Transforming growth factor-beta-activated kinase 1 is essential for differentiation and the prevention of apoptosis in epidermis

Transforming growth factor-beta-activated kinase 1 (TAK1) is a member of the mitogen-activated protein (MAP) kinase family and is an upstream signaling molecule of nuclear factor-kappaB (NF-kappaB). Given that NF-kappaB regulates keratinocyte differentiation and apoptosis, TAK1 may be essential for epidermal functions. To test this, we generated keratinocyte-specific TAK1-deficient mice from Map3k7(flox/flox) mice and K5-Cre mice. The keratinocyte-specific TAK1-deficient mice were macroscopically indistinguishable from their littermates until postnatal day 2 or 3, when the skin started to roughen and wrinkle. This phenotype progressed, and the mice died by postnatal day 7. Histological analysis showed thickening of the epidermis with foci of keratinocyte apoptosis and intra-epidermal micro-abscesses. Immunohistochemical analysis showed that the suprabasal keratinocytes of the TAK1-deficient epidermis expressed keratin 5 and keratin 14, which are normally confined to the basal layer. The expression of keratin 1, keratin 10, and loricrin, which are markers for the suprabasal and late phase differentiation of the epidermis, was absent from the TAK1-deficient epidermis. Furthermore, the TAK1-deficient epidermis expressed keratin 16 and had an increased number of Ki67-positive cells. These data indicate that TAK1 deficiency in keratinocytes results in abnormal differentiation, increased proliferation, and apoptosis in the epidermis. However, the keratinocytes from the TAK1-deficient epidermis induced keratin 1 in suspension culture, indicating that the TAK1-deficient keratinocytes retain the ability to differentiate. Moreover, the removal of TAK1 from cultured keratinocytes of Map3k7(flox/flox) mice resulted in apoptosis, indicating that TAK1 is essential for preventing apoptosis. In conclusion, TAK1 is essential in the regulation of keratinocyte growth, differentiation, and apoptosis.

Bone morphogenetic protein-2 modulates Wnt and frizzled expression and enhances the canonical pathway of Wnt signaling in normal keratinocytes

BACKGROUND

Bone morphogenetic protein-2 (BMP-2) and Wnt are involved in the normal development and tumorigenesis of several organs, and in the development of skin and skin appendages as a morphogen. However, the crosstalk between BMP-2 and the Wnt/beta-catenin signaling pathway is not clear.

OBJECTIVE

We examined BMP-2-dependent expression of Wnt and its receptor frizzled in normal human keratinocytes.

METHODS

The mRNA expression of the Wnt and frizzled families was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) or ribonuclease protection assay. beta-Catenin expression was measured using RT-PCR and Western blotting. T-cell factor/lymphoid enhancing factor activity was analyzed using the luciferase reporter assay.

RESULTS

We detected the expression of Wnt-2b/13, -4, -5a, -5b, -7a, -7b, and -10a, frizzled-1, -4, -5, -6, -8, -9, and -10, MFRP, and SFRP-1/SARP-2 in keratinocytes. BMP-2 increased Wnt-2b/13, -5b, and -7b, and frizzled-6, -8, and -10. Conversely, BMP-2 suppressed Wnt-10a and SFRP-1/SARP-2. Although Wnt-4 expression was not affected by BMP-2 in confluent conditioned keratinocytes, BMP-2 suppressed cell density-dependent Wnt-4 induction. The transcriptional activity of TCF/LEF, which is a target of the canonical Wnt pathway, was upregulated by BMP-2 in both time- and dose-dependent manners. However, BMP-2-dependent differentiation of keratinocytes suppressed TCF/LEF transcriptional activity.

CONCLUSION

These results suggest that BMP-2 modulates the expression of molecules involved in Wnt signaling, and activates the canonical Wnt pathway in normal human keratinocytes. Moreover, Wnt signaling may be influenced by the fate of keratinocytes, such as proliferation, migration, and differentiation.

SOCS1-negative feedback of STAT1 activation is a key pathway in the dsRNA-induced innate immune response of human keratinocytes

Toll-like receptor (TLR)3 is a receptor for virus-associated double-stranded RNA, and triggers antiviral immune responses during viral infection. Epidermal keratinocytes express TLR3 and provide an innate immune defense against viral infection. Since the intracellular regulatory mechanism is unknown, we hypothesized that the signal transducers and activators of transcription (STAT)-suppressors of cytokine signaling (SOCS) system regulates the innate immune response of keratinocytes. Treatment with polyinosinic-polycytidylic acid (poly(I:C)) resulted in the rapid translocation of IFN regulatory factor (IRF)-3 into the nucleus, followed by phosphorylation of STAT1 and STAT3. The activation of STATs by poly(I:C) probably occurs in an indirect fashion, through poly(I:C)-induced IFN. We infected cells with the dominant-negative forms of STAT1 (STAT1F), STAT3 (STAT3F), and SOCS1 using adenovirus vectors. Infection with STAT1F suppressed the induction of macrophage inflammatory protein (MIP)-1alpha by poly(I:C), whereas STAT3F had a minimal effect, which indicates that STAT1 mediates MIP-1alpha induction. SOCS1, which is a negative feedback regulator of STAT1 signaling, was induced by treatment with poly(I:C). SOCS1 infection inhibited the phosphorylation of STAT1 and significantly reduced poly(I:C)-induced MIP-1alpha production. Furthermore, STAT1-SOCS1 regulated poly(I:C)-induced TLR3 and IRF-7 expression. However, SOCS1 did not affect NF-kappaB signaling. Thus, the STAT1-SOCS1 pathway regulates the innate immune response via TLR3 signaling in epidermal keratinocytes.

A novel function of angiotensin II in skin wound healing. Induction of fibroblast and keratinocyte migration by angiotensin II via heparin-binding epidermal growth factor (EGF)-like growth factor-mediated EGF receptor transactivation

The role of angiotensin II (Ang II) in the control of systemic blood pressure and volume homeostasis is well known and has been extensively studied. Recently, Ang II was suggested to also have a function in skin wound healing. In the present study, the in vivo function of Ang II in skin wound healing was investigated using Ang II type 1 receptor (AT1R) knock-out mice. Wound healing in these mice was found to be markedly delayed. Keratinocytes and fibroblasts play important roles in wound healing, and thus the effect of Ang II on the migration of these cells was examined. Ang II stimulated keratinocyte and fibroblast migration in a dose-dependent manner. It has been reported that G protein-coupled receptor (GPCR) activation induces epidermal growth factor (EGF) receptor (EGFR) transactivation through the shedding of heparin-binding EGF-like growth factor (HB-EGF). As AT1R is a GPCR, it was hypothesized that Ang II-induced keratinocyte and fibroblast migration is mediated by EGFR transactivation. Ang II induced EGFR phosphorylation, which was inhibited by an AT1R antagonist, HB-EGF neutralizing antibody, and an HB-EGF antagonist in both keratinocytes and in fibroblasts. Moreover, Ang II-induced migration of keratinocytes and fibroblasts was also prevented by these inhibitors. Taken together, these findings clearly demonstrate, for the first time, that Ang II plays an important role in skin wound healing and that it functions by accelerating keratinocyte and fibroblast migration in a process mediated by HB-EGF shedding.

