RUNX1
Encyclopedia
Runt-related transcription factor 1 (RUNX1) also known as acute myeloid leukemia 1 protein (AML1) or core-binding factor subunit alpha-2 (CBFA2) is a protein
that in humans is encoded by the RUNX1 gene
.
RUNX1 is a transcription factor
that regulates the differentiation of hematopoietic stem cells into mature blood cells. It belongs to the Runt-related transcription factor (RUNX) family of genes which are also called core binding factor-α (CBFα). RUNX proteins form a heterodimeric
complex with CBFβ
which confers increased DNA
binding and stability to the complex.
Chromosomal translocation
s involving the RUNX1 gene are associated with several types of leukemia
including M2 AML
.
from 2 alternative promoters, promoter 1 (distal) or promoter 2 (proximal). As a result, various isoforms
of RUNX1 can be synthesized, facilitated by alternative splicing
. The full-length RUNX1 protein is encoded by 12 exon
s. Among the exons, contain two defined domains, namely the runt homology domain (RHD) or the runt domain
(exons 2, 3 and 4), and the transactivation domain (TAD) (exon 6). These domains are necessary for RUNX1 to mediate DNA binding and protein-protein interactions respectively. The transcription of RUNX1 is regulated by 2 enhancers
(regulatory element 1 and regulatory element 2), and these tissue specific enhancers enable the binding of lymphoid or erythroid regulatory proteins, therefore the gene activity of RUNX1 is highly active in the haematopoietic system.
The protein RUNX1 is composed of 453 amino acids. As a transcription factor (TF), its DNA binding ability is encoded by the runt domain (residues 50 – 177), which is homologous to the p53
family. The runt domain of RUNX1 binds to the core consensus sequence TGTGNNN, whereby NNN can stand for TTT or TCA. DNA recognition is achieved by loops of the 12-stranded β-barrel
and the C-terminus “tail” (residues 170 – 177), which clamp around the sugar phosphate backbone and fits into the major and minor grooves of DNA. Specificity is achieved by making direct or water-mediated contacts with the bases. RUNX1 can bind DNA as a monomer
, but its DNA binding affinity is enhanced by 10 fold if it heterodimerises with the core binding factor β (CBFβ), also via the runt domain. In fact, the RUNX family is often referred to as α-subunits, together with binding of a common β-subunit CBFβ, RUNX can behave as heterodimeric transcription factors collectively called the core binding factor
s (CBFs).
The consensus binding site for CBF has been identified to be a 7 bp sequence PyGPyGGTPy. Py denotes pyrimidine
which can be either cytosine
or thymine
.
Similar experiments from a different research group demonstrated that the knockout embryos die between embryonic days 11.5 and 12.5 due to hemorrhaging in the central nervous system (CNS).
during embryonic development. It is expressed in all haematopoietic sites that contribute to the formation of haematopoietic stem and progenitor cells (HSPCs), including the yolk sac, allantois
, placenta, para-aortic splanchnopleura (P-Sp; (the visceral mesoderm
al layer), aorta-gonad-mesonephros
(AGM) and the umbilical and vitelline
arteries. HSPCs are generated via the hemogenic endothelium
, a special subset of endothelial cells scattered within blood vessels that can differentiate into haematopoietic cells. The emergence of HSPCs is often studied in mouse and zebrafish animal models, in which HSPCs appear as “intra-aortic” clusters that adhere to the ventral wall of the dorsal aorta. RUNX1 or CBF takes part in this process by mediating the transition of an endothelial cell to become a haematopoietic cell. Interestingly, there is increasing evidence that RUNX1 may also be important during primitive haematopoiesis. This is because in RUNX1 knockout mice, primitive erythrocytes displayed a defective morphology and the size of blast cell population was substantially reduced, apart from the absence of HSPCs which would result in embryonic lethality by Embryonic day (E) 11.5 – 12.5.
At a molecular level, expression of the gene RUNX1 is upregulated by the RUNX1 intronic cis-regulatory element (+23 RUNX1 enhancer). This +23 RUNX1 enhancer contains conserved motifs that encourage binding of various haematopoiesis related regulators such as Gata2
, ETS factor
s (Fli-1, Elf-1, PU.1) and the SCL / Lmo2 / Ldb1 complex, as well as RUNX1 itself acting in an auto-regulatory loop. As mentioned before, the main role of RUNX1 is to modulate the fate of haematopoietic cells. This can be achieved by binding to the thrombopoietin
(TPO) recaptor/ c-Mpl promoter, followed by the recruitment of transcription activators or repressors in order to promote transition of the hemogenic endothelium to HSCs, or differentiation into linages of lower haematopoetic hierarchies. RUNX1 can also function as a rheostat by upregulating the expression of Smad6 to target itself for proteasome
degradation.
neoplasms (MDN) or therapy-related myeloid neoplasms (t-MN), to chromosomal translocation of the RUNX1 gene with the ETO / MTG8 / RUNX1T1 gene located on chromosome 8q22, t(8; 21), generating a fusion protein AML-ETO, categorized as acute myeloid leukemia
(AML) M2.
