ABSTRACT
Certain mutations in the mammalian ras gene are oncogenic and are often detected in human cancers. Oncogenic Ras induces the transcription activity of NF-kappaB that confers cell survival. Oncogenic Ras also down-modulates the expression of Par-4, a transcriptional repressor protein, that is essential but not sufficient on its own to induce apoptosis. Here we show that reintroduction of Par-4 by transient transfection leads to apoptosis in cells expressing oncogenic Ras but not in those that lack oncogenic Ras expression. Par-4 abrogates oncogenic Ras-inducible NF-kappaB transcription activity but does not interfere with cytoplasmic activation, or the DNA binding activity, of NF-kappaB. Because abrogation of NF-kappaB transcription activity is sufficient to cause apoptosis in cells expressing oncogenic Ras, our findings identify Par-4 as a novel example of a pro-apoptotic protein that selectively inhibits oncogenic Ras-dependent NF-kappaB function at the transcription level and suggest a mechanism by which Par-4 expression may selectively induce apoptosis in oncogenic Ras-expressing cells.
Subject(s)
Apoptosis/physiology , Carrier Proteins/physiology , I-kappa B Proteins , Intracellular Signaling Peptides and Proteins , Oncogene Protein p21(ras)/physiology , 3T3 Cells , Animals , Apoptosis Regulatory Proteins , DNA/metabolism , DNA-Binding Proteins/metabolism , Humans , Hydrolysis , Ligases/antagonists & inhibitors , Ligases/metabolism , Mice , NF-KappaB Inhibitor alpha , NF-kappa B/antagonists & inhibitors , NF-kappa B/metabolism , Proto-Oncogene Proteins c-raf/metabolism , Transcription, GeneticABSTRACT
Interleukin-1 (IL-1) causes G1-phase growth arrest of A375-C6 human melanoma cells by hypophosphorylation of the retinoblastoma susceptibility gene product Rb. Because p53 and p21/WAF1 proteins are key components of growth arrest pathways involving Rb hypophosphorylation, we tested the functional role of these two proteins in IL-1 action. Exposure to IL-1 caused induction of both p53 and p21/WAF1 proteins. However, inhibition of p53 function by the K1 mutant of SV40-T antigen or by m175 (Arg to His) dominant-negative mutant of p53 did not result in abrogation of IL-1 action, suggesting that p53 function is not required for growth arrest by IL-1. Studies aimed at testing the role of p21/WAF1 in IL-1 action indicated that IL-1 induced p21/WAF1 expression independently of the p53 status of the cells. However, inhibition of p21/WAF1 expression resulted in only a marginal rescue from the growth-arresting action of IL-1. These findings imply that despite their induction, neither wild-type p53 nor p21 can fully account for the growth arrest by IL-1. Thus, a p53- and p21-independent pathway(s) mediates IL-1 action.