Expression of heregulin alpha, erbB2, and erbB3 and their influences on proliferation of gastric epithelial cells

Integrative Analysis of Neuregulin Family Members-Related Tumor Microenvironment for Predicting the Prognosis in Gliomas

Gliomas, including brain lower grade glioma (LGG) and glioblastoma multiforme (GBM), are the most common primary brain tumors in the central nervous system. Neuregulin (NRG) family proteins belong to the epidermal growth factor (EGF) family of extracellular ligands and they play an essential role in both the central and peripheral nervous systems. However, roles of NRGs in gliomas, especially their effects on prognosis, still remain to be elucidated. In this study, we obtained raw counts of RNA-sequencing data and corresponding clinical information from 510 LGG and 153 GBM samples from The Cancer Genome Atlas (TCGA) database. We analyzed the association of NRG1-4 expression levels with tumor immune microenvironment in LGG and GBM. GSVA (Gene Set Variation Analysis) was performed to determine the prognostic difference of NRGs gene set between LGG and GBM. ROC (receiver operating characteristic) curve and the nomogram model were constructed to estimate the prognostic value of NRGs in LGG and GBM. The results demonstrated that NRG1-4 were differentially expressed in LGG and GBM in comparison to normal tissue. Immune score analysis revealed that NRG1-4 were significantly related to the tumor immune microenvironment and remarkably correlated with immune cell infiltration. The investigation of roles of m⁶A (N6-methyladenosine, m⁶A)-related genes in gliomas revealed that NRGs were prominently involved in m⁶A RNA modification. GSVA score showed that NRG family members are more associated with prognosis in LGG compared with GBM. Prognostic analysis showed that NRG3 and NRG1 can serve as potential independent biomarkers in LGG and GBM, respectively. Moreover, GDSC drug sensitivity analysis revealed that NRG1 was more correlated with drug response compared with other NRG subtypes. Based on these public databases, we preliminarily identified the relationship between NRG family members and tumor immune microenvironment, and the prognostic value of NRGs in gliomas. In conclusion, our study provides comprehensive roles of NRG family members in gliomas, supporting modulation of NRG signaling in the management of glioma.

SATB1-Mediated Upregulation of the Oncogenic Receptor Tyrosine Kinase HER3 Antagonizes MET Inhibition in Gastric Cancer Cells

MET-amplified gastric cancer cells are extremely sensitive to MET inhibition in vitro, whereas clinical efficacy of MET inhibitors is disappointing. The compensatory activation of other oncogenic growth factor receptors may serve as an underlying mechanism of resistance. In this study, we analyzed the role of HER receptors, in particular HER3 and its ligand heregulin, in this respect. This also included the chromatin-organizer protein SATB1, as an established regulator of HER expression in other tumor entities. In a panel of MET-amplified gastric carcinoma cell lines, cell growth under anchorage-dependent and independent conditions was studied upon inhibitor treatment or siRNA-mediated knockdown. Expression analyses were performed using RT-qPCR, FACS, and immunoblots. Signal transduction was monitored via antibody arrays and immunoblots. As expected, MET inhibition led to a growth arrest and inhibition of MAPK signaling. Strikingly, however, this was accompanied by a rapid and profound upregulation of the oncogenic receptor HER3. This finding was determined as functionally relevant, since HER3 activation by HRG led to partial MET inhibitor resistance, and MAPK/Akt signaling was even found enhanced upon HRG+MET inhibitor treatment compared to HRG alone. SATB1 was identified as mediator of HER3 upregulation. Concomitantly, SATB1 knockdown prevented upregulation of HER3, thus abrogating the HRG-promoted rescue from MET inhibition. Taken together, our results introduce the combined HER3/MET inhibition as strategy to overcome resistance towards MET inhibitors.

Exploitation of receptor tyrosine kinases by viral-encoded growth factors

Receptor tyrosine kinases (RTKs) are essential components of cell communication pathways utilized from the embryonic to adult stages of life. These transmembrane receptors bind polypeptide ligands, such as growth factors, inducing signalling cascades that control cellular processes such as proliferation, survival, differentiation, motility and inflammation. Many viruses have acquired homologs of growth factors encoded by the hosts that they infect. Production of growth factors during infection allows viruses to exploit RTKs for entry and replication in cells, as well as for host and environmental dissemination. This review describes the genetic diversity amongst virus-derived growth factors and the mechanisms by which RTK exploitation enhances virus survival, then highlights how viral ligands can be used to further understanding of RTK signalling and function during embryogenesis, homeostasis and disease scenarios.

mTOR Signaling Confers Resistance to Targeted Cancer Drugs

Cancer is a complex disease and a leading cause of death worldwide. Extensive research over decades has led to the development of therapies that target cancer-specific signaling pathways. However, the clinical benefits of such drugs are at best transient due to tumors displaying intrinsic or adaptive resistance. The underlying compensatory pathways that allow cancer cells to circumvent a drug blockade are poorly understood. We review here recent studies suggesting that mammalian TOR (mTOR) signaling is a major compensatory pathway conferring resistance to many cancer drugs. mTOR-mediated resistance can be cell-autonomous or non-cell-autonomous. These findings suggest that mTOR signaling should be monitored routinely in tumors and that an mTOR inhibitor should be considered as a co-therapy.

