Cdc6

Last updated
Cell division protein Cdc6/18
Identifiers
SymbolCdc6
InterPro IPR016314
Orc1/Cdc6-type DNA replication protein, archaea
Cdc6.png
Crystal Structure of CDC6 from P. aerophilum ( PDB: 1FNN ​). Green and blue domains are AAA domains; red domain is the Cdc6 C-terminal HTH domain (infobox below). [1]
Identifiers
SymbolOrc1/Cdc6_arc
InterPro IPR014277
Cdc6/Orc1, C-terminal
Identifiers
SymbolCdc6_C
Pfam PF09079
InterPro IPR015163
CDD cd08768
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary

Cdc6, or cell division cycle 6, is a protein in eukaryotic cells. It is mainly studied in the budding yeast Saccharomyces cerevisiae ( P09119 ). It is an essential regulator of DNA replication and plays important roles in the activation and maintenance of the checkpoint mechanisms in the cell cycle that coordinate S phase and mitosis. It is part of the pre-replicative complex (pre-RC) and is required for loading minichromosome maintenance (MCM) proteins onto the DNA, an essential step in the initiation of DNA synthesis. In addition, it is a member of the family of AAA+ ATPases and highly related to ORC1; both are the same protein in archaea. [2]

Contents

Function

Potential role of Cdc6 at the initiation of DNA replication. CDC6 Function.jpg
Potential role of Cdc6 at the initiation of DNA replication.

CDC6 is an ATP binding protein and a member of the pre-replicative complex (pre-RC) together with the origin recognition complex (ORC), Cdt1 and the MCM complex (containing MCM2-7p). CDC6 assembles after ORC in an ATP dependent manner and is required for loading MCM proteins onto the DNA. Reconstruction of electron microscope images showed that the ORC-CDC6 complex forms a ring-shaped structure with similar dimensions to those of ring-shaped MCM helicase. [4] A near-atomic resolution model of the entire ORC-Cdc6-Cdt1-Mcm2-7 (OCCM) complex with DNA was assembled from EM data in 2017. [5] It is thought that the CDC6-Cdt1 complex uses ATP hydrolysis to thread DNA through the central hole of the MCM doughnut. [6] Mutations in the binding motif of CDC6 strongly suggest that ATP binding and hydrolysis is essential for its function. [7] The minimal requirement for DNA binding has been mapped within its 47-amino acid sequence. [8] Furthermore, Cdc6 indirectly inhibits activation of the p34cdc2/CDC28 M phase kinase, thus nuclear division is suppressed. [9]

Regulation

CDC6 is normally present at high levels during the G1 phase of the cell cycle. This is partly because the CDC6 gene is only transcribed during G1 phase. On the onset of the S phase, CDC6 gets phosphorylated by the Cdc28-Clb5-Clb6 complex (Cdk2) and consequently becoming inactivated. This has been shown by introducing mutations in CDC6 at the consensus sites for Cdk2 phosphorylation (near the N-terminus) which inhibit degradation. The phosphorylation can furthermore be catalyzed by Cdc28-Cln. The inactivated CDC6 is then targeted for degradation by SCFCDC4-dependent ubiquitinylation and afterwards degraded by the proteasome. Thus, the regulation of CDC6 is tightly correlated to the activity of Cdk2 and since Cdk2-activity is oscillating once per cell cycle, the accumulation and degradation of CDC6 also oscillates.

Two states can be distinguished. In the first state (during G1 phase) Cdk2-activity is low, CDC6 can accumulate, hence the pre-RC can be formed but not activated. In the second state Cdk2-activity is high, CDC6 becomes inactivated, hence the pre-RC is activated but not formed. This change assures that DNA replication is performed only once per cell cycle. It has been shown that overexpression of CDC6 does not induce re-replication in cognate cells, probably due to inhibition through CDK that resets the cell cycle clock to G1. Nevertheless, it has been suggested that regulation of CDC6 is one of several redundant mechanisms that prevent re-replication of the DNA in eukaryotic cells. [10]

Structure

Crystal Structure of CDC6 from Pyrobaculum aerophilum. Domain I in green, domain II in blue and domain III in red. Beta-sheets are shown in orange. Cdc6.png
Crystal Structure of CDC6 from Pyrobaculum aerophilum. Domain I in green, domain II in blue and domain III in red. Beta-sheets are shown in orange.

