Chromodomain-helicase-DNA-binding protein 1-like (ALC1) is an enzyme that in humans is encoded by the CHD1L gene. [5] [6] It has been implicated in chromatin remodeling and DNA relaxation process required for DNA replication, repair and transcription. The ALC1 comprises ATPase domain and macro domain. On the basis of homology within the ATPase domain, ALC1 belongs to Snf2 family. [7]
It has 897 amino acids and is approximately 101kDa in size. [8]
CHD1L, a DNA helicase, possesses chromatin remodeling activity and interacts with PARP1/PARylation in regulating pluripotency during developmental reprogramming. The CHD1L macro-domain interacts with the PAR moiety of PARylated-PARP1 to facilitate early-stage reprogramming and pluripotency in stem cells. [9] It appears that CHD1L expression is vital for early events in embryonic development. [10] CHD1L's role in embryonic development is related to its role as a transcriptional activator of several genes (Akt, METP2, TCF4) which lead to EMT (epithelial to mesenchymal transition) [11] Notably, EMT is also implicated in tumor metastasis, [12] further complicating CHD1L's role in both healthy and diseased cells.
To allow the critical cellular process of DNA repair, the chromatin must be remodeled at sites of damage. CHD1L (ALC1) a chromatin remodeling protein, acts very early in DNA repair. Chromatin relaxation occurs rapidly at the site of a DNA damage. [13] This process is initiated by PARP1 protein that starts to appear at DNA damage in less than a second, with half maximum accumulation within 1.6 seconds after the damage occurs. [14] PARP1 then PARylates itself, with these PAR chains attracting the macro domain of CHD1L, relieving autoinhibition and allowing the N-terminal domains to interact with chromatin. [15] The linker between the macro and N-terminal domains wraps around the histone, interacting with the acidic nucleosome patch via an R611 anchor. [16] Next the chromatin remodeler CHD1L (ALC1) quickly attaches to the product of PARP1, and completes arrival at the DNA damage within 10 seconds of the damage. [13] About half of the maximum chromatin relaxation, due to action of CHD1L (ALC1), occurs by 10 seconds. [13] This then allows recruitment of the DNA repair enzyme MRE11, to initiate DNA repair, within 13 seconds. [14] MRE11 is involved in homologous recombinational repair. CHD1L (ALC1) is also required for repair of UV-damaged chromatin through nucleotide excision repair. [17]
With 1q21.1 deletion syndrome a disturbance occurs, which leads to increased DNA breaks. The role of CHD1L is similar to that of helicase with the Werner syndrome [18]
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 reinforcing the DNA during cell division, preventing DNA damage, and regulating gene expression and DNA replication. During mitosis and meiosis, chromatin facilitates proper segregation of the chromosomes in anaphase; the characteristic shapes of chromosomes visible during this stage are the result of DNA being coiled into highly condensed chromatin.
DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA damage, resulting in tens of thousands of individual molecular lesions per cell per day. Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to transcribe the gene that the affected DNA encodes. Other lesions induce potentially harmful mutations in the cell's genome, which affect the survival of its daughter cells after it undergoes mitosis. As a consequence, the DNA repair process is constantly active as it responds to damage in the DNA structure. When normal repair processes fail, and when cellular apoptosis does not occur, irreparable DNA damage may occur. This can eventually lead to malignant tumors, or cancer as per the two-hit hypothesis.
Poly (ADP-ribose) polymerase (PARP) is a family of proteins involved in a number of cellular processes such as DNA repair, genomic stability, and programmed cell death.
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.
c-Jun N-terminal kinases (JNKs), were originally identified as kinases that bind and phosphorylate c-Jun on Ser-63 and Ser-73 within its transcriptional activation domain. They belong to the mitogen-activated protein kinase family, and are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock. They also play a role in T cell differentiation and the cellular apoptosis pathway. Activation occurs through a dual phosphorylation of threonine (Thr) and tyrosine (Tyr) residues within a Thr-Pro-Tyr motif located in kinase subdomain VIII. Activation is carried out by two MAP kinase kinases, MKK4 and MKK7, and JNK can be inactivated by Ser/Thr and Tyr protein phosphatases. It has been suggested that this signaling pathway contributes to inflammatory responses in mammals and insects.