Overexpression of NRG1 promotes progression of gastric cancer by regulating the self-renewal of cancer stem cells

BACKGROUND

Gastric cancer stem cells (GCSCs) have been successfully isolated from patients. However, the molecular mechanisms underlying the self-renewal of GCSCs and their relationship with the microenvironment are poorly characterized.

METHODS

GCSCs and cancer-associated fibroblasts (CAFs) were cultured directly from gastric cancer patients. The self-renewal of GCSCs was assayed by sphere formation assay and in vivo tumorigenicity. Expression of neuregulin1 (NRG1) was examined by immunohistochemistry, real-time PCR and western blotting.

RESULTS

CAFs increased the self-renewal of GCSCs by secreting NRG1. NRG1 activated NF-κB signaling and this activation regulated GCSC self-renewal. Moreover, NF-κB-active GCSCs were tumorigenic, however NF-κB-inactive GCSCs were not. The overexpression of NRG1 in stromal cells and cancer cells was observed in the tumor tissues of gastric cancer patients and was associated with clinical stage lymph node metastasis and survival in gastric cancer patients. In addition, we also found that NRG1 can regulate the proliferation and invasion of gastric cancer cells.

CONCLUSIONS

These results indicate that NRG1, which can be secreted by CAFs or cancer cells, promotes progression of gastric cancer by regulating the self-renewal of GCSCs and its overexpression is associated with a prognosis of gastric cancer.

Activation of EGFR and ERBB2 by Helicobacter pylori results in survival of gastric epithelial cells with DNA damage

BACKGROUND & AIMS

The gastric cancer-causing pathogen Helicobacter pylori up-regulates spermine oxidase (SMOX) in gastric epithelial cells, causing oxidative stress-induced apoptosis and DNA damage. A subpopulation of SMOX(high) cells are resistant to apoptosis, despite their high levels of DNA damage. Because epidermal growth factor receptor (EGFR) activation can regulate apoptosis, we determined its role in SMOX-mediated effects.

METHODS

SMOX, apoptosis, and DNA damage were measured in gastric epithelial cells from H. pylori-infected Egfr(wa5) mice (which have attenuated EGFR activity), Egfr wild-type mice, or in infected cells incubated with EGFR inhibitors or deficient in EGFR. A phosphoproteomic analysis was performed. Two independent tissue microarrays containing each stage of disease, from gastritis to carcinoma, and gastric biopsy specimens from Colombian and Honduran cohorts were analyzed by immunohistochemistry.

RESULTS

SMOX expression and DNA damage were decreased, and apoptosis increased in H. pylori-infected Egfr(wa5) mice. H. pylori-infected cells with deletion or inhibition of EGFR had reduced levels of SMOX, DNA damage, and DNA damage(high) apoptosis(low) cells. Phosphoproteomic analysis showed increased EGFR and erythroblastic leukemia-associated viral oncogene B (ERBB)2 signaling. Immunoblot analysis showed the presence of a phosphorylated (p)EGFR-ERBB2 heterodimer and pERBB2; knockdown of ErbB2 facilitated apoptosis of DNA damage(high) apoptosis(low) cells. SMOX was increased in all stages of gastric disease, peaking in tissues with intestinal metaplasia, whereas pEGFR, pEGFR-ERBB2, and pERBB2 were increased predominantly in tissues showing gastritis or atrophic gastritis. Principal component analysis separated gastritis tissues from patients with cancer vs those without cancer. pEGFR, pEGFR-ERBB2, pERBB2, and SMOX were increased in gastric samples from patients whose disease progressed to intestinal metaplasia or dysplasia, compared with patients whose disease did not progress.

CONCLUSIONS

In an analysis of gastric tissues from mice and patients, we identified a molecular signature (based on levels of pEGFR, pERBB2, and SMOX) for the initiation of gastric carcinogenesis.