In t(8; 21), breakpoints frequently occur at intron
5 – 6 of RUNX1 and intron 1b – 2 of ETO, creating chimeric
transcripts that inherit the runt domain from RUNX1, and all Nervy homology regions (NHR) 1-4 from ETO. As a consequence, AML-ETO retains the ability to bind at RUNX1 target genes whilst acting as a transcription repressor via the recruitment of corepressors and histone deacetylase
s, which is an intrinsic function of ETO. Oncogenic potential of AML-ETO is exerted because it blocks differentiation and promote self-renewal in blast cells, resulting in massive accumulation of blasts (>20%) in the bone marrow. This is further characterized histologically by the presence of Auer rods and epigenetically by lysine
acetylation
on residues 24 and 43. Other actions of AML-ETO that could induce leukemogenesis include downregulation of the DNA repair enzyme 8-oxoguanine DNA glycosylase (OGG1
) and increase in the level of intracellular reactive oxygen species
, making cells that express AML-ETO more susceptible to additional genetic mutations.
with:
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the RUNX1 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
RUNX1 is a transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
that regulates the differentiation of hematopoietic stem cells into mature blood cells. It belongs to the Runt-related transcription factor (RUNX) family of genes which are also called core binding factor-α (CBFα). RUNX proteins form a heterodimeric
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...
complex with CBFβ
CBFB
Core-binding factor subunit beta is a protein that in humans is encoded by the CBFB gene.-Further reading:...
which confers increased DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
binding and stability to the complex.
Chromosomal translocation
Chromosomal translocation
In genetics, a chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A gene fusion may be created when the translocation joins two otherwise separated genes, the occurrence of which is common in cancer. It is detected on...
s involving the RUNX1 gene are associated with several types of leukemia
Leukemia
Leukemia or leukaemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts". Leukemia is a broad term covering a spectrum of diseases...
including M2 AML
Acute myeloblastic leukemia with maturation
M2 is a subtype of AML .It is also known as "Acute Myeloblastic Leukemia with Maturation".-Cause:This subtype is characterized by a translocation of a part of chromosome 8 to chromosome 21, written as t...
.
Gene and protein
In humans, the gene RUNX1 is 260 kilobases (kb) in length, and is located on chromosome 21 (21q22.12). The gene can be transcribedTranscription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
from 2 alternative promoters, promoter 1 (distal) or promoter 2 (proximal). As a result, various isoforms
Protein isoform
A protein isoform is any of several different forms of the same protein. Different forms of a protein may be produced from related genes, or may arise from the same gene by alternative splicing. A large number of isoforms are caused by single-nucleotide polymorphisms or SNPs, small genetic...
of RUNX1 can be synthesized, facilitated by alternative splicing
Alternative splicing
Alternative splicing is a process by which the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing...
. The full-length RUNX1 protein is encoded by 12 exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
s. Among the exons, contain two defined domains, namely the runt homology domain (RHD) or the runt domain
Runt domain
The Runt domain is an evolutionary conserved protein domain.The AML1/RUNX1 gene is rearranged by the t translocation in acute myeloid leukemia. The gene is highly similar to the Drosophila melanogaster segmentation gene runt and to the mouse transcription factor PEBP2 alpha subunit gene...
(exons 2, 3 and 4), and the transactivation domain (TAD) (exon 6). These domains are necessary for RUNX1 to mediate DNA binding and protein-protein interactions respectively. The transcription of RUNX1 is regulated by 2 enhancers
Enhancer (genetics)
In genetics, an enhancer is a short region of DNA that can be bound with proteins to enhance transcription levels of genes in a gene cluster...
(regulatory element 1 and regulatory element 2), and these tissue specific enhancers enable the binding of lymphoid or erythroid regulatory proteins, therefore the gene activity of RUNX1 is highly active in the haematopoietic system.
