Phorbol ester augments butyrate-induced apoptosis of colon cancer cells

PKC theta and p38 MAPK activate the EBV lytic cycle through autophagy induction

PKC activation by combining TPA with sodium butyrate (T/B) represents the most effective and widely used strategy to induce the Epstein-Barr virus (EBV) lytic cycle. The results obtained in this study show that novel PKCθ is involved in such process and that it acts through the activation of p38 MAPK and autophagy induction. Autophagy, a mechanism of cellular defense in stressful conditions, is manipulated by EBV to enhance viral replication. Besides promoting the EBV lytic cycle, the activation of p38 and autophagy resulted in a pro-survival effect, as indicated by p38 or ATG5 knocking down experiments. However, this pro-survival role was counteracted by a pro-death activity of PKCθ, due to the dephosphorylation of AKT. In conclusion, this study reports, for the first time, that T/B activates a PKCθ-p38 MAPK axis in EBV infected B cells, that promotes the viral lytic cycle and cell survival and dephosphorylates AKT, balancing cell life and cell death.

Sodium butyrate sensitises human pancreatic cancer cells to both the intrinsic and the extrinsic apoptotic pathways

Pancreatic cancer is characterised by a highly malignant phenotype with a marked resistance to conventional therapies and to apoptotic activators. Here, we demonstrate that sodium butyrate (NaBt), an inhibitor of histone deacetylases, sensitises human pancreatic cancer cell lines to both mitochondria- and Fas-mediated apoptosis. The analysis of anti-apoptotic and pro-apoptotic members of the Bcl-2 family in untreated pancreatic cancer cell lines shows a generalised low expression of Bcl-2 and a strong expression of Bcl-xL. NaBt treatment results in a marked down-regulation of Bcl-xL expression, mitochondrial membrane depolarization, cytochrome c release from mitochondria, activation of caspase-9 and -3 and apoptosis induction. Furthermore, NaBt sensitises pancreatic cancer cells to Fas-mediated apoptosis as well. In fact, the combined treatment with NaBt and the agonistic antibody anti-Fas (CH11) is able to induce apoptosis at an early time, in which neither NaBt nor CH11 alone induce apoptosis. Down-regulation of FLIP and activation of caspase-8 allow apoptosis to occur. These findings suggest that sodium butyrate could represent a good candidate for the development of new therapeutic strategies aimed at improving chemotherapy and immunotherapy in pancreatic cancer.

Does butyrate protect from colorectal cancer?

Butyrate, the four-carbon fatty acid, is formed in the human colon by bacterial fermentation of carbohydrates (including dietary fiber), and putatively suppresses colorectal cancer (CRC). Butyrate has diverse and apparently paradoxical effects on cellular proliferation, apoptosis and differentiation that may be either pro-neoplastic or anti-neoplastic, depending upon factors such as the level of exposure, availability of other metabolic substrate and the intracellular milieu. In humans, the relationship between luminal butyrate exposure and CRC has been examined only indirectly in case-control studies, by measuring fecal butyrate concentrations, although this may not accurately reflect effective butyrate exposure during carcinogenesis. Perhaps not surprisingly, results of these investigations have been mutually contradictory. The direct effect of butyrate on tumorigenesis has been assessed in a number of in vivo animal models, which have also yielded conflicting results. In part, this may be explained by methodological differences in the amount and route of butyrate administration, which are likely to significantly influence delivery of butyrate to the distal colon. Nonetheless, there appears to be some evidence that delivery of an adequate amount of butyrate to the appropriate site protects against early tumorigenic events. Future study of the relationship between butyrate and CRC in humans needs to focus on risk stratification and the development of feasible strategies for butyrate delivery.

