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REACTIVITY SENSITIVITY MW (kDa) Isotype
Endogenous Rabbit 
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Flow cytometric analysis of HeLa cells using 4F2hc/CD98 (D6O3P) Rabbit mAb (blue) compared to Rabbit (DA1E) mAb IgG XP® Isotype Control #3900 (red). Anti-rabbit IgG (H+L), F(ab')2 Fragment (Alexa Fluor® 488 conjugate) #4412 was used as a secondary antibody.

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Immunofluorescence (Immunocytochemistry)

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 1L 1X PBS: add 50 ml 20X PBS to 950 ml dH2O, mix. Adjust pH to 8.0.
  2. Formaldehyde: 16%, methanol free, Polysciences, Inc. (cat# 18814), use fresh and store opened vials at 4°C in dark, dilute in 1X PBS for use.
  3. Blocking Buffer (1X PBS / 5% normal serum / 0.3% Triton™ X-100): To prepare 10 ml, add 0.5 ml normal serum from the same species as the secondary antibody (e.g., Normal Goat Serum (#5425)) and 0.5 mL 20X PBS to 9.0 mL dH2O, mix well. While stirring, add 30 µl Triton™ X-100.
  4. Antibody Dilution Buffer (1X PBS / 1% BSA / 0.3% Triton X-100): To prepare 10 ml, add 30 µl Triton™ X-100 to 10 ml 1X PBS. Mix well then add 0.1 g BSA (9998), mix.
  5. Recommended Fluorochrome-conjugated Anti-Rabbit secondary antibodies:

  6. Prolong® Gold AntiFade Reagent (#9071), Prolong® Gold AntiFade Reagent with DAPI (#8961).

B. Specimen Preparation - Cultured Cell Lines (IF-IC)

NOTE: Cells should be grown, treated, fixed and stained directly in multi-well plates, chamber slides or on coverslips.

  1. Aspirate liquid, then cover cells to a depth of 2–3 mm with 4% formaldehyde diluted in 1X PBS.

    NOTE: Formaldehyde is toxic, use only in a fume hood.

  2. Allow cells to fix for 15 min at room temperature.
  3. Aspirate fixative, rinse three times in 1X PBS for 5 min each.
  4. Proceed with Immunostaining (Section C).

C. Immunostaining

NOTE: All subsequent incubations should be carried out at room temperature unless otherwise noted in a humid light-tight box or covered dish/plate to prevent drying and fluorochrome fading.

  1. Block specimen in Blocking Buffer for 60 min.
  2. While blocking, prepare primary antibody by diluting as indicated on datasheet in Antibody Dilution Buffer.
  3. Aspirate blocking solution, apply diluted primary antibody.
  4. Incubate overnight at 4°C.
  5. Rinse three times in 1X PBS for 5 min each.
  6. Incubate specimen in fluorochrome-conjugated secondary antibody diluted in Antibody Dilution Buffer for 1–2 hr at room temperature in the dark.
  7. Rinse three times in 1X PBS for 5 min each.
  8. Coverslip slides with Prolong® Gold Antifade Reagent (#9071) or Prolong® Gold Antifade Reagent with DAPI (#8961).
  9. For best results, allow mountant to cure overnight at room temperature. For long-term storage, store slides flat at 4°C protected from light.

posted November 2006

revised November 2013

protocol id: 24

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Flow Cytometry

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.
  5. Recommended Anti-Mouse secondary antibodies::

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 fluorochrome-conjugated secondary antibody, diluted in incubation buffer at the recommended dilution.
  7. Incubate for 30 min at room temperature.
  8. Wash by centrifugation in 2–3 ml incubation buffer.
  9. 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 June 2005

protocol id: 12

Product Usage Information

Application Dilutions
Immunofluorescence 1:200
Flow Cytometry 1:400

Storage: Supplied in 10 mM sodium HEPES (pH 7.5), 150 mM NaCl, 100 µg/ml BSA, 50% glycerol and less than 0.02% sodium azide. Store at –20°C. Do not aliquot the antibody.

Specificity / Sensitivity

Phospho-Smad2 (Ser465/467)/Smad3 (Ser423/425) (D6G10) XP® Rabbit mAb detects endogenous levels of phosporylated Smad2 and Smad3. Some reactivity is observed with non-phosphorylated Smad2 and 3 by western blot analysis. This antibody does not cross-react with other Smad-related proteins.


Species predicted to react based on 100% sequence homology: Mouse, Rat, Monkey, Xenopus, Bovine

Source / Purification

Monoclonal antibody is produced by immunizing animals with a synthetic phosphopeptide corresponding to residues surrounding Ser465/467 of human Smad2. This region is highly conserved with Smad3 at Ser423/425.

Members of the Smad family of signal transduction molecules are components of a critical intracellular pathway that transmit TGF-β signals from the cell surface into the nucleus. Three distinct classes of Smads have been defined: the receptor-regulated Smads (R-Smads), which include Smad1, 2, 3, 5, and 8; the common-mediator Smad (co-Smad), Smad4; and the antagonistic or inhibitory Smads (I-Smads), Smad6 and 7 (1-5). Activated type I receptors associate with specific R-Smads and phosphorylate them on a conserved carboxy terminal SSXS motif. The phosphorylated R-Smad dissociates from the receptor and forms a heteromeric complex with the co-Smad (Smad4), allowing translocation of the complex to the nucleus. Once in the nucleus, Smads can target a variety of DNA binding proteins to regulate transcriptional responses (6-8).


Following stimulation by TGF-β, Smad2 and Smad3 become phosphorylated at their carboxyl termini (serines 465 and 467 on Smad2; serines 423 and 425 on Smad3) by the receptor kinase TGF-β R1(9-11). Following phosphorylation, Smad2 and Smad3 form a heteromeric complex with the co-smad family member Smad4. These complexes are translocated to the nucleus where they bind DNA and regulate gene transcription.


1.  Heldin, C.H. et al. (1997) Nature 390, 465-71.

2.  Attisano, L. and Wrana, J.L. (1998) Curr Opin Cell Biol 10, 188-94.

3.  Derynck, R. et al. (1998) Cell 95, 737-40.

4.  Massagué, J. (1998) Annu Rev Biochem 67, 753-91.

5.  Whitman, M. (1998) Genes Dev 12, 2445-62.

6.  Wu, G. et al. (2000) Science 287, 92-7.

7.  Attisano, L. and Wrana, J.L. (2002) Science 296, 1646-7.

8.  Moustakas, A. et al. (2001) J Cell Sci 114, 4359-69.

9.  Abdollah, S. et al. (1997) J. Biol. Chem. 272, 27678-27685.

10.  Souchelnytskyi, S. et al. (1997) J. Biol. Chem. 272, 28107-28115.

11.  Liu, X. et al. (1997) Proc. Natl. Acad. Sci. USA 94, 10669-10674.


Entrez-Gene Id 4087, 4088
Swiss-Prot Acc. Q15796, P84022


For Research Use Only. Not For Use In Diagnostic Procedures.
Cell Signaling Technology® is a trademark of Cell Signaling Technology, Inc.
XP® is a trademark of Cell Signaling Technology, Inc.