Phospho-CDC25C (S198) Antibody

What is CDC25C and what role does phosphorylation at Ser198 play?

CDC25C (M-phase inducer phosphatase 3) is a dual-specificity phosphatase that plays a key role in cell cycle regulation, particularly during the G2/M transition. During prophase, polo-like kinase 1 (PLK1) phosphorylates CDC25C at Ser198, triggering its translocation from the cytoplasm to the nucleus. Once in the nucleus, CDC25C can interact with and activate the CDC2 (CDK1)/cyclin B complex by removing inhibitory phosphates, allowing cell cycle progression through the remaining stages of mitosis .

The Ser198 phosphorylation site is therefore a critical regulatory switch that controls the spatial distribution and activity of CDC25C during cell division. This phosphorylation event represents one of several post-translational modifications that fine-tune CDC25C activity in response to cell cycle cues and checkpoint signals.

How do researchers detect phosphorylation of CDC25C at Ser198?

Researchers typically detect CDC25C phosphorylation at Ser198 using phospho-specific antibodies that recognize only the phosphorylated form of the protein. These antibodies are designed to bind specifically to the amino acid sequence surrounding Ser198 only when the serine residue is phosphorylated.

Common experimental applications include:

For Western blotting applications, phospho-CDC25C (Ser198) typically appears as a band at approximately 75 kDa . Researchers should include appropriate controls, such as phosphatase-treated samples or cells with CDC25C knockdown, to confirm the specificity of the antibody signal .

What is the relationship between PLK1 and CDC25C phosphorylation at Ser198?

Polo-like kinase 1 (PLK1) directly phosphorylates CDC25C at Ser198 during early mitosis, specifically in prophase. This kinase-substrate relationship represents a critical regulatory mechanism in mitotic entry .

The relationship functions as follows:

• PLK1 is activated during G2/M transition

• Activated PLK1 phosphorylates CDC25C at Ser198

• This phosphorylation triggers CDC25C nuclear translocation

• Nuclear CDC25C activates CDK1/cyclin B complexes by removing inhibitory phosphates

• Activated CDK1/cyclin B drives mitotic progression

This PLK1-CDC25C axis creates a positive feedback loop that ensures rapid and decisive commitment to mitosis. Interference with this relationship, through either PLK1 inhibition or mutation of the Ser198 site on CDC25C, disrupts normal mitotic entry and progression .

What are the available commercial antibodies for detecting phospho-CDC25C (Ser198)?

Multiple commercial antibodies are available for detecting CDC25C phosphorylated at Ser198. Based on the search results, at least two manufacturers produce such antibodies:

• Cell Signaling Technology (product #9529):

  • Host species: Rabbit

  • Applications: Western Blotting (1:1000), Flow Cytometry (1:25)

  • Reactivity: Human

  • Sensitivity: Transfected only

  • Format: Liquid

• ELK Biotech (product #ES8144):

  • Host species: Rabbit

  • Applications: IHC, IF, ELISA

  • Species cross-reactivity: Human, Rat, Mouse

  • Format: Liquid in PBS containing 50% glycerol, 0.5% BSA and 0.02% sodium azide

  • Concentration: 1 mg/ml

Researchers should select the appropriate antibody based on their experimental design, target species, and preferred application method. Validation experiments should be performed to confirm specificity in each experimental system.

How do different phosphorylation patterns of CDC25C affect its localization and function during cell cycle progression?

CDC25C undergoes multiple phosphorylation events at different sites that collectively regulate its localization and function throughout the cell cycle. Research using phospho-specific antibodies has revealed that distinct phospho-forms of CDC25C represent separate pools with differential localization during human mitosis .

