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Gene Section
Review
PA2G4 (proliferation-associated 2G4, 38kDa)
Anne Hamburger, Arundhati Ghosh, Smita Awasthi
University of Maryland School of Medicine, Department of Pathology and University of Maryland
Greenebaum Cancer Center, Baltimore, USA (AH, AG, SA)
Published in Atlas Database: September 2011
Online updated version : http://AtlasGeneticsOncology.org/Genes/PA2G4ID41628ch12q13.html
DOI: 10.4267/2042/46944
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.0 France Licence.
© 2012 Atlas of Genetics and Cytogenetics in Oncology and Haematology
Identity
DNA/RNA
Other names: EBP1, HG4-1, ITAF45, p38-2G4
HGNC (Hugo): PA2G4
Location: 12q13.2
Note
PA2G4 encodes a cell-cycle regulated protein capable
of interacting with DNA, RNA and protein. The gene
was isolated as a DNA binding protein (p38-2g4)
(Radomski and Jost, 1995) and also as an ErbB3interacting protein (EBP1) (Yoo et al., 2000). Two
different isoforms of EBP1 play a role in cell survival,
cell cycle arrest and differentiation. The long form may
have an oncogenic function when overexpressed, and
the short form acts as a tumor suppressor (Liu et al.,
2006). EPB1 also functions as a transcriptional
repressor of E2F1-regulated genes (Zhang et al., 2004)
and the androgen receptor (AR) (Zhang et al., 2005)
through its interactions with histone deacetylases and
Sin3A.
Description
The PA2G4 gene contains 13 exons. The sizes of the
exons 1-13 are 88, 128, 105, 69, 92, 63, 78, 78, 133, 94,
127, 53 and 65 bp (to the stop codon). Exon 1 contains
the translation initiation ATG. Exon 13 contains the
stop codon.
Transcription
The human PA2G4 promoter contains several putative
transcription factor binding sites. The major transcript
length is 2643 nt. Two proteins are translated due to
alternative splicing (Liu et al., 2006). An alternatively
spliced version missing 29 NT between the first and
third ATGs has been observed.
The PA2G4 promoter contains two tandem DNA
elements that bind E2F1. E2F1 increases endogenous
EBP1 mRNA levels in cancer cells, but decreases
EBP1 mRNA abundance in non transformed cells
(Judah et al., 2010).
Pseudogene
Six pseudogenes, located on chromosomes 3, 6, 9, 18,
20 and X, have been identified.
The alignment of PA2G4 mRNA to its genomic sequence.
Atlas Genet Cytogenet Oncol Haematol. 2012; 16(2)
131
PA2G4 (proliferation-associated 2G4, 38kDa)
Hamburger A, et al.
The linear schematic of EBP1. Functional domains, including Nucleolar Localization Signal (NuLS), σ70 RNA binding region (σ70),
amphipathic helical domain (AHD), LXXLL nuclear receptor binding motif (LX) and demonstrated in vivo phosphorylation sites (*).
Localisation
Protein
Description
p38-2G4 was initially isolated as a DNA binding
protein from mouse Ehrlich ascites cells (Radomski
and Jost, 1995). The MW of this protein is predicted to
be 38058 D, consisting of 340 amino acids. The human
orthologue EBP1 was later identified as an ErbB3
binding protein of the same MW as the mouse protein
(Yoo et al., 2000). This form migrates at approximately
42 kD in SDS-PAGE gels. Later, a larger 394 amino
acid form (predicted MW 43787 D, migrating at 48 kD)
was observed in mammalian cells (Xia et al., 2001).
The two forms have been demonstrated to be the result
of alternative splicing (Liu et al., 2006) or usage of
alternative translation initiation sites (Xia et al., 2001).
Amino acids 1-48 are required for nucleolar
localization and the C terminal domain (aa 364-394) is
required for interactions with nucleic acids (Moonie et
al., 2007) and protein (Zhang et al., 2002).
EBP1 is post translationally modified at several
phosphorylation sites (Ser 360 (Ahn et al., 2006), Ser
363 (Akinmade et al., 2007) and Thr 261 (Akinmade et
al., 2008)) in vivo. The protein stability of the short
form is regulated by ubiquitination (Liu et al., 2009).
