Rottlerin, a selective inhibitor of novel
isoforms of
protein kinase C δ (PKC δ), has been shown to exert multiple effects on
cancer cells, including inhibition of cell proliferation and migration. However, the molecular mechanisms responsible for these effects are not fully understood. We found that
rottlerin dramatically induced non-steroidal anti-inflammatory
drug activated gene-1 (NAG-1) expression in both p53 wild-type and p53-null
cancer cell lines, suggesting that NAG-1 upregulation is a common response to
rottlerin that occurs independently of p53 in multiple cell lines. Although
rottlerin is known to inhibit PKC δ, PKC δ
siRNA and overexpression of dominant-negative (DN)-PKC δ did not affect
rottlerin-mediated induction of NAG-1. These results suggest that
rottlerin induces NAG-1 upregulation via a PKC δ-independent pathway. We also observed that CHOP
protein levels were significantly increased by
rottlerin, but CHOP
siRNA did not affect
rottlerin-induced NAG-1 expression. In addition, we demonstrated the involvement of the
mitogen-activated protein kinase (MAP
kinase) signal transduction pathway in
rottlerin-induced NAG-1 expression. Inhibitors of
MEK (
PD98059) and
p38 MAP kinase (
SB203580) prevented
rottlerin-induced NAG-1 expression. Furthermore, we found that down-regulation of NAG-1 attenuated
rottlerin-induced apoptosis. Collectively, the results of this study demonstrate, for the first time, that upregulation of NAG-1 contributes to
rottlerin-induced apoptosis in
cancer cells.