protein for eight days resulted in a significant reduction of semaphorin 3A messenger RNA expression within injury sites compared with saline-treated control animals. Both in situ hybridization and immunostaining confirmed that semaphorin 3A messenger RNA expression and protein levels are significantly reduced in decorin-treated animals. Similarly, decorin treatment decreased the expression of semaphorin 3A messenger RNA in cultured rat leptomeningeal fibroblasts compared with untreated cells. Mechanistic studies revealed that decorin-mediated suppression of semaphorin 3A critically depends on erythroblastic leukaemia viral oncogene homologue B4 and signal transducer and activator of transcription 3 function. Collectively, our studies show that in addition to suppressing the levels of inhibitory chondroitin sulphate proteoglycans, decorin has the ability to suppress semaphorin 3A in the injured central nervous system. Our findings provide further evidence for the use of decorin as a potential therapy for promoting axonal growth and repair in the injured adult mammalian brain and spinal cord.

Expression and function of heregulin-alpha and its receptors in the mouse mammary gland

Heregulin-alpha (HRGalpha) is a cytokine secreted by the mammary mesenchyme, adjacent to lobuloalveolar structures. To understand the role of HRGalpha and its receptors in mammary glands, and the underlying mechanisms, we performed this study to determine the expression and localization of HRGalpha and its receptors ErbB2 and ErbB3. We also determined the role of HRGalpha in the development of mammary glands, beta-casein expression and secretion, Rab3A protein expression and the phosphorylation of HRGalpha signaling molecules using confocal laser scanning microscopy, tissue culture, capillary electrophoresis, Western blotting and enzyme-linked immunosorbent assays. We found that a peak was on pregnancy day 15. Changes of ErbB2 and ErbB3 expression were positively and linearly correlated with HRGalpha, indicating that HRGalpha positively regulates ErbB2 and ErbB3 expression. During pregnancy, HRGalpha enhanced the phosphorylation of STAT5, p42/p44, p38, PKC and Rab3A protein expression, stimulated the proliferation and differentiation of the ductal epithelial cells of mammary glands, and increased and maintained the expression and secretion of beta-casein. During lactation, HRGalpha enhanced the phosphorylation of STAT5 and p38, inhibited the phosphorylation of PKC and Rab3A protein expression, maintained the morphology of the mammary glands and increased the secretion of lactoprotein to reduce the expression of beta-casein in mammary epithelial cells. During involution, HRGalpha induced the phosphorylation of STAT3 and Rab3A protein expression, and inhibited the phosphorylation of PKC to stimulate the degeneration of mammary epithelial cells. It also inhibited the secretion of beta-casein, resulting in increased levels of beta-casein in mammary epithelial cells.

Mouse mammary tumors display Stat3 activation dependent on leukemia inhibitory factor signaling

Introduction

It has been demonstrated that leukemia inhibitory factor (LIF) induces epithelium apoptosis through Stat3 activation during mouse mammary gland involution. In contrast, it has been shown that this transcription factor is commonly activated in breast cancer cells, although what causes this effect remains unknown. Here we have tested the hypothesis that locally produced LIF can be responsible for Stat3 activation in mouse mammary tumors.

Methods

The studies were performed in different tumorigenic and non-tumorigenic mammary cells. The expression of LIF and LIF receptor was tested by RT-PCR analysis. In tumors, LIF and Stat3 proteins were analyzed by immunohistochemistry, whereas Stat3 and extracellular signal-regulated kinase (ERK)1/2 expression and phosphorylation were studied by Western blot analysis. A LIF-specific blocking antibody was used to determine whether this cytokine was responsible for Stat3 phosphorylation induced by conditioned medium. Specific pharmacological inhibitors (PD98059 and Stat3ip) that affect ERK1/2 and Stat3 activation were used to study their involvement in LIF-induced effects. To analyze cell survival, assays with crystal violet were performed.

