Superoxide-mediated early oxidation and activation of ASK1 are important for initiating methylglyoxal-induced apoptosis process

Methylglyoxal (MG) is a physiological metabolite, but it is known to be toxic, inducing stress and causing apoptosis. Our previous studies demonstrated that MG induced apoptosis in Jurkat cells by activating the c-Jun N-terminal kinase (JNK) signal transduction pathway, which induced an obvious decrease in mitochondrial membrane potential, followed by caspase-3 activation. Here, we observed that MG-induced apoptosis was associated with both rapid production of superoxide anion (O(2)(-)) followed by a marked increase in ROS and striking and temporal activation of ASK1. Overexpression of wild-type ASK1 could enhance the rate of apoptosis induced by MG, whereas the expression of the kinase-inactive form of ASK1 notably prevented cells from MG-induced death. NAC and PDTC blocked the activation of ASK1 and MG-induced apoptosis completely. Moreover, nonthiol antioxidants SOD-mimic MnTBAP and catalase together obviously inhibited MG-induced ASK1 activation and apoptosis induction. Correspondingly, MG-mediated ASK1 activation was enhanced by diethyldithiocarbamate (DDC). Addition of antioxidant into the culture of cells at a later stage (4-8 h after the initial MG treatment) failed to prevent their death. These results suggest that activating ASK1 at the early stage linking to production of O(2)(-) is crucial for subsequent progression of apoptosis in MG-treated Jurkat cells.

Distinct involvement of NF-kappaB and p38 mitogen-activated protein kinase pathways in serum deprivation-mediated stimulation of inducible nitric oxide synthase and its inhibition by 4-hydroxynonenal

Cytokine-induced expression of inducible nitric oxide synthase (iNOS) and concomitant production of nitric oxide (NO) involve activation of mitogen-activated protein (MAP) kinases and are in most cases mediated by the transcription factor NF-kappaB. We investigated the role of p38 MAP kinase activation and IkappaB phosphorylation in iNOS expression in a novel iNOS-inducing model in mouse macrophages. Deprivation of serum from the culture medium of RAW 264.7 cells up-regulated iNOS and NO production, which were inhibited by 4-hydroxy-2-nonenal (HNE), a component of oxidatively modified low-density lipoprotein (oxLDL). Serum withdrawal induced phosphorylation of Akt, IkappaB, and p38 MAP kinase. Pretreatment with the potent PI3 kinase inhibitor wortmannin, the NF-kappaB inhibitor PDTC or the specific p38 MAP kinase inhibitor SB203580 each partially attenuated the induction of iNOS and NO production, demonstrating that both p38 activation and IkappaB phosphorylation are required for iNOS expression. SB203580, however, did not prevent the phosphorylation of Akt and IkappaB, suggesting that the p38 MAP kinase signal contributes to iNOS gene expression through an IkappaB-phosphorylation-independent pathway. HNE, which markedly inhibited iNOS expression and NO production, prevented the serum withdrawal-triggered IkappaB phosphorylation but not that of Akt or p38 MAP kinase. A high concentration of HNE stimulated dephosphorylation of IkappaB but promoted activation of p38 MAP kinase. Taken together, these results suggest that NF-kappaB and p38 MAP kinase lie in separate signal pathways for serum deprivation-stimulated iNOS expression and NO production. HNE selectively suppresses the former pathway, targeting a site downstream of Akt.

Glyoxal and methylglyoxal trigger distinct signals for map family kinases and caspase activation in human endothelial cells

