Oncogenic Ras Promotes Butyrate-induced Apoptosis through Inhibition of Gelsolin Expression

Potential therapeutic effects of apigenin for colorectal adenocarcinoma: A systematic review and meta-analysis

PURPOSE

Therapeutic management of colorectal cancer (CRC) does not yet yield promising long-term results. Therefore, there is a need for further investigation of possible therapeutic options. Various experiments have studied the effects of apigenin on CRC and have shown conflicting results. This systematic review and meta-analysis investigates the currently existing evidence on the effect of apigenin on CRC.

METHODS

Medline, Embase, Scopus, and Web of Science databases were searched for articles related to apigenin and its effect on CRC in the preclinical setting. Cell viability, growth inhibition, apoptosis, and cell cycle arrest for in-vitro, and body weight, tumor size, and mortality in in-vivo studies were extracted as outcomes.

RESULTS

Thirty-nine articles investigating colorectal adenocarcinoma were included in this meta-analysis. Thirty-seven of these studies had data for in vitro experiments, with eight studies having data for in vivo experiments. Six articles had both in vitro and in vivo assessments. Our analysis showed apigenin reduces cell viability and induces growth inhibition, apoptosis, and cell cycle arrest in in vitro studies. The few in vivo studies indicate that apigenin decreases tumor size while showing no effects on the body weight of animal colorectal adenocarcinoma models.

CONCLUSION

Our results demonstrated that apigenin, through reducing cell viability, inducing growth inhibition, apoptosis, and cell cycle arrest, and also by decreasing the tumor size, can be considered as a possible adjuvant agent in the management of colorectal adenocarcinoma. However, further in vivo studies are needed before any efforts to translate the current evidence into clinical studies.

The role of vitamin D through SphK1/S1P in the regulation of MS progression

Sphingosine-1-phosphate (S1P) is biologically active lipid, leading to neuroinflammation and macrophage invasion in central nervous system, plays an important role in the development of multiple sclerosis (MS) model in experimental allergic encephalomyelitis (EAE) rats. Vitamin D is observed to be a key factor in regulating cell S1P levels. We detected vitamin D can alleviate the symptoms of EAE rats, but the exact mechanism is unclear. In PC12 cells, vitamin D can reverse S1P-induced cell death, but the signaling pathway unclear. This study was aimed to investigate S1P regulation mechanism or signaling pathway mediated by vitamin D in EAE and PC12 model. In our experiments, S1P and Sphingosine kinase type 1 (SphK1) mRNA and protein expression in EAE rats group, control group, vitamin D feeding group were detected by HPLC, ELISA, RT-PCR and western blot. PC12 cell death was detected by Propidium (PI) staining. VDR plasmid overexpression and RNA interference, immunofluorescence, real-time cell analysis, protein immunoblotting was used to detect SphK1 transcriptional regulation, cell-substrate attachment quality, the signaling pathway of cell apoptosis and inflammation related gene expression (Bax/Bcl-2, Casepase-3, Il-6, TGF-β, TNF-α). Our study showed vitamin D can reverse the elevation of S1P level in EAE rats, reduce the severity and shorten the course of EAE. 1,25-(OH) 2D3 coupled with vitamin D receptor (VDR) inhibited SphK1 transcription. 1,25-(OH)2D3 significantly reduced PC12 cell death rate induced by S1P, in addition improved the cell substrate attachment quality. 1,25-(OH) 2D3 can block S1P-induced p-ERK activation and PI3K /Akt signaling pathway reduced Il-6, TGF-β, TNF-α cytokine release and Bax/Bcl-2, Casepase-3 apoptosis protein expression. On the other hand, immunofluorescence staining showed 1,25-(OH) 2D3 can increase the expression of neuronal perinuclear protein MAP2 in PC12 cells probably protect nerve cells further. In summary, the ameliorative effect of vitamin D was derived from its ability to reduce S1P levels, provides an idea for vitamin D as a combination therapy for disease.

Effects of different short-chain fatty acids (SCFA) on gene expression of proteins involved in barrier function in IPEC-J2

Background

Gut microbial anaerobic fermentation produces short-chain fatty acids (SCFA), which are important substrates for energy metabolism and anabolic processes in mammals. SCFA can regulate the inflammatory response and increase the intestinal barrier integrity by enhancing the tight junction protein (TJp) functions, which prevent the passage of antigens through the paracellular space. The aim of this study was to evaluate the effect of in vitro supplementation with SCFA (acetate, propionate, butyrate, and lactate) at different concentrations on viability, nitric oxide (NO) release (oxidative stress parameter) in cell culture supernatants, and gene expression of TJp (occludin, zonula occludens-1, and claudin-4) and pro-inflammatory pathway-related mediators (β-defensin 1, TNF-α, and NF-κB) in intestinal porcine epithelial cell line J2 (IPEC-J2).

Results

The SCFA tested showed significant effects on IPEC-J2, which proved to be dependent on the type and specific concentration of the fatty acid. Acetate stimulated cell viability and NO production in a dose-dependent manner (P < 0.05), and specifically, 5 mM acetate activated the barrier response through claudin-4, and immunity through β-defensin 1 (P < 0.05). The same effect on these parameters was shown by propionate supplementation, especially at 1 mM (P < 0.05). Contrarily, lactate and butyrate showed different effects compared to acetate and propionate, as they did not stimulate an increase of cell viability and regulated barrier integrity through zonula occludens-1 and occludin, especially at 30 mM and 0.5 mM, respectively (P < 0.05). Upon supplementation with SCFA, the increase of NO release at low levels proved not to have detrimental effects on IPEC-J2 proliferation/survival, and in the case of acetate and propionate, such levels were associated with beneficial effects. Furthermore, the results showed that SCFA supplementation induced β-defensin 1 (P < 0.05) that, in turn, may have been involved in the inhibition of TNF-α and NF-κB gene expression (P < 0.05).

Conclusions

The present study demonstrates that the supplementation with specific SCFA in IPEC-J2 can significantly modulate the process of barrier protection, and that particularly acetate and propionate sustain cell viability, low oxidative stress activity and intestinal barrier function.

NRAS mutant E132K identified in young-onset sporadic colorectal cancer and the canonical mutants G12D and Q61K affect distinct oncogenic phenotypes

Recent data show a global increase in colorectal cancer (CRC) cases among younger demographics, which portends poorer prognosis. The cause of rising incidence is uncertain, and its mutational landscape remains largely unexplored, including those in genes of the epidermal growth factor receptor pathway. Among these are NRAS mutants where there is paucity of functional studies compared to KRAS. Here, the novel NRAS mutant E132K, identified in three tumor samples from Filipino young-onset, sporadic colorectal cancer patients, was investigated for its effects on different cancer hallmarks, alongside the NRAS canonical mutants G12D and Q61K which are yet poorly characterized in the context of CRC. The novel NRAS mutant E132K and the canonical G12D and Q61K mutants show resistance to apoptosis, cytoskeletal reorganization, and loss of adhesion. In contrast to activating KRAS mutations, including the analogous KRAS G12D and Q61K mutations, all three NRAS mutants have no apparent effect on cell proliferation and motility. The results highlight the need to characterize isoform- and mutation-specific oncogenic phenotypes which can have repercussions in disease management and choice of therapeutic intervention. Further analyses of young-onset versus late-onset CRC datasets are necessary to qualify NRAS E132K as a biomarker for the young-onset subtype.

