Autophagy Inhibition Sensitizes Renal Tubular Epithelial Cell to G1 Arrest Induced by Transforming Growth Factor beta (TGF-β)

Background: Cell cycle arrest and autophagy have been demonstrated to be involved in various transforming growth factor (TGF)-beta-mediated phenotype alterations of tubular epithelial cells (TECs) and tubulointerstitial fibrosis. But the relationship between cell cycle arrest and the autophagy induced by TGF-beta has not been explored well. Material/Methods: The effects of autophagy inhibition on TGF-beta-induced cell cycle arrest in TECs were explored in vitro. Human kidney-2 (HK-2) cells were stimulated by TGF-beta with or without a combined treatment of autophagy inhibitor chloroquine (CQ) or bafilomycin A1 (Baf). Results: Autophagy inhibition by CQ or Baf promotes the suppression of growth in TGF-beta-treated HK-2 cells, as detected by the Cell Counting Kit-8 (CCK-8) method. In addition, CQ or Baf stimulation enhances G1 arrest in TGF-beta treated HK-2 cells, as investigated using propidium iodide (PI) staining and flow cytometry, which was further confirmed by a decrease in the expression of phosphorylated retinoblastoma protein (p-RB) and cyclin-dependent kinase 4 (CDK4). The upregulation of p21 induced by CQ or Baf may mediate an enhanced G1 arrest in TGF-beta treated HK-2 cells. Western blot analysis showed that TGF-beta-induced expression of extracellular matrix fibronectin was notably upregulated in the presence of autophagy inhibitors. Conclusions: Inhibition of autophagy sensitizes the TECs to G1 arrest and proliferation suppression induced by TGF-beta that contributes to the induction of tubulointerstitial fibrosis.