DCZ3112

Western blotting (WB) is a commonly used experimental method in molecular biology, biochemistry, and immunogenetics for identifying and quantifying target proteins. It combines gel electrophoresis with immunoassay, enabling researchers to analyze protein expression, post-translational modifications, and molecular weight.

Annexin V-based apoptosis assays rely on the detection of phosphatidylserine (PS) externalization from the inner leaflet of the plasma membrane to the outer leaflet, an early biochemical hallmark of apoptosis. Fluorescently labeled Annexin V binds PS in a calcium-dependent manner, enabling identification of early apoptotic cells by flow cytometry or fluorescence microscopy. When combined with a membrane-impermeant DNA-binding dye (e. g. , propidium iodide), this approach allows discrimination between viable (Annexin V−/dye−), early apoptotic (Annexin V+/dye−), and late apoptotic or necrotic (Annexin V+/dye+) cell populations by assessing membrane integrity and PS exposure.

Immunoprecipitation (IP) is an experimental method that uses the principle of antibody specific binding to purify and enrich target proteins.

Bromodeoxyuridine (BrdU) incorporation assay is based on the principle that BrdU, a thymidine analog, is incorporated into newly synthesized DNA during the S phase of the cell cycle, thereby serving as a marker of DNA replication and cellular proliferation. Incorporated BrdU can be detected using anti-BrdU antibodies following DNA denaturation, enabling visualization or quantification of proliferating cells through immunochemical detection methods such as immunofluorescence or immunohistochemistry.

Bimolecular fluorescence complementation detects protein-protein proximity in living or fixed cells by fusing two candidate interaction partners to nonfluorescent N- and C-terminal fragments of a fluorescent protein; when the partners interact or remain close enough, the fluorescent fragments complement, mature, and generate a fluorescent signal at the site of the protein complex. The BiFC readout is fluorescence intensity and subcellular localization of the reconstituted fluorophore, which reflects formation or stabilization of a protein complex rather than direct biochemical binding kinetics; BiFC is therefore useful for mapping where interactions occur in cancer cells, neurons, macrophages, organoid-derived cells, or drug-screening systems, but results should be validated by independent assays such as co-IP or Western blot. BiFC signal formation is delayed by fluorophore maturation and can stabilize otherwise transient complexes, so it is not a real-time reversible interaction assay

Cell-cycle analysis by flow cytometry measures DNA content in single cells to estimate the fraction of cells in G0/G1, S, and G2/M phases. Propidium iodide intercalates into DNA, and after RNA removal with RNase, fluorescence intensity reflects cellular DNA content: 2N cells are assigned to G0/G1, cells between 2N and 4N to S phase, and 4N cells to G2/M. DNA-content analysis alone cannot reliably separate G0 from G1 or G2 from M. Ki-67 can distinguish quiescent G0 cells from cycling cells, EdU or BrdU incorporation marks active DNA synthesis in S phase, and phospho-histone H3 staining identifies mitotic cells within the 4N population.

Breast cancer is a heterogeneous cancer, and it has been distinguished into four subtypes: luminal A, luminal B, HER2-positive and basal-like. Molecular mutations, epigenetic alterations, hormone exposure and immune microenvironment are related to the progression of breast cancer.

The following protocol uses the MTT colorimetric assay as a classic literature-established method for assessing cell viability/metabolic activity in cultured mammalian cells. MTT[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] is reduced by metabolically active cells to a colored formazan product; the amount of formazan is quantified spectrophotometrically and provides an indirect measure of metabolically active viable cells. Importantly, MTT reduction reflects cellular oxidoreductase/metabolic activity rather than an absolute direct count of living cells, so changes in cellular metabolism can alter the signal independently of cell number.

Kinase activity assays measure the ability of kinases to transfer phosphate groups from ATP to specific substrates, while phosphorylation assays detect the presence and levels of phosphorylated proteins. Common methods include radiolabeled ATP incorporation (e. g. ,), ADP release detection via bioluminescence (e. g. ,[3]), enzyme-linked immunosorbent assays (ELISA) for phospho-specific epitopes (e. g. ,[6]), and microtiter-based formats for high-throughput screening (e. g. ,[8]). The ADP-Glo assay quantifies kinase activity by measuring ADP produced during phosphorylation using a luciferase-based system. Radiometric assays involve autoradiography or scintillation counting after incorporation of ³²P-labeled ATP into substrate proteins. ELISA-based approaches rely on phospho-specific antibodies to detect activated kinases in cell lysates or purified samples.

