Biomedical subjects

J Han

Publications and source records attributed to J Han.

At least 19 recordsLinked to original sources

PubMed2001

Physical properties and stability of two emulsion formulations of propofol.

We have compared the physical properties of two commercial emulsion formulations of the intravenous anaesthetic propofol, (Diprivan, AstraZeneca, and Propofol Intravenous Emulsion, Gensia Sicor Pharmaceuticals) which appear to differ primarily in the additive content and formulation pH. Diprivan contains disodium edetate and has a pH of 7-8.5, while the Gensia product contains sodium metabisulphite and is formulated to a pH of 4.5-6.4. The average zeta potential of Diprivan at pH 8 was -50 mV while that of the Gensia product at pH 4-5 was -40 mV. This information suggests that the physical stability of Propofol Intravenous Emulsion should be lower than that of Diprivan. Three random batches of both products were subjected to a range of stability tests, including shaking, thermal cycling, and freeze-thaw cycling, and the emulsion droplet size distribution was then assessed by dynamic light scattering, light diffraction, and electrical and optical zone sensing. Both emulsions initially showed narrow submicrometre particle size distributions. An increased level of droplets larger than 5 microm could be detected in Propofol Intravenous Emulsion after as little as 4 h shaking (300 strokes/min at room temperature) and visible free oil could be detected after 8-12 h shaking. In contrast, Diprivan showed no increase in the large droplet count after shaking for times up to 16 h. A similar difference in the emulsions was found after one freeze-thaw cycle, with Propofol Intravenous Emulsion exhibiting extensive coalescence, while that of Diprivan was at the limits of detection. We conclude that these two products have different physical stability characteristics, and that this may in part be due to the reduced zeta potential in Propofol Intravenous Emulsion compared to that of Diprivan.

Anesthetics, Intravenous↗

PubMed2001

9-cis-Retinoic acid represses transcription of the gonadotropin-releasing hormone (GnRH) gene via proximal promoter region that is distinct from all-trans-retinoic acid response element.

We previously reported an enhancing effect of all-trans-retinoic acid (all-trans-RA) on gonadotropin-releasing hormone (GnRH) gene transcription via distal promoter elements of the rat GnRH gene. The present study examined the effects of another biologically active retinoid, 9-cis-retinoic acid (9-cis-RA), on GnRH transcription in GT1-1 cells. Similar to the action of all-trans-RA, 9-cis-RA significantly induced the luciferase activity of the strong retinoic acid response element (RARE) reporter construct, 3X beta RARE-Luc, by about 60-fold, indicating that GT1-1 cells are also responsive to 9-cis-RA. In contrast to the stimulatory effect of all-trans-RA on GnRH transcription, 9-cis-RA inhibited the GnRH promoter activity in a dose- and time-dependent manner. Significant inhibition by 9-cis-RA required at least an 18 h treatment and a further decrease of GnRH promoter-driven luciferase activity was observed up to 48 h of incubation. Accordingly, GnRH mRNA levels were decreased by 9-cis-RA treatment in a similar dose- and time-related manner, indicating that mouse GnRH expression is also negatively regulated by 9-cis-RA. Transient transfections of serial deletion constructs of the rat GnRH promoter revealed that the --230/--110 sequence of the rat GnRH promoter is responsible for 9-cis-RA-induced inhibition of GnRH transcription. Within this region, however, no consensus retinoid X receptor response element was found. To gain insights into the role of retinoid X receptors (RXRs) in GnRH expression, we examined the effects of RXR overexpression on GnRH transcriptional activity. Interestingly, co-transfection of RXR overexpression vectors significantly increased the GnRH promoter-driven luciferase activity, while treatment with 9-cis-RA not only nullified the enhancing effect of RXR overexpression but also decreased the basal GnRH promoter-driven luciferase activity by 50% compared to vehicle-treated controls. This implies that RXRs in the absence of its cognate ligand 9-cis-RA contribute to the maintenance of basal GnRH gene transcription. Northern blot analysis revealed that 9-cis-RA, but not all-trans-RA, down-regulated RXR beta expression in GT1-1 cells, suggesting that one possible mechanism of 9-cis-RA-induced repression involves down-regulation of RXR expression. In conclusion, the present study clearly demonstrates that 9-cis-RA is a negative regulator of GnRH gene expression in immortalized GnRH neurons.

