Induction of bcl-2 expression by phosphorylated CREB proteins during B-cell activation and rescue from apoptosis

Antidepressant properties of the 5-HT4 receptor partial agonist, SL65.0155: behavioral and neurochemical studies in rats

This study was undertaken to investigate the potential antidepressant-like properties of SL65.0155, a serotonin 5-HT(4) receptor partial agonist, in male rats of the Wistar strain tested in the forced swim test (FST), an experimental model widely used to assess antidepressant-like activity. The expression of hippocampal neurotrophic factors, such as the brain-derived neurotrophic factor (BDNF), the phosphorilated cAMP response element-binding protein (p-CREB), the B cell lymphoma-2 (Bcl-2), the Bax and the vascular endothelium growth factor (VEGF) were also evaluated by Western Blot analysis. Different groups of rats received intraperitoneally (i.p.) injections of SL65.0155 (0.1, 0.5 and 1 mg/kg), clomipramine (50 mg/kg), citalopram (15 mg/kg) or vehicle, respectively, 24, 5 and 1 h prior to the FST. Compared to the control group, SL65.0155 (0.5 and 1 mg/kg), clomipramine or citalopram injected animals showed an increased swimming and climbing behavior and reduced immobility time in the FST. Interestingly, this effect was not due to changes in the locomotor activity since all treated groups failed to show any change in motor ability as assessed in the open field test. Western blot analysis of hippocampal homogenates showed an enhancement of p-CREB, BDNF Bcl-2 and VEGF protein levels in SL65.0155 treated groups, but not in citalopram or clomipramine treated groups, used here as positive control. No change was found in Bax expression in any treated group. These findings give further support to the hypothesis that the stimulation of serotonin 5-HT(4) receptors may be a therapeutic target for depression.

Induction of Akt activity by chemotherapy confers acquired resistance

Resistance to chemotherapy is a major cause of treatment failure in human cancer. Accumulating evidence has indicated that the acquisition of resistance to chemotherapeutic drugs involves the activation of the PI3K/Akt pathway. Modulating Akt activity in response to chemotherapy has been observed often in chemoresistant cancers. The potential molecular mechanisms by which chemotherapeutic agents activate the PI3K/Akt pathway are emerging. Activation of this pathway evades the cytotoxic effects of chemotherapeutic agents via regulation of essential cellular functions such as protein synthesis, antiapoptosis, survival and proliferation in cancer. How chemotherapeutic agents induce Akt activation and how activated Akt confers chemoresistance through regulation of signaling networks are discussed in this review. Combining PI3K/Akt inhibitors with standard chemotherapy has been successful in increasing the efficacy of chemotherapeutic agents both in vivo and in vitro. Several small molecules have been developed to specifically target PI3K/Akt and other components of this pathway, which in combination with chemotherapy may be a valid approach to overcome therapeutic resistance. We propose several feedback and feedforward regulatory mechanisms of signaling networks for maintenance of the Akt activity for cell survival. These regulatory mechanisms may limit the efficacy of PI3K/Akt-targeted therapy; therefore, disruption of these mechanisms may be an effective strategy for development of novel anti-cancer therapies.

(S)-1-(alpha-naphthylmethyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (CKD712) reduces rat myocardial apoptosis against ischemia and reperfusion injury by activation of phosphatidylinositol 3-kinase/Akt signaling and anti-inflammatory action in vivo

We examined our hypothesis that (S)-1-(alpha-naphthylmethyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (CKD712) inhibits apoptosis in myocardial ischemia and reperfusion (I/R) injury in vivo via activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and by reducing inflammation during I/R. To do this, we induced a 30-min period of ischemia by occlusion of the left anterior descending coronary artery of the rat followed by a 2-h (for phosphorylation of Akt), 6-h (for biochemical analysis), or 24-h (for functional analysis) period of reperfusion to determine the effect of CKD712 treatment. Pretreatment with CKD712 significantly improved myocardial function as evidenced by an increase in the +/-dP/dt and a decrease in the infarct size, which were antagonized by a PI3K inhibitor, wortmannin (WT). Interestingly, CKD712 increased the phosphorylation of Akt and cAMP-response element-binding protein and increased the expression of the Bcl-2 gene, but it reduced the expression of the Bax gene. CKD712 decreased not only the expression but also the activity of the caspase-3 protein in the myocardium after reperfusion. Thus, all of the antiapoptotic effects of CKD712 were significantly inhibited by WT. Furthermore, the antiapoptotic effects of CKD712 and its inhibition by WT in myocardium after reperfusion were confirmed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining. Finally, CKD712 was found to reduce the serum levels of the high-mobility group box 1 protein, tumor necrosis factor-alpha, and the cardiac troponin I protein in addition to tissue levels of malondialdehyde and myeloperoxidase activity in I/R hearts. Taken together, both the activation of PI3K/Akt and its anti-inflammatory action prevent apoptosis in myocardial I/R injury by CKD712.

Desipramine prevents stress-induced changes in depressive-like behavior and hippocampal markers of neuroprotection

Extracellular signal-regulated kinases (ERKs) are widely implicated in multiple physiological processes. Although ERK1/2 has been proposed as a common mediator of antidepressant action in naive rodents, it remains to be determined whether the ERK1/2 pathway plays a role in depressive disorder. Here, we investigated whether chronic restraint stress (14 days) and antidepressant treatment [desipramine (DMI), 10 mg/kg intraperitoneally] induce changes in animal behavior and hippocampal levels of phospho-ERK1/2 and its substrate phospho-cAMP response element-binding protein (CREB). The results indicated that stress-induced depressive-like behaviors were correlated with an increase in P-ERK1/2 and P-CREB in the hippocampus evaluated by immunoblot analysis. As an indication of CREB activity, we evaluated changes in mRNA levels of its target genes. Brain-derived neurotrophic factor (BDNF) mRNA was reduced by stress, an effect prevented by DMI only in the CA3 area of hippocampus. Bcl-2 mRNA was reduced in all hippocampal regions by stress, an effect independent of DMI treatment. However, immunoblot from hippocampal extracts revealed that stress increased BCL-2 levels, an effect prevented by chronic DMI. These results suggest that ERKs and BDNF may be altered in depressive disorder, modifications that are sensitive to DMI action. In contrast, the stress-induced increase in BCL-2 may correspond to a neuroprotective response.

CREB, a possible upstream regulator of Bcl-2 in trichosanthin-induced HeLa cell apoptosis

Our previous reports indicated that cyclic AMP response element-binding (CREB) protein was involved in the regulation of Bcl-2 expression in apoptotic HeLa cells induced by trichosanthin (TCS). Here we presented that blockade the binding site of CREB to Bcl-2 by a CRE decoy oligonucleotide abrogated the TCS-decreased Bcl-2 expression. Furthermore, overexpression of phosphorylated CREB (p-CREB) in cells transfected with p-CREB/GFP fusion construct resulted in an increase of Bcl-2 protein content, however, this increase was attenuated by TCS treatment. Therefore, this data supports the hypothesis that CREB is a possible upstream regulator of Bcl-2 in apoptotic HeLa cells induced by TCS. The study provides new insights into understanding the mechanism of TCS in the treatment of cervical cancer.

