Akt/protein kinase B up-regulates Bcl-2 expression through cAMP-response element-binding protein

Modulation of tamoxifen sensitivity by antisenseBcl-2 and trastuzumab in breast carcinoma cells

BACKGROUND

Because the overexpression of HER-2 and Bcl-2 is associated with resistance to tamoxifen (TAM), the authors examined the effect of antisense (AS) Bcl-2 on sensitivity to TAM compared with the effect of trastuzumab on sensitivity to TAM in breast carcinoma cell lines.

METHODS

Drug sensitivity was assessed in vitro using a [3-4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay with the breast carcinoma cell lines ZR-75-1, MDA-MB-453, and BT-474. AS Bcl-2 18-mer phosphorothioate oligonucleotide was applied. Apoptotic cell death was assessed with the terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick-end labeling method, and gene expression was evaluated with Western blot analysis.

RESULTS

The expression of Bcl-2 was identified in ZR-75-1 and BT-474 cells and, to a lesser extent, in MDA-MB-453 cells. Overexpression of HER-2 was identified in BT-474 cells, and moderate expression was identified in MDA-MB-453 and ZR-75-1 cells. Combination treatment with trastuzumab or AS Bcl-2 enhanced TAM sensitivity in ZR-75-1 cells, which showed 50% inhibitory concentration (IC50) values of 0.9 microM (7.2-fold increase) and 0.5 microM (13.0-fold), respectively. Combination treatment with trastuzumab or AS Bcl-2 slightly enhanced TAM sensitivity of BT-474 cells, with IC50 values of 3.0 microM (1.3-fold) and 1.5 microM (2.6-fold), respectively. The sensitivity of MDA-MB-453 cells to TAM was not enhanced by combination with trastuzumab or AS Bcl-2. Modulation of TAM sensitivity by AS Bcl-2 was superior to modulation by trastuzumab in HER-2-expressing and Bcl-2-expressing breast carcinoma cells. Enhanced sensitivity in combination with AS Bcl-2 was associated with down-regulation of Bcl-2 and pAkt, which was correlated with the induction of Bax and caspase-3, leading to apoptosis.

CONCLUSIONS

AS Bcl-2 appeared to be superior to trastuzumab with respect to regulating the signal-transduction pathways involved in breast carcinoma cells.

Clinical and Experimental Evidence for Prevention of Acute Renal Failure Induced by Radiographic Contrast Media

Acute renal failure still occurs as a complication after radiographic examination using iodinated radiocontrast medium. The incidence rate of radiocontrast medium-induced nephropathy (radiocontrast nephropathy) is low (2 - 3%) in general. However, the rate is remarkably elevated in patients with pre-existing renal insufficiency. Radiocontrast nephropathy is associated with increased morbidity and mortality, particularly in patients with percutaneous coronary interventions. Although the reduction in renal blood flow and direct toxic action on renal tubular cells are considered to be involved, little is known about the etiology of radiocontrast nephropathy. A number of agents that improve renal circulation have been clinically tested for prevention of radiocontrast nephropathy, but none of them has succeeded. Protection of renal tubular cells against oxidative stress is another approach to avoid radiocontrast nephropathy. Prophylactic effects of antioxidants such as N-acetylcysteine and ascorbic acid have been reported by several investigators, although the effectiveness of these compounds is still a matter of debate. At present, hydration is regarded as the only effective, though incomplete, prophylactic regimen for radiocontrast nephropathy. Recently, we have shown that caspase-dependent apoptosis is an important factor in the pathogenesis of radiocontrast nephropathy and clarified cellular mechanisms underlying the radiocontrast media-induced apoptosis. This review summarizes clinical and experimental evidence for the etiology and prevention of radiocontrast nephropathy.

PGE2 inhibits chondrocyte differentiation through PKA and PKC signaling

Prostaglandins are ubiquitous metabolites of arachidonic acid, and cyclooxygenase inhibitors prevent their production and secretion. Animals with loss of cyclooxygenase-2 function have reduced reparative bone formation, but the role of prostaglandins during endochondral bone formation is not defined. The role of PGE2 as a regulator of chondrocyte differentiation in chick growth plate chondrocytes (GPCs) was examined. While PGE2, PGD2, PGF2alpha, and PGJ2 all inhibited colX expression, approximately 80% at 10(-6) M, PGE2 was the most potent activator of cAMP response element (CRE)-mediated transcription. PGE2 dose-dependently inhibited the expression of the differentiation-related genes, colX, VEGF, MMP-13, and alkaline phosphatase gene, and enzyme activity with significant effects at concentrations as low as 10(-10) M. PGE2 induced cyclic AMP response element binding protein (CREB) phosphorylation and increased c-Fos protein levels by 5 min, and activated transcription at CRE-Luc, AP-1-Luc, and c-Fos promoter constructs. The protein kinase A (PKA) inhibitor, H-89, completely blocked PGE2-mediated induction of CRE-Luc and c-Fos promoter-Luc promoters, and partially inhibited induction of AP-1-Luc, while the protein kinase C (PKC) inhibitor Go-6976 partially inhibited all three promoters, demonstrating substantial cross-talk between these signaling pathways. PGE2 inhibition of colX gene expression was dependent upon both PKA and PKC signaling. These observations demonstrate potent prostaglandin regulatory effects on chondrocyte maturation and show a role for both PKA and PKC signaling in PGE2 regulatory events.

What turns CREB on?

The transactivation domain of the cAMP response element-binding protein (CREB) consists of two major domains. The glutamine-rich Q2 domain, which interacts with the general transcription factor TAFII130/135, is sufficient for the recruitment of a functional RNA polymerase II complex and allows basal transcriptional activity. The kinase-inducible domain, however, mediates signal-induced activation of CREB-mediated transcription. It is generally believed that recruitment of the coactivators CREB-binding protein (CBP) and p300 after signal-induced phosphorylation of this domain at serine-133 strongly enhances CREB-dependent transcription. Transcriptional activity of CREB can also be potentiated by phosphoserine-133-independent mechanisms, and not all stimuli that provoke phosphorylation of serine-133 stimulate CREB-dependent transcription. This review presents an overview of the diversity of stimuli that induce CREB phosphorylation at Ser-133, focuses on phosphoserine-133-dependent and -independent mechanisms that affect CREB-mediated transcription, and discusses different models that may explain the discrepancy between CREB Ser-133 phosphorylation and activation of CREB-mediated transcription.

VEGF165 and angiopoietin-1 decreased myocardium infarct size through phosphatidylinositol-3 kinase and Bcl-2 pathways

Angiogenic growth factors, vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1) could decrease myocardial infarct size, which was assumed to be related with newly formed capillaries. We doubted that these capillaries could do this solely and the potential protective mechanisms of VEGF and Ang1 on myocardium need to be evaluated. Three types of adenoviruses encoding human VEGF(165) (Ad-VEGF(165)), human angiopoietin-1 (Ad-Ang1) and green fluorescent protein (Ad-GFP, as a parallel control) were constructed. Experiments were taken both in vitro and in vivo. As in vitro, the antiapoptosis effect of VEGF(165), Ang1 and VEGF(165)+Ang1 on cardiac myoblasts was observed, which seemed to be related with the activation of phosphatidylinositol-3 kinase and Bcl-2 pathways. As in vivo, adenoviruses were intramyocardially injected immediately after the ligation of the left anterior descending coronay arteries in rats. The results showed positive effect of VEGF(165), Ang1 and VEGF(165)+Ang1 on decreasing the myocardial infarct size at the 7th day. Myocardial PI-3K activity and Bcl-2 expression were elevated relatively at the 3rd day. The protective effect of VEGF(165) and Ang1 on the myocardium may broaden their functional research and contribute to their clinical use in the future.

Nerve growth factor modulates the proliferative capacity of the intrahepatic biliary epithelium in experimental cholestasis

BACKGROUND & AIMS

We evaluated the expression of neurotrophins in rat cholangiocytes and the role and mechanisms by which nerve growth factor (NGF) modulates cholangiocyte proliferation.

METHODS

The expression of neurotrophins and their receptors was investigated by immunohistochemistry in liver sections and reverse-transcription polymerase chain reaction and immunoblots in isolated cholangiocytes. In vitro, the effect of NGF on cholangiocyte proliferation and signal transduction was investigated by immunoblotting for proliferating cell nuclear antigen, phosphorylated AKT (p-AKT), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), phosphorylated c-jun-N-terminal kinase, and phosphorylated p38. In vivo, rats that had undergone bile duct ligation (BDL) were treated with an anti-NGF antibody to immunoneutralize NGF and bile duct mass, proliferation, apoptosis, and inflammation were investigated by immunohistochemistry.

