E3 ubiquitin-protein ligase RNF8 is an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

that in humans is encoded by the ''RNF8''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

. RNF8 has activity both in immune system functions and in DNA repair.

Function

The protein encoded by this gene contains a RING finger motif and an FHA domain. This protein has been shown to interact with several class II

ubiquitin-conjugating enzyme Ubiquitin-conjugating enzymes, also known as E2 enzymes and more rarely as ''ubiquitin-carrier enzymes'', perform the second step in the ubiquitination reaction that targets a protein for degradation via the proteasome. The ubiquitination process ...

s (E2), including UBE2E1/UBCH6, UBE2E2, and UBE2E3, and may act as a

ubiquitin ligase A ubiquitin ligase (also called an E3 ubiquitin ligase) is a protein that recruits an E2 ubiquitin-conjugating enzyme that has been loaded with ubiquitin, recognizes a protein substrate, and assists or directly catalyzes the transfer of ubiquitin ...

(E3) in the

ubiquitination Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 19 ...

of certain nuclear proteins. Alternatively spliced transcript variants encoding distinct isoforms have been reported. RNF8 promotes repair of DNA damage through three DNA repair pathways:

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

al repair (HRR),

non-homologous end joining Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. It is called "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology directed repair ...

(NHEJ), and

nucleotide excision repair Nucleotide excision repair is a DNA repair mechanism. DNA damage occurs constantly because of chemicals (e.g. Intercalation (biochemistry), intercalating agents), radiation and other mutagens. Three excision repair pathways exist to repair single ...

(NER). DNA damage is considered to be the primary cause of

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

, and deficiency in DNA repair can cause

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...

s leading to cancer. A deficiency in RNF8 predisposes mice to cancer.

Chromatin remodeling

After the occurrence of a double-strand break in DNA, the

chromatin Chromatin is a complex of DNA and protein found in eukaryote, 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 r ...

needs to be relaxed to allow DNA repair, either by

HRR HRR may refer to: * Haploid-relative-risk, a method for determining gene allele association to a disease * Color vision test#HRR plates, Hardy, Rand & Rittler pseudoisochromatic plates, a type of color vision test * Harrington railway station, in ...

or by NHEJ. There are two pathways that result in chromatin relaxation, one initiated by PARP1 and one initiated by γH2AX (the phosphorylated form of the H2AX protein) (see

Chromatin remodeling Chromatin remodeling is the dynamic modification of chromatin architecture to allow access of condensed genomic DNA to the regulatory transcription machinery proteins, and thereby control gene expression. Such remodeling is principally carried out ...

). Chromatin remodeling initiated by γH2AX depends on RNF8, as described below. The

histone In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei and in most Archaeal phyla. They act as spools around which DNA winds to create structural units called nucleosomes ...

variant H2AX constitutes about 10% of the H2A histones in human chromatin. At the site of a DNA double-strand break, the extent of chromatin with phosphorylated γH2AX is about two million base pairs. γH2AX does not, by itself, cause chromatin decondensation, but within seconds of irradiation the protein "Mediator of the DNA damage checkpoint 1" (

MDC1 Mediator of DNA damage checkpoint protein 1 is a 2080 amino acid long protein that in humans is encoded by the ''MDC1'' gene located on the short arm (p) of chromosome 6. MDC1 protein is a regulator of the Intra-S phase and the G2/M cell cycle ch ...

) specifically attaches to γH2AX. This is accompanied by simultaneous accumulation of RNF8 protein and the DNA repair protein

NBS1 Nibrin, also known as NBN or NBS1, is a protein which in humans is encoded by the ''NBN'' gene. Function Nibrin is a protein associated with the repair of double strand breaks (DSBs) which pose serious damage to a genome. It is a 754 amino a ...

which bind to

. RNF8 mediates extensive chromatin decondensation through its subsequent interaction with

CHD4 Chromodomain-helicase-DNA-binding protein 4 is an enzyme that in humans is encoded by the ''CHD4'' gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleo ...

protein, a component of the nucleosome remodeling and deacetylase complex NuRD.

RNF8 in Homologous Recombinational Repair

DNA end resection DNA end resection, also called 5′–3′ degradation, is a biochemical process where the blunt end of a section of double-stranded DNA (dsDNA) is modified by cutting away some nucleotides from the 5' end to produce a 3' single-stranded sequence. ...

is a pivotal step in HRR repair that produces 3’ overhangs that provide a platform to recruit proteins involved in HRR repair. The MRN complex, consisting of Mre11,

Rad50 DNA repair protein RAD50, also known as RAD50, is a protein that in humans is encoded by the ''RAD50'' gene. Function The protein encoded by this gene is highly similar to ''Saccharomyces cerevisiae'' Rad50, a protein involved in DNA double- ...

and

, carries out the initial steps of this end resection. RNF8 ubiquitinates

(both before and after DNA damage occurs), and this ubiquitination is required for effective homologous recombinational repair. Ubiquitination of NBS1 by RNF8 is, however, not required for the role of NBS1 in another DNA repair process, the error-prone

microhomology-mediated end joining Microhomology-mediated end joining (MMEJ), also known as alternative nonhomologous end-joining (Alt-NHEJ) is one of the pathways for repairing double-strand breaks in DNA. As reviewed by McVey and Lee, the foremost distinguishing property of MMEJ ...