Results

High levels of LIF expression and activated Stat3 were found in mammary tumors growing in vivo and in their primary cultures. We found a single mouse mammary tumor cell line, LM3, that showed low levels of activated Stat3. Incidentally, these cells also showed very little expression of LIF receptor. This suggested that autocrine/paracrine LIF would be responsible for Stat3 activation in mouse mammary tumors. This hypothesis was confirmed by the ability of conditioned medium of mammary tumor primary cultures to induce Stat3 phosphorylation, activity that was prevented by pretreatment with LIF-blocking antibody. Besides, we found that LIF increased tumor cell viability. Interestingly, blocking Stat3 activation enhanced this effect in mammary tumor cells.

Conclusion

LIF is overexpressed in mouse mammary tumors, where it acts as the main Stat3 activator. Interestingly, the positive LIF effect on tumor cell viability is not dependent on Stat3 activation, which inhibits tumor cell survival as it does in normal mammary epithelium.

Ligand-independent regulation of ErbB4 receptor phosphorylation by activated Ras

The ErbB family of receptor tyrosine kinases regulates cell growth, differentiation and survival. Activation of the receptors is induced by specific growth factors in an autocrine, paracrine or juxtacrine manner. The activated ErbB receptors turn on a large variety of signaling cascades, including the prominent Ras-dependent signaling pathways. The activated Ras can induce secretion of growth factors such as EGF and neuregulin, which activate their respective receptors. In the present study, we demonstrate for the first time that activated Ras can activate ErbB4 receptor in a ligand-independent manner. Expression of constitutively active H-Ras(12V), K-Ras(12V) or N-Ras(13V) in PC12-ErbB4 cells induced ErbB4-receptor phosphorylation, indicating that each of the most abundant Ras isoforms can induce receptor activation. NRG-induced phosphorylation of ErbB4 receptor was blocked by the soluble ErbB4 receptor, which had no effect on the Ras-induced receptor phosphorylation. Moreover, conditioned medium from H-Ras(12V)-transfected PC12-ErbB4 cells had no effect on receptor phosphorylation. It thus indicates that Ras induces ErbB4 phosphorylation in a ligand-independent manner. Each of the Ras effector domain mutants, H-Ras(12V)S35, H-Ras(12V)C40, and H-Ras(12V)G37, which respectively activate Raf1, PI3K, and RalGEF, induced a small but significant receptor phosphorylation. The PI3K inhibitor LY294002 and the MEK inhibitor PD98059 caused a partial inhibition of the Ras-induced ErbB4 receptor phosphorylation. Using a mutant ErbB4 receptor, which lacks kinase activity, we demonstrated that the Ras-mediated ErbB4 phosphorylation depends on the kinase activity of the receptor and facilitates ligand-independent neurite outgrowth in PC12-ErbB4 cells. These experiments demonstrate a novel mechanism controlling ErbB receptor activation. Ras induces ErbB4 receptor phosphorylation in a non-autocrine manner and this activation depends on multiple Ras effector pathways and on ErbB4 kinase activity.

Phosphorylation of ErbB4 on Tyr1056 is critical for inhibition of colony formation by prostate tumor cell lines

We have previously demonstrated that the constitutively active Q646C mutant of the ErbB4 receptor tyrosine kinase inhibits colony formation by human prostate tumor cell lines. Here we use ErbB4 mutants to identify ErbB4 functions critical for inhibiting colony formation. A derivative of ErbB4 Q646 that lacks kinase activity fails to inhibit colony formation by prostate tumor cells. Likewise, an ErbB4 Q646C mutant in the context of the CT-b splicing isoform fails to inhibit colony formation. Mutation of tyrosine 1056 to phenylalanine abrogates inhibition of colony formation whereas an ErbB4 mutant that lacks all of the putative sites of tyrosine phosphorylation except for tyrosine 1056 still inhibits colony formation. Given that tyrosine 1056 is missing in the CT-b isoform, these results suggest that phosphorylation of tyrosine 1056 is critical for function. Indeed, an ErbB4 mutant that lacks kinase activity but has a glutamate phosphomimic residue substituted for tyrosine 1056 inhibits colony formation. Finally, 1-dimensional phosphopeptide mapping indicates that ErbB4 Q646C is phosphorylated on tyrosine 1056. These data suggest that phosphorylation of ErbB4 tyrosine 1056 is critical for coupling ErbB4 to prostate tumor suppression.

