Sodium butyrate stimulates PKC activation and induces differential expression of certain PKC isoforms during erythroid differentiation

Folate depletion induces erythroid differentiation through perturbation of de novo purine synthesis

Folate, an essential vitamin, is a one-carbon acceptor and donor in key metabolic reactions. Erythroid cells harbor a unique sensitivity to folate deprivation, as revealed by the primary pathological manifestation of nutritional folate deprivation: megaloblastic anemia. To study this metabolic sensitivity, we applied mild folate depletion to human and mouse erythroid cell lines and primary murine erythroid progenitors. We show that folate depletion induces early blockade of purine synthesis and accumulation of the purine synthesis intermediate and signaling molecule, 5'-phosphoribosyl-5-aminoimidazole-4-carboxamide (AICAR), followed by enhanced heme metabolism, hemoglobin synthesis, and erythroid differentiation. This is phenocopied by inhibition of folate metabolism using the inhibitor SHIN1, and by AICAR supplementation. Mechanistically, the metabolically driven differentiation is independent of mechanistic target of rapamycin complex 1 (mTORC1) and adenosine 5'-monophosphate-activated protein kinase (AMPK) and is instead mediated by protein kinase C. Our findings suggest that folate deprivation-induced premature differentiation of erythroid progenitor cells is a molecular etiology to folate deficiency-induced anemia.

Effects of Intestinal Microbial⁻Elaborated Butyrate on Oncogenic Signaling Pathways

The intestinal microbiota is well known to have multiple benefits on human health, including cancer prevention and treatment. The effects are partially mediated by microbiota-produced short chain fatty acids (SCFAs) such as butyrate, propionate and acetate. The anti-cancer effect of butyrate has been demonstrated in cancer cell cultures and animal models of cancer. Butyrate, as a signaling molecule, has effects on multiple signaling pathways. The most studied effect is its inhibition on histone deacetylase (HDAC), which leads to alterations of several important oncogenic signaling pathways such as JAK2/STAT3, VEGF. Butyrate can interfere with both mitochondrial apoptotic and extrinsic apoptotic pathways. In addition, butyrate also reduces gut inflammation by promoting T-regulatory cell differentiation with decreased activities of the NF-κB and STAT3 pathways. Through PKC and Wnt pathways, butyrate increases cancer cell differentiation. Furthermore, butyrate regulates oncogenic signaling molecules through microRNAs and methylation. Therefore, butyrate has the potential to be incorporated into cancer prevention and treatment regimens. In this review we summarize recent progress in butyrate research and discuss the future development of butyrate as an anti-cancer agent with emphasis on its effects on oncogenic signaling pathways. The low bioavailability of butyrate is a problem, which precludes clinical application. The disadvantage of butyrate for medicinal applications may be overcome by several approaches including nano-delivery, analogue development and combination use with other anti-cancer agents or phytochemicals.

Targeting Histone Deacetylase Activity to Arrest Cell Growth and Promote Neural Differentiation in Ewing Sarcoma

There is an urgent need for advances in the treatment of Ewing sarcoma (EWS), an aggressive childhood tumor with possible neuroectodermal origin. Inhibition of histone deacetylases (HDAC) can revert aberrant epigenetic states and reduce growth in different experimental cancer types. Here, we investigated whether the potent HDAC inhibitor, sodium butyrate (NaB), has the ability to reprogram EWS cells towards a more differentiated state and affect their growth and survival. Exposure of two EWS cell lines to NaB resulted in rapid and potent inhibition of HDAC activity (1 h, IC₅₀ 1.5 mM) and a significant arrest of cell cycle progression (72 h, IC₅₀ 0.68-0.76 mM), marked by G0/G1 accumulation. Delayed cell proliferation and reduced colony formation ability were observed in EWS cells after long-term culture. NaB-induced effects included suppression of cell proliferation accompanied by reduced transcriptional expression of the EWS-FLI1 fusion oncogene, decreased expression of key survival and pluripotency-associated genes, and re-expression of the differentiation neuronal marker βIII-tubulin. Finally, NaB reduced c-MYC levels and impaired survival in putative EWS cancer stem cells. Our findings support the use of HDAC inhibition as a strategy to impair cell growth and survival and to reprogram EWS tumors towards differentiation. These results are consistent with our previous studies indicating that HDis can inhibit the growth and modulate differentiation of cells from other types of childhood pediatric tumors possibly originating from neural stem cells.

Sodium butyrate enhanced physical barrier function referring to Nrf2, JNK and MLCK signaling pathways in the intestine of young grass carp (Ctenopharyngodon idella)

This study evaluated the effect of dietary sodium butyrate (SB) supplementation on the intestinal physical barrier function of young grass carp (Ctenopharyngodon idella). The fish were fed one powdery sodium butyrate (PSB) diet (1000.0 mg kg^-1 diet) and five graded levels of microencapsulated sodium butyrate (MSB) diets: 0.0 (control), 500.0, 1000.0, 1500.0 and 2000.0 mg kg^-1 diet for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila to explore the effect of SB supplementation on intestinal physical barrier function and the potential mechanisms in fish. The results showed that optimal SB supplementation: (1) down-regulated the cysteine-aspartic protease-2 (caspase-2), caspase-3 (rather than PI), caspase-7, caspase-8 (rather than PI), caspase-9, fatty acid synthetase ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), B-cell lymphoma 2 associated X protein (Bax) and c-Jun Nterminal protein kinase (JNK) mRNA levels, up-regulated the B-cell lymphoma protein-2 (Bcl-2) (rather than PI), inhibitor of apoptosis proteins (IAP) and myeloid cell leukemia-1 (Mcl-1) mRNA levels in the intestine (P < 0.05), inhibited the intestinal cell apoptosis, maintained the intestine cell structure integrity; (2) increased NF-E2-related factor 2 (Nrf2) mRNA levels and nucleus protein levels, and down-regulated kelch-like-ECH-associated protein (Keap1b) (rather than Keap1a) mRNA levels in the intestine, up-regulated copper/zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase 1a (GPx1a), GPx1b, GPx4a, GPx4b, glutathione S-transferases R (GSTR), GSTP1, GSTP2, GSTO1, GSTO2 and glutathione reductase (GR) mRNA levels in the intestine, increased the corresponding antioxidant enzymes activity (P < 0.05), thus enhancing the ability of scavenging free radicals and decreasing the reactive oxygen species (ROS) content, decreasing the lipid and protein peroxidation, as well as alleviating oxidative damage; (3) down-regulated the molecule myosin light-chain kinase (MLCK) mRNA levels in the intestine, and up-regulated the occludin, zonula occludens-1 (ZO-1), ZO-2, claudin-b, claudin-c, claudin-f, claudin-3c (rather than PI), claudin-7a, claudin-7b and claudin-11 mRNA levels, down-regulated claudin-12, claudin-15a and claudin-15b mRNA levels (P < 0.05), thus maintaining the structural integrity between cells. This study suggests that SB supplementation could improve fish intestinal physical barrier function. Furthermore, according to the positive effect, MSB was superior to PSB on improving intestinal physical barrier function of fish. Finally, based on protein carbonyl content in the PI, the optimal SB supplementation (MSB as SB source) for young grass carp was estimated to be 338.8 mg kg^-1 diet.

