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Encyclopedia of Experiments: Cancer Research

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Cytoskeleton and Focal Adhesion Organization Assay

 

Cytoskeleton and Focal Adhesion Organization Assay: An Immunofluorescence-based Method to Study Cell Adhesion and Spreading on Substrates

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- Substrate morphology greatly influences cancer cells' behavior and metastatic responses. A dynamic network of actin cytoskeleton provides structural support to cells and mediates cellular movement. Large membrane-associated protein complexes called focal adhesions connect the cytoskeleton with the extracellular matrix, facilitating cell-spreading.

To begin staining, take a cancer cell culture, and treat them with paraformaldehyde to fix and permeabilize the cells. Now, incubate the cells with a signal enhancer reagent containing proteins to prepare the cells to reduce background staining. Add anti-vinculin primary antibodies that bind to vinculin, one of the proteins within the focal adhesion complex.

Next, incubate the sample with a fluorescent dye conjugated secondary antibody targeting the primary antibody. Finally, treat the cells with fluorescent tagged phalloidin conjugates that selectively bind to actin filaments of the cytoskeleton. Observe the cells under a confocal laser scanning microscope to study their fluorescent signals.

Cells with well-spread morphology exhibit defined actin fibers and present distinct and elongated vinculin-containing focal adhesions. Conversely, poorly spread cells do not possess defined actin filaments, but display punctate vinculin-containing focal adhesions. In the following protocol, we will demonstrate an immunofluorescence assay to study cytoskeleton and focal adhesion organization in primary colon cancer cells.

- Take the substrates to be immunostained to the laminar hood and remove the culture media. Then, rinse the substrates with phosphate-buffered saline, or PBS, and fix the cells with 4% paraformaldehyde in PBS for 20 minutes at room temperature. Wash the substrates with PBS for five minutes a total of three times. Then, incubate the substrates with 500 microliters of signal enhancer for 30 minutes before rinsing with PBS.

Next, incubate the cells with monoclonal anti-vinculin antibody at a 1 to 250 dilution in PBS for 45 minutes at room temperature. Then, wash the substrates with PBS for five minutes a total of three times. Incubate the samples with a secondary antibody Alexa Fluor 488 goat anti-mouse IgG at a 1 to 200 dilution in PBS at room temperature for 30 minutes. Then, wash the substrates again with PBS for five minutes a total of three times.

To visualize the F-actin structure, incubate the cells with tetramethylrhodamine-phalloidin conjugates at a concentration of 50 microliters per milliliter for 45 minutes at room temperature. Then, wash the substrates again as before. Finally, proceed to image the samples using a confocal scanning laser microscope.

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