Key phosphorylation patterns include:

• Ser198 phosphorylation by PLK1:

  • Occurs during prophase

  • Triggers nuclear translocation

  • Promotes interaction with CDK1/cyclin B complexes

• Thr67 phosphorylation:

  • Appears from prophase onward

  • The CDC25C-pT67 form associates closely with condensed chromosomes throughout mitosis

  • Co-precipitates with MPM2-reactive proteins

• Thr130 phosphorylation:

  • Arises in late G2

  • Associates predominantly with centrosomes from prophase to anaphase B

  • Colocalizes with PLK1 at centrosomes

  • Associated with PLK1 in immunoprecipitation experiments

• Ser216 phosphorylation by CHK1:

  • Inactivates CDC25C

  • Functions as part of checkpoint control mechanisms

Importantly, immunoprecipitation studies have demonstrated that these phospho-forms are not simultaneously phosphorylated on multiple sites, suggesting that each phospho-form represents a distinct pool of CDC25C with unique functions and localizations . This compartmentalization likely allows for precise spatial and temporal control of CDC25C activity during mitotic progression.

What methodological approaches can be used to study the dynamics of CDC25C phosphorylation at Ser198 in live cells?

Studying the dynamics of CDC25C phosphorylation at Ser198 in live cells requires sophisticated methodological approaches that preserve temporal and spatial information. Several approaches can be employed:

• Fluorescent biosensors:

  • Design FRET-based sensors with phospho-binding domains that recognize pSer198

  • Express CDC25C tagged with fluorescent proteins to track localization in real-time

  • Combine with cell cycle phase markers to correlate phosphorylation with cell cycle stages

• Optogenetic tools:

  • Develop light-inducible PLK1 activation systems to trigger CDC25C phosphorylation

  • Monitor subsequent changes in CDC25C localization and downstream effects

• Advanced microscopy:

  • Employ fluorescence recovery after photobleaching (FRAP) to measure mobility changes upon phosphorylation

  • Use super-resolution microscopy to precisely map the subcellular localization of phospho-CDC25C

• Phosphorylation-state indicators:

  • Generate cell lines expressing CDC25C with phospho-mimetic (S198D/E) or non-phosphorylatable (S198A) mutations

  • Compare localization patterns and cell cycle effects with wild-type protein

When designing these experiments, researchers should consider using synchronized cell populations to enhance detection of cell-cycle specific events, and employ appropriate controls such as PLK1 inhibitors to validate phosphorylation-dependent effects .

How does Ser198 phosphorylation of CDC25C interact with other post-translational modifications to regulate its function?

CDC25C activity is regulated by a complex network of post-translational modifications beyond Ser198 phosphorylation. These modifications interact to create a sophisticated regulatory code that governs CDC25C function during normal cell cycle progression and in response to cellular stresses.

Key interactions between Ser198 phosphorylation and other modifications include:

• Relationship with Ser216 phosphorylation:

  • Ser216 is phosphorylated by checkpoint kinase 1 (CHK1), which inactivates CDC25C

  • Ser198 phosphorylation by PLK1 promotes nuclear localization and activation

  • These opposing modifications create a regulatory switch controlled by the balance between PLK1 and CHK1 activities

• Coordination with other mitotic phosphorylation sites:

  • Research shows that CDC25C phospho-isoforms are typically phosphorylated on single TP motifs rather than simultaneously on multiple sites

  • The pT67, pT130, and pT48 forms represent distinct pools with different localizations and functions

  • This suggests a complex phosphorylation code rather than a simple on/off switch mechanism

• Potential modification crosstalk:

  • Other post-translational modifications like ubiquitination may be affected by phosphorylation status

  • SUMOylation and acetylation could potentially interact with the phosphorylation state

Research approaches to study these interactions include mass spectrometry to map modification patterns, mutation analysis to determine site interdependencies, and proximity ligation assays to examine how modifications affect protein-protein interactions in situ.

What is the role of CDC25C phosphorylation in chemoresistance mechanisms, particularly in docetaxel-resistant cancer?