Physiological TLR5 expression in the intestine is regulated by differential DNA binding of Sp1/Sp3 through simultaneous Sp1 dephosphorylation and Sp3 phosphorylation by two different PKC isoforms

Toll-like receptor 5 (TLR5) expression in the intestinal epithelial cells (IECs) is critical to maintain health, as underscored by multiple intestinal and extra-intestinal diseases in mice genetically engineered for IEC-specific TLR5 knockout. A gradient of expression exists in the colonic epithelial cells from the cecum to the distal colon. Intriguingly, an identical gradient for the dietary metabolite, butyrate also exists in the luminal contents. However, both being critical for intestinal homeostasis and immune response, no studies examined the role of butyrate in the regulation of TLR5 expression. We showed that butyrate transcriptionally upregulates TLR5 in the IECs and augments flagellin-induced immune responses. Both basal and butyrate-induced transcription is regulated by differential binding of Sp-family transcription factors to the GC-box sequences over the TLR5 promoter. Butyrate activates two different protein kinase C isoforms to dephosphorylate/acetylate Sp1 by serine/threonine phosphatases and phosphorylate Sp3 by ERK-MAPK, respectively. This resulted in Sp1 displacement from the promoter and binding of Sp3 to it, leading to p300 recruitment and histone acetylation, activating transcription. This is the first study addressing the mechanisms of physiological TLR5 expression in the intestine. Additionally, a novel insight is gained into Sp1/Sp3-mediated gene regulation that may apply to other genes.

Effect of spent turmeric on kidney glycoconjugates in streptozotocin-induced diabetic rats

Background

Curcumin known to have number of medicinal use and masked the fiber containing ukonan like active polysaccharide in turmeric and its pharmacological effect will be addressed on diabetic nephropathy particularly the glycoconjugates of extracellular components viz., glycoproteins and glycosaminoglycans - heparan sulfate (HS).

Methods

Male Wistar rats were maintained on AIN-76 diet containing 10% spent turmeric and were grouped into control and STZ induced diabetes SFC/TFC and SFD/TFD, respectively. Diabetic status was monitored using blood and urine, and at the end, harvested kidneys were used to study the amelioration of glycoprotiens (collagen) and HS by enzymatic digestion, spectrophotometric, hydroxyproline and agarose electrophoretic methods.

Results

In the present study spent turmeric (10%) fed diabetic rats showed improved glomerular filtration rate (50%), kidney enlargement (60%) and other glycoconjugate metabolism in kidney. Increased collagen content in diabetic group was observed by hydroxyproline estimation (24%) and periodic acid-Schiff’s (PAS) staining. Furthermore, elevated activities of enzymes involved in the synthesis and degradation of glycosaminoglycans (GAGs) were significantly lowered in spent turmeric fed diabetic group. Improvement in total GAGs (43%) and sulfate content (18%) followed by fractionation of GAGs using specific enzymes led to HS (28%) in the spent turmeric fed diabetic group, when compared to starch fed diabetic group and was further confirmed by electrophoresis of GAG.

Conclusion

These results clearly indicate beneficial role of spent turmeric in controlling glycoconjugates such as glycoproteins and heparan sulfate related kidney complications during diabetes.

Tight regulation of a timed nuclear import wave of EKLF by PKCθ and FOE during Pro-E to Baso-E transition

Erythropoiesis is a highly regulated process during which BFU-E are differentiated into RBCs through CFU-E, Pro-E, PolyCh-E, OrthoCh-E, and reticulocyte stages. Uniquely, most erythroid-specific genes are activated during the Pro-E to Baso-E transition. We show that a wave of nuclear import of the erythroid-specific transcription factor EKLF occurs during the Pro-E to Baso-E transition. We further demonstrate that this wave results from a series of finely tuned events, including timed activation of PKCθ, phosphorylation of EKLF at S68 by P-PKCθ(S676), and sumoylation of EKLF at K74. The latter EKLF modifications modulate its interactions with a cytoplasmic ankyrin-repeat-protein FOE and importinβ1, respectively. The role of FOE in the control of EKLF nuclear import is further supported by analysis of the subcellular distribution patterns of EKLF in FOE-knockout mice. This study reveals the regulatory mechanisms of the nuclear import of EKLF, which may also be utilized in the nuclear import of other factors.

Butyrate produced by commensal bacteria potentiates phorbol esters induced AP-1 response in human intestinal epithelial cells

The human intestine is a balanced ecosystem well suited for bacterial survival, colonization and growth, which has evolved to be beneficial both for the host and the commensal bacteria. Here, we investigated the effect of bacterial metabolites produced by commensal bacteria on AP-1 signaling pathway, which has a plethora of effects on host physiology. Using intestinal epithelial cell lines, HT-29 and Caco-2, stably transfected with AP-1-dependent luciferase reporter gene, we tested the effect of culture supernatant from 49 commensal strains. We observed that several bacteria were able to activate the AP-1 pathway and this was correlated to the amount of short chain fatty acids (SCFAs) produced. Besides being a major source of energy for epithelial cells, SCFAs have been shown to regulate several signaling pathways in these cells. We show that propionate and butyrate are potent activators of the AP-1 pathway, butyrate being the more efficient of the two. We also observed a strong synergistic activation of AP-1 pathway when using butyrate with PMA, a PKC activator. Moreover, butyrate enhanced the PMA-induced expression of c-fos and ERK1/2 phosphorylation, but not p38 and JNK. In conclusion, we showed that SCFAs especially butyrate regulate the AP-1 signaling pathway, a feature that may contribute to the physiological impact of the gut microbiota on the host. Our results provide support for the involvement of butyrate in modulating the action of PKC in colon cancer cells.

Okadaic acid inhibits the trichostatin A-mediated increase of human CYP46A1 neuronal expression in a ERK1/2-Sp3-dependent pathway

The CYP46A1 gene codes for the cholesterol 24-hydroxylase, a cytochrome P450 specifically expressed in neurons and responsible for the majority of cholesterol turnover in the central nervous system. Previously, we have demonstrated the critical participation of Sp transcription factors in the CYP46A1 response to histone deacetylase (HDAC) inhibitors, and in this study we investigated the involvement of intracellular signaling pathways in the trichostatin A (TSA) effect. Our results show that pretreatment of neuroblastoma cells with chemical inhibitors of mitogen-activated kinase kinase (MEK)1 significantly potentiates the TSA-dependent induction of cholesterol 24-hydroxylase, whereas inhibition of protein phosphatases by okadaic acid (OA) or overexpression of MEK1 partially impairs the TSA effect without affecting histone hyperacetylation at the promoter. Immunoblotting revealed that TSA treatment decreases ERK1/2 phosphorylation concomitantly with a decrease in Sp3 binding activity, which are both reversed by pretreatment with OA. Chromatin immunoprecipitation analysis demonstrated that TSA induces the release of p-ERK1/2 from the CYP46A1 proximal promoter, whereas pretreatment with OA restores the co-occupancy of Sp3-ERK1/2 in the same promoter fragments. We demonstrate for the first time the participation of MEK-ERK1/2 signaling pathway in HDAC inhibitor-dependent induction of cytochrome P450 gene expression, underlying the importance of this regulatory signaling mechanism in the control of brain cholesterol elimination.