Estradiol rescues neurons from global ischemia-induced cell death: multiple cellular pathways of neuroprotection

The potential neuroprotective role of sex hormones in chronic neurodegenerative disorders and acute brain ischemia following cardiac arrest and stroke is of a great therapeutic interest. Long-term pretreatment with estradiol and other estrogens affords robust neuroprotection in male and female rodents subjected to focal and global ischemia. However, the receptors (e.g., cell surface or nuclear), intracellular signaling pathways and networks of estrogen-regulated genes that intervene in neuronal apoptosis are as yet unclear. We have shown that estradiol administered at physiological levels for two weeks before ischemia rescues neurons destined to die in the hippocampal CA1 and ameliorates ischemia-induced cognitive deficits in ovariectomized female rats. This regimen of estradiol treatment involves classical intracellular estrogen receptors, transactivation of IGF-1 receptors and stimulation of the ERK/MAPK signaling pathway, which in turn maintains CREB activity in the ischemic CA1. We also find that a single, acute injection of estradiol administrated into the brain ventricle immediately after an ischemic event reduces both neuronal death and cognitive deficits. Because these findings suggest that hormones could be used to treat patients when given after brain ischemia, it is critical to determine whether the same or different pathways mediate this form of neuroprotection. We find that an agonist of the membrane estrogen receptor GPR30 mimics short latency estradiol facilitation of synaptic transmission in the hippocampus. Therefore, we are testing the hypothesis that GPR30 may act together with intracellular estrogen receptors to activate cell signaling pathways to promote neuron survival after global ischemia.

Transcriptional down-regulation of Bcl-2 by vinorelbine: identification of a novel binding site of p53 on Bcl-2 promoter

The Bcl-2 family contains a panel of proteins which are conserved regulators of apoptosis in mammalian cells, like the anti-apoptotic protein Bcl-2. According to its significant role in altering susceptibility to apoptosis, the deciphering of the mechanism of Bcl-2 expression modulation may be crucial for identifying therapeutics strategies for cancer. Treatment with microtubule-targeting agents, including taxanes and Vinca alkaloids, generally leads to a decrease in Bcl-2 intracellular amounts. Whereas the interest for these chemotherapeutics is accompanied by advances in the fundamental understanding of their anticancer properties, the molecular mechanism underlying changes in Bcl2 expression remains poorly understood. We report here that p53 contributes to vinorelbine-induced Bcl-2 down-regulation. Indeed, the decrease in Bcl-2 protein levels observed during vinorelbine-induced apoptosis was correlated to the decrease in mRNA levels, as a result of the inhibition of Bcl-2 transcription and promoter activity. In this context, we evaluated p53 contribution in the Bcl-2 transcriptional down-regulation. We identified, by chromatin immunoprecipitation, a novel p53 binding site in the Bcl-2 promoter, within a region upstream P(1) promoter. We showed that vinorelbine treatment increased this interaction in A549 cells. This work strengthens the links between p53 and Bcl-2 at a transcriptional level, upon microtubule-targeting agent treatment. Our study also provides answers that will be useful to assess microtubule-targeting agents' mechanism of action and that may help to better understand and increase their effectiveness.

VIP down-regulates the inflammatory potential and promotes survival of dying (neural crest-derived) corneal endothelial cells ex vivo: necrosis to apoptosis switch and up-regulation of Bcl-2 and N-cadherin

The neuropeptide vasoactive intestinal peptide (VIP) is anti-inflammatory and protective in the immune and nervous systems, respectively. This study demonstrated in corneal endothelial (CE) cells injured by severe oxidative stress (1.4 mM H(2)O(2)) in bovine corneal organ cultures that VIP pre-treatment (0, 10(-10), 10(-8), and 10(-6) M; 15 min), in a VIP concentration-dependent manner, switched the inflammation-causing necrosis to inflammation-neutral apoptosis (showing annexin V-binding, chromatin condensation, and DNA fragmentation) and upheld ATP levels in a VIP antagonist (SN)VIPhyb-sensitive manner, while up-regulated mRNA levels of the anti-apoptotic Bcl-2 and the differentiation marker N-cadherin in a kinase A inhibitor-sensitive manner. As a result, VIP, in a concentration-dependent and VIP antagonist-sensitive manners, promoted long-term CE cell survival. ATP levels, a determining factor in the choice of apoptosis versus necrosis, measured after VIP pre-treatment and 0.5 min post-H(2)O(2) were 39.6 +/- 3.3, 50.8 +/- 6.2, 60.1 +/- 4.8, and 53.6 +/- 5.3 pmoles/microg protein (mean +/- SEM), respectively (p < 0.05, anova). VIP treatment alone concentration-dependently increased levels of N-cadherin (Koh et al. 2008), the phosphorylated cAMP-responsive-element binding protein and Bcl-2, while 10(-8) M VIP, in a VIP antagonist (SN)VIPhyb-sensitive manner, increased ATP level by 38% (p < 0.02) and decreased glycogen level by 32% (p < 0.02). VPAC1 (not VPAC2) receptor was expressed in CE cells. Thus, CE cell VIP/VPAC1 signaling is both anti-inflammatory and protective in the corneal endothelium.

Transforming growth factor-beta1 causes pulmonary microvascular endothelial cell apoptosis via ALK5

We have previously shown that transforming growth factor (TGF)-beta1 protected against main pulmonary artery endothelial cell (PAEC) apoptosis induced by serum deprivation and VEGF receptor blockade through a mechanism associated with ALK5-mediated Bcl-2 upregulation. In the current study, we investigated the effect of TGF-beta1 on pulmonary microvascular endothelial cell (PMVEC) apoptosis. We found that, in contrast to the results seen in conduit PAEC, TGF-beta1 caused apoptosis of PMVEC, an effect that was also dependent on ALK5 activity. We noted that non-SMAD signaling pathways did not play a role in TGF-beta1-induced apoptosis. Both SMAD2 and SMAD1/5 were activated upon exposure to TGF-beta1. TGF-beta1-induced activation of SMAD2, but not SMAD1/5, was abolished by ALK5 inhibition, an effect that associated with prevention of TGF-beta1-induced apoptosis. These results suggest that SMAD2 is important in TGF-beta1-induced apoptosis of PMVEC. While caspase-12 activity was not altered, caspase-8 was activated by TGF-beta1, an effect that correlated with a reduction of cFLIP protein levels. Additionally, TGF-beta1 decreased Bcl-2 protein levels and induced cytochrome c cytosolic redistribution. These results suggest that TGF-beta1 caused apoptosis of PMVEC likely through both caspase-8-dependent extrinsic pathway and mitochondria-mediated intrinsic pathway. We noted that inhibition of ALK5 attenuated serum deprivation-induced apoptosis, an effect that correlated with increased expression and activation of CREB and its potential target genes, Bcl-2 and cFLIP. These results suggest that CREB may be important in mediating apoptosis resistance of PMVEC upon ALK5 inhibition perhaps through upregulation of Bcl-2 and cFLIP. Finally, we noted that SMAD1/5 were activated upon ALK5 inhibition in the presence of low levels of TGF-beta1, an effect associated with enhanced endothelial proliferation. We speculate that imbalance of ALK1 and ALK5 may contribute to the development of pulmonary artery hypertension.

Evidence for involvement of ERK, PI3K, and RSK in induction of Bcl-2 by valproate

Valproate, an anticonvulsant and mood stabilizer, up-regulates Bcl-2, a neurotrophic/neuroprotective protein. In this study, we investigated the molecular mechanism through which Bcl-2 is up-regulated by valproate using cultured human neuron-like cells. Valproate, within therapeutically relevant ranges, induced time- and concentration-dependent up-regulations of both Bcl-2 messenger RNA and protein implicating an underlying gene transcriptional-mediated mechanism. Bcl-2 up-regulations were associated with ERK1/2 and PI3K pathway activations and elevated levels of activated phospho-RSK and phospho-CREB, convergent targets of the ERK1/2 and PI3K pathways. Valproate increased transcriptional activity of a human bcl-2 promoter-reporter gene construct. This effect was attenuated, but not blocked, by mutation of a CREB DNA binding site, a CRE site in the human bcl-2 promoter sequence. ERK and/or PI3K pathway inhibitors and RSK1 small hairpin RNA knockdown reduced, but did not abolish, baseline and valproate-induced promoter activities and lowered Bcl-2 protein levels. These data collectively suggest that valproate induces Bcl-2 regulation partially through activations of the ERK and PI3K cascades and their convergent kinase, RSK, although other unknown mechanism(s) are likely involved. Given the known roles of Bcl-2 in the central nervous system, the current findings offer a partial yet complex molecular mechanistic explanation for the known neurobiological effects of valproate including neurite growth, neuronal survival, and neurogenesis.

