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Biomedical subjects

J Han

Publications and source records attributed to J Han.

At least 163 records · Page 9Linked to original sources
PubMed1999

Transforming growth factor-beta induces collagenase-3 expression by human gingival fibroblasts via p38 mitogen-activated protein kinase.

Human collagenase-3 (matrix metalloproteinase 13 (MMP-13)) is characterized by exceptionally wide substrate specificity and restricted tissue specific expression. Human skin fibroblasts in culture express MMP-13 only when they are in three-dimensional collagen (Ravanti, L., Heino, J., López-Otín, C., and Kähäri. V.-M. (1999) J. Biol. Chem. 274, 2446-2455). Here we show that MMP-13 is expressed by fibroblasts during normal human gingival wound repair. Expression of MMP-13 by human gingival fibroblasts cultured in monolayer or in collagen gel was induced by transforming growth factor-beta1 (TGF-beta1). Treatment of gingival fibroblasts with TGF-beta1 activated two distinct mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase 1/2 (ERK1/2) in 15 min and p38 MAPK in 1 and 2 h. Induction of MMP-13 expression by TGF-beta1 was blocked by SB203580, a specific inhibitor of p38 MAPK, but not by PD98059, a selective inhibitor of ERK1/2 activation. Adenovirus-mediated expression of dominant negative p38alpha and c-Jun potently inhibited induction of MMP-13 expression in gingival fibroblasts by TGF-beta1. Infection of gingival fibroblasts with adenovirus for constitutively active MEK1 resulted in activation of ERK1/2 and JNK1 and up-regulation of collagenase-1 (MMP-1) and stromelysin-1 (MMP-3) production but did not induce MMP-13 expression. In addition, activation of p38 MAPK by constitutively active MKK6b or MKK3b was not sufficient to induce MMP-13 expression. These results show that TGF-beta-elicited induction of MMP-13 expression by gingival fibroblasts is dependent on the activity of p38 MAPK and the presence of functional AP-1 dimers. These observations demonstrate a fundamental difference in the regulation of collagenolytic capacity between gingival and dermal fibroblasts and suggest a role for MMP-13 in rapid turnover of collagenous matrix during repair of gingival wounds, which heal with minimal scarring.

Cells, Cultured↗
PubMed1999

Axin forms a complex with MEKK1 and activates c-Jun NH(2)-terminal kinase/stress-activated protein kinase through domains distinct from Wnt signaling.

Axin negatively regulates the Wnt pathway during axis formation and plays a central role in cell growth control and tumorigenesis. We found that Axin also serves as a scaffold protein for mitogen-activated protein kinase activation and further determined the structural requirement for this activation. Overexpression of Axin in 293T cells leads to differential activation of mitogen-activated protein kinases, with robust induction for c-Jun NH(2)-terminal kinase (JNK)/stress-activated protein kinase, moderate induction for p38, and negligible induction for extracellular signal-regulated kinase. Axin forms a complex with MEKK1 through a novel domain that we term MEKK1-interacting domain. MKK4 and MKK7, which act downstream of MEKK1, are also involved in Axin-mediated JNK activation. Domains essential in Wnt signaling, i. e. binding sites for adenomatous polyposis coli, glycogen synthase kinase-3beta, and beta-catenin, are not required for JNK activation, suggesting distinct domain utilization between the Wnt pathway and JNK signal transduction. Dimerization/oligomerization of Axin through its C terminus is required for JNK activation, although MEKK1 is capable of binding C terminus-deleted monomeric Axin. Furthermore, Axin without the MEKK1-interacting domain has a dominant-negative effect on JNK activation by wild-type Axin. Our results suggest that Axin, in addition to its function in the Wnt pathway, may play a dual role in cells through its activation of JNK/stress-activated protein kinase signaling cascade.

Axin Protein↗
PubMed1999

p38 mitogen-activated protein kinase is involved in Fas ligand expression.

p38 mitogen-activated protein kinase (MAPK) is activated by T cell receptor engagement. Here we showed that T cell receptor activated p38alpha but not p38delta. Inhibition of p38alpha by the specific inhibitor SB 203580 prevented activation-induced cell death in T cells. SB 203580 had no effect on Fas-initiated apoptosis. Instead, SB 203580 preferentially inhibited activation-induced Fas ligand (FasL) expression. The inhibition on FasL expression by SB 203580 was correlated with the suppression on the FasL promoter activation. Overexpression of active MAPK kinase 3b, the activator of p38 MAPK, led to activation of FasL promoter and induction of FasL transcripts in T cells. Stress stimulation of T cells by anisomycin also induced FasL expression in a p38 MAPK-dependent manner. The induction of FasL expression in nonlymphoid cells such as 293T also required activation of p38 MAPK. Our results suggest that p38 MAPK is essential for FasL expression.