Valproic acid antagonizes the capacity of other histone deacetylase inhibitors to activate the Epstein-barr virus lytic cycle

Diverse stimuli reactivate the Epstein-Barr virus (EBV) lytic cycle in Burkitt lymphoma (BL) cells. In HH514-16 BL cells, two histone deacetylase (HDAC) inhibitors, sodium butyrate (NaB) and trichostatin A (TSA), and the DNA methyltransferase inhibitor azacytidine (AzaCdR) promote lytic reactivation. Valproic acid (VPA), which, like NaB, belongs to the short-chain fatty acid class of HDAC inhibitors, fails to induce the EBV lytic cycle in these cells. Nonetheless, VPA behaves as an HDAC inhibitor; it causes hyperacetylation of histone H3 (J. K. Countryman, L. Gradoville, and G. Miller, J. Virol. 82:4706-4719, 2008). Here we show that VPA blocked the induction of EBV early lytic proteins ZEBRA and EA-D in response to NaB, TSA, or AzaCdR. The block in lytic activation occurred prior to the accumulation of BZLF1 transcripts. Reactivation of EBV in Akata cells, in response to anti-IgG, and in Raji cells, in response to tetradecanoyl phorbol acetate (TPA), was also inhibited by VPA. MS-275 and apicidin, representing two additional classes of HDAC inhibitors, and suberoylanilide hydroxamic acid (SAHA) reactivated EBV in HH514-16 cells; this activity was also inhibited by VPA. Although VPA potently blocked the expression of viral lytic-cycle transcripts, it did not generally block the transcription of cellular genes and was not toxic. The levels and kinetics of specific cellular transcripts, such as Stat3, Frmd6, Mad1, Sepp1, c-fos, c-jun, and egr1, which were activated by NaB and TSA, were similar in HH514-16 cells treated with VPA. When combined with NaB or TSA, VPA did not inhibit the activation of these cellular genes. Changes in cellular gene expression in response to VPA, NaB, or TSA were globally similar as assessed by human genome arrays; however, VPA selectively stimulated the expression of some cellular genes, such as MEF2D, YY1, and ZEB1, that could repress the EBV lytic cycle. We describe a novel example of functional antagonism between HDAC inhibitors.

Dose and chemical modification considerations for continuous cyclic AMP analog delivery to the injured CNS

In this investigation, two cell-permeable synthetic analogs of cAMP, dibutyryl-cAMP (db-cAMP) and 8-bromo-cAMP, which are widely used to elevate intracellular cAMP levels under experimental conditions, were investigated for their ability to dose-dependently improve histological and functional outcomes following continuous delivery in two models of incomplete spinal cord injury (SCI). The cAMP analogs were delivered via osmotic minipumps at 1-250 mM through an indwelling cortical cannula or by intrathecal infusion for up to 4 weeks after either a T8 unilateral over-hemisection or a C2-3 dorsolateral quadrant lesion, respectively. In both SCI models, continuous db-cAMP delivery was associated with histopathological changes that included sporadic micro-hemorrhage formation and cavitation, enhanced macrophage infiltration and tissue damage at regions beyond the immediate application site; no deleterious or beneficial effect of agent delivery was observed at the spinal injury site. Furthermore, these changes were accompanied by pronounced behavioral deficits that included an absence of progressive locomotor recovery, increased extensor tone, paralysis, and sensory abnormalities. These deleterious effects were not observed in saline-treated animals, in animals in which the db-cAMP dose did not exceed 1 mM, or in those animals that received a high dose (250 mM) of the alternative cAMP analog, 8-bromo-cAMP. These results demonstrate that, for continuous intraparenchymal or intrathecal administration of cAMP analogs for the study of biological or therapeutic effects within the central nervous system (CNS), consideration of the effective concentration applied as well as the potential toxicity of chemical moieties on the parent molecule and/or their activity needs to be taken into account.

Extrinsic pathway- and cathepsin-dependent induction of mitochondrial dysfunction are essential for synergistic flavopiridol and vorinostat lethality in breast cancer cells

The present studies have determined whether interactions between the cyclin-dependent kinase inhibitor flavopiridol and the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA; vorinostat; Zolinza) occur in breast cancer cells. MDA-MB-231 and MCF7 cells were treated with flavopiridol (25-100 nmol/L) and vorinostat (125-500 nmol/L) in vitro, and mechanisms of cell killing were determined. Concurrent treatment of cells with flavopiridol and vorinostat or treatment of cells with flavopiridol followed by vorinostat promoted cell killing in a greater than additive fashion. Similar data were obtained with the CDK inhibitor roscovitine. Flavopiridol suppressed c-FLIP-l/s and BCL-xL expression, whereas vorinostat reduced expression of BCL-xL, and combined exposure to flavopiridol and vorinostat reduced MCL-1 and X-chromosome-linked inhibitor of apoptosis protein (XIAP) levels. Pharmacologic or genetic inhibition of caspase-8 reduced flavopiridol toxicity, but abolished killing by vorinostat and cell death caused by the vorinostat/flavopiridol regimen. Loss of BAX/BAK function or loss of BID function modestly reduced flavopiridol toxicity, but abolished vorinostat-mediated potentiation of flavopiridol toxicity, as did inhibition of caspase-9. Inhibition and/or deletion of cathepsin B function significantly attenuated vorinostat/flavopiridol lethality. Flavopiridol suppressed extracellular signal-regulated kinase 1/2 (ERK1/2) and AKT activity and expression of activated forms of AKT and mitogen-activated protein/ERK kinase 1 maintained c-FLIP-l/s, BCL-xL, and XIAP expression and protected cells against flavopiridol/vorinostat lethality. Overexpression of c-FLIP-s and BCL-xL abolished the lethality of flavopiridol/vorinostat. Collectively, these data argue that flavopiridol enhances the lethality of vorinostat in breast cancer cells in part through the inhibition of AKT and ERK1/2 function, leading to reduced expression of multiple inhibitors of the extrinsic and intrinsic apoptosis pathways, as well as activation of cathepsin protease-dependent pathways.

PKCε is essential for gelsolin expression by histone deacetylase inhibitor apicidin in human cervix cancer cells

Down-regulation of gelsolin expression is associated with cellular transformation and induction of gelsolin exerts antitumorigenic effects. In this study, we show that protein kinase C (PKC) signaling pathway is required for the induction of gelsolin by the histone deacetylase inhibitor apicidin in HeLa cells. Apicidin induces gelsolin mRNA independently of the de novo protein synthesis. Inhibitor study has revealed that the PKC signaling pathway is involved in the gelsolin expression. Furthermore, inhibition of PKCepsilon by either siRNA or dominant-negative mutant completely abrogates the expression of gelsolin by apicidin, indicating that PKCepsilon is the major isoform for this process. In parallel, apicidin induction of gelsolin is antagonized by the inhibition of Sp1 using dominant-negative Sp1 or specific Sp1 inhibitor mithramycin, and inhibition of PKC leads to suppression of Sp1 promoter activity. Our results provide mechanistic insights into molecular mechanisms of gelsolin induction by apicidin.

