Differential gene expression in apoptotic 32Dcl3 cells: induction of metallothionein

Growth factor deprivation induced cell death of the hematopoietic cell line 32Dcl3 is widely used as a model system to study apoptotic signalling pathways. Here we show that the onset of cell death after IL-3 withdrawal can be strongly delayed by either cycloheximide or actinomycin D, indicating that de novo protein synthesis is required. Subtractive cDNA library hybridization was used to identify genes upregulated in apoptotic 32Dcl3 cells. Here we present data showing metallothionein-I (MT-I) mRNA transiently upregulated by a factor of three- to 20-fold. Increased levels of total MT-I+II protein after IL-3 withdrawal were demonstrated. An induction of MT-I RNA as well as of MT-I+II total protein was also observed in serum deprived NIH3T3 fibroblasts. Testing the effect of different inducers of apoptosis on 32Dcl3 cells we found that only IL-3 withdrawal and ethanol treatment led to an upregulation of MT-I mRNA level. Since MTs are believed to play a role in the metabolism of zinc, we tested the effect of zinc on induced cell death. When 32Dcl3 cells are treated with zinc (50-300 M) in the absence of IL-3, loss of viability as well as degradation of the cellular DNA were delayed, indicating that zinc represses apoptosis. On the other hand zinc pre-treatment induced MT expression and accelerated the onset of apoptosis. Our data, therefore, suggest that MT exerts a proapoptotic function.