Bile acid deoxycholate induces differential subcellular localisation of the PKC isoenzymes beta 1, epsilon and delta in colonic epithelial cells in a sodium butyrate insensitive manner

Elevated levels of bile acids have been implicated in the abnormal morphogenesis of the colonic epithelium thus contributing to colorectal cancer (CRC). Alternatively sodium butyrate (NaB) produced by anaerobic fermentation of dietary fibre is regarded as being protective against colon cancer. Bile acids such as deoxycholic acid (DCA) are thought to mediate some of their actions by differentially activating protein kinase C (PKC). We examined the effects of DCA on the subcellular localisation of PKC-beta(1), -epsilon and -delta and whether these responses could be modulated by NaB. HCT116 cells endogenously express PKC-epsilon and -delta but not PKC-beta. DCA treatment results in endogenous PKC-epsilon translocation but not PKC-delta after 1 hr. To study the subcellular localisation of PKC isoforms in response to DCA in real time, PKC-beta(1), PKC-epsilon and PKC-delta functionally intact green fluorescent protein (GFP) fusion constructs were used. Stimulation with 300 microM DCA induces rapid translocation of PKC-beta(1)-GFP and PKC-epsilon-GFP but not PKC-delta-GFP from the cytosol to the plasma membrane in 15 min. Interestingly, pretreatment with 4mM NaB does not modify the response of the PKC isoenzymes to DCA as PKC-beta(1)-GFP and PKC-epsilon-GFP translocates to the plasma membrane in 15 min whereas PKC-delta-GFP localisation remains unaltered. Immunofluorescence shows that PKC-beta(1)-GFP and PKC-epsilon-GFP cells treated with DCA colocalise with the cytoskeletal elements actin and tubulin adjacent to the plasma membrane. Our findings demonstrate that the differential activation of the PKC isoenzymes by DCA may be of critical importance for the functional responses of colonic epithelial cells. Supplementary material for this article can be found on the International Journal of Cancer website at http://www.interscience.wiley.com/jpages/0020-7136/suppmat/index.html.

Sodium butyrate and tributyrin induce in vivo growth inhibition and apoptosis in human prostate cancer

Histone deacetylase inhibitors (HDACs) are known to exhibit antiproliferative effects on various carcinoma cells. In this study, the in vivo efficiency of two HDACs, sodium butyrate and tributyrin, on prostate cancer growth inhibition were investigated. To gain an insight into the possible underlying pathways, cell culture experiments were performed focusing on the expression of p21, Rb and c-myc. For in vivo testing, prostate cancer cell lines (PC3 and TSU-Pr1) were seeded on the chorioallantois membrane (CAM) and implanted in a xenograft model using nude mice. Standard Western blot analysis was performed for protein expression of p21, Rb and c-myc in HDAC-treated vs untreated prostate cancer cells. Both sodium butyrate and tributyrin had a considerable treatment effect on microtumours on the chicken egg at already very low concentrations of 0.1 mM. Tributyrin-treated tumours showed the strongest effect with 38% apoptotic nuclei in the prostate cancer cell line PC3. In the mouse model, there was almost no difference between sodium butyrate and tributyrin. In untreated animals the tumours were almost double the size 4 weeks after implantation. Tumours of the treatment groups had a significantly lower percentage of Ki-67-positive-stained nuclei. As demonstrated by Western blot analysis, these effects seem to be independent of p53 status and a pathway via p21–Rb–c-myc is possibly involved. In this study we have demonstrated a substantial in vivo treatment effect, which can be induced by the application of sodium butyrate or the orally applicable tributyrin in human prostate cancer. The given results may provide the rationale to apply these drugs in well-controlled clinical trials in patients being at high risk of recurrence after specific therapy or in patients with locally or distant advanced prostate cancer.

