Enhanced Epithelial-to-Mesenchymal Transition Associated with Lysosome Dysfunction in Podocytes: Role of p62/Sequestosome 1 as a Signaling Hub

Abstract

Background: Autophagy is of importance in the regulation of cell differentiation and senescence in podocytes. It is possible that derangement of autophagy under different pathological conditions activates or enhances Epithelial-to-Mesenchymal Transition (EMT) in podocytes, resulting in glomerular sclerosis. To test this hypothesis, the present study produced lysosome dysfunction by inhibition of the vacuolar H⁺-ATPase (V-ATPase) to test whether deficiency of autophagic flux leads to enhancement of EMT in podocytes. Methods and Results: By Western blot and confocal analysis, lysosome inhibition using a V-ATPase inhibitor or its siRNA was found to markedly decreases the epithelial markers (P-cadherin and ZO-1) and increases the mesenchymal markers (FSP-1 and α-SMA). This enhancement was accompanied by deficient autophagic flux, as demonstrated by marked increases in LC3B-II and p62/Sequestosome 1. However, inhibition of autophagosome formation using spaudin-1 significantly attenuated both enhancement of EMT and deficiency of autophagic flux. To explore the mechanisms by which deficient autophagic flux enhances EMT, we tested the role of accumulated p62 as a signal hub in this process. Neither the nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear kappa-light-chain-enhancer pathways of p62 contributed to enhanced EMT. However, inhibition of cyclin-dependent kinase 1 (CDK1) activity reduced the phosphorylation of p62 and enhanced EMT in podocytes similar to lysosome dysfunction. Conclusion: The lack of phosphorylated p62 leads to a faster exit from cell mitosis, enhanced EMT associated with lysosome dysfunction may be attributed to accumulation of p62 and associated reduction of p62 phosphorylation.