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

Wu D, Peng F, Zhang B, Ingram AJ, Kelly DJ, Gilbert RE, Gao B, Kumar S, Krepinsky JC. EGFR-PLC gamma 1 signaling mediates high glucose-induced PKC beta 1-Akt activation and collagen I upregulation in mesangial cells. Am J Physiol Renal Physiol 297: F822-F834, 2009. First published July 15, 2009; doi:10.1152/ajprenal.00054.2009.-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-PKC beta 1-Akt signaling in mesangial cells (MC). Phospholipase C gamma 1 (PLC gamma 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 gamma 1 membrane translocation and Y783 phosphorylation, both indicative of its activation. Mannitol was without effect. PLC gamma 1 Y783 phosphorylation was also seen in cortex and glomeruli of diabetic rats. HG induced a physical association between EGFR and PLC gamma 1 as identified by coimmuno-precipitation. PLC gamma 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 gamma 1 activation. HG-induced Akt S473 phosphorylation, effected by PKC beta 1, was inhibited by the PLC gamma inhibitor U73122. PLC gamma 1 inhibition or downregulation by small interference RNA also prevented HG-induced collagen I upregulation. Our results indicate that EGFR-PLC gamma 1 signaling mediates HG-induced PKC beta 1-Akt activation and subsequent collagen I upregulation in MC. Inhibition of EGFR or PLC gamma 1 may provide attractive therapeutic targets for the treatment of diabetic nephropathy.