Endothelin-1 activates mesangial cell ERK1/2 via EGF-receptor transactivation and caveolin-1 interaction

Increased intraglomerular pressure is an important hemodynamic determinant of glomerulosclerosis and can be modeled in vitro by exposing mesangial cells to cyclic mechanical strain. A previous study showed that RhoA mediates strain-induced production of fibronectin; herein is investigated the role of caveolae in RhoA activation. Cyclodextrin and filipin, agents that disrupt caveolae, abrogated strain-induced RhoA activation in mesangial cells. Caveolin-1 (cav-1), the defining protein of caveolae, was Y14 phosphorylated by strain, and this was inhibited by PP1, showing Src dependence. Strain also induced c-SrcY416 phosphorylation and hence activation. Strain increased RhoA association with cav-1, which was blocked by PP1. Cyclodextrin and filipin inhibited the strain-induced RhoA/cav-1 association, indicating dependence on caveolar structural integrity. Restoration of caveolae by coincubation of cyclodextrin with cholesterol rescued both RhoA activation and RhoA/cav-1 association in response to strain. Sucrose gradient detected a significant portion of RhoA in caveolae, with Src located exclusively in these domains. Finally, in cells that were infected with retrovirus that encodes the nonphosphorylatable cav-1 Y14A, RhoA/cav-1 association, RhoA activation, and fibronectin secretion in response to strain were abrogated. It is concluded that strain-induced RhoA activation depends on the integrity of caveolae and on physical association of cav-1 and RhoA. The phosphorylation of cav-1 at Y14 by Src kinases is required for this to occur. These studies define a novel function for cav-1 and caveolae as positive effectors of RhoA activation. Targeting caveolae thus may provide a new therapeutic option for glomerular sclerosis that is associated with elevated intraglomerular pressure.

Section: Discussionmentioning

confidence: 99%

RhoA Activation in Mesangial Cells by Mechanical Strain Depends on Caveolae and Caveolin-1 Interaction

Peng

Wu²,

Ingram³

et al. 2007

“…For example, lipid rafts may be important in the signal transduction events dependent on the EGFR, and the EGFR, as well as other components of MAPK pathways, have been localized to caveolae (49,(52)(53)(54). In this regard, it is tempting to speculate that caveolae may serve to facilitate the propagation of albumin-induced cell signaling because treatment with membrane cholesterol-depleting drugs, ␤-cyclodextrin and filipin III, attenuated albumin-induced activation of ERK1/ERK2 in our cells.…”

Section: Discussionmentioning

confidence: 99%

Albumin Activates ERK Via EGF Receptor in Human Renal Epithelial Cells

Reich¹,

Tritchler²,

Herzenberg³

et al. 2005

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.

“…In addition, other non-EGFR ligands, such as angiotensin II and endothelin 1, and some environmental stimuli, such as oxidative stress, can also induce EGFR transactivation. [37][38][39][40] Because all these stimuli can induce renal fibrogensis, [41][42][43] EGFR may act as a common mediator in transducing diverse signals that lead to renal fibrosis.…”

mentioning

confidence: 99%

EGF Receptor Inhibition Alleviates Hyperuricemic Nephropathy

Liu¹,

Wang²,

Yang

et al. 2015

141

Hyperuricemia is an independent risk factor for CKD and contributes to kidney fibrosis. In this study, we investigated the effect of EGF receptor (EGFR) inhibition on the development of hyperuricemic nephropathy (HN) and the mechanisms involved. In a rat model of HN induced by feeding a mixture of adenine and potassium oxonate, increased EGFR phosphorylation and severe glomerular sclerosis and renal interstitial fibrosis were evident, accompanied by renal dysfunction and increased urine microalbumin excretion. Administration of gefitinib, a highly selective EGFR inhibitor, prevented renal dysfunction, reduced urine microalbumin, and inhibited activation of renal interstitial fibroblasts and expression of extracellular proteins. Gefitinib treatment also inhibited hyperuricemia-induced activation of the TGF-b1 and NF-kB signaling pathways and expression of multiple profibrogenic cytokines/chemokines in the kidney. Furthermore, gefitinib treatment suppressed xanthine oxidase activity, which mediates uric acid production, and preserved expression of organic anion transporters 1 and 3, which promotes uric acid excretion in the kidney of hyperuricemic rats. Thus, blocking EGFR can attenuate development of HN via suppression of TGF-b1 signaling and inflammation and promotion of the molecular processes that reduce uric acid accumulation in the body. Serum uric acid is enhanced in patients with CKD regardless of whether it is primary or secondary. Hyperuricemia-related diseases were historically viewed with limited interest. 1 However, increasing evidence has indicated that the increased level of uric acid is tightly associated with the development and progression of CKD as well as many other diseases, such as hypertension, cardiovascular diseases, and diabetes. [2][3][4][5][6][7] For example, a recent meta-analysis of a prospective cohort study showed a 12% rise in mortality for every 1-mg/dl rise in serum uric acid in persons with coronary heart disease. 8 Other pilot investigations indicate that lowering plasma uric acid concentrations slows and delays the development of CKD. [9][10][11][12][13][14][15] Thus, uric acid is likely an important mediator and risk marker in CKD.Uric acid is the final metabolic product of purine metabolism in humans and is excreted in urine. Serum uric acid levels are controlled by the balance of