A truncated form of p23 down-regulates telomerase activity via disruption of Hsp90 function

The Hsp90-associated protein p23 modulates Hsp90 activity during the final stages of the chaperone pathway to facilitate maturation of client proteins. Previous reports indicate that p23 cleavage induced by caspases during cell death triggers destabilization of client proteins. However, the specific role of truncated p23 (Delta p23) in this process and the underlying mechanisms remain to be determined. One such client protein, hTERT, is a telomerase catalytic subunit regulated by several chaperone proteins, including Hsp90 and p23. In the present study, we examined the effects of p23 cleavage on hTERT stability and telomerase activity. Our data showed that overexpression of Delta p23 resulted in a decrease in hTERT levels, and a down-regulation in telomerase activity. Serine phosphorylation of Hsp90 was significantly reduced in cells expressing high levels of Delta p23 compared with those expressing full-length p23. Mutation analyses revealed that two serine residues (Ser-231 and Ser-263) in Hsp90 are important for activation of telomerase, and down-regulation of telomerase activity by Delta p23 was associated with inhibition of cell growth and sensitization of cells to cisplatin. Our data aid in determining the mechanism underlying the regulation of telomerase activity by the chaperone complex during caspase-dependent cell death.

Evaluation of equol function on anti- or prooxidant status in vivo

The present study was performed to investigate the effects of equol on oxidative stress and the antioxidant defense system in the livers of mice. Mice were orally administered equol at either 5 or 25 mg/kg body weight/day for 1, 3, or 7 wk. Equol administration significantly inhibited biomarkers of oxidative stress (thiobarbituric acid-reactive substances value, carbonyl content, and serum 8-OH-dG) at all doses and for all durations of administration, and this phenomenon was most pronounced at 3 wk. Moreover, catalase and total superoxide dismutase (SOD) activities and their mRNA expression were significantly increased by equol. Although equol increased the glutathione peroxidase (GSH-px) activity in mice treated with equol for 1 wk, long-term administration of equol (7 wk) caused a decrease in the ratio of reduced/oxidized glutathione (GSH/GSSG) and the activities of GSH-px and glutathione reductase (GR). Taken together, these results suggest that equol may act as an antioxidant through an inhibition of oxidative stress and stimulation of catalase and SOD, but can also cause prooxidant effects such as reduction of the GSH/GSSG ratio, depending on the treatment period.

CIIA induces the epithelial-mesenchymal transition and cell invasion

Epithelial-mesenchymal transition (EMT) and the acquisition of invasive potential are key events in tumor progression. We now show that CIIA, originally identified as an anti-apoptotic protein, induces the EMT and promotes cell migration and invasion. Ectopic expression of CIIA induced down-regulation of E-cadherin and claudin-1 as well as up-regulation of N-cadherin in MDCK cells. It also disrupted the differentiated epithelial morphology of MDCK cells grown in three-dimensional Matrigel cultures as well as increased the migration and invasion of MDCK cells in vitro. Furthermore, depletion of endogenous CIIA by RNA interference inhibited the migration and invasion of HeLa cells, and this inhibition was abolished by RNA interference-mediated depletion of claudin-1. These results suggest that CIIA functions as an inducer of cell invasion, and this effect is mediated, at least in part, through down-regulation of claudin-1.

Preparation of biopolymer-coated magnetite nanoparticles for magnetic resonance image contrast agent

The magnetite nanoparticles were synthesized using the sonochemical method with oleic acid as surfactant. The average size of the magnetite particles can be controlled by the ratio R = [H2O]/[surfactant] in the range of 2 to 9 nm. The size of the magnetite nanoparticles prepared by this method shows the narrow distribution. To prepare biopolymer(beta-glucan)-coated magnetite nanoparticles, beta-glucan solution was added to the magnetic colloid suspensions under the ultrasonication at room temperature. The beta-glucan coated magnetite colloidal suspensions of various concentrations did not agglomerate for 15 days, indicating their good stability. The beta-glucan-coated magnetite colloidal suspensions exhibited the enhancement of MRI contrasts in vitro.

