Activation of ErbB4 by the bifunctional epidermal growth factor family hormone epiregulin is regulated by ErbB2

Non-enzymatic role of SOD1 in intestinal stem cell growth

Superoxide dismutase 1 (SOD1) modulates intestinal barrier integrity and intestinal homeostasis as an antioxidant enzyme. Intestinal homeostasis is maintained by the intestinal stem cells (ISCs). However, whether and how SOD1 regulates ISCs is unknown. In this study, we established intestinal organoids from tamoxifen-inducible intestinal epithelial cell-specific Sod1 knockout (Sod1^f/f; Vil-creERT2) mice. We found that loss of Sod1 in organoids suppressed the proliferation and survival of cells and Lgr5 gene expression. SOD1 is known for nearly half a century for its canonical role as an antioxidant enzyme. We identified its enzyme-independent function in ISC: inhibition of SOD1 enzymatic activity had no impact on organoid growth, and enzymatically inactive Sod1 mutants could completely rescue the growth defects of Sod1 deficient organoids, suggesting that SOD1-mediated ISC growth is independent of its enzymatic activity. Moreover, Sod1 deficiency did not affect the ROS levels of the organoid, but induced the elevated WNT signaling and excessive Paneth cell differentiation, which mediates the occurrence of growth defects in Sod1 deficient organoids. In vivo, epithelial Sod1 loss induced a higher incidence of apoptosis in the stem cell regions and increased Paneth cell numbers, accompanied by enhanced expression of EGFR ligand Epiregulin (EREG) in the stromal tissue, which may compensate for Sod1 loss and maintain intestinal structure in vivo. Totally, our results show a novel enzyme-independent function of SOD1 in ISC growth under homeostasis.

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.

Development and application of high-throughput screens for the discovery of compounds that disrupt ErbB4 signaling: Candidate cancer therapeutics

Whereas recent clinical studies report metastatic melanoma survival rates high as 30-50%, many tumors remain nonresponsive or become resistant to current therapeutic strategies. Analyses of The Cancer Genome Atlas (TCGA) skin cutaneous melanoma (SKCM) data set suggests that a significant fraction of melanomas potentially harbor gain-of-function mutations in the gene that encodes for the ErbB4 receptor tyrosine kinase. In this work, a drug discovery strategy was developed that is based on the observation that the Q43L mutant of the naturally occurring ErbB4 agonist Neuregulin-2beta (NRG2β) functions as a partial agonist at ErbB4. NRG2β/Q43L stimulates tyrosine phosphorylation, fails to stimulate ErbB4-dependent cell proliferation, and inhibits agonist-induced ErbB4-dependent cell proliferation. Compounds that exhibit these characteristics likely function as ErbB4 partial agonists, and as such hold promise as therapies for ErbB4-dependent melanomas. Consequently, three highly sensitive and reproducible (Z' > 0.5) screening assays were developed and deployed for the identification of small-molecule ErbB4 partial agonists. Six compounds were identified that stimulate ErbB4 phosphorylation, fail to stimulate ErbB4-dependent cell proliferation, and appear to selectively inhibit ErbB4-dependent cell proliferation. Whereas further characterization is needed to evaluate the full therapeutic potential of these molecules, this drug discovery platform establishes reliable and scalable approaches for the discovery of ErbB4 inhibitors.

Investigating mutations at the hotspot position of the ERBB2 and screening for the novel lead compound to treat breast cancer - a computational approach

Membrane proteins are the most common types of cancer that are active in the prognosis. Membrane proteins are a distinguishing characteristic of a cancer cell. In tumor cell therapy, the overexpressed membrane proteins are becoming ever more relevant. The 3-kinase (PI3K)/AKT phosphatidylinositol pathway is downstream triggered by different extracellular signals, and this signaling pathway activation impacts a variety of proliferation of the cellular processes like cell growth and surviving. Frequent PI3K/AKT dysregulation in human cancer has rendered proteins of this pathway desirable for diagnostic markers. Members of the ERBB family-like ERBB2 and ERBB3 activate intracellular signaling pathways such as PI3K/AKT. The mutations in these proteins dysfunctions the proteins in the downstream. Considering this importance, we have developed a computational pipeline to identify the mutation position with a highest number of mutations and to screen them for pathogenicity, stability, conservation, and structural changes using PredictSNP, iStable, ConSurf, and GROMACS simulation software respectively. Further, a virtual screening approach was initiated to find the most similar non-toxic lead compound, which could be an alternative to the currently used lapatinib. To conclude, protein-ligand dynamics were undertaken to study the actions of native and mutants with the lapatinib and the lead compound. From the overall analysis, we identified position 755 with leucine in the native condition is prone to frequent mutations. The leucine at 755th position is more prone to mutate as serine and tryptophan. Further from the computational analysis, we identified that the mutation L755S is more significant than the L755W mutation. We have witnessed CID140590176 be a potential lead compound with no toxicity. The behavior of the lead compound has shown more compactness with an increased number of intermolecular hydrogen bonds in the ERBB2 with L755S. This lead compound can be further taken for experimental validations, and we believe that this lead compound could be a potent ERBB2 inhibitor.

Prognostic value of EGFR family expression in lymph node-negative esophageal squamous cell carcinoma patients

The human epidermal growth factor receptor (EGFR) family has been widely studied in cancer, however, the prognostic role of EGFR family expression in lymph node-negative esophageal squamous cell carcinoma (ESCC) patients have not been invalidated. This study was designed to determine the prognostic value of EGFR family expression in a population of lymph node-negative ESCC patients treated with curative resection. EGFR family protein expression was examined by immunohistochemical analysis of tissue microarrays of 94 patients with lymph node-negative ESCC after radical esophagectomy with three-field lymphadenectomy. Survival differences were compared using Kaplan-Meier analysis. Cox regression analyses were performed to determine the prognostic factors for overall survival and disease-free survival (DFS). ErbB4 expression was found to be an independent prognostic factor for DFS in patients without lymph node metastasis; increased ErbB4 expression was associated with decreased DFS. Additionally, patients with high ErbB4 expression tended to have worse overall survival. EGFR, ErbB2 and ErbB3 expression were not significantly associated with survival in lymph node-negative ESCC patients. Increased ErbB4 immunohistochemical expression was associated with poor prognosis in lymph node-negative ESCC patients.

Epiregulin and EGFR interactions are involved in pain processing

The EGFR belongs to the well-studied ErbB family of receptor tyrosine kinases. EGFR is activated by numerous endogenous ligands that promote cellular growth, proliferation, and tissue regeneration. In the present study, we have demonstrated a role for EGFR and its natural ligand, epiregulin (EREG), in pain processing. We show that inhibition of EGFR with clinically available compounds strongly reduced nocifensive behavior in mouse models of inflammatory and chronic pain. EREG-mediated activation of EGFR enhanced nociception through a mechanism involving the PI3K/AKT/mTOR pathway and matrix metalloproteinase-9. Moreover, EREG application potentiated capsaicin-induced calcium influx in a subset of sensory neurons. Both the EGFR and EREG genes displayed a genetic association with the development of chronic pain in several clinical cohorts of temporomandibular disorder. Thus, EGFR and EREG may be suitable therapeutic targets for persistent pain conditions.

Epiregulin is required for lung tumor promotion in a murine two-stage carcinogenesis model

Adenocarcinoma accounts for ∼40% of lung cancer, equating to ∼88 500 new patients in 2015, most of who will succumb to this disease, thus, the public health burden is evident. Unfortunately, few early biomarkers as well as effective therapies exist, hence the need for novel targets in lung cancer treatment. We previously identified epiregulin (Ereg), an EGF-like ligand, as a biomarker in several mouse lung cancer models. In the present investigation we used a primary two-stage initiation/promotion model to test our hypothesis that Ereg deficiency would reduce lung tumor promotion in mice. We used 3-methylcholanthrene (initiator) or oil vehicle followed by multiple weekly exposures to butylated hydroxytoluene (BHT; promoter) in mice lacking Ereg (Ereg^-/- ) and wildtype controls (BALB/ByJ; Ereg^+/+ ) and examined multiple time points and endpoints (bronchoalveolar lavage analysis, tumor analysis, mRNA expression, ELISA, wound assay) during tumor promotion. At the early time points (4 and 12 wk), we observed significantly reduced amounts of inflammation (macrophages, PMNs) in the Ereg^-/- mice compared to controls (Ereg^+/+ ). At 20 wk, tumor multiplicity was also significantly decreased in the Ereg^-/- mice versus controls (Ereg^+/+ ). IL10 expression, an anti-inflammatory mediator, and downstream signaling events (Stat3) were significantly increased in the Ereg^-/- mice in response to BHT, supporting both reduced inflammation and tumorigenesis. Lastly, wound healing was significantly increased with recombinant Ereg in both human and mouse lung epithelial cell lines. These results indicate that Ereg has proliferative potential and may be utilized as an early cancer biomarker as well as a novel potential therapeutic target. © 2016 Wiley Periodicals, Inc.