Trichostatin A, an inhibitor of histone deacetylase, inhibits smooth muscle cell proliferation via induction of p21(WAF1)

The proliferation of vascular smooth muscle cells (VSMCs) can contribute to a variety of pathological states, including atherosclerosis and post-angioplasty restenosis. The p21(WAF1) cyclin-dependent kinase inhibitor regulates cell-cycle progression, senescence, and differentiation in injured blood vessels. Histone deacetylase (HDAC) inhibitors have shown utility in controlling proliferation in a wide range of tumor cell lines, possibly by inducing the expression of p21(WAF1). Our goal was to investigate the effect of trichostatin A (TSA), a specific and potent HDAC inhibitor, on the proliferation of vascular smooth muscle cells (VSMCs) isolated from rat thoracic aorta. TSA suppressed the HDAC activity of VSMCs in a dose-dependent manner and inhibited VSMC proliferation as demonstrated by cell number counting and the degree of [3H] thymidine incorporation. Further, TSA reduced the phosphorylation of Rb protein, a regulator of cell-cycle progression. TSA treatment also induced the expression of p21(WAF1) but not of p16(INK4), p27(KIP1) or p53. Finally, TSA inhibited HDAC activity of VSMCs from p21(WAF1) knock-out mice but had no effect on VSMC proliferation in these animals. In conclusion, TSA inhibits VSMC proliferation via the induction of p21(WAF1) expression and subsequent cell-cycle arrest with reduction of the phosphorylation of Rb protein at the G1-S phase.

Phosphatidylinositol 3-kinase/protein kinase Czeta-induced phosphorylation of Sp1 and p107 repressor release have a critical role in histone deacetylase inhibitor-mediated derepression [corrected] of transcription of the luteinizing hormone receptor gene

We have demonstrated that silencing of luteinizing hormone receptor (LHR) gene transcription is mediated via a proximal Sp1 site at its promoter. Trichostatin A (TSA) induced histone acetylation and gene activation in JAR cells that prevailed in the absence of changes in Sp1/Sp3 expression, their binding activity, disassociation of the histone deacetylase/mSin3A complex from the Sp1 site, or demethylation of the promoter. This indicated a different mechanism involved in TSA-induced derepression. The present studies have revealed that phosphatidylinositol 3-kinase/protein kinase Czeta (PI3K/PKCzeta)-mediated Sp1 phosphorylation accounts for Sp1 site-dependent LHR gene activation. TSA caused marked phosphorylation of Sp1 at serine 641 in JAR and MCF-7 cells. Blockade of PI3K or PKCzeta activity by specific inhibitors, kinase-deficient mutants, or small interfering RNA abolished the effect of TSA on the LHR gene and Sp1 phosphorylation. PKCzeta was shown to associate with Sp1, and this association was enhanced by TSA. Sp1 phosphorylation at serine 641 was required for the release of the pRb homologue p107 from the LHR gene promoter, while p107 acted as a repressor of the LHR gene. Inhibition of PKCzeta activity blocked the dissociation of p107 from the LHR gene promoter and markedly reduced Sp1 phosphorylation and transcription. These results have demonstrated that phosphorylation of Sp1 by PI3K/PKCzeta is critical for TSA-activated LHR gene expression. These studies have revealed a novel mechanism of TSA action through derecruitment of a repressor from the LHR gene promoter in a PI3K/PKCzeta-induced Sp1 phosphorylation-dependent manner.

The novel histone deacetylase inhibitor BML-210 exerts growth inhibitory, proapoptotic and differentiation stimulating effects on the human leukemia cell lines

Histone deacetylase inhibitors have a potent role in the strategy for the treatment of leukemias. BML-210 (N-(2-Aminophenyl)-N' phenyloctanol diamine) is the novel histone deacetylase inhibitor, and its mechanism of action has not been characterized. In this study, we examined the in vitro effects of BML-210 on the human leukemia cell lines (NB4, HL-60, THP-1, and K562). We found that BML-210 inhibits the growth of all cell lines and promotes apoptosis in a dose- and time-dependent manner. BML-210 alone induces HL-60 and K562 cell differentiation (up to 30%) to granulocytes and erythrocytes, respectively, and in combination with differentiation agents - all-trans retinoic acid and hemin, markedly potentates it. Those treatments cause G1 arrest and histone H4 acetylation, affects transcription factor NF-kappaB and Sp1 binding activity to their consensus sequences, the p21 or the FasL promoters, and influences expression of Sp1, NF-kappaB, p21 and FasL. These findings suggest that BML-210 could be a promising antileukemic agent to induce apoptosis and to modulate differentiation through the modulation of histone acetylation and gene expression.

Short chain fatty acids induce TH gene expression via ERK-dependent phosphorylation of CREB protein

Butyrate modulates specific gene expression through various second-messenger signal transduction systems including activation of the PKA/cAMP pathway (Decastro, M., Nankova, B.B., Shah, P., Patel, P., Mally, P.V., Mishra, R., La Gamma, E.F., 2005. Short chain fatty acids regulate tyrosine hydroxylase gene expression through a cAMP-dependent signaling pathway, Brain Res. Mol. Brain Res. 142 28-38; Mally, P., Mishra, R., Gandhi, S., Decastro, M.H., Nankova, B.B., Lagamma, E.F., 2004. Stereospecific regulation of tyrosine hydroxylase and proenkephalin genes by short-chain fatty acids in rat PC12 cells, Pediatr. Res. 55 847-854). In the current report, we provide additional evidence that exposure to butyrate causes a rapid activation of the MAP kinase pathway, associated with increased phosphorylation of CREB. Under these conditions, no changes in relative amounts of CREB protein were observed by Western blot. Pre-treatment with the MAPK specific inhibitor (U0126) or the adenylate cyclase inhibitor dideoxyadenosine (ddA) abolished the butyrate-induced: (i) accumulation of TH mRNA, (ii) the phosphorylation of ERK1/2 as well as (iii) CREB phosphorylation. PC12 cells transfected with a TH promoter-luciferase reporter gene showed a robust induction in response to butyrate that was significantly reduced after co-transfection of either of two dominant-negative CREB expression vectors. Nuclear run-on assays demonstrated that butyrate increases endogenous TH gene transcription. We conclude that the initial steps of butyrate-induced gene activation are mediated through the CREB/CREB family of transcription factors which are coupled to both the MAP kinase and cAMP-dependent second messenger systems. Our data delineate a molecular mechanism through which short chain fatty acid's, their related drug-congeners (e.g., valproate) or even diet-derived butyrate (from fermentation of carbohydrates in the gut) can in principle, modulate brain catecholaminergic systems by modifying TH gene expression, dopaminergic levels and the corresponding animal behavior. These molecular relationships also offer a plausible explanation of how the well-recognized clinical effects of ketogenic diets can alter human behavior via the same central mechanisms.

