A cytokine-responsive IkappaB kinase that activates the transcription factor NF-kappaB

Nuclear transcription factors of the NF-kappaB/Rel family are inhibited by IkappaB proteins, which inactivate NF-kappaB by trapping it in the cell cytoplasm. Phosphorylation of IkappaBs marks them out for destruction, thereby relieving their inhibitory effect on NF-kappaB. A cytokine-activated protein kinase complex, IKK (for IkappaB kinase), has now been purified that phosphorylates IkappaBs on the sites that trigger their degradation. A component of IKK was molecularly cloned and identified as a serine kinase. IKK turns out to be the long-sought-after protein kinase that mediates the critical regulatory step in NF-kappaB activation.

The IkappaB kinase complex (IKK) contains two kinase subunits, IKKalpha and IKKbeta, necessary for IkappaB phosphorylation and NF-kappaB activation

Recently we purified a 900 kDa cytokine-responsive IkappaB kinase complex (IKK) and molecularly cloned one of its subunits, IKKalpha, a serine kinase. We now describe the molecular cloning and characterization of IKKbeta, a second subunit of the IKK complex. IKKbeta is 50% identical to IKKalpha and like it contains a kinase domain, a leucine zipper, and a helix-loop-helix. Although IKKalpha and IKKbeta can undergo homotypic interaction, they also interact with each other and the functional IKK complex contains both subunits. The catalytic activities of both IKKalpha and IKKbeta make essential contributions to IkappaB phosphorylation and NF-kappaB activation. While the interactions between IKKalpha and IKKbeta may be mediated through their leucine zipper motifs, their helix-loop-helix motifs may be involved in interactions with essential regulatory subunits.

Positive and negative regulation of IkappaB kinase activity through IKKbeta subunit phosphorylation

IkappaB [inhibitor of nuclear factor kappaB (NF-kappaB)] kinase (IKK) phosphorylates IkappaB inhibitory proteins, causing their degradation and activation of transcription factor NF-kappaB, a master activator of inflammatory responses. IKK is composed of three subunits-IKKalpha and IKKbeta, which are highly similar protein kinases, and IKKgamma, a regulatory subunit. In mammalian cells, phosphorylation of two sites at the activation loop of IKKbeta was essential for activation of IKK by tumor necrosis factor and interleukin-1. Elimination of equivalent sites in IKKalpha, however, did not interfere with IKK activation. Thus, IKKbeta, not IKKalpha, is the target for proinflammatory stimuli. Once activated, IKKbeta autophosphorylated at a carboxyl-terminal serine cluster. Such phosphorylation decreased IKK activity and may prevent prolonged activation of the inflammatory response.

Tyrosine phosphorylation of beta-catenin and plakoglobin enhanced by hepatocyte growth factor and epidermal growth factor in human carcinoma cells

The effect of hepatocyte growth factor/scatter factor (HGF/SF) and epidermal growth factor (EGF) on cadherin-mediated adhesion of human carcinoma cells was studied. HGF/SF induced scattering of colonic adenocarcinoma HT29 and gastric adenocarcinomas MKN7 and MKN74 cells. Likewise, EGF induced scattering of HT29 and MKN7 cells. These cells expressed E-cadherin, which was concentrated at cell-cell contact sites. When the scattering of these cells was induced by HGF/SF or EGF, the E-cadherin concentration at cell-cell boundaries tended to decrease. Immunoblotting analyses, however, demonstrated that these growth factor treatments did not alter the expression of E-cadherin and E-cadherin-associated proteins, alpha- and beta-catenin and plakoglobin. beta-Catenin, plakoglobin and an unidentified 115-kDa molecule associated with E-cadherin were found to be phosphorylated at tyrosine residues, and these phosphorylations were enhanced by the growth factor treatments. These results suggest that HGF/SF and EGF may modulate the function of the cadherin-catenin system via tyrosine phosphorylation of cadherin-associated proteins.

