[Proteomic analysis of differentially expressed proteins in gastrointestinal neuroendocrine tumors and their liver metastasis].

To investigate the differences of protein expressions in the primary tumors, adjacent tissues, and metastatic tumors of gastrointestinal neuroendocrine neoplasms. Nine patients with gastrointestinal neuroendocrine tumors (GI-NENs) with liver metastasis who underwent surgery at the National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences from July 2015 to April 2019 were selected. The protein expressions of the primary tissues, liver metastatic tissues, and adjacent tissues were detected by the data independent acquisition (DIA) technology. <0.05 and | logFC|>0.5 (FC as the difference multiple) were used as the criteria to identify the differentially expressed proteins in the primary tissues vs adjacent tissues, primary tissues vs liver metastatic tissues, primary tissues with different degrees of differentiation, and liver metastatic tissues with different degrees of differentiation. The differentially expressed proteins were investigated by volcano map analysis, cluster analysis, Gene Ontology (GO) function analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Compared with adjacent tissues, 85 proteins were downregulated and 42 proteins were upregulated in the primary tissues of gastric NENs. The differentially expressed proteins were mainly enriched in the biological processes related to the regulation of guanosidase triphosphate activity and the catabolism of deoxyribonucleoside monophosphate, the glycosaminoglycan biosynthesis chondroitin sulfate/dermatan sulfate, pantothenate, and CoA biosynthesis signaling pathways. 114 proteins were downregulated and 155 proteins were upregulated in the primary tissues of intestinal NENs. The differentially expressed proteins were mainly enriched in the biological processes related to glutathione metabolism and sulfur compound metabolism, collecting duct acid secretion, and taurine and hytaurine metabolism signaling pathways. Compared with the primary tissues of neuroendocrine cancers (NECs), 168 proteins were downregulated and 278 proteins were upregulated in G1-2 differentiation primary tissues. The differentially expressed proteins were significantly enriched in biological processes such as DNA metabolism and DNA replication, as well as replication, mismatch repair, and other pathways. Compared with the metastatic tissues of NECs, 95 proteins were downregulated and 97 proteins were upregulated in G1-2 differentiated metastases. The differentially expressed proteins were significantly enriched in the activity and catalytic activity of transcriptional coactivators, base excision repair, and protein efflux pathways. Compared with G1 differentiated primary tissues, 530 proteins were downregulated and 211 proteins were upregulated in G1 differentiated metastatic tissues. Compared with G2 differentiated primary lesions, 53 proteins were downregulated and 96 proteins were upregulated in G2 differentiated metastatic tissues. Compared with the primary lesions of NECs, 109 proteins were downregulated and 92 proteins were upregulated in the metastatic tissues of NECs. In G1 and G2 differentiated GI-NENs, there are many similar signal pathways enriched in differentially expressed proteins between primary lesions and metastases, while only one signal pathway enriched in differentially expressed proteins between primary and metastatic tissues of NECs is the same as that enriched in differentially expressed proteins between primary and metastatic tissues of GI-NENs, which is the drug metabolism signal pathway. The differentially expressed proteins in G1 differentiated primary and metastatic tissues were mainly expressed in cytoplasm (20.26%), mitochondria (18.67%), and nucleus (15.48%). The differentially expressed proteins in the primary and metastatic tissues of G2 differentiation were mainly expressed in the cytoplasm (20.24%), nucleus (18.25%), and cell membrane (15.08%). The differentially expressed proteins in the primary and metastatic tissues of NECs were mainly expressed in the nucleus (23.78%), cytoplasm (22.7%), and cell membrane (11.35%). The protein expressions of GI-NENs in the primary tissues, adjacent tissues, and metastatic tissues were significantly different in different sites and degrees of differentiation.