Heregulin induces resistance to lapatinib-mediated growth inhibition of HER2-amplified cancer cells

Human epidermal growth factor receptor 2 (HER2) amplification occurs in approximately 20% of gastric and gastroesophageal junction cancers in the United States and European Union. Lapatinib, a dual HER2 and epidermal growth factor receptor tyrosine kinase inhibitor, has demonstrated clinical efficacy in HER2-amplified cancer cells. However, several studies have shown that some cytokines can mediate resistance to lapatinib using their receptor tyrosine kinase (RTK) pathways. One of these, Heregulin1 (HRG1), can confer resistance to lapatinib-mediated growth inhibition in HER2-amplified breast cancer cells, but the underlying mechanisms remain unknown. Here, we investigated whether and how HRG1 causes resistance to lapatinib in gastric and gastroesophageal junction cancers in vitro. HER2-amplified gastric and gastroesophageal junction cancer cell lines were highly sensitive to lapatinib. Exposure to HRG1 together with lapatinib rescued cells from lapatinib-induced cell cycle arrest and apoptosis. Downregulation of HER3 with siRNA in the presence of HRG1 re-sensitized HER2-amplified cancer cells to lapatinib. Immunoblotting analysis indicated that HRG1 re-activated HER3 and AKT in the presence of lapatinib, which persisted for at least 72 h. Activation of HER3 and downstream AKT was mediated by residual activity of HER2. HRG1-mediated resistance could be reduced by PI3K/mTOR inhibitors or by complete inhibition of HER2. Thus, we conclude that HRG1 mediates resistance to lapatinib through HER3 and AKT activation, and that this depends on residual HER2 activity. Lapatinib in combination with anti-PI3K therapies or more potent HER2 inhibitors would improve the efficacy and avoid the emergence of resistant cells.

Hepatic myofibroblasts promote the progression of human cholangiocarcinoma through activation of epidermal growth factor receptor

Intrahepatic cholangiocarcinoma (CCA) is characterized by an abundant desmoplastic environment. Poor prognosis of CCA has been associated with the presence of alpha-smooth muscle actin (α-SMA)-positive myofibroblasts (MFs) in the stroma and with the sustained activation of the epidermal growth factor receptor (EGFR) in tumor cells. Among EGFR ligands, heparin-binding epidermal growth factor (HB-EGF) has emerged as a paracrine factor that contributes to intercellular communications between MFs and tumor cells in several cancers. This study was designed to test whether hepatic MFs contributed to CCA progression through EGFR signaling. The interplay between CCA cells and hepatic MFs was examined first in vivo, using subcutaneous xenografts into immunocompromised mice. In these experiments, cotransplantation of CCA cells with human liver myofibroblasts (HLMFs) increased tumor incidence, size, and metastatic dissemination of tumors. These effects were abolished by gefitinib, an EGFR tyrosine kinase inhibitor. Immunohistochemical analyses of human CCA tissues showed that stromal MFs expressed HB-EGF, whereas EGFR was detected in cancer cells. In vitro, HLMFs produced HB-EGF and their conditioned media induced EGFR activation and promoted disruption of adherens junctions, migratory and invasive properties in CCA cells. These effects were abolished in the presence of gefitinib or HB-EGF-neutralizing antibody. We also showed that CCA cells produced transforming growth factor beta 1, which, in turn, induced HB-EGF expression in HLMFs.

CONCLUSION

A reciprocal cross-talk between CCA cells and myofibroblasts through the HB-EGF/EGFR axis contributes to CCA progression.

Systemic analysis of gene expression profiles identifies ErbB3 as a potential drug target in pediatric alveolar rhabdomyosarcoma

Pediatric sarcomas, including rhabdomyosarcomas, Ewing's sarcoma, and osteosarcoma, are aggressive tumors with poor survival rates. To overcome problems associated with nonselectivity of the current therapeutic approaches, targeted therapeutics have been developed. Currently, an increasing number of such drugs are used for treating malignancies of adult patients but little is known about their effects in pediatric patients. We analyzed expression of 24 clinically approved target genes in a wide variety of pediatric normal and malignant tissues using a novel high-throughput systems biology approach. Analysis of the Genesapiens database of human transcriptomes demonstrated statistically significant up-regulation of VEGFC and EPHA2 in Ewing's sarcoma, and ERBB3 in alveolar rhabdomyosarcomas. In silico data for ERBB3 was validated by demonstrating ErbB3 protein expression in pediatric rhabdomyosarcoma in vitro and in vivo. ERBB3 overexpression promoted whereas ERBB3-targeted siRNA suppressed rhabdomyosarcoma cell gowth, indicating a functional role for ErbB3 signaling in rhabdomyosarcoma. These data suggest that drugs targeting ErbB3, EphA2 or VEGF-C could be further tested as therapeutic targets for pediatric sarcomas.