Natural history of the neck remnant of a cerebral aneurysm treated with the Guglielmi detachable coil system

OBJECT

The long-term durability of Guglielmi detachable coil (GDC) embolization of cerebral aneurysms is still unknown. The purpose of this study was to evaluate the anatomical evolution of neck remnants in aneurysms treated with GDCs.

METHODS

Of 455 aneurysms treated with GDCs from 1990 to 1998 at the University of California at Los Angeles Medical Center, 178 aneurysms (39%) had residual necks postembolization. Long-term follow-up angiograms were obtained in 73 of these aneurysms in 71 patients. The mean duration of angiographic follow up was 17.3 months. Twenty-four of the aneurysms were small with small necks, 24 were small with wide necks, 15 were large, and 10 were giant aneurysms. In small aneurysms with small necks, postembolization angiography revealed 12 aneurysms (50%) with progressive thrombosis, eight (33%) unchanged, and four (17%) with recanalization. In small aneurysms with wide necks, six (25%) had progressive thrombosis, eight (33%) remained unchanged, and 10 (42%) had recanalization. In large aneurysms, two (13%) were unchanged and 13 (87%) had recanalization. Of the giant aneurysms only one (10%) remained unchanged and nine (90%) had recanalization. Overall, 18 aneurysms (25%) exhibited progressive thrombosis, 19 (26%) remained unchanged, and 36 (49%) displayed recanalization on follow-up angiography. During the last 2 years of the study, the recanalization rate decreased and a higher rate of progressive thrombosis was noted in aneurysms with small necks. These positive changes are related to important new technical developments.

CONCLUSIONS

Treatment with GDCs appears to be effective and the results permanent in most small aneurysms with small necks. However, there are important technical limitations in the current GDC technology that prevent recanalization in wide-necked or large or giant aneurysms.

Age-associated oxygen damage and mutations in mitochondrial DNA in human hearts

Some mutations in mitochondrial DNA (mtDNA) causing a number of neuromuscular diseases are suggested to arise spontaneously during the life of an individual. To substantiate the extent and the rate of these somatic mutations, mtDNA specimens from post-mortem human heart muscles of subjects in differing age groups were hydrolyzed. 8-Hydroxy-deoxyguanosine (8-OH-dG), a hydroxyl-radical adduct of deoxyguanosine, in mtDNA, was quantitatively determined using a micro high-performance liquid chromatography/mass spectrometry system. In each specimen, the mtDNA with a 7.4 kilo base-pair deletion was quantified by the kinetic polymerase chain reaction method. In association with age, the 8-OH-dG content accumulated exponentially up to 1.5% with a correlative increase in the content of the deleted mtDNA up to 7%. Clear correlation between the 8-OH-dG content in mtDNA and the population of mtDNA with a deletion (r = 0.93, P < 0.01) gives insight into the mechanism for the generation of a large deletion. These results indicate that accumulation of somatically acquired oxygen damage together with age-associated mutations in mtDNA which lead to bioenergetic deficiency and the heart muscle weakness are inevitable in human life.

Cloning of a Streptococcus mutans glucosyltransferase gene coding for insoluble glucan synthesis

The gtfB gene coding for a glucosyltransferase (GTF) activity of Streptococcus mutans GS-5 was isolated on a 15.4-kilobase DNA fragment by using a lambda L47.1 gene library. The activity was catalyzed by gene products of 150 and 145 kilodaltons which reacted with antibodies directed against both soluble and insoluble glucan-synthesizing GTFs. The enzyme present in crude Escherichia coli extracts synthesized both soluble and insoluble glucans. The enzyme was partially purified from lysates of the lambda DS-76 clone and synthesized both types of glucans in a primer-independent fashion. In addition, the purified enzyme exhibited a pI of approximately 5.0. Southern blot analysis indicated that the cloned GTF gene represented a contiguous nucleotide sequence on the strain GS-5 chromosome. Furthermore, evidence for the existence of a distinct gene sharing partial homology with gtfB was also obtained. The gtfB gene was subcloned into plasmid pACYC184 into E. coli and exhibited GTF activity when carried on GS-5 inserts as small as 5 kilobases. The approximate location of the GTF promoter and the direction of gene transcription were also determined. The cloned enzyme was not secreted through the cytoplasmic membrane of E. coli, since most of the activity was found in the cytoplasm and, in lesser amounts, associated with the cytoplasmic membrane. The gtfB gene was insertionally inactivated by introducing a gene fragment coding for erythromycin resistance into the GTF coding region. After transformation of strain GS-5 with the altered gene, transformants defective in insoluble glucan synthesis were identified. These results indicate that the gtfB gene codes for a GTF involved in insoluble glucan synthesis in strain GS-5.