The crystallographic structure of a Cdc6/Orc1-related protein from the archaeon Pyrobaculum aerophilum has been solved and three structural domains have been identified. [1] Domain I and II form the ATP binding/hydrolysis site and are similar to other AAA+ ATPases. Domain III is structurally related to a winged-helix domain, thus may interact with origin DNA. From studies with E. coli γ clamp loading complex, it was suggested that domain III mediates protein-protein interactions with other AAA+ ATPases in the pre-RC, thus suggesting that the CDC6 builds a homodimer in its native form. The domains I and II form a cashew-shaped molecule that bind ATP in the cleft and additionally build the sensor motif for ATP/ADP recognition. These domains are also thought to mediate subsequent conformational changes. Nevertheless, the exact functional roles of these domains remain unclear. [8]

Disease

It has been shown CDC6 shows proto-oncogenic activity. Cdc6 overexpression interferes with the expression of INK4/ARF tumor suppressor genes through a mechanism involving the epigenetic modification of chromatin at the INK4/ARF locus. In addition, CDC6 overexpression in primary cells may promote DNA hyper-replication and induce a senescence response similar to that caused by oncogene activation. These findings indicate that deregulation of CDC6 expression in human cells poses a serious risk of carcinogenesis. [3] Down-regulation of CDC6 in prostate cancer was observed and associated with phenotypic characteristics of aggressive prostate cancer. [11] Furthermore, it has been observed that Cdc6 is greatly up-regulated in cervical cancer, lung cancer and brain cancer. [12]

See also

Related Research Articles

<span class="mw-page-title-main">DNA replication</span> Biological process

In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part of biological inheritance. This is essential for cell division during growth and repair of damaged tissues, while it also ensures that each of the new cells receives its own copy of the DNA. The cell possesses the distinctive property of division, which makes replication of DNA essential.

<span class="mw-page-title-main">Origin of replication</span> Sequence in a genome

The origin of replication is a particular sequence in a genome at which replication is initiated. Propagation of the genetic material between generations requires timely and accurate duplication of DNA by semiconservative replication prior to cell division to ensure each daughter cell receives the full complement of chromosomes. This can either involve the replication of DNA in living organisms such as prokaryotes and eukaryotes, or that of DNA or RNA in viruses, such as double-stranded RNA viruses. Synthesis of daughter strands starts at discrete sites, termed replication origins, and proceeds in a bidirectional manner until all genomic DNA is replicated. Despite the fundamental nature of these events, organisms have evolved surprisingly divergent strategies that control replication onset. Although the specific replication origin organization structure and recognition varies from species to species, some common characteristics are shared.

<span class="mw-page-title-main">Pre-replication complex</span>

A pre-replication complex (pre-RC) is a protein complex that forms at the origin of replication during the initiation step of DNA replication. Formation of the pre-RC is required for DNA replication to occur. Complete and faithful replication of the genome ensures that each daughter cell will carry the same genetic information as the parent cell. Accordingly, formation of the pre-RC is a very important part of the cell cycle.

<span class="mw-page-title-main">S phase</span> DNA replication phase of the cell cycle, between G1 and G2 phase

S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase. Since accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved.

E2F is a group of genes that encodes a family of transcription factors (TF) in higher eukaryotes. Three of them are activators: E2F1, 2 and E2F3a. Six others act as suppressors: E2F3b, E2F4-8. All of them are involved in the cell cycle regulation and synthesis of DNA in mammalian cells. E2Fs as TFs bind to the TTTCCCGC consensus binding site in the target promoter sequence.

<span class="mw-page-title-main">MCM6</span>

DNA replication licensing factor MCM6 is a protein that in humans is encoded by the MCM6 gene. MCM6 is one of the highly conserved mini-chromosome maintenance proteins (MCM) that are essential for the initiation of eukaryotic genome replication.