Carbonyl compounds with diverse carbon skeletons may be differentially related to the pathogenesis of vascular diseases. In this study, we compared intracellular signals delivered into cultured human umbilical vein endothelial cells (HUVECs) by glyoxal (GO) and methylglyoxal (MGO), which differ only by a methyl group. Depending on their concentrations, GO and MGO promoted phosphorylations of ERK1 and ERK2, which were blocked by the protein-tyrosine kinase (PTK) inhibitors herbimycin A and staurosporine, thereby being PTK-dependent. GO and MGO also induced phosphorylations of JNK, p38 MAPK, and c-Jun, either PTK-dependently (GO) or -independently (MGO). Next, we found that MGO, but not GO, induced degradation of poly(ADP-ribose) polymerase (PARP) as the intracellular substrate of caspase-3. Curcumin and SB203580, which inhibit JNK and p38 MAPK signaling pathways, but not herbimycin A/staurosporine, prevented the MGO-induced PARP degradation. We then found that MGO, but not GO, reduced the intracellular glutathione level, and that cysteine, but not cystine, inhibited the MGO-mediated activation of ERK, JNK, p38 MAPK, or c-Jun more extensively than did lysine or arginine. In addition, all the signals triggered by GO and MGO were blocked by amino guanidine (AG), which traps carbonyls. These results demonstrated that GO and MGO triggered two distinct signal cascades, one for PTK-dependent control of ERK and another for PTK-independent redox-linked activation of JNK/p38 MAPK and caspases in HUVECs, depending on the structure of the carbon skeleton of the chemicals.

Acrolein induces activation of the epidermal growth factor receptor of human keratinocytes for cell death

Acrolein, which is a highly reactive formaldehyde generated by lipid peroxidation, can affect skin and cause various disorders. The effect of exposure of human keratinocytes to acrolein on cell surface-oriented signal transduction into cells was examined. Incubation of human keratinocytes with a relatively low concentration (50 microM) of acrolein caused a prompt and selective induction of tyrosine phosphorylation of the epidermal growth factor receptor (EGFR) as a 180-kDa molecule during the period from 5-30 min after the start of incubation. This early event was followed by an increase in the density and number of phosphotyrosine-containing proteins during the period from 60-120 min after the start of incubation. The catalytic activity of EGFR as measured by the levels of autophorphorylation and phosphorylation of an exogenously added substrate, casein, in in vitro kinase assay, greatly increased as early as 1 min after the start of incubation and then decreased gradually 30 min later. MAP family kinases, including ERK, JNK, and p38 kinase, and the potentially downstream transcription factor c-Jun were all promoted for phosphorylation/activation during a period of 5-30 min. Selective prompt phosphorylation/activation of EGFR followed by phosphorylation of MAP family kinases and c-Jun and their blockade by a specific EGFR inhibitor, AG1478, suggested that activation of EGFR is the major, and possibly single, cell surface element for intracellular signal transduction in acrolein-treated cells. Incubation of human keratinocytes with 50 microM of acrolein induced atypical apoptosis with morphologic apoptotic features with low-grade oligonucleoside-sized DNA fragmentation. Partial inhibition of such a cytopathic effect of acrolein on human keratinocytes by preincubation with AG1478 suggests the involvement of an EGFR-mediated signal pathway for atypical apoptosis. These results provide new information on acrolein-induced cell surface-oriented signal transduction to human keratinocytes, and this information may be useful for understanding the pathogenesis of a number of skin diseases in response to environmental acrolein and acrolein-generating ultraviolet irradiation.

Osmotic stress-mediated activation of RET kinases involves intracellular disulfide-bonded dimer formation

We showed that osmotic stress induces activation of c-RET and second-set activation of constitutively activated RET-MEN2B. A few percentage of RET proteins normally formed disulfide-bonded dimers in the cell, and osmotic stress promoted formation of these dimers. The disulfide-bonded dimers displayed higher levels of autophosphorylation and catalytic activity per molecule than did monomers. Osmotic stress also promoted activation and disulfide-bonded dimerization of the extracellular domain-depleted mutant RET (RET-PTC-1), suggesting that the target amino acid(s) for dimerization is located intracellularly rather than in the cysteine-rich region of the extracellular domain. In the mutant c-RET and RET-PTC-1 in which Cys987 of c-RET or Cys376 of RET-PTC-1 was replaced with Ala, the levels of intrinsic kinase activity were greatly reduced and barely increased in response to osmotic stress. Correspondingly, the Cys376-defective RET-PTC-1 did not form any demonstrable levels of dimers even after exposure to osmotic stress. In contrast, another RET-PTC-1 mutant that had a replacement of Cys365 with Ala mostly behaved like parental RET-PTC-1. These results suggest that Cys987 of c-RET or Cys376 of RET-PTC-1 plays a crucial role in maintenance and promotion of dimerization and activation of the RET kinases.