The histone deacetylase inhibitor sodium butyrate interacts synergistically with phorbol myristate acetate (PMA) to induce mitochondrial damage and apoptosis in human myeloid leukemia cells through a tumor necrosis factor-alpha-mediated process

Interactions between the histone deacetylase inhibitor sodium butyrate (SB) and phorbol 12-myristate 13-acetate (PMA) were examined in human myeloid leukemia cells (U937 and HL-60). Exposure of U937 cells to 1 mM SB and 1 nM PMA (24 h) markedly induced caspase activation and apoptosis, events accompanied by impaired differentiation induction (e.g., reduced plastic adherence and diminished expression of CD11b) as well as reduced clonogenic survival. The PKC inhibitor GF109203X blocked SB-/PMA-mediated apoptosis. Comparable results were obtained in HL-60 cells. Apoptosis was associated with early procaspase 8 activation and Bid cleavage, accompanied by pronounced mitochondrial damage (e.g., loss of mitochondrial membrane potential (DeltaPsi(m)) and cytochrome c release). Neutralization of endogenous TNFalpha by a human soluble TNF receptor substantially blocked SB-/PMA-induced cytochrome c release and apoptosis. Consistent with this, ectopic expression of a mutant dominant-negative caspase 8 or CrmA resulted in a significant decrease in SB-/PMA-induced apoptosis, whereas Bcl-2 overexpression did not. SB/PMA treatment also triggered a decline in the S and G(2)M populations, and dephosphorylation of p34(cdc2). These results indicate that SB interacts with low concentrations of PMA to induce apoptosis in human leukemia cells and that this process proceeds through a PKC-/TNFalpha-dependent pathway in which procaspase 8 and Bid activation play key roles.

Cell type- and promoter-dependent modulation of the Wnt signaling pathway by sodium butyrate

The Wnt signaling pathway modulates the transcription of genes linked to proliferation, differentiation and tumor progression. beta-Catenin-Tcf (BCT)-dependent Wnt signaling is influenced by the short-chain fatty acid sodium butyrate, which induces growth arrest and/or maturation of colonic carcinoma cells. We have compared the effects of sodium butyrate on BCT-dependent signaling in 2 colon carcinoma cell lines that differ in their physiologic response to butyrate, with SW620 cells responding to butyrate by undergoing terminal differentiation and apoptosis, and HCT-116 cells undergoing reversible growth arrest, but no significant apoptotic cell death. Furthermore, these colon carcinoma cell lines differ in their mechanism of Wnt pathway activation, with adenomatous polyposis coli (APC) mutant SW620 cells having high levels of BCT complexes and APC wild-type HCT-116 cells having mutant beta-catenin, low levels of BCT complexes and correspondingly higher levels of free Tcf. We have demonstrated that in SW620 cells, butyrate downregulates BCT-dependent expression of the Tcf-TK, matrilysin and cyclin D1 promoters, whereas in HCT-116 cells, butyrate upregulates expression of these promoters. Cotransfection with expression vectors that interfere with the Wnt pathway suggests that butyrate enhances BCT complex-DNA binding. Butyrate reduces the expression of Tcf4 in HCT-116 cells, consistent with the induction by butyrate of Tcf-repressible promoters in these cells. These findings indicate that sodium butyrate modulates the Wnt pathway in SW620 and HCT-116 cells in a different manner and that these differences have consequences for promoter activity that may influence the physiologic response to butyrate.

Overexpression of Bcl-2 regulates sodium butyrate- and/or docetaxel-induced apoptosis in human bladder cancer cells both in vitro and in vivo