Association of p120, a tyrosine kinase substrate, with E-cadherin/catenin complexes

p120 was originally identified as a substrate of pp60src and several receptor tyrosine kinases, but its function is not known. Recent studies revealed that this protein shows homology to a group of proteins, beta-catenin/Armadillo and plakoglobin (gamma-catenin), which are associated with the cell adhesion molecules cadherins. In this study, we examined whether p120 is associated with E-cadherin using the human carcinoma cell line HT29, as well as other cell lines, which express both of these proteins. When proteins that copurified with E-cadherin were analyzed, not only alpha-catenin, beta-catenin, and plakoglobin but also p120 were detected. Conversely, immunoprecipitates of p120 contained E-cadherin and all the catenins, although a large subpopulation of p120 was not associated with E-cadherin. Analysis of these immunoprecipitates suggests that 20% or less of the extractable E-cadherin is associated with p120. When p120 immunoprecipitation was performed with cell lysates depleted of E-cadherin, beta-catenin was no longer coprecipitated, and the amount of plakoglobin copurified was greatly reduced. This finding suggests that there are various forms of p120 complexes, including p120/E-cadherin/beta-catenin and p120/E-cadherin/plakoglobin complexes; this association profile contrasts with the mutually exclusive association of beta-catenin and plakoglobin with cadherins. When the COOH-terminal catenin binding site was truncated from E-cadherin, not only beta-catenin but also p120 did not coprecipitate with this mutated E-cadherin. Immunocytological studies showed that p120 colocalized with E-cadherin at cell-cell contact sites, even after non-ionic detergent extraction. Treatment of cells with hepatocyte growth factor/scatter factor altered the level of tyrosine phosphorylation of p120 as well as of beta-catenin and plakoglobin. These results suggest that p120 associates with E-cadherin at its COOH-terminal region, but the mechanism for this association differs from that for the association of beta-catenin and plakoglobin with E-cadherin, and thus, that p120, whose function could be modulated by growth factors, may play a unique role in regulation of the cadherin-catenin adhesion system.

Cerebral amyloid angiopathy: a significant cause of cerebellar as well as lobar cerebral hemorrhage in the elderly

We investigated consecutive 1000 autopsied cases (average age 82.9 years) clinicopathologically in order to reveal the significance of cerebral amyloid angiopathy (CAA) as a cause of senile intracranial hemorrhages. We found 101 cases with intracerebral hemorrhages, and CAA accounted for 10.9% of them (31.0% of lobar cerebral hemorrhages, and 14.3% of cerebellar ones). In contrast to hypertensive hemorrhages, CAA-related ones (1) ruptured into the subarachnoid space without exception, (2) often coexisted with dementia of Alzheimer's type, and (3) frequently occurred in the night without elevated blood pressure at onset. The cerebrovascular amyloid was strongly immunoreactive with antibody to beta-protein in all of the cases with CAA-related hemorrhages, and less intensively with antibody to cystatin C in 91% of them. Our data indicate that CAA is an important etiological factor of cerebellar hemorrhages, as well as lobar cerebral hemorrhages, in normotensive, aged patients.