Apoptosis↗
PubMed1999

Selective activation of p38alpha and p38gamma by hypoxia. Role in regulation of cyclin D1 by hypoxia in PC12 cells.

Hypoxic/ischemic trauma is a primary factor in the pathology of a multitude of disease states. The effects of hypoxia on the stress- and mitogen-activated protein kinase signaling pathways were studied in PC12 cells. Exposure to moderate hypoxia (5% O(2)) progressively stimulated phosphorylation and activation of p38gamma in particular, and also p38alpha, two stress-activated protein kinases. In contrast, hypoxia had no effect on enzyme activity of p38beta, p38beta(2), p38delta, or on c-Jun N-terminal kinase, another stress-activated protein kinase. Prolonged hypoxia also induced phosphorylation and activation of p42/p44 mitogen-activated protein kinase, although this activation was modest compared with nerve growth factor- and ultraviolet light-induced activation. Hypoxia also dramatically down-regulated immunoreactivity of cyclin D1, a gene that is known to be regulated negatively by p38 at the level of gene expression (Lavoie, J. N., L'Allemain, G., Brunet, A., Muller, R., and Pouyssegur, J. (1996) J. Biol. Chem. 271, 20608-20616). This effect was partially blocked by SB203580, an inhibitor of p38alpha but not p38gamma. Overexpression of a kinase-inactive form of p38gamma was also able to reverse in part the effect of hypoxia on cyclin D1 levels, suggesting that p38alpha and p38gamma converge to regulate cyclin D1 during hypoxia. These studies demonstrate that an extremely typical physiological stress (hypoxia) causes selective activation of specific p38 signaling elements; and they also identify a downstream target of these pathways.

Animals↗
PubMed1999

Cell stress and MKK6b-mediated p38 MAP kinase activation inhibit tumor necrosis factor-induced IkappaB phosphorylation and NF-kappaB activation.

Tumor necrosis factor (TNF) exerts many actions through activation of the transcription factor NF-kappaB. NF-kappaB is sequestered in the cytosol by an inhibitory subunit IkappaB, which is inducibly phosphorylated by an IkappaB kinase complex and subsequently degraded. Sodium salicylate (NaSal) can block NF-kappaB activation by inhibiting IkappaBalpha phosphorylation. Recently, we used the specific p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 to demonstrate that inhibition of TNF-induced IkappaBalpha phosphorylation requires NaSal-induced p38 activation. We demonstrate that NaSal similarly inhibits TNF-induced IkappaBbeta degradation in a p38-dependent manner. To further examine the role of p38, we determined whether other agents that activate p38 can block TNF-induced IkappaB phosphorylation and degradation. Sorbitol, H(2)O(2), and arsenite each blocked IkappaBalpha phosphorylation induced by TNF, and SB203580 reversed the inhibitory effects of sorbitol and H(2)O(2), but not arsenite. In addition, sorbitol and H(2)O(2) blocked TNF-induced but not interleukin-1-induced IkappaBalpha phosphorylation, whereas arsenite inhibited IkappaBalpha phosphorylation induced by TNF and interleukin-1. Transient expression of MAP kinase kinase (MKK) 6b(E), a constitutive activator of p38, reduced both TNF-induced phosphorylation of IkappaBalpha and NF-kappaB-dependent reporter activity. However, MKK7(D), a constitutive activator of c-Jun N-terminal kinases, failed to inhibit these TNF actions. Thus, sustained p38 activation by various stimuli inhibits TNF-induced IkappaB phosphorylation and NF-kappaB activation.

Animals↗
PubMed1999

RGS16 attenuates galphaq-dependent p38 mitogen-activated protein kinase activation by platelet-activating factor.

The large gene family encoding the regulators of G protein signaling (RGS) proteins has been implicated in the fine tuning of a variety of cellular events in response to G protein-coupled receptor activation. Several studies have shown that the RGS proteins can attenuate G protein-activated extracellular signal-regulated kinase (ERK) group of mitogen-activated protein kinases. We demonstrate herein that the production of inositol trisphosphate and the activation of the p38 group of mitogen-activated protein kinases by the G protein-coupled platelet-activating factor (PAF) receptor was attenuated by RGS16 in both CHO cells transiently and stably expressing RGS16. The inhibition was not observed with RGS2, RGS5, and a functionally defective form of RGS16, RGS16(R169S/F170C). The PAF-induced p38 and ERK pathways appeared to be preferentially regulated by RGS16 and RGS1, respectively. Overexpression of a constitutively active form of Galpha11 (Galpha11Q209L) prevented the RGS16-mediated attenuation of p38 activity, suggesting that Galphaq/11 is involved in PAF activation of p38. The Galphaq/11 involvement is further supported by the observation that p38 activation by PAF was pertussis toxin-insensitive. These results demonstrate for the first time that apart from ERK, p38 activation by a G protein-coupled receptor can be attenuated by an RGS protein and provide further evidence for the specificity of RGS function in G protein signaling pathways.

