A novel neuroprotective compound FR901459 with dual inhibition of calcineurin and cyclophilins

Brain ischemia leads to severe damage in the form of delayed neuronal cell death. In our study, we show that the marked neuroprotection of the new immunosuppressant FR901495 in forebrain ischemia is due not only to inhibition of calcineurin, but also to protection against mitochondrial damage caused by mitochondrial permeability transition pore formation through cyclophilin D, one of the prolyl cis/trans isomerase family members. These findings shed light on the clinical application and development of new drugs for the treatment of ischemic damage in the brain as well as in the heart and liver.

Search for novel gene markers of traumatic brain injury by time differential microarray analysis

Neuronal and glial cell death caused by axonal injury sometimes contributes to whole brain pathology after traumatic brain injury (TBI). We show that neuroprotection by 2 types of immunosuppressants, cyclosporin A (CsA) and tacrolimus (FK506), in a cryogenic brain injury model results from inhibition of calcineurin and protection from mitochondrial damage caused by formation of a mitochondrial permeability transition pore induced by cyclophilin D (CyPD), one of the prolyl cis/trans isomerase family members. We evaluated why CsA is neuroprotective by microarray analysis of gene expression in the cryogenic brain injury rat model. Analyses of expression patterns demonstrated that expression of over 14,000 genes changed between the groups with and without CsA treatment, and about 350 genes among them were extracted showing a significant difference. We learned that the differential expression of several gene targets showed specific patterns in a time-dependent manner. These results may help elucidate the mechanisms of neuronal cell death after TBI and the neuroprotective effects of CsA after TBI.

Calcineurin and cyclophilin D are differential targets of neuroprotection by immunosuppressants CsA and FK506 in ischemic brain damage

The search for an effective treatment for global ischemia following cardiac arrest has proved to be very difficult. However, studies by Uchino et al. show that the immunosuppressant cyclosporin A (CsA), when administered in such a way that the drug can bypass the blood brain barrier (BBB), dramatically reduces ischemic damage in rat forebrain preparations. An alternative immunosuppressant, FK506, is apparently less efficacious. Both CsA and FK506 are specific inhibitors of immunophilins, (CsA inhibits cyclophilins, FK506 inhibits FKBPs), and of calcineurin, a type 2B Ser/Thr phosphatase that is abundant in the central nervous system. The superiority of CsA may be partly attributable to its selective amelioration of mitochondrial damage, as assayed in vivo and in vitro. Our results suggest that pathways involving calcineurin and cyclophilins, particularly mitochondrial cyclophilin D, play pivotal roles in the development of ischemic brain damage. The present findings may inform the search for new drugs in the treatment of global ischemic damage to the brain, and in other organs.

Co-transduction of Apaf-1 and caspase-9 highly enhances p53-mediated apoptosis in gliomas

Mutation of the p53 gene plays a critical role in the development of cancer and response to cancer therapy. To analyze the mechanism of cancer development and to improve cancer therapy, it is important to assess which genes are downstream components of p53 in cancers, and whether the expression levels of these genes affect p53-mediated apoptosis. In this study, we transduced the wild type p53 gene along with the Apaf-1 and caspase-9 genes via adenovirus vectors into U251 and U-373MG glioma cells harbouring a mutated p53, and evaluated the degree of apoptosis. Co-induction of Apaf-1 and caspase-9 genes highly enhanced p53-mediated apoptosis in glioma cells. Induction of wild type p53 enhanced the expression levels of Bax, p21/WAF1, and Fas protein. To determine which gene is activated by wild type p53 induction and, in turn, activates Apaf-1 and caspase-9, we transduced the Bax, p21/WAF1 or Fas gene via adenovirus vector to U251 cells to achieve a similar expression level as that induced by the Adv for p53 in U251 cells. U251 cells transduced with Fas concomitant with the Apaf-1 and caspase-9 genes underwent drastic apoptosis. This suggests that induction of wild type p53 upregulates Fas, which in turn may play a role in the activation of Apaf-1 and caspase-9. These results are important for analyzing the mechanism of tumour development and for predicting the therapeutic effect of p53 replacement gene therapy in a particular patient.

Dissociation of Bax from a Bcl-2/Bax heterodimer triggered by phosphorylation of serine 70 of Bcl-2

Serine 70 in the loop region of Bcl-2 is specifically phosphorylated by paclitaxel-treatment in tumor cells and BHK cells expressing Bcl-2. The phosphorylation of serine 70 of Bcl-2 (pS70-Bcl-2) peaks 24 to 48 h after paclitaxel treatment and accelerates apoptosis. Phosphorylation is effectively inhibited in the presence of actinomycin D or cycloheximide, which restore cell viability to the same level as control cells not expressing Bcl-2. These results indicate that paclitaxel-induced kinase(s) and/or its activator(s) are synthesized de novo and play an important role in paclitaxel-induced apoptosis by phosphorylating Bcl-2. In binding assays using the phosphorylation-specific antibody against pS70-Bcl-2, the induction of serine 70 phosphorylation 70 results in a loss of the binding ability of Bcl-2 to Bax, a pro-apoptotic partner, and induces subsequent cell death. When the pS70-Bcl-2 antibody was added to human breast cancer tissue, serine 70 phosphorylation was also detected, even prior to treatment with anticancer agents. Further study of breast cancers revealed 83% of tumors with high pS70-Bcl-2 expression responded to paclitaxel or docetaxel treatment, whereas 57% of those with low expression not respond. These findings suggest that pS70-Bcl-2 might be a predictive factor for prognosis and sensitivity to paclitaxel treatment for breast cancer.

