ABSTRACT
BACKGROUND: Angiotensin II (Ang II) has been implicated in the development of glomerulosclerosis by stimulating fibronectin (FN) synthesis. The processing and release of heparin binding-endothelin growth factor (HB-EGF) are activated by protein kinase C (PKC) and Ca2+ signaling. We studied the roles of HB-EGF and endothelial growth factor (EGF) receptor (EGFR) in Ang II-induced FN expression using mesangial cells. METHODS: Mesangial cells were prepared from mouse kidneys by the explant method and cells were used at passages 4 and 5. RESULTS: Ang II stimulated FN mRNA levels dose-dependently with a maximal increase (3.4-fold) after 12 hours of incubation. This action was completely inhibited by PKC inhibitors and slightly blocked by Ca2+ chelating agents. FN mRNA accumulation by Ang II was abolished by tyrosine kinase inhibitors, a specific inhibitor for EGFR (AG1478) and extracellular signal-regulated kinase (ERK) inactivation. Addition of neutralizing anti-HB-EGF antibody, as well as pretreatment with heparin or the metalloproteinase inhibitor batimastat abolished induction of FN expression by Ang II. In mesangial cells stably transfected with a chimeric construct containing HB-EGF and alkaline phosphatase (ALP) genes, ALP activity in incubation medium was rapidly increased by Ang II (1.7-fold at 0.5 min) and reached a 4.1-fold increase at two minutes. Ang II phosphorylated EGFR (maximal at 2 min) and ERK (maximal at 8 min) in a PKC- and metalloproteinase-dependent manner. Ang II stimulated the expression and release of transforming growth factor-beta (TGF-beta) via EGFR-mediated signaling, and the released TGF-beta also contributed to Ang II-mediated FN expression via EGFR transactivation. CONCLUSIONS: Ang II-mediated FN expression was regulated by autocrine effects of HB-EGF and TGF-beta, suggesting a novel paradigm for cross-talk between Ang II and growth factor receptor signaling pathways.
Subject(s)
Angiotensin II/physiology , Epidermal Growth Factor/metabolism , Glomerular Mesangium/metabolism , Metalloendopeptidases/metabolism , Signal Transduction/physiology , Angiotensin II/pharmacology , Animals , Cells, Cultured , Enzyme Activation , ErbB Receptors/physiology , Fibronectins/genetics , Glomerular Mesangium/cytology , Heparin-binding EGF-like Growth Factor , Intercellular Signaling Peptides and Proteins , Male , Mice , Mice, Inbred C57BL , Mitogen-Activated Protein Kinases/metabolism , Mitogen-Activated Protein Kinases/physiology , Phosphorylation , Protein Kinase C/physiology , RNA, Messenger/metabolism , Receptor, Angiotensin, Type 1 , Receptors, Angiotensin/physiology , Tetradecanoylphorbol Acetate/pharmacology , Transforming Growth Factor beta/genetics , Up-RegulationABSTRACT
Venous drainage to the portal vein in pulmonary sequestration is rare. A 7-month-old girl was referred to our hospital following surgery for ventricular septal defect because of a left upper abdominal mass with a large feeding artery from the abdominal aorta and venous drainage to the portal vein. She had had frequent pulmonary infections and was growth retarded. MRI demonstrated that the mass was above the left diaphragm, suggesting extralobar sequestration. An extralobar sequestered lung was resected at thoracotomy. Diagnostic problems and clinical features are presented.
