TRIM28
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Tripartite motif-containing 28 (TRIM28), also known as transcriptional intermediary factor 1β (TIF1β) and KAP1 (KRAB-associated protein-1), is a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
that in humans is encoded by the ''TRIM28''
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.


Function

The protein encoded by this gene mediates transcriptional control by interaction with the
Krüppel Krüppel is a gap gene in ''Drosophila melanogaster'', located on the 2R chromosome, which encodes a zinc finger C2H2 transcription factor. Gap genes work together to establish the anterior-posterior segment patterning of the insect through r ...
-associated box repression domain found in many
transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...
s. The protein localizes to the
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...
and is thought to associate with specific
chromatin Chromatin is a complex of DNA and protein found in eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in r ...
regions. The protein is a member of the
tripartite motif family The tripartite motif family (TRIM) is a protein family. Function Many TRIM proteins are induced by interferons, which are important component of resistance to pathogens and several TRIM proteins are known to be required for the restriction of infe ...
. This tripartite motif includes three zinc-binding domains, a RING, a B-box type 1 and a B-box type 2, and a
coiled-coil A coiled coil is a structural motif in proteins in which 2–7 alpha helix, alpha-helices are coiled together like the strands of a rope. (Protein dimer, Dimers and Protein trimer, trimers are the most common types.) Many coiled coil-type protei ...
region. KAP1 is a ubiquitously expressed protein involved in many critical functions including: transcriptional regulation, cellular differentiation and proliferation, DNA damage repair, viral suppression, and apoptosis. Its functionality is dependent upon post-translational modifications. Sumoylated TRIM28 can assemble epigenetic machinery for gene silencing, while phosphorylated TRIM28 is involved in DNA repair.


Cellular differentiation and proliferation

Studies have shown that deletion of KAP1 in mice before gastrulation results in death (implicating it as a necessary protein for proliferation) while deletion in adult mice results in increased anxiety and stress-induced alterations in learning and memory. KAP1 has been shown to participate in the maintenance of pluripotency of embryonic stem cells and to promote and inhibit cellular differentiation of adult cell lines. Increased levels of KAP1 have been found in liver, gastric, breast, lung, and prostate cancers as well, indicating that it may play an important role in tumor cell proliferation (possibly by inhibiting apoptosis).


Transcriptional regulation

KAP1 can regulate genomic transcription through a variety of mechanisms, many of which remain somewhat unclear. Studies have shown that KAP1 can repress transcription by binding directly to the genome (which can be sufficient in and of itself) or through the induction of heterochromatin formation via the Mi2α-SETB1-HP1 macromolecular complex. KAP1 can also interact with histone methyltransferases and deacetylases via the C-terminal PHD and Bromodomain to control transcription epigenetically.


DNA damage repair response

It has been shown that ATM phosphorylates KAP1 upon the discovery of damaged or broken DNA. Phosphorylated KAP1, along with many other DNA damage proteins, rapidly migrate to the site of the DNA damage. Its exact involvement in this pathway is somewhat unclear, but it has been implicated in triggering cell arrest, allowing for the damaged DNA to be repaired.


Apoptosis

KAP1 forms a complex with MDM2 (a ubiquitin E3 ligase) that binds to p53. The complex marks the bound p53 for degradation. p53 is a known precursor of apoptosis that facilitates the synthesis of proteins necessary for cell death so its degradation results in apoptosis inhibition.


Clinical significance


Role in the establishment of viral latency

KAP1 facilitates the establishment of viral latency in certain cell types for Human Cytomegalovirus (HCMV) and other endogenous retroviruses . KAP1 acts as a transcriptional corepressor of the viral genome. The protein binds to the histones of the viral chromatin and then recruits Mi2α and SETB1. SETB1 is a histone methyltransferase that recruits HP1, thus inducing heterochromatin formation. This heterochromatin formation prevents the transcription of the viral genome. mTOR has been implicated in the phosphorylation of KAP1 resulting in a switch from latency to the lytic cycle.


Manipulations and potential for future treatment

Ataxia telangiectasia mutated (ATM) is a kinase that (similar to mTOR) can phosphorylate KAP1 resulting in the switch from viral latency to the lytic cycle. Chloroquine (an ATM) activator has been shown to result in increases in transcription of the HCMV genome. This effect is augmented by the use of tumor necrosis factor It has been proposed that this treatment (accompanied by antiretroviral treatment) has the potential to purge the virus from infected individuals.


Interactions

TRIM28 has been shown to
interact Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...
with: * CBX5, *
CEBPB CCAAT/enhancer-binding protein beta is a protein that in humans is encoded by the ''CEBPB'' gene. Function The protein encoded by this intronless gene is a bZIP transcription factor that can bind as a homodimer to certain DNA regulatory regi ...
, *
Glucocorticoid receptor The glucocorticoid receptor (GR, or GCR) also known as NR3C1 (nuclear receptor subfamily 3, group C, member 1) is the receptor to which cortisol and other glucocorticoids bind. The GR is expressed in almost every cell in the body and regulates ...
, *
SETDB1 Histone-lysine N-methyltransferase SETDB1 is an enzyme that in humans is encoded by the ''SETDB1'' gene. SETDB1 is also known as KMT1E or H3K9 methyltransferase ESET. Function The SET domain is a highly conserved, approximately 150-amino acid ...
and *
ZNF10 Zinc finger protein 10 is a protein that in humans is encoded by the ''ZNF10'' gene. Function The protein encoded by this gene contains a C2H2 zinc finger, and has been shown to function as a transcriptional repressor. The Kruppel-associated b ...
.


See also

*
Transcription coregulator In molecular biology and genetics, transcription coregulators are proteins that interact with transcription factors to either activate or repress the transcription of specific genes. Transcription coregulators that activate gene transcription are ...


References


Further reading

* * * * * * * * * * * * * * * * * * *


External links

* * * * * {{Transcription coregulators Gene expression Transcription coregulators