Download Gene Section GCNT3 (glucosaminyl (N-acetyl) transferase 3, mucin type)

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GCNT3 (glucosaminyl (N-acetyl) transferase 3,
mucin type)
Prakash Radhakrishnan, Pi-Wan Cheng
Department of Biochemistry and Molecular Biology, College of Medicine, University of Nebraska Medical
Center, 985870 Nebraska Medical Center, Omaha, NE 68198-5870, USA
Published in Atlas Database: November 2007
Online updated version: http://AtlasGeneticsOncology.org/Genes/GCNT3ID44105ch15q21.html
DOI: 10.4267/2042/38541
This work is licensed under a Creative Commons Attribution-Non-commercial-No Derivative Works 2.0 France Licence.
© 2008 Atlas of Genetics and Cytogenetics in Oncology and Haematology
Identity
DNA/RNA
Hugo: GCNT3
Other names: C2GnT-M; hC2GnT-M; C2GnT2;
C2/C4gnT; GnT-M; mucus type C2GnT
Location: 15q21.3
Note: GCNT3/C2GnT-M is a single pass type II
membrane protein belonging to glycosyltransferase 14
family.
Note: Human GCNT3/C2GnT-M is located on
chromosome 15 in the region of q21.3, oriented from
centromere to telomere.
Description
Human GCNT3/C2GnT-M gene is approximatively
8.26 kb in size and located in chromosome 15q21.3 at
the position of 57,691,415 - 57,699,501.
Schematic representation of Human GCNT3/C2GnT-M gene and transcripts. There are three different sized transcripts. (TIS,
Transcription Initiation Site designated as +1; E, Exon; I, Intron; UTR, Untranslated region; ATG, start codon; ORF, Open reading
frame).
Atlas Genet Cytogenet Oncol Haematol. 2008;12(4)
276
GCNT3 (glucosaminyl (N-acetyl) transferase 3, mucin type)
Radhakrishnan P, Cheng PW
Recently, the GCNT3/C2GnT-M promoter (-417/+187)
containing two basal cis-regulatory region (-291/-182
and -62/-43) was identified. The Th2 cytokine and
retinoic acid responsive cis-regulatory elements reside
in -417/+187 region.
Expression
Human GCNT3/C2GnT-M gene is expressed in mucussecretory tissues in the following decreasing order of
expression: Colon; testis; stomach; small intestine;
adrenal gland; kidney; trachea; thyroid gland; Uterus;
Ovary; Pancreas; fetal liver; Prostate. Unlike bovine
GCNT3/C2GnT-M gene, the type of transcript
expressed by hC2GnT-M gene is not tissue specific
among the mucus secretory tissues. Expression of
GCNT3/C2GnT-M gene is down regulated in colon
and colorectal tumors and various colorectal cancer
cells. GCNT3/C2GnT-M expression is regulated by
various external agent(s). It is inhibited by EGF and
enhanced by Th2 cytokines, retinoic acids and sodium
butyrate.
Transcription
Human GCNT3/C2GnT-M contains three different
sized transcripts: 2.3-2.5, 3.6-3.8 and 6.8-7.0 kb. The
transcript 1 (approximatively 2.3-2.5kb) is made of 3
exons, exon 1 (69-198 bp), exon 2 (333-401 bp), and
exon 3 (1864 bp). Exon 3 contains 59 bp of 5' UTR,
1314 bp of ORF and 491 bp of 3'UTR. It does not
contain any introns. Whereas, the intermediate sized
transcript (3.6-3.8kb) contains 1.3kb of intron 2 and the
large sized transcript (6.8-7.0 kb) contains 4.5kb of
intron 1 in addition to all three exons. Exon 1 is
heterogeneous in size, which ranges from 69 to 198 bp
depending on tissues and cells. Exon 1 is present in all
transcripts and has same 3' end but different 5' ends. A
333 bp Exon 2 is identified in most of the mucus
secreting tissues and airway epithelial cells while a 401
bp of exon 2 is only detected in A549 cells.
Localisation
Golgi membrane.
Function
GCNT3/C2GnT-M is responsible for the synthesis of
all three branch structures, including core 2, core 4, and
I antigen found in the glycans of secreted mucins.
These three branch structures are generated by the
transfer of GlcNAc from UDP-GlcNAc to core 1, core
3, and I antigen, respectively as shown below.
