Etoposide-Induced Cellular Senescence Suppresses Autophagy in Human Keratinocytes

Autophagy and senescence play important roles in cellular homeostasis. However, it remains unknown whether autophagy positively or negatively affects cellular senescence. We cultured human keratinocytes (HaCaT) with or without etoposide (ETO) treatment to examine whether autophagy mediates induction of DNA damage response (DDR)-related cel-lular senescence. DDR-related cellular senescence was observed in 5.0-mu M ETO-treated cells through increased expression of gamma H2AX, p53 binding protein1 (53BP1), and senescence-associated beta-galactosidase (SA-beta-Gal), whereas no senescent changes were observed in 1.0-mu M ETO-treated cells. Senescent cells also showed increased expression of activated ataxia- telangiectasia mutated (ATM) signaling pathway-related factor, such as pATM, pp53, and p21. The 5.0-mu M ETO-treated se-nescent cells showed downregulated expression of LC3 and Beclin-1, but expression of Rubicon, which is a negative regu-lator of autophagy, was upregulated even though no senescent-induced cells (1.0-mu M treated cells) revealed increased expression of LC3 and Beclin-1. The 1.0-mu M ETO-treated cells pretreated with N-acetylcysteine (NAC) showed increased expression of senescent markers and p21 as well as Rubicon. This study revealed that Rubicon-regulated autophagy mediates ETO-induced DDR-related cellular senescence through the activation of the ATM/p53/p21 signaling pathway. Impaired autophagy due to Rubicon overexpression accelerates induction of DDR-related cellular senescence.