Apoptosis, also called programmed cell death, is generally characterized by distinct morphological characteristics.

TUNEL staining detects DNA strand breaks by using terminal deoxynucleotidyl transferase to add labeled nucleotides to exposed 3′-OH DNA termini, generating either microscopic staining in fixed cells or tissue sections, or fluorescence/cytometric signal in cell suspensions. TUNEL positivity reflects DNA fragmentation but should not be interpreted alone as definitive apoptosis, because TUNEL can also label necrotic, autolytic, mechanically damaged, or DNA-repair-associated DNA breaks.

Flow cytometric DNA-content cell-cycle staining measures the fluorescence intensity of DNA-bound fluorochromes in single cells or nuclei to estimate DNA content distributions, allowing assignment of populations to G0/G1, S, and G2/M phases by DNA histogram deconvolution. Propidium iodide (PI) intercalates into DNA, and PI fluorescence is proportional to cellular DNA content when staining is performed under conditions that make DNA accessible and minimize non-DNA signal. Cells with G2/M DNA content are expected to show approximately twice the fluorescence intensity of G0/G1 cells, while S-phase cells occupy intermediate fluorescence values. PI-based DNA-content analysis can also detect cells with fractional DNA content, often reported as sub-G1, when DNA fragmentation and extraction during staining reduce retained DNA signal in apoptotic cells. DAPI is an alternative DNA fluorochrome for univariate DNA-content analysis, while bivariate approaches combining DNA content with proliferation

The pull-down assay is an in vitro technique used to detect physical interactions between two or more proteins and an invaluable tool for confirming a predicted protein-protein interaction or identifying novel interacting partners. This method typically involves the use of affinity purification with various wash and elution steps.

Apoptosis is a regulated, generally non-lytic cell-death pathway that removes unwanted, damaged, infected, or abnormal cells through coordinated morphological changes, caspase activation, DNA fragmentation, and membrane remodeling. The intrinsic apoptosis pathway is controlled mainly by mitochondrial outer membrane permeabilization, BCL-2 family proteins, cytochrome c release, apoptosome formation, caspase-9 activation, and downstream executioner caspase-3/7 activation. The extrinsic apoptosis pathway is initiated by death receptors such as Fas, TNFR, and TRAIL receptors, which recruit adaptor proteins and activate caspase-8 before engaging executioner caspases or mitochondrial amplification through BID cleavage. Apoptosis is linked to many phenotypes, including cancer cell killing, tissue homeostasis, immune regulation, neurodegeneration, infection response, and treatment-induced cytotoxicity; unresolved questions include how apoptosis interacts with necroptosis, pyroptosis, ferroptos

Kinase activity assays measure transfer of phosphate from ATP to a protein or peptide substrate, generating phosphorylated substrate, ADP, or incorporated radiolabeled phosphate as the readout; phosphorylation assays measure site-specific phosphorylation in cells or tissues as a proxy for kinase-pathway activation, inhibition, or substrate regulation. Phosphorylation can be detected by phospho-specific Western blot, immunoprecipitation kinase assay, phospho-immunofluorescence, phospho-flow cytometry, luminescent ADP detection, radiolabeled ATP incorporation, or reporter-based pathway assays, and these readouts can be applied to cancer cells, primary neurons, mouse tumors, organoids, inflammatory macrophages, ferroptosis studies, and mitophagy studies when the kinase target is biologically relevant.

Co-immunoprecipitation technology can verify protein interaction based on the specific immune reaction between antibodies and antigens.

The yeast two-hybrid assay detects binary protein-protein interactions by separating a transcription factor into a DNA-binding domain fused to a "bait" protein and a transcriptional activation domain fused to a "prey" protein; if bait and prey interact in yeast, the transcription factor is reconstituted and activates reporter genes such as HIS3, ADE2, lacZ, MEL1, or other selectable/readable reporters. The readout is yeast growth on selective medium and/or reporter activity, which reflects proximity-dependent transcriptional activation in the yeast nucleus rather than direct biochemical binding in the original mammalian, tumor, neuronal, macrophage, or organoid context. Because yeast two-hybrid can generate false positives and false negatives, interaction claims should be validated using independent assays such as co-immunoprecipitation, Western blot, immunofluorescence colocalization, BiFC, pull-down, or mammalian two-hybrid assays.