Involvement of the brain-derived neurotrophic factor/TrkB pathway in neuroprotecive effect of cyclosporin A in forebrain ischemia

Recent studies have shown that cyclosporin A, a specific antagonist of calcineurin, a phosphatase, ameliorates neuronal cell death in the CA1 sector of the hippocampus after forebrain ischemia in animal models. The mechanism of this neuroprotective effect, however, has not yet been established. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophins, is one of the potent survival and developmental factors whose expression is regulated by cyclic AMP-response element-binding protein (CREB). Activation of CREB is dependent on its phosphorylation at Ser(133), and calcineurin has been reported to dephosphorylate CREB via protein phosphatase 1. Based on these observations, we attempted to investigate how cyclosporin A treatment would affect the changes of phosphorylated CREB (pCREB), BDNF and its receptor tyrosine kinase B (TrkB) after forebrain ischemia in rats. Phosphorylation of CREB was kept augmented throughout the time course examined in cyclosporin A-treated animals, while it ceased without cyclosporin A. Reverse transcription-polymerase chain reaction revealed prolonged maintenance of BDNF mRNA expression in the CA1 sector of cyclosporin A-treated animals. The protein expression of BDNF and TrkB appeared to be up-regulated in cyclosporin A-treated animals, whereas it was transiently up-regulated but decreased to the marginal level of expression without cyclosporin A.From these results we suggest that cyclosporin A induces pCREB by an inhibition of calcineurin, resulting in the induction of BDNF. The mechanisms by which cyclosporin A protects the CA1 region from neuronal cell death in forebrain ischemia may involve the interaction of pCREB, BDNF and TrkB.

Isoproterenol activates extracellular signal-regulated protein kinases in cardiomyocytes through calcineurin

BACKGROUND

Extracellular signal-regulated kinases (ERKs) and calcineurin have been reported to play important roles in the development of cardiac hypertrophy. We examined here the relation between calcineurin and ERKs in cardiomyocytes.

METHODS AND RESULTS

Isoproterenol activated ERKs in cultured cardiomyocytes of neonatal rats, and the activation was abolished by chelation of extracellular Ca(2+) with EGTA, blockade of L-type Ca(2+) channels with nifedipine, or depletion of intracellular Ca(2+) stores with thapsigargin. Isoproterenol-induced activation of ERKs was also significantly suppressed by calcineurin inhibitors in cultured cardiomyocytes as well as in the hearts of mice. Isoproterenol failed to activate ERKs in either the cultured cardiomyocytes or the hearts of mice that overexpress the dominant negative mutant of calcineurin. Isoproterenol elevated intracellular Ca(2+) levels at both systolic and diastolic phases and dose-dependently activated calcineurin. Inhibition of calcineurin also attenuated isoproterenol-stimulated phosphorylation of Src, Shc, and Raf-1 kinase. The immunocytochemistry revealed that calcineurin was localized in the Z band, and isoproterenol induced translocation of calcineurin and ERKs into the nucleus.

CONCLUSIONS

Calcineurin, which is activated by marked elevation of intracellular Ca(2+) levels by the Ca(2+)-induced Ca(2+) release mechanism, regulates isoproterenol-induced activation of ERKs in cardiomyocytes.

Calcineurin plays a critical role in the development of pressure overload-induced cardiac hypertrophy

BACKGROUND

Although activation of the Ca(2+)-dependent phosphatase calcineurin has been reported to induce cardiomyocyte hypertrophy, whether calcineurin is involved in pressure overload-induced cardiac hypertrophy remains controversial.

METHODS AND RESULTS

We examined in the present study the role of calcineurin in pressure overload-induced cardiac hypertrophy using transgenic mice that overexpress the dominant negative mutant of calcineurin specifically in the heart. There were no significant differences in body weight, blood pressure, heart rate, heart weight, and the cardiac calcineurin activity between the transgenic mice and their littermate wild-type mice at basal state. The activity of calcineurin was markedly increased by pressure overload produced by constriction of the abdominal aorta in the heart of wild-type mice but less increased in the heart of the transgenic mice. Pressure overload induced increases in heart weight, wall thickness of the left ventricle, and diameter of cardiomyocytes; reprogramming of expressions of immediate early response genes and fetal-type genes; activation of extracellular signal-regulated protein kinases; and fibrosis. All these hypertrophic responses were more prominent in the wild-type mice than in the transgenic mice.

CONCLUSIONS

These results suggest that calcineurin plays a critical role in the development of pressure overload-induced cardiac hypertrophy.

Adenovirus-mediated transfer of p53 augments hyperthermia-induced apoptosis in U251 glioma cells

PURPOSE

Hyperthermia kills glioma cells by inducing apoptosis and is thereby an effective therapeutic modality for the treatment of malignant gliomas. However, cells harboring mutated p53 are refractory to hyperthermia-induced apoptosis. In this study, we assessed whether or not adenovirus (Adv)-mediated transduction of p53 overrides this resistant mechanism.

METHODS AND MATERIALS

We transduced the p53 wild-type tumor suppressor gene into U251 glioma cells harboring mutated p53 using Adv vectors in combination with hyperthermia (43, 44.5 degrees C), and evaluated the degree of cell death and apoptosis.

RESULTS

The percentage of cells that had died, as measured by trypan blue staining, among U251 cells infected with the Adv for p53 (Adv-p53) and treated with hyperthermia, was significantly higher than the percentage of cells that had died among U251 cells infected with Adv-p53 and not treated with hyperthermia, or those infected with the control Adv for dE (Adv-dE) and treated with hyperthermia. The degree of apoptosis, measured at 24 h after treatment, in hyperthermia-treated U251 cells infected with Adv-p53 (43 degrees C, 73%; 44.5 degrees C, 92%) was much higher than that infected with Adv-p53 (41%), or that infected with control Adv-dE and treated with hyperthermia (43 degrees C, 1.3%; 44.5 degrees C, 19%). Treatment with combined hyperthermia and Adv-p53 infection induced cleavage of caspase-3 in U251 cells.

