Proteomics Study On Serum-derived Exosomes From Patients With Malignant Tumors

Exosomes are small extracellular vesicles,which are actively secreted by living cells.They contain proteins,nucleic acids,lipids,and other biomolecules.They can participate in information transmission between cells and play an essential role in the development of tumors.Exosomes may contain specific biomolecules from parental tumor cells.In recent years,exosomes have been considered as a new carrier of biomarkers for tumor diagnosis and prognosis,which has potential clinical application value.The purpose of this study is to analyze the expression profiles of serum-derived exosomes from heathy controls and malignant patients(including gastric cancer,colorectal cancer,and prostate cancer patients).Then,we aim to screen tumor-related proteins in exosomes to provide ideas for exploring new biomarkers and therapeutic targets for malignant tumors.Due to the lack of standardized exosomes isolation methods,it’s hard to ensure the yield and purity of exosomes.This situation creates a technical obstacle for the discovery of tumor biomarkers based on exosomes.Therefore,we compared several methods for exosomes isolation,including ultracentrifugation,polymer precipitation,and membrane affinity adsorption.The particle concentration,particle size distribution,protein yield,and the expression of exosomes marker were detected.Then,the conditions and methods for exosomes isolation suitable for this study were determined.Next,we collected serum samples from healthy people and cancer patients(including gastric cancer,colorectal cancer,and prostate cancer patients).We isolated and characterized the serum-derived exosomes from healthy people and cancer patients.The results showed that there was no significant difference in the morphology and particle size distribution of exosomes from serum sources between patients with gastric cancer,colorectal cancer,prostate cancer,and healthy people.Furthermore,we analyzed the protein expression profiles of the exosomes of the above groups with the method of label-free quantitative proteomics.The results showed that 372,377,373,and 412 proteins were identified in the healthy control group,the gastric cancer group,the colorectal cancer group,and the prostate cancer group,respectively.We screened 218 proteins with a different expression between the healthy control group and at least one tumor group.We analyzed their biological functions and protein-protein interactions with various bioinformatics analyses.The human 26 S proteasome a subunit a3 and 6(PSMA3 and PSMA6)were further analyzed by the western blot analysis.Compared with healthy people and patients with early gastric cancer,the expression level of exosomal PSMA3 and PSMA6 in patients with advanced metastatic gastric cancer was significantly higher,suggesting that PSMA3 may be a new diagnostic marker for clinical staging of gastric cancer.Still,this finding needs to be further verified by expanding samples.This study provided a comprehensive description of serum exosomal proteins from patients with gastric cancer,colorectal cancer,and prostate cancer.It provides new resources for further exploring the pathogenesis of gastric cancer,colorectal cancer,and prostate cancer,and for exploring potential biomarkers and therapeutic targets of gastric cancer,colorectal cancer,and prostate cancer.