Cytoplasmic-Nuclear Fractionated Protein Extraction
Materials Required
Principle
Cytoplasmic-nuclear fractionated protein extraction separates soluble cytoplasmic proteins from nuclear-enriched proteins by mild plasma-membrane permeabilization, differential centrifugation, washing of nuclei, and extraction of nuclear proteins for downstream immunoblotting or related molecular analysis[1][2][3][4][5]. The readout is the relative abundance of a protein in cytoplasmic and nuclear fractions, commonly assessed by western blotting together with compartment markers such as tubulin or pyruvate kinase for cytoplasm and lamin, nucleoporin, hnRNP, H2AX, or Lamin B for nuclear fractions[1][2][5].
MCE has not independently verified the accuracy of these methods. They are for reference only.
Experimental Materials
• Use ice-cold PBS, 0.1% NP-40 in PBS or comparable mild non-ionic detergent lysis conditions, Laemmli sample buffer for SDS-PAGE-compatible protein extraction, and nuclear extraction conditions when downstream nuclear protein analysis is required[1][2][3][4][5][8].
• For chromatin-associated nuclear proteins, differential salt fractionation can be used after nuclei isolation to separate soluble nuclear proteins from chromatin-associated proteins[6].
• Use antibodies against the target protein and fraction-purity controls; reported cytoplasmic controls include α-tubulin and pyruvate kinase, while reported nuclear controls include lamin A, Lamin B, nucleoporin, hnRNP, H2AX, and snRNP[1][2][5].
• Required equipment includes a refrigerated microcentrifuge or tabletop microfuge, micropipettes for trituration, microcentrifuge tubes, ice, and SDS-PAGE/western blotting equipment for protein detection[1][5][8].
• For chromatin-associated nuclear proteins, differential salt fractionation can be used after nuclei isolation to separate soluble nuclear proteins from chromatin-associated proteins[6].
• Use antibodies against the target protein and fraction-purity controls; reported cytoplasmic controls include α-tubulin and pyruvate kinase, while reported nuclear controls include lamin A, Lamin B, nucleoporin, hnRNP, H2AX, and snRNP[1][2][5].
• Required equipment includes a refrigerated microcentrifuge or tabletop microfuge, micropipettes for trituration, microcentrifuge tubes, ice, and SDS-PAGE/western blotting equipment for protein detection[1][5][8].
Experimental Procedure
• Prepare adherent cultured mammalian cells by washing with ice-cold PBS, scraping cells on ice, collecting cells in microcentrifuge tubes, and keeping samples cold during fractionation[1][5].
• Prepare the lysis solution immediately before use when detergent-containing buffer is required; the REAP protocol used 0.1% NP-40 in PBS, while the lyse-and-wash protocol tested NP-40 or digitonin at 0.1% final concentration[1][2][3].
• Wash cell pellets with ice-cold PBS, resuspend cells in ice-cold 0.1% NP-40/PBS, triturate five times with a P1000 pipette, and reserve an aliquot as whole-cell lysate when direct comparison of total, cytoplasmic, and nuclear signal is required[1].
• Centrifuge the lysate briefly to pellet nuclei; in REAP, a 10-second microfuge spin was used, the supernatant was collected as the cytoplasmic fraction, and the nuclear pellet was washed once with ice-cold 0.1% NP-40/PBS before nuclear extraction[1].
• Extract the nuclear pellet in Laemmli sample buffer for western blot analysis; REAP sonicated DNA-containing nuclear and whole-cell lysate samples twice for 5 seconds and boiled samples for 1 minute before SDS-PAGE[1][8].
• For apoptotic or fragile samples, use a stepwise lyse-and-wash approach because apoptotic bodies and cell fragments can contaminate fractions in standard workflows, and the lyse-and-wash method was validated in cells treated with staurosporine, TNF-α plus cycloheximide, or cisplatin[2].
• For nuclear protein subclasses, isolated nuclei may be further separated into nucleosolic and insoluble nuclear fractions, and differential salt fractionation can be used when the experimental goal is analysis of chromatin-associated proteins[2][6].
• Analyze equal or explicitly reported sample volumes or protein amounts by SDS-PAGE and western blotting, and interpret fractionation only after confirming that cytoplasmic markers are enriched in cytoplasmic fractions and nuclear markers are enriched in nuclear fractions[1][2][5][8].
• A valid protein-translocation experiment should include whole-cell lysate, cytoplasmic fraction, nuclear fraction, target-protein blotting, and compartment-marker blotting on the same experimental set; REAP was validated by detecting TNF-α-induced NF-κB nuclear translocation and comparing the fractionation result with immunofluorescence[1][5].
• Prepare the lysis solution immediately before use when detergent-containing buffer is required; the REAP protocol used 0.1% NP-40 in PBS, while the lyse-and-wash protocol tested NP-40 or digitonin at 0.1% final concentration[1][2][3].
