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Gene Section
Review
MAL (mal, T-cell differentiation protein)
Levent B Beder, Noboru Yamanaka
Department of Otolaryngology Head and Neck Surgery, Wakayama Medical University, 811-1, Kimiidera,
Wakayama, 641-8509, Japan (LBB, NY)
Published in Atlas Database: July 2010
Online updated version : http://AtlasGeneticsOncology.org/Genes/MALID46222ch2q11.html
DOI: 10.4267/2042/44995
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.0 France Licence.
© 2011 Atlas of Genetics and Cytogenetics in Oncology and Haematology
Identity
MAL has context dependent roles as both a tumor
suppressor and an oncogene in different cancers.
HGNC (Hugo): MAL
Location: 2q11.1
Local order: Centromere - TEKT4 - RPS24P6 - MAL
- MRPS5 - ZNF514 - ZNF2 - SLC2AXP1 - PROM2 Telomere.
Note: MAL gene is the member of MAL family and
takes part in intracellular transportation of certain
proteins in apical direction and myelin formation.
There is a consensus sequence shared by all family
members, and by biochemical features (Magyar et al.,
1997; Perez et al., 1997).
DNA/RNA
Description
Genomic DNA of MAL gene is located on
chromosome 2q11.1 spans 21 kb and includes 4 exons
interrupted by three introns.
The promoter lacks a consensus TATA box in the
vicinity of transcription start side and there is no
consensus polyadenylation signal, although ATAAAA
sequence exists.
Amplification of cDNA from different T-cell samples by PCR revealed that there are four different splicing variants of mRNA named as
MAL-a (462 bp), MAL-b (333 bp), MAL-c (294 bp), and MAL-d (168 bp). These variants defined according to involvement of exon2 and/or
exon3, while MAL-a includes all 4 exons. As the three introns were located between complete codons, the reading frame was maintained
in all the transcripts. (Figure adapted from Atlas of Genetics and Cytogenetics in Oncology and Haematology).
Atlas Genet Cytogenet Oncol Haematol. 2011; 15(4)
331
MAL (mal, T-cell differentiation protein)
Beder LB, Yamanaka N
There are two separated promoter CpG islands at a
totally 1500 bp length of region extending into the first
intron and contains up to 116 CpG dinucleotides. CpG
island is divided into two regions and usually
methylation status of these regions are evaluated
separately by specifically designed primer sets.
MAL promoter at 110 bp upstream of the
transcriptional start site contains also several SP1
binding sites, which may be regulated by
transcriptional activator SP1 (Tugores et al., 1997).
This domain is also found approximately in 20 open
reading frames of human genome (Sanchez-Pulido et
al., 2002). Furthermore, the domain is also found in the
tight-junction-associated proteins including occluding,
tricellulin, marvelD3 and in the synaptic-membranelocalized synaptophysin and synaptogyrin. Thus, a
common characteristic of proteins containing the
MARVEL domain is localization to specialized
domains within surface membranes (Magal et al.,
2009).
Transcription
Expression
MAL coding sequence: bases 60-518, accession
NM_002371.2.
The mRNA is 1051 bp and open reading frame is 460
bp in length. Translation begins from a start codon in
exon 1, ends at a stop codon in exon 4, and results in a
153 amino acid protein product. mRNA orientation is
forward and transcription occurs on plus strand. The
first exon encodes the 5' untranslated region and the
first 31 amino acids. The second and the third exons
encode 56 and 42 amino acids, respectively. Fourth
exon encodes the 24 amino acids at COOH-terminal
and the 3' untranslated region. The intron boundaries
follow the AG/GT rule of acceptor/donor splice signal
sequences and splicing between exons occurs between
the last nucleotide of a codon and the first one of the
next codon (Rancano et al., 1994b).
Alonso and Weissman originally identified MAL
expression in intermediate and late stages of Tlymphocyte differentiation (Alonso and Weissman,
1987). Furthermore, expression of MAL mRNA is also
found to be related with differentiation in urothelial
cells, neuronal cells (Liebert et al., 1997; Wakeman et
al., 1997) and esophageal epithelium (Mimori et al.,
2007). Accordingly, expression is prominent in upper
layers, while it is weak or absent in basal layers of
esophageal epithelium (Marazuela et al., 2003). These
results implied a strong relation between differentiation
status and MAL expression.
Although four transcripts identified, MAL-a variant
containing the all four exons is found to be the most
abundantly expressed in several tissues including
peripheral blood lymphocytes and HNSCC tissues
(Rancano et al., 1994b; Beder et al., 2009).
Maruzela et al. defined a detailed expression status for
MAL protein by immunostaining in a wide range of
human tissues and expression is found to be mainly
localized in epithelial cells, myelinating cells and Tlymphocytes (Marazuela et al., 2003). Detailed results
according to this study:
A- MAL negative cells and tissues:
- Fibroblasts, endothelial cells, B lymphocytes, skeletal
and smooth muscle, skin (keratinized squamous
epithelium and subcutaneous fibro-adipose tissue).