Filamin B serves as a molecular scaffold for type I interferon-induced c-Jun NH2-terminal kinase signaling pathway

Type I interferons (IFNs) activate Janus tyrosine kinase-signal transducer and activator of transcription pathway for exerting pleiotropic biological effects, including antiviral, antiproliferative, and immunomodulatory responses. Here, we demonstrate that filamin B functions as a scaffold that links between activated Rac1 and a c-Jun NH(2)-terminal kinase (JNK) cascade module for mediating type I IFN signaling. Filamin B interacted with Rac1, mitogen-activated protein kinase kinase kinase 1, mitogen-activated protein kinase kinase 4, and JNK. Filamin B markedly enhanced IFNalpha-dependent Rac1 activation and the sequential activation of the JNK cascade members. Complementation assays using M2 melanoma cells revealed that filamin B, but not filamin A, is required for IFNalpha-dependent activation of JNK. Furthermore, filamin B promoted IFNalpha-induced apoptosis, whereas short hairpin RNA-mediated knockdown of filamin B prevented it. These results establish a novel function of filamin B as a molecular scaffold in the JNK signaling pathway for type I IFN-induced apoptosis, thus providing the biological basis for antitumor and antiviral functions of type I IFNs.

SB203580 induces prolonged B-Raf activation and promotes neuronal differentiation upon EGF treatment of PC12 cells

SB203580 is a p38 MAPK inhibitor that has been implicated in the activation of c-Raf. This study shows that the addition of SB203580 to PC12 cells causes the sustained activation of B-Raf but not of ERK. The addition of SB203580 prolonged the transient activation of both B-Raf and ERK by EGF alone. No significant change was detected in MAPKAPK-2 activity at low concentrations of SB203580, which induced neurite outgrowth in the EGF-stimulated PC12 cells. Therefore, these results indicate that SB203580 influences not only c-Raf as previously reported, but can also induce the activation of B-Raf, which in conjunction with EGF causes the sustained activation of ERK and differentiation in PC12 cells.

Downregulation by lipopolysaccharide of Notch signaling, via nitric oxide

The Notch signaling pathway appears to perform an important function in inflammation. Here, we present evidence to suggest that lipopolysaccharide (LPS) suppresses Notch signaling via the direct modification of Notch by the nitration of tyrosine residues in macrophages. In the RAW264.7 macrophage cell line and in rat primary alveolar macrophages, LPS was found to inhibit Notch1 intracellular domain (Notch1-IC) transcription activity, which could then be rescued by treatment with N(G)-nitro-l-arginine, a nitric oxide synthase (NOS) inhibitor. Nitric oxide (NO), which was produced in cells that stably express endothelial NOS (eNOS) and brain NOS (bNOS), also induced the inhibition of Notch1 signaling. The NO-induced inhibition of Notch1 signaling remained unchanged after treatment with 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), a guanylyl-cyclase inhibitor, and was not found to be mimicked by 8-bromo-cyclic GMP in the primary alveolar macrophages. With regards to the control of Notch signaling, NO appears to have a significant negative influence, via the nitration of Notch1-IC, on the binding that occurs between Notch1-IC and RBP-Jk, both in vitro and in vivo. By intrinsic fluorescence, we also determined that nitration could mediate conformational changes of Notch1-IC. The substitution of phenylalanine for tyrosine at residue 1905 in Notch1-IC abolished the nitration of Notch1-IC by LPS. Overall, our data suggest that an important relationship exists between LPS-mediated inflammation and the Notch1 signaling pathway, and that this relationship intimately involves the nitration of Notch1-IC tyrosine residues.

Comparison between coronal reformatted images and direct coronal CT images of the swine lung specimen: assessment of image quality with 64-detector row CT

The aims of this study were to compare the image quality of coronal multiplanar reconstruction (MPR) images from axial spiral images with that of direct coronal spiral and sequential images, and to estimate and analyse the effect of an incremental change on the image quality using 64-detector row CT. 12 swine lungs were used. Five kinds of images from each lung specimen were obtained using 64-detector row CT. All images were analysed by categories and grades, and the direct coronal sequential images were used as the reference standard for the image quality. Statistical analysis was performed for the following categories: (i) inter-observer reliability, (ii) interaction between the observers and images, (iii) image analysis, (iv) anatomical structural analysis of each observer, (v) stair-step artefact and (vi) background noise. The overall image quality and the image quality of all anatomical structures of coronal MPR images with 0.67 mm slice increments were inferior to the image quality of the other images; this difference was statistically significant (p<0.05). Stair-step artefact was detected on coronal MPR images, and was more prominent on coronal MPR images with 0.67 mm slice increments than on coronal MPR images with 0.34 mm slice increments. The most severe background noise was detected on the direct coronal sequential images, but there was no significant difference between the direct coronal sequential images and the direct coronal spiral images. Background noise was least prominent on coronal MPR images with 0.67 mm slice increments. The increment process is important for improving the image quality of MPR images even when using 64-detector row CT. Coronal MPR images with 0.34 mm slice increments using 64-detector row CT showed a similar image quality to that obtained from the direct coronal images, and can be used instead. This means that the coronal MPR images obtained with 64-detector row CT could be as useful for evaluating the lung parenchyma as the axial high-resolution CT images.

