The mitogenic response of AML blasts to tumor necrosis factor-alpha requires functional c-jun/AP-1

The c-jun proto-oncogene belongs to the family of immediate early response genes and is inducible by serum growth factors and Tumor Necrosis Factor (TNF). In the present study we have addressed the role of c-jun for the mitogenic response of primary acute myelogenous leukemia (AML) blasts to TNF-alpha. Our data indicate that TNF-alpha treatment of these cells is associated with transcriptional activation of c-jun and accumulation of c-jun mRNA. In order to elucidate the role of c-jun for TNF-mediated growth stimulation, an antisense (AS) oligomer directed towards the translation initiation site of c-jun was instrumental. Uptake studies of oligonucleotides showed that incorporation of oligomers was maximal at 4 hours. Oligodeoxynucleotides remained stable in these cells for up to 24 hours. Treatment of AML blasts with the AS oligonucleotide resulted in intracellular duplex formation followed by efficient translation blockade of c-jun/AP-1. In contrast, sense (S) and none-sense (NS) oligodeoxynucleotides failed to form intracellular duplexes and also did not interfere with translation of c-jun/AP-1, suggesting specific elimination of c-jun/AP-1 by the AS oligomer. AML blasts cultured in the presence of AS to c-jun, but not of S or NS, failed to proliferatively respond to TNF-alpha stimulation. Taken together, our results indicate that activation of c-jun/AP-1 plays a pivotal role in the signaling cascade initiated by TNF which leads to a proliferative response of its target cells.