High expression of HER3 is associated with a decreased survival in gastric cancer

BACKGROUND

The role of human epidermal growth factor receptor (HER) 3 and HER4 has been elucidated in gastric cancer. HER1 and HER2 overexpression are regarded as prognostic factors and targets of treatment. The dimerization of the HER family receptors activates downstream signal pathways and promotes tumor progression. This study investigated the positive correlation between HER1 and HER4 expression and the prognosis of patients with gastric cancers.

EXPERIMENTAL DESIGN

Tumor samples were obtained from gastric adenocarcinomas of 134 patients who underwent a gastrectomy from 1999 to 2002. The expression of each HER was analyzed in the tumor by immunohistochemical staining. Parametric correlations were done between HER expression and the clinicopathologic findings. A multivariate analysis was done with the overall survival.

RESULTS

HER3 expression was significantly associated with parameters involved with tumor progression, including the depth of tumor invasion (T1 versus T2-T4; P = 0.000), involved lymph nodes (P = 0.000), distant metastasis (P = 0.008), tumor stage (P = 0.000), and recurrent disease (P = 0.000). HER1 was also significantly associated with those factors excluding distant metastasis. A significant relationship was observed between the expression of HER1 and HER3 (P = 0.000). HER3 overexpression was associated with a significantly worse survival (P = 0.0000) and was an independent prognostic factor in the multivariate analysis (hazard ratio, 2.382; 95% confidence interval, 1.009-5.625; P = 0.048).

CONCLUSIONS

HER3 overexpression is strongly associated with tumor progression and poor prognosis of patients with gastric cancer. It may become a new prognostic factor and a target of treatment.

The ERBB3 receptor in cancer and cancer gene therapy

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

Evaluation of malignant and benign gastric biopsy specimens by mRNA expression profile and multivariate statistical methods

BACKGROUND

mRNA expression array and multivariate statistical analysis of gastric biopsies can yield insight into the molecular biology basis of local alterations, supporting expression-based identification of morphological alterations.

METHODS

From 11 patients with erosive gastritis(EG), 5 with adenocarcinoma (GC), 11 with atrophic gastritis (AG) gastric biopsies were collected, total RNA isolated, T7 amplification and expression analysis of 1047 mRNAs was performed using commercial glass arrays (Clontech, USA). After microarray quality control, applicable data were available from 7 EG, 4 GC, and 5 AG. Multivariate statistical and cell functional analysis were performed. Real-time RT-PCR and immunohistochemistry were used for validation.

RESULTS

GC was characterized by overregulated v-raf, v-erb-a, BCL2-associated- athanogene, immediate-early-response-3, Polo-like kinase, CDK-2, cyclin-C, Pin1 genes, and downregulated ADP-ribosyltransferase, sialophorin and DCC. AG cases had increased PDGF-receptor, TGF-beta-receptor-3, and decreased death-associated-protein-3, beta-1-catenin, topoisomerase-1 levels. In EG upregulation of IGF-receptor-1, CD9, transferrin receptor, integrins, and underexpression of keratin-5, caspase-4 was found. Discriminant analysis could reclassify all samples correctly using four parameters.

CONCLUSIONS

mRNA expression array analysis of gastric biopsies yields previously known and new data in the evaluation of local gastric alterations.

Heregulin-alpha and heregulin-beta expression is linked to a COX-2-PGE2 pathway in human gastric fibroblasts

We have previously shown heregulin (HRG)-alpha expression in human gastric fibroblasts and its stimulation of gastric epithelial cell growth. Although cyclooxygenase (COX)-2 has also been shown to stimulate growth factor production in these cells, the interaction between COX-2 and HRG remains unknown. Conditioned media (CM) from gastric fibroblasts incubated with PGE(2) or interleukin (IL)-1beta, a well known COX-2 inducer, were analyzed for their effect on erbB3 tyrosine phosphorylation in MKN28 gastric epithelial cells. HRG protein expression in fibroblast lysates and CM was also examined by western blot. HRG-alpha and HRG-beta mRNA expression in gastric fibroblasts and human gastric tissue was examined by real-time quantitative PCR. HRG and COX-2 expressions in surgical resections of human gastric ulcer tissue were examined immunohistochemically. CM from fibroblasts incubated with PGE(2), or IL-1beta, stimulated erbB3 phosphorylation in MKN28 cells. Preincubation of the fibroblasts with celecoxib, a selective COX-2 inhibitor, suppressed CM-induced erbB3 phosphorylation. This inhibition was reversed by exogenous PGE(2). As with erbB3 phophorylation, IL-1beta stimulated both HRG-alpha and HRG-beta mRNA expression, as well as HRG release into gastric fibroblast CM. IL-1beta-stimulated HRG expression and release were also inhibited by celecoxib, and exogenous PGE(2) restored this inhibitory effect, suggesting the activation of an IL-1beta-COX-2-PGE(2) pathway that culminates in the release of HRG from fibroblasts. HRG-alpha and HRG-beta mRNA levels were significantly higher in gastric ulcer tissue than in normal gastric mucosa. HRG immunoreactivity was found in interstitial cells of the gastric ulcer bed and coexpressed with COX-2. These results suggest that HRG might be a new member of the growth factor family involved in the COX-2-dependent ulcer repair process.