Functional long-range interactions of the IgH 3' enhancers with the bcl-2 promoter region in t(14;18) lymphoma cells

To better understand the mechanisms underlying the role of the immunoglobulin heavy-chain gene (IgH) 3' enhancers on bcl-2 transcriptional deregulation in t(14;18) lymphoma, we characterized the physical interactions of the IgH 3' enhancer region with the bcl-2 promoters. Using the chromosome conformation capture technique, we found that the IgH 3' enhancers physically interact with the bcl-2 promoter region over a 350 kb genomic region in t(14;18) lymphoma cells. No interactions of the bcl-2 promoter region with sequences distant to the IgH enhancers were observed. The physical interactions of the IgH enhancers with the bcl-2 5' region are functionally involved in the transcriptional control of bcl-2. The histone deacetylase inhibitor, trichostatin A, repressed bcl-2 transcription and decreased the IgH enhancer-bcl-2 promoter region interactions. We showed by chromatin immunoprecipitation assay and small interference RNA transfection studies that the POU2 family transcription factor Oct-2 and its cofactor Bob-1 have an important function in mediating the IgH enhancer-bcl-2 promoter region interactions. This study reveals a new aspect of the regulatory role of the IgH 3' enhancers on bcl-2 transcription in t(14;18) lymphomas.

Hypercholesterolemia-induced Abeta accumulation in rabbit brain is associated with alteration in IGF-1 signaling

Hypercholesterolemia increases levels of beta-amyloid (Abeta), a peptide that accumulates in Alzheimer's disease brains. Because cholesterol in the blood does not cross the blood brain barrier (BBB), the link between circulating cholesterol and Abeta accumulation is not understood. In contrast to cholesterol, the oxidized cholesterol metabolite 27-hydroxycholesterol can cross the BBB, potentially increasing Abeta levels. However, the mechanisms by which cholesterol or 27-hydroxycholesterol regulate Abeta levels are not known. The insulin-like growth factor-1 (IGF-1) regulates the glycogen-synthase kinase-3alpha (GSK-3alpha) and the insulin degrading enzyme (IDE). While GSK-3alpha increases Abeta production, IDE is a major Abeta-degrading enzyme. We report here that feeding rabbits with a cholesterol-enriched diet increases Abeta levels in the hippocampus, an effect that is associated with reduced IGF-1 levels. 27-hydroxycholesterol also increases Abeta and reduces IGF-1 levels in organotypic hippocampal slices from adult rabbits. We suggest that hypercholesterolemia-induced Abeta accumulation may be mediated by 27-hydroxycholesterol, involving IGF-1 signaling.

Trichosanthin suppresses HeLa cell proliferation through inhibition of the PKC/MAPK signaling pathway

Trichosanthin (TCS) possesses a broad spectrum of biological and pharmacological activities, including anti-tumor activities. Our previous studies have shown that TCS inhibits HeLa cell proliferation by activating the apoptotic pathway. In particular, the transcriptional factor cAMP response element binding (CREB) protein plays a pivotal role in apoptotic HeLa cells. However, no information, to date, is available about the signaling pathways involved in the inhibition of cell proliferation induced by TCS. The present study showed that PKA and PKC activities were significantly inhibited by TCS treatment. However, specific inhibitor of PKA activity failed to affect the inhibition of HeLa cell proliferation induced by TCS, even in the presence of cAMP agonists. In contrast, PKC activator/inhibitor significantly attenuated/enhanced the inhibitory effect of TCS on cell proliferation. In particular, the reversed effect of cAMP agonist on cell proliferation was partly prevented by PKC, ERK1/2, and p38 MAPK blockade. Consistent with these results, the reversed effect of cAMP agonists on CREB phosphorylation was significantly decreased by inhibitors of these kinases, but not PKA inhibitor. Therefore, our results suggested that HeLa cell proliferation was inhibited by TCS via suppression of PKC/MAPK signaling pathway.

[Etiology of iodinated radiocontrast nephrotoxicity and its attenuation by beraprost]

Radiocontrast nephropathy (RCN) is a major complication after radiographical examination with iodinated contrast media (CM). Although little is known about the mechanism of RCN, a direct toxic action on renal cells and/or decrease in renal blood flow are considered to be implicated in the pathogenesis of the disease/the condition, A large number of vasodilatory agents, including endothelin antagonists, adenosine antagonists, atrial natriuretic peptide, calcium channel blockers, dopamine, dopamine D1 receptor agonist fenoldopam, and prostaglandin E1 have been tried clinically to prevent RCN, however, most of them have failed. Although prophylactic effects of antioxidant N-acetylcysteine have recently been reported by several investigators, only hydration is a universally accepted protocol to prevent it. In our recent in vitro and in vivo study, we have elucidated that CM induced apoptosis of renal tubular cells through the reduction in Bcl-2 expression and the subsequent activation of caspase-9 and caspase-3. Moreover, we found that CM caused an increase in ceramide content in renal tubular cells, which leads to apoptosis by inhibiting the phosphorylation of Akt and cAMP responsive element binding protein (CREB) and the subsequent reduction in Bcl-2 expression. The inhibitor of ceramide synthase, fumonisin B1, reversed both the elevation of ceramide content and renal cell injury induced by CM. On the other hand, a prostacyclin analog beraprost prevented RCN in mice by the increase of endogenous cAMP and subsequent CREB phosphorylation resulted in enhancement of Bcl-2 expression. These findings suggest that ceramide synthesis inhibitor or beraprost is potentially useful for the prophylaxis of RCN.

Characterization and function of CREB homologue from Crassostrea ariakensis stimulated by rickettsia-like organism

The cAMP response element-binding protein (CREB) is a transcription factor that plays important roles in cellular growth, proliferation and survival. Here, we report that a homologue of CREB transcription factor, Ca-CREB, was identified and functionally characterized in oyster, Crassostrea ariakensis. The full-length cDNA consists of 1397bp with an ORF encoding a 39.3kDa protein. Amino acid sequence analysis revealed that Ca-CREB shares conserved signature motifs with other CREB proteins. Ca-CREB was ubiquitously and constitutively expressed in oyster, and the expression level in hemocytes was higher than that in other tissues. The expression level of Ca-CREB was not modified after RLO stimulation, while tumor necrosis factor-alpha (TNF-alpha) expression was increased obviously, which was revealed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). Electrophoretic mobility shift assay (EMSA) and Western blotting showed that recombinant CREB proteins specifically bind the consensus CREB binding site, and DNA-binding activity and phosphorylation of Ca-CREB were induced by RLO. These results suggest that Ca-CREB is a CREB homologue and may be involved in immune responses against RLO.

