# Cdc25

**Cdc25** (cell division cycle 25) is a family of dual-specificity protein phosphatases that activate cyclin-dependent kinases (CDKs) by removing the inhibitory phosphates on their threonine and tyrosine residues, thereby driving transitions between phases of the eukaryotic cell cycle.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup><sup> • </sup><sup>[2](https://www.sciencedirect.com/science/article/pii/S0955067406000159)</sup> The founding member was identified in fission yeast as the 25th gene found to regulate cell division, and the family is conserved across eukaryotes as the inducer of M phase.<sup>[3](https://d-scholarship.pitt.edu/8132/1/RJTjrThesisETD2008.pdf)</sup><sup> • </sup><sup>[4](https://www.sciencedirect.com/science/chapter/bookseries/abs/pii/S1569255808600107)</sup> In mammals the family comprises three isoforms, CDC25A, CDC25B, and CDC25C, which are also key targets of the DNA damage checkpoint machinery and are overexpressed in many cancers, making them long-standing candidates for anticancer drug development.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup><sup> • </sup><sup>[5](https://doi.org/10.1038/nrc2169)</sup>

| Key fact | Detail |
|---|---|
| Enzyme class | Dual-specificity phosphatases (class III protein tyrosine phosphatases) with the signature motif HCX\(_{5}\)R containing the catalytic cysteine<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup><sup> • </sup><sup>[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC8158066/)</sup> |
| Human isoforms | CDC25A, CDC25B, CDC25C; 20–25% amino-acid identity in the N-terminal region and about 60% in the C-terminal catalytic region<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> |
| Substrates | Dephosphorylate inhibitory phosphates on CDKs, notably Cdk1/cyclin B and Cdk2/cyclin E and A complexes<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> |
| Structural fold | Catalytic domain resembles the rhodanese sulfur-transfer protein fold; the active-site loop has seven residues versus six in sulfurtransferases, giving a wider pocket that fits a phosphorus atom (van der Waals radius 1.9 versus 1.85 Å)<sup>[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC1084204/)</sup> |
| Checkpoint role | After DNA damage, ATM/ATR kinases activate Chk1 and Chk2, which hyperphosphorylate Cdc25A and trigger its ubiquitylation and proteolysis, delaying cell-cycle progression<sup>[8](https://pubmed.ncbi.nlm.nih.gov/15021892/)</sup> |
| Cancer link | Cdc25A and Cdc25B are overexpressed in many primary human cancers, for example 70% and 57% of breast cancers respectively<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> |
| Drug development | Many inhibitor classes have been identified, but CDC25 inhibitors, including experimental compounds such as PM-20, BN82002, and JUN1111 (while pexiganan is an antimicrobial peptide, not a CDC25 inhibitor), have not entered clinical trials<sup>[9](https://www.sciencedirect.com/science/article/abs/pii/S0019452224000864)</sup><sup> • </sup><sup>[19](https://ibecbarcelona.eu/wp-content/uploads/2022/11/Call-Proceso-Seleccion-ESP.pdf)</sup> |

## Function in the cell cycle

Progression through the cell division cycle is driven by the activation of specific cyclin-dependent kinase complexes, and the Cdc25 phosphatases are the enzymes that switch these complexes on by dephosphorylating specific tyrosine and threonine residues on the CDKs.<sup>[2](https://www.sciencedirect.com/science/article/pii/S0955067406000159)</sup> In human cells, Cdc25A controls the G1/S transition by activating Cdk2/cyclin E and Cdk2/cyclin A, and also activates Cdk1/cyclin B to provoke the G2/M transition. Cdc25B and Cdc25C mainly regulate the G2/M transition and mitosis: Cdc25B accumulates from late S and early G2 with activity peaking at G2/M, and is proposed to act as a "starter" that triggers mitosis by activating Cdk1/cyclin B at the centrosome, while Cdc25C controls progression into mitosis.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup>

**Isoform cooperation.** Earlier work assigned each isoform to a single cell-cycle stage, but later studies indicate that all three CDC25 isoforms cooperate to regulate normal cell division in human cells.<sup>[2](https://www.sciencedirect.com/science/article/pii/S0955067406000159)</sup> Their protein levels also differ in behavior: Cdc25C levels remain constant throughout the cycle, whereas Cdc25A and Cdc25B fluctuate greatly.<sup>[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC1326326/)</sup>

