ULK1 and gastric cancer: To further verify the effect of the ubiquitination of ULK1 on the role of AQP5 in regulating GC-CSCs, we knocked down the expression of endogenous ubiquitin and generated GC-CSCs that exogenously expressed HA-ubiquitin (K63-Ub) or K63R-mutant ubiquitin (K63R).