Proteomic profiling and identification of significant markers from high-grade osteosarcoma after cryotherapy and irradiation

Biological reconstruction of allografts and recycled autografts have been widely implemented in high-grade osteogenic sarcoma. For treating tumor-bearing autografts, extracorporeal irradiation (ECIR) and liquid nitrogen (LN) freezing techniques are being used worldwide as a gold standard treatment procedure. Both the methods aim to eradicate the tumor cells from the local recurrence and restore the limb function. Therefore, it is essential and crucial to find, and compare the alterations at molecular and physiological levels of the treated and untreated OGS recycled autografts to obtain valuable clinical information for better clinical practice. Thus, we aimed to investigate the significantly expressed altered proteins from ECIR-and cryotherapy/freezing- treated OGS (n = 12) were compared to untreated OGS (n = 12) samples using LC-ESI-MS/MS analysis, and the selected proteins from this protein panel were verified using immunoblot analysis. From our comparative proteomic analysis identified a total of 131 differentially expressed proteins (DEPs) from OGS. Among these, 91 proteins were up-regulated (2.5 to 3.5-folds), and 40 proteins were down-regulated (0.2 to 0.5 folds) (p < 0.01 and 0.05). The functional enrichment analysis revealed that the identified DEPs have belonged to more than 10 different protein categories include cytoskeletal, extracellular matrix, immune, enzyme modulators, and cell signaling molecules. Among these, we have confirmed two potential candidates’ expressions levels such as Fibronectin and Protein S100 A4 using western blot analysis. Our proteomic study revealed that LN-freezing and ECIR treatments are effectively eradicating tumor cells, and reducing the higher expressions of DEPs at molecular levels which may help in restoring the limb functions of OGS autografts effectively. To the best of our knowledge, this is the first proteomic study that compared proteomic profiles among freezing, ECIR treated with untreated OGS in recycled autografts. Moreover, the verified proteins could be used as prognostic or diagnostic markers that reveal valuable scientific information which may open various therapeutic avenues in clinical practice to improve patient outcomes.

Steroidal glycoalkaloids from Solanum nigrum target cytoskeletal proteins: an in silico analysis

Background

Solanum nigrum (black nightshade; S. nigrum), a member of family Solanaceae, has been endowed with a heterogeneous array of secondary metabolites of which the steroidal glycoalkaloids (SGAs) and steroidal saponins (SS) have vast potential to serve as anticancer agents. Since there has been much controversy regarding safety of use of glycoalkaloids as anticancer agents, this area has remained more or less unexplored. Cytoskeletal proteins like actin play an important role in maintaining cell shape, synchronizing cell division, cell motility, etc. and along with their accessory proteins may also serve as important therapeutic targets for potential anticancer candidates. In the present study, glycoalkaloids and saponins from S. nigrum were screened for their interaction and binding affinity to cytoskeletal proteins, using molecular docking.

Methods

Bioactivity score and Prediction of Activity Spectra for Substances (PASS) analysis were performed using softwares Molinspiration and Osiris Data Explorer respectively, to assess the feasibility of selected phytoconstituents as potential drug candidates. The results were compared with two standard reference drugs doxorubicin hydrochloride (anticancer) and tetracycline (antibiotic). Multivariate data obtained were analyzed using principal component analysis (PCA).

Results

Docking analysis revealed that the binding affinities of the phytoconstituents towards the target cytoskeletal proteins decreased in the order coronin>villin>ezrin>vimentin>gelsolin>thymosin>cofilin. Glycoalkaloid solasonine displayed the greatest binding affinity towards the target proteins followed by alpha-solanine whereas amongst the saponins, nigrumnin-I showed maximum binding affinity. PASS Analysis of the selected phytoconstituents revealed 1 to 3 violations of Lipinski’s parameters indicating the need for modification of their structure-activity relationship (SAR) for improvement of their bioactivity and bioavailability. Glycoalkaloids and saponins all had bioactivity scores between −5.0 and 0.0 with respect to various receptor proteins and target enzymes. Solanidine, solasodine and solamargine had positive values of druglikeness which indicated that these compounds have the potential for development into future anticancer drugs. Toxicity potential evaluation revealed that glycoalkaloids and saponins had no toxicity, tumorigenicity or irritant effect(s). SAR analysis revealed that the number, type and location of sugar or the substitution of hydroxyl group on alkaloid backbone had an effect on the activity and that the presence of α-L-rhamnopyranose sugar at C-2 was critical for a compound to exhibit anticancer activity.

Conclusion

The present study revealed some cytoskeletal target(s) for S. nigrum phytoconstituents by docking analysis that have not been previously reported and thus warrant further investigations both in vitro and in vivo.

Butyric acid regulates progesterone and estradiol secretion via cAMP signaling pathway in porcine granulosa cells

Butyric acid (BA), one of the short chain fatty acids (SCFAs), has positive actions on the metabolism, inflammation, etc. However, whether it influences the reproductive physiology and if so the detail mechanism involved has not yet been determined. In this study, the porcine granulosa cells (PGCs) were treated with gradient concentrations of BA. After 24h culture, 0.05mM BA significantly stimulated the progesterone (P₄) secretion (P<0.05), 5mM and 10mM BA significantly inhibited the P₄ secretion (P<0.05). Simultaneously, BA up-regulated the estradiol (E₂) secretion in a dose dependent manner, 5mM and 10mM BA significantly promoted the E₂ level (P<0.05). In addition, 10mM BA significantly promoted the G-protein-coupled receptor 41/43 mRNA (P<0.05). Interestingly, 5mM BA treatment significantly down-regulated cyclic adenosine monophosphate (cAMP) content (P<0.05), steroidogenic acute regulatory (StAR), steroidogenic factor 1 (SF1), P450scc in the mRNA and/or protein level (P<0.05), and these actions were reversed by cAMP activator forskolin (FK). Moreover, the co-treatment of 5mM BA and bupivacaine (BPC, the cAMP inhibitor) significantly accumulated the inhibition action of BPC on cAMP, the secretion of P₄, and the abundance of StAR mRNA (P<0.05), inhibited the up-regulation of 5mM BA on the E₂ secretion (P<0.05). Further, the Global Proteome and KEGG pathway analysis found that 5mM BA significantly up-regulated the I3LM80 proteins (P<0.05), which is involved in the steroid biosynthesis signaling pathway. 5mM BA significantly decreased the F2Z5G3 protein level (P<0.05), and the cAMP signaling pathway. In conclusion, present findings for the first time demonstrated that BA could regulate the P₄ and E₂ hormone synthesis in PGCs via the cAMP signaling pathway.

