Nonsteroidal anti-inflammatory drugs (
NSAIDs) are known to prevent colorectal
tumorigenesis. Although antitumor effects of
NSAIDs are mainly due to inhibition of
cyclooxygenase activity, there is increasing evidence that
cyclooxygenase-independent mechanisms may also play an important role. The early growth response-1 (EGR-1) gene is a member of the immediate-early gene family and has been identified as a tumor suppressor gene.
Tolfenamic acid is a
NSAID that exhibits anticancer activity in a
pancreatic cancer model. In the present study, we investigated the anticancer activity of
tolfenamic acid in human
colorectal cancer cells.
Tolfenamic acid treatment inhibited cell growth and induced apoptosis as measured by
caspase activity and bioelectric impedance.
Tolfenamic acid induced EGR-1 expression at the transcription level, and analysis of the EGR-1 promoter showed that a putative ETS-binding site, located at -400 and -394 bp, was required for activation by
tolfenamic acid. The electrophoretic mobility shift assay and
chromatin immunoprecipitation assay confirmed that this sequence specifically bound to the ETS family
protein epithelial-specific ETS-1 (ESE-1)
transcription factor.
Tolfenamic acid also facilitated translocation of endogenous and exogenous ESE-1 to the nucleus in
colorectal cancer cells, and gene silencing using ESE-1
small interfering RNA attenuated
tolfenamic acid-induced EGR-1 expression and apoptosis. Overexpression of EGR-1 increased apoptosis and decreased bioelectrical impedance, and silencing of endogenous EGR-1 prevented
tolfenamic acid-induced apoptosis. These results show that activation of ESE-1 via enhanced nuclear translocation mediates
tolfenamic acid-induced EGR-1 expression, which plays a critical role in the activation of apoptosis.