Niacin activates the PI3K/Akt cascade via PKC- and EGFR-transactivation-dependent pathways through hydroxyl-carboxylic acid receptor 2

Niacin has been demonstrated to activate a PI3K/Akt signaling cascade to prevent brain damage after stroke and UV-induced skin damage; however, the underlying molecular mechanisms for HCA₂-induced Akt activation remain to be elucidated. Using CHO-K1 cells stably expressing HCA₂ and A431 cells, a human epidermoid cell line with high levels of endogenous expression of functional HCA₂ receptors, we first demonstrated that niacin induced a robust Akt phosphorylation at both Thr³⁰⁸ and Ser⁴⁷³ in a time-dependent fashion, with a maximal activation at 5 min and a subsequent reduction to baseline by 30 min through HCA₂, and that the activation was significantly blocked by pertussis toxin. The HCA₂-mediated activation of Akt was also significantly inhibited by the PKC inhibitors GF109203x and Go6983 in both cell lines, by the PDGFR-selective inhibitor tyrphostin A9 in CHO-HCA₂ cells and by the MMP inhibitor GM6001 and EGFR-specific inhibitor AG1478 in A431 cells. These results suggest that the PKC pathway and PDGFR/EGFR transactivation pathway play important roles in HCA₂-mediated Akt activation. Further investigation indicated that PI3K and the G_βγ subunit were likely to play an essential role in HCA₂-induced Akt activation. Moreover, Immunobloting analyses using an antibody that recognizes p70S6K1 phosphorylated at Thr³⁸⁹ showed that niacin evoked p70S6K1 activation via the PI3K/Akt pathway. The results of our study provide new insight into the signaling pathways involved in HCA₂ activation.

EGFR signaling patterns are regulated by its different ligands

EGF receptor (EGFR) and its signaling have been investigated for many years, but how its different ligands regulate signaling has not been thoroughly explored. When investigating EGFR activation and downstream signaling in HeLa cells using a panel of ligands, we found a ligand-dependent differential activation of EGFR and the signaling pathways Akt, PLCγ and STAT with HB-EGF and BTC being the most potent ligands. All the tested ligands induced full activation of Erk signaling at 1 nM, whereas only HB-EGF and partly BTC and EGF induced strong activation of Akt, STAT3 and PLCγ at this concentration. Interestingly, we also found that the high activation potencies of HB-EGF and BTC could only partially be explained by their binding affinities, and are therefore likely to be regulated by other mechanisms. We thus suggest that the signaling pathways initiated from the EGFR vary depending on the ligands bound in a cell specific manner.

Epiregulin: roles in normal physiology and cancer

Epiregulin is a 46-amino acid protein that belongs to the epidermal growth factor (EGF) family of peptide hormones. Epiregulin binds to the EGF receptor (EGFR/ErbB1) and ErbB4 (HER4) and can stimulate signaling of ErbB2 (HER2/Neu) and ErbB3 (HER3) through ligand-induced heterodimerization with a cognate receptor. Epiregulin possesses a range of functions in both normal physiologic states as well as in pathologic conditions. Epiregulin contributes to inflammation, wound healing, tissue repair, and oocyte maturation by regulating angiogenesis and vascular remodeling and by stimulating cell proliferation. Deregulated epiregulin activity appears to contribute to the progression of a number of different malignancies, including cancers of the bladder, stomach, colon, breast, lung, head and neck, and liver. Therefore, epiregulin and the elements of the EGF/ErbB signaling network that lie downstream of epiregulin appear to be good targets for therapeutic intervention.

Soluble-E-cadherin activates HER and IAP family members in HER2+ and TNBC human breast cancers

Recent literature suggests that sEcad exerts pro-oncogenic effects, possibly acting as a ligand for the human epidermal growth factor family. Here we show that sEcad is a novel candidate protein for drug targeting since it is increased in human and mouse HER2-positive (HER2+) breast tumors, MMTV-PyMT bodily fluids and human cell culture systems. Mechanistically, we show that endogenous sEcad, and to a lesser extent membrane-bound E-cadherin, associates with HER1, HER2, and HER3 in human and MMTV-PyMT mouse HER2+ tumors and with HER1 in triple negative breast cancer (TNBC) specimens. Furthermore, addition of exogenous recombinant human E-cadherin/Fc chimeric protein (rhEcad/Fc; sEcad) to HER2+ MCF-7, SKBR3, and HER2-negative MDA-MB-231 TNBC cells, resulted in sEcad-HER receptor family interactions, activation of HER1-4 and downstream pro-survival signaling, including the MAPK-PI3K/Akt/mTOR pathways and IAP family members. Lastly, we demonstrate that sEcad exerts pro-oncogenic effects via HER signaling, and acts additively with the HER ligand EGF to promote HER2+ breast cancer proliferation and migration, as well as TNBC invasion. Because sEcad associates and activates many of the oncogenic pathways that tumors utilize for growth and survival and serum levels in patients correlates with clinical response, suggests that targeted therapy against sEcad in combination with other therapies may potentially offer a novel therapeutic strategy for the treatment of breast cancers.

Epiregulin induces human SK-N-BE cell differentiation through ERK1/2 signaling pathway

Epidermal growth factor (EGF) and other EGF-related growth factors, such as transforming growth factor-α, are able to stimulate neuroblastoma (NB) cell proliferation. Epiregulin (Epi) is a growth factor belonging to the EGF family known to be more potent than EGF in mediating mitogenic signals. In this study, we tested the ability of Epi to stimulate a human NB cell line (SK-N-BE) proliferation. Surprisingly, Epi (50-1000 ng/ml) induced a reduction in SK-N-BE proliferation along with a morphological differentiation, associated with an increase in MMP-9 expression. Moreover, Epi-induced differentiation was inhibited by ERK1/2 phosphorilation inhibition. In conclusion, Epi could represent a novel and useful tool to oppose NB cell proliferation.

Human chorionic gonadotropin-dependent up-regulation of epiregulin and amphiregulin in equine and bovine follicles during the ovulatory process

Little is known about the expression and regulation of epiregulin (EREG) and amphiregulin (AREG) in ovarian follicles of large monoovulatory animal species. To characterize the gonadotropin-dependent regulation of EREG and AREG mRNAs in equine follicles prior to ovulation, extracts were prepared from equine follicles collected during estrus between 0 and 39h post-hCG and corpora lutea obtained on day 8 of the estrous cycle (day 0=day of ovulation). Results from RT-PCR/Southern blot analyses showed that levels of EREG and AREG mRNAs were very low in follicles obtained at 0h but increased thereafter (P<0.05), with maximal levels observed 33-39h post-hCG. This significant increase was observed in both granulosa and theca cells. Immunohistochemistry and immunoblot analyses confirmed the hCG-dependent induction of EREG protein in both cell types. RT-PCR/Southern blot analyses of ADAM17, which encodes an enzyme that cleaves and releases soluble bioactive EREG and AREG, showed that levels of its transcript were high and remained constant throughout the period studied. Studies on the hCG-dependent regulation of EREG and AREG in bovine preovulatory follicles in vivo showed that the induction of both transcripts was transient, observed predominantly at 6h post-hCG and localized only in granulosa cells. To characterize the effect of epidermal growth factor receptor (EGFR) activation on the expression of ovulation-related genes in granulosa cells of a large monoovulatory animal species, primary cultures of bovine granulosa cells were established. Results from RT-PCR analyses revealed that EREG and AREG mRNAs were induced by forskolin treatment in vitro; but the EGFR inhibitor PD153035 suppressed the forskolin-dependent induction of several ovulation-related transcripts, including PTGS2, PTGER2, TNFAIP6, PGR, MMP1, VEGFA, and CTSL2 mRNAs. Moreover, these transcripts were induced in granulosa cell cultures by EGF, an analog of EREG and AREG. Collectively, this study identifies differences in the temporal and cellular localization of EREG and AREG expression in equine and bovine preovulatory follicles, and underscores the potential role of follicular EGFR activation in the regulation of ovulation-regulated genes in large monoovulatory species.