CONCLUSION

These results indicate that Adv-mediated transduction of p53 would render glioma cells highly sensitive to hyperthermia.

Inhibition of cytochrome c release in Fas-mediated signaling pathway in transgenic mice induced to express hepatitis C viral proteins

Persistent hepatitis C virus (HCV) infection often progresses to chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Numerous viruses have been reported to escape from apoptotic mechanism to maintain persistent infection. In the present study, we characterized the effect of HCV proteins on the Fas signal using HCV transgenic mice, which expressed core, E1, E2, and NS2 proteins, regulated by the Cre/loxP switching system. The transgene expression of HCV transgenic mice caused resistance to Fas antibody stimulated lethality. Apoptotic cell death in the liver of HCV protein expressing mice was significantly reduced compared with nonexpressing mice. Histopathological analysis and DNA fragmentation analysis revealed that the HCV proteins suppressed Fas-mediated apoptotic cell death. To identify the target pathway of HCV proteins, we characterized caspase activity. The activation of caspase-9 and -3/7 but not caspase-8 was inhibited by HCV proteins. Cytochrome c release from mitochondria was inhibited in HCV protein expressing mice. These results indicated that the expression of HCV proteins may directly or indirectly inhibit Fas-mediated apoptosis and death in mice by repressing the release of cytochrome c from mitochondria, thereby suppressing caspase-9 and -3/7 activation. These results suggest that HCV may cause persistent infection, as a result of suppression of Fas-mediated cell death.

Two distinct action mechanisms of immunophilin-ligand complexes for the blockade of T-cell activation

The immunosuppressive effects of cyclosporin A (CsA) and FK506 are mediated through binding to immunophilins. Here we show that FK506-FKBP complex suppresses the activation of JNK and p38 pathways at a level upstream of mitogen-activated protein kinase (MAPK) kinase kinase (MAPKK-K) besides the calcineurin-NFAT pathway. A238L, a viral gene product that binds to immunophilin, also blocks activation of both pathways. In contrast, direct inhibitors of calcineurin, Cabin 1 and FR901725, suppress the activation of NFAT but not the JNK or p38 pathway. We further demonstrate that co-expression of a constitutively active NFAT and a constitutively active MEKK1 renders the interleukin-2 promoter in Jurkat T lymphocytes resistant to CsA and FK506, whereas Jurkat cells expressing a constitutively active NFAT alone are still sensitive to CsA or FK506. Therefore, CsA and FK506 exert their immunosuppressive effects through targeting both the calcineurin-dependent NFAT pathway and calcineurin-independent activation pathway for JNK and p38.

beta-Adrenergic pathway induces apoptosis through calcineurin activation in cardiac myocytes

Apoptosis of cardiac myocytes is one of the causes of heart failure. Here we examine the mechanism by which the activation of beta-adrenergic receptor induces cardiomyocyte apoptosis. Terminal deoxynucleotide transferase-mediated dUTP nick end labeling and DNA ladder analyses revealed that isoproterenol (Iso) induced the apoptosis of cardiac myocytes of neonatal rats through an increase in intracellular Ca(2+) levels. The Iso-induced cardiomyocyte apoptosis was strongly inhibited by the L-type Ca(2+) channel antagonist nifedipine and by the calcineurin inhibitors cyclosporin A and FK506. Iso reduced the phosphorylation levels of the proapoptotic Bcl-2 family protein Bad and induced cytochrome c release from mitochondria to the cytosol through calcineurin activation. Infusion of Iso increased calcineurin activity by approximately 3-fold in the hearts of wild-type mice but not in the hearts of transgenic mice that overexpress dominant negative mutants of calcineurin. Terminal deoxynucleotide transferase-mediated dUTP nick end labeling analysis revealed that infusion of Iso induced apoptosis of cardiac myocytes and that the number of apoptotic cardiomyocytes was significantly less in the hearts of the transgenic mice compared with the wild-type mice. These results suggest that calcineurin plays a critical role in Iso-induced apoptosis of cardiac myocytes, possibly through dephosphorylating Bad.

Bcl-2 inhibits calcineurin-mediated Fas ligand expression in antitumor drug-treated baby hamster kidney cells

It is well known that human leukemia cells, such as HL-60 and U937 are sensitive to antitumor drugs, but human normal lung fibroblasts, such as WI-38 cells are resistant to the drugs. However, the mechanisms of the different responses to apoptosis in these cell lines remain unclear. We report here that an increase of Fas and Fas ligand (FasL) expression was required for antitumor drug-induced apoptosis in WI-38 and baby hamster kidney (BHK) cells, but not in HL-60 cells. Then, we used BHK cells transfected with the bcl-2 gene to investigate the involvement of complex formation of Bcl-2 and calcineurin. Calcineurin was imported to the nucleus in response to the drug treatment. Overexpression of Bcl-2 and cyclosporin A treatment inhibited the nuclear import and FasL expression, and as a result, both inhibited apoptosis. Although a caspase inhibitor, z-Asp-CH2-DCB, suppressed the drug-induced apoptosis, it failed to inhibit the drug-induced expression of Fas and FasL. These findings suggest that initially the Fas / FasL system is activated by calcineurin-dependent transcription followed by activation of the downstream caspase cascade resulting in antitumor drug-induced apoptosis in BHK cells, but not in HL-60 cells. Furthermore, Bcl-2 inhibits the nuclear import of calcineurin and suppresses calcineurin-mediated FasL expression during antitumor drug-induced apoptosis.