Microbubble-enhanced ultrasound for gene transfer into living skin equivalents

BACKGROUND

Gene transfer to skin is an attractive therapeutic approach because of the accessibility of the skin and the high rate of cure for many cutaneous diseases. However, safety concerns over viral vectors and the low efficiency of most non-viral gene transfer techniques have encumbered their clinical application for gene transfer. By contrast, efficient gene transfers into various cell types using microbubble-enhanced ultrasound has been reported.

OBJECTIVES

The purpose of this study was to investigate whether ultrasound with microbubble enhancement allowed effective transfer of foreign genes into living skin equivalents (LSEs).

METHODS

Microbubbles and plasmid DNA encoding green fluorescent protein (GFP) were added to the dermal-epidermal junctions of LSEs, which were then exposed to ultrasound. The LSEs were harvested at different time points to investigate transgene expression using confocal laser microscopy. Transfected LSEs were also transplanted onto nude mice, and the in vivo transgene expression was observed.

RESULTS

From days 2 to 7 after transfection, most GFP-positive cells continued to migrate upward from the basal layer, while other GFP-positive cells lagged behind or remained in the basal layer on days 5 and 7. Transfection resulted in 20-30% GFP-positive cells. Multiple transfections further increased the percentage of transfected cells and resulted in multi-layer transgene expression. Grafts from the transfected LSEs survived on nude mice and continued to express GFP up to 2 weeks post-transplantation.

CONCLUSION

Gene transfer into LSE using ultrasound with microbubble enhancement is an effective alternative to viral and non-viral methods.

dsRNA-mediated innate immunity of epidermal keratinocytes

MIP-1alpha, a CC chemokine, recruits monocytes, natural killer cells, lymphocytes, and neutrophils, and plays a critical role in viral infection. Since, the lesional epidermis of herpes zoster expressed MIP-1alpha, we hypothesized that keratinocytes produce MIP-1alpha in response to virus-associated dsRNA via TLR3. To investigate this, we examined cultured human keratinocytes for MIP-1alpha production induced by poly(I:C), a TLR3 ligand. Poly(I:C) treatment induced MIP-1alpha production, interestingly, poly(I:C)-induced IFN-alpha and -beta production preceded MIP-1alpha production. A neutralizing antibody for IFN-beta significantly inhibited the poly(I:C)-induced MIP-1alpha production indicating that MIP-1alpha production is via IFN-beta. IFN-alpha priming enhanced TLR3 expression and MIP-1alpha production in poly(I:C)-treated keratinocytes. This suggests that IFN-alpha enhanced the TLR3 expression and reinforced the response of keratinocytes to poly(I:C), which resulted in an increase in MIP-1alpha production. In conclusion, normal human keratinocytes produce MIP-1alpha in response to dsRNA via TLR3, and this production is regulated by IFN-alpha/beta.

Induction of Keratinocyte Migration via Transactivation of the Epidermal Growth Factor Receptor by the Antimicrobial Peptide LL-37

The closure of skin wounds is essential for resistance against microbial pathogens, and keratinocyte migration is an important step in skin wound healing. Cathelicidin hCAP18/LL-37 is an innate antimicrobial peptide that is expressed in the skin and acts to eliminate microbial pathogens. Because hCAP18/LL-37 is up-regulated at skin wound sites, we hypothesized that LL-37 induces keratinocyte migration. In this study, we found that 1 microg/ml LL-37 induced the maximum level of keratinocyte migration in the Boyden chamber assay. In addition, LL-37 phosphorylated the epidermal growth factor receptor (EGFR) after 10 min, which suggests that LL-37-induced keratinocyte migration occurs via EGFR transactivation. To test this assumption, we used inhibitors that block the sequential steps of EGFR transactivation, such as OSU8-1, CRM197, anti-EGFR no. 225 Ab, and AG1478. All of these inhibitors completely blocked LL-37-induced keratinocyte migration, which indicates that migration occurs via HB-EGF-mediated EGFR transactivation. Furthermore, CRM197, anti-EGFR no. 225, and AG1478 blocked the LL-37-induced phosphorylation of STAT3, and transfection with a dominant-negative mutant of STAT3 abolished LL-37-induced keratinocyte migration, indicating the involvement of the STAT3 pathway downstream of EGFR transactivation. Finally, we tested whether the suppressor of cytokine signaling (SOCS)/cytokine-inducible Src homology 2-containing protein (CIS) family of negative regulators of STAT3 regulates LL-37-induced keratinocyte migration. Transfection with SOCS1/Jak2 binding protein or SOCS3/CIS3 almost completely abolished LL-37-induced keratinocyte migration. In conclusion, LL-37 induces keratinocyte migration via heparin-binding-EGF-mediated transactivation of EGFR, and SOCS1/Jak 2 binding and SOCS3/CIS3 negatively regulate this migration. The results of this study suggest that LL-37 closes skin wounds by the induction of keratinocyte migration.

New mechanisms of skin innate immunity: ASK1-mediated keratinocyte differentiation regulates the expression of β-defensins, LL37, and TLR2

Epidermal keratinocytes differentiate and form a multilayered epidermis, which is the primary barrier between the body and the outer environment. As the epidermis is constantly exposed to a variety of microbial pathogens, its function of resisting microbial pathogens is vital. This characteristic feature is formed during differentiation. Immunohistochemical analysis revealed that the upper epidermis of normal human skin expresses beta-defensins 1-3 and LL37. We hypothesized that epidermal keratinocytes develop an innate immune barrier based on human beta-defensins (hBD) and LL37 during differentiation. To prove this, we introduced an active form of the apoptosis signal-regulating kinase-1 (ASK1), an intracellular regulator of keratinocyte differentiation, into cultured normal human keratinocytes. Transfection of this active form, ASK1-DeltaN, significantly enhanced the expression of hBD1-3 and LL37. In addition, a p38 inhibitor abolished this induction, indicating that the ASK1-p38 cascade regulates the expression of hBD1-3 and LL37. Furthermore, the ASK1-p38 pathway also regulated the expression of Toll-like receptor (TLR)2 in keratinocytes. Contact between S. aureus and keratinocytes resulted in the phosphorylation of p38 and induced the expression of hBD2 and hBD3. Moreover, the p38 inhibitor reduced this induction. In conclusion, the ASK1-p38 cascade regulates the innate immunity of the skin by forming an immune barrier consisting of hBD, LL37, and TLR2 during epidermal differentiation.