Alitretinoin↗

PubMed2001

Analysis of exonic splicing enhancers in the mouse gonadotropin-releasing hormone (GnRH) gene.

We have previously reported that efficient removal of the first intron (intron A) of gonadotropin-releasing hormone (GnRH) pre-mRNA is the prerequisite event for post-transcriptional regulation. In the present study, using an in vitro HeLa splicing system, we examined the enhancing activities of exonic elements for GnRH pre-mRNA splicing. While not excised by exon 2 alone, intron A was efficiently excised when exon 3 and/or exon 4 was combined with exon 2, suggesting the presence of exonic splicing enhancers (ESEs) in exons 3 and 4. Purine-rich sequences located in the border of exons 2 and 3 (denoted ESE3) and in exon 4 (ESE4) revealed strong splicing enhancing activities. Mutation in ESE3 decreased pre-mRNA splicing, while mutation in purine-rich sequences in exon 2 did not. We further analyzed the functional activity of ESE4 by mutations or deletions of the ESE4 sequence that consists of three purine-repeats separated by two spacers and a putative hairpin constructing sequence. An UV cross-linking assay using the RNA sequence of ESE4 examined the presence of ESE4-specific binding proteins in the nuclear extracts from GT1 hypothalamic GnRH neurons. Collectively, this study indicates that a sequence context of ESE4 and its binding proteins may be crucially involved in enhanced GnRH pre-mRNA splicing. However, it should be further clarified as to which splicing factor(s) is responsible for ESE4-dependent GnRH pre-mRNA splicing.

Animals↗

PubMed2001

A high-resolution map of human chromosome 12.

Our sequence-tagged site-content map of chromosome 12 is now integrated with the whole-genome fingerprinting effort. It provides accurate and nearly complete bacterial clone coverage of chromosome 12. We propose that this integrated mapping protocol serves as a model for constructing physical maps for entire genomes.

Chromosomes, Artificial, Bacterial↗

PubMed2001

Tumor necrosis factor markers show sex-influenced association with rheumatoid arthritis.

OBJECTIVE: The observation that not all shared-epitope genotypes confer the same risk suggests that a second HLA-region locus may confer risk. Tumor necrosis factor alpha (TNFgamma) is a possible candidate. We examined TNFalpha for sex influences on HLA-associated risk for rheumatoid arthritis (RA). METHODS: DRB1 and TNF microsatellite typing of 297 Caucasian RA patients (132 men, 165 women) and 267 Caucasian controls was performed. RESULTS: The TNFab microsatellite haplotype distribution differed among the male RA, female RA, and control groups (P < 0.01); the difference was largely an excess of TNFa2b1 haplotypes in the male RA group. However, this did not simply reflect an excess of shared-epitope haplotypes bearing TNFa2b1. In RA, not all shared-epitope-bearing haplotypes had the same TNFab. The *0401-bearing haplotypes commonly had TNFa6b5, TNFa2b1, TNFa10b4, and TNFa11b4, while the *0404-bearing haplotypes had TNFa11b4. In the female RA group, TNFa2b1 was most often on *0401-bearing haplotypes. In the male RA group, there was a surprise: TNFa2b1 was often on HLA haplotypes without shared-epitope DRB1 alleles. To estimate the relative strength of associated HLA markers, we performed logistic regression analyses stratified by sex and controlling for a potential confounder, age at disease onset. Among women, TNFa2b3 favored RA (odds ratio 1.932, P < 0.05) while TNFa6b5 was protective (odds ratio 0.522, P < 0.05). Among males, TNFa2b1 and TNFa11b4 conferred elevated odds ratios (2.58 and 1.681, respectively, P < 0.05). However, the odds ratios for TNFa2b1 in men and TNFa2b3 in women were generally well below those for RA-associated DRB1 markers (for example, DRB1*0401 3.553 in male RA patients and 6.991 in female RA patients). CONCLUSION: Certain TNFab-bearing HLA haplotypes modify RA risk in a manner influenced by sex but independent of DRB1, particularly TNFa2b1 in men.