## Regulation

CDC25 expression and activity are controlled by many mechanisms, including alternative exon splicing, phosphorylation and dephosphorylation cycles, interactions with 14-3-3 proteins, intracellular localization, and cell-cycle-controlled degradation.<sup>[5](https://doi.org/10.1038/nrc2169)</sup> The N-terminal regions, which are highly divergent in sequence, carry numerous phosphorylation and ubiquitination sites that regulate activity, protein interactions, and expression levels.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup><sup> • </sup><sup>[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC8158066/)</sup>

**Positive feedback.** Cdc25 activity itself is regulated by phosphorylation during the cell cycle, and Cdc25 can be activated by the cdc2/cyclin B kinase it turns on, creating a positive feedback loop that contributes to the self-amplification of MPF (maturation-promoting factor) at mitotic entry. A type-2A protein phosphatase can specifically dephosphorylate and activate Cdc25.<sup>[4](https://www.sciencedirect.com/science/chapter/bookseries/abs/pii/S1569255808600107)</sup> Human PLK kinase also phosphorylates and activates CDC25C, and CDC25C is a substrate for CaM kinase II, whose phosphorylation increases its phosphatase activity.<sup>[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC4862931/)</sup>

**Proteolysis.** Cdc25A abundance is tuned by two ubiquitin ligases: the APC/C regulates Cdc25A at the exit of mitosis, and the [SCF complex](https://www.edgepedia.org/scf-complex) regulates its abundance in S phase and G2.<sup>[8](https://pubmed.ncbi.nlm.nih.gov/15021892/)</sup>

## Role in DNA damage checkpoints

When DNA is damaged or replication stalls, the checkpoint machinery prevents Cdk/cyclin activation, and the Cdc25 phosphatases are its key targets.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup><sup> • </sup><sup>[5](https://doi.org/10.1038/nrc2169)</sup> Activation of the ATM and ATR protein kinases leads to Chk1 and Chk2 activation and to Cdc25A hyperphosphorylation, which stimulates SCF-mediated ubiquitylation of Cdc25A and its proteolysis; this delays cell-cycle progression and helps prevent genomic instability.<sup>[8](https://pubmed.ncbi.nlm.nih.gov/15021892/)</sup> Chk1 and Chk2 phosphorylation also creates 14-3-3 binding sites (for example Ser 216) that regulate the protein's nuclear-cytoplasmic shuttling, and a p38–MAPKAP pathway additionally controls CDC25 activity during G2/M checkpoint activation.<sup>[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC1326326/)</sup><sup> • </sup><sup>[2](https://www.sciencedirect.com/science/article/pii/S0955067406000159)</sup> Phosphorylation of CDC25B on Ser323 by p38 MAPK promotes 14-3-3 binding and cytoplasmic retention during interphase.<sup>[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC6406801/)</sup>

## Structure and catalytic mechanism

The Cdc25 proteins are 450–600 residues long, divided into a divergent N-terminal regulatory region and a C-terminal catalytic region with about 60% pairwise identity among isoforms.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> Crystal structures of the catalytic domains of Cdc25A and Cdc25B revealed a rhodanese-like three-dimensional fold with the active-site cysteine in the same position as in sulfur-transfer enzymes, even though the two families share only about 17% sequence identity and are thought to stem from a common ancestor.<sup>[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC1084204/)</sup> Within the protein tyrosine phosphatase (PTP) superfamily, the CDC25 proteins form class III, defined by the conserved P-loop signature C(X)\(_{5}\)R; unlike class I PTPs, the CDC25 catalytic domain lacks pTyr-, WPD-, and Q-loops, and its comparatively shallow active site admits both phosphotyrosine- and phosphothreonine-containing substrates.<sup>[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC8158066/)</sup>

