Enhanced expression of the ß4-N-acetylgalactosaminyltransferase 4 gene impairs tumor growth of human breast cancer cells.

Two ß4-N-acetylgalactosaminyltransferases (ß4GalNAcTs), ß4GalNAcT3 and ß4GalNAcT4, have been shown to be involved in the synthesis of the GalNAcß1 â†’ 4GlcNAc (LacdiNAc) group expressed on the outer branches of N- and/or O-glycans, and only ß4GalNAcT4 is expressed in human mammary gland. We found that the expression level of the LacdiNAc group decreases as human breast cancers progress. To investigate biological significances of this disaccharide in human breast cancers, we transfected the FLAG-tagged ß4GalNAcT4 cDNA into MDA-MB-231 cells, and obtained several clones showing enhanced expression of the gene. Clones 1 and 2 showed 15 and 9 times more transcript than mock-transfected cells. The FLAG-ß4GalNAcT4 protein and its product, the LacdiNAc group, were detected in clone 1 and 2 cells. No change was observed in their growth rates while significant decreases in colony forming and invasive abilities were observed for clone 1 and 2 cells. When clone 1 cells were transplanted subcutaneously into nude mice, no tumors were formed while tumors were formed with mock-transfected cells. These results indicate that the expression of the LacdiNAc group is quite important for the suppression of malignancies of the MDA-MB-231 cells.

UBE2S promotes malignant properties via VHL/HIF-1α and VHL/JAK2/STAT3 signaling pathways and decreases sensitivity to sorafenib in hepatocellular carcinoma.

BACKGROUND: Ubiquitin-conjugating enzyme E2S (UBE2S), an E2 enzyme, is associated with the development of various tumors and exerts oncogenic activities. UBE2S is overexpressed in tumors, including hepatocellular carcinoma (HCC). However, the key molecular mechanisms of UBE2S in HCC still need additional research. The aim of this study was to explore the role of UBE2S in HCC. METHODS: The expression levels of UBE2S in HCC tissues and cells were detected by western blot analysis, quantitative real-time polymerase chain reaction analysis (qRT-PCR), and immunohistochemistry (IHC). A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, wound healing assay, colony formation assay transwell assay, and animal models were used to detect the proliferation and migration ability of HCC cells. Western blot analysis, qRT-PCR, immunofluorescence, small-interfering RNA (siRNA), and plasmid transfection and coimmunoprecipitation (Co-IP) assays were performed to detect the interaction among UBE2S, von Hippel-Lindau (VHL), hypoxia-inducible factor 1-alpha (HIF-1α), Janus kinase-2 (JAK2), and signal transducer and activator of transcription 3 (STAT3). RESULTS: In this study, we found that high UBE2S expression was associated with poor prognosis in HCC patients. In addition, UBE2S expression was upregulated in HCC tissues and cell lines. Knockdown of UBE2S inhibited the proliferation and migration of HCC cells in vitro and in vivo by directly interacting with VHL to downregulate the HIF-1α and JAK2/STAT3 signaling pathways. Accordingly, overexpression of UBE2S significantly enhanced the proliferation and migration of HCC cells in vitro via VHL to upregulate HIF-1α and JAK2/STAT3 signaling pathways. Furthermore, we found that downregulation of UBE2S expression enhanced the sensitivity of HCC cells to sorafenib in vivo and in vitro. CONCLUSION: UBE2S enhances malignant properties via the VHL/HIF-1α and VHL/JAK2/STAT3 signaling pathways and reduces sensitivity to sorafenib in HCC. The findings of this study may open a new approach for HCC diagnosis and provide a potential option for the treatment of HCC.