The biochemical consequences of alpha2,6(N) sialyltransferase induction by dexamethasone on sialoglycoprotein expression in the rat H411e hepatoma cell line

Glycogene expression profiles from a HaCaT cell line stably transfected with HPV16 E5 oncogene

The altered expression of glycan antigens has been reported during cervix transformation, demonstrating increased mRNA levels of certain glycogenes. Human papillomavirus (HPV) is the aetiological agent of cervical cancer. High risk HPV E5 is considered an oncogene and has been implicated in cell transformation. E6 and E7 HPV oncoproteins modify the expression of certain glycogenes. The role of the E5 HPV protein in glycogene expression changes has not yet been reported. The aim of the present study was to determine the effects of HPV16 E5 oncoprotein on glycogene expression. For these, a microarray assay was performed using the HaCaT cell line and altered glycogenes were identified. The mRNA levels of certain glycogenes were determined via reverse transcription-quantitative PCR (RT-qPCR). Using in silico analysis, the present study identified that glycosylation pathways were altered by E5. Microarray analysis revealed alterations in certain glycogenes, including the upregulation of ST6GAL1, ST3GAL3, CHST2 and MANBA, and the downregulation of UGT2B15, GALNT11, NDST2 and UGT1A10. Increased mRNA levels were confirmed via RT-qPCR for sialyltransferases genes. Additionally, in silico analysis was performed to identify glycosylation networks altered in the presence of the E5 oncoprotein. The analysis revealed that E5 could modify glycan sialylation, the N-glycosylation pathway, keratan sulfate and glycosaminoglycan synthesis. To the best of our knowledge, the current study was the first to determine the role of the HPV16 E5 oncoprotein in glycogene expression changes. The results indicated that increased sialyltransferase mRNA levels reported in pre-malignant and malignant cervical tissues could be the result of E5 oncoprotein expression. The results provide a possible role of HPV infection on glycosylation changes reported during cervix transformation.

Purification and MALDI-MS characterization of stressin, a stress-associated glycoprotein

Glycoconjugates have a whole spectrum of biological roles, from those that appear trivial to those that are crucial. Results accumulated in the past years indicate they might also play an important role in the response to stress, a complex physiological response of the human organism to various threats. We have recently identified stressin, a human serum glycoprotein, which was found to be increased under stress conditions. Here we report the purification of stressin from sera of professional soldiers and partial characterization of its protein and carbohydrate parts using lectin blotting and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Stressin was purified using a combination of ammonium sulfate precipitation, ion exchange chromatography, preparative gel electrophoresis and reverse-phase HPLC. It was found to be a highly glycosylated protein. Only 21.9 kDa (out of 36.7 kDa) was the protein part, whereas the remaining 40% of the mass originated from N-linked oligosaccharides. The carbohydrate part contained 12 sialic acids moieties, nearly 90% of which were lost due to post-source decay in the field-free tube. Tryptic fragments were produced from glycosylated and deglycosylated stressin, separated by reverse-phase HPLC and their exact molecular masses were determined using MALDI-MS. Comparison with tryptic maps of other proteins in computer databases indicated that stressin does not correspond to any already described protein.

Stimulation of sialyltransferase by subchronic low-level lead exposure in the developing nervous system. A potential mechanism of teratogen action

Chronic low-level lead exposure has been associated with mental deficits in young children, possibly due to its actions on specific targets in the developing nervous system. Protein glycosylation has been demonstrated to play a critical role during CNS development, and the negatively charged sialic acid group has been particularly associated with the modulation of cell adhesion. In this study, we have used an in vitro model system to examine the effect of subchronic low-level lead on the expression and activity of the sialyltransferase (ST) enzyme family. Subchronic exposure of neuronal cells to low concentrations of lead (10(-6)-10(-16) M) resulted in up to a 3-fold induction of total cellular ST activity, the level of induction being more pronounced in embryonically derived cells compared with postnatally derived cells. The increase was not due to a direct interaction of the metal with the enzyme and was only observed after at least 72 h exposure to the metal. The induction was blocked by the protein synthesis inhibitor, cycloheximide, and could be reversed upon removal of the metal. The increase was due primarily to the induction of the alpha2,3(N) ST enzyme with no effect on the expression of the alpha2,6(N) enzyme. These results suggest that the ST enzyme may serve as a target for the actions of chronic low-level lead in vivo with an alteration in the developmental regulation of protein glycosylation being at least partially responsible for the behavioral deficits associated with toxin exposure.