Critical role of the c-JunNH2-terminal kinase and p38 mitogen-activated protein kinase pathways on sodium butyrate-induced apoptosis in DU145 human prostate cancer cells

Sodium butyrate (NaBu) is known to exhibit anti-cancer effects via the differentiation and apoptosis of various carcinoma cells. However, the mechanism by which NaBu induces apoptosis and the involvement of protein kinases during apoptosis is not completely understood. To investigate the underlying pathways, we performed cell culture experiments in androgen-independent human prostate cancer (DU145 cells) focusing on various protein kinases. NaBu causes concentration-dependent cell detachment and growth inhibition. Exposure of DU145 cells to NaBu for 24 h caused a strong apoptotic effect with 26% nuclear fragmentation and condensation. In addition, NaBu induced caspase-3 and poly-ADP ribose polymerase cleavage and up-regulation of bax, suggesting that mitochondrial damage is involved in NaBu-induced caspase-dependent apoptosis. Interestingly, NaBu stimulated p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK) activation, but not extracellular signal-regulated kinase 1/2 activation during apoptosis. Furthermore, NaBu up-regulated total protein levels and phospho forms of MAPK kinase 3 (MKK3) and MAPK kinase 4 (MKK4) as the upstream kinases of p38 MAPK and JNK independently of oxidative stress. Taken together, it is suggested that NaBu can be a promising chemopreventive agent for prostate cancer and the p38 MAPK and JNK pathways have critical roles in NaBu-induced apoptosis in DU145 cells.

Parthenolide sensitizes ultraviolet (UV)-B-induced apoptosis via protein kinase C-dependent pathways

Parthenolide (PN) is the principal sesquiterpene lactone in feverfew (Tanacetum parthenium) with proven anti-inflammatory properties. We have previously reported that PN possesses strong anticancer activity in ultraviolet B (UVB)-induced skin cancer in SKH-1 hairless mice. In order to further understand the mechanism(s) involved in the anticancer activity of PN, we investigated the role of protein kinase C (PKC) in the sensitization activity of PN on UVB-induced apoptosis. Several subtypes of PKC have been reported to be involved in UVB-induced signaling cascade with both pro- and anti-apoptotic activities. Here we focused on two isoforms of PKC: novel PKCdelta and atypical PKCzeta. In JB6 murine epidermal cells, UVB induces the membrane translocations of both PKCs, and PN pre-treatment enhances the membrane translocation of PKCdelta, but inhibits the translocation of PKCzeta. Similar results were also detected when the activities of these PKCs were tested with the PKC kinase assay. Moreover, pre-treatment with a specific PKCdelta inhibitor, rotterlin, completely diminishes the sensitization effect of PN on UVB-induced apoptosis. When cells were transiently transfected with dominant negative PKCdelta or wild-type PKCzeta, the sensitization effect of PN on UVB-induced apoptosis was also drastically reduced. Further mechanistic study revealed that PKCzeta, but not PKCdelta, is required for UVB-induced p38 MAPK activation and PN is likely to act through PKCzeta to suppress p38 activation in UVB-treated JB6 cells. In conclusion, we demonstrated that PN sensitizes UVB-induced apoptosis via PKC-dependent pathways.

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.

Contribution of disruption of the nuclear factor-kappaB pathway to induction of apoptosis in human leukemia cells by histone deacetylase inhibitors and flavopiridol

Interactions between the cyclin-dependent kinase inhibitor flavopiridol and the histone deacetylase inhibitors (HDACIs) sodium butyrate (NaB) and suberoylanilide hydroxamic acid (SAHA) have been examined in human leukemia cells in relation to effects on nuclear factor kappaB (NF-kappaB) activation. Exposure (24 h) of U937 human leukemia cells to NaB (1 mM) or SAHA (1.5 microM) resulted in a marked increase in NF-kappaB DNA binding, effects that were essentially abrogated by coadministration of flavopiridol (100 nM). These events were accompanied by a marked increase in mitochondrial injury, caspase activation, and apoptosis. Mutant cells expressing an IkappaBalpha super-repressor exhibited impairment of NF-kappaB DNA binding in response to HDACIs and a significant although modest increase in apoptosis. However, disruption of the NF-kappaB pathway also increased mitochondrial injury and caspase activation in response to flavopiridol and to an even greater extent to the combination of flavopiridol and HDACIs. Coadministration of flavopiridol with HDACIs down-regulated the X-linked inhibitor of apoptosis (XIAP), Mcl-1, and p21CIP1/WAF1 and activated c-Jun NH2-terminal kinase; moreover, these effects were considerably more pronounced in IkappaBalpha mutants. Similar responses were observed in U937 mutant cells stably expressing RelA/p65 small interfering RNA. In all cases, flavopiridol was significantly more potent than genetic interruption of the NF-kappaB cascade in promoting HDACI-mediated lethality. Together, these findings are consistent with the notion that although inhibition of NF-kappaB activation by flavopiridol contributes to antileukemic interactions with HDACIs, other NF-kappaB-independent flavopiridol actions (e.g., down-regulation of Mcl-1, XIAP, and p21CIP1/WAF1) play particularly critical roles in this phenomenon.

Expression of p21(WAF1/Cip1) through Sp1 sites by histone deacetylase inhibitor apicidin requires PI 3-kinase-PKC epsilon signaling pathway

We previously reported that the activation of p21(WAF1/Cip1) transcription by histone deacetylase inhibitor apicidin was mediated through Sp1 sites and pointed to the possible participation of protein kinase C (PKC). In this study, we investigated the role and identity of the specific isoforms of PKC involved and identified phosphatidylinositol 3-kinase (PI 3-kinase) as an upstream effector in HeLa cells. Using an isoform-specific pharmacological inhibitor of PKC, a PKC epsilon dominant-negative mutant, and antisense oligonucleotide to inhibit PKC epsilon specifically, we found that among PKC isoforms, PKC epsilon was required for the p21(WAF1/Cip1) expression by apicidin. In addition to PKC epsilon, PI 3-kinase appeared to participate in the activation of p21(WAF1/Cip1) promoter by apicidin, since inactivation of PI 3-kinase either by transient expression of dominant-negative mutant of PI 3-kinase or its specific inhibitors, LY294002 and wortmannin, attenuated the activation of p21(WAF1/Cip1) promoter and p21(WAF1/Cip1) protein expression by apicidin. Furthermore, membrane translocation of PKC epsilon in response to apicidin was blocked by the PI 3-kinase inhibitor, indicating the role of PI 3-kinase as an upstream molecule of PKC epsilon in the p21(WAF1/Cip1) promoter activation by apicidin. However, the p21(WAF1/Cip1) expression by apicidin appeared to be independent of the histone hyperacetylation, since apicidin-induced histone hyperacetylation of p21(WAF1/Cip1) promoter region was not affected by inhibition of PI 3-kinase and PKC, suggesting that the chromatin remodeling through the histone hyperacetylation alone might not be sufficient for the expression of p21(WAF1/Cip1) by apicidin. Taken together, these results suggest that the PI 3-kinase-PKC epsilon signaling pathway plays a pivotal role in the expression of the p21(WAF1/Cip1) by apicidin.

p300/CBP-associated factor (P/CAF) interacts with nuclear respiratory factor-1 to regulate the UDP-N-acetyl-alpha-d-galactosamine: polypeptide N-acetylgalactosaminyltransferase-3 gene