The protein RUNX1 is composed of 453 amino acids. As a transcription factor (TF), its DNA binding ability is encoded by the runt domain (residues 50 – 177), which is homologous to the p53
P53
p53 , is a tumor suppressor protein that in humans is encoded by the TP53 gene. p53 is crucial in multicellular organisms, where it regulates the cell cycle and, thus, functions as a tumor suppressor that is involved in preventing cancer...
family. The runt domain of RUNX1 binds to the core consensus sequence TGTGNNN, whereby NNN can stand for TTT or TCA. DNA recognition is achieved by loops of the 12-stranded β-barrel
Beta barrel
A beta barrel is a large beta-sheet that twists and coils to form a closed structure in which the first strand is hydrogen bonded to the last.Beta-strands in beta-barrels are typically arranged in an antiparallel fashion...
and the C-terminus “tail” (residues 170 – 177), which clamp around the sugar phosphate backbone and fits into the major and minor grooves of DNA. Specificity is achieved by making direct or water-mediated contacts with the bases. RUNX1 can bind DNA as a monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
, but its DNA binding affinity is enhanced by 10 fold if it heterodimerises with the core binding factor β (CBFβ), also via the runt domain. In fact, the RUNX family is often referred to as α-subunits, together with binding of a common β-subunit CBFβ, RUNX can behave as heterodimeric transcription factors collectively called the core binding factor
Core binding factor
The Core binding factor is a group of heterodimeric transcription factors.Core binding factors are composed of:* a non-DNA-binding CBFβ chain * a DNA-binding CBFα chain...
s (CBFs).
The consensus binding site for CBF has been identified to be a 7 bp sequence PyGPyGGTPy. Py denotes pyrimidine
Pyrimidine
Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring...
which can be either cytosine
Cytosine
Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...
or thymine
Thymine
Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...
.
Mouse knockout
Mice embryos with homozygous mutations on RUNX1 died at about 12.5 days. The embryos displayed lack of fetal liver hematopoiesis.Similar experiments from a different research group demonstrated that the knockout embryos die between embryonic days 11.5 and 12.5 due to hemorrhaging in the central nervous system (CNS).
Participation in haematopoiesis
RUNX1 plays a crucial role in adult (definitive) haematopoiesisHaematopoiesis
Haematopoiesis is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells...
during embryonic development. It is expressed in all haematopoietic sites that contribute to the formation of haematopoietic stem and progenitor cells (HSPCs), including the yolk sac, allantois
Allantois
Allantois is a part of a developing animal conceptus . It helps the embryo exchange gases and handle liquid waste....
, placenta, para-aortic splanchnopleura (P-Sp; (the visceral mesoderm
Mesoderm
In all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and endoderm , with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme , mesothelium, non-epithelial blood corpuscles and...
al layer), aorta-gonad-mesonephros
Mesonephros
The mesonephros is one of three excretory organs that develop in vertebrates. It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in reptiles, birds, and mammals. The mesonephros is included in the Wolffian body after Caspar Friedrich Wolff who described it in 1759...
(AGM) and the umbilical and vitelline
Vitelline veins
-Path:They run upward at first in front, and subsequently on either side of the intestinal canal.They unite on the ventral aspect of the canal, and beyond this are connected to one another by two anastomotic branches, one on the dorsal, and the other on the ventral aspect of the duodenal portion of...
arteries. HSPCs are generated via the hemogenic endothelium
Endothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...
, a special subset of endothelial cells scattered within blood vessels that can differentiate into haematopoietic cells. The emergence of HSPCs is often studied in mouse and zebrafish animal models, in which HSPCs appear as “intra-aortic” clusters that adhere to the ventral wall of the dorsal aorta. RUNX1 or CBF takes part in this process by mediating the transition of an endothelial cell to become a haematopoietic cell. Interestingly, there is increasing evidence that RUNX1 may also be important during primitive haematopoiesis. This is because in RUNX1 knockout mice, primitive erythrocytes displayed a defective morphology and the size of blast cell population was substantially reduced, apart from the absence of HSPCs which would result in embryonic lethality by Embryonic day (E) 11.5 – 12.5.
At a molecular level, expression of the gene RUNX1 is upregulated by the RUNX1 intronic cis-regulatory element (+23 RUNX1 enhancer). This +23 RUNX1 enhancer contains conserved motifs that encourage binding of various haematopoiesis related regulators such as Gata2
GATA2
GATA binding protein 2, also known as GATA2, is a human gene. The protein encoded by this gene is a transcription factor.The GATA family of transcription factors, which contain zinc fingers in their DNA binding domain, have emerged as candidate regulators of gene expression in hematopoietic cells...
, ETS factor
ETS transcription factor family
In the field of molecular biology, the ETS family is one of the largest families of transcription factors and is unique to metazoans. There are 29 genes in humans, 28 in the mouse, 10 in Caenorhabditis elegans and 9 in Drosophila. The founding member of this family was identified as a gene...
s (Fli-1, Elf-1, PU.1) and the SCL / Lmo2 / Ldb1 complex, as well as RUNX1 itself acting in an auto-regulatory loop. As mentioned before, the main role of RUNX1 is to modulate the fate of haematopoietic cells. This can be achieved by binding to the thrombopoietin
Thrombopoietin
Thrombopoietin also known as megakaryocyte growth and development factor is a protein that in humans is encoded by the THPO gene....
