Phosphoinositide 3-kinase is required for high glucose-induced hypertrophy and p21WAF1 expression in LLC-PK1 cells

Transforming growth factor-β (TGF-β), Smads, and the cyclin-dependent kinase (cdk) inhibitor p21WAF1 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 p21WAF1, 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 p21WAF1 gene transcription and protein expression at 36–48 h. LY294002 also attenuated high glucose-induced binding of p21WAF1 to the cyclin E/cdk2 complex, whereas attenuating high glucose-induced TGF-β 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, p21WAF1 transcription and expression, p21WAF1 binding to the cyclin E/cdk2 complex, TGF-β bioactivity, and Smad2/3 activity in LLC-PK1 cells.