RESULTS

NGF and its TrkA receptor were expressed by normal rat cholangiocytes and up-regulated following BDL. Cholangiocytes secrete NGF, and secretion is increased in proliferating BDL cholangiocytes. In vitro, NGF stimulated cholangiocyte proliferation, which was associated with enhanced p-AKT and p-ERK1/2 expression. NGF proliferation in vitro was partially blocked by the MEK inhibitor (UO126) and completely ablated by the phosphatidylinositol 3-kinase inhibitor (wortmannin). In vitro, NGF and estrogens have an additive effect on cholangiocyte proliferation by acting on phosphorylated TrkA and p-ERK1/2. In vivo, immunoneutralization of NGF decreased bile duct mass in BDL rats, which was associated with depressed proliferation and enhanced apoptosis and with increased portal inflammation.

CONCLUSIONS

Cholangiocytes secrete NGF and express NGF receptors. NGF induces cholangiocyte proliferation by activating the ERK and, predominantly, the phosphatidylinositol 3-kinase pathway and exerts an additive effect in combination with estrogens on proliferation.

Mitogen- and stress-activated protein kinase 1 mediates cAMP response element-binding protein phosphorylation and activation by neurotrophins

Activation of the transcription factor cAMP response element-binding protein (CREB) by neurotrophins is believed to regulate the survival, differentiation, and maturation of neurons in the CNS and PNS. Although phosphorylation of Ser133 is critical for the expression of CREB-regulated genes, the identity of neurotrophin-regulated Ser133 kinases has remained controversial. We show here that neurotrophin-induced CREB phosphorylation in CNS neurons depends exclusively on the extracellular signal-regulated kinase 1/2-activated kinase mitogen- and stress-activated protein kinase 1 (MSK1). Small interfering RNA directed against ribosomal S6 kinase 1 (RSK1) and RSK2 reduced phosphorylation of a RSK substrate but did not effect CREB-dependent transcription. However, expression of a selective inhibitory MSK1 mutant markedly attenuated BDNF-stimulated CREB phosphorylation and CREB-mediated transcription. Moreover, the ability of neurotrophins to stimulate CREB phosphorylation was abolished in CNS neurons from MSK1 knock-out mice. Consistent with a role for MSK1 in Ser133 phosphorylation, neurotrophin-induced expression of CREB-regulated genes was attenuated in MSK-deficient neurons. These results indicate that MSK1 is the major neurotrophin-activated Ser133 kinase in CNS neurons.

Similar activation of signal transduction pathways by the herpesvirus-encoded chemokine receptors US28 and ORF74

The virally encoded chemokine receptors US28 from human cytomegalovirus and ORF74 from human herpesvirus 8 are both constitutively active. We show that both receptors constitutively activate the transcription factors nuclear factor of activated T cells (NFAT) and cAMP response element binding protein (CREB) and that both pathways are modulated by their respective endogenous receptor ligands. By addition of specific pathway modulators against the G protein subunit Galphai, phospholipase C, protein kinase C, calcineurin, p38 MAP kinase, and MEK1, we find that the constitutive and ligand-dependent inductions are mediated by multiple yet similar pathways in both receptors. The NFAT and CREB transcription factors and their upstream activators are known inducers of host and virally encoded genes. We propose that the activity of these virally encoded chemokine receptors coordinates host and potentially viral gene expression similarly. As ORF74 is a known inducer of neoplasia, these findings may have important implications for cytomegalovirus-associated pathogenicity.

Overexpression of GD3 synthase induces apoptosis of vascular endothelial ECV304 cells through downregulation of Bcl-2

The disialoganglioside GD3 plays a major role in proliferation, differentiation, and apoptosis. It has been reported that ganglioside GD3 can induce apoptosis through bcl-2 mediated mitochondrial pathway. However, the relationship between ganglioside GD3 and B-cell/CLL lymphoma 2 (Bcl-2) is not fully understood. In this study, we have demonstrated that the downregulation of Bcl-2 by overexpression of CMP-NeuAc:GM3 alpha-2,8-sialyltransferase (GD3 synthase) results in an accelerated apoptosis in vascular endothelial cells (ECV304), as evidenced by DNA fragmentation and caspase-3 activation. In addition, phosphorylation of AKT and cyclic-AMP responsive element binding protein (CREB) was reduced by GD3 synthase overexpression. Moreover, the activation of CREB as a transcriptional factor was also inhibited, as evidenced by electrophoretic mobility shift assay. Therefore, we conclude that GD3 synthase has an apoptotic effect on ECV304 cells through downregulation of Bcl-2 expression via dephosphorylation of AKT and CREB.

Molecular alterations in apoptotic pathways after PKB/Akt-mediated chemoresistance in NCI H460 cells

Protein kinase B/Akt has been described as a central mediator of antiapoptotic signals in cancer cells. Furthermore, Akt has been shown to affect cell cycle progression and proliferative pathways and to possess a potential function in tumorigenesis and chemoresistance. In this study, we show that the ectopic expression of a constitutively active form of Akt1 (CA-Akt1) results in enhanced chemoresistance of NCI H460 human NSCLC cells towards a panel of chemotherapeutic agents. To understand the molecular alterations leading to impaired chemosensitivity mediated by activated Akt, we analysed various apoptotic pathways, including the activation of p53, caspases 3, 7, 8, and 9, release of cytochrome c from mitochondria, and the expression levels of pro- and antiapoptotic proteins such as Bcl-2, Bcl-x_L, Bcl-x_s, Bax, or Bfl-1. We observed that expression of CA-Akt did not interfere with single defined apoptotic switches, but modulated the apoptotic threshold of several apoptotic pathways towards increasing the threshold of onset. In particular, we found that CA-Akt-expressing cells displayed increased expression of the antiapoptotic Bcl-2 family member protein Bcl-x_l, and a delayed onset of the p53 pathway after treatment with cisplatin or Mitoxantrone. Thus, our data suggest that Akt mediates chemoresistance in NHI H460 cells by interfering with and delaying the onset of various apoptotic pathways. A complete inactivation of apoptotic pathways was observed in none of the molecular alterations investigated. Our data strengthen the role of Akt as a central mediator of cell survival signals and/or chemoresistance and as an attractive target for cancer cell chemosensitisation.

Development of Rationally Designed, Target-Based Agents for the Treatment of Advanced Colorectal Cancer

Although there have been several recent additions to the conventional armamentarium used to treat patients with advanced colorectal cancer, principally as a result of the development of selective and nonselective pharmacologic agents and antibodies, the general outcome of patients with advanced disease is still poor. However, a greater understanding of cancer biology, as well as major advances in biotechnology, is beginning to identify and characterize molecular aberrations that are common in patients with colorectal cancer. These advances have resulted in the development of a wide range of rationally designed, target-based anticancer therapeutic agents, which, by virtue of their selectivity, would be expected to produce less nonspecific toxicity and therefore higher therapeutic indices compared with nonspecific cytotoxic agents. This review will discuss several novel targets and therapeutic agents, particularly those designed to interrupt aberrant signal transduction and apoptotic processes. It will also emphasize the complexity of these systems and the need to incorporate novel clinical development paradigms based on a thorough scientific understanding of these targets.

Down-regulation of WW Domain-containing Oxidoreductase Induces Tau Phosphorylation in Vitro

Numerous enzymes hyperphosphorylate Tau in vivo, leading to the formation of neurofibrillary tangles (NFTs) in the neurons of Alzheimer's disease (AD). Compared with age-matched normal controls, we demonstrated here that the protein levels of WW domain-containing oxidoreductase WOX1 (also known as WWOX or FOR), its Tyr33-phosphorylated form, and WOX2 were significantly down-regulated in the neurons of AD hippocampi. Remarkably knock-down of WOX1 expression by small interfering RNA in neuroblastoma SK-N-SH cells spontaneously induced Tau phosphorylation at Thr212/Thr231 and Ser515/Ser516, enhanced phosphorylation of glycogen synthase kinase 3beta (GSK-3beta) and ERK, and enhanced NFT formation. Also an increased binding of phospho-GSK-3beta with phospho-Tau was observed in these WOX1 knock-down cells. In comparison, increased phosphorylation of Tau, GSK-3beta, and ERK, as well as NFT formation, was observed in the AD hippocampi. Activation of JNK1 by anisomycin further increased Tau phosphorylation, and SP600125 (a JNK inhibitor) and PD-98059 (an MEK1/2 inhibitor) blocked Tau phosphorylation and NFT formation in these WOX1 knock-down cells. Ectopic or endogenous WOX1 colocalized with Tau, JNK1, and GSK-3beta in neurons and cultured cells. 17Beta-estradiol, a neuronal protective hormone, increased the binding of WOX1 and GSK-3beta with Tau. Mapping analysis showed that WOX1 bound Tau via its COOH-terminal short-chain alcohol dehydrogenase/reductase domain. Together WOX1 binds Tau via its short-chain alcohol dehydrogenase/reductase domain and is likely to play a critical role in regulating Tau hyperphosphorylation and NFT formation in vivo.