DHA-mediated regulation of lung cancer cell migration is not directly associated with Gelsolin or Vimentin expression

AIMS

Deaths associated with cancer metastasis have steadily increased making the need for newer, anti-metastatic therapeutics imparative. Gelsolin and vimentin, actin binding proteins expressed in metastatic tumors, participate in actin remodelling and regulate cell migration. Docosahexaenoic acid (DHA) limits cancer cell proliferation and adhesion but the mechanisms involved in reducing metastatic phenotypes are unknown. We aimed to investigate the effects of DHA on gelsolin and vimentin expression, and ultimately cell migration and proliferation, in this context.

MAIN METHODS

Non-invasive lung epithelial cells (MLE12) and invasive lung cancer cells (A549) were treated with DHA (30μmol/ml) or/and 8 bromo-cyclic adenosine monophosphate (8 Br-cAMP) (300μmol/ml) for 6 or 24h either before (pre-treatment) or after (post-treatment) plating in transwells. Migration was assessed by the number of cells that progressed through the transwell. Gelsolin and vimentin expression were measured by Western blot and confocal microscopy in cells, and by immunohistochemistry in human lung cancer biopsy samples.

KEY FINDINGS

A significant decrease in cell migration was detected for A549 cells treated with DHA verses control but this same decrease was not seen in MLE12 cells. DHA and 8 Br-cAMP altered gelsolin and vimentin expression but no clear pattern of change was observed. Immunofluorescence staining indicated slightly higher vimentin expression in human lung tissue that was malignant compared to control.

SIGNIFICANCE

Collectively, our data indicate that DHA inhibits cancer cell migration and further suggests that vimentin and gelsolin may play secondary roles in cancer cell migration and proliferation, but are not the primary regulators.

Gelsolin Promotes Radioresistance in Non-Small Cell Lung Cancer Cells Through Activation of Phosphoinositide 3-Kinase/Akt Signaling

Gelsolin is an actin-binding protein and acts as an important regulator of cell survival. This study aimed to determine the function of gelsolin in the radioresistance of non-small cell lung cancer cells. We examined the expression of gelsolin in radioresistant A549 and H460 cells and their parental cells. The effects of gelsolin overexpression and knockdown on the clonogenic survival and apoptosis of non-small cell lung cancer cells after irradiation were studied. The involvement of phosphoinositide 3-kinase/Akt signaling in the action of gelsolin was checked. We found that gelsolin was significantly upregulated in radioresistant A549 and H460 cells. Overexpression of gelsolin significantly ( P < .05) increased the number of colonies from irradiated A549 and H460 cells compared to transfection of empty vector. In contrast, knockdown of gelsolin significantly ( P < .05) suppressed colony formation after irradiation. Gelsolin-overexpressing cells displayed reduced apoptosis in response to irradiation, which was coupled with decreased levels of cleaved caspase-3 and poly adenosine diphosphate-ribose polymerase. Ectopic expression of gelsolin significantly ( P < .05) enhanced the phosphorylation of Akt compared to nontransfected cells. Pretreatment with the phosphoinositide 3-kinase inhibitor LY294002 (20 μmol/L) significantly decreased clonogenic survival and enhanced apoptosis in gelsolin-overexpressing A549 and H460 cells after irradiation. Taken together, gelsolin upregulation promotes radioresistance in non-small cell lung cancer cells, at least partially, through activation of phosphoinositide 3-kinase/Akt signaling.

The Cell Death Pathway Regulates Synapse Elimination through Cleavage of Gelsolin in Caenorhabditis elegans Neurons

Synapse elimination occurs in development, plasticity, and disease. Although the importance of synapse elimination has been documented in many studies, the molecular mechanisms underlying this process are unclear. Here, using the development of C. elegans RME neurons as a model, we have uncovered a function for the apoptosis pathway in synapse elimination. We find that the conserved apoptotic cell death (CED) pathway and axonal mitochondria are required for the elimination of transiently formed clusters of presynaptic components in RME neurons. This function of the CED pathway involves the activation of the actin-filament-severing protein, GSNL-1. Furthermore, we show that caspase CED-3 cleaves GSNL-1 at a conserved C-terminal region and that the cleaved active form of GSNL-1 promotes its actin-severing ability. Our data suggest that activation of the CED pathway contributes to selective elimination of synapses through disassembly of the actin filament network.

Serine phosphorylation of vasodilator-stimulated phosphoprotein (VASP) regulates colon cancer cell survival and apoptosis

AIMS

In colon cancer, disease recurrence and death are associated with abnormal tumor cell survival. Vasodilator-stimulated phosphoprotein (VASP) is an actin binding protein regulating cell shape and polarity through the F-actin cytoskeleton, whose activity is controlled by cAMP-dependent phosphorylation at Ser157 and cGMP-dependent phosphorylation at Ser239. This study examined the role of differential VASP Ser phosphorylation in regulating cell survival and apoptosis in human colon carcinoma cells.

MAIN METHODS

Selective inhibition of VASP Ser157 or Ser239 phosphorylation in colon cancer cells was performed with specific phosphomutant constructs. F-actin organization was examined by confocal microscopy, and the balance of cell survival and death assessed by measuring acridine orange and ethidium bromide staining, caspase-3 and BAD-pS112 expression and DNA fragmentation.

KEY FINDINGS

In human colon carcinoma cells suppression of VASP Ser157 phosphorylation reduced F-actin content and survival and increased apoptosis, while inhibition of VASP Ser239 phosphorylation increased F-actin content and survival and reduced cell death. Also, while 8Br-cAMP induced VASP Ser157 phosphorylation and reduced cell death, treatments with 8CPT-cGMP elevated VASP Ser239 phosphorylation and promoted apoptosis.

SIGNIFICANCE

These findings suggest that differential VASP Ser phosphorylation represents a unique therapeutic target to control cell survival and death behavior in colon cancer. In particular, pharmacological manipulation of VASP Ser phosphorylation could be exploited to affect the malignant actin cytoskeleton and induce apoptosis in colorectal cancer cells.

The actin cytoskeleton as a sensor and mediator of apoptosis

Apoptosis is an important biological process required for the removal of unwanted or damaged cells. Mounting evidence implicates the actin cytoskeleton as both a sensor and mediator of apoptosis. Studies also suggest that actin binding proteins (ABPs) significantly contribute to apoptosis and that actin dynamics play a key role in regulating apoptosis signaling. Changes in the organization of the actin cytoskeleton has been attributed to the process of malignant transformation and it is hypothesized that remodeling of the actin cytoskeleton may enable tumor cells to evade normal apoptotic signaling. This review aims to illuminate the role of the actin cytoskeleton in apoptosis by systematically analyzing how actin and ABPs regulate different apoptosis pathways and to also highlight the potential for developing novel compounds that target tumor-specific actin filaments.

Migfilin sensitizes cisplatin-induced apoptosis in human glioma cells in vitro

AIM

Filamin binding LIM protein 1, also known as migfilin, is a skeleton organization protein that binds to mitogen-inducible gene 2 at cell-extracellular matrix adhesions. The aim of this study was to investigate the role of migfilin in cisplatin-induced apoptosis in human glioma cells, to determine the functional domains of migfilin, and to elucidate the molecular mechanisms underlying the regulation of cisplatin-related chemosensitivity.