We demonstrated recently that expression of the UDP- N -acetyl-alpha-D-galactosamine: polypeptide N -acetylgalactosaminyltrans-ferase-3 (GalNAc-T3) gene is restricted to epithelial glands [Nomoto, Izumi, Ise, Kato, Takano, Nagatani, Shibao, Ohta, Imamura, Kuwano, Matsuo, Yamada, Itoh and Kohno (1999) Cancer Res. 59, 6214-6222]. In the present study, we show that sodium butyrate treatment of human breast cancer MCF-7 cells transcriptionally activates the GalNAc-T3 gene. Transient transfection of plasmids containing a reporter gene under the control of GalNAc-T3 indicated that several transcriptional elements are involved in response to sodium butyrate, with the nuclear respiratory factor-1 (NRF-1)-binding motif located between -88 and -77nt being the most important. Incubation of a labelled probe encompassing the NRF-1-binding motif with a nuclear extract of sodium butyrate-treated MCF-7 cells yielded a higher level of specific DNA-protein complex versus controls. Flag-tagged NRF-1 expressed in MCF-7 cells can bind to the NRF-1-binding motif of the GalNAc-T3 promoter. Nuclear content of NRF-1 remained constant in MCF-7 cells treated with or without sodium butyrate. Moreover, NRF-1 interacts with and is acetylated by p300/CBP-associated factor (P/CAF). Acetylation of NRF-1 enhances DNA binding. Co-transfection of the GalNAc-T3 reporter plasmid with either NRF-1 or P/CAF expression plasmid resulted in the activation of the GalNAc-T3 promoter. These results indicate a correlation between acetylation of NRF-1 by P/CAF and the butyrate-induced expression of the GalNAc-T3 gene. Additionally, induced expression of P/CAF may be a component of the adenocarcinoma differentiation process.

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.

Butyric acid increases invasiveness of HL-60 leukemia cells: role of reactive oxygen species

Butyric acid (BA) induces differentiation of human leukemia, including HL-60 cells. By using a fluorescent probe, we showed that reactive oxygen species (ROS) were generated in BA-treated cells. BA-induced differentiation was accompanied with an increased secretion of pro-matrix metalloproteinase (MMP)-9. Both phenomena were inhibited by antioxidants. Tissue inhibitors of MMP (TIMP)-1 and -2 secretion were increased by BA, but differently affected by antioxidants. By contrast, BA did not affect MMP-9 mRNA, and decreased TIMP-1 and TIMP-2 mRNA levels. In addition, migratory and invasive properties of HL-60 cells were enhanced by BA, but differently affected by antioxidants. Altogether, these results indicate that ROS are messengers of BA-induced differentiation and increased invasiveness.

Activation of p21(WAF1/Cip1) transcription through Sp1 sites by histone deacetylase inhibitor apicidin: involvement of protein kinase C

We previously reported that apicidin, a novel histone deacetylase inhibitor, inhibited the proliferation of tumor cells via induction of p21(WAF1/Cip1). In this study, we determined the molecular mechanisms by which apicidin induced the p21(WAF1/Cip1) gene expression in HeLa cells. Apicidin induced p21(WAF1/Cip1) mRNA independent of the de novo protein synthesis and activated the p21(WAF1/Cip1) promoter through Sp1-3 site located at -82 and -77 relative to the transcription start site. This transcriptional activation appears to be mediated by protein kinase C (PKC), because calphostin C, a PKC inhibitor, significantly attenuated the activation of p21(WAF1/Cip1) promoter via Sp1 sites, which was accompanied by a marked suppression of p21(WAF1/Cip1) mRNA and protein expression induced by apicidin. Consistent with the transcriptional activation of p21(WAF1/Cip1) promoter by apicidin, apicidin treatment led to the translocation of PKCepsilon from cytosolic to particulate fraction, which was reversed by pretreatment with calphostin C, indicating the involvement of PKC in the transcriptional activation of p21(WAF1/Cip1) via Sp1 sites by apicidin. However, the PKC-mediated transcriptional activation of p21(WAF1/Cip1) by apicidin appears to be independent of the histone hyperacetylation, because apicidin-induced histone hyperacetylation was not affected by calphostin C. Furthermore, a PKC activator, phorbol 12,13-dibutyrate, alone induced the transcriptional activation of p21(WAF1/Cip1) promoter, p21(WAF1/Cip1) mRNA, and protein expression without induction of the histone hyperacetylation, suggesting that the transcriptional activation of p21(WAF1/Cip1) by apicidin might have been mediated by a mechanism other than chromatin remodeling through the histone hyperacetylation. Taken together, these results suggest that the PKC signaling pathway plays a pivotal role in the transcriptional activation of the p21(WAF1/Cip1) gene by apicidin.

Multipathways for transdifferentiation of human prostate cancer cells into neuroendocrine-like phenotype

The neuroendocrine (NE) cell is a minor cell population in normal human prostate glands. The number of NE cells is increased in advanced hormone-refractory prostate carcinomas (PCA). The mechanism of increased NE cell population in these advanced tumors is poorly understood. We examined molecular mechanisms which may be involved in the regulation of the transdifferentiation process of human PCA cells leading to a NE phenotype. We compared PCA cell lines LNCaP and PC-3 in the following medium conditions: steroid-reduced (SR), interleukin-6 (IL-6)-supplemented, or dibutyrate cAMP (db-cAMP)-supplemented. We found that androgen-responsive C-33 LNCaP cells responded to all treatments, having a neuronal-like morphology. In contrast, C-81 LNCaP cells, having a decreased androgen responsiveness, had a less pronounced effect although followed a similar trend. Androgen-unresponsive PC-3 cells showed little change in their morphology. Grown in the SR condition, the level of neuron-specific enolase (NSE), a marker of neuronal cells, was upregulated in C-33 LNCaP cells, while to a lesser degree in the presence of IL-6. In the presence of db-cAMP, the NSE level in C-33 cells was decreased, lower than that in control cells. An opposite effect was observed for C-81 LNCaP cells. Nevertheless, the NSE level was only elevated in db-cAMP-treated PC-3 cells, but no change was found in PC-3 cells grown in the SR- or IL-6-supplemented medium. Thus, a similar gross phenotypic change may correlate with differential molecular expressions. We also analyzed the expression of protein tyrosine phosphatase alpha (RPTPalpha) since it plays a critical role in normal neuronal differentiation and signaling. Our results showed that the expression of RPTPalpha correlates with the NE phenotypic change of LNCaP cells in the SR condition. In summary, our data clearly show that the molecular process by which cultured human prostate cancer cells undergo a transdifferentiation process to a NE cell-like phenotype is accompanied by differential expressions of different markers, and a gross NE cell-like phenotype can occur by exposing PCA cells to different pharmacological agents.

