5.7. Analysis of cytokeratin proteolysis and release by ELISA
In live epithelial cells, cytokeratins are insoluble because they
form aggregates constituting the intermediate filaments of the
cytoskeleton [55]. However, during cell death cytokeratin 18
(CK18) proteins are released and can be detected in the
supernatant. The type of cell death determines what this released
intermediate filament cytokeratin (CK18) looks like. The M30-
Apoptosense assay (Peviva AB, Bromma, Sweden) specifically
measures in the supernatant of dying cells a neo-epitope formed
by caspase-cleavage of CK18 at D396 (CK18D396-NE M30 neo-epitope),
reflecting caspase activation and subsequent apoptotic cell
death. The M65 ELISA (Peviva AB, Bromma, Sweden) measures
soluble full length CK18 released from dying cells and can be used
to assess overall death of epithelial cells due to both apoptosis and
necrosis [56]. The units of the two assays are calibrated against
identical standard material so that a ratio between caspase-cleaved
and total released CK18 can be calculated (M30:M65 ratio).
Induction of apoptosis in cultured cells leads to the release of caspase-
cleaved CK18 and relatively high M30:M65 ratios, whereas
induction of necrosis results almost exclusively in the release of
CK18 molecules that have not been cleaved by caspases, resulting
in a low M30:M65 ratio. The M30:M65 ratio, therefore, reflects the
type of cell death.
5.7. Analysis of cytokeratin proteolysis and release by ELISAIn live epithelial cells, cytokeratins are insoluble because theyform aggregates constituting the intermediate filaments of thecytoskeleton [55]. However, during cell death cytokeratin 18(CK18) proteins are released and can be detected in thesupernatant. The type of cell death determines what this releasedintermediate filament cytokeratin (CK18) looks like. The M30-Apoptosense assay (Peviva AB, Bromma, Sweden) specificallymeasures in the supernatant of dying cells a neo-epitope formedby caspase-cleavage of CK18 at D396 (CK18D396-NE M30 neo-epitope),reflecting caspase activation and subsequent apoptotic celldeath. The M65 ELISA (Peviva AB, Bromma, Sweden) measuressoluble full length CK18 released from dying cells and can be usedto assess overall death of epithelial cells due to both apoptosis andnecrosis [56]. The units of the two assays are calibrated againstidentical standard material so that a ratio between caspase-cleavedand total released CK18 can be calculated (M30:M65 ratio).Induction of apoptosis in cultured cells leads to the release of caspase-cleaved CK18 and relatively high M30:M65 ratios, whereasinduction of necrosis results almost exclusively in the release ofCK18 molecules that have not been cleaved by caspases, resultingin a low M30:M65 ratio. The M30:M65 ratio, therefore, reflects thetype of cell death.
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