Phospho-CHEK1 (S296) Antibody
Description
Antody Characteristics
Phospho-CHEK1 (S296) antibodies are available as monoclonal or polyclonal reagents, validated for applications including Western blot (WB), immunofluorescence (IF), and ELISA. Key features include:
Biological Role of S296 Phosphorylation
Chk1 is a serine-threonine kinase central to DNA damage and replication stress responses. Key regulatory mechanisms include:
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Activation Pathway: ATR phosphorylates Chk1 at S345 during replication stress, triggering autophosphorylation at S296 .
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Functional Significance:
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Regulatory Dynamics: S296 phosphorylation is transient, peaking during checkpoint activation and declining during recovery .
3.1. Pharmacodynamic Biomarker
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Gemcitabine/AZD7762 Studies: pS296 Chk1 serves as a biomarker for Chk1 inhibition. AZD7762 (a Chk1/2 inhibitor) blocks S296 phosphorylation, correlating with reduced kinase activity .
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DNA Damage Quantification: Elevated pS296 levels indicate replication stress in pancreatic cancer models .
3.2. Mechanistic Insights
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Autophosphorylation: S296 modification occurs via cis-autophosphorylation, independent of optimal Chk1 substrate motifs .
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Ubiquitination Link: Chk1 stability is regulated by E3 ligases (e.g., HUWE1), with S296 phosphorylation influencing proteasomal degradation .
4.1. Western Blot
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Positive Controls: HEK293 or MiaPaCa-2 cells treated with calyculin A (phosphatase inhibitor) show robust pS296 detection .
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Specificity: No cross-reactivity with non-phosphorylated Chk1 or other phospho-sites (e.g., S345) .
4.2. Limitations
Product Specs
Target Background
- Research suggests that sustained mTORC1 signaling in cancer cells, under stressful conditions, promotes survival by suppressing endogenous DNA damage. This mechanism may control cell fate by regulating CHK1. PMID: 28484242
- Chk1 and 14-3-3 proteins cooperate to inactivate the transcriptional repressor functions of atypical E2F proteins. This mechanism could be particularly important for cancer cells, given their frequent exposure to DNA-damaging therapeutic agents. PMID: 29363506
- Studies indicate that CHEK1 protein expression is elevated in breast tumors among Nigerian women and is associated with aggressive cancer phenotypes, making it a potential prognostic marker. PMID: 29075961
- The crystal structure of the human Chk1 putative kinase-associated 1 (KA1) domain reveals significant structural homology with other diverse KA1 domains. Interestingly, separately purified Chk1 kinase and KA1 domains exhibit close association in solution, leading to inhibition of Chk1 kinase activity. PMID: 28972186
- The nuclear transcription factor Y subunit beta (NFYB)-E2F transcription factor 1 (E2F1) pathway plays a crucial role in the chemoresistance of oxaliplatin-resistant colorectal cancer (OR-CRC) by inducing the expression and activation of checkpoint kinase 1 (CHK1). This finding suggests a potential therapeutic target for oxaliplatin resistance in CRC. PMID: 29203250
- Blocking apoptosis alone is insufficient to promote the growth of primary B cells lacking CHK1 in vivo or B lymphoma lines in vitro. These cells instead trigger p53-dependent cell cycle arrest in response to accumulated DNA damage. PMID: 29167438
- Chk1 and Chk2 are significantly expressed in human sperm. In the event of sperm DNA damage, elevated Chk1 expression may enhance sperm apoptosis leading to asthenospermia, while increased Chk2 expression could inhibit spermatogenesis resulting in oligospermia. PMID: 29658237
- CHK1 and CHK2, along with their activated forms, are frequently expressed in HGSC effusions, with higher expression observed following exposure to chemotherapy. Their expression is correlated with survival. PMID: 29804637
- Expression of AURKA and CHEK1 has been linked to unfavorable outcomes in patients. These data suggest a synthetic lethality interaction between CHEK1 and AURKA inhibitors, potentially translating to clinical settings. PMID: 28847989
- Expression levels of phosphorylated cdc25A (p-cdc25A) and phosphorylated Chk1 (p-Chk1), components of the ATR pathway, are decreased by treatment with Dclk1 inhibitor LRRK2-IN-1 (LRRK), suggesting Dclk1 involvement in the ATR pathway. PMID: 29048622