Activated human hydroxy-carboxylic acid receptor-3 signals to MAP kinase cascades via the PLC-dependent PKC and MMP-mediated EGFR pathways

BACKGROUND AND PURPOSE 3-Hydroxy-octanoate, recently identified as a ligand for, the orphan GPCR, HCA(3), is of particular interest given its ability to treat lipid disorders and atherosclerosis. Here we demonstrate the pathway of HCA(3)-mediated activation of ERK1/2. EXPERIMENTAL APPROACH Using CHO-K1 cells stably expressing HCA(3) receptors and A431 cells, a human epidermoid cell line with high levels of endogenous expression of functional HCA(3) receptors, HCA(3)-mediated activation of ERK1/2 was measured by Western blot. KEY RESULTS HCA(3)-mediated activation of ERK1/2 was rapid, peaking at 5 min, and was Pertussis toxin sensitive. Our data, obtained by time course analyses in combination with different kinase inhibitors, demonstrated that on agonist stimulation, HCA(3) receptors evoked ERK1/2 activation via two distinct pathways, the PLC/PKC pathway at early time points (≤ 2 min) and the MMP/ epidermal growth factor receptor (EGFR) transactivation pathway with a maximum response at 5 min. Furthermore, our present results also indicated that the βγ-subunits of the G(i) protein play a critical role in HCA(3)-activated ERK1/2 phosphorylation, whereas β-arrestins and Src were not required for ERK1/2 activation. CONCLUSIONS AND IMPLICATIONS We have described the molecular mechanisms underlying the coupling of human HCA(3) receptors to the ERK1/2 MAP kinase pathway in CHO-K1 and A431 cells, which implicate the G(i) protein-initiated, PLC/PKC -and platelet-derived growth factor receptor/EGFR transactivation-dependent pathways. These observations may provide new insights into the pharmacological effects and the physiological functions modulated by the HCA(3)-mediated activation of ERK1/2.

Oncogenic KRAS-induced epiregulin overexpression contributes to aggressive phenotype and is a promising therapeutic target in non-small-cell lung cancer

KRAS mutations are one of the most common driver mutations in non-small-cell lung cancer (NSCLC) and finding druggable target molecules to inhibit oncogenic KRAS signaling is a significant challenge in NSCLC therapy. We recently identified epiregulin (EREG) as one of several putative transcriptional targets of oncogenic KRAS signaling in both KRAS-mutant NSCLC cells and immortalized bronchial epithelial cells expressing ectopic mutant KRAS. In the current study, we found that EREG is overexpressed in NSCLCs harboring KRAS, BRAF or EGFR mutations compared with NSCLCs with wild-type KRAS/BRAF/EGFR. Small interfering RNAs (siRNAs) targeting mutant KRAS, but not an siRNA targeting wild-type KRAS, significantly reduced EREG expression in KRAS-mutant and EREG-overexpressing NSCLC cell lines. In these cell lines, EREG expression was downregulated by MEK and ERK inhibitors. Importantly, EREG expression significantly correlated with KRAS expression or KRAS copy number in KRAS-mutant NSCLC cell lines. Further expression analysis using 89 NSCLC specimens showed that EREG was predominantly expressed in NSCLCs with pleural involvement, lymphatic permeation or vascular invasion and in KRAS-mutant adenocarcinomas. In addition, multivariate analysis revealed that EREG expression is an independent prognostic marker and EREG overexpression in combination with KRAS mutations was associated with an unfavorable prognosis for lung adenocarcinoma patients. In KRAS-mutant and EREG overexpressing NSCLC cells, siRNA-mediated EREG silencing inhibited anchorage-dependent and -independent growth and induced apoptosis. Our findings suggest that oncogenic KRAS-induced EREG overexpression contributes to an aggressive phenotype and could be a promising therapeutic target in oncogenic KRAS-driven NSCLC.

ErbB2 Is Necessary for ErbB4 Ligands to Stimulate Oncogenic Activities in Models of Human Breast Cancer

ErbB4 is a member of the ErbB family of receptor tyrosine kinases. This family includes ErbB2 (HER2/Neu), a validated therapeutic target in breast cancer. Several studies indicate that ErbB4 functions as a tumor suppressor in breast cancer, whereas others indicate that ErbB4 functions as an oncogene. Here the authors explore the context in which ErbB4 functions as an oncogene. Silencing expression of either ErbB2 or ErbB4 in breast tumor cell lines results in reduced stimulation of anchorage independence and cell motility by the ErbB4 agonist neuregulin 2β. ErbB2 tyrosine kinase activity, but not ErbB4 tyrosine kinase activity, is required for neuregulin 2β to stimulate cell proliferation. Moreover, sites of ErbB4 tyrosine phosphorylation, but not sites of ErbB2 tyrosine phosphorylation, are required for neuregulin 2β to couple to cell proliferation. These data suggest that targeting ErbB2 expression or tyrosine kinase activity may be effective in treating ErbB4-dependent breast tumors, even those tumors that lack ErbB2 overexpression.

The Q43L mutant of neuregulin 2β is a pan-ErbB receptor antagonist

The ErbB4 receptor tyrosine kinase possesses both tumour suppressor and oncogenic activities. Thus pharmacological agents are needed to help elucidate ErbB4 functions. However, limitations of existing ErbB4 agonists and antagonists have led us to seek novel ErbB4 antagonists. The Q43L mutant of the ErbB4 agonist NRG2β (neuregulin 2β) stimulates ErbB4 tyrosine phosphorylation, yet fails to stimulate ErbB4 coupling to cell proliferation. Thus in the present paper we hypothesize that NRG2β/Q43L may be an ErbB4 antagonist. NRG2β/Q43L competitively antagonizes agonist stimulation of ErbB4 coupling to cell proliferation. NRG2β/Q43L stimulates less ErbB4 tyrosine phosphorylation than does NRG2β. In addition, NRG2β stimulation of cell proliferation requires PI3K (phosphoinositide 3-kinase) activity and NRG2β stimulates greater Akt phosphorylation than does NRG2β/Q43L. Moreover, EGFR [EGF (epidermal growth factor) receptor] kinase activity (but not that of ErbB4) is critical for coupling ErbB4 to proliferation. Experiments utilizing ErbB4 splicing isoforms and mutants suggest that NRG2β and NRG2β/Q43L may differentially stimulate ErbB4 coupling to the transcriptional co-regulator YAP (Yes-associated protein). Finally, NRG2β/Q43L competitively antagonizes agonist stimulation of EGFR and ErbB2/ErbB3, indicating that NRG2β/Q43L is a pan-ErbB antagonist. Thus we postulate that NRG2β/Q43L and other antagonistic ligands stimulate ErbB tyrosine phosphorylation on a set of residues distinct from that stimulated by agonists, thus suggesting a novel mechanism of ErbB receptor regulation. Moreover, NRG2β/Q43L and related ligand-based antagonists establish a paradigm for the discovery of anti-ErbB therapeutics.

Ligand stimulation of ErbB4 and a constitutively-active ErbB4 mutant result in different biological responses in human pancreatic tumor cell lines

Pancreatic cancer is the fourth leading cause of cancer death in the United States. Indeed, it has been estimated that 37,000 Americans will die from this disease in 2010. Late diagnosis, chemoresistance, and radioresistance of these tumors are major reasons for poor patient outcome, spurring the search for pancreatic cancer early diagnostic and therapeutic targets. ErbB4 (HER4) is a member of the ErbB family of receptor tyrosine kinases (RTKs), a family that also includes the Epidermal Growth Factor Receptor (EGFR/ErbB1/HER1), Neu/ErbB2/HER2, and ErbB3/HER3. These RTKs play central roles in many human malignancies by regulating cell proliferation, survival, differentiation, invasiveness, motility, and apoptosis. In this report we demonstrate that human pancreatic tumor cell lines exhibit minimal ErbB4 expression; in contrast, these cell lines exhibit varied and in some cases abundant expression and basal tyrosine phosphorylation of EGFR, ErbB2, and ErbB3. Expression of a constitutively-dimerized and -active ErbB4 mutant inhibits clonogenic proliferation of CaPan-1, HPAC, MIA PaCa-2, and PANC-1 pancreatic tumor cell lines. In contrast, expression of wild-type ErbB4 in pancreatic tumor cell lines potentiates stimulation of anchorage-independent colony formation by the ErbB4 ligand Neuregulin 1β. These results illustrate the multiple roles that ErbB4 may be playing in pancreatic tumorigenesis and tumor progression.

ErbB signaling in cardiac development and disease

The ErbB family of receptor tyrosine kinases (RTKs) is a family of receptors that allow cells to interact with the extracellular environment and transduce signals to the nucleus that promote differentiation, migration and proliferation necessary for proper heart morphogenesis and function. This review focuses on the role of the ErbB family of receptor tyrosine kinases, and their importance in proper heart morphogenesis, as well as their role in maintenance and function of the adult heart. Studies from transgenic mouse models have shown the importance of ErbB receptors in heart development, and provide insight into potential future therapeutic targets to help reduce congenital heart defect (CHD) mortality rates and prevent disease in adults. Cancer therapeutics have also shed light to the ErbB receptors and signaling network, as undesired side effects have demonstrated their importance in adult cardiomyocytes and prevention of cardiomyopathies. This review will discuss ErbB receptor tyrosine kinases (RTK) in heart development and disease including valve formation and partitioning of a four-chambered heart as well as cardiotoxicity when ErbB signaling is attenuated in adults.