Animals↗
PubMed1999

Cloning and characterization of RLPK, a novel RSK-related protein kinase.

A novel protein kinase whose activity can be stimulated by mitogen in vivo was cloned and characterized. The cDNA of this gene encodes an 802-amino acid protein (termed RLPK) with the highest homology (37% identity) to the two protein kinase families, p90(RSK) and p70(RSK). Like p90(RSR), but not p70(RSK), RLPK also contains two complete nonidentical protein kinase domains. RLPK mRNA is widely expressed in all human tissues examined and is enriched in the brain, heart, and placenta. In HeLa cells, transiently expressed epitope-tagged RLPK can be strongly induced by epidermal growth factor, serum, and phorbol 12-myristate 13-acetate, but only moderately up-regulated by tumor necrosis factor-alpha and other stress-related stimuli. The activity of RLPK stimulated by epidermal growth factor was not inhibited by several known protein kinase C inhibitors nor by rapamycin, a known specific inhibitor for p70(RSK), but could be inhibited by herbimycin A, a tyrosine kinase inhibitor, and partially inhibited by PD98059 or SB203580, inhibitors for the mitogen-activated protein kinase pathways. Recombinant RLPK possesses high phosphorylation activity toward histone 2B and the S6 peptide, RRRLSSLRA. Although purified recombinant RLPK can be phosphorylated by ERK2 and p38alpha in vitro, its activity is not affected by this phosphorylation. Moreover, the treatment of RLPK with acid phosphatase did not reduce its in vitro kinase activity. These data suggest that RLPK is structurally similar to previously isolated RSKs, but its regulatory mechanism may be distinct from either p70(RSK) or p90(RSK)s.

Amino Acid Sequence↗
PubMed1999

Capillary electrophoresis enantioseparation of drugs using beta-cyclodextrin polymer: intramolecular synergistic effect.

Enantiomers of eight basic compounds of pharmaceutical interest were studied by capillary electrophoresis (CE) using a soluble cyclodextrin (CD) polymer and native CD as chiral selectors. The effects of the polymer concentration and the pH of the buffer solution on resolution were examined. It was found that the beta-CD polymer shows higher stereoselectivity than its parent cyclodextrin. Such improvement is due to the structural difference between beta-CD and beta-CD polymer. These results suggested the existence of an intramolecular synergistic effect in CE.

Buffers↗
PubMed1999

Inhibitors of mitochondrial respiration, iron (II), and hydroxyl radical evoke release and extracellular hydrolysis of glutathione in rat striatum and substantia nigra: potential implications to Parkinson's disease.

In this investigation, microdialysis has been used to study the effects of 1-methyl-4-phenylpyridinium (MPP+), an inhibitor of mitochondrial complex I and alpha-ketoglutarate dehydrogenase and the active metabolite of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), on extracellular concentrations of glutathione (GSH) and cysteine (CySH) in the rat striatum and substantia nigra (SN). During perfusion of a neurotoxic concentration of MPP+ (2.5 mM) into the rat striatum or SN, extracellular concentrations of GSH and CySH remain at basal levels (both approximately 2 microM). However, when the perfusion is discontinued, a massive but transient release of GSH occurs, peaking at 5,000% of basal levels in the striatum and 2,000% of basal levels in the SN. The release of GSH is followed by a slightly delayed and smaller elevation of extracellular concentrations of CySH that can be blocked by the gamma-glutamyl transpeptidase (gamma-GT) inhibitor acivicin. Low-molecular-weight iron and extracellular hydroxyl radical (OH*) have been implicated as participants in the mechanism underlying the dopaminergic neurotoxicity of MPTP/MPP+. During perfusion of Fe2+ (OH*) into the rat striatum and SN, extracellular levels of GSH also remain at basal levels. When perfusions of Fe2+ are discontinued, a massive transient release of GSH occurs followed by a delayed, small, but progressive elevation of extracellular CySH level that again can be blocked by acivicin. Previous investigators have noted that extracellular concentrations of the excitatory/excitotoxic amino acid glutamate increase dramatically when perfusions of neurotoxic concentrations of MPP+ are discontinued. This observation and the fact that MPTP/MPP+ causes the loss of nigrostriatal GSH without corresponding increases of glutathione disulfide (GSSG) and the results of the present investigation suggest that the release and gamma-GT/dipeptidase-mediated hydrolysis of GSH to glutamate, glycine, and CySH may be important factors involved with the degeneration of dopamine neurons. It is interesting that a very early event in the pathogenesis of Parkinson's disease is a massive loss of GSH in the SN pars compacta that is not accompanied by corresponding increases of GSSG levels. Based on the results of this and prior investigations, a new hypothesis is proposed that might contribute to an understanding of the mechanisms that underlie the degeneration of dopamine neurons evoked by MPTP/MPP+, other agents that impair neuronal energy metabolism, and Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1999