- Research demonstrates that prexasertib is a specific inhibitor of CHK1 in neuroblastoma, leading to DNA damage and cell death in preclinical models of this pediatric malignancy. PMID: 28270495
- Findings show that HGF is involved in regulating Chk1 phosphorylation, and further demonstrate that AKT activity is responsible for this HGF-induced Chk1 phosphorylation. PMID: 28573382
- Chk1 has been linked to DNA damage response bypass by suppressing JNK activation following oxidative stress, facilitating cell cycle progression despite DNA damage. PMID: 28751935
- Inhibition of Chk1 can enhance the activity of nucleoside analogs in TP53-mutated B-lymphoid cells. PMID: 27556692
- Data indicate that protein phosphatase-1 alpha (PP1alpha) is necessary to maintain checkpoint kinase 1 (CHK1) in a dephosphorylated state and for accelerated replication fork progression in Spi1/PU.1 transcription factor-overexpressing cells. PMID: 28415748
- Chk1 inhibition with GDC-0425 in combination with gemcitabine was tolerated with manageable bone marrow suppression. The observed preliminary clinical activity warrants further investigation of this chemopotentiation strategy. PMID: 27815358
- Data reveal that the checkpoint kinase 1/2 (Chk1/Chk2) inhibitor prexasertib (LY2606368) inhibits cell viability in B-/T-ALL cell lines. PMID: 27438145
- Research demonstrates that CHK1 mRNA is overexpressed in two independent cohorts of medulloblastoma patient samples compared to normal cerebellum. PMID: 27449089
- Results suggest a Chk1-OGT-vimentin pathway that regulates the intermediate filament network during cytokinesis. PMID: 29021254
- CHEK1-mediated DNA damage checkpoint plays a role in the ESR2-NCF1-ROS pathway sensitization of esophageal cancer cells to 5-fluorouracil-induced cell death. PMID: 27310928
- Monitoring CHEK1 expression could serve as both a predictor of outcome and a marker for selecting AML patients for CHK1 inhibitor treatments. PMID: 27625304
- PLAUR is essential for the activation of Checkpoint kinase 1 (CHK1), maintenance of cell cycle arrest after DNA damage in a TP53-dependent manner, expression, nuclear import, and recruitment to DNA-damage foci of RAD51 recombinase, the primary protein involved in homologous recombination repair. PMID: 27685627
- Findings unveil a new aspect of PERK function and previously unknown roles for Claspin and Chk1 as negative regulators of DNA replication in the absence of genotoxic stress. PMID: 27375025
- Research reveals ATXN3 to be a novel deubiquitinase of Chk1, providing a new mechanism of Chk1 stabilization in genome integrity maintenance. PMID: 28180282
- These findings demonstrate an unexpected requirement for a balanced nucleotide pool for optimal Chk1 activation, both in unchallenged cells and in response to genotoxic stress. PMID: 27383768
- CHK1 overexpression is associated with T-cell and Hodgkin Lymphoma. PMID: 26988986
- Checkpoint kinase 1 and 2 signaling is essential for apoptin regulation. PMID: 27512067
- Genetic variants of the CHEK1 gene are significantly associated with overall survival and disease-free survival of esophageal squamous cell carcinoma patients. PMID: 27924519
- Role of the CHK1-RAD51 signaling pathway in osteosarcoma cells. PMID: 28000895
- High CHK1 expression is linked to increased radioresistance of non-small cell lung cancer. PMID: 27553023
- CHEK1 loss-of-function mutations have not been found in human tumors, and transgenic expression of Chek1 in mice promotes oncogene-induced transformation. [review] PMID: 26527132
- Persistence of CHK1 levels in response to DNA damage in p53-deficient cancer cells leads to CHK1-mediated activation of NF-kappaB and induction of NF-kappaB-regulated genes in cells and associated tumor-derived microvesicles. These processes are abrogated by loss or inhibition of CHK1. PMID: 26921248
- Chk1's expression is regulated by p53 and RB/E2F1 at the transcriptional level. PMID: 26867682
- High CHK1 expression correlates with urinary bladder cancer. PMID: 26657501
- This study shows that Chk1 maintains a closed conformation in the absence of DNA damage through an intramolecular interaction between a region (residues 31-87) at the N-terminal kinase domain and the distal C terminus. A highly conserved Leu-449 at the C terminus is crucial for this interaction. PMID: 27129240
- Avoiding damage formation by inactivating Mus81-Eme2 and Mre11, or preventing damage signaling by deactivating the ATM pathway, suppresses the replication phenotypes of Chk1-deficient cells. PMID: 26804904