A licensing factor is a protein or complex of proteins that allows an origin of replication to begin DNA replication at that site. Licensing factors primarily occur in eukaryotic cells, since bacteria use simpler systems to initiate replication. However, many archaea use homologues of eukaryotic licensing factors to initiate replication.

In molecular biology, origin recognition complex (ORC) is a multi-subunit DNA binding complex that binds in all eukaryotes and archaea in an ATP-dependent manner to origins of replication. The subunits of this complex are encoded by the ORC1, ORC2, ORC3, ORC4, ORC5 and ORC6 genes. ORC is a central component for eukaryotic DNA replication, and remains bound to chromatin at replication origins throughout the cell cycle.

<span class="mw-page-title-main">Eukaryotic DNA replication</span> DNA replication in eukaryotic organisms

Eukaryotic DNA replication is a conserved mechanism that restricts DNA replication to once per cell cycle. Eukaryotic DNA replication of chromosomal DNA is central for the duplication of a cell and is necessary for the maintenance of the eukaryotic genome.

<span class="mw-page-title-main">Minichromosome maintenance</span>

The minichromosome maintenance protein complex (MCM) is a DNA helicase essential for genomic DNA replication. Eukaryotic MCM consists of six gene products, Mcm2–7, which form a heterohexamer. As a critical protein for cell division, MCM is also the target of various checkpoint pathways, such as the S-phase entry and S-phase arrest checkpoints. Both the loading and activation of MCM helicase are strictly regulated and are coupled to cell growth cycles. Deregulation of MCM function has been linked to genomic instability and a variety of carcinomas.

<span class="mw-page-title-main">MCM7</span> Protein-coding gene in the species Homo sapiens

DNA replication licensing factor MCM7 is a protein that in humans is encoded by the MCM7 gene.

<span class="mw-page-title-main">MCM2</span> Protein-coding gene in the species Homo sapiens

DNA replication licensing factor MCM2 is a protein that in humans is encoded by the MCM2 gene.

<span class="mw-page-title-main">CDC6</span> Protein-coding gene in the species Homo sapiens

Cell division control protein 6 homolog is a protein that in humans is encoded by the CDC6 gene.

<span class="mw-page-title-main">MCM4</span> Protein-coding gene in the species Homo sapiens

DNA replication licensing factor MCM4 is a protein that in humans is encoded by the MCM4 gene.

<span class="mw-page-title-main">DNA replication factor CDT1</span> Protein-coding gene in the species Homo sapiens

CDT1 is a protein that in humans is encoded by the CDT1 gene. It is a licensing factor that functions to limit DNA from replicating more than once per cell cycle.

<span class="mw-page-title-main">MCM5</span> Protein-coding gene in the species Homo sapiens

DNA replication licensing factor MCM5 is a protein that in humans is encoded by the MCM5 gene.

<span class="mw-page-title-main">Cell division cycle 7-related protein kinase</span> Protein-coding gene in the species Homo sapiens

Cell division cycle 7-related protein kinase is an enzyme that in humans is encoded by the CDC7 gene. The Cdc7 kinase is involved in regulation of the cell cycle at the point of chromosomal DNA replication. The gene CDC7 appears to be conserved throughout eukaryotic evolution; this means that most eukaryotic cells have the Cdc7 kinase protein.

<span class="mw-page-title-main">Control of chromosome duplication</span>

In cell biology, eukaryotes possess a regulatory system that ensures that DNA replication occurs only once per cell cycle.

<span class="mw-page-title-main">ORC1</span> Protein-coding gene in the species Homo sapiens

Origin recognition complex subunit 1 is a protein that in humans is encoded by the ORC1 gene. It is closely related to CDC6, and both are the same protein in archaea.