Ca2+/calmodulin-dependent kinase II and calcineurin play critical roles in endothelin-1-induced cardiomyocyte hypertrophy

Endothelin-1 (ET-1) induces cardiac hypertrophy. Because Ca(2+) is a major second messenger of ET-1, the role of Ca(2+) in ET-1-induced hypertrophic responses in cultured cardiac myocytes of neonatal rats was examined. ET-1 activated the promoter of the beta-type myosin heavy chain gene (beta-MHC) (-354 to +34 base pairs) by about 4-fold. This activation was inhibited by chelation of Ca(2+) and the blocking of protein kinase C activity. Similarly, the beta-MHC promoter was activated by Ca(2+) ionophores and a protein kinase C activator. beta-MHC promoter activation induced by ET-1 was suppressed by pretreatment with the calmodulin inhibitor, W7, the Ca(2+)/calmodulin-dependent kinase II (CaMKII) inhibitor, KN62, and the calcineurin inhibitor, cyclosporin A. beta-MHC promoter activation by ET-1 was also attenuated by overexpression of dominant-negative mutants of CaMKII and calcineurin. ET-1 increased the activity of CaMKII and calcineurin in cardiac myocytes. Pretreatment with KN62 and cyclosporin A strongly suppressed ET-1-induced increases in [(3)H]phenylalanine uptake and in cell size. These results suggest that Ca(2+) plays a critical role in ET-1-induced cardiomyocyte hypertrophy by activating CaMKII- and calcineurin-dependent pathways.

Cell cycle arrest enhances the in vitro cellular toxicity of the truncated Machado-Joseph disease gene product with an expanded polyglutamine stretch

Machado-Joseph disease (MJD) is an inherited neurodegenerative disorder caused by the expansion of the polyglutamine stretch in the MJD gene-encoded protein, ataxin-3. Using a series of deletion constructs expressing ataxin-3 fragments with expanded polyglutamine stretches, we observed aggregate formation and cell death in cultured BHK-21 cells. The cytotoxic effect of N-terminal-truncated ataxin-3 with the expanded polyglutamine tract was enhanced under serum starvation culture, in which cells were arrested in the G(0)/G(1)phase. Coexpression of p21 (waf1/cip1/sdi1), a cyclin-Cdk inhibitor that induced cell cycle arrest in the G(1)phase, also increased the cell death susceptibility produced by the mutant ataxin-3 fragment in BHK-21 cells. The elevated susceptibility to cell death in the G(0)/G(1)phase was confirmed in nerve growth factor-treated, postmitotic neuronal PC12 cells compared with undifferentiated proliferating PC12 cells. These results strongly suggest that the cellular toxicity of truncated ataxin-3 with an expanded polyglutamine stretch is enhanced by cell cycle arrest in the G(0)/G(1)phase. Mutant ataxin-3 may confer a higher susceptibility to cell death on cells in the G(0)/G(1)phase.

Calcineurin plays a critical role in pressure overload-induced cardiac hypertrophy

BACKGROUND

Cardiac hypertrophy is a fundamental adaptive response to hemodynamic overload; how mechanical load induces cardiac hypertrophy, however, remains elusive. It was recently reported that activation of a calcium-dependent phosphatase, calcineurin, induces cardiac hypertrophy. In the present study, we examined whether calcineurin plays a critical role in pressure overload-induced cardiac hypertrophy.

METHODS AND RESULTS

Pressure overload produced by constriction of the abdominal aorta increased the activity of calcineurin in the rat heart and induced cardiac hypertrophy, including reprogramming of gene expression. Treatment of rats with a calcineurin inhibitor, FK506, inhibited the activation of calcineurin and prevented the pressure overload-induced cardiac hypertrophy and fibrosis without change of hemodynamic parameters. Load-induced expression of immediate-early-response genes and fetal genes was also suppressed by the FK506 treatment.

CONCLUSIONS

The present results suggest that the calcineurin signaling pathway plays a pivotal role in load-induced cardiac hypertrophy and may pave the way for a novel pharmacological approach to prevent cardiac hypertrophy.

Ca2+-induced apoptosis through calcineurin dephosphorylation of BAD

The Ca2+-activated protein phosphatase calcineurin induces apoptosis, but the mechanism is unknown. Calcineurin was found to dephosphorylate BAD, a pro-apoptotic member of the Bcl-2 family, thus enhancing BAD heterodimerization with Bcl-xL and promoting apoptosis. The Ca2+-induced dephosphorylation of BAD correlated with its dissociation from 14-3-3 in the cytosol and translocation to mitochondria where Bcl-xL resides. In hippocampal neurons, L-glutamate, an inducer of Ca2+ influx and calcineurin activation, triggered mitochondrial targeting of BAD and apoptosis, which were both suppressible by coexpression of a dominant-inhibitory mutant of calcineurin or pharmacological inhibitors of this phosphatase. Thus, a Ca2+-inducible mechanism for apoptosis induction operates by regulating BAD phosphorylation and localization in cells.

[Novel function of Calcineurin--multipotential factor as protein a phosphatase]

Calcineurin, serine/threonine phosphatase2B, is well known as a target of immunophilin-immunosuppressant complex such as cyclophilin-cyclosporinA and FKBP -FK506. It has been disclosed that Calcineurin is involved in interleukin 2 gene activation pathway lead to T lymphocyte proliferation, however, its functions as a multipotential factor still remains unknown. Here we mention about a new aspect of Calcineurin-involved pathway through its direct interaction to Bcl-2, an apoptosis suppressor. This direct binding of Calcineurin to Bcl-2 results in blockage of KFAT4 nuclear import by the prevention of Calcineurin-targetted dephosphorylation of NFAT4. Moreover, the tight binding between Calcineurin and Bcl-2 facilitate Bcl-2 activation as a apoptosis inhibitor through dephosphorylation of phosphorylated form of Bcl-2 serving to apoptosis regulation.