DNA repair. RNF8 appears to have other roles in HRR as well. RNF8, acting as a ubiquitin ligase, mono-ubiquitinates γH2AX to tether DNA repair molecules at DNA lesions. In particular, RNF8 activity is required to recruit BRCA1 for homologous recombination repair.

RNF8 in Non-Homologous End Joining

Ku protein is a dimeric protein complex, a

heterodimer In biochemistry, a protein dimer is a macromolecular complex or multimer formed by two protein monomers, or single proteins, which are usually non-covalently bound. Many macromolecules, such as proteins or nucleic acids, form dimers. The word ...

of two

polypeptides Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ami ...

Ku70 Ku70 is a heterodimeric protein made up of Ku70 and Ku80, which together form Ku. In humans, is encoded by the ''XRCC6'' gene. Ku70 plays a critical role in the DNA repair, maintenance and many other cellular processes. Function Together, Ku7 ...

and

Ku80 Ku80 is a protein that, in humans, is encoded by the ''XRCC5'' gene. Together, Ku70 and Ku80 make up the Ku heterodimer, which binds to DNA double-strand break ends and is required for the non-homologous end joining (NHEJ) pathway of DNA rep ...

. Ku protein forms a ring structure. An early step in

DNA repair of a double-strand break is the slipping of a Ku protein (with its ring protein structure) over each

end End, END, Ending, or ENDS may refer to: End Mathematics *End (category theory) * End (topology) * End (graph theory) * End (group theory) (a subcase of the previous) * End (endomorphism) Sports and games *End (gridiron football) *End, a division ...

of the broken

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

. The two Ku proteins, one on each broken end, bind to each other and form a bridge. This protects the DNA ends and forms a platform for further DNA repair enzymes to operate. After the broken ends are rejoined, the two Ku proteins still encircle the now intact DNA and can no longer slip off an end. The Ku proteins must be removed or they cause loss of cell viability. The removal of Ku protein is performed either by RNF8 ubiquitination of Ku80, allowing it to be released from the Ku protein ring, or else by

NEDD8 NEDD8 is a protein that in humans is encoded by the ''NEDD8'' gene. (in ''Saccharomyces cerevisiae'' this protein is known as Rub1) This ubiquitin-like protein, ubiquitin-like (UBL) protein becomes covalently conjugated to a limited number of cell ...

promoted ubiquitination of Ku protein, causing its release from DNA.

RNF8 in Nucleotide Excision Repair

UV-induced formation of pyrimidine dimers in DNA can lead to cell death unless the lesions are repaired. Most repair of these lesions is by nucleotide excision repair. After UV-irradiation, RNF8 is recruited to sites of UV-induced DNA damage and ubiquitinates

component

H2A. These responses provide partial protection against UV irradiation.

Impaired spermatogenesis

Spermatogenesis Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testicle. This process starts with the Mitosis, mitotic division of the stem cells located close to the basement membrane of ...

is the process in which

spermatozoa A spermatozoon (; also spelled spermatozoön; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is ...

are produced from

spermatogonial stem cells A spermatogonial stem cell (SSC), also known as a type A spermatogonium, is a spermatogonium that does not differentiate into a spermatocyte, a precursor of sperm cells. Instead, they continue dividing into other spermatogonia or remain dormant ...

by way of

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

and

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

. A major function of meiosis is

al repair of this

germline In biology and genetics, the germline is the population of a multicellular organism's cells that develop into germ cells. In other words, they are the cells that form gametes ( eggs and sperm), which can come together to form a zygote. They dif ...

DNA. RNF8 plays an essential role in signaling the presence of DNA double-strand breaks. Male mice with a

gene knockout Gene knockouts (also known as gene deletion or gene inactivation) are a widely used genetic engineering technique that involves the gene targeting, targeted removal or inactivation of a specific gene within an organism's genome. This can be done t ...

for RNF8 have impaired spermatogenesis, apparently due to a defect in homologous recombinational repair.

Interactions

RNF8 has been shown to interact with

Retinoid X receptor alpha Retinoid X receptor alpha (RXR-alpha), also known as NR2B1 (nuclear receptor subfamily 2, group B, member 1) is a nuclear receptor that in humans is encoded by the ''RXRA'' gene. Function Retinoid X receptors (RXRs) and retinoic acid receptors ...

References

External links

* {{MeshName, RNF8+protein,+human RING finger proteins