Abstract B53: Proteasome inhibitor MG132 induces NAG-1 expression through activation of p38 MAPK pathway

Abstract

Glioblastoma multiforme (GBM) is the highly invasive primary tumors with a poor prognosis despite current surgical, radiation and chemotherapy approaches. Proteasome inhibitor, an approved drug for treatment of hematological cancer is currently being tested in clinical trials against various malignancies, including GBM. The pro-apoptotic and antitumorigenic protein NAG-1(nonsteroidal anti-inflammatory drug-activated gene-1) is a divergent member of the transforming growth factor-beta (TGF-beta) superfamily. We showed that the proteasome inhibitor, MG132 induces NAG-1 protein and mRNA expression and apoptosis in a concentration-dependent manner in U87 cells. Studies with NAG-1 luciferase reporter constructs show that the −133 to +41 region of the NAG-1 promoter is activated by MG132 however activation does not require the Sp-/Egr-1 binding site. Using the selective pharmacologic p38 mitogen -activated protein kinase (MAPK) inhibitor, we showed that NAG-1 induction following MG132 is mediated by the p38 MAPK pathway. Pretreatment with MAPK inhibitor, SB203580 and SB202190, blocked the MG132-induced NAG-1 expression, whereas an inhibition of p53, JUNK, MEK, PKC, PKA activity had no effect on NAG-1 levels. In summary, our data indicate linkage between p38MAPK, NAG-1 and the proteasome inhibitor, MG132 and provides a new clue to the molecular mechanism of the antitumorigenic activity of NAG-1.