Cdc25 is a dual-specificity

phosphatase In biochemistry, a phosphatase is an enzyme that uses water to cleave a phosphoric acid monoester into a phosphate ion and an alcohol. Because a phosphatase enzyme catalyzes the hydrolysis of its substrate, it is a subcategory of hydrolase ...

first isolated from the yeast '' Schizosaccharomyces pombe'' as a

cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and sub ...

defective mutant. As with other cell cycle proteins or genes such as Cdc2 and Cdc4, the "cdc" in its name refers to "cell division control". Dual-specificity phosphatases are considered a sub-class of protein tyrosine phosphatases. By removing inhibitory phosphate residues from target

cyclin-dependent kinase Cyclin-dependent kinases (CDKs) are the families of protein kinases first discovered for their role in regulating the cell cycle. They are also involved in regulating transcription, mRNA processing, and the differentiation of nerve cells. They ...

s (Cdks), Cdc25 proteins control entry into and progression through various phases of the cell cycle, including

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintai ...

and S ("Synthesis") phase.

Function in activating Cdk1

Cdc25 activates

cyclin dependent kinases Cyclin-dependent kinases (CDKs) are the families of protein kinases first discovered for their role in regulating the cell cycle. They are also involved in regulating transcription, mRNA processing, and the differentiation of nerve cells. They a ...

by removing phosphate from residues in the Cdk active site. In turn, the phosphorylation by M-Cdk (a complex of

Cdk1 Cyclin-dependent kinase 1 also known as CDK1 or cell division cycle protein 2 homolog is a highly conserved protein that functions as a serine/threonine protein kinase, and is a key player in cell cycle regulation. It has been highly studied in t ...

and cyclin B) activates Cdc25. Together with Wee1, M-Cdk activation is switch-like. The switch-like behavior forces entry into mitosis to be quick and irreversible. Cdk activity can be reactivated after dephosphorylation by Cdc25. The Cdc25 enzymes Cdc25A-C are known to control the transitions from G1 to S phase and G2 to M phase.

Structure

The structure of Cdc25 proteins can be divided into two main regions: the N-terminal region, which is highly divergent and contains sites for its phosphorylation and ubiquitination, which regulate the phosphatase activity; and the C-terminal region, which is highly homologous and contains the catalytic site.

Evolution and species distribution

Cdc25 enzymes are well conserved through evolution, and have been isolated from

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

such as

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...

s as well as all metazoans examined to date, including humans. The exception among eukaryotes may be

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

s, as the purported plant Cdc25s have characteristics, (such as the use of cations for catalysis), that are more akin to serine/threonine phosphatases than

dual-specificity phosphatase Dual-specificity phosphatase (DUSP; DSP) is a form of phosphatase that can act upon tyrosine or serine/threonine residues. There are several families of dual-specificity phosphatase enzymes in mammals. All share a similar catalytic mechanism, by w ...

s, raising doubts as to their authenticity as Cdc25 phosphatases. The Cdc25 family appears to have expanded in relation to the complexity of the cell-cycle and life-cycle of higher animals. Yeasts have a single Cdc25 (as well as a distantly related enzyme known as Itsy-bitsy phosphatase 1, or Ibp1). ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...

'' has two Cdc25s, known as ''string'' and ''twine'', which control

and

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...

, respectively. Most other model organisms examined have three Cdc25s, designated Cdc25A, Cdc25B, and

Cdc25C M-phase inducer phosphatase 3 is an enzyme that in humans is encoded by the ''CDC25C'' gene. This gene is highly conserved during evolution and it plays a key role in the regulation of cell division. The encoded protein is a tyrosine phosphatase ...

. An exception is the

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...

Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (r ...

'', which has four distinct Cdc25 genes (Cdc-25.1 to Cdc-25.4).

Knockout models

Although the highly conserved nature of the Cdc25s implies an important role in cell physiology, Cdc25B and Cdc25C knockout mice (both single and double mutants) are viable and display no major alterations in their cell cycles, suggesting some functional compensation either via other Cdk regulatory enzymes (such as Wee1 and Myt1) or from the activity of the third member of the family, Cdc25A. Hiroaki Kiyokawa's laboratory has shown that Cdc25A knockout mice are not viable.

In human disease

The Cdc25s, and in particular Cdc25A and Cdc25B, are proto-

oncogenes An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels.

in humans and have been shown to be overexpressed in a number of

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

s. The central role of Cdc25s in the cell cycle has garnered them considerable attention from the

pharmaceutical A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...

industry as potential targets for novel

chemotherapeutic Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...

(anti-

) agents. To date, no clinically viable compounds targeting these enzymes have been described. A large number of potent small-molecule Cdc25 Inhibitors have been identified that bind to the active site and belong to various chemical classes, including natural products, lipophilic acids, quinonoids, electrophiles, sulfonylated aminothiazoles and phosphate bioisosteres. Although some progress has been made in developing potent and selective inhibitors for Cdc25 family of proteins, there is scope for development of novel therapeutic strategies to target them. A new class of peptide-derived inhibitors, based on sequence homology with the protein substrate, can be developed. It is challenging to use these compounds as drugs due to their lack of suitable ADME properties.

References

External links

Genes

* ** Human cDc25A at PDB * * {{Cell cycle proteins Enzymes Cell cycle Fungal proteins