The synthetic
retinoid N-(4-hydroxphenyl)
retinamide (4HPR) has manifold actions, which may contribute to its chemopreventive effects on
breast cancer cell growth and progression. A role for
ceramide as a stress-response signal is investigated here during the cytotoxic action of 4HPR in MCF-7 cells. N-(4-hydroxphenyl)
retinamide induced a dose-dependent decline in cell growth and survival associated with a maximal 10-fold increase in
ceramide production
at 10 microM. N-(4-hydroxphenyl)
retinamide exhibited a greater potency than
all-trans retinoic acid (ATRA) on growth inhibition and
ceramide production. The synthetic
peroxisome proliferator-activated receptors agonist
troglitazone (TGZ), but not the native
ligand 15-deoxy-delta 12,14-prostaglandin J2, abrogated both these actions of 4HPR but not that of ATRA. The
antioxidant N-acetylcysteine mimicked the abrogative effect of TGZ on 4HPR action, while the exogenous
oxidant H2O2 also stimulated
ceramide production. The inhibitors of de novo
ceramide synthesis,
fumonisin B1 and
myriocin, blocked the
ceramide response to 4HPR and partially reversed the apoptotic response, but did not prevent the overall decline in cell survival. The pancaspase inhibitor
Z-VAD fmk reduced the decrease in cell survival caused by 4HPR, but did not affect the
ceramide response. These findings describe a novel redox-sensitive elevation of
ceramide levels associated with the cytotoxic response of
breast cancer cells to 4HPR. However, a major mediatory role for this
sphingolipid in this context remains equivocal.