• Wash cell pellets with ice-cold PBS, resuspend cells in ice-cold 0.1% NP-40/PBS, triturate five times with a P1000 pipette, and reserve an aliquot as whole-cell lysate when direct comparison of total, cytoplasmic, and nuclear signal is required[1].
• Centrifuge the lysate briefly to pellet nuclei; in REAP, a 10-second microfuge spin was used, the supernatant was collected as the cytoplasmic fraction, and the nuclear pellet was washed once with ice-cold 0.1% NP-40/PBS before nuclear extraction[1].
• Extract the nuclear pellet in Laemmli sample buffer for western blot analysis; REAP sonicated DNA-containing nuclear and whole-cell lysate samples twice for 5 seconds and boiled samples for 1 minute before SDS-PAGE[1][8].
• For apoptotic or fragile samples, use a stepwise lyse-and-wash approach because apoptotic bodies and cell fragments can contaminate fractions in standard workflows, and the lyse-and-wash method was validated in cells treated with staurosporine, TNF-α plus cycloheximide, or cisplatin[2].
• For nuclear protein subclasses, isolated nuclei may be further separated into nucleosolic and insoluble nuclear fractions, and differential salt fractionation can be used when the experimental goal is analysis of chromatin-associated proteins[2][6].
• Analyze equal or explicitly reported sample volumes or protein amounts by SDS-PAGE and western blotting, and interpret fractionation only after confirming that cytoplasmic markers are enriched in cytoplasmic fractions and nuclear markers are enriched in nuclear fractions[1][2][5][8].
• A valid protein-translocation experiment should include whole-cell lysate, cytoplasmic fraction, nuclear fraction, target-protein blotting, and compartment-marker blotting on the same experimental set; REAP was validated by detecting TNF-α-induced NF-κB nuclear translocation and comparing the fractionation result with immunofluorescence[1][5].
Troubleshooting
Problem: Nuclear marker appears in the cytoplasmic fraction.
• Possible Cause: Nuclear membrane permeabilization or nuclear carryover can occur when detergent conditions are too harsh.• Literature-supported Solution: Use low detergent concentration conditions such as 0.1% NP-40/PBS, because REAP reported that 0.5% detergent caused cytoplasmic contamination with nuclei, while 0.1% NP-40 separated cytoplasmic and nuclear markers[1].
Problem: Cytoplasmic marker appears in the nuclear fraction.
• Possible Cause: Incomplete removal of cytoplasmic material from the nuclear pellet.• Literature-supported Solution: Wash the nuclear pellet after cytoplasmic fraction collection before extracting nuclear proteins, as reported in REAP and lyse-and-wash workflows[1][2].
Problem: Apoptotic samples give contaminated fractions.
• Possible Cause: Apoptotic bodies and cell fragments can contaminate fractions during standard fractionation.• Literature-supported Solution: Use the lyse-and-wash nucleus/cytoplasm fractionation approach validated for apoptotic cells treated with staurosporine, TNF-α plus cycloheximide, or cisplatin[2].
Problem: Nuclear protein signal is difficult to interpret.
• Possible Cause: Nuclear proteins may differ in soluble, insoluble, or chromatin-associated localization.• Literature-supported Solution: Separate nuclear material into nucleosolic and insoluble fractions or use differential salt fractionation when chromatin-associated proteins are the target[2][6].
References:
- [1]. Suzuki K, et al. REAP: A two minute cell fractionation method. BMC Res Notes. 2010;3:294. [Content Brief]
- [2]. Senichkin VV, et al. Simple and Efficient Protocol for Subcellular Fractionation of Normal and Apoptotic Cells. Cells. 2021;10(4):852. [Content Brief]
- [3]. Galvis AE, et al. NP-40 Fractionation and Nucleic Acid Extraction in Mammalian Cells. Bio Protoc. 2017;7(20):e2584. [Content Brief]
- [4]. Huynh HT, et al. Biochemical Separation of Cytoplasmic and Nuclear Fraction for Downstream Molecular Analysis. Curr Protoc. 2024;4(5):e1042. [Content Brief]
- [5]. Sharma AL, et al. Protocol for nucleo-cytoplasmic fractionation of mammalian cells to study protein translocation via immunoblotting. STAR Protoc. 2025;6(4):104265. [Content Brief]
- [6]. Herrmann C, et al. Differential Salt Fractionation of Nuclei to Analyze Chromatin-associated Proteins from Cultured Mammalian Cells. Bio Protoc. 2017;7(6):e2175. [Content Brief]
- [7]. Cox B, et al. Tissue subcellular fractionation and protein extraction for use in mass-spectrometry-based proteomics. Nat Protoc. 2006;1(4):1872-1878. [Content Brief]
- [8]. Laemmli UK. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature. 1970;227(5259):680-685. [Content Brief]
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