Optic-spinal form of multiple sclerosis and immune-mediated myelopathy in Japan

Optic-spinal form of multiple sclerosis (OS-MS) and HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) are two immune-mediated myelopathy relatively common in Japan. (1) Transverse myelitis, once seen in 60% of MS, mostly OS-MS, 30 years ago, drastically decreased (5%) recently in Japan. In contrast, frequency of conventional form of MS (C-MS) increased during this period of time. But unlike C-MS in white patients, cerebellar hemispheric lesions are uncommon in Japanese C-MS. These findings emphasize influence of changes in exogenous factors on manifestations of MS and distinct genetic factors related to MS in Japanese and white patients. (2) To clarify the reason of high HTLV-I proviral load in HAM/TSP, we studied cellular immune surveillance against HTLV-I and found that significant cytotoxic T lymphocyte activity, and suppressed natural killer activity and antibody-dependent cell-mediated cytotoxicity in the patients. These altered immune surveillance may be associated with the spread of HTLV-I infection and the pathogenesis of HAM/TSP.

Mice lacking interleukin-2 (IL-2)/IL-15 receptor beta chain are susceptible to infection with avirulent Salmonella enterica subsp. enterica serovar choleraesuis but mice lacking IL-2 are resistant

Interleukin-2 (IL-2)/IL-15 receptor beta (IL-15R beta)(-/-) mice were susceptible to infection with avirulent Salmonella enterica subsp. enterica serovar Choleraesuis, whereas IL-2(-/-) mice were resistant. A natural killer cell response was not evident for both types of deficient mice. A Th1 response was detected in IL-2(-/-) but not in IL-2/IL-15R beta(-/-) mice infected with Salmonella, suggesting that IL-2/IL-15R beta signaling is important for the generation of protective Th1 cells.

Cepharanthine activates caspases and induces apoptosis in Jurkat and K562 human leukemia cell lines

Cepharanthine (CEP) is a known membrane stabilizer that has been widely used in Japan for the treatment of several disorders such as anticancer therapy-provoked leukopenia. We here report that apoptosis was induced by low concentrations (1-5 microM) of CEP in a human leukemia T cell line, Jurkat, and by slightly higher concentrations (5-10 microM) in a human chronic myelogenous leukemia (CML) cell line K562, which expresses a p210 antiapoptotic Bcr-Abl fusion protein. Induction of apoptosis was confirmed in both Jurkat and K562 cells by DNA fragmentation and typical apoptotic nuclear change, which were preceded by disruption of mitochondrial membrane potential and were induced through a Fas-independent pathway. CEP treatment induced activation of caspase-9 and -3 accompanied by cleavage of PARP, Bid, lamin B1, and DFF45/ICAD in both Jurkat and K562 cells, whereas caspase-8 activation and Akt cleavage were observed only in Jurkat cells. The CEP-induced apoptosis was completely blocked by zVAD-fmk, a broad caspase inhibitor. Interestingly, CEP treatment induced remarkable degradation of the Bcr-Abl protein in K562 cells, and this degradation was prevented partially by zVAD-fmk. When used in combination with a nontoxic concentration of herbimycin A, lower concentrations (2-5 microM) of CEP induced obvious apoptosis in K562 cells with rapid degradation or decrease in the amount of Bcr-Abl and Akt proteins. Our results suggest that CEP, which does not have bone marrow toxicity, may possess therapeutic potential against human leukemias, including CML, which is resistant to anticancer drugs and radiotherapy.

Linear pontine trigeminal root lesions in multiple sclerosis: clinical and magnetic resonance imaging studies in 5 cases

BACKGROUND

Magnetic resonance imaging (MRI) is useful for demonstrating demyelinating lesions in patients with multiple sclerosis (MS). Magnetic resonance imaging studies show that MS lesions are generally not uniform in shape, size, or distribution. Linearly shaped lesions at the trigeminal root entry zone have been occasionally reported in single cases of MS, but, to our knowlege, the frequency and the clinical features of such patients have not been comprehensively characterized.

