| Recent reports support a relationship between AP-1 transcription factor activity, the ras transformation, and apoptosis. I have therefore hypothesized that high AP-1 activity will increase the susceptibility of NIH3T3 ras-transformed fibroblasts to apoptotic induction. Furthermore, cells with high AP-1 activity (AP-1+) will express pro-apoptotic genes while cells with low AP-1 activity (AP-1− ) will express anti-apoptotic genes. To investigate these hypotheses I determined in AP-1+ and AP-1− cells the affect of: (1) cis-platinum treatment, (2) Raf-1/MEK inhibition and (3) NF-κB inhibition. A DNA array analysis was also performed (F. Wang, unpublished results) to verify gene expression in these cells.; My data showed that high AP-1 activity increased the susceptibility of ras-transformed cells to death by cis-platinum and to Raf-1 or MEK inhibition. Over-expression of bcl-2 partially rescued cells from cis-platinum-induced death and completely rescued death by Raf-1 inhibition. Interestingly, AP-1− cells showed reduced resistance to cis-platinum in the presence of Raf-1/MEK inhibition.; The above experiments support a model for Ras pathway regulation of apoptosis based on analysis of activities downstream of Ras: JNK, ERK, and AP-1 upon cis-platinum treatment or Raf-1/MEK inhibition. High AP-1 activity promotes a susceptibility to death that is not influenced by the level of ERK activity. AP-1− ras-transformed and non-transformed cells have a higher resistance to death, but only when ERK activity is elevated. When ERK activity is low, AP-1− cells lose part of their resistance to death.; NF-κB activity inhibition resulted in the selective death of ras-transformed cells. High levels of AP-1 activity did not increase the susceptibility of ras-transformed cells to death. Over-expression of bcl-2 completely rescued ras-transformed cells from death.; The DNA array analysis confirmed that AP-1+ cells expressed higher levels of the pro-apoptotic genes bak1 and clu/apoJ, while AP-1− cells expressed higher levels of the anti-apoptotic gene gadd153. These differences in expression may partly explain the differences in susceptibility observed between AP-1+ and AP-1− ras-transformed cells. The apoptotic effects due to differences in AP-1 activity in ras-transformed NIH3T3 cells may model properties of human cancer subtypes, which may be of importance in the selective treatment of these cancers with apoptotic inducers. |
