Roles And The Molecular Mechanisms Of ST6Gal-Ⅰ In The Malignant Phenotypes And Chemosensitivity Of Lung Cancer

Cancer is the second deadly disease in today’s society.And it’s a serious threat to people’s life and health.According to the recent reports,lung cancer is the second large incidence and the most large mortality rate in both men and women.According to histological classification of lung cancer,lung cancer can be divided into two types: small cell lung cancer and non-small cell lung cancer.Surgical resection is the main treatment for non-small cell lung cancer.however,there is still a great chance that the new tumor of non-small cell lung cancer will emerge even if the tumor is completely removed.Therefore,it is the key point of current research to study the molecular mechanism of lung cancer in depth from the molecular level and find suitable targets for early diagnosis and treatment.Sialic acid(SA)belongs to a series of nine carbon monosaccharide family that are negatively charged,in which a terminal monosaccharide is attached to the glycan chains on the cell surface.SA is commonly found in glycoconjugates of eukaryotic cells and it can be divided into two subtypes,namely Nec5 Ac and Nec5 Gc.It can be divided into three types according to the kind of the connection which sialic acid and sugar residues of sialic acid,it is a2,3-SA,a2,6-SA and a2,8-SA.The sialyltransferase(ST)family is a group of sialylation synthases consisting of 20 members,which is subdivided into the following four main protein families: ST3 Gal,ST6Gal,ST6 GalNAc,and ST8 Sia,based on the connection types of SAs linked to the terminal glycans of the glycoconjugates.ST6Gal-Ⅰ can catalyze the transfer of sialic acid to the galactose residue at the end of the sugar chain through the α2,6-connection.According to the recent studies,it has been found that most human tissues express ST6Gal-Ⅰ.However,the level of expression between tissues is quite different,and ST6Gal-Ⅰ expression level is often accompanied changed by many tumors.For example,Jung YR et al.noted that down-regulation of ST6Gal-Ⅰ expression can increase the metastatic capacity of rectal cancer cells by inhibiting KAI1 activity.Previous studies in our laboratory showed that ST6Gal-Ⅰ can promote tumor progression in hepatoma and prostate cancer cells,as a prognostic target for liver cancer cells and prostate cancer cells.However,it has less report in effect and expression of ST6Gal-Ⅰ in lung cancer.Therefore,the research study the role of ST6Gal-Ⅰ in growth,proliferation,migration,invasion and chemosensitivity and the molecular mechanism of lung cancer cells.Objective: to analyze the expression level and clinical significance of ST6Gal-Ⅰ in lung cancer tissues,to study the effect and mechanism of ST6Gal-Ⅰ expression on growth,migration and invasion of lung cancer cells,and to explore the role and mechanism of ST6Gal-Ⅰ in chemosensitivity of lung cancer.Methods: using immunohistochemical and Western-blot methods analysis the expression level and clinical significance of ST6Gal-Ⅰ in lung cancer tissue.Real-time PCR and Western-blot methods were used to detect the different expression levels of ST6Gal-Ⅰ in normal human lung cells HBE,HLF and lung cancer cells A549,H1299.The ST6GAL-I-shRNA was transfected into lung cancer cells A549 and H1299 to knockdown the expression levels of ST6Gal-Ⅰ;using CCK8,cell clone,scratch assay and Transwell methods to analysis the role of ST6Gal-Ⅰ knockdown correlates with malignant phenotype of lung cancer cells and via Western-blot analysis its molecular mechanism;using CCK8,flow cytometry and DAPI methods to analyze the drug sensitivity of down-regulation of ST6Gal-Ⅰ on lung cancer cells and analysis its molecular mechanism by Western-blot.Results: The expression of ST6Gal-Ⅰ in lung cancer tissues was significantly higher than that in normal lung tissue;ST6Gal-Ⅰ in lung cancer cells(A549,H1299)in the expression was significantly higher than that in normal lung cells(HBE,HLF);the down-regulation of ST6Gal-Ⅰ lung cancer cell lines A549 and H1299,the proliferation,migration and invasion ability decreased significantly;lung cancer cell lines A549 and H1299 ST6Gal-Ⅰ expression downregulation of decreased expression of Notch1/MMPs signaling pathway protein;in vivo results showed that down-regulation of ST6Gal-Ⅰ lung cancer cell line A549 in the volume and weight of tumor growth in mice are less,and the expression of Notch1/MMPs signal transduction protein was significantly lower than the control group;the drug sensitivity of down-regulation of ST6Gal-Ⅰ in lung cancer cell lines A549 and H1299 were significantly enhanced with the increase of apoptosis pathway protein P-Raf1,P-JNK,P-c-Jun and cleaved-caspase-3 expression.Conclusion: ST6Gal-Ⅰ in lung cancer from the cancer promoting effects to the development;growth,migration and invasion of ST6Gal-Ⅰ lung cancer cells via Notch1/MMPs signaling pathway;down regulated expression of ST6Gal-Ⅰ may promote the sensitivity of pemetrexed for lung cancer cells via JNK/caspase signaling pathway,the research may bring a new target for clinical diagnosis and treatment of lung cancer.