METHODS

The human glioma cell lines Hs683, H4, and U-87 MG were transfected with pEGFP-C2-migfilin to elevate the expression level of migfilin. RNA interference was used to reduce the expression of migfilin. To determine the functional domains of migfilin, U-87 MG cells were transfected with plasmids of migfilin deletion mutants. After treatment with cisplatin (40 μmol/L) for 24 h, the cell viability was assessed using the MTS assay, and the cell apoptotic was examined using the DAPI staining assay and TUNEL analysis. Expression levels of apoptosis-related proteins were detected by Western blot analysis.

RESULTS

Overexpression of migfilin significantly enhanced cisplatin-induced apoptosis in Hs683, H4, and U-87 MG cells, whereas downregulation of migfilin expression inhibited the chemosensitivity of these cell lines. The N-terminal region of migfilin alone was able to enhance the cisplatin-induced apoptosis. However, despite the existence of the N-terminal region, mutants of migfilin with any one of three LIM domains deleted led to a function loss. Furthermore, apoptotic proteins (PARP and caspase-3) and the anti-apoptotic protein Bcl-xL were modulated by the expression level of migfilin in combination with cisplatin.

CONCLUSION

The LIM1-3 domains of migfilin play a key role in sensitizing glioma cells to cisplatin-induced apoptosis through regulation of apoptosis-related proteins.

The enhanced host-cell permissiveness of human cytomegalovirus is mediated by the Ras signaling pathway

Human cytomegalovirus utilizes cellular signal transduction pathways to activate viral or cellular transcription factors involved in the control of viral gene expression and DNA replication. In the present study, we demonstrate that Harvey-ras-transformed cells show increased permissiveness to human cytomegalovirus when compared to their parental non-transformed cells. Both the progeny viral yield and the protein levels were elevated in the human cytomegalovirus-infected Harvey-ras-transformed cells requiring active viral gene replication, as shown by the infection with UV-inactivated human cytomegalovirus. Inhibition of Ras or of key molecules of the Ras pathway, effectively suppressed viral infection in the Harvey-ras-transformed cells. On a cellular level, the human cytomegalovirus-infected Harvey-ras-transformed cells formed larger cellular foci, which were significantly higher in number, compared to the uninfected cells and preferentially recruited human cytomegalovirus virions, thereby incriminating human cytomegalovirus infection for the increased transformation of these cells. Furthermore, proliferation assays revealed a higher rate for the human cytomegalovirus-infected Harvey-ras-transformed cells compared to mock-infected cells, whereas human cytomegalovirus infection had no considerable effect on the proliferation of the non-transformed cells. Higher susceptibility to apoptosis was also detected in the human cytomegalovirus-infected ras-transformed cells, which in combination with the higher progeny virus reveals a mode by which human cytomegalovirus achieves efficient spread of infection in the cells expressing the oncogenic Harvey-ras (12V) gene. Collectively, our data suggest that human cytomegalovirus employs the host-cell Ras signaling pathway to ensue viral expression and ultimately successful propagation. Transformed cells with an activated Ras signaling pathway are therefore particularly susceptible to human cytomegalovirus infection.

Regulation of homeostasis and oncogenesis in the intestinal epithelium by Ras

Much of our current state of knowledge pertaining to the mechanisms controlling intestinal epithelial homeostasis derives from epidemiological, molecular genetic, cell biological, and biochemical studies of signaling pathways that are dysregulated during the process of colorectal tumorigenesis. Activating mutations in members of the RAS oncoprotein family play an important role in the progression of colorectal cancer (CRC) and, by extension, intestinal epithelial homeostasis. Mutations in K-RAS account for 90% of the RAS mutations found in CRC. As such, the study of RAS protein function in the intestinal epithelium is largely encompassed by the study of K-RAS function in CRC. In this review, we summarize the data available from genetically defined in vitro and in vivo models of CRC that aim to characterize the oncogenic properties of mutationally activated K-RAS. These studies paint a complex picture of a multi-functional oncoprotein that engages an array of downstream signaling pathways to influence cellular behaviors that are both pro- and anti-tumorigenic. While the complexity of K-RAS biology has thus far prevented a comprehensive understanding of its oncogenic properties, the work to date lays a foundation for the development of new therapeutic strategies to treat K-RAS mutant CRC.

HDAC inhibitor, scriptaid, induces glioma cell apoptosis through JNK activation and inhibits telomerase activity

The present study identified a novel mechanism of induction of apoptosis in glioblastoma cells by scriptaid – a histone deacetylase (HDAC) inhibitor. Scriptaid reduced glioma cell viability by increasing Jun N-terminal kinase (JNK) activation. Although scriptaid induced activation of both p38MAPK and JNK, it was the inhibition of JNK that attenuated scriptaid-induced apoptosis significantly. Scriptaid also increased the expression of (i) p21 and p27 involved in cell-cycle regulation and (ii) γH2AX associated with DNA damage response in a JNK-dependent manner. Treatment with scriptaid increased Ras activity in glioma cells, and transfection of cells with constitutively active RasV12 further sensitized glioma cells to scriptaid-induced apoptosis. Scriptaid also inhibited telomerase activity independent of JNK. Taken together, our findings indicate that scriptaid (i) induces apoptosis and reduces glioma cell proliferation by elevating JNK activation and (ii) also decreases telomerase activity in a JNK-independent manner.

Butyrate induces cell apoptosis through activation of JNK MAP kinase pathway in human colon cancer RKO cells

Butyrate has been shown to display anti-cancer activity through the induction of apoptosis in various cancer cells. However, the underlying mechanism involved in butyrate-induced apoptosis is still not fully understood. Here, we investigated the cytotoxicity mechanism of butyrate in human colon cancer RKO cells. The results showed that butyrate induced a strong growth inhibitory effect against RKO cells. Butyrate also effectively induced apoptosis in RKO cells, which was characterized by DNA fragmentation, nuclear staining of DAPI, and the activation of caspase-9 and caspase-3. The expression of anti-apoptotic protein Bcl-2 decreased, whereas the apoptotic protein Bax increased in a dose-dependent manner during butyrate-induced apoptosis. Moreover, treatment of RKO cells with butyrate induced a sustained activation of the phosphorylation of c-jun N-terminal kinase (JNK) in a dose- and time-dependent manner, and the pharmacological inhibition of JNK MAPK by SP600125 significantly abolished the butyrate-induced apoptosis in RKO cells. These results suggest that butyrate acts on RKO cells via the JNK but not the p38 pathway. Butyrate triggered the caspase apoptotic pathway, indicated by an enhanced Bax-to-Bcl-2 expression ratio and caspase cascade reaction, which was blocked by SP600125. Taken together, our data indicate that butyrate induces apoptosis through JNK MAPK activation in colon cancer RKO cells.

Integration of multiple signaling pathway activities resolves K-RAS/N-RAS mutation paradox in colon epithelial cell response to inflammatory cytokine stimulation

Colon tumors frequently harbor mutation in K-RAS and/or N-RAS, members of a GTPase family operating as a central hub for multiple key signaling pathways. While these proteins are strongly homologous, they exhibit diverse downstream effects on cell behavior. Utilizing an isogenic panel of human colon carcinoma cells bearing oncogenic mutations in K-RAS and/or N-RAS, we observed that K-RAS and double mutants similarly yield elevated apoptosis in response to treatment with TNFalpha compared to N-RAS mutants. Regardless, and in surprising contrast, key phospho-protein signals were more similar between N-RAS and dual mutants. This apparent contradiction could not be explained by any of the key signals individually, but a multi-pathway model constructed from the single-mutant cell line data was able to predict the behavior of the dual-mutant cell line. This success arises from a quantitative integration of multiple pro-apoptotic (pIkappaBalpha, pERK2) and pro-survival (pJNK, pHSP27) signals in manner not easily discerned from intuitive inspection.