Catalysis proceeds through a two-step reaction with a covalent phospho-cysteine intermediate. The phosphoryl group of the substrate is cradled by the active-site loop, hydrogen-bonded to backbone amides and the conserved arginine of the HCX\(_{5}\)R motif; the thiolate of the catalytic cysteine attacks the phosphorus in line, and the leaving group is protonated by a catalytic acid located on a separate loop. In the second step, water hydrolyzes the phospho-enzyme intermediate assisted by an aspartate acting as a base. Cdc25B-catalyzed dephosphorylation uses a monoprotonated phosphate with an apparent pK\(_{a}\) of 6.5, so the reaction is faster at low pH.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> The active-site cysteine is unusually reactive: Cdc25B's Cys473 is oxidized to sulfenic acid by hydrogen peroxide 15-fold faster than in the protein tyrosine phosphatase PTP1B and 400-fold faster than the cellular reductant glutathione, and an intramolecular disulfide with a second cysteine is reversibly reduced by thioredoxin, supporting a physiological role for redox regulation of Cdc25.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup>

## History

The gene was named in the cell-division-cycle genetics of fission yeast, where *cdc25* was identified as a critical player in the G2 to M-phase transition.<sup>[3](https://d-scholarship.pitt.edu/8132/1/RJTjrThesisETD2008.pdf)</sup><sup> • </sup><sup>[13](https://www.sciencedirect.com/science/article/abs/pii/S0304419X96000492)</sup> The broader CDC gene framework came from [Leland Hartwell](https://www.edgepedia.org/leland-hartwell)'s 1974 studies, which cataloged 35 partially characterized cell division-cycle (CDC) genes in yeast.<sup>[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC4666127/)</sup> Mammalian homologues were subsequently characterized, including cdc25Hs (CDC25C), cdc25Hu2 (CDC25B), and cdc25Hu3 (CDC25A), with Cdc25A identified as a phosphatase functioning early in the cell cycle.<sup>[15](https://www.embopress.org/doi/pdf/10.1002/j.1460-2075.1994.tb06417.x?download=true)</sup>

## Cdc25 in cancer and drug development

Cdc25A and Cdc25B are overexpressed in many different primary human cancers, with reported overexpression rates including breast cancer (70% for A, 57% for B), thyroid cancer (17–69% and 36–64%), hepatocellular cancer (56% and 20%), ovarian cancer (30% for both), colorectal cancer (47–53% and 43–67%), non-Hodgkin's lymphoma (50% and 65%), laryngeal cancer (41% and 57%), and esophageal cancer (46–66% and 48–79%). Cdc25B alone is overexpressed in gastric (78%), endometrial (73%), and prostate (30%) cancers and gliomas (47%), while Cdc25C overexpression has been barely reported. In 30% of tumors both A and B are overexpressed, and in 45% only one is.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> Clinical data from lung adenocarcinoma datasets (CPTAC and TCGA-LUAD) associate high CDC25A and CDC25C expression with poor prognosis.<sup>[16](https://www.sciencedirect.com/science/article/pii/S075333222500664X)</sup>

**Inhibitor design challenges.** The CDC25 active site is difficult to drug for three reasons: it is shallow, it contains a highly reactive catalytic cysteine, and the enzyme lacks homology with other protein phosphatases, so broad-acting dual-specificity phosphatase inhibitors risk disrupting MAP kinase phosphatases, protein tyrosine phosphatases, and Vaccinia H1-related phosphatase activities.<sup>[17](https://pmc.ncbi.nlm.nih.gov/articles/PMC10834672/)</sup> A large and structurally diverse set of inhibitors has been reported, many found by high-throughput screening or scaffold optimization.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> Early quinoid compounds include menadione (vitamin K\(_{3}\)), with K\(_{i}\) values of 38 ± 4, 95 ± 3, and 20 ± 4 µM against Cdc25A, B, and C, and the naphthoquinone Cpd-5, which inhibits Cdc25A, B, and C with IC\(_{50}\) values of 5, 2, and 2 µM with little effect on VHR or PTP1B. The quinone NSC 95397 was among the most active hits, and the quinoline-dione NSC 663284 is a potent irreversible inhibitor of Cdc25A and B with IC\(_{50}\) of 210 nM and 20- to 450-fold selectivity for Cdc25B over VHR or PTP1B.<sup>[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)</sup> Natural products have also been a productive source of scaffolds.<sup>[9](https://www.sciencedirect.com/science/article/abs/pii/S0019452224000864)</sup>

