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trans-Stilbenes induce cytochrome P450 1B1 (CYP1B1) inhibition and cell death. 2,4,3',5' tetramethoxystilbene (TMS), a synthetic trans-stilbene analog, induced apoptotic cell death in PC-3 prostate cancer cells, as evidenced by a decrease in the mitochondrial membrane potential. TMS-induced apoptosis was associated with an increase in the level of cell cycle inhibitor, p27(kip1), through reduction of Akt-mediated Skp2 expression. TMS-induced activation of protein phosphatase 2A (PP2A) inhibited Akt phosphorylation and p27(kip1) expression, indicating that PP2A is involved in the induction of p27(kip1) via Akt inhibition. These results suggest that TMS may inhibit the cell cycle through induction of p27(kip1), leading to apoptotic cell death in PC-3 prostate cancer cells.

Ceramide analogs are potential chemotherapeutic agents. We report that a ceramide analog induces apoptosis in human prostate cancer cells. The ceramide analog induced cell death through an apoptotic mechanism, which was demonstrated by DNA fragmentation, the cleavage of poly ADP ribose polymerase (PARP), and a loss of membrane asymmetry. Treating the cells with ceramide analog resulted in the release of various proapoptotic mitochondrial proteins including cytochrome c and Smac/DIBLO into the cytosol, and a decrease in the mitochondrial membrane potential. In addition, the ceramide analog decreased the phospho-Akt and phospho-Bad levels. The expression of the antiapoptotic Bcl-2 decreased slightly with increasing Bax to Bcl-2 ratio. These results suggest that the ceramide analog induces apoptosis by regulating multiple signaling pathways that involve the mitochondrial pathway.

The cyclin-dependent kinase inhibitor p27kip1 (p27) has been implicated in the regulation of cell cycle and apoptosis. Recently, we have demonstrated that ceramide induces apoptotic cell death associated with increase in the level of p27 in HL-60 cells. In the present study, we showed that overexpression of p27 increases ceramide-induced apoptotic cell death in HL-60 cells. Furthermore, overexpression of p27 accelerated DNA fragmentation, PARP cleavage and cytochrome c release induced by ceramide. In addition, ceramide induced Bax expression independent of p27. These findings indicate that enhanced effect on apoptosis by p27 is associated with mitochondrial signaling which involves cytochrome c release.

3, 4'-Dimethoxy-5-hydroxystilbene (DMHS) is a hydroxystilbene compound obtained by methylation and acid hydrolysis of piceid (resveratrol-3-O-glucoside) from Polygonum cuspidatum. Herein, we report that DMHS induces programmed cell death or apoptosis in human promyelocytic leukemic HL-60 cells. We found that treatment of HL-60 cells with DMHS suppressed the cell growth in a concentration-dependent manner with an IC50 value of 25 microM. DMHS increased internucleosomal DNA fragmentation in a time-dependent manner. The cell death by DMHS was partially prevented by the caspase inhibitor, zVAD-fmk. DMHS caused activation of caspases such as caspase-3, -8, and -9. Immunoblot experiments revealed that DMHS-induced apoptosis was associated with the induction of Bax expression. The release of cytochrome c from mitochondria into the cytosol was increased in response to DMHS. Taken together, our present results indicated that DMHS leads to apoptotic cell death in HL-60 cells through increased Bax expression and release of cytochrome c into cytosol and may be considered as a good candidate for a cancer chemopreventive agent in humans.

Ceramide acts as a mediator of apoptosis in various cell lines, but little is known regarding the molecular mechanism linked to the cell cycle. In the present study, we examined the expression of p27 kip1 and its relationship to apoptosis induced by ceramide. We demonstrated that treatment of HL-60 cells with C 6 -ceramide resulted in G1 phase elevation followed by apoptotic cleavage associated with increase in the level of cdk inhibitor p27 kip1 . Ceramide inhibited the kinase activities of cdk2 and cdk4 within 24 h of treatment. Ceramide-induced inhibition of cdk2 and cdk4 kinase activities was accompanied by increase of p27 kip1 in the cdks complexes. In addition, we have shown that both the cell death and expression of p27 kip1 protein induced by ceramide were significantly decreased in HL-60 cells overexpressing bcl- 2. Furthermore, ceramide induced a significant increase in Bax protein expression coincided with increase in p27 kip1 protein level. These findings indicate that p27 kip1 may play important roles in mediating ceramide-induced apoptosis and its expression can be regulated by Bax and Bcl-2.