Alleles↗

PubMed2001

The effect of genotype on sensitivity to electroacupuncture analgesia.

Individual differences in sensitivity to pain and analgesia are well appreciated, and increasing evidence has pointed towards a role of inherited genetic factors in explaining some proportion of such variability. It has long been known by practitioners of acupuncture, an ancient modality of analgesia, that some patients are 'responders' and others 'non-responders.' The present research was aimed at defining the inherited genetic influence on acupuncture analgesia in the mouse, using 10 common inbred strains. Two pairs of metallic needles were inserted into acupoints ST 36 and SP 6, fixed in situ and then connected to the output channel of an electric pulse generator. Electroacupuncture (EA) parameters were set as constant current output (intensity: 1.0-1.5-2.0 mA, 10 min each; frequency: 2 or 100 Hz) with alteration of a positive and negative square wave, 0.3 ms in pulse width. Tail-flick latencies evoked by radiant heat were measured before, during and after EA stimulation. Narrow-sense heritability estimates of 2 and 100 Hz EA were 0.37 and 0.16, respectively. We found that the C57BL/10 strain was the most sensitive, and the SM strain was the least sensitive to both 2 and 100 Hz EA. However, the relative sensitivities of other strains to these two EA frequencies suggested some genetic dissociation between them as well. These results demonstrate a role of inherited genetic factors in EA sensitivity in the mouse, although the low-to-moderate heritability estimates suggest that environmental factors may be of greater importance in predicting who will benefit from this analgesic modality.

Acupuncture Analgesia↗

PubMed2001

Malignant thymic epithelial tumors: CT-pathologic correlation.

OBJECTIVE: The purpose of our study was to describe and compare the CT and pathologic findings of atypical thymoma and thymic carcinoma. MATERIALS AND METHODS: Twenty-seven consecutive patients (14 men, 13 women ranging in age from 22 to 77 years [mean age, 52 years]) with pathologically proven atypical thymoma (n = 9) and thymic carcinoma (n = 18) constituted the study population. The chest CT findings in each of the 27 patients were reviewed retrospectively in consensus by two chest radiologists. These findings were correlated with pathologic findings. RESULTS: The tumors were located in the anterior mediastinum, and most tumors had a lobulated margin (24/27, 89%). Atypical thymomas were significantly smaller (mean, 4.7 cm) than thymic carcinomas (mean, 7.2 cm) (p = 0.041) on CT. The findings of invasion of the great vessels, lymph node enlargement, extrathymic metastases, and phrenic nerve palsy were seen only in patients with thymic carcinoma. The frequencies of necrosis, intratumoral calcification, pleural effusion, pleural implants, pericardial effusion, and obliteration of the mediastinal fat plane were not significantly different between atypical thymomas and thymic carcinomas (p > 0.05). Various histologic subtypes were included in thymic carcinoma. The tumor necrosis and calcification seen on CT were confirmed at pathologic examination. CONCLUSION: When a large thymic tumor appears with invasion of the great vessels, lymph node enlargement, phrenic nerve palsy, or extrathymic metastases on CT, thymic carcinoma rather than atypical thymoma should be considered.

Adult↗

PubMed2001

Development of cataractous macrophthalmia in mice expressing an active MEK1 in the lens.