Sodium butyrate (NaBt), a physiologically occurring short-chain fatty acid, induces differentiation as well as apoptosis in numerous cell types, and this induction is partially regulated by Bcl-2 expression. The objectives of our study were to characterize the in vitro effects of NaBt and/or docetaxel on the growth, cell cycle and apoptosis of human bladder cancer cells, and to determine whether tumor growth in vivo is inhibited by isobutyramide, an orally bioavailable Bt analogue, and/or docetaxel by using Bcl-2-transfected human bladder cancer cell line KoTCC-1/BH and control vector only-transfected cell line KoTCC-1/C. NaBt caused a decrease in growth of both KoTCC-1/C and KoTCC-1/BH cells, however, its growth inhibitory effect was significantly greater in KoTCC-1/C cells. One mM NaBt resulted in G1 cell cycle arrest, accompanied by up-regulation of p21 (waf1/cip1) and down-regulation of cyclin D1 in KoTCC-1/C cells, whereas KoTCC-1/BH showed resistance to G1 cell cycle arrest. An amount of 5 mM NaBt induced apoptosis, accompanied by up-regulation of Bak in KoTCC-1/C cells but failed to induce apoptosis in KoTCC-1/BH cells despite substantial down-regulation of Bcl-2. Oral administration of isobutyramide significantly reduced the KoTCC-1/C tumor volume compared with the KoTCC-1/BH tumor volume in nude mice. Furthermore, docetaxel induced Bcl-2 phosphorylation in KoTCC-1/BH cells and combined treatment with isobutyramide and docetaxel synergistically inhibited the growth of KoTCC-1/BH cells both in vitro and in vivo. These findings suggest that isobutyramide therapy could be a novel therapeutic strategy for patients with bladder cancer if docetaxel is combined according to the Bcl-2 expression status.

12-O-Tetradecanoylphorbol-13-acetate Induces Apoptosis in Renal Epithelial Cells through a Growth Signal Conflict Which Is Prevented by Activated ras1

12-O-Tetradecanoylphorbol-13-acetate (TPA) induced apoptosis in the pig renal epithelial cell line LLC-PK1 after 24 h of treatment as assessed by caspase 3 activation. Cotreatment of the cells with bryostatin markedly reduced the apoptotic effects of TPA. Okadaic acid, another tumor promoter, also induced apoptosis. Expression of an activated ras gene prevented TPA-induced apoptosis, while a dominant negative ras retarded the process. Taken together, these results suggest that TPA-induced apoptosis in LLC-PK1 may be analogous to TPA-induced tumor promotion in the two-stage model of skin carcinogenesis. Mechanistically, TPA-induced apoptosis seemed to be the result of a conflict of the growth-promoting affects of serum and the growth-retarding effects of TPA. This was manifested by a pronounced hypophosphorylation of the retinoblastoma gene product, pRb, which was prevented by activated ras. Apoptosis and pRb hypophosphorylation were associated with a reduction in cyclin D1 levels, suggesting that the growth-retarding effects of TPA were produced by modulation of this cell cycle protein. Interestingly, the mechanism of protection by activated ras did not seem to result from downstream activation of phosphatidylinositol-3-kinase (PI3K) as has been implicated in other systems. Additional analysis revealed that TPA-induced apoptosis was associated with the downregulation of the anti-apoptotic proteins Bcl-x and Mcl-1 and dependent on the activity of the transcription factor Jun.

Phorbol esters rapidly attenuate glutamine uptake and growth in human colon carcinoma cells

BACKGROUND

The amino acid glutamine, while essential for gut epithelial growth, has also been shown to stimulate colon carcinoma proliferation and diminish differentiation. Human colon carcinomas are known to extract and metabolize glutamine at rates severalfold greater than those of normal tissues, but the regulation of this response is unclear. Previously we reported that phorbol esters regulate hepatoma System ASC/B(0)-mediated glutamine uptake and cell growth. As human colon carcinoma cells use this same transporter for glutamine uptake, the present studies were undertaken to determine whether similar regulation functions in colon carcinoma.

MATERIALS AND METHODS

Human colon carcinoma cell lines (WiDr and HT29) were treated with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and initial-rate transport of glutamine and other nutrients was measured at specific times thereafter. Growth rates were monitored during culture +/- PMA or an excess of System ASC/B(0) substrates relative to glutamine.