Intramolecular masking of nuclear import signal on NF-AT4 by casein kinase I and MEKK1

T cell activation requires the import of NF-AT transcription factors to the nucleus, a process promoted by calcineurin-dependent dephosphorylation and inhibited by poorly understood protein kinases. Here, we report the identification of two protein kinases that oppose NF-AT4 nuclear import. Casein kinase Ialpha directly binds and phosphorylates NF-AT4, resulting in the inhibiton of NF-AT4 nuclear translocation. MEKK1 indirectly suppresses NF-AT4 nuclear import by stabilizing the interaction between NF-AT4 and CKIalpha. CKIalpha thus acts to establish an intramolecular masking of the nuclear location signal on NF-AT4, while MEKK1 augments this mechanism, and may further provide a link to signal transduction pathways regulating NF-AT4.

Spina bifida occulta in homozygous Patch mouse embryos

In normal embryos, mRNA encoding platelet-derived growth factor A (PDGF A) and the platelet-derived growth factor receptor alpha (PDGFR alpha) are found within and adjacent to the site of vertebral development, the sclerotome. These patterns of expression are consistent with PDGF action on the developing sclerotome and dermis. Homozygous Patch (Ph) mutant mouse embryos lack the receptor gene (Pdgfra) due to an extensive deletion at that locus. Consistent with the spatial pattern of Pdgfra expression, striking deformities are found in the spine and ribcage of Ph/Ph embryos. In particular, we show that late-gestation Ph/Ph embryos have occult spina bifida involving the entire spinal column. We have analyzed the progression of the axial defects in homozygous Patch embryos in detail. By late gestation it appears that the components of the vertebrae are present, yet the neural arches of the spine are misshapen. We propose that PDGF A is required for proper positioning of the neural arch condensation at all axial levels. Furthermore, since the neural tube appears to close normally, we suggest that spina bifida in the Ph homozygote is caused primarily by a somitic mesoderm abnormality rather than a neural tube defect.

Suppression of signalling through transcription factor NF-AT by interactions between calcineurin and Bcl-2

It is not known how the protein Bcl-2 inhibits cell death induced by calcium signalling and growth-factor withdrawal. Here we report that Bcl-2 forms a tight complex with calcineurin, resulting in the targeting of calcineurin to Bcl-2 sites on cytoplasmic membranes, and show that this interaction is dependent on the BH4 domain of Bcl-2. Calcineurin bound to Bcl-2 is an active phosphatase but is unable to promote the nuclear translocation of NF-AT, a transcription-factor required for induction of interleukin-2 expression, suggesting a mechanism by which Bcl-2 suppresses NF-AT activity. We also show that Bax, a pro-apoptotic member of the Bcl-2 family, interferes with interactions between calcineurin and Bcl-2. We propose that the ability of Bcl-2 to block NF-AT signalling is due to the sequestering of active calcineurin to the same domain of Bcl-2 which associates with Rad-1 (ref. 5), and that calcineurin may act in Bcl-2-regulated functions.

Role of kinases and the phosphatase calcineurin in the nuclear shuttling of transcription factor NF-AT4

A new facet of calcium signalling involves the nuclear import of the NF-AT transcription factors from their dormant position in the cytoplasm. The protein phosphatase calcineurin appears to play an essential role in activating NF-AT nuclear import, as the calcineurin inhibitors cyclosporin A and FK506 block dephosphorylation and nuclear import of NF-AT (refs 4-7). Here we show that calcium signalling induces an association between NF-AT4 and calcineurin, and that these molecules are transported, as a complex, to the nucleus, where calcineurin continues to dephosphorylate NF-AT4. We propose that a nuclear complex of NF-AT4 and calcineurin maintains calcium signalling by counteracting a vigorous nuclear NF-AT kinase.

Molecular cloning of the human glucose-regulated protein ERp57/GRP58, a thiol-dependent reductase. Identification of its secretory form and inducible expression by the oncogenic transformation

Recently it was shown that putative phospholipase C-alpha cDNA does not code for an isotype of the phospholipase C superfamily but for one of the glucose-regulated proteins (GRPs), ERp57/GRP58. We have isolated human ERp57/GRP58 cDNA from human placenta. Sequence analysis showed that ERp57/GRP58 has two Trp-Cys-Gly-His-Cys-Lys motifs completely conserved among the mammals. Bacterially expressed recombinant ERp57/GRP58 protein contained a thiol-dependent reductase activity which was completely abolished when Ser residues were substituted for Cys residues in both of the two motifs. Furthermore, we have identified a soluble form of ERp57/GRP58 by Western blotting and biosynthetic labeling. In v-onc transformants of normal rat kidney cells, the expression level of ERp57/GRP58 was elevated at the protein level. In NIH3T3 cells transformed with v-src, activated c-src (Y527F) or c-src, the expression level of ERp57/GRP58 was upregulated in proportion to their transforming abilities. These results indicate that a soluble form of ERp57/GRP58 exists and that this protein may control both extracellular and intracellular redox activities through its thiol-dependent reductase activity. Moreover, it is likely that ERp57/GRP58 is involved in the oncogenic transformation.

Calcineurin functions in Ca(2+)-activated cell death in mammalian cells

Calcineurin is a calcium-dependent protein phosphatase that functions in T cell activation. We present evidence that calcineurin functions more generally in calcium-triggered apoptosis in mammalian cells deprived of growth factors. Specifically, expression of epitope-tagged calcineurin A induces rapid cell death upon calcium signaling in the absence of growth factors. We show that this apoptosis does not require new protein synthesis and therefore calcineurin must operate through existing substrates. Co-expression of the Bcl-2 protooncogene efficiently blocks calcineurin-induced cell death. Significantly, we demonstrate that a calcium-independent calcineurin mutant induces apoptosis in the absence of calcium, and that this apoptotic response is a direct consequence of calcineurin's phosphatase activity. These data suggest that calcineurin plays an important role in mediating the upstream events in calcium-activated cell death.