Biomechanical evaluation of wrist motor tendons after fractures of the distal radius.

We conducted a biomechanical study of changes in parameters of wrist motor tendons in fractures of the distal radius in 7 cadaveric extremities. Extra-articular distal radius fractures were simulated by distal radius osteotomy and fracture angulation was maintained by external fixators. Eight positions of the distal radius fractures were studied: dorsal angulation of 10 degrees, 20 degrees, 30 degrees, and 40 degrees and radial angulation of 5 degrees, 10 degrees, 15 degrees, and 20 degrees. Dorsal and radial angulation of the fractures were measured with respect to the shaft of the radius. Excursions of 5 principal wrist motor tendons extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris were recorded simultaneously with wrist joint angulation using a computer-assisted recording system. Data were collected from intact wrists and from wrists with fractures at each of 8 positions of angulation during wrist flexion and extension and radical and ulnar deviation. Moment arm of the wrist motor tendons was derived from tendon excursion and joint angulation. The results demonstrated that excursions and moment arms of principal wrist motor tendons are significantly affected by dorsal and radial angulation of distal radius fractures. Amplitude of changes in moment arms increased as the deformities became more severe. Statistical analysis revealed that dorsal angulation of 10 degrees or more significantly affected moment arms of all the prime wrist motors. Dorsal angulation of 30 degrees or 40 degrees changed the moment arms greatly. Radial angulation of 5 degrees did not affect moment arms of the tendons and angulation over 10 degrees had a statistically significant effect on the tendons. We conclude that deformities of distal radius fractures have a significant influence on the biomechanics of the wrist motors.

Aged↗
PubMed1999

Ciliary activity in differentiating and reactivated human respiratory epithelial cells.

OBJECTIVE: Experimental studies of mucociliary clearance, especially those involving drug effects, suffer from the difficulty of determining whether drugs act directly on ciliary motility or whether their effects are indirect, acting via changes in cell metabolism, viscous load, or alternative mechanisms. The present study provides a solution to this problem by comparing the motile characteristics of ciliated cells that have differentiated in primary cell culture with those of demembranated cilia reactivated with MgATP. METHODS: Human respiratory epithelial cells (REC) were dissociated from trachea, bronchus, nasal polyps, or turbinates and then placed in a dissociated cell culture system. Thirty-three percent of the dissociated cells contain beating cilia. Following 1 week in culture, the REC dedifferentiated, but then redifferentiated within 96 hours after they were brought to an air interface. RESULTS: The cilia on such cells beat with planar waves consisting of power and recovery strokes. Beat frequencies at 20 degrees C were 15+/-2.3 Hz. Ciliary beating often was coordinated both within and between cells with a defined antilaeoplectic pattern of coordination. Either fresh or cultured cells could be demembranated with Triton X-100 and reactivated with MgATP. The activity of these reactivated models was equivalent to those observed in living cells. CONCLUSION: The authors have demonstrated that ciliary beat frequency of demembranated human respiratory epithelial cells can be modulated by MgATP and can be adjusted to the same level of activity as measured in living cells. This allows them to selectively test whether a drug's effects on mucociliary transport are the result of direct interactions with the ciliary apparatus or are produced through other indirect mechanisms.

Adenosine Triphosphate↗
PubMed1999

Regulation of the MEF2 family of transcription factors by p38.

Members of the MEF2 family of transcription factors bind as homo- and heterodimers to the MEF2 site found in the promoter regions of numerous muscle-specific, growth- or stress-induced genes. We showed previously that the transactivation activity of MEF2C is stimulated by p38 mitogen-activated protein (MAP) kinase. In this study, we examined the potential role of the p38 MAP kinase pathway in regulating the other MEF2 family members. We found that MEF2A, but not MEF2B or MEF2D, is a substrate for p38. Among the four p38 group members, p38 is the most potent kinase for MEF2A. Threonines 312 and 319 within the transcription activation domain of MEF2A are the regulatory sites phosphorylated by p38. Phosphorylation of MEF2A in a MEF2A-MEF2D heterodimer enhances MEF2-dependent gene expression. These results demonstrate that the MAP kinase signaling pathway can discriminate between different MEF2 isoforms and can regulate MEF2-dependent genes through posttranslational activation of preexisting MEF2 protein.

