IDENTIFICATION OF KERATIN-18, KERATIN-19 AND HEAT-SHOCK-PROTEIN-90-BETA AS CANDIDATE SUBSTRATES OF PROTEOLYSIS DURING IONIZING RADIATION-INDUCED APOPTOSIS OF ESTROGEN-RECEPTOR NEGATIVE BREAST-TUMOR CELLS

Induction of apoptosis in the estrogen-receptor negative MDA-MB-468 br east turner cells has been demonstrated by treatments with cytotoxic a gents and growth factors, Using these breast tumor cells, we studied i onizing radiation-induced apoptosis. 2D-PAGE of apoptotic cells indica ted keratins 18, 19 and heat-shock protein 90 as candidate substrates of apoptosis-associated proteolysis. At the same time, a motif search revealed possible cleavage-sites in keratins 18, 19 (VEVD) and hsp-90 beta (DEED) that would yield polypeptides of molecular sizes observed experimentally by immunoblotting with specific antisera. This study pr ovides evidence that the insoluble network of intermediate filament pr oteins of epithelial cells (keratins). and the associated proteins (he at-shock protein 90 beta) constitute targets of caspase-mediated prote olysis during apoptosis triggered by ionizing radiation.