Egr-1 mediates chronic hypoxia-induced renal interstitial fibrosis via the PKC/ERK pathway

Am J Nephrol. 2014;39(5):436-48. doi: 10.1159/000362249. Epub 2014 May 10.


Background: Chronic hypoxia-induced epithelial-to-mesenchymal transition (EMT) is a crucial process in renal fibrogenesis. Egr-1, as a transcription factor, has been proven to be important in promoting EMT. However, whether it functions in hypoxia-induced renal tubular EMT has not been fully elucidated.

Methods: Egr-1 were detected at mRNA and protein levels by qPCR and Western blot analysis respectively after renal epithelial cells were subjected to hypoxia treatment. Meanwhile, EMT phenotype was also observed through identification of relevant EMT-specific markers. siRNA was used to knock down Egr-1 expression and subsequent changes were observed. Specific PKC and MAPK/ERK inhibitors were employed to determine the molecular signaling pathway involved in Egr-1-mediated EMT phenotype. In vivo assays using rat remnant kidney model were used to validate the in vitro results. Furthermore, Egr-1 expression was examined in the samples of CKD patients with the clinical relevance revealed.

Results: Hypoxia treatment enhanced the mRNA and protein levels of Egr-1 in HK-2 cells, which was accompanied by a reduced expression of the epithelial marker E-cadherin and an enhanced expression of the mesenchymal marker Fsp-1. Downregulation of Egr-1 with siRNA reversed hypoxia-induced EMT. Using the specific inhibitors to protein kinase C (calphostin C) or MAPK/ERK (PD98059), we identified that hypoxia induced Egr-1 expression through the PKC/ERK pathway. In addition, the upregulation of Egr-1 raised endogenous Snail levels, and the downregulation of Snail inhibited Egr-1-mediated EMT in HK-2 cells. Through in vivo assays using rat remnant kidney and CKD patients' kidney tissues, we found that Egr-1 and Snail were overexpressed in tubular epithelial cells with EMT.

Conclusion: Egr-1 may be an important regulator of the development of renal tubular EMT induced by hypoxia through the PKC/ERK pathway and the activation of Snail. Targeting Egr-1 expression or activity might be a novel therapeutic strategy to control renal fibrosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cadherins / metabolism
  • Calcium-Binding Proteins / metabolism
  • Cell Hypoxia
  • Cells, Cultured
  • Early Growth Response Protein 1 / analysis
  • Early Growth Response Protein 1 / genetics
  • Early Growth Response Protein 1 / metabolism*
  • Epithelial Cells
  • Epithelial-Mesenchymal Transition*
  • Fibrosis / metabolism
  • Flavonoids / pharmacology
  • Gene Knockdown Techniques
  • Humans
  • Kidney Tubules / chemistry
  • Kidney Tubules / metabolism
  • Kidney Tubules / pathology*
  • MAP Kinase Signaling System*
  • Male
  • Naphthalenes / pharmacology
  • Protein Kinase C / metabolism*
  • Protein Kinase Inhibitors / pharmacology
  • RNA, Messenger / metabolism
  • RNA, Small Interfering
  • Rats
  • Rats, Sprague-Dawley
  • Renal Insufficiency, Chronic / metabolism*
  • Renal Insufficiency, Chronic / pathology
  • S100 Calcium-Binding Protein A4
  • Snail Family Transcription Factors
  • Transcription Factors / analysis
  • Transcription Factors / metabolism
  • Transfection
  • Up-Regulation / drug effects


  • Cadherins
  • Calcium-Binding Proteins
  • EGR1 protein, human
  • Early Growth Response Protein 1
  • Flavonoids
  • Naphthalenes
  • Protein Kinase Inhibitors
  • RNA, Messenger
  • RNA, Small Interfering
  • S100 Calcium-Binding Protein A4
  • Snai2 protein, rat
  • Snail Family Transcription Factors
  • Transcription Factors
  • S100A4 protein, human
  • Protein Kinase C
  • calphostin C
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one