The effect of mosapride citrate on proximal and distal colonic motor function in the guinea-pig in vitro

Mosapride citrate (mosapride), a substituted benzamide, is a selective 5-HT(4) receptor agonist, and is known to have prokinetic properties on the stomach. However, it is unclear whether mosapride also has a prokinetic effect on the colon. We previously found that mosapride significantly shortened colonic transit time in the guinea-pig, an animal with a distribution of colonic 5-HT(4) receptors similar to that of a human. So, we aimed to separately evaluate the effect of mosapride on proximal and distal colonic motor function in the guinea-pig. Proximal (approximately 8 cm from the ileocolic junction) and distal colon (approximately 8 cm from the anus) were removed. Both ends of the colon were connected to a chamber containing a Krebs-Henseleit solution. To measure colonic transit time, artificial faeces were inserted into the oral side of the lumen and moved towards the anal side by intraluminal perfusion via a peristaltic pump. A total of 6 cm of transit was observed and time was measured in 2 cm increments. A tissue bath study, using electrical stimulation, was performed to estimate the contractile activity of the circular musculature of the colon. Immunohistochemical staining for 5-HT(4) receptors was performed in the myenteric plexus and circular muscle in both proximal and distal colon, and the stained area was measured using a microscope and computer software. Mosapride enhanced contraction at 10(-9) to 10(-7) mol L(-1), coinciding with rapid transit both in proximal and distal colon. This pattern was more prominent in proximal colon. At the high dose (10(-6) mol L(-1)) mosapride had little or no effect on colonic contraction. This stimulatory effect was attenuated by GR113808, atropine and tetrodotoxin. In the myenteric plexus, the density of 5-HT(4) receptors was significantly greater in the proximal colon than in the distal colon, but in circular muscle the density was greater in the distal colon. Thus, mosapride accelerates transit through increased contraction in the proximal colon more than distal colon. The different distribution of neuronal and muscular 5-HT(4) receptors may support these findings. Therefore, mosapride may be a useful alternative to tegaserod and cisapride for constipation.

Negative regulation of SEK1 signaling by serum- and glucocorticoid-inducible protein kinase 1

Serum- and glucocorticoid-inducible protein kinase 1 (SGK1) has been implicated in diverse cellular activities including the promotion of cell survival. The molecular mechanism of the role of SGK1 in protection against cellular stress has remained unclear, however. We have now shown that SGK1 inhibits the activation of SEK1 and thereby negatively regulates the JNK signaling pathway. SGK1 was found to physically associate with SEK1 in intact cells. Furthermore, activated SGK1 mediated the phosphorylation of SEK1 on serine 78, resulting in inhibition of the binding of SEK1 to JNK1, as well as to MEKK1. Replacement of serine 78 of SEK1 with alanine abolished SGK1-mediated SEK1 inhibition. Oxidative stress upregulated SGK1 expression, and depletion of SGK1 by RNA interference potentiated the activation of SEK1 induced by oxidative stress in Rat2 fibroblasts. Moreover, such SGK1 depletion prevented the dexamethasone-induced increase in SGK1 expression, as well as the inhibitory effects of dexamethasone on paclitaxel-induced SEK1-JNK signaling and apoptosis in MDA-MB-231 breast cancer cells. Together, our results suggest that SGK1 negatively regulates stress-activated signaling through inhibition of SEK1 function.