Bcl-2 protein family members: versatile regulators of calcium signaling in cell survival and apoptosis

Bcl-2 family members are important regulators of cell survival and cell death. Researchers have focused mainly on mitochondria, where both proapoptotic and antiapoptotic family members function to regulate the release of cytochrome c and other mediators of apoptosis. However, as reviewed here, Bcl-2 family members also operate on another front, the endoplasmic reticulum (ER), to both positively and negatively regulate the release of Ca2+. There is abundant evidence that Ca2+ signals trigger apoptosis in response to a wide variety of agents and conditions. Conversely, Ca2+ signals can also mediate cell survival. Recent findings indicate that Bcl-2 interacts with inositol 1,4,5-trisphosphate (IP3) receptor Ca2+ channels on the ER, regulating their opening in response to IP3- and thus inhibiting IP3-mediated Ca2+ signals that induce apoptosis while enhancing Ca2+ signals that support cell survival.

Mitochondrial nuclear receptors and transcription factors: who's minding the cell?

Mitochondria are power organelles generating biochemical energy, ATP, in the cell. Mitochondria play a variety of roles, including integrating extracellular signals and executing critical intracellular events, such as neuronal cell survival and death. Increasing evidence suggests that a cross-talk mechanism between mitochondria and the nucleus is closely related to neuronal function and activity. Nuclear receptors (estrogen receptors, thyroid (T3) hormone receptor, peroxisome proliferators-activated receptor gamma2) and transcription factors (cAMP response binding protein, p53) have been found to target mitochondria and exert prosurvival and prodeath pathways. In this context, the regulation of mitochondrial function via the translocation of nuclear receptors and transcription factors may underlie some of the mechanisms involved in neuronal survival and death. Understanding the function of nuclear receptors and transcription factors in the mitochondria may provide important pharmacological utility in the treatment of neurodegenerative conditions. Thus, the modulation of signaling pathways via mitochondria-targeting nuclear receptors and transcription factors is rapidly emerging as a novel therapeutic target.

BP1 transcriptionally activates bcl-2 and inhibits TNFalpha-induced cell death in MCF7 breast cancer cells

INTRODUCTION

We have previously shown that the Beta Protein 1 (BP1) homeodomain protein is expressed in 81% of invasive ductal breast carcinomas, and that increased BP1 expression correlates with tumor progression. The purpose of our current investigation was to determine whether elevated levels of BP1 in breast cancer cells are associated with increased cell survival.

METHODS

Effects on cell viability and apoptosis of MCF7 cells stably overexpressing BP1 were determined using MTT and Annexin V assays, and through examination of caspase activation. TNFalpha was used to induce apoptosis. The potential regulation of apoptosis-associated genes by BP1 was studied using real-time PCR and western blot analyses. Electrophoretic mobility shift assays, site-directed mutagenesis, and transient assays were performed to specifically characterize the interaction of BP1 with the promoter of the bcl-2 gene.

RESULTS

Stable overexpression of BP1 led to inhibition of apoptosis in MCF7 breast cancer cells challenged with TNFalpha. Increased BP1 resulted in reduced processing and activation of caspase-7, caspase-8, and caspase-9, and inactivation of the caspase substrate Poly(ADP-Ribose) Polymerase (PARP). Increased levels of full-length PARP and a decrease in procaspase-8 were also associated with BP1 overexpression. The bcl-2 gene is a direct target of BP1 since: (i) BP1 protein bound to a consensus binding sequence upstream of the bcl-2 P1 promoter in vitro. (ii) MCF7 cells overexpressing BP1 showed increased levels of bcl-2 mRNA and protein. (iii) Transient assays indicated that increased bcl-2 promoter activity is due to direct binding and modulation by BP1 protein. BP1 expression also prevented TNFalpha-mediated downregulation of bcl-2 mRNA and protein.

CONCLUSION

These findings suggest mechanisms by which increased BP1 may impart a survival advantage to breast cancer cells, which could lead to increased resistance to therapeutic agents in patients.

Xenon and hypothermia combine additively, offering long-term functional and histopathologic neuroprotection after neonatal hypoxia/ischemia

BACKGROUND AND PURPOSE

Hypoxic/ischemic (HI) brain injury affects 1 to 6 per 1000 live human births, with a mortality of 15% to 20%. A quarter of survivors have permanent disabilities. Hypothermia is the only intervention that improves outcome; however, further improvements might be obtained by combining hypothermia with additional treatments. Xenon is a noble anesthetic gas with an excellent safety profile, showing great promise in vitro and in vivo as a neuroprotectant. We investigated combinations of 50% xenon (Xe(50%)) and hypothermia of 32 degrees C (HT(32 degrees C)) as a post-HI therapy.

METHODS

An established neonatal rat HI model was used. Serial functional neurologic testing into adulthood 10 weeks after injury was performed, followed by global and regional brain histopathology evaluation.

RESULTS

In the combination Xe(50%)HT(32 degrees C) group, complete restoration of long-term functional outcomes was seen. Hypothermia produced improvement on short- (P<0.001) and long- (P<0.001) term functional testing, whereas Xe(50%) alone predominantly improved long-term function (P<0.05), suggesting that short-term testing does not always predict eventual outcome. Similarly, the Xe(50%)HT(32 degrees C) combination produced the greatest (71%) improvement in global histopathology scores, a pattern mirrored in the regional scores, whereas Xe(50%) and HT(32 degrees C) individually produced smaller improvements (P<0.05 and P<0.001, respectively). The interaction between the 2 treatments was additive.

CONCLUSIONS

The xenon/hypothermia combination additively confers greater protection after HI than either treatment alone. The functional improvement is almost complete, is sustained long term, and is accompanied by greatly improved histopathology. The unique safety profile differentiates xenon as an attractive combination therapy with hypothermia to improve the otherwise bleak outcome from neonatal HI.

t-Darpp promotes cancer cell survival by up-regulation of Bcl2 through Akt-dependent mechanism

t-Darpp is a cancer-related truncated isoform of Darpp-32 (dopamine and cyclic-AMP-regulated phosphoprotein of M(r) 32,000). We detected overexpression of t-Darpp mRNA in two thirds of gastric cancers compared with normal samples (P = 0.004). Using 20 micromol/L ceramide treatment as a model for induction of apoptosis in AGS cancer cells, we found that expression of t-Darpp led to an increase in Bcl2 protein levels and blocked the activation of caspase-3 and caspase-9. The MitoCapture mitochondrial apoptosis and cytochrome c release assays indicated that t-Darpp expression enforces the mitochondrial transmembrane potential and protects against ceramide-induced apoptosis. Interestingly, the expression of t-Darpp in AGS cells led to >or=2-fold increase in Akt kinase activity with an increase in protein levels of p-Ser(473) Akt and p-Ser(9) GSK3 beta. These findings were further confirmed using tetracycline-inducible AGS cells stably expressing t-Darpp. We also showed transcriptional up-regulation of Bcl2 using the luciferase assay with Bcl2 reporter containing P1 full promoter, quantitative reverse transcription-PCR, and t-Darpp small interfering RNA. The Bcl2 promoter contains binding sites for cyclic AMP-responsive element binding protein CREB/ATF1 transcription factors and using the electrophoretic mobility shift assay with a CREB response element, we detected a stronger binding in t-Darpp-expressing cells. The t-Darpp expression led to an increase in expression and phosphorylation of CREB and ATF-1 transcription factors that were required for up-regulating Bcl2 levels. Indeed, knockdown of Akt, CREB, or ATF1 in t-Darpp-expressing cells reduced Bcl2 protein levels. In conclusion, the t-Darpp/Akt axis underscores a novel oncogenic potential of t-Darpp in gastric carcinogenesis and resistance to drug-induced apoptosis.