Non-redundancy within the RAS oncogene family: insights into mutational disparities in cancer

The RAS family of oncoproteins has been studied extensively for almost three decades. While we know that activation of RAS represents a key feature of malignant transformation for many cancers, we are only now beginning to understand the complex underpinnings of RAS biology. Here, we will discuss emerging cancer genome sequencing data in the context of what is currently known about RAS function. Taken together, retrospective studies of primary human tissues and prospective studies of experimental models support the notion that the variable mutation frequencies exhibited by the RAS oncogenes reflect unique functions of the RAS oncoproteins.

RAS mutations affect tumor necrosis factor-induced apoptosis in colon carcinoma cells via ERK-modulatory negative and positive feedback circuits along with non-ERK pathway effects

More than 40% of colon cancers have a mutation in K-RAS or N-RAS, GTPases that operate as central hubs for multiple key signaling pathways within the cell. Utilizing an isogenic panel of colon carcinoma cells with K-RAS or N-RAS variations, we observed differences in tumor necrosis factor-alpha (TNFalpha)-induced apoptosis. When the dynamics of phosphorylated ERK response to TNFalpha were examined, K-RAS mutant cells showed lower activation whereas N-RAS mutant cells exhibited prolonged duration. These divergent trends were partially explained by differential induction of two ERK-modulatory circuits: negative feedback mediated by dual-specificity phosphatase 5 and positive feedback by autocrine transforming growth factor-alpha. Moreover, in the various RAS mutant colon carcinoma lines, the transforming growth factor-alpha autocrine loop differentially elicited a further downstream chemokine (CXCL1/CXCL8) autocrine loop, with the two loops having opposite effects on apoptosis. Although the apoptotic responses of the RAS mutant panel to TNFalpha treatment showed significant dependence on the respective phosphorylated ERK dynamics, successful prediction across the various cell lines required contextual information concerning additional pathways including IKK and p38. A quantitative computational model based on weighted linear combinations of these pathway activities successfully predicted not only the spectrum of cell death responses but also the corresponding chemokine production responses. Our findings indicate that diverse RAS mutations yield differential cell behavioral responses to inflammatory cytokine exposure by means of (a) differential effects on ERK activity via multiple feedback circuit mechanisms, and (b) differential effects on other key signaling pathways contextually modulating ERK-related dependence.

Macrophage-derived IL-1beta stimulates Wnt signaling and growth of colon cancer cells: a crosstalk interrupted by vitamin D3

Tumor associated macrophages mediate the link between inflammation and cancer progression. Here we showed that macrophage-derived soluble factors induce canonical Wnt signaling in colon cancer cells and promote their growth. Tumor cells induced the release of IL-1β from macrophages, which induced phosphorylation of GSK3β, stabilized β-catenin, enhanced TCF-dependent gene activation, and induced the expression of Wnt target genes in tumor cells. Neutralization experiments using anti IL-1β specific antibodies, or silencing of IL-1β in THP1 macrophages, revealed that IL-1β was required for macrophages to induce Wnt signaling and to support the growth of tumor cells. Constitutive activation of STAT1 in THP1 macrophages was essential for the induction of IL-1β and thus for the activation of β–catenin signaling in tumor cells.

Vitamin D₃, an effective chemopreventive agent, interrupted this crosstalk by blocking the constitutive activation of STAT1 and the production of IL-1β in macrophages, and therefore- in a vitamin D receptor dependent manner- inhibited the ability of macrophages to activate Wnt signaling in colon carcinoma cells. Our data therefore established that vitamin D₃ exerts its chemopreventive activity by interrupting a cross-talk between tumor epithelial cells and the tumor microenvironment.

Butyrate and vitamin D3 induce transcriptional attenuation at the cyclin D1 locus in colonic carcinoma cells

In stimulating maturation of colonic carcinoma cells, the short chain fatty acid butyrate, and 1alpha,25-dihydroxyvitamin D(3), were shown to attenuate transcription of the cyclin D1 gene, giving rise to truncated transcripts of this locus. Moreover, a sequence which is highly conserved in the human, mouse, rat, and dog genome was found in the 4 kb long intron 3 of the human cyclin D1 gene, and is capable of forming a hairpin structure similar to that of microRNA precursors. The expression of this sequence is also decreased by the attenuation. Thus, the transcriptional attenuation at the cyclin D1 locus not only down-regulates the expression of this key gene in mucosal cell maturation and tumorigenesis, but may also abrogate the generation of a molecule that encompasses this conserved sequence in cyclin D1 intron 3.

Activated kRas protects colon cancer cells from cucurbitacin-induced apoptosis: the role of p53 and p21

Cucurbitacins have been shown to inhibit proliferation in a variety of cancer cell lines. The aim of this study was to determine their biological activity in colon cancer cell lines that do not harbor activated STAT3, the key target of cucurbitacin. In order to establish the role of activated kRas in the responsiveness of cells to cucurbitacins, we performed experiments in isogenic colon cancer cell lines, HCT116 and Hke-3, which differ only by the presence of an activated kRas allele. We compared the activity of 23, 24-dihydrocucurbitacin B (DHCB) and cucurbitacin R (CCR), two cucurbitacins that we recently isolated, with cucurbitacin I (CCI), a cucurbitacin with established antitumorigenic activity. We showed that cucurbitacins induced dramatic changes in the cytoskeleton (collapse of actin and bundling of tubulin microfilaments), inhibited proliferation and finally induced apoptosis of both HCT116 and Hke-3 cells. However, the presence of oncogenic kRas significantly decreased the sensitivity of cells to the three cucurbitacins tested, CCR, DHCB and CCI. We confirmed that mutational activation of kRas protects cells from cucurbitacin-induced apoptosis using nontransformed intestinal epithelial cells with inducible expression of kRasV12. Cucurbitacins induced the expression of p53 and p21 predominantly in HCT116 cells that harbor mutant Ras. Using HCT116 cells with targeted deletion of p53 or p21 we confirmed that p53 and p21 protect cells from apoptosis induced by cucurbitacins. These results demonstrated that sensitivity of human colon cancer cell lines to cucurbitacins depends on the kRas and p53/p21 status, and established that cucurbitacins can exert antitumorigenic activity in the absence of activated STAT3.