Integrin-linked kinase controls Notch1 signaling by down-regulation of protein stability through Fbw7 ubiquitin ligase

Integrin-linked kinase (ILK) is a scaffold and protein kinase that acts as a pivotal effector in integrin signaling for various cellular functions. In this study, we found that ILK remarkably reduced the protein stability of Notch1 through Fbw7. The kinase activity of ILK was essential for the inhibition of Notch1 signaling. Notably, the protein level and transcriptional activity of the endogenous Notch1 intracellular domain (Notch1-IC) were higher in ILK-null cells than in ILK wild-type cells, and the level of endogenous Notch1-IC was increased by the blocking of the proteasome, suggesting that ILK enhances the proteasomal degradation of Notch1-IC. ILK directly bound and phosphorylated Notch1-IC, thereby facilitating proteasomal protein degradation through Fbw7. Furthermore, we found down-regulation of Notch1-IC and up-regulation of ILK in basal cell carcinoma and melanoma patients but not in squamous cell carcinoma patients. These results suggest that ILK down-regulated the protein stability of Notch1-IC through the ubiquitin-proteasome pathway by means of Fbw7.

Zinc-induced downregulation of Notch signaling is associated with cytoplasmic retention of Notch1-IC and RBP-Jk via PI3k-Akt signaling pathway

The Notch signaling pathway appears to perform an important function in the determination of cell fate and in differentiation, in a wide variety of organisms and cell types. In this study, we provide evidence that the inactivation of Notch signaling by zinc is achieved via a PI3K-Akt-dependent, cytoplasmic retention of Notch1-IC and RBP-Jk. Extracellular zinc has been determined to inhibit constitutive active mutants of both Notch1 (DeltaEN1) and Notch1-IC-mediated transcription. However, in such cases, neither the cleavage pattern of Notch nor the protein stability of Notch1-IC and RBP-Jk was found to have significantly changed. With regard to the modulation of Notch signaling, zinc appears to exert a significant negative influence on the binding occurring between Notch1 and RBP-Jk, both in vivo and in vitro. The zinc-induced inhibition of Notch signaling can be rescued via pretreatment with wortmannin or LY294002, both of which are specific PI3K signaling pathway inhibitors. Furthermore, we ascertained that zinc triggers the cytoplasmic retention of Notch1-IC and RBP-Jk, and that cytoplasmic retention could be rescued via treatment with wortmannin. Overall, we have determined that an important relationship exists between zinc and the Notch1 signaling pathway, and that this relationship is intimately involved with the cytoplasmic retention of Notch and RBP-Jk.

Novel candidate targets of Wnt/beta-catenin signaling in hepatoma cells

The activity of beta-catenin/TCF, the key component of Wnt signaling pathway, is frequently deregulated in HCC, resulting in the activation of genes whose dysregulation has significant consequences on tumor development. Therefore, identifying the target genes of Wnt signaling is important for understanding beta-catenin-mediated carcinogenesis. We analyzed the transcriptome profile of human hepatoma cell lines using cDNA microarrays representing 15,127 unique, liver-enriched gene loci to identify the target genes of beta-catenin-mediated transcription (p<0.005). This analysis yielded 130 potential Wnt-associated classifier genes, and we found 33 of them contain consensus TCF-binding sites in presumptive transcriptional regulatory sequences. These genes were, then, tested for their Wnt-dependence of expression in experimental models of Wnt activation. Genes such as RPL29, NEDD4L, FUT8, LYZ, STMN2, STARD7 and KIAA0998 were proven to be up-regulated upon Wnt/beta-catenin activation. Gene ontology analysis of the 33 candidate genes indicated the presence of functional categories relevant to Wnt pathway such as cell growth, proliferation, adhesion and signal transduction. In conclusion, we identified a number of candidate Wnt/beta-catenin target genes that can be useful for studying the role of altered Wnt signaling in liver cancer development, and showed that some of them might be direct targets of Wnt signaling in hepatoma cells.

Nitric oxide inhibits an interaction between JNK1 and c-Jun through nitrosylation

Nitric oxide (NO) has been shown to negatively regulate c-Jun N-terminal kinase (JNK) through S-nitrosylation. Here, we show that disruption of an interaction between JNK and its substrate c-Jun is an important mechanism underlying the NO-mediated inhibition of JNK signaling. Endogenous NO, which was generated by interferon-gamma treatment, suppressed anisomycin-stimulated JNK activity in microglial BV-2 cells. The interferon-gamma-induced suppression of JNK1 activation in BV-2 cells was prevented completely by treatment with N(G)-nitro-l-arginine, an inhibitor of NO synthase. A NO donor S-nitro-N-acetyl-dl-penicillamine (SNAP) inhibited JNK activity in vitro, and this inhibition was reversed by a thiol-reducing agent, dithiothreitol. Nitric oxide disrupts a physical interaction between JNK and its substrate c-Jun both in vitro and in intact cells without affecting an interaction between SEK1 and JNK. Collectively, our results suggest that the inhibition of the interaction between JNK and c-Jun may be an integral part of the mechanism underlying the negative regulation of the JNK signaling pathway by NO.

