Runt-related transcription factor 3 is a protein that in humans is encoded by the RUNX3 gene. [5]
Runt-related transcription factor 3 is a protein that in humans is encoded by the RUNX3 gene. [5]
This gene encodes a member of the runt domain-containing family of transcription factors. A heterodimer of this protein and a beta subunit forms a complex that binds to the core DNA sequence 5'-YGYGGT-3' found in a number of enhancers and promoters, [6] and can either activate or suppress transcription. It also interacts with other transcription factors. It functions as a tumor suppressor, and the gene is frequently deleted or transcriptionally silenced in cancer. Multiple transcript variants encoding different isoforms have been found for this gene. [7]
In melanocytic cells RUNX3 gene expression may be regulated by MITF. [8]
RUNX3 plays a fundamental role in defense against early tumor formation. In response to growth factors, RUNX3 is acetylated by p300 to complex with bromodomain-containing protein 2 (BRD2; a member of the BET family of transcription co-regulators) [9] and to subsequent transient induction of CDKN1A and ARF. [10] CDKN1A (also known as CIP1 or p21) inhibits the cell cycle, and ARF inhibits MDM2, increasing the stability of the cancer-suppressing gene p53. [10]
The expression of CDKN1A and ARF under wild-type cell cycles is temporary, which results from the RUNX3-BRD2 complex replacing the RUNX3-cyclinD1 complex. However, oncogenic mitogen signals such as KRASG12D cause the RUNX3-BRD2 complex to be maintained continuously, resulting in the continuous expression of p21, ARF, and p53. Therefore, RUNX3 can function as a sensor for unregulated mitogenic signals, and its inactivation can ultimately lead to cancer due to the loss of function as a sensor. [10]
Runx3 null mouse gastric mucosa exhibits hyperplasia due to stimulated proliferation and suppressed apoptosis in epithelial cells, and the cells are resistant to TGF-beta stimulation. [11]
In 2011 doubt was cast over the tumor suppressor function of Runx3 originated from the earlier publication by Li and co-workers. [12] On the basis of the original study by Li and co-workers (2002), the majority of later literature citing Li and co-workers (2002) assumed that RUNX3 was expressed in the normal gut epithelium and that it is therefore likely to act as a tumor suppressor in the particular epithelial cancer investigated. Most of this literature used RUNX3 promoter methylation status in various cancers as a proxy for its expression. However, quite many genes are known to be methylated in tumor cell genomes, and the majority of these genes are not expressed in the normal tissue of origin of these cancers. Others used poorly characterized (or fully invalidated) antibodies to detect the RUNX3 protein, or used RT-PCR or validated antibodies and failed to detect RUNX3 in the gut epithelium but still did not question the original finding by Li and co-workers (2002). This facts have recently been discussed in a book by Ülo Maiväli. [13]
In late 2009, a report written by Kosei Ito and his co-workers resolved the controversy by verifying that RUNX3 is indeed expressed in human and mouse gastrointestinal tract (GIT) epithelium and it functions as a tumor suppressor in gastric and colorectal tissues. [14] The authors of the paper suggested that the previous conflicting report might be caused by use of a specific antibody, known as G-poly. Ito and his team generated multiple anti-RUNX3 monoclonal antibodies recognizing the RUNX3 N-terminal region (residues 1-234). The researchers found that the antibodies react with RUNX3 in gastric epithelial cells, whereas those recognizing the C-terminal region did not. G-poly primarily recognizes the region beyond 234 and hence, is unable to detect Runx3 in this tissue.
Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abnormal cell division. Cell division is a physiological process that occurs in almost all tissues and under a variety of circumstances. Normally, the balance between proliferation and programmed cell death, in the form of apoptosis, is maintained to ensure the integrity of tissues and organs. According to the prevailing accepted theory of carcinogenesis, the somatic mutation theory, mutations in DNA and epimutations that lead to cancer disrupt these orderly processes by interfering with the programming regulating the processes, upsetting the normal balance between proliferation and cell death. This results in uncontrolled cell division and the evolution of those cells by natural selection in the body. Only certain mutations lead to cancer whereas the majority of mutations do not.
The Von Hippel–Lindau tumor suppressor also known as pVHL is a protein that, in humans, is encoded by the VHL gene. Mutations of the VHL gene are associated with Von Hippel–Lindau disease, which is characterized by hemangioblastomas of the brain, spinal cord and retina. It is also associated with kidney and pancreatic lesions.
Runt-related transcription factor 2 (RUNX2) also known as core-binding factor subunit alpha-1 (CBF-alpha-1) is a protein that in humans is encoded by the RUNX2 gene. RUNX2 is a key transcription factor associated with osteoblast differentiation.
Transcription factor Jun is a protein that in humans is encoded by the JUN gene. c-Jun, in combination with protein 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 JUN gene. c-jun was the first oncogenic transcription factor discovered. The proto-oncogene c-Jun is the cellular homolog of the viral oncoprotein v-jun. The viral homolog v-jun was discovered in avian sarcoma virus 17 and was named for ju-nana, the Japanese word for 17. The human JUN encodes a protein that is highly similar to the viral protein, which interacts directly with specific target DNA sequences to regulate gene expression. This gene is intronless and is mapped to 1p32-p31, a chromosomal region involved in both translocations and deletions in human malignancies.
Enolase 1 (ENO1), more commonly known as alpha-enolase, is a glycolytic enzyme expressed in most tissues, one of the isozymes of enolase. Each isoenzyme is a homodimer composed of 2 alpha, 2 gamma, or 2 beta subunits, and functions as a glycolytic enzyme. Alpha-enolase, in addition, functions as a structural lens protein (tau-crystallin) in the monomeric form. Alternative splicing of this gene results in a shorter isoform that has been shown to bind to the c-myc promoter and function as a tumor suppressor. Several pseudogenes have been identified, including one on the long arm of chromosome 1. Alpha-enolase has also been identified as an autoantigen in Hashimoto encephalopathy.