Ceramide acts as a mediator of programmed cell death in various cell types, but its molecular mechanisms linked to the cell cycle are poorly understood. In this study, we investigated the expression of the p21 gene and its relationship to apoptosis induced by ceramide. In SK-HEP-1 cells, the addition of C6-ceramide resulted in a dose- and time-dependent growth suppression and DNA fragmentation characteristics of apoptosis. p21 protein was induced during that process, while the protein level of p53, known as a transcriptional activator of p21, was not elevated under the same condition. This apoptotic cell death with p21 induction was also observed in the Hep 3B cells lacking functional p53 after exposure to C6-ceramide. These findings suggest that ceramide-induced apoptosis is associated with the upregulation of p21 mRNA and protein in a p53-independent pathway.

Ceramide induces cell cycle arrest and apoptotic cell death associated with increased levels of p27(kip1). The aim of this study was to examine the effects of ceramide on p27(kip1) protein levels as a measure of cell cycle arrest and apoptosis. Results showed that ceramide increased p27(kip1) protein levels through activation of protein phosphatase 2A (PP2A) in PC-3 prostate cancer cells. Treatment of cells with the PP2A inhibitor okadaic acid or with PP2A-Cα siRNA inhibited ceramide-induced enhanced p27(kip1) protein expression and Akt dephosphorylation, and prevented Skp2 downregulation. Overexpression of constitutively active Akt attenuated ceramide-induced Skp2 downregulation and p27(kip1) upregulation. In addition, ceramide stimulated binding of the PP2A catalytic subunit PP2A-Cαβ to Akt as assessed by immunoprecipitation experiments, indicating that PP2A is involved in the induction of p27(kip1) via inhibition of Akt pathway. Finally, whether PP2A can regulate p27(kip1) expression independently of Akt pathway was determined. Knockdown of PP2A-Cα with siRNA reduced p27(kip1) levels in the presence of Akt inhibitor. These data reveal that PP2A is a regulator of ceramide-induced p27(kip1) expression via Akt-dependent and Akt-independent pathways.

trans-Stilbenes have been reported to induce cytochrome P450 1B1 (CYP1B1) inhibition and cell death, however, the molecular mechanisms of the effects are not fully understood. We report here that (1-(2-{3-[2-(2,4-dimethoxy-phenyl)-vinyl]-5-methoxy-phenoxy}ethyl)-1H-imidazole), a synthetic stilbene analog (SA) significantly suppressed TCDD-stimulated CYP1B1 mRNA expression. In HL-60 cells, SA induced apoptosis through activation of p38 MAPK and inactivation of Akt, which in turn activated Bad and mitochondrial death signaling pathway, as evidenced by Bax translocation and cytochrome c release. Expression of dominant negative p38 MAPK or constitutively active Akt significantly prevented cell death and mitochondrial Bax translocation, implicating that p38 MAPK and Akt signaling pathways play crucial roles in stilbene-induced apoptosis of HL-60 cells. These results suggest that SA induces apoptotic cell death as well as CYP1B1 inhibition and may thus be beneficial in cancer prevention.

Ceramide induces apoptosis through caspase activation, cytochrome c release, and Bax translocation in HL-60 cells. However, the upstream signal transduction pathways that induce Bax translocation during ceramide-mediated apoptosis have not been well defined yet. In this study, the activation of p38 mitogen-activated protein kinase (MAPK) was found to be critical for the induction of apoptosis and subcellular redistribution of Bax. Pharmacological inhibition of p38 MAPK with SB203580 or expression of a dominant-negative p38 MAPK attenuated DNA fragmentation, caspase-3 activation, and Bax translocation in response to ceramide. Overexpression of Akt also led to suppression of Bax translocation to mitochondria during ceramide-induced apoptosis in HL-60 cells. We also provide evidence for cross-talk between p38 MAPK and Akt pathways. Expression of myr-Akt or inhibition of phosphatidylinositol 3-kinase (PI3K) with LY294002 had no effect on p38 MAPK activation by ceramide as assessed by phosphorylation, while inhibition of p38 MAPK by a pharmacological inhibitor or a dominant-negative p38 inhibited Akt dephosphorylation in response to ceramide, suggesting that ceramide-induced p38 MAPK activation negatively regulates the Akt pathway.

