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12268S 100 µl (50 tests)

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REACTIVITY SENSITIVITY MW (kDa) Isotype
H M R Mk Endogenous 56 Rabbit IgG
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Flow Cytometry

Flow cytometric analysis of HeLa cells, untreated (blue) and UV-treated (green), using Phospho-Chk1 (Ser345) (133D3) Rabbit mAb (PE Conjugate).

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Flow Cytometry General Protocol

If using whole blood, please follow the Flow Cytometry Whole Blood Protocol.

A. Solutions and Reagents

NOTE: Prepare solutions with reverse osmosis deionized (RODI) or equivalent grade water.

  1. 20X Phosphate Buffered Saline (PBS): (#9808) To prepare 1 L 1X PBS: add 50 ml 20X PBS to 950 ml dH2O, mix.
  2. 16% Formaldehyde (methanol free).
  3. 100% methanol.
  4. Incubation Buffer: Dissolve 0.5 g Bovine Serum Albumin (BSA) (#9998) in 100 ml 1X PBS. Store at 4°C.

B. Fixation

  1. Collect cells by centrifugation and aspirate supernatant.
  2. Resuspend cells in 0.5–1 ml 1X PBS. Add formaldehyde to obtain a final concentration of 4%.
  3. Fix for 10 min at 37°C.
  4. Chill tubes on ice for 1 min.
  5. For extracellular staining with antibodies that do not require permeabilization, proceed to immunostaining (Section D) or store cells in PBS with 0.1% sodium azide at 4°C; for intracellular staining, proceed to permeabilization (Section C).

C. Permeabilization

NOTE: This step is critical for many CST antibodies.

  1. Permeabilize cells by adding ice-cold 100% methanol slowly to pre-chilled cells, while gently vortexing, to a final concentration of 90% methanol. Alternatively, remove fix prior to permeabilization by centrifugation and resuspend in 90% methanol as described above.
  2. Incubate 30 min on ice.
  3. Proceed with immunostaining (Section D) or store cells at -20°C in 90% methanol.

D. Immunostaining

NOTE: Account for isotype matched controls for monoclonal antibodies or species matched IgG for polyclonal antibodies. Count cells using a hemocytometer or alternative method.

  1. Aliquot 0.5–1 x 106 cells into each assay tube (by volume).
  2. Add 2–3 ml incubation buffer to each tube and wash by centrifugation. Repeat.
  3. Resuspend cells in 100 µl of diluted primary antibody (prepared in incubation buffer at the recommended dilution).
  4. Incubate for 1 hr at room temperature.
  5. Wash by centrifugation in 2–3 ml incubation buffer.
  6. Resuspend cells in 0.5 ml PBS and analyze on flow cytometer; alternatively, for DNA staining, proceed to optional DNA stain (Section E).

E. Optional DNA Dye

  1. Resuspend cells in 0.5 ml of DNA dye (e.g. Propidium Iodide (PI)/RNase Staining Solution #4087).
  2. Incubate for at least 30 min at room temperature.
  3. Analyze cells in DNA staining solution on flow cytometer.

posted July 2009

revised September 2013

Flow Cytometry Whole Blood Protocol

If using cell lines, please follow the Flow Cytometry General Protocol.

A. Solutions and Reagents

NOTE: Prepare solutions with reverse osmosis deionized (RODI) or equivalent grade water.

  1. 20X Phosphate Buffered Saline (PBS): (#9808) To prepare 1 L 1X PBS: add 50 ml 20X PBS to 950 ml dH2O, mix.
  2. 16% Formaldehyde (methanol free).
  3. Triton™ X-100: To prepare 50 ml of 0.1% Triton™ X-100 add 50 μl Triton™ X-100 to 50 ml 1 X PBS and mix well.
  4. 50% methanol.
  5. Incubation Buffer: Dissolve 0.5 g Bovine Serum Albumin (BSA) (#9998) in 100 ml 1X PBS. Store at 4°C.

B. Preparation of Whole Blood (fixation, lysis, and permeabilization) for Immunostaining

  1. Aliquot 100 μl fresh whole blood per assay tube.
  2. OPTIONAL: Place tubes in rack in 37°C water bath for short-term treatments with ligands, inhibitors, drugs, etc.
  3. Add 65 μl of 10% formaldehyde to each tube.
  4. Vortex briefly and let stand for 15 min at room temperature.
  5. Add 1 ml of 0.1% Triton™ X-100 to each tube.
  6. Vortex and let stand for 30 min at room temperature.
  7. Add 1 ml incubation buffer.
  8. Pellet cells by centrifugation and aspirate supernatant.
  9. Repeat steps 7 and 8.
  10. Resuspend cells in ice-cold 50% methanol in PBS (store methanol solution at -20°C until use).
  11. Incubate at least 10 min on ice.
  12. Proceed with staining or store cells at -20°C in 50% methanol.