HDAC2 deficiency sensitizes colon cancer cells to TNFalpha-induced apoptosis through inhibition of NF-kappaB activity

HDAC inhibitors exert potent anti-tumorigenic and anti-inflammatory activity. Their effects are selective for transformed cells, and we recently demonstrated that transformation of epithelial cells with k-Ras sensitizes cells to HDACi induced apoptosis. The aim of this study was to determine whether the ability of HDACi to modulate signaling by a major pro-inflammatory cytokine, TNFalpha, is also restricted to cells that harbor mutant k-Ras. We used the system of two isogenic cell lines that differ by the presence of mutant k-Ras, HCT116 and Hke3 cells. Treatment of cells with TNFalpha alone did not induce apoptosis; however HDACi potentiated TNFalpha-induced apoptosis in both HCT116 and Hke3 cells. Thus, the ability of HDACi to sensitize cells to TNFalpha-induced apoptosis appears to be k-Ras independent. We demonstrated that HDACi inhibited TNFalpha-induced NF-kappaB transcriptional and DNA binding activity in both cell lines, underlying the increased apoptosis in cells treated with both agents. We showed that overexpression of HDAC2 enhanced TNFalpha-induced NF-kappaB activity and that silencing of HDAC2 decreased NF-kappaB activity. Finally, silencing of HDAC2 expression was sufficient to sensitize colon cancer cells to TNFalpha-induced apoptosis. The ability of HDACi to interfere with NF-kappaB activity is likely to contribute to their potent anti-tumorigenic and anti-inflammatory activity.

Histone deacetylase inhibitors induce cell death selectively in cells that harbor activated kRasV12: The role of signal transducers and activators of transcription 1 and p21

Histone deacetylase (HDAC) inhibitors (HDACi) show potent and selective antitumor activity despite the fact that they induce histone hyperacetylation in both normal and tumor cells. In this study, we showed that the inducible expression of kRasV12 in nontransformed intestinal epithelial cells significantly lowered the mitochondrial membrane potential (MMP) and sensitized cells to HDACi-induced apoptosis. Consistent with our finding that colon cancer cell lines with mutant Ras have reduced expression of signal transducers and activators of transcription 1 (STAT1), we showed that inducible expression of mutant Ras markedly decreased both basal and inducible expression of STAT1, a transcription factor with tumor suppressor activity. To investigate whether reduced expression of STAT1 in cells that harbor mutant Ras contributes to their increased sensitivity to HDACi, we silenced the expression of STAT1 in HKe-3 cells with small interfering RNA. Despite the fact that silencing of STAT1 was not sufficient to alter the MMP, STAT1 deficiency, like Ras mutations, sensitized cells to apoptosis induced by HDACi. We showed that the induction of p21 by HDACi was significantly impaired in HKe-3 cells with silenced STAT1 expression and showed that the ability of butyrate to activate p21 transcription was diminished in STAT1-deficient HKe-3 cells. Finally, we used cells with targeted deletion of p21 to confirm that p21 protects cells from butyrate-induced apoptosis, strongly suggesting that in these cells STAT1 deficiency promotes butyrate-induced apoptosis through impaired induction of p21. Our data therefore establish that Ras mutations, and consequent reduction in the expression of STAT1, underlie the increased susceptibility of transformed cells to undergo apoptosis in response to treatment with inhibitors of HDAC activity.

Proteomic investigation of glucose metabolism in the butyrate-producing gut anaerobeFusobacterium varium

A proteome survey and MS analysis were conducted to investigate glucose metabolism in Fusobacterium varium, a butyrate-producing constituent of the indigenous human gut microflora. The bacterium was capable of catabolizing glucose as the main energy source via the Embden-Meyerhof-Parnas pathway. 2-DE analyses revealed that the apparent concentrations of the six identified glycolytic enzymes (pyruvate kinase, enolase, glucose-6-phosphate isomerase, phosphoglycerate kinase, triosephosphate isomerase, and glyceraldehyde-3-phosphate dehydrogenase) were specifically increased in response to the presence of glucose in the chemically defined minimal growth medium, and did not diminish when the medium was additionally supplemented with L-glutamate, an amino acid readily fermented by members of the Fusobacterium genus. A substrate pool depletion study revealed that the sugar, and not the amino acid, is the more efficient growth substrate. Both proteomics and substrate pool depletion studies revealed that F. varium can simultaneously utilize both glucose and L-glutamate as energy sources. Enzymes involved in L-glutamate metabolism were also identified, including an NAD-dependent glutamate dehydrogenase and two enzymes of the methylaspartate pathway of L-glutamate catabolism (glutamate mutase and methylaspartate ammonia-lyase). Their apparent intracellular concentrations were elevated when the bacterium was cultured in media supplemented with excess L-glutamate. Our observation that the apparent concentrations of specific proteins were elevated in response to a particular growth substrate supplied as an energy source provides the first evidence for the presence of a nutrient-responsive mechanism governing intracellular protein concentration in F. varium.

The short chain fatty acid, butyrate, stimulates MUC2 mucin production in the human colon cancer cell line, LS174T

The short fatty acid, butyrate, which is produced by intestinal anaerobic bacteria in the colon, has inhibitory activity on histone deacetylases (HDACs). Treatment of the human colon cancer cell line, LS174T, with 1-2 mM sodium butyrate stimulated MUC2 mucin production, as determined by histological PAS staining of carbohydrate chains of mucin, and confirmed at the protein and mRNA levels by immunoblotting with anti-MUC2 antibody and real-time RT-PCR, respectively. Increases in acetylated histone H3 in the LS174T cells treated with butyrate suggest inhibition of HDACs in these cells. Butyrate-stimulated MUC2 production in the LS174T cells was inhibited by the MEK inhibitor, U0126, implicating the involvement of extracellular signal-regulated kinase (ERK) cascades in this process. Proliferation of the LS174T cells was inhibited by butyrate treatment. Although apoptotic nuclear DNA fragmentation could not be detected, cell-cycle arrest at the G0/G1 phase in the butyrate-treated cells was demonstrated by flow cytometry. Thus butyrate, an HDAC inhibitor, inhibits proliferation of LS174T cells but stimulates MUC2 production in individual cells.

Essential role of the JAK/STAT1 signaling pathway in the expression of inducible nitric-oxide synthase in intestinal epithelial cells and its regulation by butyrate

Nitric oxide (NO) is a highly reactive free radical that modulates tumorigenesis through its ability to regulate cell proliferation, cell death, migration and angiogenesis. Although the role of NO has been well studied in inflammatory cells, much less is known about the regulation of NO production in epithelial cells. We demonstrated that in intestinal epithelial cells the expression of inducible NO synthase (iNOS), the critical enzyme in the synthesis of NO, is synergistically stimulated by bacterial lipopolysaccharide (LPS) and interferon gamma (IFNgamma) or by the combination of tumor necrosis factor (TNF) and IFNgamma at the transcriptional level. Expression of iNOS and the production of NO in response to LPS/IFNgamma were significantly increased upon induction of oncogenic K-Ras, underlying frequently elevated expression of iNOS in colon cancer. Silencing of STAT1, a major transcription factor involved in signaling by IFNgamma, or pharmacological inhibition of JAKs, kinases that phosphorylate STATs, prevented the induction of iNOS and the production of NO in response to stimulation of cells with LPS/IFNgamma or TNF/IFNgamma, underscoring the importance of the intact JAK/STAT signaling in the regulation of iNOS expression in intestinal epithelial cells. Butyrate, a histone deacetylase (HDAC) inhibitor and a dietary chemopreventive agent, decreased NO production in macrophages and in intestinal myofibroblasts, consistent with its anti-inflammatory activity. In contrast, in intestinal epithelial cells, butyrate significantly enhanced the expression of iNOS and the production of NO in response to treatment with LPS/IFNgamma. Despite the fact that, like butyrate, three structurally unrelated inhibitors of HDAC activity, trichostatin A, suberoylanilide hydroxamic acid, and apicidin, induced acetylation of H3 and H4 in epithelial cells, they failed to increase the production of NO, demonstrating that butyrate regulates NO production in epithelial cells in an HDAC-independent manner. The ability of butyrate to regulate the production of NO in a variety of cell types is likely to underlie its potent chemopreventive and anti-inflammatory activity.

