Download Gene Section HRK (harakiri, BCL2 interacting protein (contains only BH3 domain))

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Gene Section
Review
HRK (harakiri, BCL2 interacting protein (contains
only BH3 domain))
Jonathan Ham
Molecular Haematology and Cancer Biology Unit, UCL Institute of Child Health, 30 Guilford Street,
London WC1N 1EH, UK (JH)
Published in Atlas Database: July 2011
Online updated version : http://AtlasGeneticsOncology.org/Genes/HRKID40865ch12q24.html
DOI: 10.4267/2042/46085
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
following Nerve Growth Factor (NGF) withdrawal in
sympathetic neurons, neuronally differentiated PC12
cells and dorsal root ganglion (DRG) neurons, KCl
deprivation in cerebellar granule neurons, beta amyloid
treatment in cortical neurons and following axotomy of
motor neurons in vivo (Imaizumi et al., 1997; Imaizumi
et al., 1999; Harris and Johnson, 2001; Imaizumi et al.,
2004; Coultas et al., 2007; Ma et al., 2007; Towers et
al., 2009). Experiments with HRK-/- knockout mice
have shown that HRK is not essential for normal
embryonic development but does contribute to the
death of DRG neurons following NGF deprivation in
vitro (Coultas et al., 2007) and the death of
motoneurons in vivo following hypoglossal nerve
transection (Imaizumi et al., 2004).
Other names: DP5; HARAKIRI; BID3
HGNC (Hugo): HRK
Location: 12q24.22
Local order: According to Ensembl and the NCBI
Map Viewer, the genes flanking HRK in the plus strand
direction are: RNFT2, which is downstream of HRK
and transcribed towards it, and FBXW8, which is
upstream of HRK and transcribed divergently.
Note: HRK / Dp5 / Bid3 is a BH3-only member of the
Bcl-2 family of apoptosis regulators. Bcl-2 family
proteins regulate the mitochondrial (intrinsic) pathway
of apoptosis by regulating mitochondrial outer
membrane permeability (Chipuk et al., 2010).
Interactions between the pro- and anti-apoptotic
members of the Bcl-2 family determine the fate of cells
in response to signals that induce apoptosis. BH3-only
proteins are activated in response to a variety of signals
including survival factor withdrawal, DNA damage, ER
stress and oxidative stress. HRK expression increases
DNA/RNA
Description
The human HRK gene spans 20206 bases, telomere to
centromere orientation. Exon 2, which encodes the 3
UTR of the HRK mRNA, is much longer in the mouse '
Figure 1. Genomic context of the human HRK gene. HRK is located on chromosome 12 between the RNFT2 and FBXW8 genes.
Arrows indicate the 5' to 3' orientation of each gene. Adapted from the NCBI Map Viewer.
Atlas Genet Cytogenet Oncol Haematol. 2010; 14(10)
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HRK (harakiri, BCL2 interacting protein (contains only BH3 domain))
Ham J
Figure 2. HRK gene and promoter structure. A. Structure of the HRK gene. The structure of the human and rat HRK genes is shown.
The HRK gene consists of two exons separated by a large intron. The transcriptional start site is indicated as +1 (see panel B for DNA
sequence). Exon 1 contains the HRK open reading frame (black box) as well as a small region of the 3' UTR, the remainder of which is in
exon 2. Exon 2 is longer in the rat and mouse genes compared to Exon 2 in human HRK. The human HRK transcript is 716 nucleotides
long (Inohara et al., 1997) whereas the rat HRK transcript is 5253 nucleotides long due to the larger size of Exon 2 (Imaizumi et al.,
1997). B. HRK promoter sequence. Alignment of the promoter sequences for the rat, mouse, human and cow HRK genes. Shaded
regions indicate a conserved ATF site, a GC box, an E box and a TATA box. * represent bases conserved in all four species. Overall,
80% of the nucleotides are conserved. The transcriptional start site of the rat HRK gene determined by 5' RACE is indicated as +1,
together with the direction of transcription (Towers et al., 2009). The HRK promoter has a similar structure in the four species except that
there is a 10 bp deletion between the ATF site and putative GC box in the human gene, compared to the other species. Adapted from
Figure 3 in Towers et al. (2009).
and rat genes compared to human HRK (see Figure
2A). In the three species only one major transcript
encoding a single protein isoform has been described.
liver, lung, testis, heart, intestine or skeletal muscle
(Imaizumi et al., 1997; Coultas et al., 2007).