Emerging research indicates that CDC25C phosphorylation plays a significant role in chemoresistance mechanisms, particularly in docetaxel-resistant prostate cancer. The search results reveal several important findings:

• CDC25C involvement in docetaxel resistance:

  • CDC25C is upregulated in docetaxel-resistant prostate cancer cells (IGR-CaP1-R100)

  • Docetaxel-resistant cells show altered sensitivity to CDC25C inhibition

• Regulatory interactions:

  • CDC25C is regulated by PLK1 (activating) and CHK1 (inhibitory)

  • LZTS1 deficiency in resistant cells may contribute to CDC25C dysregulation

  • CDC25C interacts with LZTS1 in 293 cells, suggesting a regulatory relationship

• Therapeutic vulnerability:

  • Docetaxel-resistant cells (IGR-CaP1-R100) show heightened sensitivity to the CDC25 phosphatases inhibitor NSC663284

  • Flow cytometry analysis showed massive cell death (89%) in resistant cells treated with NSC663284 compared to only 3% in parental cells

  • The IC50 for NSC663284 was ~33-fold lower in resistant cells, indicating a potential therapeutic window

These findings suggest that altered CDC25C phosphorylation and activity contribute to the resistant phenotype in cancer cells. Targeting CDC25C or its regulatory kinases (PLK1, CHK1) represents a potential strategy to overcome chemoresistance. Researchers investigating chemoresistance mechanisms should consider the phosphorylation status of CDC25C at Ser198 and other sites as potential biomarkers for resistance and therapeutic targets.

What experimental approaches can be used to study the specific interactome of phosphorylated CDC25C (Ser198) versus unphosphorylated CDC25C?

Understanding the differential interactome of phosphorylated versus unphosphorylated CDC25C at Ser198 requires sophisticated experimental approaches that can distinguish between these forms while preserving physiologically relevant interactions. Several methodological approaches are particularly valuable:

• Phospho-specific immunoprecipitation coupled with mass spectrometry:

  • Use phospho-Ser198 specific antibodies to isolate only the phosphorylated form

  • Perform parallel immunoprecipitation with pan-CDC25C antibodies

  • Compare interacting partners identified by mass spectrometry

  • Include phosphatase inhibitors throughout to preserve phosphorylation status

• Proximity-based labeling techniques:

  • Express CDC25C wild-type, S198A (non-phosphorylatable) or S198D/E (phospho-mimetic) fused to BioID or APEX2

  • These enzymes biotinylate proximal proteins in living cells

  • Identify differentially biotinylated proteins as potential phosphorylation-dependent interactors

• In vitro binding assays with phosphorylated proteins:

  • Generate recombinant CDC25C phosphorylated at Ser198 using PLK1 or chemical methods

  • Compare binding to potential partners with unphosphorylated protein

  • Validate interactions using techniques like surface plasmon resonance

• FRET/BRET interaction screening:

  • Create fusion proteins of CDC25C variants with donor fluorophores

  • Screen potential interactors tagged with acceptor fluorophores

  • Measure energy transfer as indicator of proximity/interaction

When implementing these approaches, researchers should consider the following technical considerations:

• Use phosphatase inhibitors (okadaic acid, tautomycin, calyculin A) and phosphatase attenuators (PBS, beta-glycero-phosphate, sodium vanadate and fluoride) to preserve phosphorylation status

• Include appropriate controls such as phospho-site mutants

• Consider the timing of interaction by synchronizing cells at specific cell cycle stages

• Validate key interactions using orthogonal methods

What are the critical parameters for validating phospho-CDC25C (Ser198) antibody specificity?