The short form is also sumoylated by the TLF/FUS E3
ligase and this sumoylation is required for the antiproliferative effects of EBP1 (Oh et al., 2010).
The crystal structure of both murine (Monie et al.,
2007) and human (Kowalinski et al., 2007) EBP1 has
been solved. There is a core domain that is homologous
to methionine aminopeptidases, although no enzymatic
activity has been reported. The C terminal domain
containing a Lys-rich nuclear hormone receptor binding
motif (LKALL) was reported to mediate RNA binding
(Monie et al., 2007).
Expression
EBP1 has been found to be ubiquitously expressed with
high expression levels in skeletal muscle (Yoo et al.,
2000).
Atlas Genet Cytogenet Oncol Haematol. 2012; 16(2)
132
Under logarithmically growing conditions in cell
culture, EBP1 localizes to the nucleolus and the
cytoplasm (Xia et al., 2001; Squatrito et al., 2004).
Upon stimulation with the ErbB3 ligand heregulin, the
short form of EBP1 is recruited to the nucleus in
AU565 breast cancer cells (Yoo et al., 2000).
Sumoylation is required for nuclear translocation (Oh
et al., 2010). In primary normal epithelial cells, EBP1
is confined to the cytoplasm (Zhang et al., 2008b).
Function
EBP1 was initially isolated as a cell cycle-regulated
DNA binding protein (Radomski and Jost, 1995) and
has been shown to induce cell cycle arrest in the G2/M
phase of the cell cycle (Zhang et al., 2005). EBP1 acts
as a corepressor for several proliferation-associated
genes including Cyclin D1, E2F1 (Zhang and
Hamburger, 2004) and the androgen receptor (Zhang et
al., 2005). EBP1 inhibits transcription of these genes by
recruiting HDAC2 via Sin3A to the E2F1 and ARregulated promoters (Zhang et al., 2005). EBP1
interacts with RB1 and the interaction is enhanced upon
EBP1 dephosphorylation (Xia et al., 2001).
EBP1 was isolated as an ErbB3 binding protein using a
yeast-two hybrid screen (Yoo et al., 2000). The
interactions of EBP1 with ErbB3 is disrupted by the
ErbB3 ligand heregulin, leading to EBP1 nuclear
translocation. This leads to the eventual inhibition of
heregulin-stimulated proliferation, presumably due to
the repression of proliferation associated genes (Zhang
et al., 2008a).
EBP1 also binds RNA and associates with 28S, 18S
and 5.8S mature rRNAs, several rRNA precursors and
probably U3 small nucleolar RNA. It has been
implicated in the regulation of intermediate and late
steps of rRNA processing (Squatrito et al., 2004;
Squatrito et al., 2006). EBP1 also mediates capindependent translation of specific viral IRES (internal
ribosome entry site) (Pilipenko et al., 2000). EBP1
PA2G4 (proliferation-associated 2G4, 38kDa)
Hamburger A, et al.
regulates translation of AR mRNA (Zhou et al., 2010).
EBP1 has also been implicated in protein stability via
its interaction with the proteasome. Overexpression of
EBP1 results in decreased stability of ErbB2 protein in
breast cancer cells via a proteasome-mediated pathway
(Lu et al., 2011). The long form of EBP1 binds to the
p53 E3 ligase HDM2, enhancing HDM2-p53
interactions and promoting p53 degradation (Kim et al.,
2011).
The long (p48) and short (p42) forms of EBP1 have
opposing biological effects, with the longer form
inducing cell survival and the shorter form inhibiting
cell growth (Liu et al., 2006). The long form binds
HDM2, promoting degradation of p53 (Kim et al.,
2010).
Homology
Similar (30% identity) to the 42 kDA DNA binding
protein SF00553 in S. pombe yeast (Yamada et al.,
1994) and StEBP1 in potato (Horvath et al., 2006). The
orthologue in potatoes (StEBP1) has 69% sequence
similarity to human EBP1 and can inhibit growth of
human breast cancer cell lines and E2F1 expression in
these cells.
