ST6Gal-I sialyltransferase adds α2,6-linked sialic acids to the terminal ends of glycan chains of glycoproteins and glycolipids. ST6Gal-I is reportedly upregulated in many cancers, including hepatocellular carcinoma, ovarian cancer and breast cancer. However, the expression and function of ST6Gal-I in prostate cancer (PCa) and the mechanism underlying this function remain largely unknown. In this study, we observed that ST6Gal-I expression was upregulated in human PCa tissues compared to non-malignant prostate tissues. High ST6Gal-I expression was positively correlated with Gleason scores, seminal vesicle involvement and poor survival in patients with PCa. ST6Gal-I knockdown in aggressive prostate cancer PC-3 and DU145 cells significantly inhibited the proliferation, growth, migration and invasion capabilities of these cells. ST6Gal-I knockdown decreased the levels of several PI3K/Akt/GSK-3β/ β-catenin pathway components, such as p-PI3K, (Ser473)p-Akt, (Ser9)p-GSK-3β and β-catenin. Furthermore, targeting this pathway with a PI3K inhibitor or Akt RNA interference decreased p-Akt, p-GSK-3β and β-catenin expression, resulting in decreased PC-3 and DU145 proliferation, migration and invasion. Taken together, these results indicate that ST6Gal-I plays a critical role in cell proliferation and invasion via the PI3K/Akt/GSK-3β/β-catenin signaling pathway during PCa progression and that it might be a promising target for PCa prognosis determination and therapy.

Abnormal sialylation due to overexpression of sialyltransferases has been associated with tumorigenesis and tumor progression. Although ST6Gal-I influences cancer persistence and progression by affecting various receptors, the underlying mechanisms and mediators remain largely obscure, especially in hepatocellular carcinoma (HCC). We found that ST6Gal-I expression was markedly upregulated in HCC tissues and cells, high levels being associated with aggressive phenotype and poor prognosis. Furthermore, we examined the roles and mechanisms of ST6Gal-I in HCC tumorigenesis and metastasis in vitro and in vivo. ST6Gal-I overexpression promoted proliferation, migration and invasion of Huh-7 cells, whereas its knockdown restricted these abilities in MHCC97-H cells. Additionally, in a mouse xenograft model, ST6Gal-I-knockdown MHCC97-H cells formed significantly smaller tumors, implying that ST6Gal-I overexpression can induce HCC cell malignant transformation. Importantly, enhanced HCC tumorigenesis and metastasis by ST6Gal-I may be associated with Wnt/β-catenin signaling promotion, including β-catenin nuclear transition and upregulation of downstream molecules. Together, our results suggest a role for ST6Gal-I in promoting the growth and invasion of HCC cells through the modulation of Wnt/β-catenin signaling molecules, and that ST6Gal-I might be a promising marker for prognosis and therapy of HCC.

The alterations of cell surface sialylation play a key role in tumor metastasis. Enhanced α2,6-sialylation on N-glycans results from overexpression of the sialyltransferase ST6Gal-I. Hca-F and Hca-P cells are murine hepatocarcinoma cell lines which metastasize only to the lymph nodes. Our previous study revealed that ST6Gal-I was involved in the adhesion of Hca-F cells to fibronectin. However, the roles of sialic acids in the adhesion of Hca-F cells to lymph nodes still remain poorly understood. In this study, we observed that expression levels of α2,6-linked sialic acids on Hca-F cells were higher compared to Hca-P cells. Knockdown of ST6Gal-I by small hairpin RNA (shRNA) transfection decreased the expression of α2,6-linked sialic acids and inhibited the adhesion of Hca-F cells to lymph nodes. The adhesion ability was reported to be mediated by siglec-2 which preferentially binds to α2,6-linked sialic acids, and in addition, ST6Gal-I knockdown inhibited the phosphorylated levels of focal adhesion kinase (FAK) and paxillin when cells were treated with siglec-2. Taken together, these results suggest that interaction of α2,6-linked sialic acids with siglec-2 might modulate the adhesion of hepatocarcinoma cells to lymph nodes through the FAK signaling pathway.

ST3Gal IV is one of the principal sialyltransferases responsible for the biosynthesis of α2, 3-sialic acid to the termini N-glycans or O-glycans of glycoproteins and glycolipids. It has been reported that ST3Gal IV expression is associated with gastric carcinoma, pancreatic adenocarcinoma and breast cancer. While the expression and functions of ST3Gal IV in cervical cancer are still poorly understood. In this study, we found that ST3Gal IV was downregulated in human cervical cancer tissues compared to normal cervix tissues, and ST3Gal IV expression was negatively associated with the pathological grade of cervical cancer. ST3Gal IV upregulation inhibited the growth and proliferation of cervical cancer HeLa and SiHa cells in vitro and in vivo. Furthermore, ST3Gal IV overexpression enhanced the expression of several Notch pathway components such as Jagged1, Notch1, Hes1 and Hey1, while cell cycle protein expression like Cyclin D1, Cyclin E1, CDK2 and CDK4 were decreased. These results indicate that expression of ST3Gal IV is reduced in cervical cancer and plays a negative role in cell proliferation via Notch/p21/CDKs signaling pathway. Thus, sialyltransferase ST3Gal IV might be a target for the diagnosis and therapy of cervical cancer.

The authors have retracted this article [1] because there are errors in some images. In Fig. 2g, a colony picture for Mock group was incorrect. In Fig. 2k, the invasion pictures for Mock and overexpression ST6Gal-1 cells were incorrect. In Fig. 3g, the colony picture for shNC was incorrect. In Fig. 4f, the authors mistakenly provided WB band for GAPDH. In Fig. 4g, the IHC pictures for 10w in Negative Control and DENA-induced Groups were incorrect, and in Fig. 7f, a IHC picture for GSK-3β in DENA-induced Group (10w) was presented incorrectly. Due to these errors the findings are no longer reliable.