ABSTRACT
BACKGROUND/AIMS: Heregulin (HRG/NRG) ligation to erbB3/4 promotes their respective heterodimerization with erbB2, and consequent erbB2 tyrosine phosphorylation. Although HRG has been shown to be expressed in a variety of cancer tissues, its expression and role in colon cancer have yet to be clarified. We therefore examined the link between the expression of these erbB receptors, and the relationship between HRG and vascular endothelial growth factor (VEGF) expression in colon cancer. METHODS: We analyzed the effects of HRG on VEGF secretion in 6 colorectal cancer cell lines by enzyme-linked immunosorbent assay, and HRG-induced p85 subunit of phosphatidylinositol 3-kinase (p85 PI-3K), Akt, extracellular signal-regulated kinase 1/2 (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) activation in Caco-2 colon cancer cell lines by Western blot. We also examined HRG and VEGF mRNA expression in 16 colon cancer biopsy samples by real-time PCR. The localization of HRG and VEGF protein expression in colon cancer tissue was detected by immunohistochemistry. RESULTS: Exogenous HRG stimulated VEGF secretion in all cell lines examined, and VEGF mRNA expression in Caco-2 cells. HRG also activated p85 PI-3K, Akt, ERK1/2, and p38 MAPK. VEGF secretion was inhibited by both specific p38 MAPK inhibitor and proteasome inhibitor that inhibit nuclear factor kappa B (NF-kappaB) activation. In colon cancer biopsy samples, HRG mRNA expression correlated with VEGF mRNA expression. HRG immunoreactivity was observed both in cancer cells and in mesenchymal cells in colon cancer tissues. CONCLUSION: These data suggest that HRG might affect colon cancer growth by regulating VEGF secretion via the erbB3 signaling pathway through autocrine and paracrine mechanisms.
Subject(s)
Adenocarcinoma/metabolism , Colonic Neoplasms/metabolism , Neuregulin-1/metabolism , Receptor, ErbB-3/metabolism , Vascular Endothelial Growth Factor A/metabolism , Caco-2 Cells , Extracellular Signal-Regulated MAP Kinases/metabolism , HT29 Cells , Humans , Immunohistochemistry , Intestinal Mucosa/metabolism , MAP Kinase Signaling System , Phosphatidylinositol 3-Kinases/metabolism , Phosphorylation , Polymerase Chain Reaction , Proto-Oncogene Proteins c-akt/metabolism , RNA, Messenger/metabolismABSTRACT
BACKGROUND: Endogenous and exogenous prostaglandins (PGs) have been shown to contribute to reducing the gastric injury caused by irritants given subsequently. The aim of this study was to clarify whether cyclooxygenase-2 (COX-2) protein induced by pretreatment was involved in the prevention of subsequent ethanol-caused gastric injury in mice. METHODS: Mice were pretreated with acidified ethanol or saline and then COX-2 protein expression in the stomach was immunohistochemically determined every 8h. Mice were administered 95% ethanol 24h after the acidified ethanol pretreatment, and gastric mucosal damage was evaluated macroscopically and histologically. The effects of NS-398 or indomethacin on the 95% ethanol-caused damage were also examined. RESULTS: Acidified ethanol pretreatment induced COX-2 protein expression in lamina propria macrophages of the gastric mucosa, with a peak level 24h after the pretreatment. The 95% ethanol treatment caused gastric mucosal damage. The degree of the damage was not different between mice pretreated with acidified ethanol and those pretreated with saline. However, NS-398 aggravated the ethanol-caused damage only in mice pretreated with acidified ethanol, while indomethacin aggravated the damage, evaluated histologically, irrespective of the pretreatment. CONCLUSIONS: Pretreatment-induced COX-2, in addition to COX-1, seemed to be involved in the defense mechanism through minimizing the damage caused by a subsequent irritant.
Subject(s)
Gastric Mucosa/drug effects , Irritants/pharmacology , Isoenzymes/physiology , Prostaglandin-Endoperoxide Synthases/physiology , Stomach Ulcer/prevention & control , Animals , Central Nervous System Depressants/pharmacology , Cyclooxygenase 1 , Cyclooxygenase 2 , Cyclooxygenase 2 Inhibitors , Cyclooxygenase Inhibitors/pharmacology , Cytoprotection , Ethanol/pharmacology , Gastric Mucosa/enzymology , Immunohistochemistry/methods , Indomethacin/pharmacology , Male , Membrane Proteins , Mice , Models, Animal , Nitrobenzenes/pharmacology , Stomach Ulcer/chemically induced , Sulfonamides/pharmacologyABSTRACT
The shedding mechanism for the tomoregulin (TR) ectodomain, which contains two follistatin modules and a single epidermal growth factor (EGF)-like domain, remains unclear. Our study provides the first evidence that proinflammatory cytokines, IL-1beta and TNF-alpha, induce TR-ectodomain shedding in cultured A172 human glioma cells, without affecting TR mRNA expression. In addition, it appears that this shedding process is induced via activation of the NF-kappaB signaling pathway; with consequent increase in the production of metalloproteinases. Furthermore, since due to erbB4 tyrosine phosphorylation TR may have functions similar to EGF/neuregulin (NRG) family growth factors, our results suggest that following inflammation-induced injury, increases in TR shedding may contribute to tissue growth and repair in the central nervous system.