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T Konta

Publications and source records attributed to T Konta.

12 recordsLinked to original sources
PubMed2001

Unexpected transcriptional induction of monocyte chemoattractant protein 1 by proteasome inhibition: involvement of the c-Jun N-terminal kinase-activator protein 1 pathway.

Proteasome inhibitors, the well-known inhibitors of NF-kappaB, are recently considered therapeutic agents for inflammation. However, the anti-inflammatory properties of these agents have not been fully evaluated. In this report we describe a novel effect of proteasome inhibitors on the expression of monocyte chemoattractant protein 1 (MCP-1) in mesangial cells. We found that proteasome inhibitor MG132 dose-dependently induced expression of MCP-1 at the transcriptional level. The stimulatory effect was similarly observed with other proteasome inhibitors (proteasome inhibitor 1 and lactacystin) and in other cell types (NRK fibroblasts). The 5'-flanking region of the MCP-1 gene contains multiple AP-1 sites. To explore the mechanisms involved, we examined the effects of proteasome inhibition on the AP-1 pathway. Northern blot analysis showed that MG132 rapidly induced the expression of c-jun, but not c-fos. Immunoblot analysis showed that MG132 prevented degradation of c-Jun protein. Kinase assay revealed that c-Jun N-terminal kinase (JNK) was rapidly activated by MG132. Consistent with these results, a reporter assay showed that AP-1 activity was up-regulated after treatment with MG132. Curcumin, a pharmacological inhibitor of the JNK-AP-1 pathway, abrogated the induction of MCP-1 by MG132. Similarly, stable transfection with a dominant-negative mutant of c-Jun attenuated both MG132-induced activation of AP-1 and expression of MCP-1. The transcriptional activation by proteasome inhibitors was observed not only in MCP-1, but also in other AP-1-dependent genes, including stromelysin and mitogen-activated protein kinase phosphatase 1. These data revealed that proteasome inhibition triggered the expression of MCP-1 and other genes via the multistep induction of the JNK-c-Jun/AP-1 pathway.

Animals↗
PubMed2001

Selective roles of retinoic acid receptor and retinoid x receptor in the suppression of apoptosis by all-trans-retinoic acid.

Retinoic acids exert profound effects on many biological processes including cell proliferation, differentiation, and morphogenesis. We previously reported that all-trans-retinoic acid (t-RA) protected mesangial cells from H(2)O(2)-triggered apoptosis by suppressing the activator protein 1 (AP-1) pathway. It was via inhibition of c-fos and c-jun expression and suppression of c-Jun N-terminal kinase (JNK) activation. In this report, we investigated the involvement of retinoic acid receptor (RAR) and retinoid X receptor (RXR) in the antiapoptotic effect of t-RA in H(2)O(2)-exposed cells. We found that pretreatment with RAR pan-antagonist (AGN193109) or RXR pan-antagonist (HX531) attenuated the antiapoptotic effect of t-RA. Similarly, transient transfection with a dominant-negative mutant of RAR or a dominant-negative RXR diminished the antiapoptotic effect of t-RA. Both RAR and RXR antagonists reversed the suppressive effect of t-RA on AP-1 activity. However, the roles of RAR and RXR in the suppression of AP-1 components by t-RA were found to be different. RAR antagonist reversed the suppressive effect of t-RA on both c-fos and c-jun, whereas RXR antagonist reversed the effect of t-RA on c-fos but not c-jun. Furthermore, suppression of JNK activation by t-RA was observed even in the presence of RAR and RXR antagonists. Consistently, suppression of JNK by t-RA was not affected by overexpression of either the dominant-negative RAR or the dominant-negative RXR. These data elucidated that the antiapoptotic effect of t-RA is mediated by both nuclear receptor-dependent and -independent mechanisms.

Animals↗
PubMed2001

Expression, regulation, and function of inhibitor of apoptosis family genes in rat mesangial cells.

BACKGROUND: The inhibitor of apoptosis (IAP) family of proteins regulates programmed cell death triggered by various stimuli. The purpose of this investigation was to examine the expression, regulation, and function of IAP genes in cultured rat mesangial cells. METHODS: Basal and inducible expression of c-IAP1, c-IAP2, XIAP, and TIAP mRNAs was examined in mesangial cells, isolated glomeruli, and other cell lines under unstimulated and tumor necrosis factor-alpha (TNF-alpha)-stimulated conditions. To examine a role of nuclear factor-kappa B (NF-kappa B) in the regulation of IAPs, expression of IAPs in NF-kappa B-inactive mesangial cells was compared with that in wild-type cells. To investigate roles of IAPs in mesangial cell apoptosis, NF-kappa B--inactive cells were stably supertransfected with c-IAP1 or c-IAP2, and the susceptibility of these cells to TNF-alpha--induced apoptosis was evaluated quantitatively. RESULTS: Substantial, constitutive expression of c-IAP2, XIAP, and TIAP was observed in serum-deprived rat mesangial cells and c-IAP2 and XIAP in isolated normal rat glomeruli. In response to TNF-alpha, expression of c-IAP1 and c-IAP2 was induced in HeLa cells and ECV304 endothelial cells, but not in mesangial cells. In contrast to previous reports on other cell types, the expression of IAPs in rat mesangial cells was independent of NF-kappa B; that is, expression levels of IAPs in NF-kappa B--inactive cells were same as those in NF-kappa B--active cells under both unstimulated and TNF-alpha--stimulated conditions. Even without the induction of IAPs, NF-kappa B--active mesangial cells were more resistant to TNF-alpha--induced apoptosis than NF-kappa B--inactive cells. Interestingly, overexpression of either c-IAP1 or c-IAP2 completely compensated for the lack of resistance to apoptosis in NF-kappa B--inactive cells. CONCLUSIONS: IAPs are constitutively expressed in cultured rat mesangial cells and isolated normal rat glomeruli. IAPs can contribute to the survival of rat mesangial cells, but unexpectedly, these molecules are not involved in the TNF-alpha--induced, NF-kappa B--dependent cytoprotection in this cell type.