RESULTS

PMA treatment induced a rapid inhibition of glutamine uptake rates in WiDr and HT29 cells by 30 and 57%, respectively, after 1 h. Cycloheximide failed to block this response, indicating that the mechanism by which PMA exerts its effects is posttranslational. The inhibition of glutamine uptake by PMA was abrogated by the PKC inhibitor staurosporine, suggesting that this rapid System ASC/B(0) regulation may be mediated by a PKC-dependent pathway. PMA also significantly decreased transport via System y(+) (arginine) and System A (small zwitterionic amino acids). Chronic phorbol ester treatment inhibited WiDr cell growth, as did attenuation of System B(0)-mediated glutamine uptake with other transporter substrates.

CONCLUSIONS

System ASC/B(0) uptake governs glutamine-dependent growth in colon carcinoma cell lines, and is regulated by a phorbol ester-sensitive pathway that may involve PKC. The results further establish the link between glutamine uptake and colon carcinoma cell growth, a relationship worthy of further investigation with the goal of discovering novel cancer therapeutic targets.

Short-chain fatty acids reduce expression of specific protein kinase C isoforms in human colonic epithelial cells

LIM1215 colon cancer cells were used as a model of human colonic epithelium to examine the effects of butyrate on protein kinase C (PKC) activity and isoform expression. On Western blot analysis, LIM1215 cells express the PKC isoforms alpha, beta, epsilon, zeta, and lambda, but not gamma, straight theta, or micro. Treatment with 2 mM butyrate for 48 h reduced cellular PKC activity up to 50% and specifically reduced the expression of PKC alpha and PKC epsilon. Similar results were obtained using Caco-2 colon cancer cells. These effects were neither a consequence of the induction of differentiation itself nor the result of direct or indirect activation of PKC. Although dependent on gene transcription and protein synthesis, the effect was not due to a reduction in the synthesis of PKC protein. Butyrate's effect was independent of its beta-oxidation but was mimicked, at least in part, by trichostatin A, an inhibitor of histone deacetylase.

Butyrate augments interferon-alpha-induced S phase accumulation and persistent tyrosine phosphorylation of cdc2 in K562 cells

Interferon-alpha (IFN-alpha) is a clinically useful cytokine for treatment of a variety of cancers, including chronic myelocytic leukaemia (CML). Most CML cells are sensitive to IFN-alpha; however, its biological effects on leukaemic cells are incompletely characterized. Here, we provide evidence that IFN-alpha induces a significant increase in the S phase population in human CML leukaemic cell line, K562, and that the S phase accumulation was augmented by sodium butyrate. In contrast, neither sodium butyrate alone, nor sodium butyrate plus IFN-gamma, affected the cell cycle in K562 cells. These data suggest that the effect of sodium butyrate depended upon IFN-alpha-mediated signalling. The ability of leukaemic cells to exhibit the S phase accumulation after stimulation by IFN-alpha plus sodium butyrate correlated well with persistent tyrosine phosphorylation of cdc2, whereas treatment with IFN-gamma plus sodium butyrate did not affect its phosphorylation levels. Considering that dephosphorylation of cdc2 leads to entry to the M phase, the persistent tyrosine phosphorylation of cdc2 may be associated with the S phase accumulation induced by IFN-alpha and sodium butyrate. In addition, another human CML leukaemic cell line, MEG-01, also showed the S phase accumulation after stimulation with IFN-alpha plus sodium butyrate. Taken together, our studies reveal a novel effect of sodium butyrate on the S phase accumulation and suggest its clinical application for a combination therapy with IFN-alpha, leading to a great improvement of clinical effects of IFN-alpha against CML cells.