Physiological roles of the Ca2+/CaM-dependent protein kinase cascade in health and disease

Numerous hormones, growth factors and physiological processes cause a rise in cytosolic Ca2+, which is translated into meaningful cellular responses by interacting with a large number of Ca2(+)-binding proteins. The Ca2(+)-binding protein that is most pervasive in mediating these responses is calmodulin (CaM), which acts as a primary receptor for Ca2+ in all eukaryotic cells. In turn, Ca2+/CaM functions as an allosteric activator of a host of enzymatic proteins including a considerable number of protein kinases. The topic of this review is to discuss the physiological roles of a sub-set of these protein kinases which can function in cells as a Ca2+/CaM-dependent kinase signaling cascade. The cascade was originally believed to consist of a CaM kinase kinase that phosphorylates and activates one of two CaM kinases, CaMKI or CaMKIV. The unusual aspect of this cascade is that both the kinase kinase and the kinase require the binding of Ca2+/CaM for activation. More recently, one of the CaM kinase kinases has been found to activate another important enzyme, the AMP-dependent protein kinase so the concept of the CaM kinase cascade must be expanded. A CaM kinase cascade is important for many normal physiological processes that when misregulated can lead to a variety of disease states. These processes include: cell proliferation and apoptosis that may conspire in the genesis of cancer; neuronal growth and function related to brain development, synaptic plasticity as well as memory formation and maintenance; proper function of the immune system including the inflammatory response, activation of T lymphocytes and hematopoietic stem cell maintenance; and the central control of energy balance that, when altered, can lead to obesity and diabetes. Although the study of the CaM-dependent kinase cascades is still in its infancy continued analysis of the pathways regulated by these Ca2(+)-initiated signaling cascades holds considerable promise for the future of disease-related research.

Inhibition of Raf-1 alters multiple downstream pathways to induce pancreatic beta-cell apoptosis

The serine threonine kinase Raf-1 plays a protective role in many cell types, but its function in pancreatic beta-cells has not been elucidated. In the present study, we examined whether primary beta-cells possess Raf-1 and tested the hypothesis that Raf-1 is critical for beta-cell survival. Using reverse transcriptase-PCR, Western blot, and immunofluorescence, we identified Raf-1 in human islets, mouse islets, and in the MIN6 beta-cell line. Blocking Raf-1 activity using a specific Raf-1 inhibitor or dominant-negative Raf-1 mutants led to a time- and dose-dependent increase in cell death, assessed by real-time imaging of propidium iodide incorporation, TUNEL, PCR-enhanced DNA laddering, and Caspase-3 cleavage. Although the rapid increase in apoptotic cell death was associated with decreased Erk phosphorylation, studies with two Mek inhibitors suggested that the classical Erk-dependent pathway could explain only part of the cell death observed after inhibition of Raf-1. An alternative Erk-independent pathway downstream of Raf-1 kinase involving the pro-apoptotic protein Bad has recently been characterized in other tissues. Inhibiting Raf-1 in beta-cells led to a striking loss of Bad phosphorylation at serine 112 and an increase in the protein levels of both Bad and Bax. Together, our data strongly suggest that Raf-1 signaling plays an important role regulating beta-cell survival, via both Erk-dependent and Bad-dependent mechanisms. Conversely, acutely inhibiting phosphatidylinositol 3-kinase Akt had more modest effects on beta-cell death. These studies identify Raf-1 as a critical anti-apoptotic kinase in pancreatic beta-cells and contribute to our understanding of survival signaling in this cell type.

Glucose-dependent insulinotropic polypeptide-mediated up-regulation of beta-cell antiapoptotic Bcl-2 gene expression is coordinated by cyclic AMP (cAMP) response element binding protein (CREB) and cAMP-responsive CREB coactivator 2

The cyclic AMP (cAMP)/protein kinase A (PKA) cascade plays a central role in beta-cell proliferation and apoptosis. Here, we show that the incretin hormone glucose-dependent insulinotropic polypeptide (GIP) stimulates expression of the antiapoptotic Bcl-2 gene in pancreatic beta cells through a pathway involving AMP-activated protein kinase (AMPK), cAMP-responsive CREB coactivator 2 (TORC2), and cAMP response element binding protein (CREB). Stimulation of beta-INS-1 (clone 832/13) cells with GIP resulted in increased Bcl-2 promoter activity. Analysis of the rat Bcl-2 promoter revealed two potential cAMP response elements, one of which (CRE-I [GTGACGTAC]) was shown, using mutagenesis and deletion analysis, to be functional. Subsequent studies established that GIP increased the nuclear localization of TORC2 and phosphorylation of CREB serine 133 through a pathway involving PKA activation and reduced AMPK phosphorylation. At the nuclear level, phospho-CREB and TORC2 were demonstrated to bind to CRE-I of the Bcl-2 promoter, and GIP treatment resulted in increases in their interaction. Furthermore, GIP-mediated cytoprotection was partially reversed by small interfering RNA-mediated reduction in BCL-2 or TORC2/CREB or by pharmacological activation of AMPK. The antiapoptotic effect of GIP in beta cells is therefore partially mediated through a novel mode of transcriptional regulation of Bcl-2 involving cAMP/PKA/AMPK-dependent regulation of CREB/TORC2 activity.

Identification of a novel Bcl-2 promoter region that counteracts in a p53-dependent manner the inhibitory P2 region

Expression of the anti-apoptotic proto-oncogene bcl-2 is negatively affected by the pro-apoptotic p53. To understand the regulation of bcl-2 expression by p53, we studied the bcl-2 promoter regions individually and in the context of the full-length promoter. While the P1 promoter displayed the highest p53-independent activity, the P2 promoter activity was suppressed in p53-sufficient cancer cell lines. In addition, P2 activity was higher in primary airway epithelial cells from p53(-/-) mice compared to those from p53(+/+) mice. Chromatin immunoprecipitation assays confirmed that p53 interacts within a 140 bp sequence of P2 that contained the CCAAT- and TATA-elements. However, when P1 and P2 are linked in one construct, P2 suppressed P1 activity independent of p53. A potential novel promoter with a p53-dependent activity was identified located between P1 and P2, and was designated M. In the context of the full-length bcl-2 promoter, M counteracted in a p53-dependent manner the suppressive activity of P2 on P1. Collectively, these data suggest that P1 promoter is the main driving force for transcribing the bcl-2 gene and P1 activity is modulated by M and P2 in a p53-dependent and -independent manner. These findings may have implications for therapies that are geared towards inhibiting bcl-2 gene expression and inducing cell death.

CREB-mediated Bcl-2 expression in trichosanthin-induced Hela cell apoptosis

Bcl-2 plays a pivotal role in the control of cell death and is down-regulated in trichosanthin (TCS)-induced cell apoptosis. Because Bcl-2 expression is regulated by the transcription factor cyclic AMP response element-binding protein (CREB), we investigated the role of CREB activation in TCS-induced Hela cells apoptosis. Our results showed that TCS-caused Hela cell apoptosis was accompanied by the decrease of Bcl-2 and phosphorylated CREB protein levels. Interesting, this inhibitive effect can be abolished by the combined treatment of TCS/cAMP agonists. Furthermore, TCS-mediated Bcl-2 protein was abrogated by the suppression of CREB expression with antisense treatment, and blocking the interaction between CREB-binding protein and the Bcl-2 cyclic AMP-responsive element (CRE) by a CRE decoy oligonucleotide. Therefore, these data support the hypothesis that CREB plays a critical role in the regulation of Bcl-2 expression in TCS-induced Hela cell death.

c-Maf interacts with c-Myb to down-regulate Bcl-2 expression and increase apoptosis in peripheral CD4 cells

The transcription factor c-Maf is critical for IL-4 production and the development of Th2 cells, which promote humoral immunity and protect against extracellular parasites. Yet, little else is known of c-Maf function in CD4 cells. Here, we identify a novel role for c-Maf in regulating susceptibility to apoptosis. Overexpression of c-Maf results in increased susceptibility of CD4 cells to apoptosis induced by multiple stimuli, including growth factor withdrawal, dexamethasone, irradiation, and TCR engagement. This effect is independent of Fas or p53; however, Bcl-2 expression is reduced in c-Maf Tg CD4 cells. Immunoprecipitation and Western blot analyses demonstrate that c-Maf-c-Myb complex formation is enhanced among T cells from c-Maf Tg mice compared to non-Tg littermates following TCR engagement. Unlike non-Tg T cells, c-Myb binding to the Bcl-2 promoter is not detectable in c-Maf Tg T cells by chromatin immunoprecipitation. In reporter assays, Bcl-2 promoter activity is reduced by c-Maf in a dose-dependent manner. Furthermore, transgene-mediated Bcl-2 expression corrects the apoptosis defect observed among c-Maf Tg CD4 cells. These data suggest that c-Maf can interact with c-Myb to reduce Bcl-2 expression, thereby limiting CD4 cell survival following TCR engagement.