PURPOSE: To characterize the extracellular signal-regulated kinase (ERK) pathway in the lens and to try to understand how this pathway contributes to lens function and cataractogenesis. METHODS: The members of the ERK pathway in the lens were examined by Western blotting, immunohistochemical staining, and kinase assay. A gain-of-function approach was used to perturb the ERK pathway in the lenses of transgenic mice via expression of a constitutively active mutant of the mitogen-activated protein kinase kinase 1 (MEK1(E)), the direct upstream kinase of the ERK1 and ERK2 kinases, under the alphaA-crystallin promoter. RESULTS: The presence of an active ERK pathway was found in lens epithelial cells and in differentiating fibers. Transgenic mice that expressed MEK1(E) developed postnatal cataracts as well as macrophthalmia. Distinct morphologic alterations, such as lens enlargement, swelling fiber cells, enlarged extracellular space, and vacuole formation, were observed in the lenses of these transgenic mice. A significant increase in the glucose transporter 1 (GLUT1) level, as well as in the glucose level, was detected in the lens. CONCLUSIONS: The MAP kinase pathway is involved in the regulation of glucose metabolism and balance in the mouse lens. Moreover, the alteration of MAP kinase activity in the lens is sufficient to cause cataract formation with enlarged extracellular space and vacuoles in the differentiating fibers. This transgenic mouse may provide a useful model for understanding the mechanism(s) for some aspects of human cataracts.

Animals↗

PubMed2000

The p38 pathway provides negative feedback for Ras proliferative signaling.

Ras activates three mitogen-activated protein kinases (MAPKs) including ERK, JNK, and p38. Whereas the essential roles of ERK and JNK in Ras signaling has been established, the contribution of p38 remains unclear. Here we demonstrate that the p38 pathway functions as a negative regulator of Ras proliferative signaling via a feedback mechanism. Oncogenic Ras activated p38 and two p38-activated protein kinases, MAPK-activated protein kinase 2 (MK2) and p38-related/activated protein kinase (PRAK). MK2 and PRAK in turn suppressed Ras-induced gene expression and cell proliferation, whereas two mutant PRAKs, unresponsive to Ras, had little effect. Moreover, the constitutive p38 activator MKK6 also suppressed Ras activity in a p38-dependent manner whereas arsenite, a potent chemical inducer of p38, inhibited proliferation only in a tumor cell line that required Ras activity. MEK was required for Ras stimulation of the p38 pathway. The p38 pathway inhibited Ras activity by blocking activation of JNK, without effect upon ERK, as evidenced by the fact that PRAK-mediated suppression of Ras-induced cell proliferation was reversed by coexpression of JNKK2 or JNK1. These studies thus establish a negative feedback mechanism by which Ras proliferative activity is regulated via signaling integrations of MAPK pathways.

3T3 Cells↗

PubMed2000

Induction of prostaglandin endoperoxide synthase 2 by mitogen-activated protein kinase cascades.

Prostaglandin endoperoxide synthase (PGHS) catalyses the rate-limiting step in the formation of prostaglandin and thromboxane eicosanoids from arachidonic acid released by phospholipase A(2). Two forms of PGHS exist, PGHS-1 and PGHS-2. PGHS-2, normally absent from cells, is rapidly expressed in response to a wide variety of stimuli and has been implicated in the pathogenesis of colon cancer and several inflammatory diseases. The three principal mitogen-activated protein kinase (MAPK) pathways are the extracellular signal-regulated protein kinase (ERK), the c-Jun N-terminal kinase (JNK) cascade and the p38-MAPK cascade. The present study was undertaken to investigate the putative involvement of the MAPK cascades in PGHS-2 induction. The potential role of ERK in PGHS-2 up-regulation was assessed by using cell lines expressing, both stably and after adenoviral infection, constitutively active forms of its upstream activator MAPK/ERK kinase (MEK1). The possible involvement of JNK and p38-MAPK in positively modulating PGHS-2 transcription was investigated by using adenovirus-mediated transfer of active forms of their respective specific upstream kinases, mitogen-activated protein kinase kinase (MKK) 7 and MKK3/MKK6. ERK activation promoted the induction of PGHS-2 mRNA and protein. Similarly, activation of JNK by Ad-MKK7D and p38-MAPK by Ad-MKK3bE/Ad-MKK6bE resulted in the increased expression of PGHS-2. These results provide evidence that activation of all three of the major mammalian MAPK leads to the induction of PGHS-2 mRNA and protein. Because PGHS-2 is up-regulated by a diverse range of stimuli, both mitogenic and stress-evoking, these results provide evidence that the convergence point of these stimuli could be the activation of one or more MAPK cascade(s).