Text mining of full-text journal articles combined with gene expression analysis reveals a relationship between sphingosine-1-phosphate and invasiveness of a glioblastoma cell line

Background

Sphingosine 1-phosphate (S1P), a lysophospholipid, is involved in various cellular processes such as migration, proliferation, and survival. To date, the impact of S1P on human glioblastoma is not fully understood. Particularly, the concerted role played by matrix metalloproteinases (MMP) and S1P in aggressive tumor behavior and angiogenesis remains to be elucidated.

Results

To gain new insights in the effect of S1P on angiogenesis and invasion of this type of malignant tumor, we used microarrays to investigate the gene expression in glioblastoma as a response to S1P administration in vitro. We compared the expression profiles for the same cell lines under the influence of epidermal growth factor (EGF), an important growth factor. We found a set of 72 genes that are significantly differentially expressed as a unique response to S1P. Based on the result of mining full-text articles from 20 scientific journals in the field of cancer research published over a period of five years, we inferred gene-gene interaction networks for these 72 differentially expressed genes. Among the generated networks, we identified a particularly interesting one. It describes a cascading event, triggered by S1P, leading to the transactivation of MMP-9 via neuregulin-1 (NRG-1), vascular endothelial growth factor (VEGF), and the urokinase-type plasminogen activator (uPA). This interaction network has the potential to shed new light on our understanding of the role played by MMP-9 in invasive glioblastomas.

Conclusion

Automated extraction of information from biological literature promises to play an increasingly important role in biological knowledge discovery. This is particularly true for high-throughput approaches, such as microarrays, and for combining and integrating data from different sources. Text mining may hold the key to unraveling previously unknown relationships between biological entities and could develop into an indispensable instrument in the process of formulating novel and potentially promising hypotheses.

Progestin-induced caveolin-1 expression mediates breast cancer cell proliferation

Progestin regulation of gene expression was assessed in the progestin-dependent murine tumor line C4HD which requires MPA, a synthetic progestin, for in vivo growth and expresses high levels of progesterone receptor (PR). By using suppressive subtractive hybridization, caveolin-1 was identified as a gene whose expression was increased with in vivo MPA treatment. By Northern and Western blot analysis, we further confirmed that caveolin-1 mRNA and protein expression increased in MPA-treated tumors as compared with untreated tumors. When primary cultures of C4HD cells were treated in vitro with MPA, caveolin-1 levels also increased, effect that was abolished by pre-treatment with progestin antagonist RU486. In addition, MPA promoted strong caveolin-1 promoter transcriptional activation both in mouse and human breast cancer cells. We also showed that MPA regulation of caveolin-1 expression involved in activation of two signaling pathways: MAPK and PI-3K. Short-term MPA treatment of C4HD cells led to tyrosine phosphorylation of caveolin-1 protein, where Src was the kinase involved. Additionally, we showed that MPA-induced association of caveolin-1 and PR, which was detected by coimmunoprecipitation and by confocal microscopy. Finally, we proved that MPA-induced proliferation of C4HD cells was inhibited by suppression of caveolin-1 expression with antisense oligodeoxynucleotides to caveolin-1 mRNA. Furthermore, we observed that inhibition of caveolin-1 expression abrogated PR capacity to induced luciferase activity from a progesterone response element-driven reporter plasmid. Comprehensively, our results demonstrated for the first time that caveolin-1 expression is upregulated by progestin in breast cancer. We also demonstrated that caveolin-1 is a downstream effector of MPA that is partially responsible for the stimulation of growth of breast cancer cells.