Synergistic induction of apoptosis in human leukemia cells (U937) exposed to bryostatin 1 and the proteasome inhibitor lactacystin involves dysregulation of the PKC/MAPK cascade

Cotreatment with a minimally toxic concentration of the protein kinase C (PKC) activator (and down-regulator) bryostatin 1 (BRY) induced a marked increase in mitochondrial dysfunction and apoptosis in U937 monocytic leukemia cells exposed to the proteasome inhibitor lactacystin (LC). This effect was blocked by cycloheximide, but not by alpha-amanitin or actinomycin D. Qualitatively similar interactions were observed with other PKC activators (eg, phorbol 12-myristate 13-acetate and mezerein), but not phospholipase C, which does not down-regulate the enzyme. These events were examined in relationship to functional alterations in stress (eg, SAPK, JNK) and survival (eg, MAPK, ERK) signaling pathways. The observations that LC/BRY treatment failed to trigger JNK activation and that cell death was unaffected by a dominant-interfering form of c-JUN (TAM67) or by pretreatment with either curcumin or the p38/RK inhibitor, SB203580, suggested that the SAPK pathway was not involved in potentiation of apoptosis. In marked contrast, perturbations in the PKC/Raf/MAPK pathway played an integral role in LC/BRY-mediated cell death based on evidence that pretreatment of cells with bisindolylmaleimide I, a selective PKC inhibitor, or geldanamycin, a benzoquinone ansamycin, which destabilizes and depletes Raf-1, markedly suppressed apoptosis. Furthermore, ERK phosphorylation was substantially prolonged in LC/BRY-treated cells compared to those exposed to BRY alone, and pretreatment with the highly specific MEK inhibitors, PD98059, U0126, and SL327, opposed ERK activation while protecting cells from LC/BRY-induced lethality. Together, these findings suggest a role for activation and/or dysregulation of the PKC/MAPK cascade in modulation of leukemic cell apoptosis following exposure to the proteasome inhibitor LC. (Blood. 2001;97:2105-2114)

GTP-mediated differentiation of the human K562 cell line: transient overexpression of GATA-1 and stabilization of the gamma-globin mRNA

Induction of specific gene expression may provide an alternative or a support to conventional cytotoxic chemotherapy of cancer, as well as to therapy for sickle cell diseases. In this respect, pharmacological induction of expression of the endogenous gamma-globin gene is a realistic approach to therapy of beta-globin disorders. Erythroid differentiation and inhibition of proliferation of the human CML K562 cell line was induced by guanosine 5'-triphosphate (GTP). The hemoglobin production in cells was correlated to an increase in alpha- and gamma-globin mRNA expression. At the transcriptional level, we showed that both the expression of the major erythroid transcription factor GATA-1 (protein and mRNA) and its binding capacity to the gamma-globin gene promoter was transiently increased. Moreover, GTP moderately stimulated the gamma-globin gene promoter after 48 h of treatment. At the post-transcriptional level, GTP treatment led to a drastic increase of the gamma-globin mRNA half-life. This stabilizing effect of GTP was mediated via the 3'-untranslated region (3'-UTR) of the gamma-globin mRNA. In conclusion, mechanism of GTP-mediated differentiation of K562 cells is linked to an early activation of gamma-globin gene transcription followed by a stabilization of its mRNA.

Cyclic nucleotide analogs as biochemical tools and prospective drugs

Cyclic AMP (cAMP) and cyclic GMP (cGMP) are key second messengers involved in a multitude of cellular events. From the wealth of synthetic analogs of cAMP and cGMP, only a few have been explored with regard to their therapeutic potential. Some of the first-generation cyclic nucleotide analogs were promising enough to be tested as drugs, for instance N(6),O(2)'-dibutyryl-cAMP and 8-chloro-cAMP (currently in clinical Phase II trials as an anticancer agent). Moreover, 8-bromo and dibutyryl analogs of cAMP and cGMP have become standard tools for investigations of biochemical and physiological signal transduction pathways. The discovery of the Rp-diastereomers of adenosine 3',5'-cyclic monophosphorothioate and guanosine 3',5'-cyclic monophosphorothioate as competitive inhibitors of cAMP- and cGMP-dependent protein kinases, as well as subsequent development of related analogs, has proven very useful for studying the molecular basis of signal transduction. These analogs exhibit a higher membrane permeability, increased resistance against degradation, and improved target specificity. Furthermore, better understanding of signaling pathways and ligand/protein interactions has led to new therapeutic strategies. For instance, Rp-8-bromo-adenosine 3',5'-cyclic monophosphorothioate is employed against diseases of the immune system. This review will focus mainly on recent developments in cyclic nucleotide-related biochemical and pharmacological research, but also highlights some historical findings in the field.

Bile acids reduce the apoptosis-inducing effects of sodium butyrate on human colon adenoma (AA/C1) cells: implications for colon carcinogenesis

Butyrate is produced in the colon by fermentation of dietary fibre and induces apoptosis in colon adenoma and cancer cell lines, which may contribute to the protective effect of a high fibre diet against colorectal cancer (CRC). However, butyrate is present in the colon together with unconjugated bile acids, which are tumour promoters in the colon. We show here that bile acids deoxycholate (DCA) and chenodeoxycholate (CDCA), at levels present in the colon, gave a modest increase in cell proliferation and decreased spontaneous apoptosis in AA/C1 adenoma cells. Bile acids significantly inhibited the induction of apoptosis by butyrate in AA/C1 cells. However, the survival-inducing effects of bile acids on AA/C1 cells could be overcome by increasing the concentration of sodium butyrate. These results suggest that dysregulation of apoptosis in colonic epithelial cells by dietary factors is a key factor in the pathophysiology of CRC.

Protein kinase C-α isoform is involved in erythropoietin-induced erythroid differentiation of CD34+ progenitor cells from human bone marrow

Protein kinase C (PKC) is a family of serine/threonine protein kinases involved in many cellular responses. Although the analysis of PKC activity in many systems has provided crucial insights to its biologic function, the precise role of different isoforms on the differentiation of normal hematopoietic progenitor cells into the various lineages remains to be investigated. The authors have assessed the state of activation and protein expression of PKC isoforms after cytokine stimulation of CD34+ progenitor cells from human bone marrow. Freshly isolated CD34+ cells were found to express PKC-, PKC-β2, and PKC-ɛ, whereas PKC-δ, PKC-γ, and PKC-ζ were not detected. Treatment with erythropoietin (EPO) or with EPO and stem cell factor (SCF) induced a predominantly erythroid differentiation of CD34+ cells that was accompanied by the up-regulation of PKC- and PKC-β2 protein levels (11.8- and 2.5-fold, respectively) compared with cells cultured in medium. Stimulation with EPO also resulted in the nuclear translocation of PKC- and PKC-β2 isoforms. Notably, none of the PKC isoforms tested were detectable in CD34+ cells induced to myeloid differentiation by G-CSF and SCF stimulation. The PKC inhibitors staurosporine and calphostin C prevented EPO-induced erythroid differentiation. Down-regulation of the PKC-, PKC-β2, and PKC-ɛ expression by TPA pretreatment, or the down-regulation of PKC- with a specific ribozyme, also inhibited the EPO-induced erythroid differentiation of CD34+ cells. No effect was seen with PKC-β2–specific ribozymes. Taken together, these findings point to a novel role for the PKC- isoform in mediating EPO-induced erythroid differentiation of the CD34+ progenitor cells from human bone marrow.