The role of cyclooxygenase in gastric mucosal protection

COX-1 and COX-2 are two cyclooxygenase enzymes responsible for prostanoid production. COX-2 is expressed in inflammatory cells and fibroblasts of the gastric mucosa, and through the production of various growth factors including hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF), plays a key role in the tissue repair process. Aspirin induces and acetylates COX-2 to produce 15-(R)-epi-lipoxinA4, an anti-inflammatory mediator thought to protect the gastric mucosa against aspirin-induced injury. Recently, three different PGE synthases have been identified, that convert COX-2 metabolites into PGE2. mPGE synthase (mPGES)-1 has been shown to be inducible, and to colocalize with COX-2 in fibroblasts and macrophages infiltrating the gastric ulcer bed. cPGES and mPGES-2 have been found expressed in normal gastric mucosa, with no change in expression levels seen in gastritis or gastric ulcer tissue. Finally, this review discusses the role of these enzymes in the pathophysiology of the gastric mucosa, as well as the biologcal significance of their inhibition.

Trans-10,cis-12, not cis-9,trans-11, conjugated linoleic acid decreases ErbB3 expression in HT-29 human colon cancer cells

AIM: To examine whether trans-10,cis-12 CLA (t10c12) or cis-9,trans-11 CLA (c9t11) inhibits heregulin (HRG)-β-stimulated cell growth and HRG-β-ErbB3 signaling in HT-29 cells.

METHODS: We cultured HT-29 cells in the absence or presence of the CLA isomers and/or the ErbB3 ligand HRG-β. MTT assay, [³H]thymidine incorporation, Annexin V staining, RT-PCR, Western blotting, immunoprecipitation, and in vitro kinase assay were performed.

RESULTS: HRG-β increased cell growth, but did not prevent t10c12-induced growth inhibition. T10c12 inhibited DNA synthesis and induced apoptosis of HT-29 cells, whereas c9t11 had no effect. T10c12 decreased the levels of ErbB1, ErbB2, and ErbB3 proteins and transcripts in a dose-dependent manner, whereas c9t11 had no effect. Immunoprecipitation/Western blot studies revealed that t10c12 inhibited HRG-β-stimulated phosphorylation of ErbB3, recruitment of the p85 subunit of phosphoinositide 3-kinase (PI3K) to ErbB3, ErbB3-associated PI3K activities, and phosphorylation of Akt. However, c9t11 had no effect on phospho Akt levels. Neither t10c12 nor c9t11 had any effect on HRG-β-induced phosphorylation of ERK-1/2.

CONCLUSION: These results indicate that the inhibition of HT-29 cell growth by t10c12 may be induced via its modulation of ErbB3 signaling leading to inhibition of Akt activation.

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.

Inactivation of ErbB3 by siRNA promotes apoptosis and attenuates growth and invasiveness of human lung adenocarcinoma cell line A549

The ErbB3 receptor and the downstream signaling kinase Akt are implicated in proliferation of lung adenocarcinoma cells. Inhibition by siRNAs to ErbB3 and Akt isoforms 1, 2 and 3 was utilized to investigate the contribution of these molecules to tumor survival, spreading and invasiveness, and the roles of specific Akt isoforms. ErbB3 siRNA stably and dose-dependently suppressed ErbB3 protein for 2 days or more, and reduced cell numbers, by both suppressing cell cycle and causing apoptosis and necrosis. It also inhibited soft agar growth, cell motility and migration, and invasiveness. Akt1, 2 and 3 siRNAs had similar suppressive effects on cell number, apoptosis/necrosis and soft agar growth. However, although Akt1 siRNA had no effect on cell migration or invasion, Akt2 siRNA effectively suppressed both activities, and Akt3 siRNA had moderate effectiveness. In A549 cells, ErbB3 is indicated as having major effects on cell division, survival, motility, migration and invasiveness. All three Akt isoforms are to varying degrees involved in these cell behaviors, with Akt2 especially implicated in migration and invasion. ErbB3 and the Akts are promising targets for therapy, and siRNAs may be useful for this purpose.