Molecular cloning and characterization of a cDNA for bovine phospholipase C-alpha: proposal of redesignation of phospholipase C-alpha

We have isolated bovine phospholipase C (PLC)-alpha cDNA from bovine thymus. Sequence analysis showed that PLC-alpha is highly conserved among rat, mouse, and calf and that it has two Trp-Cys-Gly-His-Cys-Lys motifs completely conserved in the mammals. Southern blot analysis revealed that bovine PLC-alpha is derived from a single gene. When PLC-alpha cDNA was stably transfected in NIH3T3 cells, there was no increase in PLC activity. PLC-alpha is supposed to be a member not of PLC superfamily but of Trp-Cys-Gly-His-Cys-Lys motif-containing proteins consisting of protein disulfide isomerase, P5, ERp72, and thioredoxin. PLC-alpha should be redesignated ERp57 (ER-resided p57).

Phosphatidylinositol 3-kinase binds to alpha-actinin through the p85 subunit

Phosphatidylinositol 3-kinase (PI 3-kinase) has been shown to play an important role in the signal transduction of cell growth. It is also suggested that it is involved in cytoskeletal reorganization. We have found that alpha-actinin copurifies with PI 3-kinase from bovine thymus. The antibody against PI 3-kinase 85 kDa subunit (p85) also co-immunoprecipitates alpha-actinin from lysates of NIH/3T3 cells. In addition, anti-alpha-actinin antibody coprecipitates PI 3-kinase activity. This coprecipitation was observed even after depolymerization of actin fibres, suggesting that PI 3-kinase binds directly to alpha-actinin. As alpha-actinin is a phosphatidylinositol 4,5-bisphosphate (PI4,5P2)-binding protein, binding experiments using various constructs of truncated p85 were carried out in the presence or absence of PI4,5P2. In the absence of PI4,5P2, chicken gizzard alpha-actinin binds only to the whole p85 construct, but it binds to the proline-rich region of p85 fragments in the presence of PI4,5P2. This binding is enhanced with increased concentrations of Pi4,5P2 up to 10 microM, whereas phosphatidylinositol and phosphatidylinositol 4-phosphate were not good activators of alpha-actinin binding. These results suggest that PI 3-kinase binds to alpha-actinin and regulates cytoskeletal reorganization.

Ash/Grb-2, a SH2/SH3-containing protein, couples to signaling for mitogenesis and cytoskeletal reorganization by EGF and PDGF

The Src homology (SH) region 2 binds to phosphorylated tyrosine residues and SH3 domains may interact with cytoskeletal molecules and GTPase-activating proteins for Rho/Rac proteins (the small GTP-binding proteins related to Ras). The recently cloned Ash/Grb-2 protein, a 25-28 kDa molecule composed entirely of SH2 and SH3 domains, is a mammalian homolog of the Caenorhabditis elegans Sem-5 protein, which communicates between a receptor protein tyrosine kinase and a Ras protein. In the present study the function of Ash/Grb-2 was investigated by microinjecting cells with an anti-Ash antibody. The antibody abolished both S phase entry and the reorganization of actin assembly to ruffle formation upon stimulation with epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). On the other hand, anti-Ash antibody had no effect on S phase entry or actin stress fiber formation induced by either serum or lysophosphatidic acid. Since the induction of DNA synthesis, ruffle induction and stress fiber formation involve a function of Ras, Rac activation and Rho activation respectively, the findings strongly suggest that Ash plays a critical role in the signaling of both pathways downstream from growth factor receptors to Ras and Rac. Consistent with this, Ash co-precipitated with EGF receptor from EGF-stimulated cells. Other proteins of approximately 21, 29, 135 and 160 kDa were also detected in the anti-Ash antibody immunoprecipitates, suggesting a role of Ash as a linker molecule in signal transduction downstream of growth factor receptors.

Phospholipase C-gamma 1 associates with viral and cellular src kinases

A tyrosine kinase inhibitor, genistein, caused the subcellular translocation of phosphoinositide-specific phospholipase C (PLC) activity from membrane fractions to cytosolic fractions in rat 3Y1 fibroblasts and their transformants by Rous sarcoma virus, SR-3Y1. The ratio of PLC activities associated with the membrane fractions to those of the homogenate fractions was greater in SR-3Y1 (32.6%) than in 3Y1 (20.8%) whereas membrane-associated PLC activities were strikingly reduced to the same levels in both cells by treatment with genistein. Moreover, it was found by immunoblotting analyses of membrane fractions that the amounts of PLC-gamma 1 isozyme were reduced to 20.4% of initial level in SR-3Y1 and to 30.2% of that in 3Y1 cells. While the levels of PLC-delta, another detectable PLC isozyme, were not altered by genistein suggesting that tyrosine kinase plays an important role in the association of PLC-gamma 1 with membranes. PLC-gamma 1 molecules were detected in anti-p60arc antibody immunoprecipitates of both 3Y1 and SR-3Y1 cells. The amounts of PLC-gamma 1 co-immunoprecipitating with src kinases were higher in SR-3Y1 than 3Y1 cells and were reduced in both cell types by treatment with genistein. In addition, it was confirmed that PLC-gamma 1 purified from rat liver was phosphorylated at a tyrosine residue and associated with viral src kinase and that src kinases associated with the recombinant SH2 region of PLC-gamma 1, expressed in Escherichia coli, depending upon phosphorylation of tyrosine residues. These findings suggest that both viral and cellular src kinases associate with PLC-gamma 1 and may mediate cellular signaling in normal and transformant cell growth.