ATP-induced mitogenesis is mediated by cyclic AMP response element-binding protein-enhanced TRPC4 expression and activity in human pulmonary artery smooth muscle cells

Extracellular ATP and intracellular cyclic AMP response element-binding protein (CREB, a transcription factor) promote cell proliferation in many cell types. The canonical transient receptor potential (TRPC) channels, which putatively participate in forming store- and receptor-operated Ca2+ channels, have been implicated in the pulmonary vascular remodeling processes. A link between extracellular ATP, CREB activation, and TRPC4 channel expression and activity has not been shown in human pulmonary artery smooth muscle cells (PASMC). Long-term (24-48 h) treatment of human PASMC with a low dose (100 microM) of ATP, which did not trigger a transient rise in free cytosolic Ca2+ concentration ([Ca2+]i) when applied acutely to the cells, caused marked increases in CREB phosphorylation and TRPC4 protein expression. The time course indicated that the ATP-mediated CREB phosphorylation preceded TRPC4 upregulation, whereas transfection of a nonphosphorylatable CREB mutant abolished ATP-mediated TRPC4 expression. Furthermore, treatment of human PASMC with ATP also enhanced the amplitude of capacitative Ca2+ entry (CCE) induced by passive store depletion, whereas the small interfering RNA specifically targeting TRPC4 attenuated ATP-mediated increases in TRPC4 expression and CCE amplitude and inhibited ATP-induced PASMC proliferation. These data suggest that low-dose ATP exerts part of its mitogenic effect in human PASMC via CREB-mediated upregulation of TRPC4 channel expression and activity and the subsequent increase in CCE and [Ca2+]i.

Alpha-synuclein, Parkinson's disease, and Alzheimer's disease

Alpha synuclein (alpha-SN) is a ubiquitous protein that is especially abundant in the brain and has been postulated to play a central role in the pathogenesis of Parkinson's disease (PD), Alzheimer's disease, and other neurodegenerative disorders. Here, we show that alpha-SN plays dual role of neuroprotection and neurotoxicity depending on its concentration or level of expression. In addition, our study shows that alpha-synuclein is differentially expressed in human peripheral blood mononuclear cells. PD patients expressed more alpha-synuclein than healthy controls. Thus, the alpha-synuclein expression in the peripheral immune system might be one of the primary causes of immune abnormalities in PD patients.

Neurotrophin-3 and a CREB-mediated signaling pathway regulate Bcl-2 expression in oligodendrocyte progenitor cells

Our previous results suggested that the transcription factor CREB mediates the actions of neuroligands and growth factor signals that coupled to different signaling pathways may play different roles along oligodendrocyte (OLG) development. We showed before that CREB phosphorylation in OLG progenitors is up-regulated by neurotrophin-3 (NT-3); and moreover CREB is required for NT-3 to stimulate the proliferation of these cells. We now show that treatment of OLG progenitors with NT-3 is also accompanied by an increase in the levels of the anti-apoptotic protein Bcl-2. Interestingly, the presence of a putative CREB binding site (CRE) in the Bcl-2 gene raised the possibility that CREB could also be involved in regulating Bcl-2 expression in the OLGs. Supporting this hypothesis, the NT-3 dependent increase in Bcl-2 levels is abolished by inhibition of CREB expression. In addition, transient transfection experiments using various regions of the Bcl-2 promoter and mutation of the CRE site indicate a direct role of CREB in regulating Bcl-2 gene activity in response to NT-3. Furthermore, protein-DNA binding assays show that the CREB protein from freshly isolated OLGs indeed binds to the Bcl-2 promoter CRE. Together with our previous results, these observations suggest that CREB may play an important role in linking proliferation and survival pathways in the OLG progenitors.

Proinflammatory cytokines and skeletal muscle

PURPOSE OF REVIEW

Metabolic abnormalities leading to a catabolic syndrome with progressive muscular atrophy are a common final stage of various chronic diseases. Proinflammatory cytokines have been suggested both to induce and mediate local catabolic mechanisms. This review focuses on the role of proinflammatory cytokines in the development of muscular abnormalities resulting in a loss of muscle mass and function. In addition, the underlying molecular signaling pathways, their transcriptional regulation, and the cellular systems contributing to enhanced muscular protein breakdown are discussed.

RECENT FINDINGS

Using transcriptional screening techniques, specific changes in gene expression have been identified that are characteristic of muscular wasting processes. Of particular interest is the atrophy-related and cytokine-inducible expression of a number of E3 ligases (e.g. atrogin-1, muscle ring finger protein 1), highly specific regulators of the ubiquitin-proteasome pathway, which target proteins for proteolytic breakdown by the proteasome. Furthermore, the activity of several transcription factors (e.g. nuclear factor kappa B) has been involved in specific transcriptional mechanisms of local inflammation and muscular atrophy. Finally, proinflammatory cytokines suppress the expression and function of the local anabolic growth factor insulin-like growth factor 1.

SUMMARY

Pronounced catabolic effects of proinflammatory cytokines in various tissues contribute to local catabolism, with progressive atrophic alterations of the skeletal muscle in chronic disease states. Recent developments in this field have explored the underlying pathways of muscular wasting and have already resulted in the description of new molecular targets that might lead to new therapeutic options for the treatment of muscular atrophy.

Potential roles of NF-kappaB and ERK1/2 in cytoprotection against oxidative cell death induced by tetrahydropapaveroline

Tetrahydropapaveroline (THP), a dopamine-derived tetrahydroisoquinoline catechol, has been suspected to be dopaminergic neurotoxin that elicits parkinsonism and neurobehavioral abnormalities associated with chronic alcoholism. THP has been detected in the brains of parkinsonian patients, and its urinary as well as brain level increases after l-3,4-dihydroxyphenylalanine treatment. Autoxidation or enzymatic oxidation of THP and subsequent generation of reactive oxygen species (ROS) may contribute to the degeneration of dopaminergic neurons induced by this tetrahydroisoquinoline alkaloid. In the present study, THP was found to elicit cytotoxicity in cultured rat pheochromocytoma (PC12) cells, which was completely blocked by reduced glutathione and N-acetyl-L-cysteine. THP-treated PC12 cells exhibited increased intracellular accumulation of ROS and underwent apoptosis as determined by poly(ADP-ribose)polymerase cleavage, an increased ratio of Bax to BclxL, terminal transferase-mediated dUTP nick end labeling, and nuclear fragmentation or condensation. THP treatment caused activation of the redox-sensitive transcription factor nuclear factor kappaB (NF-kappaB). Pretreatment of PC12 cells with NF-kappaB inhibitors, such as l-1-tosylamido-2-phenylethyl chloromethyl ketone and parthenolide, aggravated THP-induced cell death. THP treatment resulted in differential activation of mitogen-activated protein kinases as well as Akt/protein kinase B, thereby transmitting cell survival or death signals. In conclusion, THP induces apoptosis in PC12 cells by generating ROS. THP-mediated oxidative stress was accompanied by differential activation of intracellular signaling kinases and NF-kappaB.

Up-regulation and altered distribution of lysyl oxidase in the central nervous system of mutant SOD1 transgenic mouse model of amyotrophic lateral sclerosis

Mutations of the copper-zinc superoxide dismutase (SOD1) gene can result in the development of amyotrophic lateral sclerosis (ALS). The exact cellular mechanisms causing ALS are not known, but oxidative stress is thought to play a prominent role. Lysyl oxidase (LOX) is one of the genes that are known to be up-regulated in ALS patients. In this study, we examined LOX localization in wild type rat and mouse brain sections using immunohistochemistry coupled with laser-scanning confocal microscope. The results showed that LOX, an extracellular matrix protein, was expressed in the choroid plexus, blood vessel walls, brain matrix, and neurons of normal rat and mice. In neurons, LOX was localized within the cytoplasm. LOX immunoreactivity increased in neurons of the spinal cord, brain stem and cortex, and the Purkinje cells of the cerebellum in transgenic G93A SOD1 (mSOD1) mouse model of ALS. In situ hybridization indicated that LOX gene expression was enhanced in the neurons of the spinal cord, brain stem, cortex, caudoputamen and cerebellum in mSOD1 mice compared with wild type controls. LOX enzyme activity was increased in mSOD1 mice. An increase in the amount of LOX mRNA, protein and enzyme activity was coincidental with late stage ALS, indicating that LOX may be associated with the progression of the neurodegenerative process in the mSOD1 model of ALS.