Roles for neuregulins in human cancer

The human epidermal growth factor (EGF) receptor (HER) family of receptor tyrosine kinases has frequently been implicated in cancer. Apart from overexpression or mutation of these receptors, also the aberrant autocrine or paracrine activation of HERs by EGF-like ligands may be important in cancer progression. Neuregulins constitute a family of EGF-like ligands that bind to HER3 or HER4, preferably forming heterodimers with the orphan receptor HER2. Mesenchymal neuregulin typically serves as a pro-survival and pro-differentiation signal for adjacent epithelia. Disruption of the balance between proliferation and differentiation, because of autocrine production by the epithelial cells, increased sensitivity to paracrine signals or disruption of the spatial organization, may lead to constitutive receptor activation, in the absence of receptor overexpression. Consequently, the analysis of ligand expression and/or activated receptors in tumor samples may broaden the group of patients that can benefit from targeted therapies.

Progestins induce transcriptional activation of signal transducer and activator of transcription 3 (Stat3) via a Jak- and Src-dependent mechanism in breast cancer cells

Interactions between steroid hormone receptors and signal transducer and activator of transcription (Stat)-mediated signaling pathways have already been described. In the present study, we explored the capacity of progestins to modulate Stat3 transcriptional activation in an experimental model of hormonal carcinogenesis in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in BALB/c mice and in the human breast cancer cell line T47D. We found that C4HD epithelial cells, from the MPA-induced mammary tumor model, expressed Stat3 and that MPA treatment of C4HD cells up-regulated Stat3 protein expression. In addition, MPA induced rapid, nongenomic Stat3, Jak1, and Jak2 tyrosine phosphorylation in C4HD and T47D cells. MPA treatment of C4HD cells also resulted in rapid c-Src tyrosine phosphorylation. These effects were completely abolished by the progestin antagonist RU486. Abrogation of Jak1 and Jak2 activity by transient transfection of C4HD cells with dominant negative (DN) Jak1 or DN Jak2 vectors, or inhibition of Src activity by preincubation of cells with the Src family kinase inhibitor PP2, blocked the capacity of MPA to induce Stat3 phosphorylation. Treatment of C4HD cells with MPA induced Stat3 binding to DNA. In addition, MPA promoted strong Stat3 transcriptional activation in C4HD and T47D cells that was inhibited by RU486 and by blockage of Jak1, Jak2, and Src activities. To investigate the correlation between MPA-induced Stat3 activation and cell growth, C4HD cells were transiently transfected with a DN Stat3 expression vector, Stat3Y705-F, or with a constitutively activated Stat3 mutant, Stat3-C. While expression of Stat3Y705-F mutant had an inhibitory effect on MPA-induced growth of C4HD cells, transfection with the constitutively activated Stat3-C vector resulted in MPA-independent proliferation. Finally, we addressed the effect of targeting Stat3 in in vivo growth of C4HD breast tumors. Blockage of Stat3 activation by transfection of C4HD cells with the DN Stat3Y705-F expression vector significantly inhibited these cells' ability to form tumors in syngeneic mice. Our results have for the first time demonstrated that progestins are able to induce Stat3 transcriptional activation, which is in turn an obligatory requirement for progestin stimulation of both in vitro and in vivo breast cancer growth.

Novel role for cyclin-dependent kinase 2 in neuregulin-induced acetylcholine receptor epsilon subunit expression in differentiated myotubes

Cyclin-dependent kinases (CDKs) are a family of evolutionarily conserved serine/threonine kinases. CDK2 acts as a checkpoint for the G(1)/S transition in the cell cycle. Despite a down-regulation of CDK2 activity in postmitotic cells, many cell types, including muscle cells, maintain abundant levels of CDK2 protein. This led us to hypothesize that CDK2 may have a function in postmitotic cells. We show here for the first time that CDK2 can be activated by neuregulin (NRG) in differentiated C2C12 myotubes. In addition, this activity is required for expression of the acetylcholine receptor (AChR) epsilon subunit. The switch from the fetal AChRgamma subunit to the adult-type AChRepsilon is required for synapse maturation and the neuromuscular junction. Inhibition of CDK2 activity with either the specific CDK2 inhibitory peptide Tat-LFG or by RNA interference abolished neuregulin-induced AChRepsilon expression. Neuregulin-induced activation of CDK2 also depended on the ErbB receptor, MAPK, and PI3K, all of which have previously been shown to be required for AChRepsilon expression. Neuregulin regulated CDK2 activity through coordinating phosphorylation of CDK2 on Thr-160, accumulation of CDK2 in the nucleus, and down-regulation of the CDK2 inhibitory protein p27 in the nucleus. In addition, we also observed a novel mechanism of regulation of CDK2 activity by a low molecular weight variant of cyclin E in response to NRG. These findings establish CDK2 as an intermediate molecule that integrates NRG-activated signals from both the MAPK and PI3K pathways to AChRepsilon expression and reveal an undiscovered physiological role for CDK2 in postmitotic cells.