Toll-like receptor 4 differentially regulates epidermal growth factor-related growth factors in response to intestinal mucosal injury

Epiregulin (EPI) and amphiregulin (AR) are epidermal growth factor receptor (EGFR) ligands implicated in mucosal repair and tumorigenesis. We have shown that Toll-like receptor 4 (TLR4) induces intestinal epithelial cell (IEC) proliferation by activating EGFR through AR expression. We examined whether TLR4 differentially regulates expression of EGFR ligands in response to mucosal injury. The human IEC line SW480 was examined expression of EGFR ligands, EGFR phosphorylation, and proliferation in response to lipopolysaccharide (LPS). Small-interfering RNA (siRNA) was used to block TLR4. Neutralizing antibodies to EGFR ligands were used to examine inhibition of LPS-dependent EGFR activation. Acute colitis and recovery were examined in the mice given 2.5% dextran sodium sulfate (DSS). Colonic secretion of EPI and AR was analyzed by enzyme-linked immunosorbent assay. LPS selectively induces EPI and AR but not other EGFR ligands. LPS induced early EPI mRNA expression between 30 min and 24 h. The neutralizing antibodies to EPI and AR prevented activation of EGFR by LPS. LPS induces IEC proliferation (200%, P=0.01) in 24 h but blocking EPI and AR significantly decreased proliferation. In vivo, mucosal EPI and AR expression are significantly decreased in TLR4(-/-) mice (P=0.02) compared to wild-type mice during acute colitis. EPI and AR exhibit different kinetics in response to mucosal damage: EPI expression is upregulated acutely at day 7 of DSS, but falls during recovery at day 14. By contrast, a sustained upregulation of AR expression is seen during mucosal injury and repair. We show that TLR4 regulates EPI and AR expression and that both these EGFR ligands are necessary for optimal proliferation of IEC. The diverse kinetics of EPI and AR expression suggest that they function in distinct roles with respect to acute injury vs repair. Our results highlight the role of bacterial sensing for IEC homeostasis and may lead to targeted therapy for mucosal healing and prevention of tumorigenesis.

Amphiregulin-deficient mice develop spasmolytic polypeptide expressing metaplasia and intestinal metaplasia

BACKGROUND & AIMS

The loss of parietal cells from the fundic mucosa leads to the emergence of metaplastic lineages associated with an increased susceptibility to neoplastic transformation. Both intestinal metaplasia (IM) and spasmolytic polypeptide (TFF2/SP) expressing metaplasia (SPEM) have been identified in human stomach, but only SPEM is present in most mouse models of gastric metaplasia. We previously determined that loss of amphiregulin (AR) promotes SPEM induced by acute oxyntic atrophy. We have now examined whether SPEM in the AR-/- mouse predisposes the stomach to gastric neoplasia.

METHODS

Gross pathology of 18-month-old wild-type, AR-/-, and TGF-alpha-/- mice were examined. Ki-67, beta-catenin, Pdx-1, TFF3, and TFF2/SP expression was analyzed by immunohistochemistry. Metaplastic gastric mucosa was analyzed by dual immunostaining for TFF2/SP with MUC2 or TFF3.

RESULTS

By 18 months of age, more than 70% of AR-/- mice developed SPEM while 42% showed goblet cell IM labeled with MUC2, TFF3, and Pdx-1. A total of 28% had invasive gastric lesions in the fundus. No antral abnormalities were observed in AR-/- mice. Metaplastic cell lineages in AR-/- mice showed increases in cell proliferation and cytosolic beta-catenin expression. Dual staining for TFF2/SP with MUC2 or TFF3 showed glands containing both SPEM and IM with intervening cells expressing both TFF2/SP and MUC2 or TFF2/SP and TFF3.

CONCLUSIONS

AR-/- mice develop SPEM, which gives rise to goblet cell IM and invasive fundic dysplastic lesions. The AR-/- mouse represents the first mouse model for spontaneous development of fundic SPEM with progression to IM.

Markers involved in resistance to cytotoxics and targeted therapeutics in pancreatic cancer

Pancreatic cancer retains a poor prognosis among the gastrointestinal cancers and remains a challenge in oncology. In 1997, gemcitabine became the standard of care in metastatic setting. In the last decades, despite a number of clinical trials assessing novel cytotoxic agents and cell signaling inhibitors, overall survival has reached a plateau that remains difficult to improve. Development of mechanisms implicated in intrinsic and acquired resistance to chemotherapy are considered to play a key role that could explain the limited benefit of most treatment in pancreatic cancers. Key molecular factors implicated in this process include: deficiencies in drugs uptake, activations of DNA repair pathways, resistance to apoptosis, and tumor microenvironment. Moreover, for cell signaling inhibitors, mutations in kinase domains, activation of alternative pathways, mutations of genes downstream of the target, activation of autocrine/paracrine pathways and/or feed-back amplification of the target represent the most important mechanisms achieving resistance of pancreatic cancer cells.

ERBB3/HER3 and ERBB2/HER2 duet in mammary development and breast cancer

ERBB3/HER3 is one of the four members of the epidermal growth factor receptor (ERBB) family. It is activated by binding to ligands Neuregulin-1 and Neuregulin-2. Since ERBB3 lacks intrinsic kinase activity, signal transduction occurs through formation of heterodimers with EGFR, ERBB2, and ERBB4. ERBB3 is a signaling specialist since it has six binding sites for the p85 SH2 adapter subunit of phosphoinositide 3' kinases. These lipid kinases coordinate regulation of metabolism, cell size, proliferation, survival, and angiogenesis. Not surprisingly, ERBB3 signaling has been linked to cancer etiology and progression. In breast cancer, the partnership of ERBB2 and ERBB3 may be crucial for the aggressive properties of cancers with ERBB2 amplification, and may contribute to pre-existing and acquired resistance to therapy. This partnership creates opportunities for improving efficacy of ERBB-targeted pharmaceuticals, by interfering with coupling of ERBB2 to ERBB3 through dimerization inhibitors, and by use of therapeutic compounds that target AKT-dependent pathways activated through ERBB3. Additional therapeutic opportunities may be identified through better understanding of how ERBBs are regulated and deployed in normal mammary gland processes. Work using mouse models has identified the main processes regulated by each of the four ERBBs, which has practical implications in understanding breast cancer etiology, and eventual development of better prognostic, predictive, and therapeutic tools.

Clinical implications of the ErbB/epidermal growth factor (EGF) receptor family and its ligands in ovarian cancer

The ERBB or EGF receptor (EGFR) proto-oncogene family, which consists of four structurally-related transmembrane receptors (i.e., EGFR, ErbB2, ErbB3, and ErbB4), plays an etiological role in the molecular pathogenesis of cancer and is a key therapeutic target in many types of cancer, including ovarian cancer. These ErbB/EGF receptor tyrosine kinases play important physiologic roles in cell proliferation, survival, adhesion, motility, invasion, and angiogenesis. It is, therefore, not surprising that gene amplification, genetic mutation, and altered transcription/translation result in aberrant ErbB/EGF receptor expression and/or signal transduction, contributing to the development of malignant transformation. Clinically, the diagnostic, prognostic, and theragnostic significance of any single ErbB receptor and/or ErbB ligand is controversial, but generally, ErbB receptor overexpression has been correlated with poor prognosis and decreased therapeutic responsiveness in ovarian cancer patients. Thus, anticancer agents targeting ErbB/EGF receptors hold great promise for personalized cancer treatment. Yet, challenges remain in designing prospective clinical trials to assess the clinical utility of ErbB receptors and their ligands to diagnose cancer; to predict progression-free and overall survival, therapeutic responsiveness, and disease recurrence; and to monitor treatment responsiveness. Here, we review the tissue expression and serum biomarker studies that have evaluated the diagnostic, prognostic, and theragnostic utility of ErbB/EGF receptors, their circulating soluble isoforms (sEGFR/sErbBs), and their cognate ligands in ovarian cancer patients.

Cross talk between c-Met and epidermal growth factor receptor during retinal pigment epithelial wound healing

PURPOSE

The authors sought to determine how hepatocyte growth factor (HGF) receptor c-Met and epidermal growth factor receptor (EGFR) cross talk in response to injury in human ARPE-19 cells.

METHODS

A scratch wound was made on a cell monolayer of ARPE-19 cells using a sequence-comb or a pipet tip, and it was allowed to heal in the presence or absence of HGF and heparin-binding EGF-like growth factor (HB-EGF). The activation of EGFR was analyzed by immunoprecipitation with EGFR antibody, followed by Western blotting with phosphotyrosine-specific antibody. Phosphorylation of extracellular signal-regulated kinase (ERK) and AKT (a major substrate of phosphatidylinositol 3'-kinase (PI3K) was assessed by Western blotting. The release of c-Met ectodomain into the culture media was determined by Western blotting using an antibody against the extracellular region. Cell migration was assessed by Boyden chamber migration assay.