SRF regulates Bcl-2 expression and promotes cell survival during murine embryonic development

The transcription factor serum response factor (SRF) controls the expression of genes involved in cellular proliferation and differentiation. Interestingly, SRF also promotes cell survival by regulating the expression of antiapoptotic genes. In in vitro differentiating murine embryonic stem (ES) cells, SRF deficiency leads to increased apoptosis. Loss of SRF correlates with impaired expression of the antiapoptotic Bcl-2 and Bcl-xl genes. SRF binds the Bcl-2 promoter in vivo and activates Bcl-2 transcription. Reconstituting Bcl-2 in Srf-/- ES cells rescues these cells from apoptosis, demonstrating that SRF-dependent Bcl-2 expression is critical for ES cell survival. At the multicellular level, SRF deficiency leads to impaired cavitation and reduced Bcl-2 expression in embryoid bodies (EBs) and inappropriate apoptosis in both EBs and pregastrulation mouse embryos. Thus, our data from genetic and cellular studies uncover SRF-regulated Bcl-2 expression as a novel mechanism that is important for cell survival during early murine embryogenesis.

Regulation of caspase activation in axotomized retinal ganglion cells

Transection of the optic nerve initiates massive death of retinal ganglion cells (RGCs). Interestingly, despite the severity of the injury, RGC loss was not observed until several days after axotomy. The mechanisms responsible for this initial lack of RGC death remained unknown. In the current study, immunohistochemical analysis revealed that caspases-3 and -9 activation in the RGCs were not detected until day 3 post-axotomy, coinciding with the onset of axotomy-induced RGC loss. Interestingly, elevated Akt phosphorylation was observed in axotomized retinas during the absence of caspase activation. Inhibiting the increase in Akt phosphorylation by intravitreal injection of wortmannin and LY294002, inhibitors of PI3K, resulted in premature nuclear fragmentation, caspases-3 and -9 activation in the ganglion cell layer. Our findings thus indicate that the PI3K/Akt pathway may serve as an endogenous regulator of caspase activation in axotomized RGCs, thereby, contributing to the late onset of RGC death following axotomy.

The costimulation-regulated duration of PKB activation controls T cell longevity

A brief antigenic stimulus can promote T cell proliferation, but the duration and nature of intracellular signals required for survival are unclear. Here we show that in the absence of OX40 costimulation, antigen-activated CD4+ cells are short-lived because the activity of protein kinase B (PKB; also known as Akt) is not maintained over time. Activated T cells that express a dominant-negative variant of PKB also undergo apoptosis, reproducing the OX40-deficient phenotype. In contrast, an active form of PKB prevents downregulation of antiapoptotic proteins in OX40-deficient T cells, rescues antigen-induced cell survival in vivo, and controls inflammation in recall responses. Thus, sustained and periodic PKB signaling has an integral role in regulating T cell longevity.

Ras, Akt, and Mechanotransduction in the Cardiac Myocyte

The Ras subfamily of 21-kDa ("small") guanine nucleotide binding proteins [which includes Ha-Ras, Ki(A)-Ras, Ki(B)-Ras, and N-Ras] is universally important in regulating intracellular signaling events in mammalian cells and controls their growth, proliferation, senescence, differentiation, and survival. These Ras isoforms act as membrane-associated biological switches that transduce signals from transmembrane receptors, thus potentially activating a variety of downstream signaling proteins. These include ultimately two Ser/Thr protein kinase families, the extracellular signal-regulated kinases 1/2 (ERK1/2) and Akt (or protein kinase B). Activation of ERK1/2 has been associated with cardiac myocyte hypertrophy (ie, increased cell size and myofibrillogenesis, with concurrent transcriptional changes to a fetal pattern of gene expression), whereas activation of Akt is associated with the increased protein accretion in hypertrophy. Both ERK1/2 and Akt may promote myocyte survival. In the intact heart in vivo and in primary cultures of cardiac myocytes, mechanical strain induces hypertrophy, a process known as mechanotransduction, which may involve Ras, ERK1/2, and Akt. In this study, general and cardiospecific aspects of the regulation of Ras and Akt will be described. The various mechanisms through which mechanical strain might initiate Ras- or Akt-dependent signaling will be discussed. The overall conclusion is that although an involvement of Ras and Akt in mechanotransduction is likely, more work (particularly focusing on mechanoreception) needs to be undertaken before it is unequivocally established.

Activation of vascular endothelial growth factor receptor-1 sustains angiogenesis and Bcl-2 expression via the phosphatidylinositol 3-kinase pathway in endothelial cells

Vascular insufficiency and retinal ischemia precede many proliferative retinopathies and stimulate secretion of various vasoactive growth factors, including vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF). It is unclear, however, how PlGF, which is elevated in proliferative diabetic retinopathy and is a VEGF homolog that binds only to VEGF receptor (VEGFR)-1, promotes pathological angiogenesis. When primary microvascular endothelial cells were grown on collagen gels, PlGF-containing ligands upregulated Bcl-2 expression and stimulated the formation of capillary-like tube networks that were retained for up to 14 days in culture. The inhibition of VEGFR-1 results in a dramatic decrease in the number of capillary connections, indicating that VEGFR-1 ligands promote branching angiogenesis. In contrast, VEGF-induced tube formations and Bcl-2 expression were significantly decreased at the end of this period. Flow cytometry analysis of annexin-V/propidium iodide-stained cells revealed that PlGF and PlGF/VEGF heterodimer inhibited apoptosis in serum-deprived endothelial cells. These two growth factors stimulated a survival signaling pathway phosphatidylinositol 3-kinase (PI3K), as identified by increased Akt phosphorylation and because blocking PI3K signalling by adenovirus-mediated overexpression of wild-type phosphatase and tensin homolog on chromosome 10 (PTEN) disrupted angiogenesis and decreased Bcl-2 expression by PlGF and PlGF/VEGF heterodimer, whereas a dominant-negative PTEN mutant enhanced endothelial sprout formation and Bcl-2 expression. Together, these findings indicate that PlGF-containing ligands contribute to pathological angiogenesis by prolonging cell survival signals and maintaining vascular networks.

Differential expression of Akt/protein kinase B, Bcl-2 and Bax proteins in human leiomyoma and myometrium

The expression and activation of serine/threonine protein kinase, Akt, in leiomyoma and in adjacent myometrium of human uteri was studied parallel with the changes of Bcl-2, Bax proteins, estrogen and progesterone receptors during menstrual cycle and early stage of the menopause. Abundant expression of Akt protein was detected in the studied tissues during menstrual cycle, the rate of increase was higher in leiomyoma than in corresponding myometrium. The expression of estrogen receptor alpha, progesterone receptor and of Bcl-2 protein changed parallel with that of Akt protein. The level of phosphorylated Akt (pAkt(473)) was seen only in leiomyoma samples from the growing period of tumors. At early stage of menopause levels of all studied proteins were lower than that in the menstrual cycle with the exception of Bax protein expression, which was high in leiomyoma. Our data suggest the involvement of phosphatidylinositol 3-kinase/Akt signaling in the pathomechanism of leiomyoma.

Cell-cycle regulation of T-cell responses - novel approaches to the control of alloimmunity

Alloreactive T cells undergo clonal expansion before they participate in allograft rejection. Current estimates suggest that roughly 1 in 20 peripheral T cells are alloreactive, and these cells may expand at least 20-50-fold during an alloimmune response in vivo. The majority of immunosuppressive drugs currently used to facilitate graft survival in experimental models and in the clinic act to inhibit T-cell proliferation. This review focuses on 1) recent advances in monitoring alloreactive T-cell proliferation during alloimmune responses, 2) the link between cell division, anergy avoidance, and effector T-cell differentiation, and 3) an overview of growth factor receptor-coupled signal transduction pathways, with emphasis on key cell-cycle regulators that may serve as potential targets for novel immunosuppressive or tolerance-inducing strategies.

Control of Bcl-2 expression by reactive oxygen species

Reactive oxygen species (ROS) mediate apoptosis in many different cell types. We have previously shown that the antioxidant Mn(III) tetrakis(5,10,15,20-benzoic acid)porphyrin (MnTBAP) decreased intracellular ROS and prevented the apoptosis of activated T cells in vitro. To determine the mechanism(s) by which MnTBAP afforded such protection, we used Affymetrix (Santa Clara, CA) gene arrays to compare gene expression in T cells activated with staphylococcal enterotoxin B in vivo then cultured with or without MnTBAP. This analysis showed that the antioxidant increased the expression of Bcl-2, an antiapoptotic molecule whose levels are normally decreased by T cell activation. Culture with MnTBAP revealed a tight inverse correlation between the levels of Bcl-2 and ROS within T cells. In vivo, production of ROS in activated T cells occurred before Bcl-2 down-regulation. Furthermore, MnTBAP's ability to prevent death required the expression of Bcl-2 in most T cells. Finally, neither ROS production nor the effects on Bcl-2 expression required Bim, the Bcl-2 antagonist that mediates the death of activated T cells in vivo. Taken together, our results suggest that ROS sensitize T cells to apoptosis by decreasing expression of Bcl-2.