Gelsolin segment 5 inhibits HIV-induced T-cell apoptosis via Vpr-binding to VDAC

Viral protein R (Vpr) from the human immunodeficiency virus induces cell cycle arrest in proliferating cells, stimulates virus transcription, and regulates activation and apoptosis of infected T-lymphocytes. We report that Jurkat cells overexpressing full-length gelsolin show resistance to Vpr-induced T-cell apoptosis with abrogation of mitochondrial membrane potential loss and the release of cytochrome c. Co-immunoprecipitation assays in HEK293T cells demonstrated that overexpression of full-length or segment 5 (G5) but not G5-deleted gelsolin (DeltaG5) bound to the voltage-dependent anion channel (VDAC), and that the G5 subunit can inhibit HIV-1-Vpr-binding to VDAC. We also confirmed that full-length gelsolin has the same effect in Jurkat cells. Clonogenic analysis showed that transfection of G5 but not DeltaG5 cDNA protects Jurkat T cells from HIV-Vpr-Tet induced T-cell apoptosis and promoted cell survival, as did full-length gelsolin. These results suggest that the gelsolin G5 domain inhibits HIV-Vpr-induced T-cell apoptosis by blocking the interaction between Vpr and VDAC, and might be used as a protective treatment against HIV-Vpr-induced T-cell apoptosis.

Polyphenols and cancer cell growth

Polyphenols constitute an important group of phytochemicals that gained increased research attention since it was found that they could affect cancer cell growth. Initial evidence came from epidemiologic studies suggesting that a diet that includes regular consumption of fruits and vegetables (rich in polyphenols) significantly reduces the risk of many cancers. In the present work we briefly review the effects of polyphenols on cancer cell fate, leading towards growth, differentiation and apoptosis. Their action can be attributed not only to their ability to act as antioxidants but also to their ability to interact with basic cellular mechanisms. Such interactions include interference with membrane and intracellular receptors, modulation of signaling cascades, interaction with the basic enzymes involved in tumor promotion and metastasis, interaction with oncogenes and oncoproteins, and, finally, direct or indirect interactions with nucleic acids and nucleoproteins. These actions involve almost the whole spectrum of basic cellular machinery--from the cell membrane to signaling cytoplasmic molecules and to the major nuclear components--and provide insights into their beneficial health effects. In addition, the actions justify the scientific interest in this class of compounds, and provide clues about their possible pharmaceutical exploitation in the field of oncology.

Pro-survival role of gelsolin in mouse beta-cells

We have previously shown that the Ca(2+)-dependent actin-severing protein gelsolin plays an important role in regulated insulin secretion. The aim of this study was to determine the role of gelsolin in beta-cell survival as it has been shown to play a dual role in apoptosis in other cell types. MIN6 subclones B1 and C3, shown previously to express gelsolin at different levels (B1>>C3 cells), were used for this purpose. We demonstrate that B1 cells have lower levels of apoptosis and active caspase-3 when compared with C3 cells, in both standard (25 mmol/l glucose and 15% FCS) and deprived (5 mmol/l glucose and 1% FCS) conditions. Overexpression of gelsolin resulted in a decrease in the percentage of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)(+) and active caspase-3(+) cells. Conversely, knockdown of gelsolin by RNA interference in B1 cells caused an increase in the number of TUNEL(+) and active caspase-3(+) cells. Finally, the anti-apoptotic role of gelsolin was confirmed in purified primary mouse beta-cells where overexpression of gelsolin resulted in a decrease in the percentage of TUNEL(+) cells. In summary, our results show for the first time that gelsolin plays a pro-survival role in pancreatic beta-cells.

Stem cell gene expression changes induced specifically by mutated K-ras

K-Ras proteins transduce signals from membrane-bound receptors via multiple downstream effector pathways and thereby regulate fundamental stem cell processes that affect neoplasia, including proliferation, apoptosis, and differentiation, but their contribution to tumourigenesis is unclear. Because cancers develop from stem cells, we set out to determine the characteristic changes in gene expression brought about by mutated K-ras (without interference from normal K-ras) in otherwise normal stem cells. cDNA microarrays were used to analyze gene expression profiles comparing wild-type murine embryonic stem (ES) cells with K-ras(Val12) expressing ES cells (previously made null for both endogenous K-ras alleles and transfected with K-ras(Val12), with valine for glycine at codon 12). K-ras(Val12) was expressed at 1.2-fold normal K-ras levels and produced transcripts for both activated K-Ras4A and 4B isoforms. The array expression data were confirmed by real-time quantitative PCR analysis of selected genes expressed both in the K-ras(Val12) expressing ES cells (R = 0.91 with array data) and in the normal intestinal tissues of K-ras(Val12) transgenic mice (R = 0.91 with array data). Changes in gene expression were correlated with the effects of K-ras(Val12) expression on ES cells of enhancing self-renewal in an undifferentiated state, increasing susceptibility to DNA damage-induced apoptosis, and increased proliferation. These expression data may explain, at least in part, some neoplasia-related aspects of the phenotypic changes brought about in this ES cell line by mutated K-ras, in that upregulation of cell growth-related proteins and DNA-associated proteins is consistent with increased proliferation; upregulation of certain apoptosis-related proteins is consistent with a greater susceptibility to DNA damage-induced apoptosis; and downregulation of structural proteins, extracellular matrix components, secretory proteins and receptors is consistent with a less differentiated phenotype.

Oncogenic K-RAS subverts the antiapoptotic role of N-RAS and alters modulation of the N-RAS:gelsolin complex

Activating mutations in members of the RAS family of genes are among the most common genetic events in human tumorigenesis. Once thought to be functionally interchangeable, it is increasingly recognized that the classical members of this protein family (H-RAS, N-RAS and K-RAS4B) exhibit unique and shared functions that are highly context-dependent. Herein, we demonstrate that the presence of an oncogenic KRAS allele results in elevated levels of GTP-bound N-RAS (N-RAS.GTP) in two human colorectal cancer cell lines, HCT 116 and DLD-1, compared to their isogenic counterparts in which the mutant KRAS allele has been disrupted by homologous recombination. N-RAS subserves an antiapoptotic role in cells expressing wild-type K-RAS; this function is compromised, however, by the presence of mutant K-RAS, and these cells display increased sensitivity to apoptotic stimuli. We additionally identify a physical interaction between N-RAS and gelsolin, a factor that has been shown to promote survival and show that the N-RAS:gelsolin complex is modulated differently in wild-type and mutant K-RAS environments following apoptotic challenge. These findings represent the first biochemical evidence of a functional relationship between endogenous RAS proteins and identify a dynamic physical interaction between endogenous N-RAS and gelsolin that correlates with survival.