GRP94 reduces cell death in SH-SY5Y cells perturbated calcium homeostasis

The endoplasmic reticulum (ER) resident-94 kDa glucose-regulated protein (GRP94), plays a pivotal role in cell death due to ER stress. In our study expression of GRP94 was increased in human neuroblastoma SH-SY5Y cells due to exposure to calcium ionophore A23187. A23187-mediated cell death was associated with activation of the major cysteine proteases, caspase-3 and calpain. Pretreatment with adenovirus-mediated antisense GRP94 (AdGRP94AS) reduced viability of SH-SY5Y cells subjected to A23187 treatment compared with wild type cells or cells with adenovirus-mediated overexpression of GRP94 (AdGRP94S). These results indicated that suppression of GRP94 is associated with accelerated cell death. Moreover, expression of GRP94 suppressed A23187-induced cell death and stabilized calcium homeostasis.

SOCS3/CIS3 negative regulation of STAT3 in HGF-induced keratinocyte migration

Hepatocyte growth factor (HGF) is a potent mitogen for mature hepatocytes. Because HGF has strong effects on the motility of keratinocytes and is produced by fibroblasts, HGF is thought to regulate keratinocyte migration during wound healing. However, the intracellular signaling mechanism of HGF-induced keratinocyte migration is poorly understood. In this report, we clarify the roles of STAT3 and SOCS/CIS family in HGF-induced keratinocyte migration. HGF activated STAT3 and strongly induced keratinocyte migration. Transfection with the dominant-negative mutant of STAT3 almost completely abolished HGF-induced keratinocyte migration and STAT3 phosphorylation. Next, we studied the mechanisms that regulate STAT3 phosphorylation. HGF enhanced the expression of SOCS3/CIS3 by sixfold within 1h, but had minimum effect on SOCS1/JAB expression. Transfection with SOCS3/CIS3 almost completely abolished HGF-induced STAT3 phosphorylation and keratinocyte migration, indicating that SOCS3/CIS3 acts as a negative regulator of HGF-induced keratinocyte migration. In conclusion, SOCS3/CIS3 regulates HGF-induced keratinocyte migration by inhibiting STAT3 phosphorylation.

Transcriptional downregulation of DC-SIGN in human herpesvirus 6-infected dendritic cells

DC-SIGN expressed on dendritic cells (DCs) efficiently binds and transmits various pathogens, including human immunodeficiency virus, to lymphoid tissues and permissive cells. Consequently, alteration of DC-SIGN expression may affect susceptibility and resistance to pathogens. The present study shows that infection with human herpesvirus 6 (HHV-6) induces downregulation of DC-SIGN expression on immature DCs. Expression levels of DC-SIGN mRNA and intracellular protein appeared to decrease following infection with HHV-6, indicating that downregulation of surface DC-SIGN occurs at the transcriptional level. Downregulation of DC-SIGN was not induced by inoculation of UV-inactivated HHV-6 or culture supernatant of HHV-6-infected DCs, indicating that replication of HHV-6 in DCs is required for downregulation of DC-SIGN. The present study demonstrates for the first time that expression of DC-SIGN is altered at the transcriptional level by virus infection.

TGF-β is not involved in early phase growth inhibition of keratinocytes by 1α,25(OH)2vitamin D3

BACKGROUND

It has been proposed that transforming growth factor-beta (TGF-beta) is involved in the growth inhibition of normal human epidermal keratinocytes (NHEK) by 1alpha,25-dihydoxyvitamin D(3) (1alpha,25(OH)(2)D(3)), although this is still controversial because of the difficulty in blocking TGF-beta activity completely.

OBJECTIVE

To determine whether TGF-beta is involved in early phase growth inhibition by 1alpha,25(OH)(2)D(3).

METHODS

TGF-beta mRNA was detected by ribonuclease protection assay (RPA), and biological active TGF-beta was determined by a luciferase reporter assay. To block intrinsic TGF-beta activity completely, we constructed an adenovirus vector expressing a truncated TGF-beta type II receptor with a dominant negative effect (AdexTbetaTR) that blocks TGF-beta signal transduction.

RESULTS

1alpha,25(OH)(2)D(3) slightly upregulated TGF-beta1 and TGF-beta2 after 24 h according to an RPA and a luciferase reporter assay, however growth inhibition by 1alpha,25(OH)(2)D(3) occurred at 6 h. The addition of 10(-6) M of 1alpha,25(OH)(2)D(3) to NHEK infected with AdexTbetaTR or AdexLacZ (control vector) reduced DNA synthesis to 59.3 and 62.2% at 6 h, respectively. There was no significant difference in cell number after a 3-day incubation with AdexTbetaTR or AdexLacZ-infected cells treated with 1alpha,25(OH)(2)D(3).

CONCLUSION

Since 1alpha,25(OH)(2)D(3) rapidly inhibits NHEK growth regardless of the prevention of TGF-beta signal transduction, TGF-beta is not involved in early phase growth inhibition by 1alpha,25(OH)(2)D(3).

Keratinocyte G2/M growth arrest by 1,25-dihydroxyvitamin D3 is caused by Cdc2 phosphorylation through Wee1 and Myt1 regulation

1,25-dihydroxyvitamin D3 (1,25[OH]2VD3) has an antiproliferative effect on keratinocyte growth, and its derivatives are used for the treatment of psoriasis. It was reported previously that 1,25[OH]2VD3 induced cell cycle arrest not only at the G0/G1 phase but also at the G2/M phase. However, the mechanism of 1,25[OH]2VD3-induced G2/M phase arrest in keratinocytes has not been fully understood. The addition of 10(-8) to 10(-6) M 1,25[OH]2VD3 to cultured normal human keratinocytes enhanced the expression of Myt1 mRNA preceding Wee1 mRNA; 10(-6) M 1,25[OH]2VD3 unregulated Myt1 mRNA from 6 h to 24 h and Wee1 mRNA from 12 to 48 h. Interestingly, the levels of phosphorylated Cdc2 were increased between 6 h and 48 h after 1,25[OH]2VD3 treatment, although the expression levels of Cdc2 mRNA and its protein production were reduced. 1,25[OH]2VD3 also decreased the expression of cyclin B1, which forms a complex with Cdc2. These data indicated that the increase of Myt1 and Wee1 induced the phosphorylation of Cdc2 leading to G2/M arrest. In conclusion, the induction of Cdc2 phosphorylation due to the increase of Wee1 and Myt1 as well as the reduction of Cdc2 and cyclin B1 are involved in 1,25[OH]2VD3-induced G2/M arrest of keratinocytes.

Cytoplasmic p21Cip1/WAF1 enhances axonal regeneration and functional recovery after spinal cord injury in rats

p21(Cip1/WAF1), known as a cell-cycle inhibitory protein, facilitates neurite outgrowth from neurons when present in the cytoplasm. The molecular mechanism of this action is that p21(Cip1/WAF1) forms a complex with Rho-kinase and inhibits its activity. As myelin-derived inhibitors of axonal outgrowth act on neurons by activating Rho, that is responsible for the lack of spontaneous regeneration of the injured central nervous system (CNS), Rho-kinase may be a good molecular target against injuries in the CNS. In this study, we delivered TAT-fusion protein of cytoplasmic p21(Cip1/WAF1) locally after dorsal hemisection of the thoracic spinal cord in rats. The treatment significantly stimulated axonal regeneration and recovery of hindlimb function, and inhibited the cavity formation in the spinal cord after the injury. Cytoplasmic p21(Cip1/WAF1) may provide a potential therapeutic agent that produces functional regeneration following CNS injuries.