Prosurvival and proapoptotic intracellular signaling in rat spiral ganglion neurons in vivo after the loss of hair cells

Neurons depend on afferent input for survival. Rats were given daily kanamycin injections from P8 to P16 to destroy hair cells, the sole afferent input to spiral ganglion neurons (SGNs). Most SGNs die over an approximately 14-week period after deafferentation. During this period, the SGN population is heterogeneous. At any given time, some SGNs exhibit apoptotic markers--TUNEL and cytochrome c loss--whereas others appear nonapoptotic. We asked whether differences among SGNs in intracellular signaling relevant to apoptotic regulation could account for this heterogeneity. cAMP response element binding protein (CREB) phosphorylation, which reflects neurotrophic signaling, is reduced in many SGNs at P16, P23, and P32, when SGNs begin to die. In particular, nearly all apoptotic SGNs exhibit reduced phospho-CREB, implying that apoptosis is due to insufficient neurotrophic support. However, >32% of SGNs maintain high phospho-CREB levels, implying access to neurotrophic support. By P60, when approximately 50% of the SGNs have died, phospho-CREB levels in surviving neurons are not reduced, and SGN death is no longer correlated with reduced phospho-CREB. Activity in the proapoptotic Jun N-terminal kinase (JNK)-Jun signaling pathway is elevated in SGNs during the cell death period. This too is heterogeneous: <42% of the SGNs exhibited high phospho-Jun levels, but nearly all SGNs undergoing apoptosis exhibited elevated phospho-Jun. Thus, heterogeneity among SGNs in prosurvival and proapoptotic signaling is correlated with apoptosis. SGN death following deafferentation has an early phase in which apoptosis is correlated with reduced phospho-CREB and a later phase in which it is not. Proapoptotic JNK-Jun signaling is tightly correlated with SGN apoptosis.

Bcl-2 overexpression in PhIP-induced colon tumors: cloning of the rat Bcl-2 promoter and characterization of a pathway involving beta-catenin, c-Myc and E2F1

Beta-catenin/T-cell factor (Tcf) signaling is constitutively active in the majority of human colorectal cancers, and there are accompanying changes in Bcl-2 expression. Similarly, 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP)-induced colon tumors in the rat have increased beta-catenin and elevated Bcl-2. To examine the possible direct transcriptional regulation of rat Bcl-2 by beta-catenin/Tcf, we cloned and characterized the corresponding promoter region and found 70.1% similarity with its human counterpart, BCL2. Bcl-2 promoter activity was increased in response to LiCl and exogenous beta-catenin, including oncogenic mutants of beta-catenin found in PhIP-induced colon tumors. Protein/DNA arrays identified E2F1, but not beta-catenin/Tcf, as interacting most strongly with the rat Bcl-2 promoter. Exogenous E2F1 increased the promoter activity of rat Bcl-2, except in mutants lacking the E2F1 sites. As expected, beta-catenin induced its downstream target c-Myc, as well as E2F1 and Bcl-2, and this was blocked by siRNA to c-Myc or E2F1. These findings suggest an indirect pathway for Bcl-2 over-expression in PhIP-induced colon tumors involving beta-catenin, c-Myc and E2F1.

CaMKII and CaMKIV mediate distinct prosurvival signaling pathways in response to depolarization in neurons

By fusing the CaMKII-inhibitory peptide AIP to GFP, we constructed a specific and effective CaMKII inhibitor, GFP-AIP. Expression of GFP-AIP and/or dominant-inhibitory CaMKIV in cultured neonatal rat spiral ganglion neurons (SGNs) shows that CaMKII and CaMKIV act additively and in parallel to mediate the prosurvival effect of depolarization. Depolarization or expression of constitutively active CaMKII functionally inactivates Bad, indicating that this is one means by which CaMKII promotes neuronal survival. CaMKIV, but not CaMKII, requires CREB to promote SGN survival, consistent with the exclusively nuclear localization of CaMKIV and indicating that the principal prosurvival function of CaMKIV is activation of CREB. Consistent with this, a constitutively active CREB construct that provides a high level of CREB activity promotes SGN survival, although low levels of CREB activity did not do so. Also, in apoptotic SGNs, activation of CREB by depolarization is disabled, presumably as part of a cellular commitment to apoptosis.

Dominant negative mutant forms of the cAMP response element binding protein induce apoptosis and decrease the anti-apoptotic action of growth factors in human islets

AIMS/HYPOTHESIS

Transplantation of islets is a viable option for the treatment of diabetes. A significant proportion of islets is lost during isolation, storage and after transplantation as a result of apoptosis. cAMP response element binding protein (CREB) is an important cell survival factor. The aim of the present study was to determine whether preservation of CREB function is needed for survival of human islets.

MATERIALS AND METHODS

To determine the effects of downregulation of CREB activity on beta cell apoptosis in a transplantation setting, adenoviral vectors were used to express two dominant negative mutant forms of CREB in human islets isolated from cadaveric donors. Markers of apoptosis were determined in these transduced islets under basal conditions and following treatment with growth factor.

RESULTS

Expression of CREB mutants in human islets resulted in significant (p < 0.001) activation of caspase-9, a key regulatory enzyme in the mitochondrial pathway of apoptosis, when compared with islets transduced with adenoviral beta galactosidase. Immunocytochemical analysis showed the activation of caspase-9 to be predominantly in beta cells. Other definitive markers of apoptosis such as parallel activation of caspase-3, accumulation of cleaved poly-(ADP-ribose) polymerase and nuclear condensation were also observed. Furthermore, the anti-apoptotic action of growth factors exendin-4 and betacellulin in human islets exposed to cytokines was partially lost when CREB function was impaired.

CONCLUSIONS/INTERPRETATION

Our findings suggest that impairment of CREB-mediated transcription could lead to loss of islets by apoptosis with potential implications in islet transplantation as well as in the mechanism of beta cell loss leading to diabetes.