RESULTS

ARPE-19 cells underwent spontaneous wound healing in basal medium, and exogenously added HB-EGF and HGF significantly enhanced wound closure. Basal and growth factor-enhanced wound closures were attenuated but not slowed by hydroxyurea, a cell proliferation inhibitor. RPE cells expressed all four erbBs, and wounding induced EGFR transactivation and downstream ERK and PI3K phosphorylation in ARPE-19 cells. HGF also induced EGFR tyrosine phosphorylation. The EGFR kinase inhibitor AG1478 blocked wound- and HGF-stimulated EGFR transactivation and attenuated spontaneous and growth factor-induced wound closure. Wounding and EGFR ligands induced the release of c-Met into the culture media. Moreover, pretreatment of cells with HB-EGF impaired ARPE-19 migration toward HGF in a matrix metalloproteinase inhibitor-sensitive manner.

CONCLUSIONS

EGFR modulates HGF/c-Met activity by inducing c-Met ectodomain shedding, and HGF/c-Met transactivates EGFR, leading to an enhanced activation of downstream signaling pathways. Cross talk between EGFR and c-Met may play a key role in regulating RPE cell migration, proliferation, and wound healing.

Cross talk between c-Met and epidermal growth factor receptor during retinal pigment epithelial wound healing

PURPOSE

The authors sought to determine how hepatocyte growth factor (HGF) receptor c-Met and epidermal growth factor receptor (EGFR) cross talk in response to injury in human ARPE-19 cells.

METHODS

A scratch wound was made on a cell monolayer of ARPE-19 cells using a sequence-comb or a pipet tip, and it was allowed to heal in the presence or absence of HGF and heparin-binding EGF-like growth factor (HB-EGF). The activation of EGFR was analyzed by immunoprecipitation with EGFR antibody, followed by Western blotting with phosphotyrosine-specific antibody. Phosphorylation of extracellular signal-regulated kinase (ERK) and AKT (a major substrate of phosphatidylinositol 3'-kinase (PI3K) was assessed by Western blotting. The release of c-Met ectodomain into the culture media was determined by Western blotting using an antibody against the extracellular region. Cell migration was assessed by Boyden chamber migration assay.

RESULTS

ARPE-19 cells underwent spontaneous wound healing in basal medium, and exogenously added HB-EGF and HGF significantly enhanced wound closure. Basal and growth factor-enhanced wound closures were attenuated but not slowed by hydroxyurea, a cell proliferation inhibitor. RPE cells expressed all four erbBs, and wounding induced EGFR transactivation and downstream ERK and PI3K phosphorylation in ARPE-19 cells. HGF also induced EGFR tyrosine phosphorylation. The EGFR kinase inhibitor AG1478 blocked wound- and HGF-stimulated EGFR transactivation and attenuated spontaneous and growth factor-induced wound closure. Wounding and EGFR ligands induced the release of c-Met into the culture media. Moreover, pretreatment of cells with HB-EGF impaired ARPE-19 migration toward HGF in a matrix metalloproteinase inhibitor-sensitive manner.

CONCLUSIONS

EGFR modulates HGF/c-Met activity by inducing c-Met ectodomain shedding, and HGF/c-Met transactivates EGFR, leading to an enhanced activation of downstream signaling pathways. Cross talk between EGFR and c-Met may play a key role in regulating RPE cell migration, proliferation, and wound healing.

Heregulin-mediated ErbB2-ERK signaling activates hyaluronan synthases leading to CD44-dependent ovarian tumor cell growth and migration

Heregulin (HRG)-induced cell responses are mediated by the ErbB family of tyrosine kinase receptors. In this study we have investigated HRG activation of ErbB2, extracellular signal-regulated kinase (ERK) signaling, and their role in regulating hyaluronan synthase (HAS) activity in human ovarian tumor cells (SK-OV-3.ipl cells). Immunological and biochemical analyses indicate that ErbB2, ErbB3, and ErbB4 are all expressed in SK-OV-3.ipl cells and that ErbB4 (but not ErbB3) is physically linked to ErbB2 following HRG stimulation. Furthermore, our data indicate that the HRG-induced ErbB2.ErbB4 complexes stimulate ErbB2 tyrosine kinase, which induces both ERK phosphorylation and kinase activity. The activated ERK then increases the phosphorylation of HAS1, HAS2, and HAS3. Consequently, all three HAS isozymes are activated resulting in hyaluronan (HA) production. Because HRG-mediated HAS isozyme phosphorylation/activation can be effectively blocked by either AG825 (an ErbB2 inhibitor) or thiazolidinedione compound (an ERK blocker), we conclude that ErbB2-ERK signaling and HAS isozyme phosphorylation/HA production are functionally coupled in SK-OV-3.ipl cells. HRG also promotes HA- and CD44-dependent oncogenic events (e.g. CD44-Cdc42 association, p21-activated kinase 1 activation, and p21-activated kinase 1-filamin complex formation) and tumor cell-specific behaviors in an ErbB2-ERK signaling-dependent manner. Finally, we have found that the down-regulation of HAS isozyme expression (by transfecting cells with HAS1/HAS2/HAS3-specific small interfering RNAs) not only inhibits HRG-mediated HAS phosphorylation/activation and HA production but also impairs CD44-specific Cdc42-PAK1/filamin signaling, cytoskeleton activation and tumor cell behaviors. Taken together, these findings clearly indicate that HRG activation of ErbB2-ERK signaling modulates HAS phosphorylation/activation and HA production leading to CD44-mediated oncogenic events and ovarian cancer progression.

The ErbB4 receptor in fetal rat lung fibroblasts and epithelial type II cells

ErbB receptors are important regulators of fetal organ development, including the fetal lung. They exhibit diversity in signaling potential, acting through homo- and heterodimers to cause different biological responses. We hypothesized that ErbB receptors show cell-specific and stimuli-specific activation, heterodimerization, and cellular localization patterns in fetal lung. We investigated this using immunoblotting, co-immunoprecipitation, and confocal microscopy in primary isolated E19 fetal rat lung fibroblasts and epithelial type II cells, stimulated with epidermal growth factor, transforming growth factor alpha, neuregulin 1beta, or treated with conditioned medium (CM) from the respective other cell type. Fetal type II cells expressed significantly more ErbB1, ErbB2, and ErbB3 protein than fibroblasts. ErbB4 was consistently identified by co-immunoprecipitation of all other ErbB receptors in both cell types independent of the treatments. Downregulation of ErbB4 in fibroblasts initiated cell-cell communication that stimulated surfactant phospholipid synthesis in type II cells. Confocal microscopy in type II cells revealed nuclear localization of all receptors, most prominently for ErbB4. Neuregulin treatment resulted in relocation to the extra-nuclear cytoplasmic region, which was distinct from fibroblast CM treatment which led to nuclear localization of ErbB4 and ErbB2, inducing co-localization of both receptors. We speculate that ErbB4 plays a prominent role in fetal lung mesenchyme-epithelial communication.

Cellular responses to EGFR inhibitors and their relevance to cancer therapy

EGFR is a trans-membrane receptor tyrosine kinase that belongs to the HER family of receptors. The EGFR family plays an essential role in normal organ development by mediating morphogenesis and differentiation. Unlike normal cells that have tight regulatory mechanisms controlling EGFR pathways, tumor cells often have dysregulated EGFR signaling through receptor overexpression and/or mutation. This leads to proliferation under adverse conditions, invasion of surrounding tissues, and increased angiogenesis as well as resistance to radiation and chemotherapy. Therefore, EGFR is a legitimate therapeutic target. Numerous EGFR inhibitors are under development, but to date only four of them are FDA-approved, including two that inhibit the receptor's intracellular tyrosine kinase activity (gefitinib and erlotinib) and two that block extracellular ligand binding (cetuximab, and most recently panitumumab). In this review, we focus on how these different inhibitors affect EGFR signaling and the mechanisms by which they potentiate the effects of chemotherapy and radiation therapy. Numerous clinical trials have been conducted with these agents either as monotherapy, in combination with chemotherapy, or concurrently with radiation. Unfortunately, many of the clinical trials reported so far have shown at best limited gains; therefore, understanding the actions of these agents is essential to improving their efficacy in the treatment of cancers.

Lysophosphatidic acid promoting corneal epithelial wound healing by transactivation of epidermal growth factor receptor

PURPOSE

To identify the underlying mechanisms by which lipid mediator lysophosphatidic acid (LPA) acts as a growth factor in stimulating extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3K) during corneal epithelial wound healing.

