Study On The Mechanism Of PD-L1 Lactylation Driven By Latate To Promote Gastric Cancer Progression

Objective: Lactate is an important component in the tumor microenvironment(TME).By regul ating various signaling pathways,it maintains the immunosupp ression of TME and promotes tumor immune escape,metastasis and drug resistance.The purpose of this study is to investigate the role and mechanism o f lactate-regulated programmed death ligand 1(PD-L1)affecting the biological function o f gastric cancer cells.Methods:(1)The effects of lactate on the proliferation,migration,invasion,drug resistance and apoptosis of gastric cancer cell line SG C-7901 were detected by CCK-8 method,scratch test,Transwell migration and invasion test,and flow cytometry.(2)SGC-7901 cells were treated with different concentrations of lactate,and the expression of PD-L1 was detected by RT-q PCR and Western blot.Sh RNA was used to knock down the expression of P D-L1 in SGC-7901 cells,and the knockdown e fficiency was dete cted by RT-q PCR and Western blot.On the basis of knocking down PD-L1,lactate was used to treat SGC-7901 cells to observe whether the effec t of lactate on the biological activity of gastric canc er cells was dependent on the PD-L1 pathway.(3)Nuclear protein separation and immunofluorescence staining were used to observe the subcellular localization of PD-L1 in SGC-7901 cells,and Western blot was used to detect the expression of PD-L1 in the nucleus and cytoplasm.Co-IP assay was used t o detect the lactylation level of PD-L1 in SGC-7901 cells.After treatment with lactylation inhibitor sodium oxamate(SO),the lactylation level and subcellular localization of PD-L1 were detected.(4)Immunohistochemical st aining was used to detect the correlation between the expression of lactate dehydrogenase(LDHA)and PD-L1 in gastric cancer tissue samples of clinical patients,and the Kmplot database was used to analyze the relationship between the expressio n level of LDHA or PD-L1 and the overall survival rate of gastric cancer patients.Results:(1)20m M concentration of lactate can inhibit the proliferation of gastric cancer cells,while 0-15 m M low concentration of lactate has no obvious effect on the pr oliferation.Lactate can promote the migrat ion and invasion ability of gastric cancer cells,and improve the tolerance of gastric cancer cells to chemotherapy drug s,but has no obvious effect on the apoptosis of gastric cancer cells.(2)The expression of PD-L1 in gastric cancer cells showed a lactat e concentration-dependent increase.After knocking down PD-L1,the migration,invasion ability and chemotherapy re sistance of gastric cancer cells were significantly inhibited,and their migration and invasion abilities were not affected after lactate supplementation Significantly improved.(3)After lactate treatment,the expression level of PD-L1 and the modification level of lysine lactylation(Kla)in the nucleus of gastric cancer cells were significant ly increased.SO can inhibit PD-L1 lactylation and nuclear transl ocation.(4)The expressions of LDHA and PD-L1 in tumor tissues of patients with gastric cancer were increased compared with those in adjacent tissues,and there was a positive correlation betwe en the two expressions.The expressions of PD-L1 and LDHA in patients with gastric cancer were negatively correlated with the overall survival rate,which had certain guiding value for the prognosis of patients with gastric cancer.Conclusions: Lactate drives the lactylation of PD-L1 protein,promotes the expression of PD-L1 in the nucleu s of gastric cancer cells,and plays an important role in tumor metastasis and drug resistance.This study revealed a new pathway of PD-L1 regulation and provided a new dir ection for the treatment of gastric cancer.