Hippocampal Bcl-2 expression is selectively increased following chronic but not acute treatment with antidepressants, 5-HT1A or 5-HT2C/2B receptor antagonists

Expression of the anti-apoptotic protein Bcl-2 has been shown to increase in the hippocampus and cortex following chronic administration of mood stabilizers such as lithium and valproate, but the effects of long-term antidepressant administration have not been demonstrated. CD1 mice were dosed either acutely or chronically with either antidepressants or 5-HT receptor subtype selective antagonists. Cortex, hippocampus and hypothalamus from these mice were analysed by Western blot for changes in expression of Bcl-2 and Bax protein. Fourteen day but not acute treatment with citalopram (20 mg/kg), imipramine (10 mg/kg) and amitriptyline (10 mg/kg) in mice significantly elevated hippocampal Bcl-2 protein expression as compared to vehicle treated animals (59, 48 and 42% respectively). Similarly, fourteen day but not acute treatment with the 5-HT(1A) and 5-HT(2C/2B) receptor antagonists WAY100635 (0.3 mg/kg) and SB221284 (1 mg/kg) also markedly and significantly increased hippocampal Bcl-2 expression (95 and 52% respectively). Bcl-2 expression was unaffected in cortex by any treatment. There was a smaller increase of hippocampal Bax protein levels following treatment with imipramine after 1 or 14 days, and following citalopram and amitriptyline after 14 but not 1 day. These data present the first substantive evidence that clinically used antidepressants increase the expression of hippocampal Bcl-2 as did chronic blockade of 5-HT(1A) and 5-HT(2C/2B) receptors, which may be involved in the mechanism of action of antidepressants. The induction of hippocampal Bcl-2 expression by long-term antidepressant treatment may contribute to the clinical efficacy of such compounds via its well described neurotrophic and/or anti-apoptotic effects on neuronal function.

TORC2 regulates germinal center repression of the TCL1 oncoprotein to promote B cell development and inhibit transformation

Aberrant expression of the TCL1 oncoprotein promotes malignant transformation of germinal center (GC) B cells. Repression of TCL1 in GC B cells facilitates FAS-mediated apoptosis and prevents lymphoma formation. However, the mechanism for this repression is unknown. Here we show that the CREB coactivator TORC2 directly regulates TCL1 expression independent of CREB Ser-133 phosphorylation and CBP/p300 recruitment. GC signaling through CD40 or the BCR, which activates pCREB-dependent genes, caused TORC2 phosphorylation, cytosolic emigration, and TCL1 repression. Signaling via cAMP-inducible pathways inhibited TCL1 repression and reduced apoptosis, consistent with a prosurvival role for TCL1 before GC selection and supporting an initiating role for aberrant TCL1 expression during GC lymphomagenesis. Our data indicate that a novel CREB/TORC2 regulatory mode controls the normal program of GC gene activation and repression that promotes B cell development and circumvents oncogenic progression. Our results also reconcile a paradox in which signals that activate pCREB/CBP/p300 genes concurrently repress TCL1 to initiate its silencing.

Restoration of CREB function is linked to completion and stabilization of adaptive cardiac hypertrophy in response to exercise

Potential regulation of two factors linked to physiological outcomes with left ventricular (LV) hypertrophy, resistance to apoptosis, and matching of metabolic capacity, by the transcription factor cyclic-nucleotide regulatory element binding protein (CREB), was examined in the two models of physiological LV hypertrophy: involuntary treadmill running of female Sprague-Dawley rats and voluntary exercise wheel running in female C57Bl/6 mice. Comparative studies were performed in the models of pathological LV hypertrophy and failure: the spontaneously hypertension heart failure (SHHF) rat and the hypertrophic cardiomyopathy (HCM) transgenic mouse, a model of familial idiopathic cardiomyopathy. Activating CREB serine-133 phosphorylation was decreased early in remodeling in response to both physiological (decreased 50-80%) and pathological (decreased 60-80%) hypertrophic stimuli. Restoration of LV CREB phosphorylation occurred concurrent with completion of physiological hypertrophy (94% of sedentary control), but remained decreased (by 90%) during pathological hypertrophy. In all models of hypertrophy, CREB phosphorylation/activation demonstrated strong positive correlations with 1) expression of the anti-apoptotic protein bcl-2 (a CREB-dependent gene) and subsequent reductions in the activation of caspase 9 and caspase 3; 2) expression of peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1; a major regulator of mitochondrial content and respiratory capacity), and 3) LV mitochondrial respiratory rates and mitochondrial protein content. Exercise-induced increases in LV mitochondrial respiratory capacity were commensurate with increases observed in LV mass, as previously reported in the literature. Exercise training of SHHF rats and HCM mice in LV failure improved cardiac phenotype, increased CREB activation (31 and 118%, respectively), increased bcl-2 content, improved apoptotic status, and enhanced PGC-1 content and mitochondrial gene expression. Adenovirus-mediated expression of constitutively active CREB in neonatal rat cardiac recapitulated exercise-induced upregulation of PGC-1 content and mitochondrial oxidative gene expression. These data support a model wherein CREB contributes to physiological hypertrophy by enhancing expression of genes important for efficient oxidative capacity and resistance to apoptosis.

Failure of stress-induced downregulation of Bcl-2 contributes to apoptosis resistance in senescent human diploid fibroblasts

We previously reported that senescent human diploid fibroblasts (HDFs) are resistant to apoptosis induced by H(2)O(2) and staurosporine. We report here that senescent HDFs are resistant to thapsigargin-induced apoptosis as well. These agonists caused the reductions in mitochondrial membrane potential (MMP) and in the apoptosis inhibitory protein (B-cell lymphoma) only in young HDFs but not in senescent HDFs. In addition, downregulation of Bcl-2 increased the sensitivity of senescent HDFs to apoptosis induction, suggesting the significant role of Bcl-2 in apoptosis resistance of the senescent HDFs. We further found that P-cAMP response element-binding protein (CREB), a positive regulator of Bcl-2, decreased in stress-induced apoptosis of young HDFs but not in senescent HDFs, and that Bcl-2 was markedly reduced in CREB small interfering RNA (siRNA), transfected senescent HDFs. In addition, activity of protein phosphatase 2A (PP2A), which dephosphorylates p-CREB, significantly increased in young HDFs but not in senescent HDFs treated with H(2)O(2), staurosporine or thapsigargin. Taken together, these results suggest that failure of stress-induced downregulation of Bcl-2 underlies resistance of senescent HDFs to apoptosis.

Activating transcription factor 2 controls Bcl-2 promoter activity in growth plate chondrocytes

Activating transcription factor 2 (ATF-2) is expressed ubiquitously in mammals. Mice deficient in ATF-2 (ATF-2 m/m) are slightly smaller than their normal littermates at birth. Approximately 50% of mice born mutant in both alleles die within the first month. Those that survive develop a hypochondroplasia-like dwarfism, characterized by shortened growth plates and kyphosis. Expression of ATF-2 within the growth plate is limited to the resting and proliferating zones. We have previously shown that ATF-2 targets the cyclic AMP response element (CRE) in the promoters of cyclin A and cyclin D1 in growth plate chondrocytes to activate their expression. Here, we demonstrate that Bcl-2, a cell death inhibitor that regulates apoptosis, is expressed within the growth plate in proliferative and prehypertrophic chondrocytes. However, Bcl-2 expression declines in hypertrophic chondrocytes. The Bcl-2 promoter contains a CRE at -1,552 bp upstream of the translation start. Mutations within this CRE cause reduced Bcl-2 promoter activity. We show here that the absence of ATF-2 in growth plate chondrocytes corresponds to a decline in Bcl-2 promoter activity, as well as a reduction in Bcl-2 protein levels. In addition, we show that ATF-2 as well as CREB, a transcription factor that can heterodimerize with ATF-2, bind to the CRE within the Bcl-2 promoter. These data identify the Bcl-2 gene as a novel target of ATF-2 and CREB in growth plate chondrocytes.