Activation of Ras Up-regulates Pro-apoptotic BNIP3 in Nitric Oxide-induced Cell Death

Nitric oxide (NO) produced by NO synthases causes nitration and nitrosylation of cellular factors. We have shown previously that endogenously produced or exogenously added NO induces expression of BNIP3 (Bcl-2/adenovirus E1B 19 kDa-interacting protein 3), leading to death of macrophages (Yook, Y.-H., Kang, K.-H., Maeng, O., Kim, T.-R., Lee, J.-O., Kang, K.-i., Kim, Y.-S., Paik, S.-G., and Lee, H. (2004) Biochem. Biophys. Res. Commun. 321, 298-305). We now provide evidence that Ras mediates NO-induced BNIP3 expression via the MEK/ERK/hypoxia-inducible factor (HIF)-1 pathway. (a) ras-Q61L, a constitutively active form of Ras, up-regulated BNIP3 protein expression by enhancing Bnip3 promoter activity, and ras-S17N, a dominant-negative form, and ras-C118S, an S-nitrosylation mutant, blocked NO-induced BNIP3 expression, suggesting that Ras acts downstream of NO and that NO activates Ras by nitrosylation. (b) U0126, a specific MEK inhibitor, completely abolished BNIP3 expression and the stimulation of promoter activity by NO and Ras, whereas 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, SB203580, and wortmannin, specific inhibitors of soluble guanylyl cyclase, p38 MAPK, and phosphatidylinositol 3-kinase, respectively, had no effect. Ras, MEK1/2, and ERK1/2 were sequentially activated by NO treatment of macrophages. (c) Mutation of the HIF-1-binding site (hypoxia-response element) in the Bnip3 promoter abolished BNIP3 induction, and HIF-1alpha was strongly induced by NO. (d) Transient expression of activated Ras promoted macrophage death, as did NO, and this Ras-mediated cell death was inhibited by silencing BNIP3 expression. These results suggest that NO-induced death of macrophages is mediated, at least in part, by BNIP3 induction.

Selective transcription and cellular proliferation induced by PDGF require histone deacetylase activity

Histone deacetylases (HDACs) are key regulatory enzymes involved in the control of gene expression and their inhibition by specific drugs has been widely correlated to cell cycle arrest, terminal differentiation, and apoptosis. Here, we investigated whether HDAC activity was required for PDGF-dependent signal transduction and cellular proliferation. Exposure of PDGF-stimulated NIH3T3 fibroblasts to the HDAC inhibitor trichostatin A (TSA) potently repressed the expression of a group of genes correlated to PDGF-dependent cellular growth and pro-survival activity. Moreover, we show that TSA interfered with STAT3-dependent transcriptional activity induced by PDGF. Still, neither phosphorylation nor nuclear translocation and DNA-binding in vitro and in vivo of STAT3 were affected by using TSA to interfere with PDGF stimulation. Finally, TSA treatment resulted in the suppression of PDGF-dependent cellular proliferation without affecting cellular survival of NIH3T3 cells. Our data indicate that inhibition of HDAC activity antagonizes the mitogenic effect of PDGF, suggesting that these drugs may specifically act on the expression of STAT-dependent, PDGF-responsive genes.

An overview of apoptosis and the prevention of colorectal cancer

Colorectal cancer arises as a result of the accumulation of genetic errors many of which affect the control of apoptosis. Effective chemoprevention strategies for colorectal cancer must rectify these genetic defects. Mutation of apc is often the initiating genetic lesion in colorectal cancers that develop along the chromosomal instability pathway. Depending on the cellular context, loss of apc activates the Wnt signalling pathway causing immediate widespread apoptosis of colorectal epithelial cells and defects in differentiation and cell migration. Only cells that are inherently resistant to apoptosis survive this initial wave of apoptosis. These surviving cells constitute the epithelial population that develop into adenomas. Two gene targets of the Wnt signalling pathway are of particular relevance to apoptosis. Although controversial, survivin may function to inhibit apoptosis. MYC has two outputs in normal cells, the induction of apoptosis and proliferation. These opposing functions work so that MYC can only induce cell proliferation in cells if apoptosis is disabled. p53 couples apoptosis to mitogenic signals and survival pathways. Under some circumstances, NF-kappaB can act as an inhibitor of apoptosis possibly through increased expression of bcl-x(L). Tumours that evolve by the microsatellite instability pathway often have mutations in the proapoptotic gene bax. Colonic adenomas express cyclo-oxygenase-2 (COX-2) and may be targets of chemoprevention before the development of malignancy. However, the recent discovery that coxibs increase the risk of serious cardiovascular events limits their use as chemopreventive agents. Nevertheless, aspirin remains a drug of great interest as it is already known to reduce the risk of colorectal cancer by up to 50%. The balance of evidence shows that high vegetable fibre diets can prevent colorectal cancer, probably via the fermentation of butyrate enhancing the apoptotic response to DNA damage.

Oncogenic Ras increases sensitivity of colon cancer cells to 5-FU-induced apoptosis

Despite the fact that objective response rates to 5-FU are as low as 20%, 5-FU remains the most commonly used drug for the treatment of colorectal cancer. The lack of understanding of resistance to 5-FU, therefore, remains a significant impediment in maximizing its efficacy. We used intestinal epithelial cells with an inducible K-RasV12 to demonstrate that expression of oncogenic Ras promotes cell death upon 5-FU treatment. Accordingly, transient expression of the mutant RasV12, but not the WT Ras, enhanced 5-FU-induced apoptosis in 293T cells. Consistent with these data, we showed that targeted deletion of the mutant Ras allele in the HCT116 colon cancer cell line protected cells from 5-FU-induced apoptosis. Using isogenic colon cancer cell lines that differ only by the presence of the mutant Ras allele, HCT116 and Hke-3 cells, we demonstrated that signaling by oncogenic Ras promotes both accumulation of p53 and its phosphorylation on serine15 in response to 5-FU, a situation that favors apoptosis over growth arrest. However, despite the differential induction of p53 in HCT116 and Hke-3 cells, the expression of Puma, a gene with an important role in p53-dependent apoptosis, was not affected by Ras signaling. In contrast, we showed that Ras interferes with 5-FU-induced expression of gelsolin, a protein with known antiapoptotic activity. We ascertained the role of gelsolin in 5-FU-induced apoptosis by demonstrating that silencing of gelsolin expression through RNAi sensitized cells to 5-FU-induced apoptosis and that re-expression of gelsolin in cells harboring mutant Ras protected cells from 5-FU-induced apoptosis. These data therefore demonstrate that Ras mutations increase sensitivity to 5-FU-induced apoptosis at least in part through the negative regulation of gelsolin expression. Our data indicate that Ras mutations promote apoptosis in response to 5-FU treatment and imply that tumors with Ras mutations and/or reduced expression of gelsolin may show enhanced apoptosis in response to 5-FU also in vivo.