Human herpes virus 6 encephalitis in allopurinol-induced hypersensitivity syndrome

Hypersensitivity syndrome is one of the most severe forms of drug eruption, and is characterized by a severe, potentially lethal, multiorgan involvement. Recently, reactivation of human herpesvirus 6 (HHV-6) has been suggested to be involved in this syndrome, although the exact role of HHV-6 remains elusive. In addition to exanthem subitum, neurological illnesses, such as infantile febrile illness without rash and encephalitis in immunocompromised patients have been attributed to HHV-6. A 51-year-old man developed a generalized erythematous eruption during treatment with allopurinol. Prednisolone improved his condition, but after the dose of prednisolone was reduced neurological abnormalities such as mental deterioration and positive meningeal signs developed. HHV-6 DNA in his blood by PCR analysis was positive. Furthermore, we detected HHV-6 DNA in the cerebrospinal fluid. The titers of anti-HHV-6-IgG increased during the course. His neurological symptoms gradually improved and no neurological sequelae were noted. Neurological abnormalities associated with hypersensitivity syndrome are very rare. However, the detection of HHV-6 DNA in the cerebrospinal fluid strongly indicates an involvement of reactivated HHV-6 in encephalitis.

Human herpesvirus 6 and drug allergy

PURPOSE OF REVIEW

The similarity between viral skin eruption and drug-induced rash has inspired many researchers to seek an association between viral infection and drug allergy. Hypersensitivity syndrome (referred to in this review as drug-induced hypersensitivity syndrome) is one of the severe adverse reactions to drugs and was reported more than 50 years ago. However, the mechanism of drug-induced hypersensitivity syndrome has not been fully elucidated. Several groups reported the association between human herpesvirus 6 reactivation and drug-induced hypersensitivity syndrome 5 years ago. Recently, similar case reports have accumulated. Recent findings concerning human herpesvirus 6 and drug-induced hypersensitivity syndrome are reviewed here.

RECENT FINDINGS

In drug-induced hypersensitivity syndrome, examination of serial serum samples revealed a marked and sudden increase in anti-human herpesvirus 6 IgG titers in the third or fourth week after the onset of clinical manifestations. In addition, active human herpesvirus 6 replication precedes the rise in antibody titers. Furthermore, the recurrence or worsening of signs and symptoms was observed concurrently with human herpesvirus 6 reactivation. In encephalitis associated with drug-induced hypersensitivity syndrome, human herpesvirus 6 DNA was detected in cerebrospinal fluid. This strongly indicates the involvement of reactivated human herpesvirus 6 in the pathogenesis of encephalitis. Similarly, reactivation of human herpesvirus 6 was observed in fulminant type 1 diabetes mellitus associated with drug-induced hypersensitivity syndrome caused by carbamazepine.

SUMMARY

The reactivation of human herpesvirus 6 in drug-induced hypersensitivity syndrome is not a coincidental phenomenon. Human herpesvirus 6 reactivation plays an important role in the pathogenesis of drug-induced hypersensitivity syndrome, especially in the latter half of the clinical symptoms. Reactivated human herpesvirus 6 sometimes leads to the severe complications of drug-induced hypersensitivity syndrome, such as encephalitis and type 1 diabetes mellitus. In conclusion, drug-induced hypersensitivity syndrome is a complex disease composed of drug allergy and human herpesvirus 6.

Disrupted-In-Schizophrenia 1, a candidate gene for schizophrenia, participates in neurite outgrowth

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a novel gene disrupted by a (1;11)(q42.1;q14.3) translocation that segregated with schizophrenia in a Scottish family. Predicted DISC1 product has no significant homology to other known proteins. Here, we demonstrated the existence of DISC1 protein and identified fasciculation and elongation protein zeta-1 (FEZ1) as an interacting partner of DISC1 by a yeast two-hybrid study. FEZ1 and its nematode homolog are reported to represent a new protein family involved in axonal outgrowth and fasciculation. In cultured hippocampal neurons, DISC1 and FEZ1 colocalized in growth cones. Interactions of these proteins were associated with F-actin. In the course of neuronal differentiation of PC12 cells, upregulation of DISC1/FEZ1 interaction was observed as along with enhanced extension of neurites by overexpression of DISC1. The present study shows that DISC1 participates in neurite outgrowth through its interaction with FEZ1. Recent studies have provided reliable evidence that schizophrenia is a neurodevelopmental disorder. As there is a high level of DISC1 expression in developing rat brain, dysfunction of DISC1 may confer susceptibility to psychiatric illnesses through abnormal development of the nervous system.

Induced HMGA1a expression causes aberrant splicing of Presenilin-2 pre-mRNA in sporadic Alzheimer's disease

The aberrant splicing isoform (PS2V), generated by exon 5 skipping of the Presenilin-2 (PS2) gene transcript, is a diagnostic feature of sporadic Alzheimer's disease (AD). We found PS2V is hypoxia-inducible in human neuroblastoma SK-N-SH cells. We purified a responsible trans-acting factor based on its binding to an exon 5 fragment. The factor was identified as the high mobility group A1a protein (HMGA1a; formerly HMG-I). HMGA1a bound to a specific sequence on exon 5, located upstream of the 5' splice site. HMGA1a expression was induced by hypoxia and the protein was accumulated in the nuclear speckles with the endogenous splicing factor SC35. Overexpression of HMGA1a generated PS2V, but PS2V was repressed by cotransfection with the U1 snRNP 70K protein that has a strong affinity to HMGA1a. HMGA1a could interfere with U1 snRNP binding to the 5' splice site and caused exon 5 skipping. HMGA1a levels were significantly increased in the brain tissue from sporadic AD patients. We propose a novel mechanism of sporadic AD that involves HMGA1a-induced aberrant splicing of PS2 pre-mRNA in the absence of any mutations.

Lack of evidence for TARC/CCL17 production by normal human keratinocytes in vitro

BACKGROUND

thymus and activation-regulated chemokine (TARC)/CCL17 is a CC chemokine that selectively attracts Th2-type lymphocytes. Immunohistochemical analyses have revealed that TARC is expressed in the epidermal keratinocytes of atopic dermatitis (AD), suggesting TARC involvement in the pathogenesis of the disease. However, keratinocyte TARC production has been described only in the transformed keratinocyte cell line HaCaT.

OBJECTIVE

to examine TARC production in normal human epidermal keratinocytes (NHEK) in vitro.

METHODS

the expression of TARC mRNA and protein were examined in NHEK and HaCaT cells stimulated with various cytokines.

RESULTS

stimulation with inflammatory cytokines, including interleukin (IL)-1, IL-4, IL-6, IL-10, interferon (IFN)-alpha, IFN-beta, IFN-gamma, and tumor necrosis factor (TNF)-alpha failed to induce TARC mRNA expression in NHEK. However, stimulation with IFN-gamma and TNF-alpha together enhanced expression slightly. ELISA analysis failed to detect TARC protein in NHEK culture supernatant, even following stimulation with IFN-gamma and TNF-alpha. In contrast, HaCaT cells produced TARC protein even without stimulation of cytokines.