OBJECTIVE

To describe the frequency and the clinical and laboratory features of patients with MS who had linearly shaped lesions at the trigeminal root as seen on MRI.

DESIGN AND SETTING

A retrospective review of medical records and MRI films of Japanese patients with MS admitted to a university hospital and its affiliated hospital in Sendai, Japan.

PATIENTS AND METHODS

Brain MRI films of 74 consecutive Japanese patients with MS (51 females and 23 males) were studied retrospectively and the clinical and laboratory features of the patients with linearly shaped lesions at the trigeminal root were also investigated retrospectively.

RESULTS

Five patients (6.8%) were shown to have T1-weighted-hypointense, T2-weighted-hyperintense, nonenhanced linear lesions in the pons on MRI, and these were uniformly localized in the intramedullary portion of the trigeminal root. All of these patients had clinically definite MS and had various types of facial sensory disturbances, such as neuralgia (1 patient), hypesthesia (2 patients), or paresthesia (3 patients). No other clinical or laboratory feature was characteristic in these 5 patients.

CONCLUSIONS

Linear pontine trigeminal root lesions were common in our patients with MS. They were associated with various facial sensory symptoms. Since similar lesions are formed in animal models of herpes simplex virus infection, further study is needed to clarify whether these MS lesions are virally induced.

Isolation of the regulatory regions and genomic organization of the porcine alpha1,3-galactosyltransferase gene

BACKGROUND

Alpha1,3-galactosyltransferase (alpha1,3GT) is an enzyme that produces carbohydrate chains termed alphaGal epitopes found in most mammals, although some species of higher primates, including human, are notable exceptions. The evolutionary origin of the lost alpha1,3GT enzyme activity is not yet known, although it has been suggested that the promoter activity of this gene in the ancestors of higher primates was inactivated.

METHODS

We used 5'-or 3'-RACE, GenomeWalking, reverse transcriptase polymerase chain reaction (RT-PCR) and dual Luciferase reporter assay for identification of the full-length cDNA, which includes the transcription initiation site and the promoter region of porcine alpha1,3GT gene.

RESULTS

The region around exon 1 is guanine and cytosine (GC)-rich (about 70%), comprising a CpG island spanning more than 1.5 kbp. The 5'-flanking region of exon 1 contains multiple transcription factor consensus motifs, including GC-box, SP1, AP2, and GATA-box sites, in the absence of TATA or CAAT-box sequences. The entire gene consists of three 5' noncoding and six coding region exons spanning more than 52 kbp. Detailed analysis of alpha1,3GT transcripts revealed two major alternative splicing patterns in the 5'-untranslated region (5'-UTR) and evidence for minor splicing activity that occurs in a tissue-specific manner. Interspecies comparison of 5'-UTR shows minimal homology between porcine and murine sequences except for exon 2, which suggests that the regulatory regions differ among species.

CONCLUSIONS

These observations have important implications for experiments involving genetic manipulation of the alpha1,3GT gene in transgenic animals in terms of promoter utilization, and particularly in genetically engineering cells for the animal cloning technology by nuclear transfer.

Mapping of melanoma modifier loci in RET transgenic mice

Transgenic mice carrying the RET oncogene under the control of the metallothionein promoter exhibit severe pigmentation of the whole skin and melanocytic tumors. The genetic background influences melanoma development in RET mice; founder mice crossed with BALB/c mice show decreased incidence and increased latency of melanocytic tumors, whereas progeny of C57BL/6 mice show the opposite effect. Using partially congenic RET mice on a C57BL/6 genetic background (N3/RET mice), we studied genetic linkage in (N3/RETxBALB/c)xN3/RET backcross mice. We mapped three melanoma modifier loci, on chromosome 1 (Melm1 and Melm2) and chromosome 11 (Melm3), that are linked with early melanoma incidence and latency. Mapping of Melm loci and of five additional regions on chromosomes 6, 8, 9, 12, and 13 indicated allelic imbalance in N3/RET mice, with a significant excess of BALB/c alleles, suggesting the presence of additional putative melanoma modifier loci on these chromosomes.