Age-associated accumulation of 8-hydroxydeoxyguanosine in mitochondrial DNA of human diaphragm

This is the first report that age-associated accumulation of 8-hydroxydeoxyguanosine (8-OH-dG) does occur in human mitochondrial DNA (mtDNA) in muscle of diaphragm. We extracted mtDNA from human diaphragm muscles from differing age groups, and determined the amount of 8-OH-dG by ultramicro-high performance liquid chromatography/mass-spectrometry system. With the same specimen, multiple deletions of mtDNA were detected by electrophoresis after amplification by the polymerase chain reaction method. In subjects below age 55, the level of 8-OH-dG in mtDNA was below 0.02% of the total deoxyguanosine (dG), whereas, in subjects over age 65, the level of 8-OH-dG increased with age at a rate of ca. 0.25% per 10 years, reaching 0.51% at age 85. Moreover, a concomitant increase in multiple deletions was detected with the increase in age. These results suggest that, in younger diaphragms, replication of mtDNA dilutes out 8-OH-dG being not detectable. In the elderly subjects aged over 65, the replication rate might be slowed down leading to the accumulation of 8-OH-dG in mtDNA, which would accelerate the age-associated multiple deletions of mtDNA observed among the subjects.

Electric and magnetic phenomena observed before the volcano-seismic activity in 2000 in the Izu Island Region, Japan

Significant anomalous changes in the ultra low frequency range (approximately 0.01 Hz) were observed in both geoelectric and geomagnetic fields before the major volcano-seismic activity in the Izu Island region, Japan. The spectral intensity of the geoelectric potential difference between some electrodes on Niijima Island and the third principal component of geomagnetic field variations at an array network in Izu Peninsula started to increase from a few months before the onset of the volcano-seismic activity, culminating immediately before nearby magnitude 6 class earthquakes. Appearance of similar changes in two different measurements conducted at two far apart sites seems to provide information supporting the reality of preseismic electromagnetic signals.

Phospholipase A2 is necessary for tumor necrosis factor alpha-induced ceramide generation in L929 cells

The role of cytosolic phospholipase A2 (cPLA2) in the regulation of ceramide formation was examined in a cell line (L929) responsive to the cytotoxic action of tumor necrosis factor alpha (TNFalpha). In L929 cells, the addition of TNFalpha resulted in the release of arachidonate, which was followed by a prolonged accumulation of ceramide occurring over 5-12 h and reaching 250% over base line. The formation of ceramide was accompanied by the hydrolysis of sphingomyelin and the activation of three distinct sphingomyelinases (neutral Mg2+-dependent, neutral Mg2+-independent, and acidic enzymes). The variant cell line C12, which lacks cPLA2, is resistant to the cytotoxic action of TNFalpha. TNFalpha was able to activate nuclear factor kappaB in both the wild-type L929 cells and the C12 cells. However, TNFalpha was unable to cause the release of arachidonate or the accumulation of ceramide in C12 cells. C6-ceramide overcame the resistance to TNFalpha and caused cell death in C12 cells to a level similar to that in L929 cells. The introduction of the cPLA2 gene into C12 cells resulted in partial restoration of TNFalpha-induced arachidonate release, ceramide accumulation, and cytotoxicity. This study suggests that cPLA2 is a necessary component in the pathways leading to ceramide accumulation and cell death.

Purification and characterization of phospholipase A2 released from rat platelets

It was found that phospholipase A2 and lysophospholipase, both of which were released from thrombin-stimulated rat platelets, had high affinity to insolubilized heparin. Phospholipase A2 released from rat platelets was purified by the sequential use of column chromatography on heparin-Sepharose and TSK gel G2000SW (high-performance liquid chromatography, HPLC). The enzyme was near homogeneous on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and HPLC, and its Mr was estimated to be 13,500. The purified enzyme was labile and lost its activity within 1 h when incubated at 37 degrees C. Phospholipids or detergent in the solution protected the enzyme against inactivation. Phospholipase activity was inhibited by p-bromophenacylbromide, but not by diisopropylfluorophosphate or iodoacetamide. Lysophospholipase, which was also released from rat platelets, was separated from phospholipase A2 by chromatography on heparin-Sepharose.