Leukemia inhibitory factor triggers activation of signal transducer and activator of transcription 3, proliferation, invasiveness, and altered protease expression in choriocarcinoma cells

Extravillous trophoblast cells resemble cancer cells with regard to their intrinsic invasiveness. They invade decidual tissue, but, unlike tumor cells, shut down their invasive properties, when they become inappropriate. Stimuli involved in the modulation of invasion, as well as their underlying signaling mechanisms require further clarification. We were especially interested in discovering signals capable of stimulating invasion in otherwise low-invasive cells involved in reproduction. Using the choriocarcinoma cell line Jeg-3 as a model, we have addressed the potential role of cytokine/growth factor-driven activation of signal transducer and activator of transcription 3 (STAT3) in this process. Jeg-3 cells were treated with various factors known to induce trophoblast proliferation, differentiation, migration, or invasiveness (insulin-like-growth-factor-II (IGF-II), hepatocyte growth factor (HGF), interleukin-6 (IL-6), and leukemia inhibitory factor (LIF)). Only LIF elicited strong tyrosine phosphorylation and specific DNA-binding activity of STAT3. It induced a significant acceleration of cell proliferation and promoted the capability of Jeg-3 cells to invade into an artificial extracellular matrix. Moreover, LIF influenced the expression pattern of proteases and protease inhibitors with potential relevance for invasiveness (downregulation of mRNA for tissue inhibitor of metalloproteinase 1 (TIMP-1) and upregulation of mRNA for caspase-4). In conjunction with earlier work, in which we found that STAT3 DNA-binding activity was increased in invasive cells (choriocarcinoma, first trimester trophoblasts) and absent in non-invasive cells (term trophoblasts), these findings suggest a connection between LIF-driven STAT3 activity and invasiveness of choriocarcinoma and trophoblast cells.

Arctigenin, a phenylpropanoid dibenzylbutyrolactone lignan, inhibits MAP kinases and AP-1 activation via potent MKK inhibition: the role in TNF-α inhibition

Arctigenin, naturally occurring in Bardanae fructus, Saussurea medusa, Arctium lappa L., Torreya nucifera and Ipomea cairica, is a phenylpropanoid dibenzylbutyrolactone lignan with antioxidant and anti-inflammatory activities. Previously, we showed that arctigenin potently inhibited the induction of nitric oxide synthase (iNOS) by lipopolysaccharide (LPS), which involved suppression of NF-kappaB activation. In the present study, we examined the effects of arctigenin on mitogen-activated protein (MAP) kinase activation in Raw264.7 cells and MAP kinase kinase (MKK) activity. The effect of arctigenin on activator protein-1 (AP-1) activation was also studied in association with tumor necrosis factor-alpha (TNF-alpha) expression. Immunoblot analysis showed that arctigenin inhibited phosphorylation of MAP kinases ERK1/2, p38 kinase and JNK and their activities in Raw264.7 cells treated with LPS. Arctigenin potently inhibited the activity of MKK1 in vitro with the IC(50) value of 1 nM. Gel shift and reporter gene analyses revealed that arctigenin inhibited LPS-inducible AP-1 binding to the AP-1 consensus oligonucleotide and AP-1-mediated reporter gene expression. In view of the potential role of AP-1 in the induction of TNF-alpha, we next examined the inhibitory effects of arctigenin on the expression of TNF-alpha. Arctigenin blocked TNF-alpha production and decreased the level of TNF-alpha mRNA in the cells exposed to LPS. These results showed that arctigenin inhibited activation of MAP kinases including ERK1/2, p38 kinase and JNK through the inhibition of MKK activities, leading to AP-1 inactivation, which might, at least in part, contribute to the inhibition of TNF-alpha production.