Significant correlation between IL-10 levels and IgG indices in the cerebrospinal fluid of patients with multiple sclerosis

We measured the interleukin (IL)-6 and IL-10 levels in the plasma and the cerebrospinal fluid (CSF) of a total of 23 relapsing multiple sclerosis (MS) patients [18 with conventional form of MS (C-MS) and 5 with optic-spinal form of MS (OS-MS)] using ELISA and correlated them with the IgG indices and oligoclonal IgG bands (OB) to determine whether these cytokines play a role in the intrathecal immunoglobulin production. IL-10 values in the CSF significantly correlated with the IgG indices and tended to be higher in OB-positive patients. In contrast, IL-10 values in the plasma and IL-6 values in the CSF and the plasma did not correlate with the IgG indices or OB. The CSF-IL-10 value in OS-MS were much lower than those of C-MS, but those of CSF IL-6 did not differ between C-MS and OS-MS. The results remained unchanged even when OS-MS patients were excluded. Our results may suggest a role of IL-10 in upregulating the intrathecal IgG synthesis in relapsing MS.

Arsenite induces apoptosis of murine T lymphocytes through membrane raft-linked signaling for activation of c-Jun amino-terminal kinase

Because of its dual roles in acute toxicity and in therapeutic application in cancer treatment, arsenic has recently attracted a renewed attention. In this study, we report NaAsO(2)-induced signal cascades from the cell surface to the nucleus of murine thymic T lymphocytes that involve membrane rafts as an initial signal transducer. NaAsO(2) induced apoptosis through fragmentation of DNA, activation of caspase, and reciprocal regulation of Bcl-2/Bax with the concomitant reduction of membrane potential. We demonstrated that NaAsO(2)-induced caspase activation is dependent on curcumin-sensitive c-Jun amino-terminal kinase and barely dependent on SB203580-sensitive p38 kinase or PD98059-sensitive extracellular signal-regulated kinase. Additionally, staurosporine, which severely inhibited the activation of mitogen-activated protein (MAP) family kinases and c-Jun, partially blocked the NaAsO(2)-mediated signal for poly(ADP-ribose) polymerase (PARP) degradation. Potentially as the initial cell surface event for intracellular signaling, NaAsO(2) induced aggregation of GPI-anchored protein Thy-1 and superoxide production. This Thy-1 aggregation and subsequent activation of MAP family kinase and c-Jun and the degradation of PARP induced by NaAsO(2) were all inhibited by DTT, suggesting the requirement of interaction between arsenic and protein sulfhydryl groups for those effects. beta cyclodextrin, which sequestrates cholesterol from the membrane rafts, inhibited NaAsO(2)-induced activation of protein tyrosine kinases and MAP family kinases, degradation of PARP, and production of superoxide. In addition, beta cyclodextrin dispersed NaAsO(2)-induced Thy-1 clustering. These results suggest that a membrane raft integrity-dependent cell surface event is a prerequisite for NaAsO(2)-induced protein tyrosine kinase/c-Jun amino-terminal kinase activation, superoxide production, and downstream caspase activation.

A protective role of interleukin-15 in a mouse model for systemic infection with herpes simplex virus

To define the role of cytokine binding to the IL-2/IL-15R beta chain in protective immunity against systemic infection with herpes simplex virus type 2 (HSV-2), IL-2/IL-15 receptor(R)beta knock-out mice were inoculated intraperitoneally with HSV-2 strain 186. IL-2/IL-15R beta-deficient mice were susceptible to systemic HSV-2 infection compared with their heterozygous littermates. The emergence of natural killer (NK) cells was impaired in IL-2/IL-15R beta knock-out mice, but CD4(+) T cell receptor (TCR) alpha beta(+) T cells were normally detected in the peritoneal cavity after infection with HSV-2. However, the generation of HSV-2-specific CD4(+) T helper (Th) 1 cells producing interferon-gamma was impaired in IL-2/IL-15R beta knock-out mice following HSV-2 infection. The serum IL-15 level in control mice was increased in the early stage after HSV-2 infection but was not detectable in IL-2/IL-15R beta knock-out mice. In vivo administration of recombinant IL-15 protected normal mice from HSV-2-induced lethality, accompanied by increases in numbers of NK cells and HSV-2-specific Th1 cells. Taken together, these results suggest that IL-15, using the IL-2/IL15R beta chain, plays an important role in mounting protective immunity during the course of systemic HSV-2 infection.