1. UDP-GlcNAc + Galbeta1-3GalNAca1-S/T gives
Galbeta1-3(GlcNAcbeta1-6) GalNAca1-S/T + UDP.
2. UDP-GlcNAc + GlcNAcbeta1-3GalNAc1a-S/T
gives GlcNAcbeta1-3(GlcNAcbeta1-6) GalNAca1-S/T
+ UDP.
3. UDP-GlcNAc + GlcNAcbeta1-3Galbeta1-R gives
GlcNAcbeta1-3(GlcNAcbeta1-6)Galbeta1-R + UDP(R:
sugars).
The primary function of secreted mucins is to protect
mucus secretory epithelium by retention of water and
maintenance of the rheological properties of the mucus,
and adherence to airborne and ingested pathogens to
facilitate their removal from these tissues. The first two
properties depend primarily on the carbohydrate
content and this property depends on the heterogeneity
of carbohydrate structure. Secreted mucins contain very
high carbohydrate content, i.e. 70-90% by weight, and
very heterogeneous carbohydrate structure, e.g. up to
100 different oligosaccharides in mucins isolated from
a single donor. The three b6GlcNAc branch structures
found in the secreted mucins are responsible for the
increase of carbohydrate content and structural
complexity. Decrease of GCNT3/C2GnT-M in the
secretory epithelium can result in dehydration of the
mucus and compromise of bacterial clearance.
Protein
Note: Human GCNT3/C2GnT-M (EC 2.4.1.102) has
438 amino acids and molecular weight of 50,863 Da.
The predicted GCNT3/C2GnT-M structure shows a short Nterminal cytoplasmic tail (CT), a transmembrane domain (TM),
a stem region and a long catalytic domain at the C-terminal
region.
Description
GCNT3/C2GnT-M is a type II membrane protein
located in the Golgi apparatus. It contains a nine-amino
acid peptide tail at the N-terminus located in the
cytoplasm, which is followed by a transmembrane
domain consisted of 18 amino acids, a stem region, and
a catalytic domain located in the Golgi lumen. The
protein contains 13 cysteines, including 4 at the Nterminal region, which are conserved among
GCNT3/C2GnT-M across species, and 9 at the Cterminal region, which are conserved among all mucin
glycan b6GlcNAc branching enzymes. Structural
information obtained from bovine GCNT3/C2GnT-M
shows that among the 9 conserved cysteines, the
second cysteine is unconjugated and the other 8
cysteines form 4 cystine bonds between first and ninth,
third and seventh, fourth and fifth, and sixth and eighth.
The disulfide bonds formed from the nine conserved
cysteines are different between GCNT3/C2GnT-M and
C2GnT-L. GCNT3/C2GnT-M contains two potential
N-glycosyltaion sites at N-69 and N-289.
Atlas Genet Cytogenet Oncol Haematol. 2008;12(4)
Homology
Human GCNT3/C2GnT-M shows a very high level of
similarity to other non-human GCNT3/C2GnT-M:
bovine (83%), rat (78%) and mouse (77%). Further, it
shows moderate level of (48% and 38%) similarity to
human C2GnT-L and C2GnT-T, respectively.
277
GCNT3 (glucosaminyl (N-acetyl) transferase 3, mucin type)
Radhakrishnan P, Cheng PW
Implicated in
References
Colorectal cancer
Schwientek T, Nomoto M, Levery SB, Merkx G, van Kessel
AG, Bennett EP,Hollingsworth MA, Clausen H. Control of Oglycan branch formation. Molecular cloning of human cDNA
encoding a novel beta1,6-N-acetylGlucosaminyl transferase
forming core 2 and core 4. J Biol Chem 1999;274(8):45044512.
Note: GCNT3/C2GnT-M enzyme is down regulated in
colon and colorectal tumors and most cancerous cells
derived from mucus-secretory tissues. Re-expression of
GCNT3/C2GnT-M suppresses tumor growth in the
xenografts of nude mice.