3T3 Cells↗

PubMed2000

Human glioma cell BT325 expresses a proteinase that converts human plasminogen to kringle 1-5-containing fragments.

Angiostatin, a specific angiogenesis inhibitor, is an internal fragment of plasminogen, and can be generated in many systems mediated by different enzymes in vitro. The mechanism of angiostatin generation in vivo has not been well defined. Here we demonstrated that human glioma cell line BT325 can express an enzyme that can convert purified plasminogen to angiostatin-like fragments with molecular masses of 65, 60, and 58 kDa, respectively. These fragments have an identical N-terminal as KVYLS, which starts from Lys(98) of the plasminogen precusor. According to their molecular mass, the three fragments should comprise kringle domain 1 to kringle domain 5 (kringle 1-5). The proteolytic fragments obtained as above can inhibit the growth of bovine aortic endothelial (BAE) cells specifically. The proteolysis process can be completely inhibited by serine proteinase inhibitors, and partially inhibited by EDTA. The molecular weight of the peptide, which contains an enzymatic activity responsible for the proteolysis, was 13 kD determined by gel filtration and SDS-PAGE. The present data suggest that glioma cell BT325 can produce a novel proteinase to generate kringle 1-5 of plasminogen as an angiogenesis inhibitor.

Amino Acid Sequence↗

PubMed2000

Activation of extracellular signal-regulated kinase 1/2 inhibits type I collagen expression by human skin fibroblasts.

Treatment with the lipid second messenger, ceramide, activates extracellular signal-regulated kinase-1/2 (ERK1/2), c-Jun N-terminal kinase, and p38 in human skin fibroblasts and induces their collagenase-1 expression (Reunanen, N., Westermarck, J., Häkkinen, L., Holmström, T. H., Elo, I., Eriksson, J. E., and Kähäri, V.-M. (1998) J. Biol. Chem. 273, 5137-5145). Here we show that C(2)-ceramide inhibits expression of type I and III collagen mRNAs in dermal fibroblasts, suppresses proalpha2(I) collagen promoter activity, and reduces stability of type I collagen mRNAs. The down-regulatory effect of C(2)-ceramide on type I collagen mRNA levels was abrogated by protein kinase C inhibitors H7, staurosporine, and Ro-31-8220 and potently inhibited by a combination of MEK1,2 inhibitor PD98059 and p38 inhibitor SB203580. Activation of ERK1/2 by adenovirus-mediated expression of constitutively active MEK1 resulted in marked down-regulation of type I collagen mRNA levels and production in fibroblasts, whereas activation of p38 by constitutively active MAPK kinase-3b and MAPK kinase-6b slightly up-regulated type I collagen expression. These results identify the ERK1/2 signaling cascade as a potent negative regulatory pathway with respect to type I collagen expression in fibroblasts, suggesting that it mediates inhibition of collagen production in response to mitogenic stimulation and transformation.

3T3 Cells↗

PubMed2000

Characterization of active-site residues of the NIa protease from tobacco vein mottling virus.

