c-myc null cells misregulate cad and gadd45 but not other proposed c-Myc targets

We report here that the expression of virtually all proposed c-Myc target g enes is unchanged in cells containing a homozygous null deletion of c-myc. Two noteworthy exceptions are the gene cad, which has reduced log phase exp ression and serum induction in c-myc null cells, and the growth arrest gene gadd45, which is derepressed by c-myc knockout. Thus, cad and gadd45 are t he only proposed targets of c-Myc that may contribute to the dramatic slow growth phenotype of c-myc null cells. Our results demonstrate that a loss-o f-function approach is critical for the evaluation of potential c-Myc targe t genes.