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Hiroshi Nakagawa

Publications and source records attributed to Hiroshi Nakagawa.

At least 19 recordsLinked to original sources
PubMed2007

A model explaining genotypic and ontogenetic variation of leaf photosynthetic rate in rice (Oryza sativa) based on leaf nitrogen content and stomatal conductance.

BACKGROUNDS AND AIMS: Identification of physiological traits associated with leaf photosynthetic rate (Pn) is important for improving potential productivity of rice (Oryza sativa). The objectives of this study were to develop a model which can explain genotypic variation and ontogenetic change of Pn in rice under optimal conditions as a function of leaf nitrogen content per unit area (N) and stomatal conductance (g(s)), and to quantify the effects of interaction between N and g(s) on the variation of Pn. METHODS: Pn, N and g(s) were measured at different developmental stages for the topmost fully expanded leaves in ten rice genotypes with diverse backgrounds grown in pots (2002) and in the field (2001 and 2002). A model of Pn that accounts for carboxylation and CO diffusion processes, and assumes that the ratio of internal conductance to g(s) is constant, was constructed, and its goodness of fit was examined. KEY RESULTS: Considerable genotypic differences in Pn were evident for rice throughout development in both the pot and field experiments. The genotypic variation of Pn was correlated with that of g(s) at a given stage, and the change of Pn with plant development was closely related to the change of N. The variation of g(s) among genotypes was independent of that of N. The model explained well the variation in Pn of the ten genotypes grown under different conditions at different developmental stages. Conclusions The response of Pn to increased N differs with g(s), and the increase in Pn of genotypes with low g(s) is smaller than that of genotypes with high g(s). Therefore, simultaneous improvements of these two traits are essential for an effective breeding of rice genotypes with increased Pn.

Electric Conductivity↗
PubMed2007

Spinal instrumentation for interfacet locking injuries of the subaxial cervical spine.

A retrospective analysis of our surgical management of traumatic interfacet locking was performed. Eleven interfacet locking injuries were surgically treated. An anterior procedure was performed in five patients, posterior fixation in three and a combined procedure in three. Five facet locks were reduced by preoperative skull traction. After general anesthesia at surgery, another two cases were corrected manually. Surgical fixation using spinal instrumentation was performed. One patient treated with posterior fixation required an additional anterior procedure because of a delayed disc herniation. Spinal instrumentation avoided a halo vest. The anterior approach may be selected in patients who are reduced manually, while a combined procedure should be performed in patients with irreducible facet dislocation with disc herniation. Delayed symptomatic disc herniation may occur when only posterior fixation is performed.

Adult↗
PubMed2006

Krüppel-like factor 5 activates MEK/ERK signaling via EGFR in primary squamous epithelial cells.

Rapid cell proliferation is a hallmark of transit amplifying cells, but the mechanisms of this localized proliferation are not well understood. The Krüppel-like factor family member Klf5 (IKLF; BTEB2) promotes cell proliferation and is highly expressed in squamous epithelia, in regions of active proliferation. Here, using mouse primary esophageal keratinocytes as a model, we identify a critical role for Klf5 in regulating squamous epithelial proliferation via the epidermal growth factor receptor (EGFR), which, like Klf5, is localized to basal cells in squamous epithelia. We show that Klf5 increases proliferation, transcriptionally up-regulates EGFR, and activates MEK/ERK signaling, as indicated by increased phosphorylation of MEK and ERK. By chromatin immunoprecipitation, we demonstrate that Klf5 binds directly to the 5' regulatory region of EGFR. In addition, we show that regulation of proliferation by Klf5 is dependent on EGFR and MEK/ERK signaling, as the proliferative response to Klf5 is blocked by pharmacologic inhibition of EGFR or MEK. Inhibition of EGFR or MEK also decreases Klf5 expression. Thus, Klf5 regulates MEK/ERK signaling via EGFR and is also downstream of MAPK signaling, providing a novel mechanism for signal amplification or suppression and control of proliferation in basal cells.

Animals↗
PubMed2006

Oncogene-induced senescence is part of the tumorigenesis barrier imposed by DNA damage checkpoints.