Amino Acid Sequence↗
PubMed1999

HDAC4, a human histone deacetylase related to yeast HDA1, is a transcriptional corepressor.

Histone acetylation plays an important role in regulating chromatin structure and thus gene expression. Here we describe the functional characterization of HDAC4, a human histone deacetylase whose C-terminal part displays significant sequence similarity to the deacetylase domain of yeast HDA1. HDAC4 is expressed in various adult human tissues, and its gene is located at chromosome band 2q37. HDAC4 possesses histone deacetylase activity intrinsic to its C-terminal domain. When tethered to a promoter, HDAC4 represses transcription through two independent repression domains, with repression domain 1 consisting of the N-terminal 208 residues and repression domain 2 containing the deacetylase domain. Through a small region located at its N-terminal domain, HDAC4 interacts with the MADS-box transcription factor MEF2C. Furthermore, HDAC4 and MEF2C individually upregulate but together downmodulate c-jun promoter activity. These results suggest that HDAC4 interacts with transcription factors such as MEF2C to negatively regulate gene expression.

Amino Acid Sequence↗
PubMed1999

Mucoepidermoid carcinoma of the tracheobronchial tree: radiographic and CT findings in 12 patients.

PURPOSE: To determine the radiographic and computed tomographic (CT) findings and clinical features of mucoepidermoid carcinoma of the tracheobronchial tree. MATERIALS AND METHODS: Chest radiographic and CT findings and clinical features of 12 histopathologically proved mucoepidermoid carcinomas in 12 consecutive patients (five male, seven female; age range, 9-72 years; mean age, 36 years) were reviewed retrospectively. RESULTS: The tumors were located at the distal trachea (n = 1) or at a main (n = 2), lobar (n = 1), or segmental (n = 8) bronchus. On chest radiographs, the tumors appeared as central masses with post-obstructive pneumonia or peripheral atelectasis in four patients and as solitary pulmonary or endotracheobronchial nodules in eight. At CT, the tumors were all smoothly oval (n = 6) or lobulated (n = 6) in shape (ranging 9-40 mm in diameter), adapting to the branching features of the airways. Punctate calcification within the tumor was seen in six patients. Neither metastasis nor recurrence was seen after the surgical resection (follow-up of 8-103 months; mean, 30 months). CONCLUSION: Mucoepidermoid carcinoma of the tracheobronchial tree, usually located in a segmental bronchus, appears at CT as a smoothly oval or lobulated airway mass. It adapts to the branching features of the airways.

Adolescent↗
PubMed1999

PKC-dependent activation of p46/p54 JNKs during ischemic preconditioning in conscious rabbits.

A conscious rabbit model was used to study the effect of ischemic preconditioning (PC) on stress-activated kinases [c-Jun NH(2)-terminal kinases (JNKs) and p38 mitogen-activated protein kinase (MAPK)] in an environment free of surgical trauma and attending external stress. Ischemic PC (6 cycles of 4-min ischemia/4-min reperfusion) induced significant activation of protein kinase C (PKC)-epsilon in the particulate fraction, which was associated with activation of p46 JNK in the nuclear fraction and p54 JNK in the cytosolic fraction; all of these changes were completely abolised by the PKC inhibitor chelerythrine. Selective enhancement of PKC-epsilon activity in adult rabbit cardiac myocytes resulted in enhanced activity of p46/p54 JNKs, providing direct in vitro evidence that PKC-epsilon is coupled to both kinases. Studies in rabbits showed that the activation of p46 JNK occurred during ischemia, whereas that of p54 JNK occurred after reperfusion. A single 4-min period of ischemia induced a robust activation of the p38 MAPK cascade, which, however, was attenuated after 5 min of reperfusion and disappeared after six cycles of 4-min ischemia/reperfusion. Overexpression of PKC-epsilon in cardiac myocytes failed to increase the p38 MAPK activity. These results demonstrate that ischemic PC activates p46 and p54 JNKs via a PKC-epsilon-dependent signaling pathway and that there are important differences between p46 and p54 JNKs with respect to the subcellular compartment (cytosolic vs. nuclear) and the mechanism (ischemia vs. reperfusion) of their activation after ischemic PC.

Alkaloids↗