The core 3 structure of theO-glycan, GlcNAcβ1–3GalNAcα1-serine/threonine, an important precursor in the biosynthesis of mucin-type glycoproteins, is synthesized by UDP-N-acetylglucosamine:GalNAc-peptide β1,3-N- acetylglucosaminyltransferase (β3Gn-T; core 3 synthase). The core 3 structure is restricted in its occurrence to mucins from specific tissues such as the stomach, small intestine, and colon. A partial sequence encoding a novel member of the human β3Gn-T family was found in one of the data bases. We cloned a complementary DNA of this gene and named it β3Gn-T6. The putative amino acid sequence of β3Gn-T6 retains the β3Gn-T motifs and is predicted to comprise a typical type II membrane protein. The soluble form of β3Gn-T6 expressed in insect cells showed β3Gn-T activity toward GalNAcα-p-nitrophenyl and GalNAcα1-serine/threonine. The β1,3-linkage between GlcNAc and GalNAc of the enzyme reaction product was confirmed by high performance liquid chromatography and NMR analyses. β3Gn-T6 effectively transferred a GlcNAc to the GalNAc residue on MUC1 mucin, resulting in the synthesis of a core 3 structure. Real time PCR analysis revealed that the β3Gn-T6 transcript was restricted in its distribution, mainly to the stomach, colon, and small intestine. We concluded that β3Gn-T6 is the most logical candidate for the core 3 synthase, which plays an important role in the synthesis of mucin-type O-glycans in digestive organs.

Background: Systemic lupus erythematosus (SLE) is a complex autoimmune disease, and the etiology is still unclear. Some studies have indicated that viral infection might contribute to the development of SLE. Methods: A total of 105 individuals with SLE and 110 matched healthy controls were tested for EBV-specific DNA fragments in peripheral blood monocytes by PCR-Southern blotting. The expression of EBV-encoded genes was determined by RT-PCR and Southern blotting in EBV-positive patients. Serum EBV-specific IgM antibody was determined by ELISA. HHV-6 DNA in peripheral blood monocytes of those SLE patients and normal controls was tested by nested PCR. Results: Statistical analysis showed that the EBV-positive rate of SLE patients was significantly higher than that of the control group (χ² = 87.329, P = 0), while the difference in the HHV-6-positive rate between the two groups was not significant (P > 0.05). An association of EBV and HHV-6 positivity in SLE patients was found (P = 0, r = 0.38). The EBV IgM level was significantly higher in SLE patients than in healthy controls (χ² = 25.184, P = 0). Forty-two of the 75 EBV DNA-positive specimens were positive for EBNA2 mRNA, and an association between EBV EBNA2 mRNA and anti-Sm antibody positivity was found (P = 0, r = 0.409). LMP1 mRNA was positive in 2 SLE patients with active phase, and no LMP2A mRNA expression was detected in EBV DNA-positive specimens. EBV early gene BARF1 mRNA was detected in 2 cases of EBV-positive SLE patients, and these 2 patients were also HHV-6 DNA positive. Thirty-eight patients were BcLF1 mRNA positive, and 33 of them were HHV-6 positive as well. These factors were associated (χ² = 15.734, P = 0). The expression of the EBV immediate early gene BZLF1 was negative in all 75 EBV-positive SLE patients. Conclusions: The results suggest that EBV infection might be related to the occurrence of SLE. Although there is no direct evidence that HHV-6 infection is associated with the development of SLE, EBV and HHV-6 infection may have a coacceleration effect in SLE patients. This study provides a new theoretical and experimental basis for the study of viral etiology and the prevention and treatment of SLE.