We have previously shown that 2,4,3',5'-tetramethoxystilbene (TMS), a synthetic trans-stilbene analog, is one of the most potently selective inhibitors of recombinant human cytochrome P450 1B1 (CYP1B1) in vitro. In the present studies, the effects of TMS on CYP1B1 expression were investigated in human cancer cells. TMS significantly inhibited CYP1-mediated 7-ethoxyresorufin O-deethylation activity in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced MCF-7 cells or lung microsomes of Sprague-Dawley rats treated with 7,12-dimethylbenz[a]anthracene. TCDD-stimulated CYP1B1 protein and mRNA expression was significantly suppressed by TMS in a concentration-dependent manner in MCF-7, MCF-10A, and HL-60 cells. Whereas TMS down-regulated TCDD-induced CYP1B1 gene expression, the levels of aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator mRNA expression were not changed by TMS treatment. In human cancer cells, TMS induced apoptotic cell death, and the cytotoxic effects of TMS were significant when the cells were incubated with TCDD. CYP1B1 was able to convert TMS to a metabolite(s) when incubated with NADPH. Metabolic activation of TMS by CYP1B1 induced by TCDD may mediate cellular toxicity of TMS in human cancer cells because the sensitivity to TMS in MCF-7 cells treated with TCDD was more significant than in HL-60 cells treated with TCDD. Taken together, our results indicate that TMS acts as a strong modulator of CYP1B1 gene expression as well as a potent selective inhibitor in vitro. The ability of TMS to induce apoptotic cell death in tumor cells, as well as CYP1B1 inhibition, may contribute to its usefulness for cancer chemoprevention.

Vitamin K-related analogs induce growth inhibition via a cell cycle arrest through cdc25A phosphatase inhibition in various cancer cell lines. We report that 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone (DDN), a naphthoquinone analog, induces mitochondria-dependent apoptosis in human promyelocytic leukemia HL-60 cells. DDN induced cytochrome c release, Bax translocation, cleavage of Bid and Bad, and activation of caspase-3, -8, -9 upon the induction of apoptosis. Cleavage of Bid, the caspase-8 substrate, was inhibited by the broad caspase inhibitor z-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk), whereas cytochrome c release was not affected, suggesting that activation of caspase-8 and subsequent Bid cleavage occur downstream of cytochrome c release. DDN inhibited the activation of Akt detected by decreasing level of phosphorylation. Overexpression of constitutively active Akt protected cells from DDN-induced apoptosis, while dominant negative Akt moderately enhanced cell death. Furthermore, Akt prevented release of cytochrome c and cleavage of Bad in DDN-treated HL-60 cells. Taken together, DDN-induced apoptosis is associated with mitochondrial signaling which involves cytochrome c release via a mechanism inhibited by Akt.

Vitamin K-related analogs induce growth inhibition in various cancer cell lines. A naphthoquinone analog, termed 2,3-dichloro-5, 8-dihydroxy-1,4-naphthoquinone (DDN), induces apoptosis in human promyeloid leukemic HL-60 cells, and shows antitumor activity in vivo. Following treatment with DDN, evidence of apoptosis, including DNA fragmentation and cleavage of poly ADP ribose polymerase (PARP), was observed. DDN induced an upregulation of proapoptotic Bax protein, and Bid cleavage. Antiapoptotic Bcl-2 protein levels were not changed by DDN, but the expression of Bcl-xL was decreased. In addition, DDN reduced the mass of solid tumor in the Sarcoma 180 tumor-bearing mouse model. These results indicate that DDN exerts antitumor activity, which appears to be related to the induction of apoptosis by regulating Bcl-2 family proteins.

Ceramide is an important lipid messenger involved in mediating a variety of cell functions including apoptosis. In this study, we show that antisense bax inhibits cytochrome c release, poly(ADP-ribose)polymerase cleavage and cell death induced by ceramide in HL-60 cells. In addition, ceramide induces translocation of Bax to mitochondria. The addition of the broad spectrum caspase inhibitor zVAD-fmk prevented ceramide-induced apoptotic cell death but did not inhibit translocation of Bax and mitochondrial cytochrome c release. Furthermore, ceramide inhibits the expression of the antiapoptotic protein Bcl-xL with an increase in the ratio of Bax to Bcl-xL. These data provide direct evidence that Bax plays an important role in regulating ceramide-induced apoptosis.