Recent studies have indicated the existence of tumorigenesis barriers that slow or inhibit the progression of preneoplastic lesions to neoplasia. One such barrier involves DNA replication stress, which leads to activation of the DNA damage checkpoint and thereby to apoptosis or cell cycle arrest, whereas a second barrier is mediated by oncogene-induced senescence. The relationship between these two barriers, if any, has not been elucidated. Here we show that oncogene-induced senescence is associated with signs of DNA replication stress, including prematurely terminated DNA replication forks and DNA double-strand breaks. Inhibiting the DNA double-strand break response kinase ataxia telangiectasia mutated (ATM) suppressed the induction of senescence and in a mouse model led to increased tumour size and invasiveness. Analysis of human precancerous lesions further indicated that DNA damage and senescence markers cosegregate closely. Thus, senescence in human preneoplastic lesions is a manifestation of oncogene-induced DNA replication stress and, together with apoptosis, provides a barrier to malignant progression.

Animals↗
PubMed2006

Tumorigenic conversion of primary human esophageal epithelial cells using oncogene combinations in the absence of exogenous Ras.

To investigate pathways of human esophageal squamous cell transformation, we generated esophageal tumor cells using human telomerase- and SV40-immortalized primary esophageal epithelial cells (EPC2) by overexpression of selected combinations of oncogenes. H-Ras, c-Myc, or Akt, but not epidermal growth factor receptor (EGFR), induced transformed colonies in soft agar. By contrast, bioluminescence imaging of genetically altered immortalized esophageal cells revealed that Akt, EGFR, or H-Ras, but not c-Myc, resulted in tumor formation in immunodeficient mice. H-Ras-driven tumors showed highly tumorigenic phenotypes with 2.6 +/- 0.6 days for doubling, whereas Akt and EGFR tumors doubled every 9.5 +/- 1.6 and 6.1 +/- 1.2 days, respectively. H-Ras-driven tumors expressed the hypoxia-inducible factor target Glut1, whereas Akt- or EGFR-driven tumors had evidence of angiogenesis and no detectable Glut1 expression. Proliferation rates among these tumors were similar, but there was reduced apoptosis in the more aggressive H-Ras-driven tumors that also developed aneuploidy and multiple centrosomes. c-Myc overexpression did not result in tumorigenic conversion but introduction of Bcl-XL into c-Myc-expressing cells generated tumors. Although cytokeratin expression was typical of squamous carcinoma, gene expression profiling was done to compare the four different types of engineered tumors with human esophageal squamous cell carcinomas and adenocarcinomas. Interestingly, c-Myc plus Bcl-XL transformants mimicked squamous carcinomas, whereas H-Ras-, EGFR-, and Akt-driven tumors were similar to adenocarcinomas in their molecular profiles. These genetically engineered models may provide new platforms for understanding human esophagus cancer and may assist in the evaluation of new therapies.

Aneuploidy↗
PubMed2006

Mechanisms involved in modulation of trigeminal primary afferent activity in rats with peripheral mononeuropathy.

In order to clarify the mechanisms underlying the changes in primary afferent neurons in trigeminal neuropathic pain, a chronic constriction nerve injury model of the infraorbital nerve (ION-CCI) was developed in rats. Mechanical allodynia was observed at 3 days after ION-CCI and lasted more than 14 days. Single-unit activities were recorded from the ION of anesthetized rats. C-, Abeta- and Adelta-units were identified on the basis of their conduction velocity. Adelta-units were frequently encountered at a later period after ION-CCI. The highest Adelta-spontaneous activity was recorded at 3 days after ION-CCI and progressively decreased after that, but spontaneous activity was still higher at 14 days after ION-CCI than that of naïve rats. Mechanical-evoked responses of Adelta-units were also highest at 3 days after ION-CCI and then gradually decreased. In consideration of these data, patch-clamp recordings were performed on medium to large size neurons of the dissociated trigeminal ganglion (TRG). Patch-clamp recordings revealed that the IK (sustained) and IA (transient) in rats with ION-CCI were significantly smaller than those of naïve rats, and correlated with an increase in duration of repolarization phase and a decrease in duration of depolarization phase, respectively. The hyperpolarization-activated current (Ih) was significantly larger in TRG neurons of rats with ION-CCI as compared with those of naïve rats. The present results suggest that Ih, IK and IA in Adelta-afferent neurons in TRG are significantly involved in the changes in afferent spontaneous activity and mechanically evoked activity that accompany mechanical allodynia produced by trigeminal nerve injury.