Akt phosphorylation and stabilization of X-linked inhibitor of apoptosis protein (XIAP)

Akt negatively regulates apoptotic pathways at a premitochondrial level through phosphorylation and modulation of proteins such as Bad, Forkhead proteins, and GSK-3beta. Akt has also been shown to protect cell death at a post-mitochondrial level, although its downstream targets have not been well documented. Here, we demonstrate that Akt, including AKT1 and AKT2, interacts with and phosphorylates X-linked inhibitor of apoptosis protein (XIAP) at residue serine-87 in vitro and in vivo. Phosphorylation of XIAP by Akt protects XIAP from ubiquitination and degradation in response to cisplatin. Moreover, autoubiquitination of XIAP is also inhibited by Akt. Consistent with this, an XIAP mutant introduced into cells which mimics the Akt-phosphorylated form (i.e. XIAP-S87D) displays reduced ubiquitination and degradation as compared with wild type XIAP. The greater stability of XIAP-S87D in cells translated to increased cell survival after cisplatin treatment. Conversely, a mutant that could not be phosphorylated by Akt (XIAP-S87A) was more rapidly degraded and showed increased cisplatin-induced apoptosis. Furthermore, suppression of XIAP by either siRNA or adenovirus of antisense of XIAP induced programmed cell death and inhibited Akt-stimulated cell survival in ovarian cancer cells. These data identify XIAP as a new downstream target of Akt and a potentially important mediator of the effect of Akt on cell survival.

Cilostazol Prevents Focal Cerebral Ischemic Injury by Enhancing Casein Kinase 2 Phosphorylation and Suppression of Phosphatase and Tensin Homolog Deleted from Chromosome 10 Phosphorylation in Rats

This study shows the in vivo neuroprotective effect of cilostazol against cerebral ischemic injury evoked by subjecting rats to 2-h occlusion of middle cerebral artery (MCAO) followed by 24-h reperfusion. We observed the signaling pathway by which cilostazol suppressed MCAO-induced increased phosphorylation of phosphatase and tensin homolog deleted from chromosome 10 (PTEN) and apoptosis via increased phosphorylation of casein kinase 2 (CK2). When rats received 30 mg/kg cilostazol orally two times at 5 min and 4 h after the completion of ischemia, the infarct area was significantly reduced in the cortex and striatum with improvement of neurological deterioration. Increased DNA fragmentation in the penumbral zone was significantly reduced by cilostazol. Cilostazol significantly elevated phosphorylation levels of CK2, Akt, and cyclic AMP response element-binding protein (CREB) in association with increased Bcl-2 in the ischemic area, whereas the elevated PTEN phosphorylation was significantly reduced, all of which were antagonized by iberiotoxin, a maxi-K channel blocker, administered intracisternally 30 min before ischemia. In conclusion, cilostazol ameliorates the neuronal damage by suppression of apoptotic cell death via the maxi-K channel opening-coupled up-regulation of CK2 phosphorylation and down-regulation of PTEN phosphorylation with resultant increase in the Akt and CREB phosphorylation and increased Bcl-2 protein.

Inhibition of phosphatidylinositol 3-kinase dephosphorylates BAD and promotes apoptosis in myeloid leukemias

The phosphatidylinositol 3-kinase (PI3K)/AKT protein kinase pathway is involved in cell growth, proliferation, and apoptosis. The functional activation of PI3K/AKT provides survival signals and blockade of this pathway may facilitate cell death. Downstream targets of PI3K-AKT include the proapoptotic protein BAD, caspase-9, NF-kappaB, and Forkhead. We have previously reported that BAD is constitutively phosphorylated in primary acute myeloid leukemia (AML) cells, a post-transcriptional modification, which inactivates its proapoptotic function. In this study, we tested the hypothesis that the inhibition of PI3K by LY294002 results in the dephosphorylation of AKT and BAD, and thus promote leukemia cell apoptosis. We investigated the effects of LY294002 in megakaryocytic leukemia-derived MO7E cells, primary AML and normal bone marrow progenitor cells. In MO7E cells, LY294002 reduced AKT kinase activity, induced dephosphorylation of AKT and BAD, and increased apoptosis. Concomitant inhibition of mitogen-activated protein kinase signaling or combination with all-trans retinoic acid further enhanced apoptosis of leukemic cells. In primary AML samples, clonogenic cell growth was significantly reduced. Normal hematopoietic progenitors were less affected, suggesting preferential targeting of leukemia cells. In conclusion, the data suggest that the inhibition of the PI3K/AKT signaling pathway restores apoptosis in AML and may be explored as a novel target for molecular therapeutics in AML.

Oxidative Stress in Type 1 Diabetes

We have been investigating the effects of preventing oxidative stress on pathogenesis and complications of type 1 diabetes in the NOD mouse model. Our studies have shown that damage caused by oxidative stress is higher in islets and vascular tissue of NOD mice than in nonautoimmune controls or a diabetes-resistant NOD mouse. In addition, phagocytic function and cytokine production by macrophages are aberrant in the NOD. We have demonstrated that treatment of prediabetic NOD mice for 2 weeks with a metalloporphyrin superoxide dismutase (SOD) mimetic results in marked reduction of oxidative stress in islets and vascular tissue and a reversal of macrophage defects.

The phosphoinositide 3-kinase/Akt pathway regulates cell cycle progression of HL60 human leukemia cells through cytoplasmic relocalization of the cyclin-dependent kinase inhibitor p27(Kip1) and control of cyclin D1 expression

The serine/threonine protein kinase Akt, a downstream effector of phosphoinositide 3-kinase (PI3K), plays a pivotal role in tumorigenesis because it affects the growth and survival of cancer cells. Several laboratories have demonstrated that Akt inhibits transcriptional activation of a number of related forkhead transcription factors now referred to as FoxO1, FoxO3, and FoxO4. Akt-regulated forkhead transcription factors are involved in the control of the expression of both the cyclin-dependent kinase (cdk) inhibitor p27(Kip1) and proapoptotic Bim protein. Very little information is available concerning the importance of the PI3K/Akt pathway in HL60 human leukemia cells. Here, we present our findings showing that the PI3K/Akt axis regulates cell cycle progression of HL60 cells through multiple mechanisms also involving the control of FoxO1 and FoxO3. To this end, we took advantage of a HL60 cell clone (HL60AR cells) with a constitutively activated PI3K/Akt axis. When compared with parental (PT) HL60 cells, HL60AR cells displayed higher levels of phosphorylated FoxO1 and FoxO3. In AR cells forkhead factors localized predominantly in the cytoplasm, whereas in PT cells they were mostly nuclear. AR cells proliferated faster than PT cells and showed a lower amount of the cdk inhibitor p27(Kip1), which was mainly found in the cytoplasm and was hyperphosphorylated on threonine residues. AR cells also displayed higher levels of cyclin D1 and phosphorylated p110 Retinoblastoma protein. The protein levels of cdk2, cdk4, and cdk6 were not altered in HL60AR cells, whereas the activities of both ckd2 and cdk6 were higher in AR than in PT cells. These results show that in HL60 cells the PI3K/Akt signaling pathway may be involved in the control of the cell cycle progression most likely through mechanisms involving the activation of forkhead transcription factors.

Cilostazol Enhances Casein Kinase 2 Phosphorylation and Suppresses Tumor Necrosis Factor-α-Induced Increased Phosphatase and Tensin Homolog Deleted from Chromosome 10 Phosphorylation and Apoptotic Cell Death in SK-N-SH Cells

This study shows the signaling pathway by which cilostazol suppresses tumor necrosis factor-alpha (TNF-alpha)-induced the phosphatase and tensin homolog deleted from chromosome 10 (PTEN) phosphorylation and apoptosis via casein kinase 2 (CK2) phosphorylation in the SK-N-SH cells (neuroblastoma cells). Cilostazol (10 microM) fully restored cell proliferation with suppression of DNA fragmentation induced by TNF-alpha and emodin, a CK2 inhibitor, which were antagonized by iberiotoxin, a maxi-K channel blocker. Under application of TNF-alpha or emodin, increased PTEN phosphorylation and decreased phosphorylation of CK2/Akt/cyclic AMP response element-binding protein (CREB), and CK2 activity were significantly reversed by cilostazol (approximately 1-100 microM), all of which were antagonized by iberiotoxin. 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619) and (3S)-(+)-(5-chloro-2-methoxyphenyl-1,3-dihydro-3-fluoro-6-(trifluoromethyl)-2H-indol-2-one (BMS 204352) maxi-K channel openers significantly elevated CK2 activities that were reversible by iberiotoxin. SK-N-SH cells treated with antisense CK2 oligodeoxynucleotide showed a prominent DNA fragmentation with little responsiveness to TNF-alpha in the phosphorylation of PTEN, indicative of the essential role of p-CK2/CK2 in cell proliferation, and the decreased cell viability of these cells was not restored by cilostazol. It is suggested that the action of cilostazol promoting cell survival is ascribed to the maxi-K channel opening-coupled up-regulation of CK2 phosphorylation and down-regulation of PTEN phosphorylation with resultant increased phosphorylation of Akt and CREB.