Nitric oxide mediates natural polyphenol-induced Bcl-2 down-regulation and activation of cell death in metastatic B16 melanoma

Intravenous administration to mice of trans-pterostilbene (t-PTER; 3,5-dimethoxy-4'-hydroxystilbene) and quercetin (QUER; 3,3',4',5,6-pentahydroxyflavone), two structurally related and naturally occurring small polyphenols, inhibits metastatic growth of highly malignant B16 melanoma F10 (B16M-F10) cells. t-PTER and QUER inhibit bcl-2 expression in metastatic cells, which sensitizes them to vascular endothelium-induced cytotoxicity. However, the molecular mechanism(s) linking polyphenol signaling and bcl-2 expression are unknown. NO is a potential bioregulator of apoptosis with controversial effects on Bcl-2 regulation. Polyphenols may affect NO generation. Short-term exposure (60 min/day) to t-PTER (40 microM) and QUER (20 microM) (approximate mean values of the plasma concentrations measured within the first hour after intravenous administration of 20 mg of each polyphenol/kg) down-regulated inducible NO synthetase in B16M-F10 cells and up-regulated endothelial NO synthetase in the vascular endothelium and thereby facilitated endothelium-induced tumor cytotoxicity. Very low and high NO levels down-regulated bcl-2 expression in B16M-F10 cells. t-PTER and QUER induced a NO shortage-dependent decrease in cAMP-response element-binding protein phosphorylation, a positive regulator of bcl-2 expression, in B16M-F10 cells. On the other hand, during cancer and endothelial cell interaction, t-PTER- and QUER-induced NO release from the vascular endothelium up-regulated neutral sphingomyelinase activity and ceramide generation in B16M-F10 cells. Direct NO-induced cytotoxicity and ceramide-induced mitochondrial permeability transition and apoptosis activation can explain the increased endothelium-induced death of Bcl-2-depleted B16M-F10 cells.

The BCL2 major breakpoint region (mbr) regulates gene expression

BCL2 expression is finely tuned by a variety of environmental and endogenous stimuli and regulated at both transcriptional and post-transcriptional levels. Our previous investigations demonstrated that the BCL2 major breakpoint region (mbr) in the 3'-UTR upregulates reporter gene expression, which implies that this region possessed intrinsic regulatory function. However, the effect of the mbr on BCL2 expression, and the underlying regulatory mechanisms, remain to be elucidated. To assess the direct effect of the mbr on the transcriptional activity of the BCL2 gene, we employed targeted homologous recombination to establish a mbr(+)/mbr(-) heterozygous Nalm-6 cell line and then compared the transcriptional activity and apoptotic effect on transcription between the wild type and targeted alleles. We found that deletion of the mbr significantly decreased the transcriptional activity of the corresponding allele in the mbr(+)/mbr(-) cell. The BCL2 allele deleted of the mbr had a slower response to apoptotic stimuli than did the wild type allele. The regulatory function of the mbr was mediated through SATB1. Overexpression of SATB1 increased BCL2 expression, while knockdown of SATB1 with RNAi decreased BCL2 expression. Our results clearly indicated that the mbr could positively regulate BCL2 gene expression and this regulatory function was closely related to SATB1.

Role of the cyclic AMP response element in the bcl-2 promoter in the regulation of endogenous Bcl-2 expression and apoptosis in murine B cells

We have previously shown for B-cell lines that the cyclic AMP response element (CRE) is a major positive regulatory site in the bcl-2 promoter. However, the role of the CRE in the regulation of endogenous bcl-2 expression in vivo has not been characterized. We used gene targeting to generate knock-in mice in which a mutated CRE was introduced into the bcl-2 promoter region (mutCRE-bcl2 mice). Quantitative chromatin immunoprecipitation assays revealed that mutation of the CRE abolished the binding of CREB/ATF and CBP transcription factors to the bcl-2 promoter and greatly diminished the binding of NF-kappaB factors. The mutant CRE significantly reduced the expression of Bcl-2 in B cells and rendered them susceptible to surface immunoglobulin- and chemotherapeutic agent-induced apoptosis. The low levels of Bcl-2 were not changed with activation of the cells. The numbers of pre-B, immature B, and mature B cells in the bone marrow were decreased, as were the numbers of splenic B cells in mutCRE-bcl2 mice. Our findings indicate that the CRE in the bcl-2 promoter has an important functional role in the regulation of endogenous Bcl-2 expression and plays a critical role in the coordination of signals that regulate B-cell survival.

Directing DNA methylation to inhibit gene expression

: 1. DNA methylation is a critical epigenetic modification that silences gene transcription, participates in X-chromosome inactivation in females, and regulates genomic imprinting. 2. We have devised a method to inhibit transcriptional initiation by constructing short methylated oligonucleotides which induce DNA methylation at specific loci. 3. The methodology by which we devise these oligonucleotides is described, using oligonucleotides directed against the oncogene, Bcl-2.4. The human Bcl-2 gene contains two promoters, each of which contains a CpG island in its core region. Oligonucleotides are designed which can inhibit Bcl-2 transcription and lead to decreased mRNA and protein in vitro. When compared to standard anti-sense oligonucleotide action, these methylated oligonucleotides are far more sensitive and potentially, longer acting. 5. In principle, using this methodology, it should be possible to design methylated oligonucleotides that can methylate CpG islands and thereby downregulate any gene.

Cellular plasticity cascades: targets for the development of novel therapeutics for bipolar disorder

For a number of patients with bipolar disorder, current pharmacotherapy is generally insufficient. Despite adequate treatment, patients continue to have recurrent mood episodes, residual symptoms, functional impairment, psychosocial disability, and significant medical and psychiatric comorbidity. Drug development for bipolar disorder may occur through one of two approaches: the first is by understanding the therapeutically relevant biochemical targets of currently effective medications. Two promising direct targets of lithium and valproate are glycogen synthase kinase-3 and histone deacetylase. The second path results from our understanding that severe mood disorders, although not classical neurodegenerative disorders, are associated with regional impairments of structural plasticity and cellular resilience. This suggests that effective treatments will need to provide both trophic and neurochemical support, which serves to enhance and maintain normal synaptic connectivity, thereby allowing the chemical signal to reinstate the optimal functioning of critical circuits necessary for normal affective functioning. For many refractory patients, drugs mimicking "traditional" strategies, which directly or indirectly alter monoaminergic levels, may be of limited benefit. Newer "plasticity enhancing" strategies that may have utility in the treatment of mood disorders include inhibitors of glutamate release, N-methyl-D-aspartate antagonists, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid potentiators, cyclic adenosine monophosphate phosphodiesterase inhibitors, and glucocorticoid receptor antagonists.

Cyclic nucleotide Response Element Binding protein (CREB) activation promotes survival signal in human K562 erythroleukemia cells exposed to ionising radiation/etoposide combined treatment

Anticancer therapy addresses the destruction of tumour cells which try to counteract the effect of drugs and/or ionising radiation. Thus the knowledge of the threshold over which the cells do not resist such agents could help in the setting up of therapy protocols. Since a key role was assigned to Cyclic nucleotide Response Element Binding protein (CREB) multigenic family (which is composed of several nuclear transcription factors involved in c-AMP signalling in cell differentiation, proliferation, apoptosis, survival and adaptive response and in hematopoiesis and acute leukemias), attention was paid to the activation of Erk cascade and of the downstream kinases and transcription factors such as p90RSK and CREB. K562 erythroleukemia cell survival to 1.5 Gy ionising radiation with or without etoposide treatment seemed to involve Erk phosphorylation which, regulating p90 RSK, should activate CREB. In parallel, p38 MAP kinase activity down-modulation, along with low caspase-3 activity, and no modification of Bax and Bcl2 levels, supported such evidence. Thus, endogenous CREB activation, triggering a potent survival signal in K562 cells exposed to 1.5 Gy with or without etoposide, led us to suggest that using specific inhibitors against CREB, such as modified phosphorothionate oligodeoxynucleotides (ODN) corresponding to CREB-1 sequence, anticancer therapy efficacy could be improved.