Expression of candidate cell death genes in cell lines during apoptosis.

We have cloned mouse candidate cell death genes RP-2 and nedd2 and used Northern blot analysis to study their expression in a growth-factor-dependent cell line (FDC-P1) that can be induced to undergo apoptosis by growth factor withdrawal and in a thymoma line (ST4) that undergoes apoptosis when irradiated. RP-2 was expressed in FDC-P1 cells even when not undergoing apoptosis, and mRNA levels did not increase when apoptosis was induced by growth factor withdrawal. FDC-P1 cells expressed two genes that are similar to the Caenorhabditis elegans cell death gene ced-3: a 3.7 kilobase (kb) nedd2 message and low levels of a 5-kb message for interleukin-1 beta converting enzyme. Levels of these messages did not change with the induction of cell death, but transfection of fibroblasts with constructs expressing nedd2 caused them to undergo apoptosis. These results suggest that expression of RP-2 and nedd2 is not sufficient for apoptosis, and if the products of these genes are involved in apoptosis of FDC-P1 cells, they are regulated by posttranslational mechanisms.