CONCLUSION

these results indicate that production of TARC by HaCaT cells is a phenomenon specific to the cell line and the observation on TARC in HaCaT cells can not be generalized. NHEK do not produce TARC protein in vitro.

Differential effects of desmoglein 1 and desmoglein 3 on desmosome formation

The desmoglein plays an important part in the formation of desmosomes. We constructed recombinant adenoviruses containing desmoglein 1 and desmoglein 3 derivatives partly lacking the extracellular domain (desmoglein 1DeltaEC and desmoglein 3DeltaEC, respectively), and full-length desmoglein 1 and desmoglein 3 and studied the involvement of desmoglein 1 and desmoglein 3 in desmosome formation. During low-level expression of desmoglein 3DeltaEC in transduced HaCaT cells, keratin insertion at cell-cell contact sites was only partially inhibited and desmoplakin was partially stained at cell-cell contact sites. Low-level expression of desmoglein 1DeltaEC, however, resulted in complete inhibition of keratin insertion at the cell-cell contact sites, and desmoplakin was stained in perinuclear dots. These results indicate the dominant-negative effect of desmoglein 1DeltaEC on desmosome formation was stronger than that of desmoglein 3DeltaEC. Desmoglein 1DeltaEC coprecipitated plakoglobin to approximately the same extent as desmoglein 3DeltaEC. Therefore, we conclude that the dominant-negative effect of desmoglein 1DeltaEC is not simply due to plakoglobin sequestration. On the other hand, during low-level expression of full-length desmoglein 3 and desmoglein 1, they both colocalized with desmoplakin. During high-level expression, however, keratin insertion at cell-cell contact sites was inhibited in desmoglein 1 but not in desmoglein 3, and desmoplakin was stained at cell-cell contact sites in desmoglein 3 but not in desmoglein 1. These data suggest desmoglein 1 and desmoglein 3 expressed at low level were incorporated into desmosome but at high-level expression, desmoglein 1 disrupted desmosomes but desmoglein 3 did not. Our findings provide biologic evidence that desmoglein 1 and desmoglein 3 play a different functional role in cell-cell adhesion of keratinocytes.

A case of cold-dependent exercise-induced anaphylaxis

Exercise-induced anaphylaxis (EIA) is a form of physical urticaria that is induced by exercise. A 16-year-old Japanese boy had a 4-year history of recurrent wealing and dyspnoea after physical exercise such as jogging, playing handball or riding a bicycle in winter. The episodes were not associated with ingestion of foods including wheat or soya bean. A provocation test, with 15 min of exercise and 2 min of cold stimulation immediately before or immediately after the exercise, elicited a weal that was localized to the test area. A challenge test with ingestion of boiled soya beans and exercise did not elicit a weal. Therefore, in this case, cold exposure, but not food ingestion, was essential for inducing EIA. Cold-dependent EIA is different from cold urticaria, food-dependent EIA, cholinergic urticaria and cold-induced cholinergic urticaria, and may be a distinct entity.

Disturbed activation of endoplasmic reticulum stress transducers by familial Alzheimer's disease-linked presenilin-1 mutations

Recent studies have shown independently that presenilin-1 (PS1) null mutants and familial Alzheimer's disease (FAD)-linked mutants should both down-regulate signaling of the unfolded protein response (UPR). However, it is difficult to accept that both mutants possess the same effects on the UPR. Furthermore, contrary to these observations, neither loss of PS1 and PS2 function nor expression of FAD-linked PS1 mutants were reported to have a discernable impact on the UPR. Therefore, re-examination and detailed analyses are needed to clarify the relationship between PS1 function and UPR signaling. Here, we report that PS1/PS2 null and dominant negative PS1 mutants, which are mutated at aspartate residue 257 or 385, did not affect signaling of the UPR. In contrast, FAD-linked PS1 mutants were confirmed to disturb UPR signaling by inhibiting activation of both Ire1alpha and ATF6, both of which are endoplasmic reticulum (ER) stress transducers in the UPR. Furthermore, PS1 mutants also disturbed activation of PERK (PKR-like ER kinase), which plays a crucial role in inhibiting translation during ER stress. Taken together, these observations suggested that PS1 mutations could affect signaling pathways controlled by each of the respective ER-stress transducers, possibly through a gain-of-function.

Hypothermic treatment restores glucose regulated protein 78 (GRP78) expression in ischemic brain

Mild hypothermia is a well-known method of reducing brain damage caused by traumatic, hypoxic, and ischemic injury. To elucidate the neuroprotective mechanism induced by hypothermic treatment, we compared gene expression profiles in the hippocampus of gerbils rendered ischemic for 15 min and then reperfused for 3 h under conditions of normothermia (37+/-0.5 degrees C) or hypothermic treatment (34+/-0.5 degrees C). Using the differential display method, we observed significantly reduced expression of the 78 kDa glucose regulated protein (GRP78), in ischemic gerbil hippocampus that underwent normothermic reperfusion, but normal GRP78 expression in animals that underwent hypothermic reperfusion. In situ hybridization and Northern blot analysis showed GRP78 mRNA expression was reduced in the CA1 region of the hippocampus under normothermic conditions, but was not reduced under hypothermic conditions. Western blot analysis also showed the levels of immunoreactive GRP78 protein decreased in neurons of the hippocampal CA-1 region under normothermia, but not under hypothermic treatments. Furthermore, adenovirus-mediated overexpression of GRP78 protects rat hippocampal neurons from cell death and inhibits the rise in intracellular calcium concentration normally induced by hydrogen peroxide. These results suggest that reduction in GRP78 expression contributes to cell damage in the ischemic brain and that hypothermia-mediated restoration of GRP78 expression is one mechanism that enhances neuronal survival.

[Hypersensitivity syndrome and HHV-6]

Hypersensitivity syndrome (HS) has been recognized as one of severe adverse drug eruptions. HS has several characteristic features as follows. First, the clinical symptoms are high fever, multiple lymphadenopathy, severe skin rash, mononucleosis and multiple visceral involvement. Secondly, those symptoms appear two to six weeks after the initiation of drug administration. Thirdly, HS is induced by the specific drugs, carbamazepine, phenytoin, salazosulfapyridine, allopurinol, diaphenylsulphone, and mexiletine. Recently, we reported the association of HS with reactivation of HHV-6, the causative virus for exanthem subitum. We propose the new disease entity of HHV-6-associated drug eruption (HADE) because HS is composed of two clinical phases, drug allergic reaction in the early phase and HHV-6 reactivation in the late phase.