Action Potentials↗
PubMed2006

Coordinated functions of E-cadherin and transforming growth factor beta receptor II in vitro and in vivo.

In epithelial cells, E-cadherin plays a key role in cell-cell adhesion, and loss of E-cadherin is a hallmark of tumor progression fostering cancer cell invasion and metastasis. To examine E-cadherin loss in squamous cell cancers, we used primary human esophageal epithelial cells (keratinocytes) as a platform and retrovirally transduced wild-type and dominant-negative forms of E-cadherin into these cells. We found decreased cell adhesion in the cells expressing dominant-negative E-cadherin, thereby resulting in enhanced migration and invasion. To analyze which molecular pathway(s) may modulate these changes, we conducted microarray analysis and found up-regulation of transforming growth factor beta receptor II (TbetaRII) in the wild-type E-cadherin-overexpressing cells, which was confirmed by real-time PCR and Western blot analyses. To investigate the in vivo relevance of this finding, we analyzed tissue microarrays of paired esophageal squamous cell carcinomas and adjacent normal esophagus, and we could show a coordinated loss of E-cadherin and TbetaRII in approximately 80% of tumors. To determine if there may be an E-cadherin-dependent regulation of TbetaRII, we show the physical interaction of E-cadherin with TbetaRII and that this is mediated through the extracellular domains of E-cadherin and TbetaRII, respectively. In addition, TbetaRI is recruited to this complex. When placed in the context of three-dimensional cell culture, which reflects the physiologic microenvironment, TbetaRII-mediated cell signaling is dependent upon intact E-cadherin function. Our results, which suggest that E-cadherin regulates TbetaRII function, have important implications for epithelial carcinogenesis characterized through the frequent occurrence of E-cadherin and TbetaRII loss.

Cadherins↗
PubMed2006

Identification of two biologically crucial hydroxyl groups of (-)-epigallocatechin gallate in osteoclast culture.

(-)-Epigallocatechin gallate (EGCG) induces cell death of osteoclasts in an Fe(2+)- and H(2)O(2)-dependent manner. In the present study, we further explore the cytotoxic mechanism of EGCG using four EGCG analogues. Molecules methylated at position 4' in the B ring (EGCG-4'-O-Me) or at position 4'' in the D-ring (EGCG-4''-O-Me) showed markedly decreased cytotoxicity to osteoclasts, indicating that hydroxyl groups at these two positions of EGCG are crucial for inducing cell death of osteoclasts. EGCG-4'-O-Me also showed the lowest Fe(3+)-reducing activity among five EGCGs. The Fe(3+)-reducing activity of EGCG was enhanced under conditions whereby protonated EGCG levels were increased, indicating that the protonated status of EGCG was involved in the Fe(3+)-reducing activity. The hydroxyl group at position 4'' in the D-ring was shown by quantum chemical calculation to be preferentially deprotonated among all of the hydroxyl groups in EGCGs. It was also shown that the highest occupied molecular orbital (HOMO) was localized to the B-ring of EGCGs, except for EGCG-4'-O-Me. We report here that the HOMO on the B-ring plays crucial roles in both the Fe(3+)-reducing activity of EGCG and the cytotoxicity of EGCG to osteoclasts, while deprotonation of the hydroxyl group at position 4'' in the D-ring plays a supplementary role.

Animals↗
PubMed2006

Hypoxic microenvironment as a cradle for melanoma development and progression.

Hypoxia-inducible factor (HIF)-1alpha, a global regulator of oxygen homeostasis, plays a crucial role in tumor cell adaptation to the hypoxic microenvironment through transcriptional regulation of its target genes. These genes in turn are involved in a plethora of biochemical as well as cell biological processes, including glucose metabolism, apoptosis and angiogenesis. In melanoma, HIF-1alpha has been implicated in tumor progression with effects upon metastasis and angiogenesis. However, its role in malignant transformation by oncogenes has not been described. Bedogni et al. (Cancer Cell 2005, 8:443-54) report that the hypoxic microenvironment in the skin contributes to melanocyte transformation and tumor growth induced by oncogenes Ras and Akt, which are frequently activated in melanoma. HIF-1alpha activity was found to be required in Akt-induced melanocyte transformation and tumor growth and it was suppressed greatly by mTOR inhibition with rapamycin. Since mTOR regulates HIF-1alpha expression and its transcriptional activity, rapamycin was proposed as a promising hypoxia-related therapeutic approach in melanoma treatment. This study sheds light upon the role of HIF-1alpha in the early stage of melanoma development and highlights the importance of the Akt-mTOR pathway in the regulation of HIF-1alpha.

