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

Transforming growth factor-beta (TGF-beta), 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 (30mm)-induced p21(WAF1), Smad2/3, and cell cycle- dependent hypertrophy in LLC-PK1 cells. We found that high glucose time- dependently (1 -48h) increased PI3K/Akt kinase activity. LY294002 (a PI3K inhibitor) attenuated high glucose-induced cell cycledependent (G(0)/G(1) phase) hypertrophy at 72h 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-beta 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-beta bioactivity, and Smad2/ activity in LLC-PK1 cells.