The alpha-type 85-kDa subunit of phosphatidylinositol 3-kinase is phosphorylated at tyrosines 368, 580, and 607 by the insulin receptor

We have shown previously that insulin stimulated the tyrosine phosphorylation of the alpha-type 85-kDa subunit (p85) of phosphatidylinositol (PI) 3-kinase in vitro and in vivo. In the present work, we identified the major tyrosine phosphorylation sites of the alpha-type p85 by the insulin receptor. [32P]Phosphopeptides obtained from lysylendopeptidase digestion of phosphorylated alpha-type p85 in intact cells after insulin treatment were analyzed using reverse-phase high performance liquid chromatography and thin layer electrophoresis. The tyrosine phosphorylation sites of alpha-type p85 in vivo were assigned to three major phosphopeptides, designated p1, p2, and p3. Highly purified insulin receptor also phosphorylated the purified p85 of PI 3-kinase from the bovine thymus at p1. The purified glutathione S-transferase (GST)-p85 (alpha-type) fusion protein and its truncated proteins from Escherichia coli were also phosphorylated by the purified insulin receptor at p1, p2, and p3 in vitro. Analysis of [32P]phosphopeptide of the truncated GST-p85 (alpha-type) fusion proteins and radiosequence analysis revealed that the p1, p2, and p3 phosphopeptides were phosphorylated at tyrosines 607, 580, and 368, respectively. In addition, phenylalanine substitutions at tyrosine 607 and 580 reduced the p1 and p2 phosphopeptides in vivo, respectively. We conclude that the alpha-type p85 of PI 3-kinase was phosphorylated at tyrosines 368, 580, and 607 by the insulin receptor in vivo.

Different properties of monomer and heterodimer forms of phosphatidylinositol 3-kinases

Phosphatidylinositol (PI) 3-kinase plays an important role in the signalling of cell growth. We previously purified two types of PI 3-kinase from bovine thymus, a monomer from (PI 3-kinase I) and a heterodimer form (PI 3-kinase II) [Shibasaki, Homma and Takenawa (1991) J. Biol. Chem. 266, 8108-8114]. Here we examine the properties of these purified PI 3-kinases. Both PI 3-kinases were inhibited strongly by quercetin and isoquercetin. The inhibition of PI 3-kinase I and PI 3-kinase II by quercetin appears to be non-competitive, with apparent Ki values of 4 microM and 2.5 microM respectively. PI 3-kinase II, but not PI 3-kinase I, co-immunoprecipitates with pp60v-src and polyoma middle T (mT)/pp60c-src, even under conditions where the PI 3-kinases are not phosphorylated, suggesting that non-phosphorylated PI 3-kinase recognizes autophosphorylated pp60v-src. PI 3-kinase II is phosphorylated by pp60v-src and binds to it. Anti-p85 (85 kDa subunit of PI 3-kinase II) antibody precipitates not only PI 3-kinase II but also co-immunoprecipitates pp60v-src in src-transformed cells, suggesting that PI 3-kinase II binds to pp60v-src in vivo. These data suggest that the two PI 3-kinases may be regulated independently.

Insulin treatment stimulates the tyrosine phosphorylation of the alpha-type 85-kDa subunit of phosphatidylinositol 3-kinase in vivo

After adding insulin to cells overexpressing the insulin receptor, the activity of phosphatidylinositol (PI) 3-kinase in the anti-phosphotyrosine immunoprecipitates was rapidly and greatly increased. This enzyme may therefore be a substrate for the insulin receptor tyrosine kinase and may be one of the mediators of insulin signal transduction. However, it is unclear whether or not activated tyrosine kinase of the insulin receptor directly phosphorylates PI 3-kinase at tyrosine residue(s) and whether insulin stimulates the specific activity of PI 3-kinase. We reported previously that the 85-kDa subunit of purified PI 3-kinase was phosphorylated at tyrosine residue(s) by the insulin receptor in vitro. To examine the tyrosine phosphorylation of PI 3-kinase and change of its activity by insulin treatment in vivo, we used a specific antibody to the 85-kDa subunit of PI 3-kinase. The activity of PI 3-kinase in immunoprecipitates with the antibody against the p85 subunit of PI 3-kinase was increased about 3-fold by insulin treatment of cells overexpressing insulin receptors. Insulin treatment also stimulated the tyrosine, serine, and threonine phosphorylation of the alpha-type 85-kDa subunit of PI 3-kinase in vivo. Phosphatase treatment of the immunoprecipitates abolished the increase in PI 3-kinase activity. The phosphorylation(s) of the kinase itself, tyrosine phosphorylation(s) of associated protein(s), or the complex formation of the phosphorylated PI 3-kinase with associated proteins may increase the activity of PI 3-kinase.

Molecular cloning of bovine actin-like protein, actin2

Actins are major cytoskeletal components and highly conserved in evolution. In mammals, there are six actin isoforms, a pair of which shows at least 93% identity in the amino acid sequence. We have cloned cDNA for a bovine protein that is distantly related to members of the mammalian actin isotypes. The predicted amino acid sequence (418 residues long, calculated molecular mass 47369) shows that this protein, which we have named actin2, exhibits 36% identity to mammalian actins and 60% identity to the yeast actin-like protein, act2. We have concluded that actin2 defines a new class of mammalian actin-like proteins. It was also revealed that actin2 messenger RNA is expressed in a broad range of tissues.