Cerebral amyloid angiopathy in the aged

Cerebral amyloid angiopathy (CAA) was found in 57% of 123 autopsy brains removed from patients aged 59-101 years. The incidence of CAA increased with age. CAA was seen most frequently in the occipital cortex. Immunohistochemically, amyloid of CAA was positive for amyloid P component and negative for human AA protein and human prealbumin. The presence and severity of CAA were significantly correlated with the number of senile plaques and neurofibrillary tangles. The incidence of CAA in 17 patients with dementia of Alzheimer type (DAT) was estimated to be 88% and was significantly higher than that in 26 patients with dementia of non-Alzheimer type. CAA had a pathogenetic relationship with both brain ageing and DAT. Lobar cerebral haemorrhage was found in 3 patients with CAA of marked or moderate degree. Lobar cerebral haemorrhage in the aged and in patients with DAT suggest the presence of CAA.

Age-associated damage in mitochondrial function in rat hearts

The aim of this study is to elucidate effects of aging on mitochondrial function and mitochondrial DNA (mtDNA) in rat heart and liver. The activities of complex I and complex IV of heart mitochondria of rats aged 100 weeks decreased significantly by 31% and 22%, respectively, compared with those of rats aged 7 weeks. No significant changes were observed in these two parameters in rats aged 7 weeks and aged 55 weeks. There were no significant differences in the specific activities of complex II and complex III among the age groups of 7, 55, and 100 weeks. The mtDNA content decreased by 58% in rats aged 100 weeks compared with that in rats aged 7 weeks. Content of 8-hydroxydeoxyguanosine (8-OH-dG), an oxidative product of deoxyguanosine (dG), increased by 130% in rats aged 100 weeks compared with that in rats aged 7 weeks. No significant changes were observed in these parameters between rats aged 7 weeks and 55 weeks. In contrast to heart mtDNA, these age-dependent changes were not observed in liver mitochondria at rats aged up to 100 weeks. From our results, age-associated decline in mitochondrial function might play an important role in cell aging, particularly in postmitotic cells such as heart muscle, and accumulation of oxidative damage to mtDNA might be involved in this mechanism.

Massive conversion of guanosine to 8-hydroxy-guanosine in mouse liver mitochondrial DNA by administration of azidothymidine

As typical mitochondrial myopathy has been reported to be expressed among many patients with AIDS treated with long-term azidothymidine (AZT) therapy, we examined changes in mouse liver mitochondrial DNA (mtDNA) after 4-week administration of AZT. Even below 1/10th the dose given to the patients (AZT, 1 mg/kg/day), 25% of the total deoxyguanosine (dG) was converted to be 8-hydroxy-deoxyguanosine (8-OH-dG). 38% of the total dG was converted to 8-OH-dG with AZT 5 mg/kg/day. In vitro, the conversion of dG to 8-OH-dG was demonstrated by incubating mtDNA in the oxygen radical producing system containing NADH and KCN treated mitochondrial inner membrane. Thus it is concluded that, by lack of repairing system, damaged mtDNA with AZT results in impaired mitochondrial respiratory chain causing oxygen radicals which are responsible for 8-OH-dG formation. These results suggest that the oxygen damage of mtDNA is the primary cause of mitochondrial myopathy with AZT therapy.

Age-associated damage in mitochondrial DNA in human hearts

Damage to mitochondrial DNA seems to be involved in the etiology of age-associated degenerative diseases. The aim of this study is to elucidate effects of aging on human mitochondrial DNA. 8-Hydroxy-deoxyguanosine, a product of free radical damage to deoxyguanosine, is reported to cause random point mutations. In human mitochondrial DNA, 8-hydroxy-deoxyguanosine increased exponentially with age, and the population of mitochondrial DNA with deletion increased also exponentially with age. Furthermore, a clear correlation existed between the accumulation of 8-hydroxy-deoxyguanosine and that of mitochondrial DNA with deletion. We also determined the effects of aging on rat mitochondrial function together with 8-hydroxy-deoxyguanosine content in mitochondrial DNA. The activities of complexes I and IV of the mitochondrial electron transport chain decreased significantly in rats aged 100 weeks compared with those in rats aged 7 weeks. A concomitant increase in 8-hydroxy-deoxyguanosine was observed in mitochondrial DNA of rats aged 100 weeks. From our results, it is concluded that the age-associated accumulation of somatically acquired oxygen damage together with deletions in mitochondrial DNA might be important contributors to the deterioration of cardiac function associated with age.

