Angiotensin II signaling and HB-EGF shedding via metalloproteinase in glomerular mesangial cells.
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.
Uchiyama-Tanaka
Y
Y
Department of Medicine II, Kansai Medical University, Osaka, Japan.
Matsubara
H
H
Nozawa
Y
Y
Murasawa
S
S
Mori
Y
Y
Kosaki
A
A
Maruyama
K
K
Masaki
H
H
Shibasaki
Y
Y
Fujiyama
S
S
Nose
A
A
Iba
O
O
Hasagawa
T
T
Tateishi
E
E
Higashiyama
S
S
Iwasaka
T
T
D000804:Angiotensin II / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000502:physiology; D005353:Fibronectins / Q000235:genetics; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism*; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D008297:Male; D008666:Metalloendopeptidases / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000235:genetics; D015854:Up-Regulation
D005353:Fibronectins; C587884:Hbegf protein, mouse; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin; D016212:Transforming Growth Factor beta; D000804:Angiotensin II; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D008666:Metalloendopeptidases; D013755:Tetradecanoylphorbol Acetate