Cilostazol prevents tumor necrosis factor-alpha-induced cell death by suppression of phosphatase and tensin homolog deleted from chromosome 10 phosphorylation and activation of Akt/cyclic AMP response element-binding protein phosphorylation

This study examines the signaling mechanism by which cilostazol prevents neuronal cell death. Cilostazol ( approximately 0.1-100 microM) prevented tumor necrosis factor-alpha (TNF-alpha)-induced decrease in viability of SK-N-SH and HCN-1A cells, which was antagonized by 1 microM iberiotoxin, a maxi-K channel blocker. TNF-alpha did not suppress the viability of the U87-MG cell, a phosphatase and tensin homolog deleted from chromosome 10 (PTEN)-null glioblastoma cell, but it did decrease viability of U87-MG cells transfected with expression vectors for the sense PTEN, and this decrease was also prevented by cilostazol. Cilostazol as well as 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619) and (3S)(+)-(5-chloro-2-methoxyphenyl)-1,3-dihydro-3-fluoro-6-(trifluoromethyl)-2H-indole-2-one (BMS 204352), maxi-K channel openers, prevented increased DNA fragmentation evoked by TNF-alpha, which were antagonizable by iberiotoxin. TNF-alpha-induced increased PTEN phosphorylation and decreased Akt/cyclic AMP response element-binding protein (CREB) phosphorylation were significantly prevented by cilostazol, those of which were antagonized by both iberiotoxin and paxilline, maxi-K channel blockers. The same results were evident in U87-MG cells transfected with expression vectors for sense PTEN. Cilostazol increases the K+ current in SK-N-SH cells by activating maxi-K channels without affecting the ATP-sensitive K+ channel. Thus, our results for the first time provide evidence that cilostazol prevents TNF-alpha-induced cell death by suppression of PTEN phosphorylation and activation of Akt/CREB phosphorylation via mediation of the maxi-K channel opening.

SP600125, an inhibitor of c-jun N-terminal kinase, activates CREB by a p38 MAPK-mediated pathway

SP600125, an anthrapyrazolone inhibitor of c-jun N-terminal kinase (JNK), has been used to characterize the role of JNK in apoptotic pathways. In this study, we have demonstrated an additional novel anti-apoptotic action of this inhibitor in MIN6 cells, a mouse beta cell line. SP600125 induced CREB-dependent promoter activation by 2.8-fold at 20 microM, the concentration at which it inhibited c-jun-dependent promoter activation by 51%. There was a significant (P<0.01) increase in CREB phosphorylation (serine 133) at 5 min, which persisted for a period of 2h. Examination of signaling pathways upstream of CREB showed a 2.5-fold increase in the active phospho form of p38 MAPK. This finding was further confirmed by an in vitro kinase assay using ATF-2 as substrate. SB203580, an inhibitor of p38 MAPK, partially blocked SP600125-mediated activation of CREB. These observations suggest that SP600125 could be used as a small molecular weight activator of CREB.

CREB is required for acquisition of ischemic tolerance in gerbil hippocampal CA1 region

Ischemic tolerance is well known as a neuroprotective effect of pre-conditioning ischemia against delayed neuronal death, however, the mechanism or mechanisms underlying this effect are not fully understood. We investigated the relationship between CREB and ischemic tolerance in gerbil hippocampal CA1 neurons using CRE decoy oligonucleotide. Sublethal ischemia led to an increase in the level of CREB phosphorylation in CA1 regions while lethal ischemia did not. Experiments with NG108-15 cells showed that adding CRE decoy oligonucleotide to culture media significantly inhibited the cell growth rate. The administration of CRE decoy oligonucleotide into gerbil cerebral ventricle decreased CREB-DNA binding activity to 38% of the control. Pre-treatment with CRE decoy oligonucleotide 24 h before the induction of ischemic tolerance decreased CA1 neuronal cell survival to 21% of the control. The present findings suggest that a CREB-mediated transcription system is necessary for the induction of ischemic tolerance.

Insulin prevents depolarization of the mitochondrial inner membrane in sensory neurons of type 1 diabetic rats in the presence of sustained hyperglycemia

Mitochondrial dysfunction has been proposed as a mediator of neurodegeneration in diabetes complications. The aim of this study was to determine whether deficits in insulin-dependent neurotrophic support contributed to depolarization of the mitochondrial membrane in sensory neurons of streptozocin (STZ)-induced diabetic rats. Whole cell fluorescent video imaging using rhodamine 123 (R123) was used to monitor mitochondrial inner membrane potential (deltapsi(m)). Treatment of cultured dorsal root ganglia (DRG) sensory neurons from normal adult rats for up to 1 day with 50 mmol/l glucose had no effect; however, 1.0 nmol/l insulin increased deltapsi(m) by 100% (P < 0.05). To determine the role of insulin in vivo, STZ-induced diabetic animals were treated with background insulin and the deltapsi(m) of DRG sensory neurons was analyzed. Insulin therapy in STZ-induced diabetic rats had no effect on raised glycated hemoglobin or sciatic nerve polyol levels, confirming that hyperglycemia was unaffected. However, insulin treatment significantly normalized diabetes-induced deficits in sensory and motor nerve conduction velocity (P < 0.05). In acutely isolated DRG sensory neurons from insulin-treated STZ animals, the diabetes-related depolarization of the deltapsi(m) was corrected (P < 0.05). The results demonstrate that loss of insulin-dependent neurotrophic support may contribute to mitochondrial membrane depolarization in sensory neurons in diabetic neuropathy.

AKT inhibition is associated with chemosensitisation in the pancreatic cancer cell line MIA-PaCa-2

Activation of the serine/threonine kinase AKT is common in pancreatic cancer; inhibition of which sensitises cells to the apoptotic effect of chemotherapy. Of the various downstream targets of AKT, we examined activation of the NF-kappaB transcription factor and subsequent transcriptional regulation of BCL-2 gene family in pancreatic cancer cells. Inhibition of either phosphatidylinositol-3 kinase or AKT led to a decreased protein level of the antiapoptotic gene BCL-2 and an increased protein level of the proapoptotic gene BAX. Furthermore, inhibition of AKT decreased the function of NF-kappaB, which is capable of transcriptional regulation of the BCL-2 gene. Inhibiting this pathway had little effect on the basal level of apoptosis in pancreatic cancer cells, but increased the apoptotic effect of chemotherapy. The antiapoptotic effect of AKT activation in pancreatic cancer cells may involve transcriptional induction of a profile of BCL-2 proteins that confer resistance to apoptosis; alteration of this balance allows sensitisation to the apoptotic effect of chemotherapy.

An estrogen replacement therapy containing nine synthetic plant-based conjugated estrogens promotes neuronal survival

Epidemiological data from retrospective and case-control studies have indicated that estrogen replacement therapy can decrease the risk of developing Alzheimer's disease. In addition, estrogen replacement therapy has been found to promote neuronal survival both in vivo and in vitro. We have shown that conjugated equine estrogens (CEE), containing 238 different molecules composed of estrogens, progestins, and androgens, exerted neurotrophic and neuroprotective effects in cultured neurons. In the current study, we sought to determine whether a steroidal formulation of nine synthetic conjugated estrogens (SCE) chemically derived from soybean and yam extracts is as effective as the complex multisteroidal formulation of CEE. Analyses of the neuroprotective efficacy indicate that SCE exhibited significant neuroprotection against beta amyloid, hydrogen peroxide, and glutamate-induced toxicity in cultured hippocampal neurons. Indices of neuroprotection included an increase in neuronal survival, a decrease in neurotoxin-induced lactate dehydrogenase release, and a reduction in neurotoxin-induced apoptotic cell death. Furthermore, SCE was found to attenuate excitotoxic glutamate-induced [Ca2+]i rise. Quantitative analyses indicate that the neuroprotective efficacy of SCE was comparable to that of the multisteroidal CEE formulation. Data derived from these investigations predict that SCE could exert neuroprotective effects comparable to CEE in vivo and therefore could reduce the risk of Alzheimer's disease in postmenopausal women.