Gefitinib (Iressa, ZD1839) inhibits SN38-triggered EGF signals and IL-8 production in gastric cancer cells

Epidermal growth factor receptor (EGFR) and its ligands are involved in tumor growth, metastasis, angiogenesis, and resistance to chemotherapy. In the experiments described here using AGS gastric cancer cells, SN38 (the active metabolite of CPT-11) induced tyrosine phosphorylation of EGFR within 5 min, and this was followed by the induction of transcripts and/or proteins of heparin-binding EGF-like growth factor, amphiregulin, transforming growth factor-alpha, and interlukin-8 (IL-8). SN38 also activates nuclear factor-kappaB and activator protein-1, both of which are critical for the transcription of the IL-8 gene. However, the blocking of EGFR activation by gefitinib (Iressa, ZD1839), an EGFR-TKI (tyrosine kinase inhibitor), abrogates all the above reactions. The SN38-triggered mechanisms include the generation of reactive oxygen species (ROS) and the activation of protein kinase C (PKC), followed by metalloproteinase activation and the sequential ectodomain shedding of EGFR ligands. These findings suggest that EGF signaling is enhanced by CPT-11 and point to the potential benefit of the use of a combination of CPT-11 with gefitinib in the treatment of certain gastric cancers.

EGF-induced proliferation of adult human pancreatic duct cells is mediated by the MEK/ERK cascade

Human postnatal pancreatic duct cells are a potential source of new beta cells. Factors regulating proliferation of human pancreatic duct cells in vitro are unknown. In several other cell types, this process is influenced by ligands of the ErbB receptor family. The expression and functionality of the ErbB family members and their possible role in duct cell proliferation were determined. In cultured adult human pancreatic duct cells the different members of the ErbB family (ErbB1-4) were present at transcript and protein level. Stimulation of the duct cells with epidermal growth factor (EGF) and betacellulin results in Tyr-phosphorylation of ErbB1 and ErbB2, followed by activation of Shc, MEK1/2 and ERK1/2. Duct cells with activated ErbB signaling changed morphology and motility. EGF induced proliferation of a fraction of the duct cells and treatment with PD98059 prevented Ki67 expression in EGF-supplemented cells. When transduced with recombinant adenovirus expressing constitutively activated MEK1, duct cells proliferate and spread even in the absence of EGF. Importantly, the adult human duct cells retain their capacity to recapitulate ngn3-induced embryonic (neuro)endocrine differentiation after proliferation. Therefore, the present data support a possible role for human adult pancreatic duct cells, following expansion and transdifferentiation, as a source of insulin by transplantation to type I diabetes patients.

Gefitinib ("Iressa", ZD1839) inhibits SN38-triggered EGF signals and IL-8 production in gastric cancer cells

The epidermal growth factor receptor (EGFR) and its ligands are involved in tumor growth, metastasis, angiogenesis, and resistance to chemotherapy. The findings reported here demonstrate that SN38 (the active metabolite of CPT-11) induces the tyrosine phosphorylation of EGFR within 5 min, followed by the induction of transcripts and/or proteins of the heparin-binding EGF-like growth factor, amphiregulin, transforming growth factor-alpha, and interlukin-8 (IL-8) in AGS gastric cancer cells. SN38 also activates nuclear factor-kappa B and activator protein-1, both of which are critical for the transcription of the IL-8 gene. However, the blocking of EGFR activation by gefitinib ("Iressa", ZD1839), an EGFR-TKI (tyrosine kinase inhibitor), abrogates all the above reactions. The SN38-triggered mechanisms include the generation of reactive oxygen species (ROS) and the activation of protein kinase C (PKC), followed by metalloproteinase activation and the sequential ectodomain shedding of EGFR ligands. These findings suggest that EGF signaling is enhanced by CPT-11 and point to the potential benefit of the use of a combination of CPT-11 with gefitinib in the treatment of certain gastric cancers.

Conjugated linoleic acid inhibits cell proliferation and ErbB3 signaling in HT-29 human colon cell line