Cell Hypoxia↗
PubMed2006

Functional validation of the genetic polymorphisms of human ATP-binding cassette (ABC) transporter ABCG2: identification of alleles that are defective in porphyrin transport.

The ATP-binding cassette (ABC) transporter ABCG2 has been implicated to play a significant role in the response of patients to medication and/or the risk of diseases. To clarify the possible physiological or pathological relevance of ABCG2 polymorphisms, we have functionally validated single nucleotide polymorphisms (SNP) of ABCG2. In the present study, based on the currently available data on SNPs and acquired mutations, we have created a total of 18 variant forms of ABCG2 (V12M, G51C, Q126stop, Q141K, T153M, Q166E, I206L, F208S, S248P, E334stop, F431L, S441N, R482G, R482T, F489L, F571I, N590Y, and D620N) by site-directed mutagenesis and expressed them in insect cells. Because porphyrins are considered to be endogenous substrates for ABCG2, we have investigated the porphyrin transport activity of those variant forms in vitro. We herein provide evidence that the variants Q126stop, F208S, S248P, E334stop, and S441N are defective in porphyrin transport, whereas F489L exhibited impaired transport, approximately 10% of the activity observed for the wild type. Furthermore, Flp-In-293 cells expressing those variants were photosensitive. Thus, among those genetic polymorphisms of ABCG2, at least the hitherto validated alleles of Q126stop, S441N, and F489L are suggested to be of clinical importance related to the potential risk of porphyria.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed2006

Reveromycin A, an agent for osteoporosis, inhibits bone resorption by inducing apoptosis specifically in osteoclasts.

Mature bone-resorbing osteoclasts (OCs) mediate excessive bone loss seen in several bone disorders, including osteoporosis. Here, we showed that reveromycin A (RM-A), a small natural product with three carboxylic groups in its structure, induced apoptosis specifically in OCs, but not in OC progenitors, nonfunctional osteoclasts, or osteoblasts. RM-A inhibited protein synthesis in OCs by selectively blocking enzymatic activity of isoleucyl-tRNA synthetase. The proapoptotic effect of RM-A was inhibited by neutralization or disruption of the acidic microenvironment, a prominent characteristic of OCs. RM-A was incorporated in OCs but not in nonfunctional osteoclasts and OC progenitors in neutral culture medium. Effects of RM-A on OC apoptosis increased under acidic culture conditions. RM-A not only was incorporated, but also induced apoptosis in OC progenitors in acidic culture medium. RM-A inhibited osteoclastic pit formation, decreased prelabeled (45)Ca release in organ cultures, and antagonized increased bone resorption in ovariectomized mice. These results suggested that preventive effects of RM-A on bone resorption in vitro and in vivo were caused by apoptosis through inhibition of isoleucyl-tRNA synthetase in OCs and that specific sensitivity of OCs to RM-A was due to the acidic microenvironment, which increased cell permeability of RM-A by suppressing dissociation of protons from carboxylic acid moieties, making them less polar. This unique mechanism suggested that RM-A might represent a type of therapeutic agent for treating bone disorders associated with increased bone loss.

Acids↗
PubMed2006

A new strategy of high-speed screening and quantitative structure-activity relationship analysis to evaluate human ATP-binding cassette transporter ABCG2-drug interactions.

