Role of ERK1/2 and PI3-K in the regulation of CTGF-induced ILK expression in HK-2 cells.
BACKGROUND
Previous studies revealed that integrin-linked kinase (ILK), an intracellular serine/threonine protein kinase, is a critical mediator for tubular epithelial to mesenchymal transition (EMT), and likely plays an important role in the pathogenesis of chronic kidney fibrosis. However, the exact signal pathway has not been well understood. In this study, we investigated the role of extracellular regulating kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3-K) in the regulation of ILK expression by connective tissue growth factor (CTGF) in HK-2 cells.


METHODS
Experiments were performed on transformed (human kidney cell (HKC)-clone 2) human proximal tubular epithelial cells (PTECs). Induction of ILK in response to CTGF was studied at the mRNA level by real-time PCR and protein by immunoblotting. Chemical inhibitors were used to assess the role of MEK/ERK1/2, PI3-K, and P38 MAPK signaling pathways in induction of ILK by CTGF.


RESULTS
CTGF induced ILK protein expression in HK-2 cells in a time- and dose-dependent manner. There was a 5.638-fold (control: 1.000+/-0.290, 50 ng/ml: 5.638+/-1.200; *P<0.05 vs. control) and 5.740-fold (0 h: 1.000+/-0.498, 48 h: 5.740+/-1.465, *P<0.05 vs. control) increase compared to control respectively. CTGF-induced ILK expression was partially reduced by inhibiting ERK1/2 and PI3-K activation. There was no influence of ILK expression by inhibiting P38 MAPK activation when cells treated with CTGF.


CONCLUSIONS
CTGF induces the expression of ILK protein in HK-2 cells. This induction is partially dependent on MEK/ERK1/2 and PI3-K signaling pathways. Inhibiting CTGF-induced ILK by targeting PI3-K and/or MEK/ERK1/2 signaling pathways could be of therapeutic value in renal fibrosis.
Liu
Xiao-Cong
XC
Institute of Nephrology, Zhong Da Hospital, Southeast University, Nanjing, China.
Liu
Bi-Cheng
BC
Zhang
Xiao-Liang
XL
Li
Min-Xia
MX
Zhang
Jian-Dong
JD
D002461:Cell Line, Transformed; D055513:Connective Tissue Growth Factor; D004847:Epithelial Cells / Q000502:physiology*; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D015854:Up-Regulation; D000099200:Scaffold Protein ILK
D055513:Connective Tissue Growth Factor; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D000099200:Scaffold Protein ILK; C526317:CCN2 protein, human