Based on studies with the rat HRK gene (Ma et al.,
2007; Towers et al., 2009), the 1 kb region upstream of
exon 1 contains elements important for the control of
HRK transcription (Figure 2B). The HRK promoter is
GC-rich but contains a conserved block of 14 A/T
nucleotides that might function as a TATA box, a
conserved E-box, a conserved GC box and a conserved
and functionally-important ATF binding site (5'TGATGTAA-3') that binds c-Jun and ATF2 and which
is important for the
Transcription
In northern blotting experiments with RNA from
human tissues, it was reported that the HRK transcript
was detected in spleen, lymph nodes, thymus, bone
marrow and appendix (Inohara et al., 1997). However,
in the rat and mouse the expression of the HRK
transcript is much more restricted and HRK is detected
in the brain but not the spleen, thymus, bone marrow,
Atlas Genet Cytogenet Oncol Haematol. 2010; 14(10)
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HRK (harakiri, BCL2 interacting protein (contains only BH3 domain))
Ham J
Figure 3. Structure of the human and rat HRK proteins. Amino acid residues in the 91 amino acid human HRK protein are numbered.
Residues that are identical in the human and rat HRK proteins are shaded. Gaps are indicated by -. The BH3 domain and
transmembrane domain are marked by black lines.
activation of HRK transcription by the JNK pathway
following survival factor withdrawal in neurons (Ma et
al., 2007; Towers et al., 2009) or exposure to proinflammatory cytokines in pancreatic beta-cells
(Gurzov et al., 2009).
HRK predominantly localizes to mitochondria
(Sunayama et al., 2004). Studies with a 27 amino acid
peptide containing the putative transmembrane domain
of HRK indicated that this domain is able
to insert into membranes, where it adopts a
transmembrane alpha-helical structure (Bernabeu et al.,
2007). This suggests that the carboxy terminal region
of HRK may insert into the mitochondrial outer
membrane.
Pseudogene
There are no known pseudogenes for HRK.
Protein
Function
Description
HRK is a pro-apoptotic BH3-only member of the Bcl-2
protein family. Overexpression of HRK can induce
apoptosis in HEK293 cells (Inohara et al., 1997;
Imaizumi et al., 1999), rat sympathetic neurons
(Imaizumi et al., 1997) and cerebellar granule neurons
(Harris and Johnson, 2001). In these cell types
HRK/DP5-induced apoptosis is blocked by coexpression of Bcl-2 or Bcl-xL (Inohara et al., 1997;
Imaizumi et al., 1997) or by knockout of the
endogenous Bax gene (Harris and Johnson, 2001). The
HRK protein contains two functional domains: a BH3
domain and a carboxy terminal transmembrane domain
(Figure 3). The HRK BH3 domain is related in amino
acid sequence to the BH3 domains of other Bcl-2
family proteins and is required for interaction with antiapoptotic Bcl-2 family proteins, such as Bcl-2 and BclxL, and for cell death induced by overexpression of
HRK (Inohara et al., 1997). A detailed study of the
binding of BH3-only proteins to anti-apoptotic Bcl-2
family members indicated that HRK binds with high
affinity to Bcl-xL, Bcl-w and A1 and with moderate
affinity to Bcl-2 and Mcl-1 (Chen et al., 2005). The
HRK transmembrane domain is rich in hydrophobic
amino acid residues and could mediate the insertion of
Only one isoform of the HRK protein has been
described. HRK is 91 amino acids long in humans and
92 amino acids in mouse and rat (Inohara et al., 1997;
Imaizumi et al., 1997; Imaizumi et al., 1999).
Expression
See section on transcription for information about
tissue specificity. The endogenous HRK protein has
been detected in immunoblotting experiments with a
number of cell types, for example: in NGF-deprived rat
primary sympathetic neurons in culture (Imaizumi et
al., 1997), in the mouse brain following focal cerebral
ischemia (middle cerebral artery occlusion; Gao et al.,
2005), in the auditory cell line HEI-OC1 exposed to
gentimicin (Kalinec et al., 2005) and in the pancreatic
beta-cell line INS-1E treated with the pro-inflammatory
cytokines IL-1beta and IFNgamma (Gurzov et al.,
2009).
