Guillouf C, Graña X, Selvakumaran M, De Luca A, Giordano A, Hoffman B, Liebermann D A
Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Blood. 1995 May 15;85(10):2691-8.
Employing the myeloblastic leukemia M1 cell line, which does not express endogenous p53, and genetically engineered variants, it was recently shown that activation of p53, using a p53 temperature-sensitive mutant transgene (p53ts), resulted in rapid apoptosis that was delayed by high level ectopic expression of bcl-2. In this report, advantage has been taken of these M1 variants to investigate the relationship between p53-mediated G1 arrest and apoptosis. Flow cytometric cell cycle analysis has provided evidence that activation of wild-type (wt) p53 function in M1 cells resulted in the induction of G1 growth arrest; this was clearly seen in the M1p53/bcl-2 cells because of the delay in apoptosis that unmasked p53-induced G1 growth arrest. This finding was further corroborated at the molecular level by analysis of the expression and function of key cell cycle regulatory genes in M1p53 versus M1p53/bcl-2 cells after the activation of wt p53 function; events that take place at early times during the p53-induced G1 arrest occur in both the M1p53 and the M1p53/bcl-2 cells, whereas later events occur only in the M1p53/bcl-2 cells, which undergo delayed apoptosis, thereby allowing the cells to complete G1 arrest. Finally, it was observed that a spectrum of p53 target genes implicated in p53-induced growth suppression and apoptosis were similarly regulated, either induced (gadd45, waf1, mdm2, and bax) or suppressed (c-myc and bcl-2), after activation of wt p53 function in M1p53 and M1p53/bcl-2 cells. Taken together, these findings show that wt p53 can simultaneously induce the genetic programs of both G1 growth arrest and apoptosis within the same cell type, in which the genetic program of cell death can proceed in either G1-arrested (M1p53/bcl-2) or cycling (M1p53) cells. These findings increase our understanding of the functions of p53 as a tumor suppressor and how alterations in these functions could contribute to malignancy.
利用不表达内源性p53的髓性白血病M1细胞系及其基因工程变体，最近研究表明，使用p53温度敏感突变转基因（p53ts）激活p53会导致快速凋亡，而高水平异位表达bcl-2可延迟这种凋亡。在本报告中，利用这些M1变体研究了p53介导的G1期阻滞与凋亡之间的关系。流式细胞术细胞周期分析提供了证据，表明M1细胞中野生型（wt）p53功能的激活导致了G1期生长阻滞的诱导；这在M1p53/bcl-2细胞中很明显，因为凋亡延迟，从而揭示了p53诱导的G1期生长阻滞。在激活wt p53功能后，通过分析M1p53与M1p53/bcl-2细胞中关键细胞周期调节基因的表达和功能，在分子水平上进一步证实了这一发现；p53诱导的G1期阻滞早期发生的事件在M1p53和M1p53/bcl-2细胞中均会出现，而后期事件仅发生在经历延迟凋亡的M1p53/bcl-2细胞中，从而使细胞能够完成G1期阻滞。最后，观察到在M1p53和M1p53/bcl-2细胞中激活wt p53功能后，一系列与p53诱导的生长抑制和凋亡相关的p53靶基因受到类似的调控，要么被诱导（gadd45、waf1、mdm2和bax），要么被抑制（c-myc和bcl-2）。综上所述，这些发现表明，wt p53可以在同一细胞类型中同时诱导G1期生长阻滞和凋亡的遗传程序，其中细胞死亡的遗传程序可以在G1期阻滞的细胞（M1p53/bcl-2）或循环细胞（M1p53）中进行。这些发现加深了我们对p53作为肿瘤抑制因子功能的理解，以及这些功能的改变如何导致恶性肿瘤。
