1. ¹Graduate Institute of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan
2. ²Department of Nephrology, Kaohsiung Medical University, Kaohsiung, Taiwan
3. ³Department of Biochemistry, Kaohsiung Medical University, Kaohsiung, Taiwan
4. ⁴Department of Biological Science and Technology, Chung Hwa College of Medical Technology, Tainan, Taiwan

Correspondence: L-Y Chuang, Department of Biochemistry, Kaohsiung Medical University, 100 Shi-Chuan 1st Road, Kaohsing 807, Taiwan. E-mail: jyuh@mail.nsysu.edu.tw

Received 25 May 2006; Revised 16 December 2006; Accepted 27 December 2006; Published online 28 February 2007.

Abstract

Transforming growth factor- (TGF-), Smads, and the cyclin-dependent kinase (cdk) inhibitor p21^WAF1 are important in the pathogenesis of diabetic tubular hypertrophy. Phosphoinositide 3 kinase (PI3K)/Akt kinase activity is increased in diabetic glomerular hypertrophy. Thus, we studied the role of PI3K in high glucose (30 mM)-induced p21^WAF1, Smad2/3, and cell cycle-dependent hypertrophy in LLC-PK1 cells. We found that high glucose time-dependently (1–48 h) increased PI3K/Akt kinase activity. LY294002 (a PI3K inhibitor) attenuated high glucose-induced cell cycle-dependent (G₀/G₁ phase) hypertrophy at 72 h while attenuating high glucose-induced p21^WAF1 gene transcription and protein expression at 36–48 h. LY294002 also attenuated high glucose-induced binding of p21^WAF1 to the cyclin E/cdk2 complex, whereas attenuating high glucose-induced TGF- bioactivity, Smad2/3 phosphorylation, and Smad2/3 DNA-binding activity at 36–48 h. We concluded that PI3K is required for high glucose-induced cell cycle-dependent hypertrophy, p21^WAF1 transcription and expression, p21^WAF1 binding to the cyclin E/cdk2 complex, TGF- bioactivity, and Smad2/3 activity in LLC-PK1 cells.