C. Staining Using Conjugated Primary Antibodies

NOTE: Account for isotype-matched controls for monoclonal antibodies or species matched IgG for polyclonal antibodies.

  1. Add 2–3 ml incubation buffer to each tube and rinse by centrifugation. Repeat.
  2. Add primary antibodies diluted as recommended on datasheet or product webpage in incubation buffer.
  3. Incubate for 1 hr at room temperature.
  4. Wash by centrifugation in 2–3 ml incubation buffer.
  5. Resuspend cells in 0.5 ml PBS and analyze on flow cytometer.

Reference: Chow S, Hedley D, Grom P, Magari R, Jacobberger JW, Shankey TV (2005) Whole blood fixation and permeabilization protocol with red blood cell lysis for flow cytometry of intracellular phosphorylated epitopes in leukocyte subpopulations. Cytometry A 67(1), 4–17.

posted November 2008

revised September 2013

protocol id: 407

Product Usage Information

Application Dilutions
Flow Cytometry 1:50

Storage: Supplied in PBS (pH 7.2), less than 0.1% sodium azide and 2 mg/ml BSA. Store at 4°C. Do not aliquot the antibodies. Protect from light. Do not freeze.

Specificity / Sensitivity

Phospho-Chk1 (Ser345) (133D3) Rabbit mAb (PE Conjugate) detects endogenous levels of Chk1 protein only when phosphorylated at Ser345.


Species Reactivity: Human, Mouse, Rat, Monkey

Source / Purification

Monoclonal antibody is produced by immunizing animals with a synthetic phosphopeptide corresponding to residues surrounding Ser345 of human Chk1 protein.

Product Description

This Cell Signaling Technology antibody is conjugated to phycoerythrin (PE) and tested in-house for direct flow cytometry analysis in human cells. The antibody is expected to exhibit the same species cross-reactivity as the unconjugated Phospho-Chk1 (Ser345) (133D3) Rabbit mAb #2348.


Chk1 kinase acts downstream of ATM/ATR kinase and plays an important role in DNA damage checkpoint control, embryonic development, and tumor suppression (1). Activation of Chk1 involves phosphorylation at Ser317 and Ser345 by ATM/ATR, followed by autophosphorylation of Ser296. Activation occurs in response to blocked DNA replication and certain forms of genotoxic stress (2). While phosphorylation at Ser345 serves to localize Chk1 to the nucleus following checkpoint activation (3), phosphorylation at Ser317 along with site-specific phosphorylation of PTEN allows for re-entry into the cell cycle following stalled DNA replication (4). Chk1 exerts its checkpoint mechanism on the cell cycle, in part, by regulating the cdc25 family of phosphatases. Chk1 phosphorylation of cdc25A targets it for proteolysis and inhibits its activity through 14-3-3 binding (5). Activated Chk1 can inactivate cdc25C via phosphorylation at Ser216, blocking the activation of cdc2 and transition into mitosis (6). Centrosomal Chk1 has been shown to phosphorylate cdc25B and inhibit its activation of CDK1-cyclin B1, thereby abrogating mitotic spindle formation and chromatin condensation (7). Furthermore, Chk1 plays a role in spindle checkpoint function through regulation of aurora B and BubR1 (8). Research studies have implicated Chk1 as a drug target for cancer therapy as its inhibition leads to cell death in many cancer cell lines (9).


1.  Liu, Q. et al. (2000) Genes Dev 14, 1448-59.

2.  Zhao, H. and Piwnica-Worms, H. (2001) Mol Cell Biol 21, 4129-39.

3.  Jiang, K. et al. (2003) J Biol Chem 278, 25207-17.

4.  Martin, S.A. and Ouchi, T. (2008) Mol Cancer Ther 7, 2509-16.

5.  Chen, M.S. et al. (2003) Mol Cell Biol 23, 7488-97.

6.  Zeng, Y. et al. (1998) Nature 395, 507-10.

7.  Löffler, H. et al. (2006) Cell Cycle 5, 2543-7.

8.  Zachos, G. et al. (2007) Dev Cell 12, 247-60.

9.  Garber, K. (2005) J Natl Cancer Inst 97, 1026-8.


Entrez-Gene Id 1111
Swiss-Prot Acc. O14757


For Research Use Only. Not For Use In Diagnostic Procedures.
Cell Signaling Technology® is a trademark of Cell Signaling Technology, Inc.
U.S. Patent No. 5,675,063.