METHODS

Epithelial debridement wounds in cultured porcine corneas and scratch wounds in an epithelial monolayer of SV40-immortalized human corneal epithelial (THCE) cells were allowed to heal in the presence or absence of an epidermal growth factor receptor (EGFR) inhibitor (tyrphostin AG1478), a matrix metalloproteinase inhibitor (GM6001), or a heparin-binding EGF-like growth factor (HB-EGF) antagonist (CRM197) with or without LPA. EGFR activation was analyzed by immunoprecipitation using EGFR antibodies and Western blotting with phosphotyrosine antibodies. Phosphorylation of ERK and AKT (a major substrate of PI3K) was analyzed by Western blotting with antibodies specific to the phosphorylated proteins. Wound- and LPA-induced shedding of HB-EGF was assessed by measuring the release of alkaline phosphatase (AP) in a stable THCE cell line that expressed HB-EGF with AP inserted in the heparin-binding site.

RESULTS

In organ and cell culture models, LPA enhanced corneal epithelial wound healing. LPA-stimulated and spontaneous wound closure was attenuated by AG1478, GM6001, or CRM197. Consistent with the effects on epithelial migration, these inhibitors, as well as the Src kinase inhibitor (PP2), retarded LPA-induced activation of EGFR and its downstream effectors ERK and AKT in THCE cells. Unlike exogenously added HB-EGF, LPA stimulated moderate EGFR phosphorylation; the level of phosphorylated EGFR was similar to that induced by wounding. However, LPA appeared to prolong wound-induced EGFR signaling. The release of HB-EGF assessed by AP activity increased significantly in response to wounding, LPA, or both, and the release of HB-EGF-AP induced by LPA was inhibited by PP2 and GM6001.

CONCLUSIONS

LPA accelerates corneal epithelial wound healing through its ability to induce autocrine HB-EGF signaling. Transactivation of EGFR by LPA represents a convergent signaling pathway accessible to stimuli such as growth factors and ligands of G-protein-coupled receptors in response to pathophysiological challenge in human corneal epithelial cells.

Luteinizing hormone-dependent activation of the epidermal growth factor network is essential for ovulation

In the preovulatory ovarian follicle, mammalian oocytes are maintained in prophase meiotic arrest until the luteinizing hormone (LH) surge induces reentry into the first meiotic division. Dramatic changes in the somatic cells surrounding the oocytes and in the follicular wall are also induced by LH and are necessary for ovulation. Here, we provide genetic evidence that LH-dependent transactivation of the epidermal growth factor receptor (EGFR) is indispensable for oocyte reentry into the meiotic cell cycle, for the synthesis of the extracellular matrix surrounding the oocyte that causes cumulus expansion, and for follicle rupture in vivo. Mice deficient in either amphiregulin or epiregulin, two EGFR ligands, display delayed or reduced oocyte maturation and cumulus expansion. In compound-mutant mice in which loss of one EGFR ligand is associated with decreased signaling from a hypomorphic allele of the EGFR, LH no longer signals oocyte meiotic resumption. Moreover, induction of genes involved in cumulus expansion and follicle rupture is compromised in these mice, resulting in impaired ovulation. Thus, these studies demonstrate that LH induction of epidermal growth factor-like growth factors and EGFR transactivation are essential for the regulation of a critical physiological process such as ovulation and provide new strategies for manipulation of fertility.

Phosphorylation of ErbB4 on tyrosine 1056 is critical for ErbB4 coupling to inhibition of colony formation by human mammary cell lines

In many studies, ErbB4 expression in breast tumor samples correlates with a favorable patient prognosis. Similarly, ErbB4 signaling is coupled to cellular differentiation and growth arrest in a variety of model systems. However, in some studies, ErbB4 expression in breast tumor samples correlates with poor outcome. Likewise, studies using some human mammary tumor cell lines suggest that ErbB4 is coupled to malignant phenotypes. Thus, the roles that ErbB4 plays in human breast cancer are still poorly defined. Here we demonstrate that a constitutively active ErbB4 mutant (ErbB4-Q646C) inhibits colony formation on plastic by two human mammary tumor cell lines (SKBR3 and MCF7) and by the MCF10A immortalized human mammary cell line, but does not inhibit colony formation by the MDA-MB-453 and T47D human mammary tumor cell lines. ErbB4 kinase activity is necessary for ErbB4 function and phosphorylation of ErbB4 Tyr1056 is necessary and appears to be sufficient for ErbB4 function. The inhibition of colony formation by MCF10A cells is accompanied by growth arrest but not cell death. These data suggest that ErbB4 behaves as a mammary tumor suppressor and that loss of ErbB4 coupling to growth arrest may be an important event in mammary tumorigenesis.

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.

Extracellular signal-regulated kinase activation by parathyroid hormone in distal tubule cells

The PTH receptor (PTH1R) activates multiple signaling pathways, including extracellular signal-regulated kinases 1 and 2 (ERK1/2). The role of epidermal growth factor receptor (EGFR) transactivation in ERK1/2 activation by PTH in distal kidney cells, a primary site of PTH action, was characterized. ERK1/2 phosphorylation was stimulated by PTH and blocked by the EGFR inhibitor, AG1478. Upon PTH stimulation, metalloprotease cleavage of membrane-bound heparin-binding fragment (HB-EGF) induced EGFR transactivation of ERK. Conditioned media from PTH-treated distal kidney cells activated ERK in HEK-293 cells. AG1478 added to HEK-293 cells ablated transactivation by conditioned media. HB-EGF directly activated ERK1/2 in HEK-293 cells. Pretreatment of distal kidney cells with the metalloprotease inhibitor GM-6001 abolished transactivation of ERK1/2 by PTH. The role of the PTH1R COOH terminus in PTX-sensitive ERK1/2 activation was characterized in HEK-293 cells transfected with wild-type PTH1R, with a PTH1R mutated at its COOH terminus, or with PTH1R truncated at position 480. PTH stimulated ERK by wild-type, mutated and truncated PTH1Rs 21-, 27- and 57-fold, respectively. Thus, the PTH1R COOH terminus exerts an inhibitory effect on ERK activation. EBP50, a scaffolding protein that binds to the PDZ recognition domain of the PTH1R, impaired PTH but not isoproterenol or calcitonin-induced ERK activation. Pertussis toxin inhibited PTH-stimulated ERK1/2 by mutated and truncated PTH1Rs and abolished ERK1/2 activation by wild-type PTH1R. We conclude that ERK phosphorylation in distal kidney cells by PTH requires PTH1R activation of G(i), which leads to stimulation of metalloprotease-mediated cleavage of HB-EGF and transactivation of the EGFR and is regulated by EBP50.

SRC-family tyrosine kinases in wound- and ligand-induced epidermal growth factor receptor activation in human corneal epithelial cells

PURPOSE

The authors have previously demonstrated that wounding of human corneal epithelial cells (HCECs) transactivates epidermal growth factor (EGF) receptor (EGFR) and its downstream signaling pathways and that this EGFR signaling is required for epithelial wound healing. In this study, the authors sought to identify the underlying mechanisms for EGFR transactivation in response to wounding in HCECs.

METHODS

SV40-immortalized HCEC (THCE) monolayer was wounded and allowed to heal in the presence or absence of a selective inhibitor of the Src family kinases PP2 and EGFR ligand heparin-binding EGF-like growth factor (HB-EGF). Wound closure was monitored by photographing of the injury immediately or 24 hours after wounding. Activation of EGFR in THCE cells and in primary HCECs was analyzed by immunoprecipitation of EGFR, followed by Western blotting with phosphotyrosine antibody. Phosphorylation of extracellular signal-regulated kinase (ERK), AKT (a major substrate of phosphatidylinositol 3'-kinase [PI3K]), Src at tyrosine Y416, and EGFR at Y845 was analyzed by Western blotting with antibodies specific to phosphorylated proteins. Effects of PP2 on THCE cell migration were determined by Boyden chamber migration assay.

RESULTS

Among several inhibitors tested, PP2 blocked wound-induced EGFR phosphorylation in THCE cells. PP2 at 12.5 microM effectively inhibited EGFR transactivation in response to wounding and to the phosphorylation of ERK and AKT in THCE cells and primary HCECs. Consistent with the inhibition of EGFR transactivation, PP2 also attenuated epithelial migration and wound closure with or without exogenously added HB-EGF. PP2 at a concentration as high as 50 microM exhibited no effects on HB-EGF induced ERK phosphorylation. On the other hand, AKT phosphorylation was much more sensitive to PP2 than ERK or EGFR phosphorylation because 3.13 microM PP2 effectively inhibited wound- or HB-EGF-induced AKT phosphorylation.

CONCLUSIONS

These results suggest that Src kinase mediates wound-induced EGFR transactivation and participates in a pathway to activate the PI3K-AKT pathway downstream of EGFR in HCECs.

