Inhibition of ubiquitin specific peptidase 14 (USP14) promotes ER-phagy by inducing ER stress in human hepatoma HepG2 cells

Autophagy plays a critical role in regulating the quality and quantity of cellular compartments; however, the mechanisms governing endoplasmic reticulum (ER) autophagy (ER-phagy) are still largely undefined. In this study, we identified several inhibitors of USP14, a ubiquitin-specific protease, including IU1 and b-AP15, as novel ER-phagy inducers through chemical library screening. While USP14 is known to act as an ER stress inducer, its precise role in ER-phagy remains unclear. Our findings demonstrate that treatment with either IU1 or b-AP15 induces ER-phagy by increasing ER stress in HepG2 cells. Similarly, depletion of USP14 augments ER-phagy and the ER stress response. The blockage of autophagy using an ULK1 inhibitor, SBI0206965, impedes ER-phagy. Moreover, inhibition of ER stress with tauroursodeoxycholic acid reverses ER-phagy by alleviating ER stress in HepG2 cells. We also found that suppression of the stress kinase JNK inhibited ER-phagy in IU1-treated cells. In conclusion, the results of this study suggest that the inhibition of USP14 accelerates ER-phagy by enhancing ER stress and JNK activation in HepG2 cells.