Validating the specificity of phospho-CDC25C (Ser198) antibodies is crucial for generating reliable experimental data. Based on the search results, several methodological approaches have been successfully employed:

• Peptide competition assays:

  • Incubate the antibody with the phospho-peptide antigen or the non-phosphorylated peptide before immunoblotting

  • Only the phospho-peptide should specifically block reactivity, demonstrating phospho-specificity

• RNA interference validation:

  • Compare antibody reactivity between normal cell extracts and extracts from cells where CDC25C has been depleted by RNAi

  • The phospho-specific band should disappear in CDC25C-depleted samples

• Phospho-site mutant analysis:

  • Test antibody reactivity against wild-type CDC25C and alanine mutants (S198A)

  • The antibody should react with phosphorylated wild-type but not with the S198A mutant

• Phosphatase treatment:

  • Treat samples with alkaline phosphatase or lambda phosphatase

  • The signal should be abolished after phosphatase treatment, confirming phospho-specificity

• Cell cycle synchronization:

  • Analyze antibody reactivity in extracts from cells synchronized at different cell cycle stages

  • Phospho-Ser198 signal should be absent in S-phase cells but present in mitotic cells, consistent with the known timing of this phosphorylation

For researchers working with phospho-CDC25C antibodies, implementing multiple validation approaches is recommended to ensure antibody specificity and experimental reproducibility.

How can researchers effectively use phospho-CDC25C (Ser198) antibodies in different experimental techniques?

Researchers can employ phospho-CDC25C (Ser198) antibodies across various experimental techniques, each requiring specific optimization strategies:

• Western Blotting:

  • Recommended dilution: 1:1000

  • Expected molecular weight: 75 kDa

  • Key considerations:

    • Include phosphatase inhibitors in lysis buffers

    • Use positive controls (mitotic cell extracts)

    • Include non-phosphorylated controls (S-phase extracts or phosphatase-treated samples)

• Flow Cytometry:

  • Recommended dilution: 1:25 for fixed/permeabilized cells

  • Key considerations:

    • Thorough permeabilization is critical for nuclear antigen access

    • Co-stain with cell cycle markers (e.g., propidium iodide)

    • Consider synchronizing cells to enrich for mitotic populations

• Immunohistochemistry/Immunofluorescence:

  • Recommended dilution: 1:100 - 1:300

  • Key considerations:

    • Antigen retrieval methods may affect phospho-epitope preservation

    • Co-stain with mitotic markers (e.g., phospho-histone H3)

    • Include phosphatase-treated sections as negative controls

• Immunoprecipitation:

  • Key considerations:

    • Include phosphatase inhibitors throughout the procedure

    • Use phosphatase attenuators (PBS, beta-glycero-phosphate, sodium vanadate and fluoride)

    • Perform the procedure at 4°C to minimize phosphatase activity

For all applications, researchers should be aware that phospho-CDC25C (Ser198) is primarily detectable during specific cell cycle phases (late G2 and mitosis), so experimental timing or cell synchronization may be necessary to optimize detection .

What are emerging areas of research regarding CDC25C phosphorylation in disease contexts beyond cancer?

While CDC25C phosphorylation has been extensively studied in cancer contexts, emerging research suggests broader implications in other disease states and physiological processes:

• Neurodegenerative disorders:

  • Aberrant cell cycle re-entry in post-mitotic neurons is associated with neurodegeneration

  • CDC25C phosphorylation status may play a role in this pathological cell cycle activation

  • Research could investigate CDC25C phosphorylation patterns in Alzheimer's and other neurodegenerative disease models

• Cardiovascular disease:

  • Vascular smooth muscle cell proliferation contributes to atherosclerosis and restenosis

  • CDC25C phosphorylation status may regulate this proliferative response

  • Studies could examine CDC25C Ser198 phosphorylation in models of vascular injury

• Development and stem cell biology:

  • Cell cycle regulation is crucial during embryonic development and in stem cell populations

  • The role of CDC25C phosphorylation in regulating stem cell self-renewal versus differentiation remains largely unexplored

  • Research could investigate how CDC25C phosphorylation patterns change during differentiation processes

• Aging and senescence:

  • Cell cycle dysregulation is a hallmark of cellular senescence and aging

  • CDC25C phosphorylation may contribute to senescence-associated cell cycle arrest

  • Studies could examine age-dependent changes in CDC25C phosphorylation patterns

Future research should employ phospho-specific antibodies against CDC25C Ser198 in these non-cancer contexts to elucidate the broader significance of this regulatory mechanism in health and disease.