Nuclear inclusion a (NIa) protease of tobacco vein mottling virus is responsible for the processing of the viral polyprotein into functional proteins. In order to identify the active-site residues of the TVMV NIa protease, the putative active-site residues, His-46, Asp-81 and Cys-151, were mutated individually to generate H46R, H46A, D81E, D81N, C151S, and C151A, and their mutational effects on the proteolytic activities were examined. Proteolytic activity was completely abolished by the mutations of H46R, H46A, D81N, and C151A, suggesting that the three residues are crucial for catalysis. The mutation of D81E decreased kcat marginally by about 4.7-fold and increased Km by about 8-fold, suggesting that the aspartic acid at position 81 is important for substrate binding but can be substituted by glutamate without any significant decrease in catalysis. The replacement of Cys-151 by Ser to mimic the catalytic triad of chymotrypsin-like serine protease resulted in the drastic decrease in kcat by about 1,260-fold. This result might be due to the difference of the active-site geometry between the NIa protease and chymotrypsin. The protease exhibited a bell-shaped pH-dependent profile with a maximum activity approximately at pH 8.3 and with the abrupt changes at the respective pKa values of approximately 6.6 and 9.2, implying the involvement of a histidine residue in catalysis. Taken together, these results demonstrate that the three residues, His-46, Asp-81, and Cys-151, play a crucial role in catalysis of the TVMV NIa protease.

Amino Acid Sequence↗

PubMed2000

The effector loop and prenylation site of R-Ras are involved in the regulation of integrin function.

The closely related small GTP-binding proteins H-Ras and R-Ras have opposing effects on the regulation of integrin cell adhesion receptors. To gain insight into the properties of R-Ras with respect to the regulation of integrin function and interactions with downstream effectors we performed an analysis of R-Ras variants containing mutations in the effector binding domain and C-terminal prenylation site. We found that the activation of the downstream effector PI 3-kinase was sensitive to mutations in the effector binding domain, as was the binding to the effectors, Ral-GDS, Raf-1 and the novel effector Nore1. Furthermore, specific mutations in the effector binding loop and C-terminal prenylation motif impaired the ability of R-Ras to regulate integrin function in CHO cells. However, the ability of the R-Ras effector loop mutants to bind, and activate known effectors did not correlate with their ability to regulate integrin function. Thus, the known R-Ras effectors are not critical for regulating integrin activation, at least in CHO cells. Consequently, these studies provide insight into the structural basis of the interactions between R-Ras and its candidate effectors and suggest the existence of novel mechanisms through which this GTPase could regulate cell adhesion.

Amino Acid Sequence↗

PubMed2000

Formulation and in vivo evaluation of omeprazole buccal adhesive tablet.

For the development of omeprazole buccal adhesive tablets, we studied the release and bioavailability of omeprazole delivered by buccal adhesive tablets composed of sodium alginate, hydroxypropylmethylcellulose (HPMC), magnesium oxide and croscarmellose sodium. Croscarmellose sodium enhanced the release of omeprazole from the tablets. The analysis of the release mechanism showed that croscarmellose sodium changed the release profile of omeprazole from first- to zero-order release kinetics by forming porous channels in the tablet matrix. However, it decreased the bioadhesive forces and stability of omeprazole tablets in human saliva. The tablet is composed of omeprazole-sodium alginate-HPMC-magnesium oxide-croscarmellose sodium (20:24:6:50:10 mg). It may be attached to the human cheek without collapse and it enhanced the stability of omeprazole in human saliva for at least 4 h, giving a fast release of omeprazole. The plasma concentration of omeprazole in hamsters increased to reach a maximum of 370 ng/ml at 45 min after buccal administration and remained at the high level of 146-366 ng/ml for 6 h. The buccal bioavailability of omeprazole in hamsters was 13.7+/-3.2%. These results demonstrate that the omeprazole buccal adhesive tablet would be useful to deliver omeprazole which degrades very rapidly in acidic aqueous medium and undergoes hepatic first-pass metabolism after oral administration.