After twenty years of research, clinical application remains modest: CDC25 inhibitors, including the experimental compounds PM-20, BN82002, and JUN1111, have not reached clinical trials.<sup>[9](https://www.sciencedirect.com/science/article/abs/pii/S0019452224000864)</sup> Newer strategies aim at the same problem from different angles, including proteolysis-targeting chimeras (PROTACs) built on quinoline-dione scaffolds that degrade Cdc25 phosphatases rather than merely inhibiting them.<sup>[18](https://pubs.acs.org/doi/abs/10.1021/acs.jmedchem.5c02112)</sup>

## References

1. [A Comprehensive Overview of the Developments of Cdc25 Phosphatase Inhibitors, Molecules (2022)](https://pmc.ncbi.nlm.nih.gov/articles/PMC9031484/)
2. [The when and wheres of CDC25 phosphatases, Current Opinion in Cell Biology (2006)](https://www.sciencedirect.com/science/article/pii/S0955067406000159)
3. [Cellular and Biochemical Regulation of CDC25A Phosphatase, University of Pittsburgh thesis (2008)](https://d-scholarship.pitt.edu/8132/1/RJTjrThesisETD2008.pdf)
4. [The cdc25 Phosphatase: Biochemistry and Regulation in the Eukaryotic Cell Cycle, Advances in Molecular and Cell Biology (1995)](https://www.sciencedirect.com/science/chapter/bookseries/abs/pii/S1569255808600107)
5. [Boutros, Lobjois & Ducommun (2007). CDC25 phosphatases in cancer cells: key players? Good targets? Nature Reviews Cancer 7, 495–507](https://doi.org/10.1038/nrc2169)
6. [Protein Tyrosine Phosphatases: Structure, Function, and Implication in Human Disease, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC8158066/)
7. [The rhodanese/Cdc25 phosphatase superfamily: Sequence–structure–function relations, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC1084204/)
8. [Cdc25A phosphatase: combinatorial phosphorylation, ubiquitylation and proteolysis, PubMed (2004)](https://pubmed.ncbi.nlm.nih.gov/15021892/)
9. [Natural product CDC25 inhibitors: A promising source for cancer drug discovery (2024)](https://www.sciencedirect.com/science/article/abs/pii/S0019452224000864)
10. [Regulating mammalian checkpoints through Cdc25 inactivation, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC1326326/)
11. [Phosphatases and Kinases Regulating CDC25 Activity in the Cell Cycle, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC4862931/)
12. [Phosphatases in Mitosis: Roles and Regulation, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC6406801/)
13. [Cdc25 protein phosphatases in cell proliferation, Biochimica et Biophysica Acta (1996)](https://www.sciencedirect.com/science/article/abs/pii/S0304419X96000492)
14. [Forty-five years of cell-cycle genetics, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC4666127/)
15. [Cdc25A is a novel phosphatase functioning early in the cell cycle, EMBO Journal (1994)](https://www.embopress.org/doi/pdf/10.1002/j.1460-2075.1994.tb06417.x?download=true)
16. [A novel quinoid-based CDC25 phosphatase inhibitor against human lung adenocarcinoma (2025)](https://www.sciencedirect.com/science/article/pii/S075333222500664X)
17. [Potential of CDC25 phosphatases in cancer research and treatment, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10834672/)
18. [First-in-Class Quinoline-Dione-Derived PROTACs: Potent Degraders of Cdc25 Phosphatases, Journal of Medicinal Chemistry (2025)](https://pubs.acs.org/doi/abs/10.1021/acs.jmedchem.5c02112)
19. [Call Proceso Seleccion ESP.pdf, ibecbarcelona.eu](https://ibecbarcelona.eu/wp-content/uploads/2022/11/Call-Proceso-Seleccion-ESP.pdf)

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*Topic: Encyclopedia › Life and health › Biological foundations › Biochemistry and metabolism › Protein families and complexes › Kinase and phosphatase families › Protein phosphatase families › Protein tyrosine phosphatases › Cdc25 phosphatases (Class III)*

*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*

*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*

License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license