(TPO) recaptor/ c-Mpl promoter, followed by the recruitment of transcription activators or repressors in order to promote transition of the hemogenic endothelium to HSCs, or differentiation into linages of lower haematopoetic hierarchies. RUNX1 can also function as a rheostat by upregulating the expression of Smad6 to target itself for proteasome
Proteasome
Proteasomes are very large protein complexes inside all eukaryotes and archaea, and in some bacteria. In eukaryotes, they are located in the nucleus and the cytoplasm. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks...
degradation.
Mutations and acute myeloid leukemia
At least 39 forms of RUNX1 mutation is implicated in various myeloid malignancies. Examples range from RUNX1 point mutations acquired from low-dose radiation leading to myelodysplasticMyelodysplastic syndrome
The myelodysplastic syndromes are a diverse collection of hematological medical conditions that involve ineffective production of the myeloid class of blood cells....
neoplasms (MDN) or therapy-related myeloid neoplasms (t-MN), to chromosomal translocation of the RUNX1 gene with the ETO / MTG8 / RUNX1T1 gene located on chromosome 8q22, t(8; 21), generating a fusion protein AML-ETO, categorized as acute myeloid leukemia
Acute myeloid leukemia
Acute myeloid leukemia , also known as acute myelogenous leukemia, is a cancer of the myeloid line of blood cells, characterized by the rapid growth of abnormal white blood cells that accumulate in the bone marrow and interfere with the production of normal blood cells. AML is the most common acute...
(AML) M2.
In t(8; 21), breakpoints frequently occur at intron
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
5 – 6 of RUNX1 and intron 1b – 2 of ETO, creating chimeric
Fusion protein
Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...
transcripts that inherit the runt domain from RUNX1, and all Nervy homology regions (NHR) 1-4 from ETO. As a consequence, AML-ETO retains the ability to bind at RUNX1 target genes whilst acting as a transcription repressor via the recruitment of corepressors and histone deacetylase
Histone deacetylase
Histone deacetylases are a class of enzymes that remove acetyl groups from an ε-N-acetyl lysine amino acid on a histone. This is important because DNA is wrapped around histones, and DNA expression is regulated by acetylation and de-acetylation. Its action is opposite to that of histone...
s, which is an intrinsic function of ETO. Oncogenic potential of AML-ETO is exerted because it blocks differentiation and promote self-renewal in blast cells, resulting in massive accumulation of blasts (>20%) in the bone marrow. This is further characterized histologically by the presence of Auer rods and epigenetically by lysine
Lysine
Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....
acetylation
Acetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
on residues 24 and 43. Other actions of AML-ETO that could induce leukemogenesis include downregulation of the DNA repair enzyme 8-oxoguanine DNA glycosylase (OGG1
Oxoguanine glycosylase
8-Oxoguanine glycosylase also known as OGG1 is a DNA glycosylase enzyme that, in humans, is encoded by the OGG1 gene. It is involved in base excision repair.- Function :...
) and increase in the level of intracellular reactive oxygen species
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....
, making cells that express AML-ETO more susceptible to additional genetic mutations.
Interactions
RUNX1 has been shown to interactProtein-protein interaction
Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...
with:
- C-FosC-FosIn the field of molecular biology and Genetics, c-Fos is a protein encoded by the FOS gene.-Structure and function:c-Fos is a cellular proto-oncogene belonging to the immediate early gene family of transcription factors. c-Fos has a leucine-zipper DNA binding domain, and a transactivation domain at...
, - C-junC-junc-Jun is the name of a gene and protein that, in combination with c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only later rediscovered as the product of the c-jun gene. It is activated through double phosphorylation by the...
, - SUV39H1SUV39H1Histone-lysine N-methyltransferase SUV39H1 is an enzyme that in humans is encoded by the SUV39H1 gene.-Interactions:SUV39H1 has been shown to interact with HDAC9, HDAC1, Histone deacetylase 2, Retinoblastoma protein, CBX5, HDAC3, DNMT3A, MBD1, RUNX1, SBF1 and CBX1.-Further reading:...
- TLE1TLE1Transducin-like enhancer protein 1 is a protein that in humans is encoded by the TLE1 gene.-Interactions:TLE1 has been shown to interact with TLE2, Glycoprotein 130, UTY, HES6, RUNX3, SIX3 and RUNX1.-Further reading:...
, and - VDRCalcitriol receptorThe calcitriol receptor, also known as the vitamin D receptor and also known as NR1I1 , is a member of the nuclear receptor family of transcription factors...
.