Adhesiveness↗

PubMed2000

European Task Force on Lymphoma project on lymphocyte predominance Hodgkin disease: histologic and immunohistologic analysis of submitted cases reveals 2 types of Hodgkin disease with a nodular growth pattern and abundant lymphocytes.

Paraffin blocks and clinical data from 521 patients with lymphocyte predominance Hodgkin disease (LPHD) diagnosed between 1970 and 1994 were collected from 16 European and United States oncological centers to establish the pathologic and clinical characteristics of a large patient cohort, to determine how frequent T-cell-rich large B-cell lymphoma (TCRLBCL) is among LPHD, and to find differential diagnostic criteria distinguishing between the 2 lymphoma categories. For this purpose, conventionally and immunohistologically stained sections were reviewed by a panel of hematopathologists. The diagnosis of LPHD was confirmed in only 219 of the 388 assessable cases (56.5%). This low confirmation rate was due mainly to the presence of a new variant of classical Hodgkin disease (CHD), which resembled, in terms of nodular growth and lymphocyte-richness, nodular LPHD and, in terms of the immunophenotype of the tumor cells, CHD and was designated nodular lymphocyte-rich CHD (NLRCHD). The nodules of LRCHD consisted-as in nodular LPHD-predominantly of B cells but differed from those present in LPHD in that they represented expanded mantle zones with atrophic germinal centers. Clinically, patients with LPHD and NLRCHD showed similar disease characteristics at presentation but differed in the frequency of multiple relapses and prognosis after relapse. Patients with LPHD and NLRCHD clearly differed from patients with CHD with nodular sclerosis or mixed cellularity, as they presented with an earlier disease stage and infrequent mediastinal involvement. As 97% of the LPHD cases showed a complete or partial nodular growth pattern, their differentiation from TCRLBCL was a rare problem in the present series. (Blood. 2000;96:1889-1899)

Adolescent↗

PubMed2000

First-principles study of Li-intercalated carbon nanotube ropes

We studied Li-intercalated carbon nanotube ropes by first-principles methods. Results show charge transfer between Li and C and small structural deformation due to intercalation. Both the interior of the nanotube and the interstitial space are susceptible for intercalation. The Li intercalation potential of a single-walled nanotube rope is comparable to that of graphite and almost independent of the Li density up to around LiC2, as observed in recent experiments. This density is significantly higher than that of Li-intercalated graphite, making the nanorope a promising candidate for the anode material in battery applications.

Journal Article↗

PubMed2000

Dimerization choices control the ability of axin and dishevelled to activate c-Jun N-terminal kinase/stress-activated protein kinase.

Axin and Dishevelled are two downstream components of the Wnt signaling pathway. Dishevelled is a positive regulator and is placed genetically between Frizzled and glycogen synthase kinase-3beta, whereas Axin is a negative regulator that acts downstream of glycogen synthase kinase-3beta. It is intriguing that they each can activate the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) when expressed in the cell. We set out to address if Axin and Dishevelled are functionally cooperative, antagonistic, or entirely independent, in terms of the JNK activation event. We found that in contrast to Axin, Dvl2 activation of JNK does not require MEKK1, and complex formation between Dvl2 and Axin is independent of Axin-MEKK1 binding. Furthermore, Dvl2-DIX and Dvl2-DeltaDEP proteins deficient for JNK activation can attenuate Axin-activated JNK activity by disrupting Axin dimerization. However, Axin-DeltaMID, Axin-DeltaC, and Axin-CT proteins deficient for JNK activation cannot interfere with Dvl2-activated JNK activity. These results indicate that unlike the strict requirement of homodimerization for Axin function, Dvl2 can activate JNK either as a monomer or homodimer/heterodimer. We suggest that there may be a switch mechanism based on dimerization combinations, that commands cells to activate Wnt signaling or JNK activation, and to turn on specific activators of JNK in response to various environmental cues.

Adaptor Proteins, Signal Transducing↗