Cytokine-mediated down-regulation of the transcription factor cAMP-response element-binding protein in pancreatic beta-cells

Cytokines are known to induce apoptosis of pancreatic beta-cells. Impaired expression of the anti-apoptotic gene bcl-2 is one of the mechanisms involved. In this study, we identified a defect involving transcription factor cAMP-response element-binding protein (CREB) in the expression of bcl-2. Exposure of mouse pancreatic beta-cell line, MIN6 cells, to cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma) led to a significant (p < 0.01) decrease in Bcl-2 protein and mRNA levels. Cytokines decreased (56%) the activity of the bcl-2 promoter that contains a cAMP-response element (CRE) site. Similar decreases were seen with a luciferase reporter gene driven by tandem repeats of CRE and a CREB-specific Gal4-luciferase reporter, suggesting a defect at the level of CREB. The active phospho form (serine 133) of CREB diminished significantly (p < 0.01) in cells exposed to cytokines. Examination of signaling pathways upstream of CREB revealed a reduction in the active form of Akt. Cytokine-induced decrease of bcl-2 promoter activity was partially restored when cells were cotransfected with a constitutively active form of Akt. Several end points of cytokine action including decreases in phospho-CREB, phospho-Akt, and BCl-2 levels and activation of caspase-9 were observed in isolated mouse islets. Overexpression of wild-type CREB in MIN6 cells by plasmid transfection and adenoviral infection led to protection against cytokine-induced apoptosis. Adenoviral transfer of dominant-negative forms of CREB, on the other hand, resulted in activation of caspase-9 and exaggeration of cytokine-induced beta-cell apoptosis. Together, these results point to CREB as a novel target for strategies aimed at improving the survival of beta-cells.

Epidermal growth factor up-regulates expression of transforming growth factor beta receptor type II in human dermal fibroblasts by phosphoinositide 3-kinase/Akt signaling pathway: Resistance to epidermal growth factor stimulation in scleroderma fibroblasts

OBJECTIVE

Transforming growth factor beta receptors (TGFbetaRs) are known to be expressed at high levels in several fibrotic diseases, including systemic sclerosis. In the present study, we investigated the mechanism of up-regulation of TGFbetaR expression.

METHODS

The levels of expression of TGFbetaR type II (TGFbetaRII) messenger RNA (mRNA), with or without stimulation by epidermal growth factor (EGF), were evaluated by Northern blot analysis, and the protein levels were determined by immunoblotting. The transcription activity of the TGFbetaRII gene was examined with luciferase assays using the -1670/+35 TGFbetaRII promoter luciferase construct.

RESULTS

EGF up-regulates the expression of TGFbetaRII mRNA and protein in human dermal fibroblasts. Actinomycin D, an RNA synthesis inhibitor, significantly blocked the EGF-mediated up-regulation of TGFbetaRII mRNA expression, whereas cycloheximide, a protein synthesis inhibitor, did not block this up-regulation. In addition, EGF treatment did not significantly affect the TGFbetaRII mRNA half-life. EGF-mediated induction of TGFbetaRII expression was inhibited by treatment of fibroblasts with the selective phosphoinositide 3-kinase (PI 3-kinase) inhibitors wortmannin or LY294002, and Akt inhibitor also blocked EGF-induced expression of TGFbetaRII. In addition, EGF induced TGFbetaRII promoter activity, and this induction was significantly blocked by wortmannin, LY294002, or Akt inhibitor. Cotransfection with a dominant-negative mutant of p85 (the regulatory component of PI 3-kinase) or Akt significantly reduced the induction of TGFbetaRII promoter activity by EGF. Moreover, a constitutive active form of p110 (a catalytic component of PI 3-kinase) induced TGFbetaRII promoter activity. In addition, scleroderma fibroblasts expressed increased levels of TGFbetaRII but did not show further up-regulation of TGFbetaRII expression by EGF.

CONCLUSION

These results indicate that EGF-mediated induction of TGFbetaRII expression occurs at the transcription level, does not require de novo protein synthesis, and involves the PI 3-kinase/Akt signaling pathway, and that abnormal activation of EGF-mediated signaling pathways, including PI 3-kinase or Akt, might play a role in the up-regulation of TGFbetaRII in scleroderma fibroblasts.

Antiangiogenic effect of KR-31372 by apoptosis via mediation of mitochondrial KATP channel opening and the phosphatase and tensin homolog deleted from chromosome 10 phosphorylation

Antiangiogenic action of (2R,3R,4S)-N"-cyano-N-(6-nitro-3,4-dihydro-hydroxy-2-methyl-2-dimethoxymethyl-2H-1-benzopyran-4yl)-N'-benzyl guanidine (KR-31372) was examined with its proapoptotic action in human umbilical vein endothelial cells (HUVECs) compared with diazoxide. KR-31372 as well as diazoxide significantly suppressed the neovascularization in mice induced by the Matrigel-containing recombinant human vascular endothelial growth factor (VEGF)165 in vivo and the basal tube formation of HUVECs in vitro with suppression of proliferation of HUVECs stimulated by VEGF165. KR-31372 and diazoxide enhanced DNA fragmentation associated with increase in phosphatase and tensin homolog deleted from chromosome 10 (PTEN) and decrease in serine/threonine kinase phosphorylation, which were accompanied by augmented Bax and cytochrome c release, and suppressed Bcl-2 in HUVECs. In the U87-MG cells, when transfected with expression vectors for sense PTEN, KR-31372 enhanced DNA fragmentation, but not in naive U87-MG cells. The suppression by KR-31372 and diazoxide of these variables was significantly antagonized by 5-hydroxydecanoic acid, a mitochondrial KATP channel blocker. Taken together, KR-31372 strongly inhibited angiogenesis in HUVECs by proapoptotic mechanism via mediation of 5-hydroxydecanoic acid-inhibitable mitochondrial KATP channel opening and PTEN phosphorylation.

PTEN regulates Akt kinase activity in hippocampal neurons and increases their sensitivity to glutamate and apoptosis

The tumor suppressor phosphatase PTEN can promote apoptosis of mitotic cells by inhibiting activation of the cell survival kinase Akt. PTEN is essential for normal embryonic development, PTEN expression is associated with neuronal differentiation, and deletion of PTEN in the mouse brain results in seizures, ataxia, and other abnormalities. However, the possible roles of PTEN in regulating neuronal survival are not known. We provide evidence that PTEN sensitizes hippocampal neurons to excitotoxic death in culture and in vivo. Overexpression of wild-type PTEN decreased, while a dominant-negative PTEN increased, levels of activated Akt in cultured hippocampal neurons. Wild-type PTEN promoted, while dominant-negative PTEN prevented, apoptotic death of neurons exposed to the excitatory amino acid neurotransmitter glutamate. Hippocampal neurons of mice with reduced PTEN levels were more resistant to seizure-induced death compared to wild-type littermates. These findings demonstrate a cell death function of PTEN in hippocampal neurons and identify PTEN as a potential therapeutic target for neurodegenerative disorders that involve excitotoxicity and apoptosis. The ability of PTEN to modify neuronal sensitivity to glutamate also suggests possible roles for PTEN in regulating developmental and synaptic plasticity.

Redox regulation of cAMP-responsive element-binding protein and induction of manganous superoxide dismutase in nerve growth factor-dependent cell survival

Reactive oxygen species (ROS) act as both signaling molecules and mediators of cell damage in the nervous system and are implicated in the pathogenesis of neurodegenerative diseases. Neurotrophic factors such as the nerve-derived growth factor (NGF) support neuronal survival during development and promote regeneration after neuronal injury through the activation of intracellular signals whose molecular effectors and downstream targets are still largely unknown. Here we present evidence that early oxidative signals initiated by NGF in PC12 cells, an NGF-responsive cell line, play a critical role in preventing apoptosis induced by serum deprivation. This redox-signaling cascade involves phosphatidylinositol 3-kinase, the small GTPase Rac-1, and the transcription factor cAMP-responsive element-binding protein (CREB), a molecule essential to promote NGF-dependent survival. We found that ROS are necessary for NGF-dependent phosphorylation of CREB, an event directly correlated with CREB activity, whereas hydrogen peroxide induces a robust CREB phosphorylation. Cells exposed to NGF show a late decrease in the intracellular content of ROS when compared with untreated cells and increased expression of the mitochondrial antioxidant enzyme manganese superoxide dismutase, a general inhibitor of cell death. Accordingly, serum deprivation-induced apoptosis was selectively inhibited by low concentrations of the mitochondrially targeted antioxidant Mito Q (mitoquinol/mitoquinone). Taken together, these data demonstrate that the oxidant-dependent activation of CREB is a component of NGF survival signaling in PC12 cells and outline an intriguing circuitry by which a cytosolic redox cascade promotes cell survival at least in part by increasing mitochondrial resistance to oxidative stress.

