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

Abstract

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 may enhance Epithelial‐to‐Mesenchymal Transition (EMT) in podocytes, resulting in glomerular injury. The present study tested whether deficiency of autophagic flux leads to enhancement of EMT in podocytes. By Western blot and confocal analysis, lysosome function inhibition by a V‐ATPase inhibitor or its siRNA was found to significantly enhance EMT in podocytes, as shown by marked decreases in epithelial markers (P‐cadherin and ZO‐1) and increases in mesenchymal markers (FSP‐1 and α‐SMA). This enhanced EMT was accompanied by deficient autophagic flux, which was demonstrated by increases in LC3B‐II levels and accumulation of p62. We further confirmed that both enhancement of podocyte EMT and deficiency of autophagic flux due to lysosome dysfunction were significantly attenuated by inhibition of autophagosome formation using SP‐1. 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. It was found that both Nrf2 and NF‐κB pathways regulated by p62 were not involved in enhanced EMT, while inhibition of CDK1 activity reduced phosphorylation of p62 and enhanced EMT in podocytes, an effect on EMT similar to lysosome dysfunction. Given that 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.