H2A histone family member X is a type of histone protein from the H2A family encoded by the H2AFX gene. An important phosphorylated form is γH2AX (S139), which forms when double-strand breaks appear.
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 by 1) covalent histone modifications by specific enzymes, e.g., histone acetyltransferases (HATs), deacetylases, methyltransferases, and kinases, and 2) ATP-dependent chromatin remodeling complexes which either move, eject or restructure nucleosomes. Besides actively regulating gene expression, dynamic remodeling of chromatin imparts an epigenetic regulatory role in several key biological processes, egg cells DNA replication and repair; apoptosis; chromosome segregation as well as development and pluripotency. Aberrations in chromatin remodeling proteins are found to be associated with human diseases, including cancer. Targeting chromatin remodeling pathways is currently evolving as a major therapeutic strategy in the treatment of several cancers.
ADP-ribosylation is the addition of one or more ADP-ribose moieties to a protein. It is a reversible post-translational modification that is involved in many cellular processes, including cell signaling, DNA repair, gene regulation and apoptosis. Improper ADP-ribosylation has been implicated in some forms of cancer. It is also the basis for the toxicity of bacterial compounds such as cholera toxin, diphtheria toxin, and others.
Poly [ADP-ribose] polymerase 1 (PARP-1) also known as NAD+ ADP-ribosyltransferase 1 or poly[ADP-ribose] synthase 1 is an enzyme that in humans is encoded by the PARP1 gene. It is the most abundant of the PARP family of enzymes, accounting for 90% of the NAD+ used by the family. PARP1 is mostly present in cell nucleus, but cytosolic fraction of this protein was also reported.
Double-strand break repair protein MRE11 is an enzyme that in humans is encoded by the MRE11 gene. The gene has been designated MRE11A to distinguish it from the pseudogene MRE11B that is nowadays named MRE11P1.
DNA damage-binding protein 2 is a protein that in humans is encoded by the DDB2 gene.
DNA repair protein RAD50, also known as RAD50, is a protein that in humans is encoded by the RAD50 gene.
DNA topoisomerase 2-binding protein 1 (TOPBP1) is a scaffold protein that in humans is encoded by the TOPBP1 gene.
AT-rich interactive domain-containing protein 1A is a protein that in humans is encoded by the ARID1A gene.
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 checkpoints and recruits repair proteins to the site of DNA damage. It is involved in determining cell survival fate in association with tumor suppressor protein p53. This protein also goes by the name Nuclear Factor with BRCT Domain 1 (NFBD1).
Core histone macro-H2A.1 is a protein that in humans is encoded by the H2AFY gene.
The Chromodomain-Helicase DNA-binding 1 is a protein that, in humans, is encoded by the CHD1 gene. CHD1 is a chromatin remodeling protein that is widely conserved across many eukaryotic organisms, from yeast to humans. CHD1 is named for three of its protein domains: two tandem chromodomains, its ATPase catalytic domain, and its DNA-binding domain.
E3 ubiquitin-protein ligase RNF8 is an enzyme that in humans is encoded by the RNF8 gene. RNF8 has activity both in immune system functions and in DNA repair.
DNA damage is an alteration in the chemical structure of DNA, such as a break in a strand of DNA, a nucleobase missing from the backbone of DNA, or a chemically changed base such as 8-OHdG. DNA damage can occur naturally or via environmental factors, but is distinctly different from mutation, although both are types of error in DNA. DNA damage is an abnormal chemical structure in DNA, while a mutation is a change in the sequence of base pairs. DNA damages cause changes in the structure of the genetic material and prevents the replication mechanism from functioning and performing properly. The DNA damage response (DDR) is a complex signal transduction pathway which recognizes when DNA is damaged and initiates the cellular response to the damage.
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. The presence of a section of single-stranded DNA (ssDNA) allows the broken end of the DNA to line up accurately with a matching sequence, so that it can be accurately repaired.
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