How can researchers integrate phospho-CDC25C (Ser198) detection with other cell cycle markers for comprehensive analysis?

Integrating phospho-CDC25C (Ser198) detection with other cell cycle markers enables comprehensive analysis of cell cycle regulation and provides context for interpreting CDC25C phosphorylation data. Here are methodological approaches for multiparametric analysis:

• Multicolor flow cytometry:

  • Combine phospho-CDC25C (Ser198) antibodies with:

    • DNA content dyes (propidium iodide, DAPI)

    • S-phase markers (EdU, BrdU incorporation)

    • Mitotic markers (phospho-histone H3)

    • Other phospho-proteins (phospho-CDK1, phospho-Rb)

  • This approach allows correlation of CDC25C phosphorylation with precise cell cycle positioning

• Multiplexed immunofluorescence imaging:

  • Use spectrally distinct fluorophores to simultaneously detect:

    • Phospho-CDC25C (Ser198)

    • PLK1 (the kinase responsible for Ser198 phosphorylation)

    • Nuclear envelope markers (lamin B)

    • Chromatin markers (DAPI)

    • Centrosome markers (γ-tubulin)

  • This enables spatial correlation of CDC25C phosphorylation with subcellular structures

• Sequential immunoprecipitation:

  • Perform sequential immunoprecipitations with antibodies against:

    • Phospho-CDC25C (Ser198)

    • Other CDC25C phospho-forms (pT67, pT130)

    • Cell cycle regulatory proteins (cyclins, CDKs)

  • This approach can reveal unique complexes formed by different phospho-forms

• Mass cytometry (CyTOF):

  • Label antibodies with distinct metal isotopes to simultaneously detect:

    • Multiple phosphorylation sites on CDC25C

    • Upstream regulators (PLK1, CHK1)

    • Downstream targets (CDK1/cyclin B)

    • Cell cycle markers

  • This enables high-dimensional analysis at single-cell resolution

By integrating multiple markers, researchers can build a comprehensive understanding of how CDC25C phosphorylation at Ser198 fits within the broader context of cell cycle regulation and potentially identify novel regulatory relationships.

What are the key considerations for designing experiments to investigate CDC25C Ser198 phosphorylation in different experimental systems?

When designing experiments to investigate CDC25C Ser198 phosphorylation across different experimental systems, researchers should consider several critical factors to ensure meaningful and reproducible results:

• Cell cycle synchronization strategies:

  • CDC25C Ser198 phosphorylation is cell cycle-dependent, appearing primarily during late G2/prophase

  • Consider using thymidine block/release, nocodazole, or CDK1 inhibitors for synchronization

  • Include time course analysis to capture dynamic changes in phosphorylation status

• Appropriate controls:

  • Positive controls: Mitotic cell extracts (known to contain phospho-Ser198 CDC25C)

  • Negative controls: S-phase cell extracts, phosphatase-treated samples

  • Specificity controls: CDC25C knockdown/knockout cells, phospho-site mutants (S198A)

• System-specific considerations:

  • Cancer cell lines: Consider potential alterations in CDC25C regulation

  • Primary cells: May have different cell cycle kinetics affecting phosphorylation timing

  • Tissue samples: Require optimization of fixation methods to preserve phospho-epitopes

  • In vivo models: Consider tissue-specific differences in CDC25C regulation

• Technical parameters:

  • Buffer composition: Include phosphatase inhibitors (okadaic acid, calyculin A)

  • Sample preparation: Maintain cold temperatures throughout to minimize phosphatase activity

  • Antibody validation: Perform peptide competition and phosphatase treatment controls

• Analytical approaches:

  • Quantification methods: Consider normalizing phospho-signal to total CDC25C

  • Statistical analysis: Account for cell cycle distribution differences between samples

  • Data interpretation: Integrate with other cell cycle markers for context