The
mitogen-activated protein kinase (MAPK) cascade plays an important role in carcinogenic development. Herein, we show that the skin
tumor promoter butylated hydroxytoluene hydroperoxide (
BHTOOH) stimulates a rapid and potent (14- to 20-fold) activation of
extracellular signal-regulated kinase (ERK) in vivo and in cultured mouse keratinocytes.
BHTOOH also moderately (5-fold) activated
c-jun-N-terminal kinase, and 38-kDa MAPK-related
protein in these same cells.
N-acetylcysteine and
o-phenanthroline abolished ERK activation by
BHTOOH, consistent with a requirement for
metal-dependent formation of reactive intermediates. Indeed, 4-CD3-BHTOOH, an analogue that generates less of the metabolite
BHT-quinone methide (2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone) and fewer
tumors in vivo, accordingly exhibited diminished potency for activating ERK. ERK activation by
BHTOOH was inhibited by
suramin, and by expression of dominant-negative Ras-N-17 in PC12 cells, suggesting overlap between the pathways for
BHTOOH and
growth factor signaling. Induction of MAPK-dependent genes c-fos and MAPK phosphatase-1 by
BHTOOH was also blocked by Ras-N-17 expression. Moreover, expression of Ras-N-17 or
kinase-defective
MAPK kinase (
MEK) diminished cell survival following
BHTOOH exposure. Similarly, pretreatment with
suramin or the
MEK inhibitor
PD098059 also potentiated the toxicity of
BHTOOH. On the other hand, expression of constitutively active
MEK enhanced cell survival. Thus, we demonstrate that the MAPK cascade is critical to the cellular response to
BHTOOH. This study suggests a functional role for MAPK activation in
tumor promotion stimulated by
oxidants and other agents.