The human ATP-binding cassette (ABC) transporter ABCG2 (BCRP/MXR1/ABCP) plays a critical role in cellular protection against xenobiotics as well as pharmacokinetics of drugs in our body. In the present study, we aimed to analyze the quantitative structure-activity relationship (QSAR) latently residing in ABCG2-drug interactions. We first established standard methods for expression of human ABCG2 in insect cells, quality control of plasma membrane samples by using electron microscopy techniques, and high-speed screening of ABCG2 inhibition with test compounds. Plasma membrane vesicles prepared from ABCG2-expressing Sf9 cells were used as a model system to measure the ATP-dependent transport of [3H]methotrexate (MTX). Forty-nine different therapeutic drugs and natural compounds were tested for their ability to inhibit ABCG2-mediated MTX transport. Based on their inhibition profiles, we performed QSAR analysis using chemical fragmentation codes deduced from the structures of test compounds. Multiple linear regression analysis delineated a relationship between the structural components and the extent of ABCG2 inhibition, allowing us to identify one set of structure-specific chemical fragmentation codes that are closely correlated with the inhibition of ABCG2 transport activity. Based on the QSAR analysis data, we predicted the potency of gefitinib to inhibit ABCG2. The validity of our QSAR-based prediction for gefitinib was examined by actual experiments. Our kinetic analysis experiments suggest that the ABCG2-ATP complex binds gefitinib. The present study provides a new strategy for analyzing ABCG2-drug interactions. This strategy is considered to be practical and useful for the molecular designing of new ABCG2 modulators.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed2006

Safeguards against acute pancreatitis associated with endoscopic papillary balloon dilatation.

BACKGROUND/PURPOSE: Endoscopic papillary balloon dilatation (EPBD) is one of the methods used to remove bile duct stones. EPBD may preserve the function of the sphincter of Oddi in spite of the potential risk of acute pancreatitis caused by the procedure. There are only few reports of attempts to reduce the risk of acute pancreatitis in EPBD. METHODS: We performed EPBD for bile duct stone removal in 201 patients. We used an 8-mm balloon followed by drip infusion of isosorbide dinitrate (ISDN) at a rate of 5 mg/h for low-pressure EPBD. The function of the minor duodenal papilla, the inflation pressure required for the disappearance of the notch sign in the bile duct, and the serum amylase level after EPBD were observed. RESULTS: The median serum amylase level after the procedure was 367 IU/l. Acute pancreatitis occurred in two patients (1.0%). The two patients with acute pancreatitis had poor function of the minor duodenal papilla, a high inflation pressure (over 5 atm) required for disappearance of the notch, sign, and severe abdominal pain during balloon inflation; as well, the procedure took a long time. The rate of duct clearance was 99.5%. CONCLUSIONS: EPBD with gradual inflation of the balloon at a low pressure, followed by ISDN drip infusion, could decrease the risk of acute pancreatitis associated with the procedure. Poor function of the minor duodenal papilla, high inflation pressure required for disappearance of the notch, sign, severe abdominal pain, and a lengthy procedure increase the risk of acute pancreatitis after EPBD.

Adult↗
PubMed2006

Clinical evaluation of traumatic central cord syndrome: emphasis on clinical significance of prevertebral hyperintensity, cord compression, and intramedullary high-signal intensity on magnetic resonance imaging.

BACKGROUND: We evaluated the prognostic and clinical value of radiological findings including prevertebral hyperintensity (HI), cord compression, intramedullary high-signal intensity (IMHSI) and instability in patients with traumatic central cord syndrome without evidence of fracture and dislocation. METHODS: The radiological and clinical findings of 23 patients who had undergone surgery between 1996 and 2002 were reviewed retrospectively. All of the patients underwent dynamic motion study and magnetic resonance (MR) imaging after trauma. Neurologic status was evaluated with American Spinal Injury Association motor score pre- and postoperatively and compared with the radiological findings. Anterior decompression and fusion were performed in 12 patients with 1- or 2-level lesions, and posterior decompression was done for 11 cases of multilevel lesions. RESULTS: Prevertebral HI was found in 17 patients. Among them, instability was revealed in 11 patients. There was significant correlation between prevertebral HI and instability (P = .014). Cord compression was found in varying degrees in all patients on MR imaging. Intramedullary high-signal intensity was found preoperatively in 19 (83%) of 23 patients, and it was revealed at the most compressed level of the spinal cord in all cases. The neurologic level was consistent with the level of instability (100%), IMHSI (95%), and cord compression (87%). Mean American Spinal Injury Association motor scores in patients with instability were lower than in those without instability (P < .05). CONCLUSIONS: The presence of prevertebral HI, IMHSI, and cord compression influenced the neurologic status of the patients. The instability was significantly associated with poor prognosis for neurologic outcome. Prevertebral HI on T2 MR imaging may be a possible indicator of instability in patients with central cord syndrome after hyperextension injury.