Disease
Colorectal cancer is the 3rd most common form of
cancer and the 2nd leading cause of cancer-related
death among men and women in the Western world. It
causes 655,000 deaths worldwide per year. The
survival rate of colorectal cancer is not much higher
than 50% even if the disease is diagnosed at an early
stage. Colorectal cancer is mostly formed from
adenomatous polyps. These polyps can be detected and
removed during colonoscopy, which would decrease
cancer death by greater than 80%. Metastasis of cancer
cells through bowel wall of the colon to lymph nodes is
very common. If metastasis is detected, 5 year survival
rate is less than 10%.
Prognosis
Recent reports suggest that deficiency or down
regulation of human GCNT3/C2GnT-M expression is
associated with development of colitis and colorectal
cancer. This enzyme may be used as a prognostic
marker for colorectal cancer.
Oncogenesis
GCNT3/C2GnT-M expression is down regulated in
colorectal
cancers.
Down
regulation
of
GCNT3/C2GnT-M would lead to the production of
secreted mucins with lower carbohydrate content and
less heterogeneous carbohydrate, which would
compromise the protective function of these mucins. As
a result, bacteria can not be cleared effectively, which
causes irritation of the epithelium and chronic
inflammation, and eventually cancer. Its re-expression
suppresses tumor cell spreading, adhesion, motility,
and invasion. It also inhibits cell growth and colonyforming ability, and induces apoptotic cell death.
In addition, expression of C2GnT-M suppresses tumor
growth in the xenografts of nude mice. The results
suggest that GCNT3/C2GnT-M is important in
protecting the normal functional architecture of colon
epithelial cells.
Atlas Genet Cytogenet Oncol Haematol. 2008;12(4)
Yeh JC, Ong E, Fukuda M. Molecular cloning and expression
of a novel beta-1,6-N-acetyl glucosaminyltransferase that
forms core 2, core 4, and I branches. J Biol Chem
1999;274(5):3215-3221.
Beum PV, Cheng PW. Biosynthesis and function of beta 1,6
branched mucin-type glycans. Adv Exp Med Biol
2001;491:279-312. (Review).
Beum PV, Bastola DR, Cheng PW. Mucin biosynthesis:
epidermal growth factor downregulates core 2 enzymes in a
human airway adenocarcinoma cell line. Am J Respir Cell Mol
Biol 2003;29(1):48-56.
Singh J, Khan GA, Kinarsky L, Cheng H, Wilken J, Choi KH,
Bedows E, Sherman S,Cheng PW. Identification of disulfide
bonds
among
the
nine
core
2
Nacetylglucosaminyltransferase-M cysteines conserved in the
mucin beta6-N-acetylglucosaminyltransferase family. J Biol
Chem 2004;279(37):38969-38977.
Beum PV, Basma H, Bastola DR, Cheng PW. Mucin
biosynthesis: upregulation of core 2 beta 1,6 N-acetyl
glucosaminyltransferase by retinoic acid and Th2 cytokines in
a human airway epithelial cell line. Am J Physiol Lung Cell Mol
Physiol 2005;288(1):L116-L124.
Ishibashi Y, Inouye Y, Okano T, Taniguchi A. Regulation of
sialyl-Lewis x epitope expression by TNF-alpha and EGF in an
airway carcinoma cell line. Glycoconj J 2005;22(1-2):53-62.
Huang MC, Chen HY, Huang HC, Huang J, Liang JT, Shen TL,
Lin NY, Ho CC, Cho IM, Hsu SM. C2GnT-M is downregulated
in colorectal cancer and its re-expression causes growth
inhibition of colon cancer cells. Oncogene 2006;25(23):32673276.
Hashimoto M, Tan S, Mori N, Cheng H, Cheng PW. Mucin
biosynthesis: molecular cloning and expression of mouse
mucus-type core 2 beta1,6 N-acetylglucosaminyl transferase.
Glycobiology 2007;17(9):994-1006.
Radhakrishnan P, Beum PV, Tan S, Cheng PW. Butyrate
induces sLex synthesis by stimulation of selective
glycosyltransferases genes. Biochem Biophys Res Commun
2007;359(3):457-462.
Tan S, Cheng PW. Mucin biosynthesis: identification of the cisregulatory elements of human C2GnT-M gene. Am J Respir
Cell Mol Biol 2007;36(6):737-745.
This article should be referenced as such:
Radhakrishnan P, Cheng PW. GCNT3 (glucosaminyl (Nacetyl) transferase 3, mucin type). Atlas Genet Cytogenet
Oncol Haematol.2008;12(4):276-278.
278