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.
Krüppel-like factor 4 is a member of the KLF family of zinc finger transcription factors, which belongs to the relatively large family of SP1-like transcription factors. KLF4 is involved in the regulation of proliferation, differentiation, apoptosis and somatic cell reprogramming. Evidence also suggests that KLF4 is a tumor suppressor in certain cancers, including colorectal cancer. It has three C2H2-zinc fingers at its carboxyl terminus that are closely related to another KLF, KLF2. It has two nuclear localization sequences that signals it to localize to the nucleus. In embryonic stem cells (ESCs), KLF4 has been demonstrated to be a good indicator of stem-like capacity. It is suggested that the same is true in mesenchymal stem cells (MSCs).
Core-binding factor subunit beta is a protein that in humans is encoded by the CBFB gene.
Secreted frizzled-related protein 1, also known as SFRP1, is a protein which in humans is encoded by the SFRP1 gene.
Transducin-like enhancer protein 1 is a protein that in humans is encoded by the TLE1 gene.
Homeobox protein Hox-A5 is a protein that in humans is encoded by the HOXA5 gene.
XIAP-associated factor 1 is a protein that in humans is encoded by the XAF1 gene.
ID4 is a protein coding gene. In humans, it encodes the protein known as DNA-binding protein inhibitor ID-4. This protein is known to be involved in the regulation of many cellular processes during both prenatal development and tumorigenesis. This is inclusive of embryonic cellular growth, senescence, cellular differentiation, apoptosis, and as an oncogene in angiogenesis.
CDKN2A, also known as cyclin-dependent kinase inhibitor 2A, is a gene which in humans is located at chromosome 9, band p21.3. It is ubiquitously expressed in many tissues and cell types. The gene codes for two proteins, including the INK4 family member p16 and p14arf. Both act as tumor suppressors by regulating the cell cycle. p16 inhibits cyclin dependent kinases 4 and 6 and thereby activates the retinoblastoma (Rb) family of proteins, which block traversal from G1 to S-phase. p14ARF activates the p53 tumor suppressor. Somatic mutations of CDKN2A are common in the majority of human cancers, with estimates that CDKN2A is the second most commonly inactivated gene in cancer after p53. Germline mutations of CDKN2A are associated with familial melanoma, glioblastoma and pancreatic cancer. The CDKN2A gene also contains one of 27 SNPs associated with increased risk of coronary artery disease.
Transcription factor 21 (TCF21), also known as pod-1, capsuling, or epicardin, is a protein that in humans is encoded by the TCF21 gene on chromosome 6. It is ubiquitously expressed in many tissues and cell types and highly significantly expressed in lung and placenta. TCF21 is crucial for the development of a number of cell types during embryogenesis of the heart, lung, kidney, and spleen. TCF21 is also deregulated in several types of cancers, and thus known to function as a tumor suppressor. The TCF21 gene also contains one of 27 SNPs associated with increased risk of coronary artery disease.
Protein CBFA2T3 is a protein that in humans is encoded by the CBFA2T3 gene.
Sodium-coupled monocarboxylate transporter 1 (i.e., SMCT1) and sodium-coupled monocarboxylate transporter 2 (i.e., SMCT2) are plasma membrane transport proteins in the solute carrier family. They transport sodium cations in association with the anionic forms (see conjugated base) of certain short-chain fatty acids (i.e., SC-FAs) through the plasma membrane from the outside to the inside of cells. For example, propionic acid (i.e., CH
3CH
2CO
2H) in its anionic "propionate" form (i.e., CH
3CH
2CO−
2) along with sodium cations (i.e., Na+) are co-transported from the extracellular fluid into a SMCT1-epxressing cell's cytoplasm. Monocarboxylate transporters (MCTs) are also transport proteins in the solute carrier family. They co-transport the anionic forms of various compounds into cells in association with proton cations (i.e. H+). Four of the 14 MCTs, i.e. SLC16A1 (i.e., MCT1), SLC16A7 (i.e., MCT22), SLC16A8 (i.e., MCT3), and SLC16A3 (i.e., MCT4), transport some of the same SC-FAs anions that the SMCTs transport into cells. SC-FAs do diffuse into cells independently of transport proteins but at the levels normally occurring in tissues far greater amounts of the SC-FAs are brought into cells that express a SC-FA transporter.
In molecular biology, miR-137 is a short non-coding RNA molecule that functions to regulate the expression levels of other genes by various mechanisms. miR-137 is located on human chromosome 1p22 and has been implicated to act as a tumor suppressor in several cancer types including colorectal cancer, squamous cell carcinoma and melanoma via cell cycle control.
Forkhead box protein J1 is a protein that in humans is encoded by the FOXJ1 gene. It is a member of the Forkhead/winged helix (FOX) family of transcription factors that is involved in ciliogenesis. FOXJ1 is expressed in ciliated cells of the lung, choroid plexus, reproductive tract, embryonic kidney and pre-somite embryo stage.
Generally, in progression to cancer, hundreds of genes are silenced or activated. Although silencing of some genes in cancers occurs by mutation, a large proportion of carcinogenic gene silencing is a result of altered DNA methylation. DNA methylation causing silencing in cancer typically occurs at multiple CpG sites in the CpG islands that are present in the promoters of protein coding genes.
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This article incorporates text from the United States National Library of Medicine, which is in the public domain.
