Albumin Activates ERK Via EGF Receptor in Human Renal Epithelial Cells

Abstract

Emerging clinical and experimental evidence strongly implicates proteinuria in the progression of kidney disease. One pathway involves the activation of NFB by albumin, and it has been demonstrated that the activation of NFB induced by albumin is dependent on mitogen-activated protein kinase ERK1/ERK2. To study the effect of albumin on gene expression, primary human renal tubular cells were exposed in vitro to albumin (1%) for 6 h, and gene expression profiling was performed with the human oligonucleotide microarray, U133A Affymetrix Gene Chip. In all, 223 genes were differentially regulated by albumin, including marked upregulation of the EGF receptor (EGFR) and IL-8. Accordingly, the authors sought to delineate the signaling pathway linking albumin to the EGFR and activation of ERK1/ERK2. It was found that albumin led to a doseand time-dependent activation of ERK1/ERK2. Treatment with albumin led to EGFR phosphorylation, but the activation of ERK1/ERK2 was prevented by pretreatment of the cells with AG-1478, the EGFR kinase inhibitor, at a dose that inhibited EGF-induced ERK1/ERK2 activation. Exogenously administered reactive oxygen species (ROS) were found to activate ERK1/ ERK2 via the EGFR and src tyrosine kinase activity and pretreatment of cells with the antioxidant N-acetylcysteine (NAC) and the NADPH oxidase inhibitor DPI abrogated albumin-induced activation of ERK1/ERK2. The src tyrosine kinase inhibitor, PP2, also inhibited the albumin-induced activation of ERK1/ERK2. Finally, pretreatment with AG-1478, the MEK inhibitor UO126, and NAC prevented the albumin-induced increase in IL-8 expression. The authors conclude that the EGF receptor plays a central role in the signaling pathway that links albumin to the activation of ERK1/ERK2 and increased expression of IL-8. Gene profiling studies suggest that there may be a positive feedback loop through the EGFR that amplifies the response of the proximal tubule cell to albumin. Taken together, these results suggest that the EGFR may be an important treatment target for kidney disease associated with proteinuria.

7-Dehydrocholesterol enhances ultraviolet A-induced oxidative stress in keratinocytes: Roles of NADPH oxidase, mitochondria, and lipid rafts

“…Activation and translocation of Rac1 to the membrane is essential for activation of a Nox1-containing NADPH oxidase [52] although pre-assembly of Nox1 with NoxO1 (the homologue of p47phox) appeared to form a active complex in HEK293 cells [53]. Activation of growth factor receptors stimulates NADPH oxidase activity in many cells types [54][55][56].However, UVA-induced activation of NADPH oxidase is unlikely to involve activation of EGFR because UVA inhibits signaling via EGFR [54]. An alternative mechanism involves ceramide because it is released in keratinocytes by UVA [7,57] and has been reported to activate NADPH oxidase in endothelial cells [58].…”

Luminal Alkalinization Attenuates Proteinuria-Induced Oxidative Damage in Proximal Tubular Cells

“…We used a range of protein concentrations (5, 15, and 30 g/L) that were comparable to those used in other previous studies. 4,5,7,23,51,52 Such concentrations are higher than those measured in the proximal tubular fluid of rats with experimental proteinuria using micropuncture studies in which the reported maximum albumin concentration was 7 g/L. 53 However, since the duration of protein exposure is much longer in in vivo settings, the total amount of proteins processed by proximal tubular cells in vivo far exceeds that of the cultured HK-2 cells.…”

Redox Control of Renal Function and Hypertension

“…In addition, DPI and rotenone also abolished NF-B activation, demonstrating that albumin stimulation of NAD(P)H oxidase leads to PKC activation and ROS/ H 2 O 2 generation, which in turn leads to NF-B-dependent inflammatory signals. Finally, albumin has been shown to activate ERK1/ERK2 by phosphorylation of EGFR, and this was reversed with AG-1478, an EGFR kinase inhibitor (265). It was further apparent that in PTCs, albumin acts through EGFR to stimulate NAD(P)H oxidase and ROS production.…”