Adult↗
PubMed2006

Heparanase regulates esophageal keratinocyte differentiation through nuclear translocation and heparan sulfate cleavage.

Heparanase is an endo-beta-glucuronidase that specifically cleaves heparan sulfate (HS) chains. Heparanase is involved in the process of metastasis and angiogenesis through the degradation of HS chains of the extracellular matrix and cell surface. Recently, we demonstrated that heparanase was localized in the cell nucleus of normal esophageal epithelium and esophageal cancer, and that its expression was correlated with cell differentiation. However, the nuclear function of heparanase remains unknown. To elucidate the role of heparanase in esophageal epithelial differentiation, primary human esophageal cells were grown in monolayer as well as organotypic cultures, and cell differentiation was induced. Expression of heparanase, HS, involucrin, and p27 was determined by immunostaining and Western blotting. SF4, a novel pharmacological inhibitor, was used to specifically inhibit heparanase activity. Upon esophageal cell differentiation, heparanase was translocated from the cytoplasm to the nucleus. Such translocation of heparanase appeared to be associated with the degradation of HS chains in the nucleus and changes in the expression of keratinocyte differentiation markers such as p27 and involucrin, whose induction was inhibited by SF4. Furthermore, these in vitro observations agreed with the expression pattern of heparanase, HS, involucrin, cytokeratin 13, and p27 in normal esophageal epithelium. Nuclear translocation of heparanase and its catalytic cleavage of HS may play a critical role in the differentiation of esophageal epithelial cells. Our study provides a novel insight into the role of heparanase in an essential differentiation process.

Blotting, Western↗
PubMed2006

Capsaicin, transient receptor potential (TRP) protein subfamilies and the particular relationship between capsaicin receptors and small primary sensory neurons.

A number of subfamilies of the capsaicin receptor, collectively called TRP, have been reported since the discovery of vanilloid receptor 1 (VR1). The term 'TRP' is derived from 'transient receptor potential', which means the transient and rapid defect of reaction following long stimulation with light in the photoreceptor cells of mutant Drosophila. The common features of TRP family members are the centrally situated six transmembrane domain, in which an ion channel is located, three to four ankirin repeats at the N-terminus and a TRP domain comprising 25 amino acids at the C-terminus. The TRP family members are present in animals, including invertebrates and vertebrates, and in the cells in various tissues in individual animals. During evolution, the original TRP seems to have acquired a wide variety of functions related to sensing the inner or outer environment (e.g. to sensing light (Drosophila), osmolarity, protons, temperature, ligands and mechanical force). In mammals, the TRPV subfamily is exclusively expressed in small- to medium-sized primary sensory neurons that also co-express some chemical markers (i.e. isolectin B4 (IB4), fluoride-resistant acid phosphatase (FRAP), the P2X3 purinoceptor (a receptor provoked by ATP-induced nociception) and Ret, a glial cell line-derived neurotrophic factor receptor). There is a paradox in that regardless of the marked or complete loss of noxious, small sensory neurons (polymodal nociceptors) in mice treated with capsaicin during the neonatal period, as well as in VR1 (TRPV1)-deficient knock-out mice, the responses to noxious heat are normal. Regarding the paradox in mice treated with capsaicin as neonates, our explanation is that although capsaicin probably reduces the number of a subgroup of small neurons (IB4-, VR1+), the remaining IB4+ (VR1-) neurons can sense noxious heat normally. One working hypothesis is that mice lacking TRPV1/2 can sense noxious heat under normal conditions, presumably via another still unknown pathway, and TRPV1 has been suggested to be involved in noxious heat transduction under pathological conditions, such as inflammation and tissue injury. Further studies will be required to clarify these complexities. Mice treated with capsaicin as neonates would provide a model to investigate the above paradoxes, as would TRPV1-knock-out mice, although different mechanisms may be operating in the two models.

Animals↗