Albumin-induced epithelial-mesenchymal transition and ER stress are regulated through a common ROS-c-Src kinase-mTOR pathway: effect of imatinib mesylate

• Published in: American journal of physiology. Renal physiology 2011-05, Vol.300 (5), p.F1214-F1222
• Main Authors: Lee, Ji Young, Chang, Jai Won, Yang, Won Seok, Kim, Soon Bae, Park, Su Kil, Park, Jung Sik, Lee, Sang Koo
• Format: Article
• Language: English
• Subjects: Albumins - metabolism; Antioxidants; Antioxidants - pharmacology; Benzamides; Blotting, Western; Cell Line; Cells; Cytoprotection; Endoplasmic Reticulum - drug effects; Endoplasmic Reticulum - enzymology; Endoplasmic Reticulum - pathology; Epithelial Cells - drug effects; Epithelial Cells - enzymology; Epithelial Cells - pathology; Epithelial-Mesenchymal Transition - drug effects; Epithelial-Mesenchymal Transition - genetics; Gene expression; Gene Expression Regulation - drug effects; Humans; Imatinib Mesylate; Kidney diseases; Kidney Tubules, Proximal - drug effects; Kidney Tubules, Proximal - enzymology; Kidney Tubules, Proximal - pathology; Morphology; Phosphorylation; Piperazines - pharmacology; Polymerase Chain Reaction; Protein Kinase Inhibitors - pharmacology; Protein-Tyrosine Kinases - antagonists & inhibitors; Protein-Tyrosine Kinases - genetics; Protein-Tyrosine Kinases - metabolism; Proteins; Proto-Oncogene Proteins - antagonists & inhibitors; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Pyrimidines - pharmacology; Reactive Oxygen Species - metabolism; RNA, Messenger - metabolism; Signal Transduction - drug effects; src-Family Kinases; Stress, Physiological - drug effects; Stress, Physiological - genetics; Time Factors; TOR Serine-Threonine Kinases - antagonists & inhibitors; TOR Serine-Threonine Kinases - genetics; TOR Serine-Threonine Kinases - metabolism
• ISSN: 1931-857X; 1522-1466
• DOI: 10.1152/ajprenal.00710.2010

The epithelial-mesenchymal transition (EMT) and endoplasmic reticulum (ER) stress induced by urinary protein, particularly albumin, play an important role in tubulointerstitial injury. However, signaling pathways regulating both albumin-induced EMT and ER stress are not precisely known. We postulated that reactive oxygen species (ROS), c-Src kinase, and mammalian target of rapamysin (mTOR) would act as upstream signaling molecules. We further examined the effect of imatinib mesylate on these processes. All experiments were performed using HK-2 cells, a human proximal tubular cell line. Protein and mRNA expression were measured by Western blot analysis and real-time PCR, respectively. Exposure of tubular cells to albumin (5 mg/ml) for up to 5 days induced EMT in a time-dependent manner, as shown by conversion to the spindle-like morphology, loss of E-cadherin protein, and upregulation of α-smooth muscle actin mRNA and protein. Albumin also induced ER stress as evidenced by phosphorylation of eukaryotic translation initiation factor-2α and increased expression of GRP78 mRNA and protein. Albumin induced ROS, c-Src kinase, and mTOR as well. Antioxidants, c-Src kinase inhibitor (PP2), and mTOR inhibitor (rapamycin) suppressed the albumin-induced EMT and ER stress. Antioxidants and PP2 inhibited the albumin-induced c-Src kinase and mTOR, respectively. Imatinib suppressed the albumin-induced EMT and ER stress via inhibition of ROS and c-Src kinase. Imatinib also inhibited the albumin-induced mRNA expression of MCP-1, VCAM-1, transforming growth factor (TGF)-β1, and collagen I (α1). In conclusion, the ROS-c-Src kinase-mTOR pathway played a central role in the signaling pathway that linked albumin to EMT and ER stress. Imatinib might be beneficial in attenuating the albumin-induced tubular injury.