Neuronal nitric oxide synthase (nNOS) modulates the JNK1 activity through redox mechanism: a cGMP independent pathway

Nitric oxide (NO) is a small, uncharged molecule, which is primarily generated by the nitric oxide synthase (NOS) family of proteins, including neuronal nitric oxide synthase (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). NO has been implicated in diverse roles in biological systems, such as the regulation of cell death and survival signaling pathways of a variety of cell types, including neuronal cells. In this study, we determined that the NO generated from l-arginine by ectopically overexpressed nNOS in HEK293 cells exerted an inhibitory effect against the activity of c-Jun N-terminal kinase (JNK), an important modulator of neuronal cell death and survival signaling pathways. NO repressed the activation of JNK, but exerted no significant effects on the activities of SEK1/MKK4 and MEKK1, which are the upstream MAPKK and MAPKKK of JNK1, respectively. This NO-mediated inhibition of JNK1 was not affected by the addition of ODQ, a guanylyl cyclase inhibitor, indicating that the effect is independent of the level of cyclic GMP. In an in vitro kinase assay, SNAP, a NO donor, was shown to directly suppress JNK1 activity, thereby indicating that NO is a direct modulator of JNK1. Moreover, the NO-mediated suppression of JNK1 was demonstrated to be redox-sensitive and dependent on the cysteine-116 in JNK1. Finally, according to the results of an immunohistochemical study using rat striatal neurons, we were able to determine that nNOS-expressing neurons evidenced significantly reduced JNK1 activation. Collectively, these data suggest that JNK1 is regulated by nNOS-mediated NO production in neurons, via a thiol-redox-sensitive mechanism.

Characteristics of CADASIL in Korea: A novel cysteine-sparing Notch3 mutation

OBJECTIVE

To elucidate the phenotype, genotype, and MRI findings of Korean patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and mutation carriers.

METHODS

The authors studied 40 members of nine unrelated Korean CADASIL families. After genetic analysis of Notch3, clinical and MRI findings were correlated in 27 mutation carriers.

RESULT

Notch3 mutation sites were C174R (one family, n = 3), R133C (one family, n = 3), R587C (one family, n = 1), R544C (two families, n = 5), and R75P (four families, n = 15). The clinical features were typical of CADASIL, but the frequency of migraine in the Korean population appears low. MRI abnormalities were found in 54% of the mutant carriers, the most common being white matter hyperintensities. The prevalence of lacunes and microbleeds increased with patient age. Anterior temporal areas were less often involved in subjects with R75P mutations than in those where mutations occurred in other sites (p = 0.02). Gradient echo imaging identified microbleedings in 33% of mutation carriers (64% of those with abnormal MRI), whereas diffusion-weighted MRI showed abnormal findings in only one patient. Neurologic disability was related to the number of lacunar infarcts and the lesion volume of white matter hyperintensities (p < 0.001) whereas MMSE score was related to the number of lacunar infarcts (p < 0.005).

CONCLUSIONS

Although Korean cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) mutation carriers show similar clinical and MRI findings, these abnormalities appear less frequently than in other populations. Relatively frequent microbleedings on gradient echo imaging suggest that treatment should be individualized according to MRI findings. The novel mutation of R75P, not involving a cysteine residue, is related to less frequent involvement of the anterior temporal area, thus broadening the spectrum of CADASIL.

STMN2 is a novel target of beta-catenin/TCF-mediated transcription in human hepatoma cells

The activity of beta-catenin/TCF, the key component of Wnt signaling pathway, is frequently deregulated in human cancers, resulting in the activation of genes whose dysregulation has significant consequences on tumor development. Therefore, identifying the target genes of Wnt signaling is important for understanding beta-catenin-mediated carcinogenesis. Here, we report STMN2, a gene implicated in the regulation of microtubule dynamics, as a novel target of beta-catenin-mediated transcription. STMN2 was up-regulated in hepatoma and cirrhotic liver tissues compared to normal liver and also in cell lines where beta-catenin/TCF is constitutively activated. Transient activation of beta-catenin/TCF either by transfection of a constitutively active form of beta-catenin or by LiCl treatment induced the STMN2 mRNA expression in PLC/PRF/5 cells. Of the four members of STMN gene family, only STMN2 showed a Wnt-dependent expression pattern. Through promoter mapping and chromatin immunoprecipitation assays, we found that STMN2 is a direct target of beta-catenin/TCF-mediated transcription and that the TCF binding site at -1713 of STMN2 promoter is critical for beta-catenin/TCF-dependent expression regulation. siRNA-mediated knock-down of STMN2 expression indicated that STMN2 is required for maintaining the anchorage-independent growth state of beta-catenin/TCF-activated hepatoma cells. Our results suggest that STMN2 might be a novel player of beta-catenin/TCF-mediated carcinogenesis in the liver.