Localisation
HRK is a non-nuclear intracellular protein (Inohara et
al., 1997). Flag-tagged HRK co-localizes with
MitoTracker in transfected COS-7 cells suggesting that
Atlas Genet Cytogenet Oncol Haematol. 2010; 14(10)
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HRK (harakiri, BCL2 interacting protein (contains only BH3 domain))
secondary glioblastomas as compared to other types of
tumours, and aberrant methylation was closely
associated with loss of expression. Reverse
transcription-PCR analysis also demonstrated a clear
agreement between reduced HRK protein levels and
low or absent HRK transcripts.
Disease
Glioblastoma (WHO grade IV) is the most frequent and
most malignant tumour of the human nervous system.
Despite advances in surgery and adjuvant therapy,
glioblastoma patients still have a very poor prognosis.
From a clinical and biological point of view,
glioblastomas are divided into two subtypes. Primary or
de novo glioblastomas develop rapidly, without clinical
or histopathological evidence of less malignant
precursor lesions and constitute the majority of
diagnosed cases, whereas secondary glioblastoma
develops more slowly and progressively from lowgrade diffuse (WHO grade II) or anaplastic (WHO
grade III) astrocytoma.
the HRK carboxy terminus into intracellular
membranes, such as the mitrochondrial outer
membrane.
Homology
The HRK protein is only related to other Bcl-2 family
proteins in the short BH3 domain.
Mutations
Note
No mutations have been described in HRK.
Implicated in
Colorectal and gastric cancer
Note
The region around the HRK transcriptional start site
was methylated in 36% of colorectal and 32% of
gastric cancer cell lines and was closely associated with
a loss of HRK expression in those cell lines (Obata et
al., 2003; Nakamura et al., 2009). HRK expression was
restored by treatment with a methyltransferase
inhibitor, 5-aza-deoxycytidine, and further enhanced by
addition of the histone deacetylase inhibitor trichostatin
A or depsipeptide. The restoration of HRK expression
correlated with an induction of apoptosis and
enhancement of Adriamycin-induced apoptosis.
Expression of other proapoptotic genes, including
BAX, BAD, BID, and PUMA, was unaffected by
treatment
with
5-aza-deoxycytidine.
Aberrant
methylation of HRK was also frequently detected in
primary colorectal cancers that showed methylation of
multiple genes.
Disease
Colorectal cancer (bowel cancer) is characterized by
neoplasia in the colon, rectum or vermiform appendix.
Colorectal cancers start in the lining of the bowel. If
left untreated, they can grow into the muscle layers
underneath, and then through the bowel wall. Most
begin as a small growth on the bowel wall - a colorectal
polyp or adenoma. These growths are usually benign,
but some develop into cancer over time. Colorectal
cancer is the third most commonly diagnosed cancer in
the world.
Gastric cancer (stomach cancer) can develop in any
part of the stomach and may spread throughout the
stomach and to other organs, in particular the
oesophagus, lungs, lymph nodes and the liver. Stomach
cancer causes about 800000 deaths worldwide per year.
References
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Inohara N, Ding L, Chen S, Núñez G. harakiri, a novel
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Imaizumi K, Morihara T, Mori Y, Katayama T, Tsuda M,
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Harris CA, Johnson EM Jr. BH3-only Bcl-2 family members are
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Obata T, Toyota M, Satoh A, Sasaki Y, Ogi K, Akino K, Suzuki
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Glioblastoma
Note
The region around the HRK transcriptional start site
was methylated in 19% of diffuse astrocytomas, in 22%
of anaplastic astrocytomas, in 27% of primary
glioblastomas, and in 43% of secondary glioblastomas
(Nakamaura et al., 2005; Nakamura et al., 2009). HRK
expression was significantly reduced in 61% of
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Colman PM, Day CL, Adams JM, Huang DC. Differential
targeting of prosurvival Bcl-2 proteins by their BH3-only ligands
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required for apoptosis induced by potassium deprivation in
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human cancer. Oncogene. 2008 Dec;27 Suppl 1:S105-13
Kalinec GM, Fernandez-Zapico ME, Urrutia R, EstebanCruciani N, Chen S, Kalinec F. Pivotal role of Harakiri in the
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This article should be referenced as such:
Ham J. HRK (harakiri, BCL2 interacting protein (contains only
BH3 domain)). Atlas Genet Cytogenet Oncol Haematol. 2011;
15(12):1033-1037.
Ma C, Ying C, Yuan Z, Song B, Li D, Liu Y, Lai B, Li W, Chen
R, Ching YP, Li M. dp5/HRK is a c-Jun target gene and
Atlas Genet Cytogenet Oncol Haematol. 2010; 14(10)
Ham J
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