Local levels of soluble tumor necrosis factor receptors in patients with allergic rhinitis are regulated by amount of antigen

OBJECTIVES

To examine the possible correlation between the amount of antigen and the level of soluble tumor necrosis factor receptor (sTNFR), and to assess its biologic significance in allergic reactions.

DESIGN

Randomized control trial.

SUBJECTS

Twelve volunteers with Japanese cedar pollinosis and 10 healthy volunteers.

INTERVENTIONS

The levels of p55 sTNFR (sTNFR1) and p75 sTNFR (sTNFR2) in samples of serum and nasal epithelial lining fluid (ELF) from 12 subjects with pollinosis and 10 healthy subjects were measured 4 times (preseason, early season, midseason, and postseason) in low (total, 415/cm( 2) per season) and high (total, 19,935/cm(2) per season) pollen-count periods, and the results were compared among the 4 groups.

RESULTS

In the low-pollen-count period, increased levels of sTNFR1 and sTNFR2 were observed in ELF samples from the allergic subjects during the midseason. In contrast, in the high-pollen-count period, those levels were already elevated during the preseason and reduced during the midseason. Especially, the levels of sTNFR2 in ELF samples from the allergic subjects during the midseason in the high-pollen-count period were significantly lower than those in the low-pollen-count period. Moreover, a significant negative correlation (sTNFR1, R = -0.82; sTNFR2, R = -0. 73) was found between the levels of sTNFR1 and sTNFR2 in ELF samples and the scores of symptoms in the allergic subjects in the high-pollen-count period, but not in the low-pollen-count period.

CONCLUSION

In patients with pollinosis, the amounts of antigen regulate the local levels of sTNFRs, possibly inhibiting nasal allergic inflammation.

Mercuric chloride stimulates distinct signal transduction pathway for DNA synthesis in a T-cell line, CTLL-2

Exposure of an interleukin-2 (IL-2)-dependent murine T-cell line (CTLL-2) to mercuric chloride in in vitro culture induced a low but definite level of DNA synthesis in the absence of exogenous IL-2, and further enhanced the IL-2-induced DNA synthesis. Addition of anti-IL-2 or anti-IL-4 antibody to the culture, which neutralized all of the IL-2 or IL-4 activity, respectively, never inhibited the mercuric chloride-mediated DNA synthesis. Correspondingly, no detectable level of IL-2, IL-4, and IL-15 mRNA was found in mercuric chloride-treated CTLL-2 cells in our test condition. Stimulation of CTLL-2 cells with IL-2 induced phosphorylation on extracellular signal-regulated kinases more intensively than on c-Jun NH2-terminal kinases (JNKs), and provoked tyrosine phosphorylation of Janus kinases (JAKs) and signal transducers and activators of transcription (STATs). In contrast, by mercuric chloride stimulation, JNKs and c-Jun were preferentially phosphorylated, but no detectable level of phosphorylation was induced on JAKs and STATs. These findings provided a possibility that mercuric chloride promoted lymphocyte proliferation through a JNK-linked signal cascade in CTLL-2 cells, which differs from that triggered by IL-2.

Methylglyoxal induces apoptosis in Jurkat leukemia T cells by activating c-Jun N-terminal kinase

Methylglyoxal (MG) is a physiological metabolite, but it is known to be toxic, inducing stress in cells and causing apoptosis. This study examines molecular mechanisms in the MG-induced signal transduction leading to apoptosis, focusing particularly on the role of JNK activation. We first confirmed that MG caused apoptosis in Jurkat cells and that it was cell type dependent because it failed to induce apoptosis in MOLT-4, HeLa, or COS-7 cells. A caspase inhibitor, Z-DEVD-fmk, completely blocked MG-induced poly(ADP-ribose)polymerase (PARP) cleavage and apoptosis, showing the critical role of caspase activation. Inhibition of JNK activity by a JNK inhibitor, curcumin, remarkably reduced MG-induced caspase-3 activation, PARP cleavage, and apoptosis. Stable expression of the dominant negative mutant of JNK also protected cells against apoptosis notably, although not completely. Correspondingly, loss of the mitochondrial membrane potential induced by MG was decreased by the dominant negative JNK. These results confirmed a crucial role of JNK working upstream of caspases, as well as an involvement of JNK in affecting the mitochondrial membrane potential.