Enhancement of phospholipase C delta 1 activity in the aortas of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR), which develop hypertension approximately 10 weeks after birth, are considered to provide a good animal model for human essential hypertension. We report here that the abnormal activation of phospholipase C delta 1 (PLC-delta 1) may be one of the main causes of hypertension. Levels of the second messengers inositol 1,4,5-trisphosphate and diacylglycerol are found to be higher in the aortas of 12-week-old SHR than in age-matched normotensive Wistar-Kyoto rats (WKY), although the levels in the aortas of 7-week-old SHR, which have normal blood pressure, are the same as in WKY. Moreover, PLC activity is also higher in the aortas of 12-week-old SHR. Judging from Western blot analysis and immunoabsorption of PLCs, this activation is found to be due to that of PLC-delta 1. PLC-delta 1 from rat aorta is expressed significantly from 7 to 12 weeks, which correlates with the development of hypertension in SHR. The activity of PLC-delta 1 in the aortas of 12-week-old SHR is more markedly activated at low Ca2+ concentration than that of age-matched WKY. These results suggest that the abnormal enhancement of PLC-delta 1 activity is responsible for accumulation of inositol 1,4,5-trisphosphate and diacylglycerol, leading to continuous hypertonicity of vascular smooth muscle in SHR. The activity of PLC-delta 1 in the aortas of 12-week-old SHR is significantly higher at low Ca2+ concentration than that of normotensive WKY.

Phosphorylation in vitro of the 85 kDa subunit of phosphatidylinositol 3-kinase and its possible activation by insulin receptor tyrosine kinase

Insulin causes a dramatic and rapid increase in phosphatidylinositol 3-kinase activity in the anti-phosphotyrosine immunoprecipitates of cells overexpressing the human insulin receptor. This enzyme may therefore be a mediator of insulin signal transduction [Endemann, Yonezawa & Roth (1990) J. Biol. Chem. 265, 396-400; Ruderman, Kapeller, White & Cantley (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 1411-1415]. At least two questions remain to be elucidated. Firstly, does the insulin receptor tyrosine kinase phosphorylate phosphatidylinositol 3-kinase directly, or does it phosphorylate a protein associated with the 3-kinase? Second, if the enzyme is a direct substrate for the insulin receptor tyrosine kinase, does tyrosine phosphorylation of phosphatidylinositol 3-kinase by the kinase alter the specific enzyme activity, or does the amount of the tyrosine-phosphorylated form of the phosphatidylinositol 3-kinase increase, with no change in the specific activity? We report here evidence that the 85 kDa subunit of highly purified phosphatidylinositol 3-kinase is phosphorylated on the tyrosine residue by the activated normal insulin receptor in vitro, but not by a mutant insulin receptor which lacks tyrosine kinase activity. We found that an increase in enzyme activity was detected in response to insulin not only in the anti-phosphotyrosine immunoprecipitates of the cytosol, but also in the cytosolic fraction before immunoprecipitation. In addition, we partially separated the tyrosine-phosphorylated form from the unphosphorylated form of the enzyme, by using a f.p.l.c. Mono Q column. The insulin-stimulated phosphatidylinositol 3-kinase activity was mainly detected in the fraction containing almost all of the tyrosine-phosphorylated form. This result suggests that tyrosine phosphorylation of phosphatidylinositol 3-kinase by the insulin receptor kinase may increase the specific activity of the former enzyme in vivo.

Two types of phosphatidylinositol 3-kinase from bovine thymus. Monomer and heterodimer form

Two types of phosphatidylinositol (PI) 3-kinase (PI3K) have been purified 6250-fold (PI3KI) and 1250-fold (PI3KII) from the cytosol fraction of bovine thymus. Purified PI3KI and PI3KII were found to have apparent molecular masses of 110 and 190 kDa, respectively, by gel filtration. On the other hand, on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, while the molecular mass of PI3KI was again estimated as 110 kDa, PI3KII showed two bands with apparent molecular masses of 110 and 85 kDa, suggesting a heterodimer form. Peptide mapping analysis demonstrated that the 110-kDa protein in PI3KII was the same protein as PI3KI. The specific activity of PI3KI was calculated as 250 nmol/min/mg of protein, while that of PI3KII was 50 nmol/min/mg of protein. The product of PI phosphorylation by PI3KI and PI3KII were confirmed as phosphatidylinositol 3-phosphate by PartiSphere Sax column chromatography. The results show that there are two types of PI 3-kinase in bovine thymus. One exists as a monomer and the other as a heterodimer form. Furthermore, the biochemical properties of these two PI 3-kinases are markedly different. These two types of PI 3-kinase may be regulated differently under physiological conditions.

Isolation and characterization of a gamma-type phosphoinositide-specific phospholipase C (PLC-gamma 2)

A novel bovine spleen phosphoinositide-specific phospholipase C (PLC) has been identified with respect to immunoreactivity with four independent antibodies against each of the PLC isoenzymes, and purified to near homogeneity by sequential column chromatography. Spleen contains three of the isoenzymes: two different gamma-types [gamma 1 and gamma 2, originally named as PLC-gamma [Rhee, Suh, Ryu & Lee (1989) Science 244, 546-550] and PLC-IV [Emori, Homma, Sorimachi, Kawasaki, Nakanishi, Suzuki & Takenawa (1989) J. Biol. Chem. 264, 21885-21890] respectively] and delta-type of the enzyme, but PLC-gamma 1 is separated from the PLC-gamma 2 pool by the first DEAE-cellulose column chromatography. Subsequently, PLC-delta is dissociated on the third heparin-Sepharose column chromatography. The purified enzyme has a molecular mass of 145 kDa on SDS/polyacrylamide-gel electrophoresis and a specific activity of 12.8 mumol/min per mg with phosphatidylinositol 4,5-bisphosphate as substrate. This enzyme activity is dependent on Ca2+ for hydrolysis of all these phosphoinositides. None of the other phospholipids examined could be its substrate at any concentration of Ca2+. The optimal pH of the enzyme is slightly acidic (pH 5.0-6.5).