Enhanced gamma interferon production through activation of Valpha14(+) natural killer T cells by alpha-galactosylceramide in interleukin-18-deficient mice with systemic cryptococcosis

We showed recently that activation of Valpha14(+) natural killer T cells (NKT cells) by alpha-galactosylceramide (alpha-GalCer) resulted in increased gamma interferon (IFN-gamma) production and host resistance to intravenous infection with Cryptococcus neoformans. In other studies, interleukin-18 (IL-18) activated NKT cells in collaboration with IL-12, suggesting the possible contribution of this cytokine to alpha-GalCer-induced IFN-gamma synthesis. Here we examined the role of IL-18 in alpha-GalCer-induced Th1 response by using IL-18KO mice with this infection. In these mice, levels of IFN-gamma in serum and its synthesis in vitro by spleen cells stimulated with live organisms were not reduced, but rather enhanced, compared to those in wild-type (WT) mice, while such production was completely absent in IL-12KO mice. The enhanced production of IFN-gamma correlated with increased IL-12 synthesis but not with reduced production of IL-4, which was rather increased. IFN-gamma synthesis in IL-18KO mice was abolished by neutralizing anti-IL-12 antibody and significantly inhibited by neutralization of endogenous IL-4 with a specific monoclonal antibody. In addition, administration of recombinant IL-4 significantly enhanced the production of IFN-gamma in WT mice. Finally, the enhanced production of IFN-gamma in IL-18KO mice correlated with increased host defense against cryptococcal infection, as indicated by enhancement in alpha-GalCer-related clearance of microorganisms. Our results indicated that in IL-18KO mice, IFN-gamma synthesis was enhanced through overproduction of IL-12 and IL-4 after intravenous infection with C. neoformans and a ligand-specific activation of Valpha14(+) NKT cells.

Differentiated keratinocytes are responsible for TNF-alpha regulated production of macrophage inflammatory protein 3alpha/CCL20, a potent chemokine for Langerhans cells

The recruitment of immature dendritic cells into the epidermis is a key step in the development of cutaneous immunity, although the mechanism remains to be clarified. Recently, it was reported that both macrophage inflammatory protein 3alpha (MIP-3alpha)/CCL20 produced by keratinocytes and TNF-alpha are important in recruiting Langerhans cells (LC) to the epidermis. In this study, we examined the production of MIP-3alpha by human keratinocytes stimulated with TNF-alpha. Cultured keratinocytes showed enhanced expression of MIP-3alpha mRNA and protein when stimulated with TNF-alpha. In addition, conditioned medium from TNF-alpha-stimulated keratinocyte cultures induced the migration of L1.2 cells expressing CCR6. We next examined the production of MIP-3alpha in stratified keratinocytes and found that, in contrast to non-stratified keratinocytes, stimulation with TNF-alpha increased the expression of MIP-3alpha mRNA and protein. Moreover, skin samples grown in organ culture and treated with TNF-alpha showed MIP-3alpha in the keratinocytes of the spinous layer, but not in the basal layer, by immunofluorescence staining. Based on these results, we postulate that MIP-3alpha produced by keratinocytes in the spinous layer in response to TNF-alpha stimulation is a key chemokine responsible for the epidermal recruitment of Langerhans cells.

Differential expression patterns of three glutamate transporters (GLAST, GLT1 and EAAC1) in the rat main olfactory bulb

Glutamate is the main neurotransmitter in the olfactory bulb. Therefore, glutamate transporters, which regulate the concentration of extracellular glutamate, might play pivotal roles in odor processing. In this study, we examined expressions of three glutamate transporters (GLAST, GLT1 and EAAC1) in the olfactory bulb using in situ hybridization and immunohistochemistry. EAAC1 mRNA was expressed in neurons, such as periglomerular cells, tufted cells, mitral cells and granule cells as shown before in other brain areas. In contrast, GLAST and GLT1 were found in glial cells throughout the olfactory bulb, with intenser expressions in the glomerular layer, external plexiform layer and internal plexiform layer where glutamatergic synapses are concentrated. In addition, using double staining immunohistochemistry we clearly showed that GLAST and GLT1 were expressed in astrocytes. Furthermore, we found that GLAST was also intensely expressed in the subependymal layer where precursor cells exist. These results suggest each glutamate transporter plays its unique role not only in glutamatergic neurotransmission but also in cell differentiation and migration in the olfactory bulb.

Interchangeable binding of Bcl10 to TRAF2 and cIAPs regulates apoptosis signaling

Bcl10 was identified as a candidate gene responsible for low grade B cell lymphomas of mucosa-associated lymphoid tissue. Overexpression of Bcl10 in cultured cells was reported to promote apoptosis, however, the mechanism of regulation of apoptosis mediated by Bcl10 has not been demonstrated. In the present study, we analysed the apoptosis signaling pathway mediated by Bcl10, focusing on phosphorylation of Bcl10 and the dynamic interaction with its binding partners during apoptosis. Previously, we have demonstrated that Bcl10 potentially interacts with the other apoptosis regulator, TNF receptor associated factor-2 (TRAF2) and inhibitor of apoptosis proteins (cIAPs). The present results showed that the complex formation of these molecules was regulated by phosphorylation of Bcl10, that is, phosphorylation of Bcl10 resulted in binding of Bcl10 to cIAPs and the dissociation of it from TRAF2. Moreover, hyperphosphorylation of Bcl10 enhanced apoptosis, suggesting that changes in the binding partners of Bcl10 were correlated to the promotion of apoptosis as mediated by Bcl10. Indeed, the mutant which was deleted from the binding site of Bcl10 for cIAPs, could not induce apoptosis. These findings indicate that Bcl10 is a mediator of apoptosis signaling, by switching over binding to cIAPs from TRAF2 through the events of Bcl10 phosphorylation.

[Dynamic variance of intracellular metabolic energies under rhythmical control for dissolved oxygen in PHB mixed cultivation]

The mixed cultivation using cheaper carbon source-wasted food material contained glucose and lactate at the same time was conducted in 5L fermentor, within which glucose was converted to lactate by L. delbrueckii in anaerobic condition and the lactate was converted to PHB by R. eutropha in aerobic condition. Considering dissolved oxygen concentration may affect the level of intracellular ATP and NADPH of the metabolic pathways for R. eutropha in lactate under autotrophy or heterotrophy, rhythmical oscillated control for DO based on chaos control method was consequently presented. This method was employed to satisfy two strains for opposite oxygen preferences, moreover, excite the intracellular metabolic energy simultaneously. The values examined through spectrophotofluorimetry represented that both ATP and NADPH exhibited fluctuations in accordance with the DO rhythm. By means of this control design, the concentration of PHB can be doubled than the usual under stable DO control.