- Chk1 is a predictive biomarker of radiotherapy resistance and early local recurrence. PMID: 26459098
- A new pathway of proliferation restriction for tetraploid untransformed cells that seems to be specific for loss of adhesion-dependent cytokinesis failure involves Chk1 and p53 activation during G2. PMID: 26693937
- Human induced pluripotent stem cells fail to activate CHK1 when exposed to DNA replication inhibitors and commit to apoptosis instead. PMID: 26810087
- Isolate and characterize mantle cell lymphoma cell line resistance to Chk1 inhibitor PF-00477736. PMID: 26439697
- Results support the inhibition of checkpoint kinase 1 (Chk1) as a new therapeutic strategy in acute lymphoblastic leukemia. PMID: 26542114
- These results demonstrate a positive feedback loop involving Rad9A-dependent activation of Chk1. PMID: 26658951
- DNA damage induces Chk1 phosphorylation on chromatin followed by releasing phospho-Chk1 from the chromatin into the soluble nucleus and cytoplasm where Chk1 activates the cell cycle checkpoints. Subsequently, Chk1 is degraded and checkpoint signaling is terminated. PMID: 26296656
- Nasopharyngeal carcinoma cells depend on CHK1 and WEE1 activity for growth. PMID: 26025928
- Suppression of CHK1 by ETS Family Members Promotes DNA Damage Response Bypass and Tumorigenesis. PMID: 25653093
- Report strong synergism observed by combining Chk1 and Wee1 inhibitors in preclinical models of mantle cell lymphoma. PMID: 25428911
- Mutations targeting the putative Chk1 KA1 domain confer constitutive biological activity by circumventing the need for ATR-mediated positive regulatory phosphorylation. PMID: 26039276
- CHEK1 was a direct target of miR-195, which decreased CHEK1 expression in lung cancer cells. High expression of CHEK1 in lung tumors was associated with poor overall survival. PMID: 25840419
- Findings suggest that the addition of a CHEK1 inhibitor increases the response of ovarian cancer cells to TPT. Moreover, reduced dosages of both drugs achieved maximal cytotoxic effects by combining TPT with a CHEK1 inhibitor. PMID: 25884494
- These results suggest that breast cancer cells may rely on the mTORC2-Chk1 pathway for survival. PMID: 25460505
Q&A
What is Phospho-CHEK1 (S296) and why is it important in cellular signaling?
Phospho-CHEK1 (S296) refers to checkpoint kinase 1 (Chk1) protein that has been phosphorylated at serine residue 296. This specific phosphorylation is an auto-phosphorylation event that serves as a pharmacodynamic biomarker of Chk1 kinase activity . Chk1 is a serine/threonine protein kinase (56 kDa) that plays a critical role in cell cycle regulation and DNA damage response pathways.
The importance of S296 phosphorylation lies in its role within the DNA damage response cascade. After DNA damage, Chk1 is initially phosphorylated by ATR at S317 and S345, which then enables Chk1 auto-phosphorylation at S296. This cascade is essential for complete activation of Chk1's checkpoint function, allowing it to target downstream substrates like Cdc25A and properly disperse through the nucleoplasm via interaction with 14-3-3 gamma proteins .
How does S296 phosphorylation relate to other phosphorylation sites on Chk1?
The phosphorylation of Chk1 follows a specific sequential pattern:
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Initial phosphorylation of S317 by ATR in response to DNA damage
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S317 phosphorylation enables subsequent phosphorylation of S345
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Both S317 and S345 phosphorylation facilitate auto-phosphorylation at S296
Research has demonstrated that S317 phosphorylation is a prerequisite for efficient phosphorylation of the flanking sites S296 and S345 in response to DNA damage or replication stress. When S317 is mutated to alanine (S317A), cells exhibit markedly defective phosphorylation at both S296 and S345 sites after treatment with hydroxyurea (HU) .
Interestingly, while S317 phosphorylation is required for S345 phosphorylation, the relationship is not reciprocal. S345A mutants still show normal S317 phosphorylation in response to DNA damage, indicating a unidirectional dependency in this phosphorylation cascade .
| Chk1 Site | Mechanism | Dependency | Function |
|---|---|---|---|
| S317 | Phosphorylated by ATR | Independent | Initiates activation |
| S345 | Phosphorylated by ATR | Requires S317 phosphorylation | Essential for viability |
| S296 | Auto-phosphorylation | Requires S317 and S345 phosphorylation | DNA damage checkpoint activation |
What are the validated applications for Phospho-Chk1 (S296) antibodies?