ErbB4 increases the proliferation potential of human lung cancer cells and its blockage can be used as a target for anti-cancer therapy

Clinical and experimental data suggest that ErbB-4, a member of the epidermal growth factor receptor family, may have a role in cancer progression and response to treatment. We found recently, using a retrospective clinical analysis, that expression of ErbB-4 receptor is correlated with metastatic potential and patient survival in non-small-cell lung cancer (NSCLC). The purpose of this work was to correlate the expression of the ErbB-4 and lung cancer cells growth in vitro and in vivo and to determine the therapeutic potential of a monoclonal antibody to ErbB-4 against lung cancer. For this aim, we ectopically expressed ErbB-4 in a human NSCLC cell line that did not express the ErbB-4 protein. Overexpression of ErbB-4 produced a constitutively activated ErbB-4 receptor. The transfected ErbB-4 positive clones showed an increased cell proliferation in vitro and in vivo in comparison with parental ErbB-4 negative cells and with the cells transfected by neomycin-resistant gene. A monoclonal antibody to ErbB-4 showed both an inhibitory effect on growth rate and an increasing apoptotic rate in the cells expressing ErbB-4. The results of the current study provide evidence that ErbB-4 plays a significant role in human lung cancer and may serve as a molecular target for anticancer therapy.

The epidermal growth factor receptor (EGFR)-S442F mutant displays increased affinity for neuregulin-2beta and agonist-independent coupling with downstream signalling events

The EGFR (epidermal growth factor receptor; ErbB1) is frequently the subject of genetic changes in human tumours which contribute to the malignant phenotype by altering EGFR signalling. Examples of such genetic changes include overexpression, extracellular domain deletions and point mutations, and small deletions in the tyrosine kinase domain. We hypothesized that a point mutation in one of the EGFR ligand-binding domains would increase the affinity of EGFR for NRG2beta (neuregulin-2beta), which is not a potent stimulus of signalling by EGFR-Wt (wild-type EGFR). This mutation would permit NRG2beta stimulation of EGFR signalling in settings in which NRG2beta does not normally do so. To test this hypothesis, we have generated and evaluated various EGFR alleles containing mutations at Val441 and Ser442. NRG2beta is a much more potent stimulus of the EGFR-S442F mutant than of EGFR-Wt. Furthermore, the affinity of NRG2beta for the EGFR-S442F mutant is greater than the affinity of NRG2beta for EGFR-Wt. Finally, the EGFR-S442F mutant constitutively suppresses apoptosis via phosphoinositide 3-kinase and Akt signalling but is not highly tyrosine phosphorylated in the absence of ligand. These results suggest that mutations in the EGFR ligand-binding domain in tumours may permit potent stimulation of EGFR signalling by ligands that are not normally potent EGFR agonists, thereby providing for a novel mechanism by which EGFR signalling may be deregulated. These results also suggest that novel EGFR mutations and signalling activities may be responsible for deregulated EGFR signalling in tumour cells.

Phe45 of NRG2beta is critical for the affinity of NRG2beta for ErbB4 and for potent stimulation of ErbB4 signaling by NRG2beta*

The Neuregulins (NRGs) are members of the epidermal growth factor (EGF) family of growth factors. EGF family members regulate the signaling of ErbB family receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR/ErbB1), ErbB2/HER2/Neu, ErbB3/HER3 and ErbB4/HER4. We have previously demonstrated that the EGF family hormone NRG2beta is a potent ErbB4 agonist, whereas NRG2alpha is a weak ErbB4 agonist. We have also previously demonstrated that Phe45 of NRG2beta regulates the potency of NRG2beta. Here, we address the hypotheses that Phe45 regulates the potency of NRG2beta by regulating the affinity of NRG2beta for ErbB4. We demonstrate that Phe45 of NRG2beta indeed regulates the affinity of NRG2beta for ErbB4. Furthermore, a hydrophobic or uncharged amino acid side chain at residue 45 contributes to NRG2beta binding to ErbB4. These data indicate that Phe45 of NRG2beta may regulate the affinity of NRG2beta for ErbB4 by interacting with hydrophobic amino acids in ErbB4.

The era of ErbB-receptor-targeted therapies: advances toward personalized medicine

Central themes in medical practice are the diagnosis, prognosis and treatment of disease. Advances have been made in a number of malignanices including breast cancer, where new therapeutic strategies have significantly improved response rates, the disease-free interval and overall survival. However, complete responses to chemotherapy are achieved in only 10–20% of patients. Recent advances in the understanding of the cellular and molecular biology of cancer have led to the identification of oncogenes and tumor suppressor genes that influence the rate of tumor cell proliferation and cancer progression. These oncogenes represent important therapeutic targets and are currently being incorporated into the design of novel therapeutic approaches. This review emphasizes the role of the ErbB oncogenic receptor family, its effect on tumor biologic behavior and its role as a target for various therapeutic regimens.

Opposing actions of TGFβ and MAP kinase signaling in undifferentiated hen granulosa cells

The present studies were conducted to establish interactions between transforming growth factor (TGF)-beta and the epidermal growth factor (EGF) family members, TGFalpha and betacellulin (BTC), relative to proliferation and differentiation of granulosa cells in hen ovarian follicles. Results presented demonstrate expression of TGFbeta isoforms, plus TGFalpha, BTC, and ErbB receptors in prehierarchal follicles, thus establishing the potential for autocrine/paracrine signaling and cross-talk within granulosa cells at the onset of differentiation. Treatment with TGFalpha or BTC increases levels of TGFbeta1 mRNA in undifferentiated granulosa cells, while the selective inhibitor of mitogen activated protein kinase signaling, U0126, reverses these effects. Moreover, TGFbeta1 attenuates c-myc mRNA expression and granulosa cell proliferation, while TGFalpha blocks both these inhibitory effects. Collectively, these data provide evidence that EGF family ligands regulate both the expression and biological actions of TGFbeta1 in hen granulosa cells, and indicate that the timely interaction of these opposing factors is an important modulator of both granulosa cell proliferation and differentiation.

Phenotypic variation resulting from a deficiency of epidermal growth factor receptor in mice is caused by extensive genetic heterogeneity that can be genetically and molecularly partitioned

The timing of lethality caused by homozygosity for a null allele of the epidermal growth factor receptor (Egfrtm1Mag) in mice is strongly dependent on genetic background. Initial attempts to genetically map background modifiers using Swiss-derived, outbred CD-1 mice were unsuccessful. To investigate the genetic architecture contributing to survival of Egfrtm1Mag homozygous embryos, the genetic variability segregating within the outbred population was partitioned by surveying viability of Egfrtm1Mag mutants using intercrosses between 129S6/SvEvTAC-Egfrtm1Mag and nine Swiss-derived, inbred strains: ALR/LtJ, ALS/LtJ, APN, APS, ICR/HaRos, NOD/LtJ, NON/LtJ, SJL/J, and SWR/J. The observations showed that these strains support varying levels of survival of Egfrtm1Mag homozygous embryos, suggesting that genetic heterogeneity within the CD-1 stock contributed to the original lack of Egfrtm1Mag modifier detection. Similar to the Swiss-derived intercrosses, nine congenic strains, derived from 129S6/SvEvTAC, AKR/J, APN, BALB/cJ, BTBR-T+ tf/tf, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ inbred backgrounds, also supported varying levels of survival of Egfrtm1Mag mutants. By intercrossing the congenic lines to create hybrid F1 embryos, different genetic backgrounds were found to have complementary modifiers. Analysis of the congenic lines argues against heterosis of outbred backgrounds contributing to Egfrtm1Mag phenotypic variability. A detailed analysis of the crosses suggests that modifiers function at three distinct stages of development. One class of modifiers supports survival of Egfrtm1Mag homozygous embryos to mid-gestation, another class supports development through the mid-gestation transition from yolk-sac to placental-derived nutrient sources, and a third class supports survival through later stages of gestation. Data from microarray analysis using RNA from wild-type and Egfrtm1Mag mutant placentas support the existence of extensive genetic heterogeneity and suggest that it can be molecularly partitioned. This method should be generally useful to partition heterogeneity contributing to other complex traits.