Conjugated linoleic acid (CLA) has chemoprotective properties in experimental cancer models, and in vitro studies have shown that CLA inhibits HT-29 colon cancer cell growth. ErbB2 and ErbB3 have been implicated in the development of colon cancer, and both proteins are expressed at high levels in the HT-29 cell line. Activation of ErbB2/ErbB3 heterodimers is regulated by the ErbB3 ligand heregulin. To examine CLA regulation of HT-29 cell proliferation and apoptosis and the influence of CLA on the ErbB3 signaling pathway, HT-29 cells were cultured in the presence of CLA and/or heregulin. CLA inhibited DNA synthesis and induced apoptosis of HT-29 cells. Although the addition of heregulin-alpha led to an increase in cell number, it was not able to counteract the negative growth regulatory effect of CLA. Immunoprecipitation/Western blot studies revealed that CLA inhibited heregulin-alpha-stimulated phosphorylation of ErbB2 and ErbB3, recruitment of the p85 subunit of phosphoinositide 3-kinase (PI3-kinase) to the ErbB3 receptor, ErbB3-associated PI3-kinase activities, and phosphorylation of Akt. CLA decreased ErbB2 and ErbB3 mRNA and protein levels in a dose-dependent manner. In conclusion, we demonstrate that CLA inhibits cell proliferation and stimulates apoptosis in HT-29 cells and that this may be mediated by its ability to downregulate ErbB3 signaling and the PI3-kinase/Akt pathway.

The role of epidermal growth factor receptor in head and neck squamous cell carcinoma

Growth factor receptors play a crucial role in the cell proliferation pathways involved in the development of cancer. One such receptor, the epidermal growth factor receptor (EGFR), is upregulated in many types of human tumors, particularly head and neck squamous cell carcinoma (HNSCC). EGFR overexpression in HNSCC has been the basis for investigation of therapeutic strategies that target EGFR. EGFR-blocking methods under evaluation involve immunotoxins, monoclonal antibodies, EGFR-specific tyrosine kinase inhibitors, and antisense approaches. These molecular targeting tactics have produced a number of agents that are currently in various stages of preclinical investigation, along with clinical trials to assess their potential as anticancer treatments.

Stimulation of the gastrin-cholecystokinin(B) receptor promotes branching morphogenesis in gastric AGS cells

Epithelial organization is maintained by cell proliferation, migration, and differentiation. In the case of the gastric epithelium, at least some of these events are regulated by the hormone gastrin. In addition, gastric epithelial cells are organized into characteristic tubular structures (the gastric glands), but the cellular mechanisms regulating the organization of tubular structures (sometimes called branching morphogenesis) are uncertain. In the present study, we examined the role of the gastrin-cholecystokinin(B) receptor in promoting branching morphogenesis of gastric epithelial cells. When gastric cancer AGS-G(R) cells were cultured on plastic, gastrin and PMA stimulated cell adhesion, formation of lamellipodia, and extension of long processes in part by activation of protein kinase C (PKC) and phosphatidylinositol (PI)-3 kinase. Branching morphogenesis was not observed in these circumstances. However, when cells were cultured on artificial basement membrane, the same stimuli increased the formation of organized multicellular arrays, exhibiting branching morphogenesis. These effects were reversed by inhibitors of PKC but not of PI-3 kinase. We conclude that, in the presence of basement membrane, activation of PKC by gastrin stimulates branching morphogenesis.

Significance of the association between heparin-binding epidermal growth factor-like growth factor and CD9 in human gastric cancer

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family. Juxtacrine activity of proHB-EGF (the membrane-anchored form of HB-EGF) has been shown to be significantly potentiated when it is coexpressed with CD9 in vitro. The purpose of our study was to investigate the issue of whether proHB-EGF and CD9 are coexpressed in gastric cancer. HB-EGF gene expression and protein production in human gastric cancers was investigated, and EGF receptor and CD9 expressions were also evaluated. HB-EGF mRNA levels in gastric cancers were elevated, compared with normal gastric tissues, especially in the intestinal type. ProHB-EGF immunoreactivity was detected primarily in the cytoplasm and plasma membrane of gastric cancer cells. Of 66 patients, 40 (60.6%) exhibited proHB-EGF immunoreactivity and the level of its expression was significantly associated with tumor status (p < 0.01) and histological differentiation (p < 0.001). In addition, proHB-EGF mRNA was detected at high levels in the intestinal type by in situ hybridization. CD9 immunoreactivity was found to be preserved in 26 of 36 patients (72.2%) and CD9 protein expression was inversely associated with lymph node status (p < 0.05). A significant correlation between its expression and histological differentiation (p < 0.01) was found, and the association of CD9 with proHB-EGF was increased in the intestinal type, as evidenced by an immunoprecipitation method. These results indicate that the coexpression of proHB-EGF and CD9 may be involved in the tumorigenesis and/or proliferation of gastric cancers in a juxtacrine manner.

