Autophagy contributes to the selective degradation of liquid droplets, including the P-Granule, Ape1-complex and p62/SQSTM1-body, although the molecular mechanisms and physiological relevance of selective degradation remain unclear. In this report, we describe the properties of endogenous p62-bodies, the effect of autophagosome biogenesis on these bodies, and the in vivo significance of their turnover. p62-bodies are low-liquidity gels containing ubiquitin and core autophagy-related proteins. Multiple autophagosomes form on the p62-gels, and the interaction of autophagosome-localizing Atg8-proteins with p62 directs autophagosome formation toward the p62-gel. Keap1 also reversibly translocates to the p62-gels in a p62-binding dependent fashion to activate the transcription factor Nrf2. Mice deficient for Atg8-interaction-dependent selective autophagy show that impaired turnover of p62-gels leads to Nrf2 hyperactivation in vivo. These results indicate that p62-gels are not simple substrates for autophagy but serve as platforms for both autophagosome formation and anti-oxidative stress.

Resistance to anticancer agents has been an obstacle to developing therapeutics and reducing medical costs. Whereas sorafenib is used for the treatment of human hepatocellular carcinoma (HCC), resistance limits its efficacy. p62, a multifunctional protein, is overexpressed in several HCC cell lines, such as Huh-1 cells. Phosphorylated p62 (p-p62) inhibits the protein–protein interaction (PPI) between Keap1 and Nrf2, resulting in the Nrf2 overactivation that causes drug resistance. We have found a unique Nrf2 inactivator, named K67, that inhibited the PPI between Keap1 and p-p62 and attenuated sorafenib resistance in Huh-1 cells. Herein, we designed and synthesized novel K67 derivatives by modification of the substituent at the 4-position of the two benzenesulfonyl groups of K67. Although these new derivatives inhibited the Keap1-p-p62 PPI to a level comparable to or weaker than that of K67, the isopropoxy derivative enhanced the sensitivity of Huh-1 cells to sorafenib to a greater extent than K67 without any influence on the viability of Huh-7 cells, which is a nonresistant HCC cell line. The isopropoxy derivative also increased the sensitivity of Huh-1 cells to regorafenib, which suggests that this derivative has the potential to be used as an agent to overcome chemoresistance based on Nrf2 inactivation.