B- MAL positive cells and tissues:
- Gastrointestinal tract: Epithelium in esophagus,
stomach, ileum, colon, liver, and pancreas.
- Genitourinary tract: Multiple sites of tract including
transitional epithelium of the urothelium.
- Respiratory tract: Ciliated columnar epithelium of
bronchi and bronchioles, and type 2 pneumocytes of
alveolae.
- Hematopoietic system: Expression is restricted to
regions rich in T-cells including cortex of thymus and
paracortical lymphocytes of lymph node and tonsil.
- Endocrine system: Thyroid follicular cells, medulla of
adrenal gland.
- Nervous system: Axons of peripheral nerves and
myelinating Schwann cells in peripheral nervous
system, oligodendrocytes of white and gray matter in
central nervous system.
- Exocrine glands: breast epithelium (Horne et al.,
2009).
Pseudogene
There is no identified pseudogene.
Protein
Description
MAL belongs to the MAL family of proteolipids
including BENE, MAL2 and Plasmolipin. In mouse,
the conserved motif of (Q/Y-G-W-V-M-F/Y-V), which
is located at the junction of the first extracellular loop
and the second membrane-associated domain serves as
a fingerprint for the MAL family, although overall
amino acid sequence identities between mouse MAL
and the related proteins are between 29-37% (Magyar
et al., 1997). This motif is also shared in human MAL
family.
Molecular mass of the MAL protein is 16700 Da and
assigned into proteolipid group based on the solubility
feature in lipophilic solvents. MAL is a nonglycosylated integral membrane protein including four
transmembrane domains as hydrophobic segments.
Each of four exons encodes a hydrophobic membraneassociated segment and its adjacent hydrophilic
sequence in the protein structure (Rancano et al.,
1994a). A model is proposed about orientation of MAL
protein in the membrane (Alonso et al., 1987).
Another feature of MAL is its transmembrane helices
constituting the MARVEL (MAL and related proteins
for vesicle trafficking and membrane link) domain.
Atlas Genet Cytogenet Oncol Haematol. 2011; 15(4)
332
MAL (mal, T-cell differentiation protein)
Beder LB, Yamanaka N
defect in neuronal and epithelial cell polarity (Harada,
2010).
Related with the location of MAL in membrane
microdomains another role is also suggested in cell
signaling (Alonso et al., 2001), although there is yet no
clear evidence concerning this function.
Localisation
The MAL proteolipid is an integral membrane protein
and generally embedded in the plasma membrane of
epithelial cells (Magal et al., 2009). Expression is
generally more pronounced in supranuclear - apical
membrane domain for most of the polarized epithelia
including gastrointestinal mucosa and thyroid follicular
cells (Marazuela et al., 2003) according with its role in
polarized sorting.
The protein has been mainly identified as an internal
component of glycolipid-enriched membrane (GEM)
domains in T-lymphocytes (Millan et al., 1997), in
polarized epithelial MDCK cells (Zacchetti et al., 1995)
and in myelin-forming cells (Kim et al., 1995). As
intracellular placement, the protein is localized to
endoplasmic reticulum of T-lymphocytes (Rancano et
al., 1994b).
Homology
MAL protein is shown to be widely conserved (9497%) across species by sequence alignment. In MAL
family of human, MAL displays 39% and 36% amino
acid sequence identity with BENE and MAL2,
respectively and all proteins have four-transmembrane
domain structure.
Mutations
Note
Direct sequencing of the entire coding region revealed
no somatic mutations in 20 cases of cervical cancers
(Hatta et al., 2004) and in 24 head and neck cancer cell
line series (Beder et al., 2009).
Currently, there is no further data in HGMD database.
Function
Plasma membrane (PM) of epithelial cells divided into
apical membrane domain involved in exchange with
the organ lumen, and the basolateral domain
maintaining contact with neighboring cells and the
underlying extracellular matrix. Localizing numerous
PM proteins to apical and basolateral domains by direct
or indirect pathways result in cell polarization. In the
direct pathway, proteins delivered directly from the
trans-golgi network (TGN) to the apical PM by raftdependent or non-raft carriers. Rafts are clustering of
glycospingolipids, sphingomyelin and cholesterol into
membrane microdomains and therefore also named as
GEM (glycosphingolipid- and cholestrol-enriched
membrane) domains. These detergent insoluble
membranes defined by resistancy to cold extraction
with Triton X-100. Several proteins participate in
structure of rafts.
MAL is an integral membrane component of raft
domains and recycles between the Golgi complex and
the apical membrane in MDCK cells (Puertollano et al.,
1999a). Although, exact mechanism of MAL function
in raft-dependent apical sorting is unknown, MAL
family proteolipids are implicated to be potent
regulator of apical transport by involving in the
assembly and targeting of apical transport platforms
and in the formation and stabilization of raft domains.
Consensus sorting motifs in the C-terminus function in
regulation of raft transport (Puertollano et al., 1997).
