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REACTIVITY SENSITIVITY Isotype
H M R Mk Endogenous Rabbit IgG
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Flow cytometric analysis of Jurkat cells, untreated (blue) or treated with TPA #4174 (green), using Phospho-p90RSK (Ser380) (D5D8) Rabbit mAb (Alexa Fluor® 647 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 antibody. Protect from light. Do not freeze.

Specificity / Sensitivity

Phospho-p90RSK (Ser380) (D5D8) Rabbit mAb (Alexa Fluor® 647 Conjugate) recognizes endogenous levels of RSK1, RSK2, and RSK3 proteins only when phosphorylated at Ser380 (RSK1), Ser386 (RSK2), or Ser377 (RSK3).


Species Reactivity: Human, Mouse, Rat, Monkey
Species predicted to react based on 100% sequence homology: Chicken, Xenopus, Zebrafish, Bovine, Dog, Pig, Horse

Source / Purification

Monoclonal antibody is produced by immunizing animals with a synthetic phosphopeptide corresponding to residues surrounding Ser377 of human p90RSK3 protein.

Product Description

This Cell Signaling Technology antibody is conjugated to Alexa Fluor® 647 fluorescent dye 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-p90RSK (Ser380) (D5D8) Rabbit mAb #12032.


The 90 kDa ribosomal S6 kinases (RSK1-4) are a family of widely expressed Ser/Thr kinases characterized by two nonidentical, functional kinase domains (1) and a carboxy-terminal docking site for extracellular signal-regulated kinases (ERKs) (2). Several sites both within and outside of the RSK kinase domain, including Ser380, Thr359, Ser363, and Thr573, are important for kinase activation (3). RSK1-3 are activated via coordinated phosphorylation by MAPKs, autophosphorylation, and phosphoinositide-3-OH kinase (PI3K) in response to many growth factors, polypeptide hormones, and neurotransmitters (3).


Upon mitogenic stimulation, p44/42 ERK1/2 and ERK5 MAP kinases cooperatively phosphorylate p90RSK at Thr573 (p90RSK1 numbering) located within the carboxy-terminal kinase domain and at Thr359/Ser363 in the linker region between the two kinase domains (3). Phosphorylation of p90RSK at Thr573 within the activation loop of the p90RSK carboxy-terminal kinase domain promotes activation and directs phosphorylation of Ser380 within the hydrophobic stretch of the linker region (4,5). The p90RSK phosphorylated at Ser380 acts as a docking site for the constitutively active Ser/Thr kinase PDK1, which in turn phosphorylates Ser221 within the amino-terminal kinase domain activation loop, resulting in full enzymatic activation of the p90RSK (6). Antibodies against these phosphorylation sites are useful for understanding the kinetics and regulation of p90RSK activation.

For more information regarding the phospho-regulatory sites within each RSK isoform, including more information regarding the seminal studies demonstrating the complex phosphorylation cascades involved, please see the references herein and PhosphoSitePlus® (www.phosphosite.org).


1.  Fisher, T.L. and Blenis, J. (1996) Mol Cell Biol 16, 1212-9.

2.  Smith, J.A. et al. (1999) J Biol Chem 274, 2893-8.

3.  Dalby, K.N. et al. (1998) J Biol Chem 273, 1496-505.

4.  Roux, P.P. et al. (2003) Mol Cell Biol 23, 4796-804.

5.  Cargnello, M. and Roux, P.P. (2011) Microbiol Mol Biol Rev 75, 50-83.

6.  Romeo, Y. et al. (2012) Biochem J 441, 553-69.


Entrez-Gene Id 6195, 6197, 6196
Swiss-Prot Acc. Q15418, P51812, Q15349


For Research Use Only. Not For Use In Diagnostic Procedures.
Cell Signaling Technology® is a trademark of Cell Signaling Technology, Inc.
Alexa Fluor® is a registered trademark of Life Technologies Corporation.
The Alexa Fluor® dye antibody conjugates in this product are sold under license from Life Technologies Corporation for research use only, except for use in combination with DNA microarrays. The Alexa Fluor® dyes (except for Alexa Fluor® 430 dye) are covered by pending and issued patents. Alexa Fluor® is a registered trademark of Molecular Probes, Inc.