EGFR-PLC[gamma]1 signaling mediates high glucose-induced PKC[beta]1-Akt activation and collagen I upregulation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. We have recently shown that epidermal growth factor receptor (EGFR) transactivation mediates high glucose (HG)-induced collagen I upregulation through PI3K-PKCβ1-Akt signaling in mesangial cells (MC). Phospholipase C...1 (PLC...1) interacts with activated growth factor receptors and activates classic PKC isoforms. We thus studied its role in HG-induced collagen I upregulation in MC. Primary rat MC were treated with HG (30 mM) or mannitol as osmotic control. Protein kinase activation was assessed by Western blotting and collagen I upregulation by Northern blotting. Diabetes was induced in rats by streptozotocin. HG treatment for 1 h led to PLC...1 membrane translocation and Y783 phosphorylation, both indicative of its activation. Mannitol was without effect. PLC...1 Y783 phosphorylation was also seen in cortex and glomeruli of diabetic rats. HG induced a physical association between EGFR and PLC...1 as identified by coimmunoprecipitation. PLC...1 activation required EGFR kinase activity since it was prevented by the EGFR inhibitor AG1478 or overexpression of kinase-inactive EGFR (K721A). Phosphoinositide-3-OH kinase inhibition also prevented PLC...1 activation. HG-induced Akt S473 phosphorylation, effected by PKCβ1, was inhibited by the PLC... inhibitor U73122. [GenBank] PLC...1 inhibition or downregulation by small interference RNA also prevented HG-induced collagen I upregulation. Our results indicate that EGFR-PLC...1 signaling mediates HG-induced PKCβ1-Akt activation and subsequent collagen I upregulation in MC. Inhibition of EGFR or PLC...1 may provide attractive therapeutic targets for the treatment of diabetic nephropathy. (ProQuest: ... denotes formulae/symbols omitted.)