The Function Mechanism Of Sialic Acid In The Metastasis Of Colorectal Cancer

Colorectal cancer,CRC is one of the most common malignant tumors in the world.Tumor metastasis is the main cause of death in CRC patients.The function mechanism of the CRC metastasis is still not clear.Therefore,it's of great significance to have a better understanding of the mechanism of metastasis to improve the survival rate and the prognosis of CRC patients,as well as to find target molecule for clinical therapy.Glycosylation is the most common post-translational modification.Sialylation is the most common form of modification at the end of the glycan,and it has been reported that the expression of ?-2,6 sialylation in colorectal cancer is significantly up-regulated,but its substrate and related mechanism are still unclear.In this study,based on metabolic labeling and glycomics,we identified and screen many sialylated membrane proteins related to metastasis in two colon cell lines with different metastatic potential abilities.Then,we searched for the specific sialylated membrane protein substrates of ST6GAL1,which primarily catalyzes terminal ?-2,6 sialylation on N-glycans,and elucidate the mechanism in CRC metastasis process regulated by ST6GAL1 and its substrates.Firstly,two colon cell lines with different metastatic potential were taken as research object,SW480(low metastatic ability)and SW620(high metastatic ability).We enriched and identified many sialylated membrane proteins using metabolic labeling and glycomics strategy,and found at least 28 sialylated membrane proteins greatly differently expressed in the two cells,including Met,E-Cadherin,CD47,ICAM-1,MCAM,et al.And these proteins are all reported to be closely associated with the tumorigenesis or metastasis of CRC.We also examined the expression of the 20 sialyltransferase in two cell lines,found the ST6GAL1 expression was significantly different,laying better foundation for further study on the regulation mechanism of ST6GAL1 in CRC.Secondly,we detected the ST6GAL1 expression in 62 paired tumor/normal CRC specimens at different stages,noticed that the ST6GAL1 was expressed significantly higher at the stage I and II than stage III and IV,showing a dynamic change in CRC progression,which suggested ST6GAL1 may negatively regulate CRC metastasis.In order to systematically study the substrate proteins of ST6GAL1,we specifically labeled and enriched sialylated membrane proteins in wild-type cells and ST6GAL1 overexpression cells,showed that 318 membrane proteins were differentially affected by ST6GAL1 overexpression,which were involved in cellular movement,cell death and survival,cellular growth and proliferation,et al by IPA analysis.We furtherly found,ST6GA1 overexpression could inhibit EGFR signaling pathway.Besides,the ICAM-1 protein was significantly upregulated by increasing its protein stability after ST6GA1 overexpression.Then,we also checked ICAM-1 expression in CRC samples,just like the ST6GAL1 expression pattern,ICAM-1 was expressed significantly higher at the stage I and II than stage III and IV,suggesting ST6GAL1 may negatively correlate with CRC progression by increasing the stability of ICAM-1.In conclusion,based on the clinical issues of high mortality in CRC patients with metastasis,using metabolic labeling and glycomics strategy,we systematically identified sialylated membrane proteins related to CRC metastasis,and clarified the functional mechanism of this progression regulated by ST6GAL1 through its sialylated protein substrates,and aimed at providing meaningful scientific clues for clinical invention,drug target and biomarker discovery in CRC patients.