SUMO-1 represses apoptosis signal-regulating kinase 1 activation through physical interaction and not through covalent modification

This study examined whether small ubiquitin-related modifier-1 (SUMO-1) regulates apoptosis signal-regulating kinase 1 (ASK 1). ASK 1 interacted with SUMO-1 in vitro as well as in BOSC 23 cells. Endogenous ASK 1-SUMO-1 interaction was disrupted following H(2)O(2) signal. SUMO-1 overexpression suppressed the self-oligomerization, kinase activity and apoptotic potential of ASK 1, whereas SUMO-1 depletion potentiated such activities. SUMO-1(Delta C 6), a sumoylation-incompetent mutant lacking carboxy-terminal six amino acids, suppressed AS 1 activation, implying that the suppressive effect of SUMO-1 on ASK 1 is independent of sumoylation. ASK 1(3M), an ASK 1 mutant in which all three lysines in the psiKXE motif were substituted with alanines, still retained the kinase activity and activated the Jun amino-terminal kinase pathway. However, SUMO-1 failed to interact with ASK 1(3M) and to suppress ASK 1(3M) activation, indicating that the three lysines are important for regulation by SUMO-1. This study shows that SUMO-1 exerts a negative regulatory effect on ASK 1 activation through physical interaction and not through covalent modification.

Apoptotic signaling pathways: caspases and stress-activated protein kinases

Apoptotic cell death is an active process mediated by various signaling pathways, which include the caspase cascade and the stress-activated protein kinase pathways. The caspase cascade is activated by two distinct routes: one from cell surface and the other from mitochondria. Activation of the route from cell surface requires the cellular components that include membrane receptors, adaptor proteins such as TRADD and FADD, and caspase-8, while activation of the other from mitochondria requires Apaf-1, caspase-9, and cytosolic cytochrome c. On the other hand, persistent stimulation of the stress-activated protein kinase pathway is also shown to mediate apoptosis in many cell types. Gene-targeting studies with jnk- or jip-null mice, in particular, strongly suggest that this signaling pathway plays a pivotal role in the cellular machinery for apoptosis.

Notch interferes with the scaffold function of JNK-interacting protein 1 to inhibit the JNK signaling pathway

The transmembrane protein Notch is cleaved by gamma-secretase to yield an active form, Notch intracellular domain (Notch-IC), in response to the binding of ligands, such as Jagged. Notch-IC contributes to the regulation of a variety of cellular events, including cell fate determination during embryonic development as well as cell growth, differentiation, and survival. We now show that Notch1-IC suppresses the scaffold activity of c-Jun N-terminal kinase (JNK)-interacting protein 1 (JIP1) in the JNK signaling pathway. Notch1-IC physically associated with the JNK binding domain of JIP1 and thereby interfered with the interaction between JIP1 and JNK. JIP1 mediated the activation of JNK1 induced by glucose deprivation in mouse embryonic fibroblasts, and ectopic expression of Notch1-IC inhibited JNK activation and apoptosis triggered by glucose deprivation. Taken together, these findings suggest that Notch1-IC negatively regulates the JNK pathway by disrupting the scaffold function of JIP1.

Presenilin acts as a positive regulator of basal level activity of ERK through the Raf-MEK1 signaling pathway

Presenilins (PS) have been reported to be functionally involved in amyloid precursor protein processing, notch receptor signaling, and programmed cell death, or apoptosis. To understand the role of PS1 in the signaling events, we investigated in this study the role of PS1 in the basal level of mitogen-activated protein kinase (MAPK) pathways using PS1(-/-) mouse embryonic fibroblast (MEF) cells from PS1-null mice. Interestingly, the basal level of ERK activity, but not JNK or p38 activity, is lower in PS1(-/-) MEF cells than in PS1(+/+) MEF cells. In PS1(-/-) MEF cells, the basal activities of Raf and MEK, the upstream signaling component of ERK, are also lower than in PS1(+/+) MEF cells. Furthermore, Elk-1 transcription activity also down-regulates in PS1(-/-) MEF cells. Collectively, our data suggest that PS can modulate the basal level of ERK activity through the Raf-MEK-dependent pathway.