FTS reduces bleomycin-induced cytokine and chemokine production and inhibits pulmonary fibrosis in mice

Bleomycin (BLM), an antitumour drug, is known to cause interstitial pneumonia followed by pulmonary fibrosis, and has often been used to produce an animal model of pulmonary fibrosis. In the present study, we examined the effect of a nonapeptide thymic hormone, facteur thymique serique (FTS), on the murine lung fibrosis induced by intratracheal instillation of BLM. Treatment with FTS ameliorated BLM-induced fibrotic changes in a dose-dependent manner, as indicated by the reduced accumulation of hydroxyproline (HP). In addition, FTS suppressed BLM-induced cellular inflammatory response in the lungs, as evidenced by inhibition of increased lung weight, reduced accumulation of inflammatory leucocytes, including lymphocytes and neutrophils, but not macrophages, and less pronounced histopathological changes. Finally, BLM challenge increased the local synthesis of proinflammatory cytokines, TNF-alpha and IL-1beta and chemokines, MCP-1, MIP-1alpha RANTES, MIP-2 and KC, while administration of FTS suppressed the production of these cytokines, except for MCP-1. These effects of FTS were observed only when mice received intratracheal instillation with BLM. Considered collectively, our results indicated that FTS treatment ameliorated the cellular inflammatory responses and fibrotic changes in the lungs caused by BLM and such inhibition was well correlated with reduced synthesis of several fibrosis-related cytokines, and suggested that FTS may be potentially useful for the treatment of pulmonary fibrosis.

[Clinical and bacteriological features of 12 cases of liver abscess caused by Streptococcus milleri group]

We described the clinical and bacteriological features of 12 cases of liver abscess caused by Streptococcus milleri group (SMG) during a 6-year period from 1993 to 1998. The gender was 11 males and 1 female with their ages ranging from 39 to 76 years old (mean: 53.4). The common symptoms were fever (100%), abdominal pain (67%), and appetite loss (58%). Nine cases had underlying diseases such as carcinomas and diabetes mellitus. Predominant causes of the liver abscess were cryptogenic (42%) and biliary tract disease (33%). Three patients died of an exacerbation of the carcinoma. Eight cases (67%) was single infection of SMG and no mixed infection with anaerobes. No strains isolated in this series showed resistance against penicillin G and ampicillin. SMG was highly isolated from the blood culture in eight of the 11 cases (73%). Liver abscess should be taken into consideration as one of the causes of SMG septicemia.

The unfolded protein response and Alzheimer's disease

Disruption of calcium homeostasis, inhibition of protein glycosylation, and reduction of disulfide bonds provoke accumulation of unfolded protein in the endoplasmic reticulum (ER), and are therefore a type of 'ER stress'. Normal cells respond to ER stress by increasing transcription of genes encoding ER-resident chaperones such as GRP78/BiP, GRP94 and protein disulfide isomerase to facilitate protein folding. This induction system is termed the unfolded protein response. Familial Alzheimer's disease-linked presenilin-1 (PS1) mutation downregulates the unfolded protein response and leads to vulnerability to ER stress. The mechanisms by which mutant PS1 affects the ER stress response are attributed to the inhibited activation of ER stress transducers such as IRE1, PERK and ATF6.

Cloning of a lymphatic peptide/histidine transporter

Although peptide transport across the plasma membrane has been characterized well in the kidney and the intestine, the functional relevance of this transport in other organs has not been addressed. Here we report the cloning of a cDNA for a novel peptide/histidine transporter found in the rat (rPHT2), whose mRNA is expressed mainly in the lymphatic system. rPHT2 encodes a protein of 582 amino acids and showed 49% identity with the brain PHT (PHT1) [Yamashita, Shimada, Guo, Sato, Kohmura, Hayakawa, Takagi and Tohyama (1997) J. Biol. Chem. 272, 10205-10211]. rPHT2 mRNA was abundant in lung, spleen and thymus, and detected faintly in brain, liver, adrenal gland and heart by Northern-blot analysis and reverse transcriptase PCR (RT-PCR). Intense signals for the gene were found in immunocytes using in situ hybridization. Ectopic expression of rPHT2 protein in HEK-293T cells and BHK cells was not found on the cell surface, but was found on the lysosomal membrane using light- and electron-microscopic analysis. Recombinant rPHT2 protein reconstituted into liposomes showed proton-dependent transport activity with histidine and histidyl-leucine. These findings suggest that rPHT2 is involved in the protein catabolic pathway in the lymphatic system.

Activation of caspase-12, an endoplastic reticulum (ER) resident caspase, through tumor necrosis factor receptor-associated factor 2-dependent mechanism in response to the ER stress

When accumulation of a malfolded protein in the endoplastic reticulum (ER) is induced by various adverse conditions, such as hypoxia, glucose starvation, and perturbation of calcium homeostasis, cells respond to the stress by increasing transcription of genes encoding ER molecular chaperones, a process known as unfolded protein response. The signaling is initiated by IRE1s, ER stress sensors. Alternatively, excessive stress to the ER results in apoptosis. Caspase-12 is known to be essential for this ER stress-induced apoptosis. In this study, we analyzed the detailed regulatory mechanisms of IRE1s during ER stress. We identified c-Jun N-terminal inhibitory kinase (JIK) as a binding partner of IRE1alpha, and JIK was seen to modulate IRE1alpha-TRAF2 (tumor necrosis factor receptor-associated factor 2) complex formation and the resultant alteration to c-Jun N-terminal kinase signaling from IRE1s in response to ER stress. We also demonstrated that TRAF2 interacts with procaspase-12 and promotes the clustering of procaspase-12 and its activation by cleavage in response to ER stress. These results indicate that TRAF2 plays crucial roles not only in the signaling of the c-Jun N-terminal kinase pathway but also in activation of caspase-12 to transduce signals from IRE1s. Thus, we provide a missing link in the ER stress-induced apoptosis-signaling pathway, one which connects the stress sensor molecule IRE1 and the activation of caspase-12.

Activated cAMP-response element-binding protein regulates neuronal expression of presenilin-1

Upon binding to the cAMP-response element of a gene's promoter, the transcription factor known as cAMP-response element-binding protein (CREB) facilitates transcription of many different neuronal genes including those involved with synaptic function. Based on our previous reports of gene structure (GenBank accession number AF029701 ), we now demonstrate that activated CREB binds to the proximal promoter of the human presenilin-1 (PS-1) gene to activate PS-1 transcription in rat and in human neuronal cells. Specific stimulation of the N-methyl-d-aspartate subtype of neuronal glutamate receptors activates CREB and results in increased PS-1 expression. Similarly, treatment with brain-derived neurotrophic factor activates CREB and increases PS-1 expression in a dose-dependent fashion. By using adenovirus vectors expressing dominant negative forms of CREB, we were able to show that induction of PS-1 expression requires the activation of CREB. Conversely, constitutive expression of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) results in activation of CREB and increased PS-1 expression that can be blocked by the addition of selective MEK inhibitors. Our findings suggest a hypothesis where stimulation of N-methyl-d-aspartate receptors signals CREB activation to enhance PS-1 gene product expression that contributes to normal neuronal functions.

Sema4c, a transmembrane semaphorin, interacts with a post-synaptic density protein, PSD-95

Semaphorins are known to act as chemorepulsive molecules that guide axons during neural development. Sema4C, a group 4 semaphorin, is a transmembrane semaphorin of unknown function. The cytoplasmic domain of Sema4C contains a proline-rich region that may interact with some signaling proteins. In this study, we demonstrate that Sema4C is enriched in the adult mouse brain and associated with PSD-95 isoforms containing PDZ (PSD-95/DLG/ZO-1) domains, such as PSD-95/SAP90, PSD-93/chapsin110, and SAP97/DLG-1, which are concentrated in the post-synaptic density of the brain. In the neocortex, S4C is enriched in the synaptic vesicle fraction and Triton X-100 insoluble post-synaptic density fraction. Immunostaining for Sema4C overlaps that for PSD-95 in superficial layers I-IV of the neocortex. In neocortical culture, S4C is colocalized with PSD-95 in neurons, with a dot-like pattern along the neurites. Sema4C thus may function in the cortical neurons as a bi-directional transmembrane ligand through interacting with PSD-95.