STAT3 inhibitor WP1066 as a novel therapeutic agent for renal cell carcinoma

Background:

Signal transducer and activator of transcription 3 (STAT3) regulates the expression of genes that mediate cell survival, proliferation, and angiogenesis and is aberrantly activated in various types of malignancies, including renal cell carcinoma (RCC). We examined whether it could be a novel therapeutic target for RCC by using the STAT3 inhibitor WP1066.

Methods:

The antitumour activities and related mechanisms of WP1066 were investigated in vitro on renal cancer cell lines and in vivo on murine xenografts.

Results:

In Caki-1 and 786-O renal cancer cells, 5 μM WP1066 prevented the phosphorylation of STAT3, and 2.5 μM WP1066 significantly (P<0.01) inhibited cell survival and proliferation. WP1066 suppressed the expression of Bcl-2, induced apoptosis, and inhibited the basal and hypoxia-induced expression of HIF1α and HIF2α, as well as vascular endothelial growth factor secretion into cell culture medium. Human umbilical vascular endothelial cells cocultured with media from WP1066-treated cells showed significantly reduced tubulogenesis (P<0.05). Systemic oral administration of WP1066 to mice for 19 days significantly inhibited the growth of Caki-1 xenograft tumours (P<0.05), and pathological analysis of xenografts of WP1066-treated mice showed decreased immunostaining of phosphorylated STAT3 and reduced length of CD34-positive vessels (P<0.05).

Conclusion:

Our results suggest that using WP1066 to inhibit the STAT3 signalling pathway could be a novel therapeutic strategy against RCC.

Tissue distribution and subcellular localization of a variant form of the human ST2 gene product, ST2V

The human ST2 gene has been known to encode three splice variants; namely, a soluble secreted form of ST2, a transmembrane form of ST2L, and ST2V of undetermined localization. Therefore, analysis of tissue distribution and subcellular localization of ST2V is important to elucidate functional relationships among the three splice variants of the human ST2 gene. RT-PCR procedure revealed that ST2V is predominantly expressed in the stomach, small intestine, and colon. Transfection of ST2V cDNA into COS7 cells in the presence of [(35)S] methionine and cysteine produced radiolabeled 40 kDa protein, which is recognized by specific monoclonal antibody against human ST2. Subcellular fractionation analysis showed that ST2V protein was distributed in the insoluble fraction of the cell lysate. Finally, ST2V protein was detected on the plasma membrane of COS7 cells, which had been transfected with ST2V cDNA, by confocal laser microscopic analysis. These findings taken together, indicate that ST2V protein localizes on the plasma membrane, suggesting its possible role in modification of the ST2L-signaling pathways.

Adverse effects of anti-tumor drug, cisplatin, on rat kidney mitochondria: disturbances in glutathione peroxidase activity

This study was designed to clarify mechanisms responsible for cisplatin-induced nephrotoxicity together with the effect of selenium. Rats were divided into 3 groups: the cisplatin group; cisplatin (60 mg/kg) was administered intraperitoneally once, the cisplatin + Se group; cisplatin (60 mg/kg) once, and selenious acid (10 mumol/kg) were administered intraperitoneally once a day for 5 consecutive days, the control group; untreated. In each group, mitochondrial respiratory function, enzymic activities in mitochondrial respiratory chain and glutathione peroxidase, and plasma creatinine and BUN contents were measured. In the cisplatin group, decreases in mitochondrial respiratory function, enzymic activities in the respiratory chain and glutathione peroxidase, and increases in plasma creatinine and BUN contents were observed compared with the control group, while the cisplatin + Se group lessened these impairments. These results suggested that cisplatin-induced nephrotoxicity was closely related to mitochondrial dysfunction through the impairment of glutathione peroxidase. This toxicity might be ascribed to free radical mediated-injury. We propose here that, with selenium, higher dose administration of cisplatin to patients might be applicable.