Phospho-Chk1 (S296) antibodies have been validated for several research applications:
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Western Blotting (WB): The primary application with recommended dilutions typically ranging from 1:500 to 1:2000
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Enzyme-Linked Immunosorbent Assay (ELISA): For quantitative measurement of Phospho-Chk1 (S296) levels
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Immunohistochemistry (IHC): For detection in paraffin-embedded or frozen tissue sections
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Immunofluorescence/Immunocytochemistry (IF/ICC): For cellular localization studies
Most commercially available Phospho-Chk1 (S296) antibodies have been rigorously validated for specificity using positive controls such as HEK293 cells treated with Calyculin or UV irradiation, providing researchers with confidence in experimental outcomes .
How should samples be prepared to optimally detect Phospho-Chk1 (S296)?
For optimal detection of Phospho-Chk1 (S296), consider the following preparation methods:
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Cell Treatment: Treat cells with DNA damaging agents (e.g., hydroxyurea, doxorubicin, UV radiation) to induce Chk1 phosphorylation
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Phosphatase Inhibitors: Include phosphatase inhibitors in lysis buffers to prevent dephosphorylation during sample preparation
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Sample Collection Timing: Harvest cells at appropriate time points after treatment, as phosphorylation is dynamic
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Protein Concentration: Load adequate protein amounts (typically 20-50 μg) for Western blot detection
When monitoring Chk1 inhibitor efficacy, samples should be collected after treatments that induce DNA damage response, as complete inhibition of Chk1 kinase activity (>90%) is typically required before markers like γH2AX can be detected .
What positive controls should be used when validating Phospho-Chk1 (S296) antibody?
For proper validation of Phospho-Chk1 (S296) antibody, the following positive controls are recommended:
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HEK293 cells treated with Calyculin: Shown to induce robust Chk1 S296 phosphorylation
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Cell lines treated with hydroxyurea (HU): HT29 and U2OS cells treated with HU exhibit strong Chk1 S296 phosphorylation
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Cells treated with DNA-damaging agents: 293T cells treated with UV radiation or doxorubicin
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Recombinant phosphorylated Chk1: For in vitro validation of antibody specificity
In experimental designs, DLD-1 cells and monoallelic DLD-Chk1 wild-type cells have also been used to demonstrate robust phosphorylation on S296, S317, and S345 after treatment with HU .
How can I quantitatively assess Chk1 kinase activity using S296 phosphorylation?
S296 auto-phosphorylation serves as a reliable pharmacodynamic biomarker for Chk1 kinase activity. Quantitative assessment can be performed as follows:
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Dose-response experiments: Treating cells with increasing concentrations of Chk1 inhibitors shows dose-dependent decreases in pS296 levels
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IC₅₀ determination: The IC₅₀ for Chk1 inhibition can be calculated based on S296 phosphorylation reduction
For example, the Chk1 inhibitor V158411 demonstrated dose-dependent decreases in pS296 with IC₅₀ and IC₉₀ values of 0.12 and 0.77 μM in HT29 cells, and 0.039 and 0.59 μM in U2OS cells, respectively . This quantitative relationship between inhibitor concentration and S296 phosphorylation makes it a valuable tool for assessing Chk1 inhibitor potency.
How do I distinguish between phosphorylation at S296 and other phosphorylation sites on Chk1?
Distinguishing between different Chk1 phosphorylation sites requires:
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Site-specific antibodies: Use highly specific antibodies that recognize only phosphorylated S296, not other phosphorylation sites like S317 or S345
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Phosphorylation pattern analysis: S296 phosphorylation follows S317 and S345 phosphorylation in response to DNA damage
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Mutational analysis: S317A mutants show reduced S296 phosphorylation, while S345A mutants maintain normal S317 phosphorylation but may show altered S296 phosphorylation
Western blot analysis with multiple site-specific antibodies can reveal the temporal and hierarchical phosphorylation pattern of Chk1. This helps distinguish the unique role of S296 phosphorylation as an auto-phosphorylation event downstream of the initial ATR-mediated phosphorylation events.
Why might I observe discrepancies between Chk1 inhibition and S296 phosphorylation levels?
Several factors can lead to discrepancies between observed Chk1 inhibition and S296 phosphorylation levels:
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Inhibitor specificity: Some Chk1 inhibitors fall into distinct classes with different effects on phosphorylation markers. For example, V158411, LY2603618, and ARRY-1A induce strong increases in γH2AX, pRPA32, and pChk1 (S317), while MK-8776 and GNE-900 do not, despite all inhibitors decreasing Chk1 auto-phosphorylation by >95%
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Temporal dynamics: The timing of sample collection can significantly impact observed phosphorylation levels
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Cell type variations: Different cell lines may show different sensitivities and phosphorylation patterns
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Off-target effects: Some inhibitors may have off-target effects that influence the phosphorylation status of Chk1 through alternative pathways
To address these discrepancies, comprehensive analysis including multiple markers of Chk1 activity and DNA damage response is recommended.
