PSMD2 Promotes Proliferation Via ASS1-mediated Decrease Of Autophagy In Esophageal Squamous Cell Carcinoma

BACKGROUND&AIMS:Ubiquitin-proteasome system(UPS)and Autophagy-lysosomal system(ALS)are closely related and jointly control the balance of intracellular proteins.Non-ATPase proteasome 26S subunit 2(Proteasome 26S Subunit,Non-ATPase2,PSMD2)has been proven to be an oncogene in many cancers.The function of PSMD2 in UPS has been well studied,but it is unclear whether it plays a role in the autophagy system.In this study,we found that PSMD2 amplification and overexpression promote cell proliferation and tumor growth in esophageal squamous cell carcinoma(ESCC).Under the condition of serum(Foetal Bovine Serum,FBS)starvation.PSMD2 attenuates the formation of autophagosomes in ESCC cells.It is worth noting that the proliferation inhibited by PSMD2 depletion can be reversed by blocking the autophagy-related protein 7(Autophagy Related7,ATG7)knocking down the autophagy pathway in cells.In addition,through proteomics and functional assays,we determined the key role of argininosuccinate synthetase 1,ASS1 in PSMD2-induced proliferation dependent on autophagy inhibition.Mechanismally,PSMD2 activates the mTOR/Akt signaling pathway by up-regulating ASS1.Overall,these results demonstrate that PSMD2 promotes cell proliferation by reducing autophagy in ESCC.Therefore,PSMD2 may be a promising prognostic marker for autophagy.Methods:We found that PSMD2,as a newly discovered receptor of the proteasome system,is highly expressed in esophageal squamous cell carcinoma(ESCC)and significantly affects the prognosis.In order to explore the molecular mechanism,we overexpress and knock down this gene by means of lentivirus and interfering RNA,and analyze its effect on the proliferation and migration of esophageal squamous cell carcinoma cell lines in vitro.At the same time,tumor formation experiments in immunodeficient mice(NOD/scid)proved that it also has an effect on proliferation in vivo.In addition,we conducted further verification in 144 cases of tissue microarrays by immunohistochemistry,and confirmed that it is highly expressed in tumors and is significantly related to clinical staging.In the case of serum starvation,PSMD2 attenuates the formation of autophagosomes in ESCC cells.In order to further explore the mechanism of its function.We carried out proteomic identification,and carried out proteomic identification of the esophageal squamous cell line that knocked down the gene and the corresponding control cell line to find the different proteins.The results were mainly enriched in the arginine metabolism pathway.Among them,ASS1 is a key enzyme in this pathway.Since both the proteasome system and the autophagy system have important effects on protein homeostasis,and the mTOR/Akt signaling pathway plays an important role in amino acid metabolism,it is considered that PSMD2 activates mTOR/by up-regulating ASS1.Akt signaling pathway.Results:Through the analysis of our database and the TCGA database,we found that the expression of PSMD2 in esophageal squamous cell carcinoma tissue was significantly higher than that in normal tissues adjacent to the cancer,and the high expression of PSMD2 was significantly related to the patient's stage,distant metastasis and poor prognosis.At the same time,because PSMD2 is a proteasome receptor,it affects the homeostasis of proteins in the body,and the study of the interaction between the proteasome system and the autophagy system is not clear.Therefore,through serum starvation stimulation,we found that PSMD2 overexpressed esophageal squamous cell lines formed The number of autophagosomes decreases,and vice versa.At the same time,in cell lines knocked down PSMD2,the in vitro proliferation ability of esophageal squamous cell carcinoma cell lines decreased.On this basis,when ATG7,a key gene of the autophagy system,was knocked down at the same time,the decrease in proliferation was restored.It shows that PSMD2 can indeed affect the autophagy pathway and thus affect the proliferation of tumor cells.At the same time,the results of proteomics found that the key enzyme of arginine metabolism played a key role.Therefore,it is considered that PSMD2 inhibits autophagy by up-regulating ASS1 to activate the mTOR/Akt signaling pathway and promote tumor proliferation.Conclusion:PSMD2 plays an important role in the occurrence and development of esophageal squamous cell carcinoma.Up-regulation of PSMD2 leads to the up-regulation of ASS1,which activates the mTOR/Akt signaling pathway,inhibits the autophagy process and promotes the proliferation of esophageal squamous cell carcinoma.PSMD2 may be a potential indicator of a poor prognosis...