Heregulin regulates the ability of the ErbB3-binding protein Ebp1 to bind E2F promoter elements and repress E2F-mediated transcription

The ErbB3/4 ligand heregulin (HRG) profoundly affects cell growth and differentiation, but its mechanism of action is poorly understood. Ebp1, a protein isolated by its binding to ErbB3, inhibits cell growth and represses transcription of E2F-regulated cell cycle genes. Since Ebp1 shares 38% identity with a Schizosaccharomyces pombe DNA-binding protein, we postulated that Ebp1 could bind E2F consensus elements in an HRG-inducible manner, leading to transcriptional repression. We show here that GST-Ebp1 bound to the DNA sequence bound by the S. pombe protein. Whereas GST-Ebp1 alone failed to bind E2F1 promoter elements, Ebp1 contained in nuclear lysates associated with E2F1 consensus sequences in the E2F1 promoter. Endogenous Ebp1 was recruited to the E2F1 promoter in vivo as demonstrated by chromatin immunoprecipitation assays. Ebp1 bound E2F consensus oligonucleotides in association with E2F1, retinoblastoma protein, and HDAC2. HRG regulated the association of Ebp1 with E2F promoter sequences and enhanced the ability of Ebp1 to repress transcription. Our findings suggest that Ebp1, by linking HRG activation of membrane receptors to E2F gene activity, may be a downstream modulator of the effects of HRG on cell cycle progression.

Heregulin-beta1 regulates the estrogen receptor-alpha gene expression and activity via the ErbB2/PI 3-K/Akt pathway

This study examines whether the serine/threonine protein kinase, Akt, is involved in the crosstalk between the ErbB2 and estrogen receptor-alpha (ER-alpha) pathways. Treatment of MCF-7 cells with 10(-9) M heregulin-beta1 (HRG-beta1) resulted in a rapid phosphorylation of Akt and a 15-fold increase in Akt activity. Akt phosphorylation was blocked by inhibitors of phosphatidylinositol 3-kinase (PI 3-K), by antiestrogens, the protein tyrosine kinase inhibitor, genistein, and by AG825, a selective ErbB2 inhibitor; but not by AG30, a selective EGFR inhibitor. Akt phosphorylation by HRG-beta1 was abrogated by an arginine to cysteine mutation (R25C) in the pleckstrin homology (PH) domain of Akt, and HRG-beta1 did not induce Akt phosphorylation in the ER-negative variant of MCF-7, MCF-7/ADR. Transient transfection of ER-alpha into these cells restored Akt phosphorylation by HRG-beta1, suggesting the requirement of ER-alpha. HRG-beta1 did not activate Akt in MCF-7 cells stably transfected with an anti-ErbB2-targeted ribozyme, further confirming a role for ErbB2. Stable transfection of the cells with a dominant negative Akt or with the R25C-Akt mutant, as well as PI 3-K inhibitors, blocked the effect of HRG-beta1 on ER-alpha expression and activity and on the growth of MCF-7 cells. Stable transfection of MCF-7 cells with a constitutively active Akt mimicked the effect of HRG-beta1. Experiments employing selective ErbB inhibitors demonstrate that the effect of HRG-beta1 on ER-alpha expression and activity is also mediated by ErbB2 and not by EGFR, demonstrating that ErbB2 is the primary mediator of the effects of HRG-beta1 on ER-alpha regulation. Taken together, our data suggest that HRG-beta1, bound to the ErbB2 ErbB3 heterodimer, in the presence of membrane ER-alpha, interacts with and activates PI 3-K/Akt. Akt leads to nuclear ER-alpha phosphorylation, thereby altering its expression and transcriptional activity.