Animals↗
PubMed2001

Explanted glomeruli: utility and limitations.

Ex vivo incubation of isolated glomeruli has been used for many years to investigate biochemical properties of glomeruli. However, little has been understood about whether and how isolation and explanation per se affect the structure and function of the glomerulus. We recently reported that ex vivo incubation of isolated normal glomeruli results in severe apoptosis of podocytes, activation of the family of mitogen-activated protein kinase and expression of several genes regulated by activator protein 1. In this article, we summarize our current findings and discuss the utility and limitations of explanted glomeruli.

Animals↗
PubMed2000

Enhancement of TNF-alpha-induced apoptosis by immobilized arginine-glycine-aspartate: involvement of a tyrosine kinase-dependent, MAP kinase-independent mechanism.

Extracellular matrix facilitates anchorage-dependent cell survival via interaction of its arginine-glycine-aspartate (RGD) motif with integrins. In this report, we describe an unexpected, apoptosis-promoting the effect of immobilized RGD (iRGD) on tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis. Mesangial cells cultured on RGD-coated plates showed enhanced susceptibility to TNF-alpha-induced apoptosis. iRGD alone did not affect cell survival. In contrast, iRGD did not facilitate but inhibited apoptosis induced by H(2)O(2). Mitogen-activated protein (MAP) kinases and tyrosine kinases are important mediators for the RGD-integrin signaling. Pretreatment with MAP kinase kinase inhibitor PD098059, c-Jun N-terminal kinase (JNK)-c-Jun/AP-1 inhibitor curcumin or p38 MAP kinase inhibitor SB203580 did not attenuate the apoptosis-promoting effect of iRGD. Consistently, transfection with dominant-negative mutants of extracellular signal-regulated kinases, JNK or p38 MAP kinase did not inhibit the effect of iRGD. In contrast, protein tyrosine kinase inhibitors, genistein, and herbimycin A, abrogated the apoptosis-promoting effect of iRGD. Of note, TNF-alpha-induced apoptosis on uncoated plates was not attenuated by tyrosine kinase inhibitors. These data provide the first evidence that iRGD accelerates certain apoptosis. We identified that the effect was mediated by the tyrosine kinase-dependent, MAP kinase-independent mechanism.

Animals↗
PubMed2000

Spontaneous shift in transcriptional profile of explanted glomeruli via activation of the MAP kinase family.

To understand how isolation and explantation of glomeruli affect the function of resident cells, the present study investigated the transcriptional profile of explanted normal glomeruli. We found that ex vivo incubation of glomeruli spontaneously expressed monocyte chemoattractant protein-1 (MCP-1) and stromelysin, the genes regulated by activator protein-1 (AP-1). The expression was suppressed by heparin and quercetin, the drugs with anti-AP-1 activities. The gene expression was preceded by 1) induction of AP-1 components c-fos and c-jun and 2) phosphorylation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein (MAP) kinase, and c-Jun NH(2)-terminal kinase (JNK), the upstream inducers/activators of AP-1. Suppression of ERK by PD098059 abrogated induction of c-fos and c-jun, and the p38 MAP kinase inhibitor SB203580 attenuated c-fos expression. Furthermore, treatment with either PD098059, SB203580, or the JNK-AP-1 inhibitor curcumin diminished the expression of MCP-1 and stromelysin. The transcriptional profile of glomerular cells thus alters dramatically after explantation of glomeruli. It is, at least in part, due to activation of multiple MAP kinases that lead to induction of AP-1-dependent gene expression.

Animals↗
PubMed1998

Acute renal failure due to oxalate ingestion.

A 47-year-old man presented with acute renal failure following oxalate ingestion. Nausea and hematoemesis appeared four hours after attempted suicide and acute oliguric renal failure ensued the following day. The patient underwent four sessions of hemodialysis and then reverted to normal state. Histopathologic examination of renal biopsy specimen revealed the degeneration of the renal tubular epithelial cells associated with intracellular calcium oxalate crystal deposition. Most of the renal tubules were patent despite the intraluminar crystal deposition. These findings suggest that dysfunction of the renal tubular epithelial cell plays a more important role than tubular obstruction in developing acute renal failure.