Evidence that protein kinase Cepsilon mediates phorbol ester inhibition of calphostin C- and tumor necrosis factor-alpha-induced apoptosis in U937 histiocytic lymphoma cells

Protein kinase C (PKC) activators, such as the tumor-promoting phorbol esters, have been reported to protect several cell lines from apoptosis induced by a variety of agents. Recent evidence suggests that PKCepsilon is involved in protection of cardiac myocytes from hypoxia-induced cell death (Gray, M. O., Karliner, J. S., and Mochly-Rosen, D. (1997) J. Biol. Chem. 272, 30945-30951). We investigated the protective effects of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on U937 histiocytic lymphoma cells induced to undergo apoptosis by tumor necrosis factor-alpha (TNF-alpha) or by the specific PKC inhibitor calphostin C. U937 cells were transiently permeabilized with a peptide (epsilonV1-2) derived from the V1 region of PKCepsilon that has been reported to specifically block translocation of PKCepsilon. The epsilonV1-2 peptide blocked the inhibitory effect of TPA on both TNF-alpha- and calphostin C-induced apoptosis. A scrambled version of epsilonV1-2 and a peptide reported to inhibit PKCbeta translocation (betaC2-4) had no effect on the ability of TPA to inhibit apoptosis. These results suggest that PKCepsilon is required for the protective effect of TPA in TNF-alpha- and calphostin C-induced apoptosis. Furthermore, calphostin C reduced membrane-associated PKCepsilon activity and immunoreactivity, suggesting that PKCepsilon may play an important role in leukemic cell survival.

Overexpression of adenovirus-encoded transgenes from the cytomegalovirus immediate early promoter in irradiated tumor cells

Efficient expression of therapeutic genes in irradiated tumor cells would facilitate the conversion of a malignant tumor nodule into a cancer vaccine in situ. We reported previously that transgene expression from an adenoviral vector could be markedly enhanced by treating transduced tumor cells with butyrate. In this study, we demonstrated that a similar butyrate effect could be achieved in irradiated tumor cells. In addition, irradiating cells at doses of 2-40 Gy prior to transduction could also amplify recombinant adenoviral transgene products in a cell-type-specific manner. This suggests that adenovirus-mediated gene therapy, radiation therapy, and butyrate-mediated cancer therapy may potentially be formulated into one synergistic protocol for cancer treatment.

Apoptotic death in adenocarcinoma cell lines induced by butyrate and other histone deacetylase inhibitors

n-Butyrate inhibits the growth of colon cancer cell lines. In the HCT 116 cell line, butyrate-induced growth inhibition is almost fully reversible, whereas in the VACO 5 cell line, a subpopulation undergoes apoptosis within 30 hr of treatment with butyrate. Concurrent treatment of VACO 5 cells with butyrate and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) accelerates and increases the incidence of cell death to nearly 100% of the population, whereas HCT 116 cells largely remain alive during treatment with this combination. The action of butyrate as an inhibitor of histone deacetylase was assessed in these cell lines by examining extracted core histones for their electrophoretic mobility in Triton/acid/urea gels. The concentrations of butyrate that were effective for inducing apoptosis were similar to the concentrations that caused hyperacetylation of core histones in the VACO 5 cell line. Furthermore, an examination of other carboxylic acids for induction of apoptosis revealed a rank order that corresponded to the order of potency in causing hyperacetylation of core histones. Specifically, the active acids were 3-5 carbons in length and lacked substitution at the 2-position. Isovaleric and propionic acids, in particular, proved to be effective inducers of both hyperacetylation and apoptosis at 5 mM concentrations, a finding of potential relevance to the unusual pancytopenia occurring after acidotic episodes in isovaleric and propionic acidemias. The duration of butyrate treatment required for chromatin fragmentation (10-20 hr) corresponded to the time required for histone H4 to become predominantly tetraacetylated. Furthermore, trichostatin A, a structurally dissimilar inhibitor of histone deacetylase, mimicked butyrate-induced apoptosis of VACO 5 cells and growth inhibition of HCT 116 cells. The dramatic enhancement of VACO 5 cell death by TPA, and the high level resistance of HCT 116 cells to butyrate were not evident from histone acetylation determinations. Thus, applications of butyrate for cytoreduction therapy will benefit from pharmacodynamic assessment of histone acetylation, but will require additional work to predict susceptibility to butyrate-induced death.