Epidermal Growth Factor Induces WISP-2/CCN5 Expression in Estrogen Receptor-α-Positive Breast Tumor Cells through Multiple Molecular Cross-talks

Epidermal growth factor (EGF) is a mitogen for estrogen receptor (ER)–positive breast tumor cells, and it has been proven that EGF occasionally mimicked estrogen action and cross-talks with ER-α to exert its activity. Therefore, the present study was undertaken to explore whether EGF is able to modulate the expression of Wnt-1-induced signaling protein-2/connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed 5 (WISP-2/CCN5), an estrogen-responsive gene, in normal and transformed cell lines of the human breast and, if so, whether this induction is critical for EGF mitogenesis and what downstream signaling pathways are associated with this event. Here, we show that EGF-induced WISP-2 expression in ER- and EGF receptor–positive noninvasive MCF-7 breast tumor cells was dose and time dependent and that expression was modulated at transcription level. A synergism was seen in combination with estrogen. Moreover, small interfering RNA–mediated inhibition of WISP-2/CCN5 activity in MCF-7 cells resulted in abrogation of proliferation by EGF. The multiple molecular cross-talks, including the interactions between phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase signaling pathways and two diverse receptors (i.e., ER-α and EGFR), were essential in the event of EGF-induced WISP-2/CCN5 up-regulation in MCF-7 cells. Moreover, EGF action on WISP-2/CCN5 is restricted to ER- and EGFR-positive noninvasive breast tumor cells, and this effect of EGF cannot be instigated in ER-α-negative and EGFR-positive normal or invasive breast tumor cells by introducing ER-α. Finally, regulation of phosphorylation of ER-α and EGFR may play critical roles in EGF-induced transcriptional activation of WISP-2 gene in breast tumor cells.

Role of ErbB2 in Corneal Epithelial Wound Healing

PURPOSE

Human corneal epithelial cells (HCECs) were functionally depleted of erbB2 to elucidate its role in epidermal growth factor (EGF) receptor (EGFR) activation-dependent cell migration.

METHODS

The retrovirus pBabe-5R, which encodes an erbB2 single-chain antibody with an endoplasmic reticulum (ER)-targeting sequence, and control pBabe-puro were used to infect THCE cells (an SV40-immortalized HCEC line). Several cell lines expressing 5R were selected along with a pBabe-puro control line. The depletion of erbB2 was verified by cell surface biotinylation of proteins, followed by streptavidin precipitation and subsequent detection of erbB2 by immunoblot analysis. Activation of erbBs was analyzed by immunoprecipitation using the phosphotyrosine antibody pY20, followed by Western blot analysis with erbB1 or erbB2 antibodies. Phosphorylation of extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3K) was analyzed by Western blot with antibodies specific to phosphorylated proteins. Effects of erbB2 depletion on heparin-binding EGF-like growth factor (HB-EGF)-induced cell migration were determined by Boyden chamber migration assay and by scratch wound assay.

RESULTS

Wounding induced erbB2 tyrosine phosphorylation. Expression of 5R encoding an erbB2 single-chain antibody with an endoplasmic reticulum-targeting sequence depleted the cell surface expression of erbB2 in HCECs. Wounding resulted in a rapid increase in the phosphorylation of erbB1 in both 5R-expressing and control cells, whereas wound-induced erbB2 phosphorylation in 5R-expressing cells was not detectable. Depletion of functional erbB2 attenuated the healing of scratch wounds in the presence of HB-EGF and impaired both chemotactic migration stimulated by HB-EGF and haptotactic migration toward a fibronectin-collagen I (3:1; FNC) coating mix. Expression of 5R affected both the intensity and the duration of wound-induced, EGFR-elicited ERK and PI3K activation. Inhibition of ERK and PI3K pathways in cultured porcine corneas impaired ex vivo epithelial wound healing.

CONCLUSIONS

ErbB2 serves as a critical component that couples erbB receptor tyrosine kinase to the migration machinery of corneal epithelial cells.

Epiregulin is not essential for development of intestinal tumors but is required for protection from intestinal damage

Epiregulin, an epidermal growth factor family member, acts as a local signal mediator and shows dual biological activity, stimulating the proliferation of fibroblasts, hepatocytes, smooth muscle cells, and keratinocytes while inhibiting the growth of several tumor-derived epithelial cell lines. The epiregulin gene (Ereg) is located on mouse chromosome 5 adjacent to three other epidermal growth factor family members, epigen, amphiregulin, and betacellulin. Gene targeting was used to insert a lacZ reporter into the mouse Ereg locus and to ablate its function. Although epiregulin is broadly expressed and regulated both spatially and temporally, Ereg null mice show no overt developmental defects, reproductive abnormalities, or altered liver regeneration. Additionally, in contrast to previous hypotheses, Ereg deficiency does not alter intestinal cancer susceptibility, as assayed in the ApcMin model, despite showing robust expression in developing tumors. However, Ereg null mice are highly susceptible to cancer-predisposing intestinal damage caused by oral administration of dextran sulfate sodium.

Epigen, the last ligand of ErbB receptors, reveals intricate relationships between affinity and mitogenicity

Four ErbB receptors and multiple growth factors sharing an epidermal growth factor (EGF) motif underlie transmembrane signaling by the ErbB family in development and cancer. Unlike other ErbB proteins, ErbB-2 binds no known EGF-like ligand. To address the existence of a direct ligand for ErbB-2, we applied algorithms based on genomic and cDNA structures to search sequence data bases. These searches reidentified all known EGF-like growth factors including Epigen (EPG), the least characterized ligand, but failed to identify novel factors. The precursor of EPG is a widely expressed transmembrane glycoprotein that undergoes cleavage at two sites to release a soluble EGF-like domain. A recombinant EPG cannot stimulate cells singly expressing ErbB-2, but it acts as a mitogen for cells expressing ErbB-1 and co-expressing ErbB-2 in combination with the other ErbBs. Interestingly, soluble EPG is more mitogenic than EGF, although its binding affinity is 100-fold lower. Our results attribute the anomalous mitogenic power of EPG to evasion of receptor-mediated depletion of ligand molecules, as well as to inefficient receptor ubiquitylation and down-regulation. In conclusion, EPG might represent the last EGF-like growth factor and define a category of low affinity ligands, whose bioactivity differs from the more extensively studied high affinity ligands.

Role of EGFR transactivation in preventing apoptosis in Pseudomonas aeruginosa-infected human corneal epithelial cells

PURPOSE

To determine the role of epidermal growth factor (EGF) receptor (EGFR)-mediated signaling pathways in preventing infection-induced apoptosis in human corneal epithelial cells (HCECs).

METHODS

Epithelial monolayers of a telomerase-immortalized HCEC line, HUCL, and primary culture of HCECs were infected with Pseudomonas aeruginosa in the presence of the EGFR inhibitor tyrphostin AG1478, the extracellular signal-regulated kinase (ERK) inhibitor U0126, the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, the heparin-binding EGF-like growth factor (HB-EGF) antagonist CRM197, the HB-EGF neutralizing antibody, or the matrix metalloproteinase inhibitor GM6001. The activation of EGFR was analyzed by immunoprecipitation using EGFR antibodies, followed by Western blot analysis with phosphotyrosine antibody. Phosphorylation of ERK and Akt, a major substrate of PI3K, and generation of cleaved caspase-3 and poly (ADP-ribose) polymerase (PARP) were determined by Western blot analysis. Apoptotic cells were characterized by positive staining of active caspase-3, loss of mitochondrial cytochrome c, and condensation of chromosomes. Apoptosis was also confirmed by measuring caspase-3 activity and assessing the generation of cleaved caspase-3 and PARP.

RESULTS

P. aeruginosa infection of HUCL cells resulted in EGFR activation and EGFR-dependent ERK1/2 and PI3K phosphorylation. Inhibition of EGFR, ERK1/2, and PI3K activities with kinase-specific inhibitors (AG1478, U0126, and LY294002, respectively) resulted in an increase in the number of apoptotic cells, in elevated cellular caspase-3 activity, and/or in increased cleaved PARP in P. aeruginosa-infected HUCL cells or primary culture of HCECs. Blocking HB-EGF ectodomain shedding by inhibition of matrix metalloproteinase-mediated proteolysis, downregulation of HB-EGF, or neutralization of its activity retarded infection-induced EGFR transactivation and, as a consequence, increased infection-induced HUCL apoptosis.

CONCLUSIONS

Bacterial infection of HCECs induces EGFR transactivation through HB-EGF ectodomain shedding. EGFR and its downstream ERK and PI3K signaling pathways play a role in preventing epithelial apoptosis in the early stage of bacterial infection.

Behavioral characteristics of a nervous system-specific erbB4 knock-out mouse

ErbB4 is an important brain receptor for the neuregulin1 growth factor. A conditional knock-out mouse was developed lacking both alleles of the erbB4 gene in neurons/glia, and one allele in other cells. The conditional mutant mice were compared to heterozygous null (one null allele and one wildtype allele in all tissues) and wildtype control (no gene deletion) littermates in a battery of behavioral tests. Conditional mutants displayed a lower level of spontaneous motor activity and reduced grip strength compared to wildtype control mice. Group mean scores of heterozygous nulls were intermediate on these measures. However, heterozygous nulls were delayed in motor development and male heterozygous nulls demonstrated altered cue use in a Morris maze learning and memory task relative to both wildtype control and conditional mutant mice. These findings were interpreted based on more detailed analysis of the behavioral data and considerations of the complex nature and multiple roles of the neuregulin/erbB4 system in the nervous system.