Regulation Of α 2,8-sialyltransferase Ⅵ In Mouse Breast Cancer Metastasis And The Preliminary Research Of The Potential Mechanism

Tumor formation, development and metastasis are closely related to the expression of sugar chains. Glycosylation changes are a universal feature of malignant transformation and tumor progression, and glycosylation changes play roles in a variety of biologic processes such as tumor cell adhesion, migration, invasion, proliferation, apoptosis, cell-cell communication, cell-matrix interaction, differentiation, signal transduction and surface expression of stage specific antigen. The different sialyllinkages are elaborated by different members of the sialyltransferase family. a2,8-sialyltransferase VI(ST8Sia VI) is one of the twenty members of the mouse sialyltransferase family, and it's the first identified sialyltransferase whose preferential substrate is O-glycans. ST8Sia VI exhibits broad substrate specificities for glycoproteins, glycolipids, and sialylated oligosaccharides because of the simple structure of the minimal acceptor substrate (NeuAcα2,3(6)Gal) at the non-reducing end of their carbohydrate groups. The human ST8Sia VI glycosyltransferase was cloned in 2005, but it's function in the cell physiological and pathological processes were not reported. This study aimed at clarifying the roles and molecular mechanisms of ST8Sia VI in breast cancer metastasis. In addition, these results will help us understand the biological importance of disialic acid structures on glycoproteins involved in tumorigenesis and progression.To determine the function of ST8Sia VI in tumor formation and metastasis, ST8Sia VI gene was stably expressed in metastatic 4T1 murine mammary cancer cell line and nonmetastatic 67NR murine mammary cancer cell line by retro viral vector mediated gene transfection. Then researchs were made to study whether ST8Sia VI could affect proliferation and migration of the two cell lines in vitro. The results from MTT assay indicated that ST8Sia VI had no effect on proliferation of two cell lines. Transwell chambers were used to assay the migration ability of the cells. The results indicated that ST8Sia VI significantly enhanced the migration ability of 4T1 and 67NR cells. These findings suggestes that ST8Sia VI plays an important role in breast cancer cell metastasis.Western Blotting was used to analyze the key regulators in pathways involved, the results showed that MAPK was activated significantly by the expression of ST8Sia VI in 4T1 cells, which might play important roles in breast cancer malignance induced by ST8Sia VI. Cytokines IL-6 could activate MAPK through gp130-JAK pathway, but receptor proteins gp130 and IL-6R were not the target proteins of ST8Sia VI. ST8Sia VI could not promote the metastasis of breast cancer cells after inhibiting the activity of MAPK, suggesting that in 4T1 cells, ST8Sia VI enhanced the migration ability of 4T1 by regulating MAPK pathway. The potential target proteins of glycosyltransferases ST8Sia VI should be studied further.In conclusion, this study demonstrated that ST8Sia VI overexpression can promote metastasis of 4T1 breast cancer cells. The activation of MAPK pathway might be the molecular mechanism underlying ST8Sia VI induced breast cancer metastasis. Gp130 and IL-6 played important roles in the process, but were not the target proteins of ST8Sia VI. These results suggest that ST8Sia VI is a target for the therapy of breast cancer and this study provided a theoretical basis for a further study of sialyltransferase in tumor formation and development.