Activation of PI3K/Akt pathway by PTEN reduction and PIK3CA mRNA amplification contributes to cisplatin resistance in an ovarian cancer cell line

OBJECTIVE

The aim of this study was to understand the role of PIK3CA and PTEN on the resistance of human ovarian cancer cells to cisplatin-induced apoptosis.

METHODS

Human ovarian cancer cell OVCAR-3 and cisplatin-resistant subclone OVCAR-3/CDDP cells were used for these studies. The expressions of apoptosis regulating proteins and PI3K/Akt signaling proteins were systematically examined.

RESULTS

OVCAR-3/CDDP cells were 4.8-fold more resistant to cisplatin compared to OVCAR-3 cells following 72 h exposure to this drug. This resistance was paralleled with reduced susceptibility to cisplatin-induced apoptosis. Apoptotic proteins were differentially expressed in OVCAR-3/CDDP cells, resulting in the inhibition of Bax translocalization. Cisplatin inhibited Akt phosphorylation and activation in OVCAR-3 cells but not in OVCAR-3/CDDP cells. The specific PI3K inhibitors LY294002 and wortmannin sensitized OVCAR-3/CDDP cells to cisplatin-induced apoptosis and decreased cell viability. A low level of PTEN expression was strongly associated with amplified PIK3CA and PI3K/Akt activities in OVCAR-3/CDDP cells. Small interfering RNA knockdown of PTEN and the expression of active p110alpha resulted in a blockade of apoptosis by cisplatin in OVCAR-3 cells.

CONCLUSIONS

These results collectively indicate that the development of resistance in OVCAR-3 cells was derived by increased PIK3CA transcription and reduction of PTEN expression. These alterations conferred cisplatin resistance to cisplatin through the activation of PI3K/Akt and the inhibition of Bax translocation.

Negative Regulation of MEKK1-induced Signaling by Glutathione S-Transferase Mu

Mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 1 (MEKK1) is an important component in the stress-activated protein kinase pathway. Glutathione S-transferase Mu 1-1 (GST M1-1) has now been shown to inhibit the stimulation of MEKK1 activity induced by cellular stresses such as UV and hydrogen peroxide. GST M1-1 inhibited MEKK1 activation in a manner independent of its glutathione-conjugating catalytic activity. In vitro binding and kinase assays revealed that GST M1-1 directly bound MEKK1 and inhibited its kinase activity. Co-immunoprecipitation analysis showed a physical association between endogenous GST M1-1 and endogenous MEKK1 in L929 cells. Overexpressed GST M1-1 interfered with the binding of MEKK1 to SEK1 in transfected HEK293 cells. Furthermore, GST M1-1 suppressed MEKK1-mediated apoptosis. Taken together, our results suggest that GST M1-1 functions as a negative regulator of MEKK1.

Promyelocytic leukemia is a direct inhibitor of SAPK2/p38 mitogen-activated protein kinase

The promyelocytic leukemia gene (PML) encodes a growth/tumor suppressor protein that is essential for the induction of apoptosis in response to various apoptotic signals. The mechanism by which PML plays a role in the regulation of cell death is still unknown. In the current study, we demonstrate that PML negatively regulated the SAPK2/p38 signaling pathway by sequestering p38 from its upstream kinases, MKK3, MKK4, and MKK6, whereas PML did not affect the SAPK1/c-Jun NH(2)-terminal kinase pathway. PML associated with p38 both in vitro and in vivo and the carboxyl terminus of PML mediated the interaction. In contrast to other studies of PML and PML-nuclear bodies (NB), our study shows that the formation of PML-NBs was not required for PML to suppress p38 activity because PML was still able to bind and inhibit p38 activity under the conditions in which PML-NBs were disrupted. In addition, we show that the promotion of Fas-induced cell death by PML correlated with the extent of p38 inhibition by PML, suggesting that PML might regulate apoptosis through manipulating SAPK2/p38 pathways. Our findings define a novel function of PML as a negative regulator of p38 kinase and provide further understanding on the mechanism of how PML induces multiple pathways of apoptosis.