Cell Growth & Differentiation, Vol 7, Issue 3 301-310, Copyright © 1996 by American Association of Cancer Research

ARTICLES

Relationship of sequence-specific transactivation and p53-regulated apoptosis in interleukin 3-dependent hematopoietic cells

E Gottlieb, S Lindner and M Oren
Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.

The p53 tumor suppressor has been implicated in the control of apoptosis in response to various signals, including DNA damage, oncogene activation, and survival factor withdrawal. The p53 protein is a transcription factor capable of sequence-specific transactivation of target genes. The relationship between p53-mediated transactivation and apoptosis was probed in interleukin 3 (IL-3)-dependent DA-1 lymphoma cells. DA-1 cells express endogenous wild-type p53, which is required for the efficient induction of apoptosis by IL-3 deprivation. IL-3 withdrawal caused no detectable increase in p53 and no concomitant activation of p53-responsive promoters. Conversely, high levels of transfected, transcriptionally active p53 did not elicit any apoptosis as long as IL-3 was present; instead, the cells underwent a viable G1 arrest. IL-3 protected DA-1 cells from the apoptotic effect of low doses of radiation. However, higher doses triggered p53-dependent apoptosis, even in the presence of IL-3. Irrespective of their different effects on viability, sublethal and lethal radiation caused a comparable augmentation of p53-dependent transactivation. Lethal radiation induced an initial p53-dependent G1 arrest, but subsequent apoptosis was preceded by cell cycle re-entry. Our data support the conjecture that activities of p53 distinct from specific transcriptional activation may contribute to apoptosis, although activation of genes such as Bax is also likely to play a role.

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