<span class="mw-page-title-main">DNA re-replication</span> Undesirable occurrence in eukaryotic cells

DNA re-replication is an undesirable and possibly fatal occurrence in eukaryotic cells in which the genome is replicated more than once per cell cycle. Rereplication is believed to lead to genomic instability and has been implicated in the pathologies of a variety of human cancers. To prevent rereplication, eukaryotic cells have evolved multiple, overlapping mechanisms to inhibit chromosomal DNA from being partially or fully rereplicated in a given cell cycle. These control mechanisms rely on cyclin-dependent kinase (CDK) activity. DNA replication control mechanisms cooperate to prevent the relicensing of replication origins and to activate cell cycle and DNA damage checkpoints. DNA rereplication must be strictly regulated to ensure that genomic information is faithfully transmitted through successive generations.

References

  1. 1 2 Liu J, Smith CL, DeRyckere D, DeAngelis K, Martin GS, Berger JM (September 2000). "Structure and function of Cdc6/Cdc18: implications for origin recognition and checkpoint control". Molecular Cell. 6 (3): 637–648. doi: 10.1016/S1097-2765(00)00062-9 . PMID   11030343.
  2. ↑ Ausiannikava D, Allers T (January 2017). "Diversity of DNA Replication in the Archaea". Genes. 8 (2): 56. doi: 10.3390/genes8020056 . PMC   5333045 . PMID   28146124.
  3. 1 2 Borlado LR, Méndez J (February 2008). "CDC6: from DNA replication to cell cycle checkpoints and oncogenesis". Carcinogenesis. 29 (2): 237–243. doi: 10.1093/carcin/bgm268 . PMID   18048387.
  4. ↑ Speck C, Chen Z, Li H, Stillman B (November 2005). "ATPase-dependent cooperative binding of ORC and Cdc6 to origin DNA". Nature Structural & Molecular Biology. 12 (11): 965–971. doi:10.1038/nsmb1002. PMC   2952294 . PMID   16228006.
  5. ↑ Yuan Z, Riera A, Bai L, Sun J, Nandi S, Spanos C, et al. (March 2017). "Structural basis of Mcm2-7 replicative helicase loading by ORC-Cdc6 and Cdt1". Nature Structural & Molecular Biology. 24 (3): 316–324. doi:10.1038/nsmb.3372. PMC   5503505 . PMID   28191893.
  6. ↑ Lippincott-Schwartz J, Pollard TD, Earnshaw W (2007). Cell biology. Saunders Elsevier. pp. 766–767. ISBN   978-1-4160-2255-8.
  7. ↑ Bell SP, Dutta A (2002). "DNA replication in eukaryotic cells". Annual Review of Biochemistry. 71: 333–374. doi:10.1146/annurev.biochem.71.110601.135425. PMID   12045100.
  8. 1 2 Feng L, Wang B, Driscoll B, Jong A (May 2000). "Identification and characterization of Saccharomyces cerevisiae Cdc6 DNA-binding properties". Molecular Biology of the Cell. 11 (5): 1673–1685. doi:10.1091/mbc.11.5.1673. PMC   14875 . PMID   10793143.
  9. ↑ Bueno A, Russell P (June 1992). "Dual functions of CDC6: a yeast protein required for DNA replication also inhibits nuclear division". The EMBO Journal. 11 (6): 2167–2176. doi:10.1002/j.1460-2075.1992.tb05276.x. PMC   556684 . PMID   1600944.
  10. ↑ Drury LS, Perkins G, Diffley JF (October 1997). "The Cdc4/34/53 pathway targets Cdc6p for proteolysis in budding yeast". The EMBO Journal. 16 (19): 5966–5976. doi:10.1093/emboj/16.19.5966. PMC   1170227 . PMID   9312054.
  11. ↑ Robles LD, Frost AR, Davila M, Hutson AD, Grizzle WE, Chakrabarti R (July 2002). "Down-regulation of Cdc6, a cell cycle regulatory gene, in prostate cancer". The Journal of Biological Chemistry. 277 (28): 25431–25438. doi: 10.1074/jbc.M201199200 . PMID   12006585.
  12. ↑ Lau E, Tsuji T, Guo L, Lu SH, Jiang W (December 2007). "The role of pre-replicative complex (pre-RC) components in oncogenesis". FASEB Journal. 21 (14): 3786–3794. doi:10.1096/fj.07-8900rev. PMID   17690155. S2CID   32435626.
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