The p38 MAPK Pathway Mediates Aryl Propionic Acid–Induced Messenger RNA Stability of p75NTR in Prostate Cancer Cells

The p75 NTR acts as a tumor suppressor in the prostate, but its expression is lost as prostate cancer progresses and is minimal in established prostate cancer cell lines such as PC-3, DU-145, and LNCaP. Previously, we showed that treatment with R-flurbiprofen or ibuprofen induced p75 NTR expression in PC-3 and DU-145 cells leading to p75 NTR -mediated decreased survival. Here, we investigate the mechanism by which these drugs induce p75 NTR expression. We show that the observed increase in p75 NTR protein due to R-flurbiprofen and ibuprofen treatment was accompanied by an increase in p75 NTR mRNA, and this increase in mRNA was the result of increased mRNA stability and not by an up-regulation of transcription. In addition, we show that treatment with R-flurbiprofen or ibuprofen led to sustained activation of the p38 mitogen-activated protein kinase (MAPK) pathway. Furthermore, inhibition of the p38 MAPK pathway with the p38 MAPK–specific inhibitor SB202190 or by small interfering RNA (siRNA) knockdown of p38 MAPK protein prevented induction of p75 NTR by R-flurbiprofen and ibuprofen. We also observed that siRNA knockdown of MAPK-activated protein kinase (MK)-2 and MK3, the kinases downstream of p38 MAPK that are responsible for the mRNA stabilizing effects of the p38 MAPK pathway, also prevented an induction of p75 NTR by R-flurbiprofen and ibuprofen. Finally, we identify the RNA stabilizing protein HuR and the posttranscriptional regulator eukaryotic translation initiation factor 4E as two possible mechanisms by which the p38 MAPK pathway may increase p75 NTR expression. Collectively, the data suggest that R-flurbiprofen and ibuprofen induce p75 NTR expression by increased mRNA stability that is mediated through the p38 MAPK pathway. [Cancer Res 2007;67(23):11402–10]