Control of O-Glycan Branch Formation

Abstract

A novel human UDP-GlcNAc:Gal/GlcNAc␤1-3GalNAc␣ ␤1,6GlcNAc-transferase, designated C2/4GnT, was identified by BLAST analysis of expressed sequence tags. The sequence of C2/4GnT encoded a putative type II transmembrane protein with significant sequence similarity to human C2GnT and IGnT. Expression of the secreted form of C2/4GnT in insect cells showed that the gene product had UDP-N-acetyl-␣-D-glucosamine:acceptor ␤1,6-N-acetylglucosaminyltransferase (␤1,6GlcNAc-transferase) activity. Analysis of substrate specificity revealed that the enzyme catalyzed O-glycan branch formation of the core 2 and core 4 type. NMR analyses of the product formed with core 3-para-nitrophenyl confirmed the product core 4-para-nitrophenyl. The coding region of C2/4GnT was contained in a single exon and located to chromosome 15q21.3. Northern analysis revealed a restricted expression pattern of C2/4GnT mainly in colon, kidney, pancreas, and small intestine. No expression of C2/4GnT was detected in brain, heart, liver, ovary, placenta, spleen, thymus, and peripheral blood leukocytes. The expression of core 2 O-glycans has been correlated with cell differentiation processes and cancer. The results confirm the predicted existence of a ␤1,6GlcNAc-transferase that functions in both core 2 and core 4 O-glycan branch formation. The redundancy in ␤1,6Glc-NAc-transferases capable of forming core 2 O-glycans is important for understanding the mechanisms leading to specific changes in core 2 branching during cell development and malignant transformation.

C2GnT-M is downregulated in colorectal cancer and its re-expression causes growth inhibition of colon cancer cells

“…The HCT116 and LoVo expressed lower levels of C2GnT-M than did normal colon tissues. However, the HT29 cells expressed C2GnT-M at high levels similar as normal colon tissues, which is consistent with previous reports (Vavasseur et al, 1995;Schwientek et al, 1999). In contrast, the expression levels of C2GnT-L and b-actin mRNA in all four colon cancer cell lines were similar to that of normal colon tissues.…”

“…The core 2 b-1,6-N-acetylglucosaminyltransferase (C2GnT) transfers GlcNAc to GalNAc of the core 1 acceptor structure Galb1-3GalNAca-Ser/Thr to form the core 2 branch in b-1,6 linkage. To date, three members of C2GnT have been cloned, leukocyte-type C2GnT (C2GnT-L or C2GnT1) (Bierhuizen and Fukuda, 1992), mucin-type C2GnT (C2GnT-M or C2GnT2) (Schwientek et al, 1999;Yeh et al, 1999), and thymusassociated C2GnT (C2GnT-T, C2GnT3) (Schwientek et al, 2000). In addition to the formation of the core 2 structure, C2GnT-M also exhibits activities to form the core 4 and I branch, as shown in Figure 1 (Schwientek et al, 1999;Yeh et al, 1999).…”

“…To date, three members of C2GnT have been cloned, leukocyte-type C2GnT (C2GnT-L or C2GnT1) (Bierhuizen and Fukuda, 1992), mucin-type C2GnT (C2GnT-M or C2GnT2) (Schwientek et al, 1999;Yeh et al, 1999), and thymusassociated C2GnT (C2GnT-T, C2GnT3) (Schwientek et al, 2000). In addition to the formation of the core 2 structure, C2GnT-M also exhibits activities to form the core 4 and I branch, as shown in Figure 1 (Schwientek et al, 1999;Yeh et al, 1999). Although C2GnT-M is highly expressed in the gastrointestinal tract, its physiologic or pathologic function in the gastrointestinal tract has not yet been studied.…”

Epigenetic silencing contributes to the loss of BRMS1 expression in breast cancer

“…CpG island B is also upstream of b3GNT1 (Fig. 2a) [47]. We saw a moderate increase in the level of β3GNT1 upon 5-aza-2′-deoxycytidine treatment of MCF10A and MCF10AT cells, whereas, treatment of the MCF10CA1a cl.1, MDA-MB-231 and MDA-MB-435 showed a decrease in the β3GNT1 levels (Supplemental Figure 2).…”

The Relative Activities of the C2GnT1 and ST3Gal-I Glycosyltransferases Determine O-Glycan Structure and Expression of a Tumor-associated Epitope on MUC1

“…The enzymes C2GnT1 and C2GnT3 (20,21) act only on core 1 to produce core 2. On the other hand, C2GnT2 or C2/4GnT (22,23) is able to catalyze the formation of core 4 from core 3 as well as core 2 from core 1. Of the C2GnTs identified to date by cloning, it appears that C2GnT1 is the enzyme most commonly expressed in breast tissue and tumors, although C2GnT3 can occasionally be expressed (this manuscript).…”