In apical sorting, PM proteins are clustered into either
glycolipid raft domains or non-raft carriers. MAL and
MAL2 together with FAPP2 take part in constitutive
apical transport of Influenza hemagglutinin (HA)
(Puertollano et al., 1999b) and GPI-anchored proteins
(decay-accelerating F factor, folate receptor, GFP-GPI,
5'-nucleotidase,
CEA)
by
lipid-raft-associated
mechanism (Weisz et al., 2009).
Based on apical sorting of many proteins, MAL is
implied to function in establishment of cell polarity,
however, MAL knockout mice did not display a clear
Atlas Genet Cytogenet Oncol Haematol. 2011; 15(4)
Implicated in
Various cancers
Diagnostic biomarker in cancer: Recent reports
revealed that epigenetic silencing of MAL by
hypermethylation may be a common event involved
during initiation and progression of epithelial cancers.
Based on specifically high hypermethylation of MAL
promoter in various carcinomas including breast,
cervix, colon and gastric cancers compared to normal
epithelium, promoter methylation of the gene is
suggested to be diagnostic marker for early detection of
tumorigenesis (Buffart et al., 2008; Lind et al., 2008;
Horne et al., 2009; Overmeer et al., 2009).
Tumor-metastasis suppressive vs oncogenic role:
Current functions attributed to MAL gene does not
reveal a clear mechanism for MAL in oncogenesis. The
gene is suggested to have tumor suppressive role in
some malignancies, while oncogenic role in others
according with expression level in tumors and normal
tissues.
In cervical carcinoma cell lines, MAL overexpression
by transfection reduces proliferation rate and
suppressed migration and anchorage-dependent growth.
Furthermore, Fas-induced apoptosis is found to be
related with reduced migration and tumorigenicity by
ectopic expression of MAL in esophageal carcinoma
(Mimori et al., 2003).
Ovarian cancer
Note
MAL mRNA is found to be the most differentially
expressed gene between short and long-term survival
groups by microarray study, and higher expression
333
MAL (mal, T-cell differentiation protein)
Beder LB, Yamanaka N
showed correlation with short survival (Berchuck et al.,
2005).
not received adjuvant chemotherapy (Horne et al.,
2009).
Esophageal carcinoma
Head and neck squamous cell
carcinoma (HNSCC)
Note
MAL expression is severely down-regulated in
esophageal carcinomas compared to normal epithelium
(Mimori et al., 2003) and up-regulation of MAL
expression induces differentiation in esophageal
carcinoma cells (Mimori et al., 2007).
Note
In a review of DNA microarray analysis related with
genetic expression profiles of HNSCC, MAL is found
to be down-regulated in 10 out of the 26 studies (Choi
et al., 2005). Interestingly, MAL expression is downregulated in metastatic tumors of HNSCC including
both cell lines derived from lymph node metastasis
(65%) and metastatic tumor tissues (43%) compared to
primary tumor counterparts. Furthermore, remarkable
LOH (loss of heterozygosity) frequency (30%) is
observed in primary tumor samples and metastatic
tumors itself (Beder et al., 2009). These results suggest
that loss of MAL expression may lead to metastasis in
HNSCC.
Cervical carcinoma
Note
MAL mRNA is found to be the most significantly
down-regulated gene both in squamous cell carcinoma
(SCC) and adenocarcinoma of cervix (Wilting et al.,
2008). Ectopic expression of MAL in SiHa cells
suppressed proliferation, migration, and anchorageindependent growth. Promoter methylation is also
remarkably high in cervical malignancies and
accordingly showed significant correlation with
decreased
expression.
Interestingly,
promoter
methylation is also shown to be predictive for highgrade lesions of cervix i.e. severity of cervical disease
(Overmeer et al., 2009).
Lymphoma
Note
Like ovarian cancers, MAL overexpression is identified
to be indicator for poor prognosis and disease outcome
in patients with T cell lymphoma and Hodgkin
lymphoma (Tracey et al., 2002; Hsi et al., 2006).
Colon carcinoma
Note
Genome wide microarray analysis revealed MAL to be
frequently hypermethylated in colon carcinoma cell
lines correlating with down-regulation of mRNA
expression (Mori et al., 2006). Another study
confirmed these results in carcinoma tissues and
defined promoter hypermethylation as 71% (45/63) and
80% (49/61) in colon adenomas and carcinomas,
respectively, while it is rare in normal mucosa.
Furthermore, protein expression were also absent in
majority (198/231) colorectal carcinoma tissues in
immunostaining (Lind et al., 2008). Based on these
results, MAL methylation is suggested as a diagnostic
marker for early colon carcinogenesis.
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This article should be referenced as such:
Beder LB, Yamanaka N. MAL (mal, T-cell differentiation
protein). Atlas Genet Cytogenet Oncol Haematol. 2011;
15(4):331-335.
Choi P, Chen C. Genetic expression profiles and biologic
pathway alterations in head and neck squamous cell
carcinoma. Cancer. 2005 Sep 15;104(6):1113-28
Atlas Genet Cytogenet Oncol Haematol. 2011; 15(4)
335