References
Yamada H, Mori H, Momoi H, Nakagawa Y, Ueguchi C,
Mizuno T. A fission yeast gene encoding a protein that
preferentially associates with curved DNA. Yeast. 1994
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Radomski N, Jost E. Molecular cloning of a murine cDNA
encoding a novel protein, p38-2G4, which varies with the cell
cycle. Exp Cell Res. 1995 Oct;220(2):434-45
Pilipenko EV, Pestova TV, Kolupaeva VG, Khitrina EV,
Poperechnaya AN, Agol VI, Hellen CU. A cell cycle-dependent
protein serves as a template-specific translation initiation
factor. Genes Dev. 2000 Aug 15;14(16):2028-45
Yoo JY, Wang XW, Rishi AK, Lessor T, Xia XM, Gustafson TA,
Hamburger AW. Interaction of the PA2G4 (EBP1) protein with
ErbB-3 and regulation of this binding by heregulin. Br J
Cancer. 2000 Feb;82(3):683-90
Xia X, Cheng A, Lessor T, Zhang Y, Hamburger AW. Ebp1, an
ErbB-3 binding protein, interacts with Rb and affects Rb
transcriptional regulation. J Cell Physiol. 2001 May;187(2):20917
Squatrito M, Mancino M, Donzelli M, Areces LB, Draetta GF.
EBP1 is a nucleolar growth-regulating protein that is part of
pre-ribosomal ribonucleoprotein complexes. Oncogene. 2004
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ErbB3-binding protein Ebp1 to bind E2F promoter elements
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Mutations
Germinal
Zhang Y, Akinmade D, Hamburger AW. The ErbB3 binding
protein Ebp1 interacts with Sin3A to repress E2F1 and ARmediated transcription. Nucleic Acids Res. 2005;33(18):602433
No mutations in the PA2G4 gene have been reported.
Somatic
None reported.
Ahn JY, Liu X, Liu Z, Pereira L, Cheng D, Peng J, Wade PA,
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Implicated in
Prostate cancer
Prognosis
Decreased expression of EBP1 is associated with
higher tumor grade and metastasis in prostate cancer
(Zhang et al., 2008b). However, another study
indicated EBP1 expression increased with disease
progression (Gannon et al., 2008).
Horváth BM, Magyar Z, Zhang Y, Hamburger AW, Bakó L,
Visser RG, Bachem CW, Bögre L. EBP1 regulates organ size
through cell growth and proliferation in plants. EMBO J. 2006
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Breast cancer
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XP, Hooi M, Chen W, Jikuya H, Ichikawa T, Kuyama H,
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proteomic
alterations
by
combined
2nitrobenzenesulfenyl chloride (NBS) isotope labeling and
2DE/MS identification. J Proteome Res. 2006 Sep;5(9):2194206
Prognosis
Deletion of EBP1 results in tamoxifen resistance in
breast cancer (Zhang et al., 2008a). However, patients
with a high level of EBP1 protein have a poor clinical
outcome (Ou et al., 2006).
Glioblastoma
Prognosis
Glioblastoma patients expressing a high level of p48
EBP1 have a worse prognosis than those expressing
lower levels of the protein (Kim et al., 2010; Kwon and
Ahn, 2011).
Atlas Genet Cytogenet Oncol Haematol. 2012; 16(2)
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Liu Z, Ahn JY, Liu X, Ye K. Ebp1 isoforms distinctively regulate
cell survival and differentiation. Proc Natl Acad Sci U S A. 2006
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eIF2alpha phosphorylation. Biochem Biophys Res Commun.
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inhibition of cell growth requires serine 363 phosphorylation. Int
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PA2G4 (proliferation-associated 2G4, 38kDa)
Hamburger A, et al.
Kowalinski E, Bange G, Bradatsch B, Hurt E, Wild K, Sinning I.
The crystal structure of Ebp1 reveals a methionine
aminopeptidase fold as binding platform for multiple
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This article should be referenced as such:
Hamburger A, Ghosh A, Awasthi S. PA2G4 (proliferationassociated 2G4, 38kDa). Atlas Genet Cytogenet Oncol
Haematol. 2012; 16(2):131-134.