4-hydroxynonenal induces a cellular redox status-related activation of the caspase cascade for apoptotic cell death

4-Hydroxynonenal (HNE), a diffusible product of lipid peroxidation, has been suggested to be a key mediator of oxidative stress-induced cell death. In this study, we partially characterized the mechanism of HNE-mediated cytotoxicity. Incubation of human T lymphoma Jurkat cells with 20–50 μM HNE led to cell death accompanied by DNA fragmentation. Western blot analysis showed that HNE-treatment induced time- and dose-dependent activation of caspase-8, caspase-9 and caspase-3. HNE-induced caspase-3 processing was confirmed by a flow cytometric demonstration of increased catalytic activity on the substrate peptide. HNE treatment also led to remarkable cleavage of poly(ADP-ribose) polymerase (PARP), which was prevented by pretreatment of cells with DEVD-FMK as a caspase-3 inhibitor. The HNE-mediated activation of caspases, cleavage of PARP and DNA fragmentation were blocked by antioxidants cysteine, N-acety-L-cysteine and dithiothreitol, but not by two other HNE-reactive amino acids lysine and histidine, or by cystine, the oxidized form of cysteine. HNE rapidly decreased levels of intracellular reduced glutathione (GSH) and its oxidized form GSSG, and these were also attenuated by the reductants. Coincubation of Jurkat cells with a blocking anti-Fas antibody prevented Fas-induced but not HNE-induced activation of caspase-3. HNE also activated caspase-3 in K562 cells that do not express functional Fas. Our results thereby demonstrate that HNE triggers oxidative stress-linked apoptotic cell death through activation of the caspase cascade. The results also suggest a possible mechanism involving a direct scavenge of intracellular GSH by HNE.

A short peptide derived from the antisense homology box of Fas ligand induces apoptosis in anti-Fas antibody-insensitive human ovarian cancer cells

We found that a short synthetic peptide corresponding to the "antisense homology box" of Fas ligand induced apoptotic cell death of Fas-expressing human ovarian cancer cell lines. The peptide was deduced from residues 256-265 of human Fas ligand, based on the hypothesis that it should contain a specific binding site to the corresponding Fas. Interestingly, the ovarian cancer cell line NOS4, which was sensitive to anti-Fas antibody induced apoptosis, was not affected by the peptide, whereas another cell line, SKOV-3, which was insensitive to anti-Fas antibody, was killed by the peptide. Thus, this short peptide was shown to have a unique activity to induce apoptosis in human ovarian cancer cells in a manner different from anti-Fas antibody.

Clustered cysteine residues in the kinase domain of v-Src: critical role for protein stability, cell transformation and sensitivity to herbimycin A

We have previously reported the activation of Src by mercuric chloride based on the sulfhydryl modification. To evaluate the significance of cysteine residues in v-Src, we replaced each cysteine to alanine by oligonucleotide-directed mutagenesis and examined its effect on cell transformation. Of ten cysteine residues scattered over v-Src, four cysteines clustered in kinase domain, Cys483, Cys487, Cys496 and Cys498, were important for protein stability and cell transformation, whereas those in SH2 domain were dispensable. A single mutation in Cys498 yielded suppression of kinase activity and a temperature-sensitivity in anchorage independent growth. Double mutation either in Cys483/Cys487 or in Cys496/Cys498 yielded clear temperature-sensitivity in cell transformation and in stability of Src protein. Instability of Src protein was magnified by quadruple mutation in the cysteines, which decreased the half-life of Src to be less than one quarter of that of wild-type. In addition, both Cys483/Cyr487 and Cys496/Cys498 kinases became resistant to in vitro inactivation by herbimycin A, which directly inactivates v-Src in addition to its effect on HSP90. Taken together, our results strongly suggest that the cysteine clustered motif of v-Src are critical for protein stability, cell transformation and in vitro inactivation by herbimycin A.