Taurocholate prevents the loss of intrahepatic bile ducts due to vagotomy in bile duct-ligated rats

The aim of this study was to determine whether taurocholate prevents vagotomy-induced cholangiocyte apoptosis. After bile duct ligation (BDL) + vagotomy, rats were fed taurocholate for 1 wk in the absence or presence of wortmannin. Caspase involvement was evaluated by measurement of caspase 8, 9, and 3 activities. Proliferation was determined by morphometry and PCNA immunoblots. Changes in phosphatidylinositol 3-kinase (PI3-kinase) activity were estimated by the expression of the phosphorylated Akt protein. Apically located Na(+)-dependent bile acid transporter (ABAT) expression and activity were evaluated by immunoblots and [(3)H]taurocholate uptake, respectively. Cholangiocyte apoptosis increased, whereas proliferation decreased in BDL + vagotomy rats. Taurocholate feeding prevented vagotomy effects on cholangiocyte functions, which were abolished by wortmannin. ABAT expression and activity as well as phosphorylated Akt protein expression were reduced by vagotomy but restored by taurocholate. The activities of caspase 8, 9, and 3 increased in BDL + vagotomy rats but were restored by taurocholate. The protective effect of taurocholate was associated with maintenance of ABAT activity, downregulation of caspase 8, 9, and 3, and activation of PI3-kinase. Bile acids are important in modulating cholangiocyte proliferation in denervated livers.

Survival pathways regulating the apoptosis induced by tumour necrosis factor-alpha in primary cultured bovine endothelial cells

The aim of the present study was to identify biochemical pathways driving the resistance of endothelial cells to apoptosis induced by tumour necrosis factor-alpha (TNF). (1) Although nuclear factor-kappa B (NF-kappaB) was activated by TNF, its inhibition by MG-132 failed to sensitize these cells. (2) The activation of protein kinase C (PKC) by phorbol ester completely abolished the TNF-induced cell death. (3) The phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin (Wo) triggered apoptosis and enhanced the TNF-induced cell death. (4) The MEK inhibitor PD98059 did not affect the TNF-induced apoptotic process. (5) The p38 is activated by TNF and its inhibition by SB203580 sensitized the cells to TNF. This is correlated with the inhibition of phosphorylation of heat-shock protein of 27 kDa (HSP27). These results indicate that TNF activates NF-kappaB, which does not drive any anti-apoptotic response, and p38, which plays an anti-apoptotic function probably through HSP27 phosphorylation. Moreover, PKC and PI3K are involved in the control of survival pathways.

Estrogen levels regulate the subcellular distribution of phosphorylated Akt in hippocampal CA1 dendrites

In addition to genomic pathways, estrogens may regulate gene expression by activating specific signal transduction pathways, such as that involving phosphatidylinositol 3-kinase (PI3-K) and the subsequent phosphorylation of Akt (protein kinase B). The Akt pathway regulates various cellular events, including the initiation of protein synthesis. Our previous studies showed that synaptogenesis in hippocampal CA1 pyramidal cell dendritic spines is highest when brain estrogen levels are highest. To address the role of Akt in this process, the subcellular distribution of phosphorylated Akt immunoreactivity (pAkt-I) in the hippocampus of female rats across the estrous cycle and male rats was analyzed by light microscopy (LM) and electron microscopy (EM). By LM, the density of pAkt-I in stratum radiatum of CA1 was significantly higher in proestrus rats (or in estrogen-supplemented ovariectomized females) compared with diestrus, estrus, or male rats. By EM, pAkt-I was found throughout the shafts and in select spines of stratum radiatum dendrites. Quantitative ultrastructural analysis identifying pAkt-I with immunogold particles revealed that proestrus rats compared with diestrus, estrus, and male rats contained significantly higher pAkt-I associated with (1) dendritic spines (both cytoplasm and plasmalemma), (2) spine apparati located within 0.1 microm of dendritic spine bases, (3) endoplasmic reticula and polyribosomes in the cytoplasm of dendritic shafts, and (4) the plasmalemma of dendritic shafts. These findings suggest that estrogens may regulate spine formation in CA1 pyramidal neurons via Akt-mediated signaling events.

From calcium to NF-kappa B signaling pathways in neurons

NF-kappa B plays crucial roles in the nervous system, including potential roles in long-term responses to synaptic plasticity, pro- or antiapoptotic effects during developmental cell death, and neurodegenerative disorders. We report here the characterization of signaling pathways leading to the constitutive activation of NF-kappa B in primary cultures of neonatal cerebellar granule neurons, consecutive to calcium entry into the cytosol. We found that opening of calcium channels at the plasma membrane and at intracellular stores is indispensable for the basal NF-kappa B activity. We demonstrated further that three cellular sensors of the cytosolic Ca(2+) levels, calmodulin, protein kinases C (PKCs), and the p21(ras)/phosphatidylinositol 3-kinase (PI3K)/Akt pathway are simultaneously involved in the steps linking the Ca(2+) second messenger to NF-kappa B activity. Calmodulin triggers the activity of calcineurin, a phosphatase which plays a role in the basal NF-kappa B activity, while stimulation of both the calmodulin kinase II and Akt kinase pathways results in the up-regulation of the transcriptional potential of the p65 subunit of NF-kappa B. Finally, using pharmacological and molecular approaches, we analyze interactions between these three pathways at different levels and demonstrate a connection between PKCs and PI3K. All three components converge towards NF-kappa B, at the level of both nuclear translocation and transcriptional activity. These results stand in contrast to the situation in nonneuronal cells, which either do not respond to Ca(2+) or do not simultaneously activate all three cascades. By using a global approach in studying signaling pathways in neurons, these results provide further evidence to validate the concept of networks of transducing cascades, specific to cells and to physiological situations.

Neutrophils and acute lung injury

OBJECTIVE

Neutrophils are an important component of the inflammatory response that characterizes acute lung injury (ALI). This discussion aims to review the contribution of neutrophils to the development and progression of ALI and to highlight the major intracellular signaling pathways that are involved in neutrophil activation in the setting of ALI.

DATA SOURCES

MEDLINE, original research papers, and review papers.

STUDY SELECTION

Relevant laboratory and clinical studies.

DATA EXTRACTION

Systemic review.

DATA SYNTHESIS

Activated neutrophils appear to play a central role in the development of most cases of ALI. In experimental models, the elimination of neutrophils markedly decreases the severity of ALI. Furthermore, in neutropenic patients with lung injury, deterioration of pulmonary function as neutropenia resolves has been well described. The neutrophils that accumulate in the lungs in models of ALI demonstrate increased activation of the kinases Akt and p38; increased nuclear accumulation of the transcriptional regulatory factor, nuclear factor-kappaB; and increased production of proinflammatory cytokines, particularly those whose transcription is dependent on nuclear factor-kappaB. Decreased apoptosis among neutrophils in the lungs is also characteristic. Inhibiting p38, Akt, or nuclear factor-kappaB activation diminishes the severity of endotoxin- or hemorrhage-induced ALI.

CONCLUSIONS

The accumulation of activated neutrophils in the lungs is an early step in the pulmonary inflammatory process that leads to ALI. Although experimental models indicate that the activation of p38, Akt, and nuclear factor-kappaB in neutrophils contributes to ALI, the relative importance of these pathways in critically ill patients remains to be determined. Nevertheless, modulation of the activation of p38, Akt, and nuclear factor-kappaB in neutrophils appears to be an appropriate therapeutic target in severely ill patients with ALI.

Congenitally learned helpless rats show abnormalities in intracellular signaling

BACKGROUND

Affective disorders and the drugs used to treat them lead to changes in intracellular signaling. We used a genetic animal model to investigate to what extent changes in intracellular signal transduction confer a vulnerability to mood or anxiety disorders.

METHODS

Levels of gene expression in a selectively bred strain of rats with a high vulnerability to develop congenitally learned helplessness (cLH), a strain highly resistant to the same behavior (cNLH) and outbred Sprague-Dawley (SD) control animals were compared using quantitative reverse transcription polymerase chain reaction.

RESULTS

Congenitally learned helpless animals had a 24%-30% reduced expression of the cyclic adenosine monophosphate response element binding protein messenger ribonucleic acid (mRNA) in the hippocampus and a 40%-41% increased level of the antiapoptotic protein bcl-2 mRNA in the prefrontal cortex compared to cNLH and SD rats. Other significant changes included changes in the expression levels of the alpha catalytic subunit of protein kinase A, glycogen synthase kinase 3beta, and protein kinase C epsilon.

CONCLUSIONS

Congenitally learned helpless animals show evidence of altered signal transduction and regulation of apoptosis compared to cNLH and SD control animals.