Background/aims: Activation of angiotensin II (ANG2) receptors stimulates extracellular signal-regulated kinases (ERKs) that, in some cell systems, are mediated by transactivating the epidermal growth factor (EGF) receptor (EGFR) through mechanisms involving matrix metalloprotease (MMP)-stimulated processing of heparin-binding EGF (HB-EGF) from its precursor.
Methods: The signaling pathways linked to ANG2-dependent ERK activation were determined in an immortalized mouse podocyte cell line by monitoring ANG2-stimulated phosphorylation of ERK1/2.
Results: ANG2 induced transient ERK phosphorylation that was maximal at 5 min and then rapidly dissipated. ANG2-dependent ERK activation was inhibited by: (1) the type-1 ANG2-selective antagonist losartan; (2) the type-2 ANG2-selective antagonist PD123319; (3) an inhibitor of MMP2/9; (4) the EGFR kinase inhibitor AG1478, and (5) the HB-EGF antagonists CRM197 and heparin. ANG2-dependent ERK activation was mediated by both protein kinase C (PKC)- and calcium-dependent mechanisms and was associated with tyrosine phosphorylation of EGFR. To determine if ANG2-dependent HB-EGF release could act in a paracrine fashion on adjacent cells, HEK293 cells were stably transfected with green fluorescent protein-tagged ERK2 (GFP-ERK2). In stably transfected HEK293 cells, EGF stimulated phosphorylation of endogenous ERK1/2 as well as GFP-ERK2. In contrast, ANG2 had no effect on ERK phosphorylation in stably transfected HEK293 cells. When podocytes were co-cultured with stably transfected HEK293 cells, however, treatment with ANG2 rapidly stimulated GFP-ERK2 phosphorylation. Both the MMP2/9 inhibitor and AG1478 attenuated ANG2-dependent phosphorylation of GFP-ERK2 in the co-culture system.
Conclusions: These data indicate that ERK activation is induced by ANG2 in podocytes by mechanisms involving ANG2-dependent release of HB-EGF which, in turn, may act in an autocrine and paracrine fashion to stimulate ERK activity.
Copyright 2006 S. Karger AG, Basel