Ultraviolet light induces redox reaction-mediated dimerization and superactivation of oncogenic Ret tyrosine kinases

The c-RET proto-oncogene encodes a receptor-type tyrosine kinase, and its mutations in the germ line are responsible for the inheritance of multiple endocrine neoplasia type 2A (MEN2A) and 2B (MEN2B). Ret kinases are constitutively activated as a result of MEN2A mutations (Ret-MEN2A) or MEN2B mutations (Ret-MEN2B). Here we demonstrate that UV light (UV) irradiation induces superactivation of the constitutively activated Ret-MEN2A and Ret-MEN2B as well as activation of c-Ret. Before UV irradiation, small percentages of c-Ret (3-4%) and Ret-MEN2B (1-2%) and large percentages of Ret-MEN2A (30-40%) were dimerized through disulfide bonds. These dimerized Ret proteins were preferentially autophosphorylated, suggesting a close relation between up-regulated kinase activity and disulfide bond-mediated dimerization of Ret proteins. We found that UV irradiation promotes the disulfide bond-mediated dimerization of the Ret proteins, in close association with activation and superactivation of Ret kinases. UV irradiation also induced dimerization and activation of the extracellular domain-deleted mutant Ret (Ret-PTC-1). Interestingly, the levels of basic kinase activity and dimerization of Ret-PTC-1-C376A, in which cysteine 376 in the tyrosine kinase domain of Ret-PTC-1 was replaced by alanine, were low and were not increased by UV irradiation. These results suggest that Ret-PTC-1 cysteine 376 is one of possibly multiple critical target amino acids of UV for Ret kinase activation. Overexpression of Cu/Zn superoxide dismutase in cells as a result of gene transfection prevented both the UV-mediated promotion of dimerization and the superactivation of Ret-MEN2A kinase. These results suggest that the UV-induced free radicals in cells attack intracellular domains of Ret to dimerize the kinase proteins for superactivation.

Molecular mechanism of activation and superactivation of Ret tyrosine kinases by ultraviolet light irradiation

The catalytic activities of Ret tyrosine kinases as the products of oncogene RET with multiple endocrine neoplasia type 2A (Ret-MEN2A) or 2B (Ret-MEN2B) mutations and the hybrid gene from c-RET and RFP (Rfp-Ret) were higher than those of c-Ret. We demonstrated that ultraviolet light (UV) irradiation induced activation of c-Ret and superactivation of genetically mutated, and thereby constitutively activated, Ret-MEN2A, Ret-MEN2B, and Rfp-Ret. We found that small proportions of c-Ret and Ret-MEN2B and a large proportion of MEN2A were dimerized due to disulfide bonds and that high kinase activity resided in these fractions. The UV-induced activation of c-Ret and superactivation of Ret-MEN2A and Ret-MEN2B were then shown to be closely associated with promotion of the disulfide bond-mediated dimerization of the Ret proteins. Furthermore, we showed that a large proportion of Rfp-Ret was dimerized or polymerized and that almost all kinase activities resided in the highly polymerized but not dimerized fraction. The UV-induced superactivation of Rfp-Ret was also found to be closely associated with promotion of polymerization but not with dimerization of Rfp-Ret. Further experiments revealed that UV induced intracellular dimerization and activation of the extracellular domain-deleted mutant Ret (Ret-PTC-1). Most importantly, the levels of basal kinase activity and dimerization of Ret-TPC-1-C376A, in which cysteine 376 in the tyrosine kinase domain of Ret-TPC-1 was replaced with alanine, were low and were not increased by UV irradiation. These results suggest that the cysteine at this position works as the primary target of dimerization of Ret proteins inside the cell for both the maintenance of the basal kinase activity and its promotion by UV, possibly in co-operation with the cysteine(s) in the extracellular domain of Ret-MEN2A and Rfp-Ret, which is the target of dimerization and polymerization outside the cell. The potential biological significance of the UV-mediated superactivation of mutant Ret through the newly proposed mechanism in oncogenesis is discussed.