How can Phospho-Chk1 (S296) antibody be used to evaluate DNA damage response in cancer research?
The Phospho-Chk1 (S296) antibody serves as a powerful tool in cancer research for:
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Evaluating Chk1 inhibitor efficacy: Measurement of S296 phosphorylation can directly assess the pharmacodynamic effects of Chk1 inhibitors in cancer cells
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Chemosensitization studies: Monitoring S296 phosphorylation helps understand how Chk1 inhibition sensitizes cancer cells to DNA-damaging agents
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Biomarker identification: S296 phosphorylation serves as a biomarker for checkpoint activation in response to genotoxic stress
Research has shown that Chk1 inhibitors sensitize various tumor cell lines to hydroxyurea or gemcitabine by up to 10 times . The combination of Chk1 inhibitors with DNA-damaging agents leads to increased accumulation of DNA damage and enhanced cell death in tumor cells .
What is the relationship between Chk1 S296 phosphorylation and protein stability/degradation?
Chk1 phosphorylation status and protein stability are intimately connected:
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Auto-phosphorylation and degradation: While S296 auto-phosphorylation is important for Chk1 activation, other auto-phosphorylation sites like T378/T382 in the C-terminal Kinase Associated 1 (KA1) domain can accelerate proteasomal degradation of Chk1
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Selective destruction: Recovery from DNA damage-induced checkpoint arrest requires deactivation of Chk1, and selective destruction of active, phosphorylated Chk1 by polyubiquitination and proteasomal degradation is part of this process
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Phosphorylation-dependent half-life: Constitutively active Chk1 mutants with phospho-mimetic modifications can have dramatically reduced half-lives compared to wild-type Chk1
This relationship between phosphorylation and degradation represents a regulatory mechanism to ensure proper temporal control of Chk1 activity during normal cell cycle progression and in response to DNA damage.
How does the phosphorylation pattern of Chk1 differ between essential and non-essential functions?
Research has revealed that Chk1's essential and non-essential functions are regulated through distinct phosphorylation events:
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DNA damage response (non-essential): The DNA damage response function of Chk1 is non-essential and can be genetically uncoupled from its essential function. Targeted mutation of S317 abrogates G2/M checkpoint activation and impairs DNA replication fork progression but does not impact cell viability
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Essential mitotic function: S345 phosphorylation plays an essential role during unperturbed cell cycles. A Chk1 allele with mutated S345 does not support cell viability, indicating this site's critical importance for essential Chk1 functions
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Distinct phosphorylation mechanisms: S345 phosphorylation during unperturbed mitosis is initiated at the centrosome and is mechanistically distinct from the ordered and sequential phosphorylation of serine residues induced by DNA damage
This differentiation between essential and non-essential functions through phosphorylation patterns provides opportunities for therapeutic interventions that target specific aspects of Chk1 function without compromising essential cellular processes.
How can Phospho-Chk1 (S296) be used as a biomarker in clinical studies of DNA damage response inhibitors?
The use of Phospho-Chk1 (S296) as a biomarker in clinical studies is an emerging area with significant potential:
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Pharmacodynamic marker: S296 phosphorylation levels can directly measure the biological activity of Chk1 inhibitors in patient samples
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Predictive biomarker: Baseline levels or changes in S296 phosphorylation might predict patient response to Chk1 inhibitors
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Combination therapy optimization: Monitoring S296 phosphorylation can help determine optimal dosing and scheduling of Chk1 inhibitors with conventional chemotherapeutics
For example, in preclinical studies, almost complete inhibition of Chk1 kinase activity (as measured by S296 phosphorylation) was required before γH2AX-positive cells were detected, suggesting a threshold effect that might be relevant in clinical applications .
What technical advances are improving the detection sensitivity and specificity of Phospho-Chk1 (S296)?
Recent technical advances improving Phospho-Chk1 (S296) detection include:
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Monoclonal antibody development: Rabbit monoclonal antibodies offer improved specificity and sensitivity compared to polyclonal alternatives
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Multiplex analysis systems: Simultaneous detection of multiple phosphorylation sites provides comprehensive insights into Chk1 activation status
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Phospho-flow cytometry: Allows single-cell analysis of Chk1 phosphorylation status in heterogeneous populations
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Proximity ligation assays: Enables detection of protein-protein interactions dependent on S296 phosphorylation
These advances facilitate more precise quantification of Chk1 activity in both research and potential clinical applications, contributing to better understanding of DNA damage response pathways and improved development of targeted therapies.
