USP22Induces Autophagy And Correlates With Poor Prognosis Of Pancreatic Cancer

Objective: Pancreatic cancer is one of common cancer for human, the incidence andmortality increase in recent years. Although surgery combined with chemo-andradio-therapy is the main treatment of pancreatic cancer, the prognosis still remians poor,which call for a new target for therapy the pancreatic cancer. Ubiquitin-specific protease22(USP22) is a component of the transcription regulatory histone acetylation complexSAGA, therefore broadly regulating gene transcription and correlating with cancerprogression, metastasis and prognosis. Autophagy, a cellular pathway with dualfunctions promotes either cell survival or cell death. Pancreatic cancer is known to havehigher level of autophagy than other epithelial cancers. Microtubule-associate protein1light chain3(LC3) is a key structural and regulatory protein for the formation ofautophagosome, it is used to detect the level of autophagy. However, the regulatoryeffect of USP22on autophagy in pancreatic cancer remains unclear. To explore themechanism of USP22affecting the pancreatic cancer, this study investigated therelationship between USP22and LC3in pancreatic cancer tissues and the prognosis ofpancreatic cancer patients. Our results showed that the the expression of USP22relatedto autophagy in pancreatic cancer cell line Panc-1and affected the survival of Panc-1cells, thus explored the theoretical basis for the treatment of pancreatic cancer inclinical. Methods: Pancreatic cancer and adjunct non-cancerous tissues sections were applied byparaffin wax embedding method. IHC staining was performed to detect USP22and LC3in situ. The relationship among the prognosis of pancreatic cancer patients, theexpression of USP22and LC3in pancreatic cancer tissues were analyzed by consultingthe case history and follow-up files.Three test groups were established as control group, USP22overexpression groupand USP22inhibition group by transient transfection. We detected the relationshipbetween USP22and autophagy by western blot, immunofluorescence, transmissionelectron microscopy. LY294002(PI3K inhibitor) and PD98059(ERK1/2inhibitor) wereused as inhibitor of PI3K/AKT/PKB and Ras/Raf/MEK/ERK signaling pathways, andinvestigated through which signaling pathway that USP22affects to autophagy bywestern blot. With autophagy inhibitor3-MA treatment, we surveyed the effect ofUSP22and autophagy to cell proliferation, apoptosis, chemotherapy resistance andnutritional deficiency resistance by using flow cytometry, CCK-8kit and DCFH-DAkit.Results: The expression of USP22and LC3in pancreatic cancer tissues weresignificantly increased compared with adjunct non-cancerous tissues (P=0.000,P=0.011). Correlative analysis showed that there was a positive correlation between theexpression of USP22and LC3in pancreatic cancer (ρ=0.385, P=0.001) as well as highexpression of USP22and LC3with poor prognosis. The expression of USP22related totumor differentiation, lymphatic vessel infiltration, pancreatic external invasion andAJCC cancer stage (P<0.05). LC3correlated with tumor differentiation, lymphaticvessel infiltration and AJCC cancer stage (P<0.05).USP22overexpression group revealed high expression of LC3and low expressionof autophagy substrate protein SQSTM1. Alteration of the expression of Beclin-1wasnot yet observed. Acidic material, lysosomes and autophagosomes increased in USP22overexpression Panc-1cells. Inhibition of phosphorylation-ERK1/2decreased the levelof autophagy, but inhibition of phosphorylation-AKT had no obvious effect toautophagy. Finally, the overexpression of USP22and the high level of autophagypromoted cell proliferation, chemotherapy resistance and nutritional deficiency resistance, but had no significant effect on apoptosis.Conclusion: The expression of USP22and LC3in pancreatic cancer are higher thannormal pancreatic tissue. USP22may induces autophagy by the phosphorylation ofERK1/2, and promote pancreatic cancer cells survival, correlate with poor prognosis ofpancreatic cancer patients. USP22and autophagy may become new targets for diagnosisand therapy of pancreatic cancer in the future. Pancreatic cancer cells can be moresensitive to chemotherapy due to the inhibition of USP22and autophagy which lead tolow survival of pancreatic cancer cells.