PBA increases CFTR expression but at high doses inhibits Cl(-) secretion in Calu-3 airway epithelial cells

Sodium 4-phenylbutyrate (PBA), a short-chain fatty acid, has been approved to treat patients with urea cycle enzyme deficiencies and is being evaluated in the management of sickle cell disease, thalassemia, cancer, and cystic fibrosis (CF). Because relatively little is known about the effects of PBA on the expression and function of the wild-type CF transmembrane conductance regulator (wt CFTR), the goal of this study was to examine the effects of PBA and related compounds on wt CFTR-mediated Cl(-) secretion. To this end, we studied Calu-3 cells, a human airway cell line that expresses endogenous wt CFTR and has a serous cell phenotype. We report that chronic treatment of Calu-3 cells with a high concentration (5 mM) of PBA, sodium butyrate, or sodium valproate but not of sodium acetate reduced basal and 8-(4-chlorophenylthio)-cAMP-stimulated Cl(-) secretion. Paradoxically, PBA enhanced CFTR protein expression 6- to 10-fold and increased the intensity of CFTR staining in the apical plasma membrane. PBA also increased protein expression of Na(+)-K(+)-ATPase. PBA reduced CFTR Cl(-) currents across the apical membrane but had no effect on Na(+)-K(+)-ATPase activity in the basolateral membrane. Thus a high concentration of PBA (5 mM) reduces Cl(-) secretion by inhibiting CFTR Cl(-) currents across the apical membrane. In contrast, lower therapeutic concentrations of PBA (0.05-2 mM) had no effect on cAMP-stimulated Cl(-) secretion across Calu-3 cells. We conclude that PBA concentrations in the therapeutic range are unlikely to have a negative effect on Cl(-) secretion. However, concentrations >5 mM might reduce transepithelial Cl(-) secretion by serous cells in submucosal glands in individuals expressing wt CFTR.

Macrophage Colony-Stimulating Factor Induces the Expression of Mitogen-Activated Protein Kinase Phosphatase-1 Through a Protein Kinase C-Dependent Pathway

M-CSF triggers the activation of extracellular signal-regulated protein kinases (ERK)-1/2. We show that inhibition of this pathway leads to the arrest of bone marrow macrophages at the G0/G1 phase of the cell cycle without inducing apoptosis. M-CSF induces the transient expression of mitogen-activated protein kinase phosphatase-1 (MKP-1), which correlates with the inactivation of ERK-1/2. Because the time course of ERK activation must be finely controlled to induce cell proliferation, we studied the mechanisms involved in the induction of MKP-1 by M-CSF. Activation of ERK-1/2 is not required for this event. Therefore, M-CSF activates ERK-1/2 and induces MKP-1 expression through different pathways. The use of two protein kinase C (PKC) inhibitors (GF109203X and calphostin C) revealed that M-CSF induces MKP-1 expression through a PKC-dependent pathway. We analyzed the expression of different PKC isoforms in bone marrow macrophages, and we only detected PKCβI, PKCε, and PKCζ. PKCζ is not inhibited by GF109203X/calphostin C. Of the other two isoforms, PKCε is the best candidate to mediate MKP-1 induction. Prolonged exposure to PMA slightly inhibits MKP-1 expression in response to M-CSF. In bone marrow macrophages, this treatment leads to a complete depletion of PKCβI, but only a partial down-regulation of PKCε. Moreover, no translocation of PKCβI or PKCζ from the cytosol to particulate fractions was detected in response to M-CSF, whereas PKCε was constitutively present at the membrane and underwent significant activation in M-CSF-stimulated macrophages. In conclusion, we remark the role of PKC, probably isoform ε, in the negative control of ERK-1/2 through the induction of their specific phosphatase.

Evidence of the role of protein kinase C during aclacinomycin induction of erythroid differentiation in K562 cells

At subtoxic concentrations, aclacinomycin is effective in controlling erythroid differentiation of K562, a human erythroleukemic cell line. To better understand early events implicated in this process, we have used bisindolylmaleimide (GF109203X), an inhibitor with a high selectivity for protein kinase C (PKC). Our data show that GF109203X inhibits aclacinomycin effects on K562, evidenced by a strong reduction of hemoglobinized cells and a marked decrease of mRNA rates of erythroid genes. To establish firmly PKC involvement, we also verified that aclacinomycin stimulates its rapid translocation, from the cytosolic to the membrane compartment. By Western blot analysis, we also show that after short induction times, PKCalpha was the most implicated.

The subcellular distribution of protein kinase Calpha, -epsilon, and -zeta isoforms during cardiac cell differentiation

There is little information on the molecular events that control the subcellular distribution of protein kinase C during cardiac cell differentiation. We examined protein kinase C activity and the subcellular distribution of representatives of the "classical," "novel," and "atypical" protein kinase C's in P19 murine teratoma cells induced to undergo differentiation into cardiac myocytes by the addition of dimethylsulfoxide to the medium (Grepin et al., Development 124, 2387-2395, 1997). Differentiation was assessed by the presence of striated myosin, a morphological marker for cardiac cells. Addition of dimethyl sulfoxide to the medium resulted in the appearance of striated myosin by 10 days postincubation. Immunolocalization and Western blot studies revealed that a significant proportion of protein kinase Calpha, -epsilon, and -zeta were associated with the particulate fraction in P19 cells prior to differentiation. Differentiation into cardiac cells resulted in a translocation of protein kinase C activity from the particulate fraction to cytosol and localization of most of protein kinase Calpha, -epsilon, and -zeta to the cytoplasmic compartment. The total cellular protein kinase C activity was unaltered during differentiation. The translocation of protein kinase C activity during differentiation of P19 cells into cardiac myocytes was associated with a decrease in the levels of cellular 1, 2-diacyl-sn-glycerol. The cellular levels of phosphatidylserine and phosphatidylinositol did not change during differentiation. Addition of 1,2-dioctanoyl-sn-glycerol, a cell-permeant 1, 2-diacyl-sn-glycerol analog, reversed the differentiation-induced switch in the relative distribution of protein kinase C activity and dramatically increased the association of protein kinase Calpha with the particulate fraction. Addition of 1,2-dioctanoyl-sn-glycerol did not reverse the pattern of distribution for protein kinase Cepsilon or -zeta. The results indicate that protein kinase C activity and protein kinase Calpha, -epsilon and -zeta isoforms are redistributed from the particulate to the cytosolic fraction during differentiation of P19 cells into cardiomyocytes. The mechanism for the redistribution of protein kinase Calpha may be related to the reduction in the cellular 1,2-diacyl-sn-glycerol levels that accompany differentiation.

Requirement of GATA-1 and p45 NF-E2 expression in butyric acid-induced erythroid differentiation

Butyric acid (BA) is known to induce overexpression of fetal hemoglobin and then erythroid differentiation. Therefore, BA is currently under clinical investigation as a potential therapy for the treatment of sickle cell disease and cancer. Nevertheless, the molecular mechanisms involved in BA-induced differentiation remain largely unknown. Previous reports have shown that BA-induced overexpression of erythroid genes occurred at the transcriptional level, suggesting the involvement of erythroid transcription factors. Here, we intend to demonstrate the requirement of GATA-1 and NF-E2 transcription factors in the BA-induced erythroid differentiation of human leukemic K562 cells. Time-course experiments showed that nuclear levels of GATA-1 and p45 NF-E2 proteins increased during BA treatment. Moreover, antisense oligodeoxynucleotides targeting either GATA-1 or p45 NF-E2 proteins inhibited both protein expression and BA-induced differentiation. In contrast, BA-induced cell growth inhibition was not affected. These results provide the first direct evidence for the requirement of GATA-1 and NF-E2 in BA-induced differentiation process.