ORP150 protects against hypoxia/ischemia-induced neuronal death

Oxygen-regulated protein 150 kD (ORP150) is a novel endoplasmic-reticulum-associated chaperone induced by hypoxia/ischemia. Although ORP150 was sparingly upregulated in neurons from human brain undergoing ischemic stress, there was robust induction in astrocytes. Cultured neurons overexpressing ORP150 were resistant to hypoxemic stress, whereas astrocytes with inhibited ORP150 expression were more vulnerable. Mice with targeted neuronal overexpression of ORP150 had smaller strokes compared with controls. Neurons with increased ORP150 demonstrated suppressed caspase-3-like activity and enhanced brain-derived neurotrophic factor (BDNF) under hypoxia signaling. These data indicate that ORP150 is an integral participant in ischemic cytoprotective pathways.

Akt activation protects hippocampal neurons from apoptosis by inhibiting transcriptional activity of p53

Survival factors suppress apoptosis by activating the serine/threonine kinase Akt. To investigate the molecular mechanism underlying activated Akt's ability to protect neurons from hypoxia or nitric oxide (NO) toxicity, we focused on the apoptosis-related functions of p53 and caspases. We eliminated p53 by employing p53-deficient neurons and increased p53 by infection with recombinant adenovirus capable of transducing p53 expression, and we now show that p53 is implicated in the apoptosis induced by hypoxia or NO treatments of primary cultured hippocampal neurons. Although hypoxia and NO induced p53, treatment with insulin-like growth factor-1 significantly inhibited caspase-3-like activation, neuronal death and transcriptional activity of p53. These insulin-like growth factor-1 effects are prevented by wortmannin, a phosphatidylinositol 3-kinase inhibitor. Adenovirus-mediated expression of activated-Akt kinase suppressed p53-dependent transcriptional activation of responsive genes such as Bax, suppressed caspase-3-like protease activity and suppressed neuronal cell death with no effect on the cellular accumulation and nuclear translocation of p53. In contrast, overexpression of kinase-defective Akt failed to suppress these same activities. These results suggest a mechanism where Akt kinase activation reduces p53's transcriptional activity that ultimately rescues neurons from hypoxia- or NO-mediated cell death.

Apolipoprotein E4 stimulates cAMP response element-binding protein transcriptional activity through the extracellular signal-regulated kinase pathway

Inheritance of the epsilon4 allele of the apolipoprotein E gene (APOE4) is a major risk factor for the development of Alzheimer's disease (AD). Although the association between APOE4 and AD is well documented, the mechanism by which apolipoprotein E exerts an isoform-specific effect on neurons in disease is unknown. In this report, we demonstrate that apoE4 stimulates the transcriptional activity of cAMP-response element-binding protein (CREB) by activating the extracellular signal-regulated kinase (ERK) cascade in rat primary hippocampal neurons. In contrast, apoE3 was unable to stimulate CREB transcriptional activity and unable to activate the ERK pathway. Elevation of intracellular Ca(2+) levels are also involved because treatment with receptor-associated protein, nifedipine, MK801, removal of Ca(2+) from the medium and dantrolene all served to inhibit calcium elevation and attenuate the activation of CREB. Treatment with an apoE peptide was also found to facilitate transcription of the CREB-dependent genes, c-fos and Bcl-2. In contrast to treatment with apoE3, our findings suggest apoE4 and apoE-peptide induce a novel signaling pathway.

Increased production of beta-amyloid and vulnerability to endoplasmic reticulum stress by an aberrant spliced form of presenilin 2

An alternative spliced form of the presinilin 2 (PS2) gene (PS2V) lacking exon 5 has previously been reported to be expressed in human brains in sporadic Alzheimer's disease (AD). PS2V encodes the amino-terminal portion of PS2, which contains residues Met1-Leu119 and 5 additional amino acid residues (SSMAG) at its carboxyl terminus. Here we report that PS2V protein impaired the signaling pathway of the unfolded protein response, similarly to familial AD-linked PS1 mutants and caused significant increases in the production of both amyloid beta40 and beta42. Interestingly, PS2V-encoding protein was expressed in neuropathologically affected neurons of the hippocampal CA1 region and temporal cortex in AD patients. These findings suggest that the aberrant splicing of the PS2 gene may be implicated in the neuropathology of sporadic AD.

Characterization of mouse Ire1 alpha: cloning, mRNA localization in the brain and functional analysis in a neural cell line

In yeast, an endoplasmic reticulum (ER)-associated protein, Ire1p, is believed to initiate the unfolded protein response (UPR), that is responsible for protein folding in the ER under stressed conditions. Two mammalian homologs of Ire1p have been identified, Ire1 alpha and Ire1 beta. We have previously reported that familial Alzheimer's disease linked presenilin-1 variants downregulate the signaling pathway of the UPR by affecting the phosphorylation of Ire1 alpha. In the present study, we cloned the mouse homolog of Ire1 alpha for generating genetically modified mice. Ire1 alpha was ubiquitously expressed in all mouse tissues examined, and was expressed preferentially in neuronal cells in mouse brain. This led us to investigate the effects of the downregulation of the UPR on the survival of neuronal cells under conditions of ER stress. Morphological and biochemical studies using a dominant-negative form of mouse Ire1 alpha have revealed that cell death caused by ER stress can be attributed to apoptosis, and that the downregulation of the UPR enhances the apoptotic process in the mouse neuroblastoma cell line, Neuro2a. Our results indicate that genetically modified mice such as transgenic mice with a dominant-negative form of Ire1 alpha might provide further understanding of the pathogenic mechanisms of Alzheimer's disease and other neurodegenerative disorders.

Absence of endoproteolysis but no effects on amyloid beta production by alternative splicing forms of presenilin-1, which lack exon 8 and replace D257A

It is well known that presenilin-1 (PS1) is involved in cleavage of amyloid precursor protein (APP) at the gamma-secretase site, and that the amino acids residues of D257 and D385 in PS1 are critical for this cleavage of APP and the endoproteolysis of itself. An alternatively spliced form of PS1 skipping exon 8 (PS1d8), which has D257A at the splice junction of exon 7/9, is expressed in human brain and in some cell lines. In this study, we examined production of Amyloid beta (A beta) and the endoproteolysis of the holoproteins in PS1d8-expressing neuroblastoma cells. Western blotting showed an absence of endoproteolysis in PS1d8. However, PS1d8 did not affect the production of A beta, which is different from the artificial point mutant PS1D257A. These results suggest that endoproteolysis of PS1 and gamma-secretase activity could be independent.