Isolation of 10 differentially expressed cDNAs in p53-induced apoptosis: Activation of the vertebrate homologue of the Drosophila seven in absentia gene (tumor suppressionydevelopmentyMEN1yZFM1yPLC)

We report the isolation of 10 differentially expressed cDNAs in the process of apoptosis induced by the p53 tumor suppressor. As a global analytical method, we performed a differential display of mRNA between mouse M1 myeloid leukemia cells and derived clone LTR6 cells, which contain a stably transfected temperature-sensitive mutant of p53. At 32°C wild-type p53 function is activated in LTR6 cells, resulting in programmed cell death. Eight genes are activated (TSAP; tumor suppressor activated pathway), and two are inhibited (TSIP, tumor suppressor inhibited pathway) in their expression. None of the 10 sequences has hitherto been recognized as part of the p53 signaling pathway. Three TSAPs are homologous to known genes. TSAP1 corresponds to phos- pholipase C b4. TSAP2 has a conserved domain homologous to a multiple endocrine neoplasia I (ZFM1) candidate gene. TSAP3 is the mouse homologue of the Drosophila seven in absentia gene. These data provide novel molecules involved in the pathway of wild-type p53 activation. They establish a functional link between a homologue of a conserved develop- mental Drosophila gene and signal transduction in tumor suppression leading to programmed cell death. A global view of the molecular events occurring during the cell cycle, development, and apoptosis, is necessary in order to understand the basis of cancer and tumor suppression. An overall and systematic analysis of gene expression modulation, responsible for tumor suppression, was hitherto hampered by two factors. A technological restriction, which has recently been overcome with the description of differential cDNA display (1), procuring the possibility to screen and compare expression of the majority of genes. The second restriction lies in the choice of the model system to be analyzed. The biological models must be well established, providing for a functional link, and suitable for differential molecular comparison. Such studies should lead beyond isolation of single tumor suppressor genes to definition of the entire molecular pathways of apo- ptosis and suppression. In human tumors, the most frequently mutated gene is that for p53 (2, 3). Two main streams of evidence indicate that p53 is a tumor suppressor gene. First, transfection experiments demonstrate that wild-type p53 in- duces growth arrest or apoptosis (4-7). Second, nullizygous mice for the p53 gene are significantly more susceptible to