Autocrine heregulin generates growth factor independence and blocks apoptosis in colon cancer cells

The aim of this study was to determine whether constitutive ErbB2 activation controls growth and apoptosis in colon cancer cells. Growth arrested GEO cells showed constitutive activation of ErbB2 in the absence of exogenous growth factors or serum supplementation. Higher levels of heregulin and ErbB2 activation were observed in the growth-arrested state and cell cycle re-entry was independent of exogenous growth factors. Blockade of ErbB2 activation by heregulin neutralizing antibodies and by AG879 resulted in prevention of cell cycle re-entry. This indicated that autocrine heregulin activity was responsible for growth factor independence and for cell cycle re-entry. Activation of ErbB2 was the result of heregulin mediated interaction with ErbB3 and generated downstream activation of the ERK and the PI3K/AKT pathways. Heregulin neutralizing antibody treatment of growth arrested GEO cells also generated apoptosis as reflected by PARP cleavage and DNA fragmentation indicating a cell survival signal was also induced by the constitutively activated ErbB2. The activation of AKT but not the MAPK pathway was responsible for cell survival in these cells.

Expression profiling of gastric adenocarcinoma using cDNA array

To investigate the expression profile of gastric adenocarcinoma, cDNA array experiments were performed using Atlas Human Cancer 1.2 K Array (Clontech Laboratories, Palo Alto, CA) on nine xenografted and two primary gastric cancer samples. The expression of the tumor samples was compared to that of two normal gastric epithelial tissues. The expression pattern of the primary tumors was similar to that of xenografted tumors. The up-regulated genes had expression ratios ranging from 2.5 to 16, whereas the down-regulated genes had a range from -2.5 to -16. No variation in gene expression was detected in the analysis of the xenografted tumors versus the primary tumors, indicating that the xenografts represented the primary tumors well. Thirty-eight genes showed altered gene expression in 5 or more samples (>45%). Thirty-one genes were up-regulated and seven genes were down-regulated. The most abundantly up-regulated genes (ratio >5) included genes such as S100A4, CDK4, MMP14 and beta catenin. The GIF was markedly down-regulated (ratio < -10). To confirm our findings, six genes (three up- and three down-regulated) were selected for semi-quantitative RT-PCR analysis. The RT-PCR results were consistent with the array findings. Our approach revealed that several genes are abnormally expressed in gastric cancer and found that genes known to interact in several common molecular pathway(s) were consistently altered.

Effects of in vivo heregulin beta1 treatment in wild-type and ErbB gene-targeted mice depend on receptor levels and pregnancy

Mice heterozygous (+/-) for either heregulin (HRG), ErbB2, or ErbB3 were created by gene targeting, resulting in the loss of one functional gene copy and an associated decrease in targeted protein. We examined the in vivo activity of recombinant HRG peptide, rHRG beta1 (amino acids 177 to 241), in the three heterozygous mouse lines and in wild-type (WT) mice, both pregnant and nonpregnant. Nonpregnant WT and HRG(+/-) mice of both sexes were sensitive to rHRG beta1 treatment as evidenced by a high mortality rate associated with abdominal enlargement and parietal cell loss. However, pregnant WT mice and ErbB2 and ErbB3 heterozygous mice treated with rHRG beta1 were less affected, with significantly lower mortality rates and a less severe abdominal phenotype. Histological analysis revealed extensive breast ductal hyperplasia in females of all genotypes after rHRG beta1 treatment. Hyperplasia of other epithelial tissues such as the pancreas and intestine and the growth of cardiac nerve bundles were also observed, independent of sex.

Tyrosine kinases and gastric cancer

Carcinoma of the stomach is one of the most prevalent cancer types in the world today. Two major forms of gastric cancer are distinguished according to their morphological and clinicopathological classifications (well differentiated/intestinal type and poorly differentiated/diffuse type), characteristics that could also be attributed to the altered expression of different types of oncogenes or tumor suppressor genes. Significant differences exist for gastric cancer incidence comparing people of different ethnic origins, implicating various genetic and epigenetic factors for gastric oncogenesis. There are only a limited number of molecular markers available for gastric cancer detection and prognostic evaluation, among which are tyrosine kinases. There is convincing evidence that tyrosine kinases are involved in oncogenesis and disease progression for many human cancers. Amplifications of certain tyrosine kinases (c-met, k-sam and erbB2/neu) have been associated with human gastric cancer progression. Alternatively spliced transcripts and enhanced protein-expression levels for some of these tyrosine kinases are correlated with clinical outcomes for gastric cancer patients. With advent of high throughput techniques, it is now possible to detect nearly all expressed tyrosine kinases in a single screen. This increases the chance to identify additional tyrosine kinases as predictive markers for gastric cancers. In this article, we will first review the literature data concerning certain tyrosine kinases implicated in gastric carcinogenesis and then summarize more recent work which provide comprehensive tyrosine kinase profiles for gastric cancer specimens and cell lines. Two new gastric cancer molecular markers (tie-1 and mkk4) have been identified through the use of these profiles and demonstrated effective as clinical prognostic indicators.