APOPTOSIS OF HUMAN KIDNEY 293-CELLS IS PROMOTED BY POLYMERIZED CADMIUM-METALLOTHIONEIN

Transformed human kidney cells (293 cells) exposed to 12.5 to 37.5 mu M CdCl2 showed apoptosis as confirmed by characteristic electron micro scopic features, a ladder on gel electrophoresis of extracted DNA, and fragmentation of nucleosomes as detected by enzyme linked immunosorbe nt assay (ELISA). Higher concentrations of Cd were less effective in i nducing apoptosis. Furthermore, addition of the protein extract from t he serum-free medium used for Cd-exposure promoted apoptosis exhibitin g the same features as that after Cd-exposure. The apoptosis induced b y the protein was dose-dependent. The molecular weight of the protein (Cd-protein) was shown to be 40 kDa by gel filtration. Two-dimensional electrophoresis revealed the Cd-protein as a single spot with a molec ular weight of 6 kDa and pI of 4.5. Competitive ELISA showed that the Cd-protein reacted with anti-metallothionein antibody. The present fin dings suggest that apoptosis is induced not only by Cd itself but also by polymerized metallothionein molecules (MT) released from cells int o the medium. (C) 1996 Academic Press, Inc.