Calcium Oxalate↗
PubMed1990

Significance of discordant ST alternans in ventricular fibrillation.

With the use of epicardial mapping, we investigated the electrical alternans of the ST segment during acute myocardial ischemia and studied the difference in ST alternans between dogs with resultant ventricular fibrillation and those without it. During the 7-minute occlusion of the left anterior descending coronary artery below its first diagonal branch, 60 epicardial unipolar electrograms were recorded simultaneously at 1-minute intervals by a computerized mapping system. ST alternans was found in the eight dogs we observed. The amplitude of ST alternans (difference in the ST segment elevation of two consecutive electrograms) was greater in dogs with ventricular fibrillation (n = 4) than in those without it (n = 4) (3.92 +/- 1.24 versus 0.58 +/- 0.49 mV, p less than 0.05). Three of the four dogs with ventricular fibrillation demonstrated discordant ST alternans (i.e., adjacent leads were out of phase). Results from the present study indicate that an increased amplitude and discordance of ST alternans during acute myocardial ischemia are related to ventricular fibrillation and act as indicators of time and spatial unevenness of ventricular repolarization.

Animals↗
PubMed1990

The role of late potentials in the assessment of myocardial degeneration in idiopathic dilated cardiomyopathy.

In order to determine whether or not late potentials indicate either a degree of myocardial fibrosis or necrosis, the relationship between late potentials and thallium-201 myocardial perfusion images was studied in 13 patients with idiopathic dilated cardiomyopathy. Late potentials were defined as low-amplitude waveforms having duration of over 20 msec after the end of the QRS complex using a high-resolution ECG (Marquette electronics, MAC 1). In the T1-201 myocardial perfusion image, the segmental perfusion state was assessed by use of a parameter called the uptake index (= normalized sector counts/maximal normalized sector counts) of each of 6 different segments. Segments which showed an uptake index of -2SD less than the normal value were judged to be abnormal. Late potentials were detected in 8 (61.5%) of the 13 patients. All of the patients showing late potentials also had ventricular tachycardia. Among the patients showing no late potential, ventricular tachycardia was observed in only one patient. Seven of the 8 patients showing late potentials and 3 of 5 patients not showing late potentials, however, had both a higher degree and a greater extent of abnormal perfusion images than the patients not showing late potentials. Therefore, late potentials may reflect a degree of myocardial fibrosis or necrosis in patients with dilated cardiomyopathy, those showing abnormal thallium images are apt to show late potentials, and these patients seem to be also at a high risk of suffering from ventricular tachycardia.

Adult↗
PubMed1988

Relationship between late potentials and left ventricular function in patients with coronary artery disease.

We examined the relationship between late potentials and left ventricular function from a hemodynamic point of view in 50 patients with prior myocardial infarction. Late potentials were found in 15 (30%) of 50 patients. A left ventricular aneurysm was found in 28 patients. Late potentials were detected in 14 (50%) of 28 patients with the aneurysm but in 1 (5%) of 22 patients without it (p less than 0.01). In the 50 patients, a hemodynamic data from the late potential positive group (n = 15) were compared to those from the late potential negative group (n = 35). The late potential positive group had a significantly lower ejection fraction, cardiac index and stroke volume than the late potential negative group. We further studied the 28 patients with left ventricular aneurysm in a similar way. The cardiac index and stroke volume were also significantly lower in the late potential positive group. The ejection fraction tended to be lower in the late potential positive group. These results suggest that left ventricular function and left ventricular aneurysm are among the factors that influence the development of late potentials.

Adult↗
PubMedDate not supplied

Modification of measurement of effective renal plasma flow from blood pool clearance curve of I-123-orthoiodohippurate using single blood sampling.

The methods of measuring effective renal plasma flow (ERPF) based on the two-compartment analysis of plasma clearance of I-123-orthoiodohippurate (OIH) disregard the distribution of I-123-OIH to erythrocytes, resulting in over-estimation of ERPF. In this study, a new simple modification was established to obtain accurate ERPF. Intercompartmental clearance rates among plasma, erythrocytes, and extracellular fluid were determined through in vitro and in vivo experiments to enable the three-compartment analysis of plasma clearance curves of I-123-OIH using multiple blood samplings in comparison with the two-compartment analysis. Multiplying renal blood flow derived from two-compartment analysis of the whole blood clearance curve by (1-hematocrit/100) was a new modification for measuring ERPF to reduce the complexity of three-compartment analysis and to supplement the distribution of I-123-OIH to erythrocytes. Comparing ERPF derived from the modified two-compartment analysis with that from three-compartment analysis demonstrated good agreement (r = 0.883, p = 0.001) between the two methods. ERPF derived by this new method was also compared with the clearance of paraaminohippurate (PAH), resulting in a regression line which was much closer to unity and a better correlation between them (r = 0.926) than that between PAH clearance and ERPF (r = 0.909) derived from conventional two-compartment analysis.

Erythrocytes↗