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Biomedical subjects

S Kumar

Publications and source records attributed to S Kumar.

At least 541 records · Page 30Linked to original sources
PubMed1999

Activation of p38 mitogen-activated protein kinase by PYK2/related adhesion focal tyrosine kinase-dependent mechanism.

The stress-activated p38 mitogen-activated protein kinase (p38 MAPK), a member of the subgroup of mammalian kinases, appears to play an important role in regulating inflammatory responses, including cytokine secretion and apoptosis. The upstream mediators that link extracellular signals with the p38 MAPK signaling pathway are currently unknown. Here we demonstrate that pp125 focal adhesion kinase-related tyrosine kinase RAFTK (also known as PYK2, CADTK) is activated specifically by methylmethane sulfonate (MMS) and hyperosmolarity but not by ultraviolet radiation, ionizing radiation, or cis-platinum. Overexpression of RAFTK leads to the activation of p38 MAPK. Furthermore, overexpression of a dominant-negative mutant of RAFTK (RAFTK K-M) inhibits MMS-induced p38 MAPK activation. MKK3 and MKK6 are known potential constituents of p38 MAPK signaling pathway, whereas SEK1 and MEK1 are upstream activators of SAPK/JNK and ERK pathways, respectively. We observe that the dominant-negative mutant of MKK3 but not of MKK6, SEK1, or MEK1 inhibits RAFTK-induced p38 MAPK activity. Furthermore, the results demonstrate that treatment of cells with 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl)-ester, a membrane-permeable calcium chelator, inhibits MMS-induced activation of RAFTK and p38 MAPK. Taken together, these findings indicate that RAFTK represents a stress-sensitive mediator of the p38 MAPK signaling pathway in response to certain cytotoxic agents.

Animals↗
PubMed1999

Inhibition of p38 mitogen-activated protein kinase decreases cardiomyocyte apoptosis and improves cardiac function after myocardial ischemia and reperfusion.

BACKGROUND: Activation of p38 mitogen-activated protein kinase (MAPK) plays an important role in apoptotic cell death. The role of p38 MAPK in myocardial injury caused by ischemia/reperfusion, an extreme stress to the heart, is unknown. METHODS AND RESULTS: Studies were performed with isolated, Langendorff-perfused rabbit hearts. Ischemia alone caused a moderate but transient increase in p38 MAPK activity (3.5-fold increase, P<0.05 versus basal). Ischemia followed by reperfusion further activated p38 MAPK, and the maximal level of activation (6.3-fold, P<0.01) was reached 10 minutes after reperfusion. Administration of SB 203580, a p38 MAPK inhibitor, decreased myocardial apoptosis (14.7+/-3.2% versus 30.6+/-3.5% in vehicle, P<0.01) and improved postischemic cardiac function. The cardioprotective effects of SB 203580 were closely related to its inhibition of p38 MAPK. Administering SB 203580 before ischemia and during reperfusion completely inhibited p38 MAPK activation and exerted the most cardioprotective effects. In contrast, administering SB 203580 10 minutes after reperfusion (a time point when maximal MAPK activation had already been achieved) failed to convey significant cardioprotection. Moreover, inhibition of p38 MAPK attenuated myocardial necrosis after a prolonged reperfusion. CONCLUSIONS: These results demonstrate that p38 MAPK plays a pivotal role in the signal transduction pathway mediating postischemic myocardial apoptosis and that inhibiting p38 MAPK may attenuate reperfusion injury.

Animals↗
PubMed1999

32P-Postlabeling analysis of lipophilic DNA adducts resulting from interaction with (+/-)-3-hydroxy-trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo [a]pyrene.

Bay-region diol epoxides are considered the putative ultimate carcinogens of polynuclear aromatic hydrocarbons. However, the results of studies on tumorigenesis and DNA binding of benzo[a]pyrene (BP) and its bay-region diol epoxide, (+)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyren e [(+)-anti-BPDE] suggest that, in addition to anti-BPDE, other reactive metabolite(s) of BP may also be involved in BP-induced carcinogenesis. Recent studies have demonstrated that 3-hydroxy-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a ]pyrene (anti-BPTE) is another highly reactive metabolite of BP. In order to identify syn- and anti-BPTE-derived DNA adducts and their base selectivity, we synthesized both compounds by two different methods and reacted in vitro with calf thymus DNA and individual nucleotides. The resultant adducts were analyzed by nuclease P1-enhanced 32P-postlabeling. Anti-BPTE produced three major and several minor adducts with DNA; dAp and dGp were the preferred substrates, while dCp and dTp were the least reactive. In contrast, syn-BPTE produced two major adducts each with DNA and dGp; dAp generated only one adduct. Co-chromatography of anti-BPTE-derived DNA adducts with those of mononucleotide adducts revealed that the major adducts in DNA were guanine derived. Further, co-chromatographic results revealed that the anti-BPTE-DNA adducts were distinctly different from that of anti-BPDE-DNA adducts. These observations indicate that both syn- and anti-BPTE can react with DNA bases and these DNA adducts may also contribute to BP-induced carcinogenesis.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1999

Phase-separated composite films for liquid crystal displays

A method of preparing liquid crystal devices by phase separation of liquid crystal from its solution in a prepolymer, which results in adjacent layers of liquid crystal and polymer, is described. Liquid crystals in these phase-separated composite films exhibit electro-optical properties not observed in devices prepared by conventional methods, polymer dispersion, or polymer-stabilization methods. Devices incorporating ferroelectric liquid crystals have gray scale and switch 100 times faster at low fields than conventional surface-stabilized devices. This method makes it possible to prepare devices with liquid crystal film thickness comparable to optical wavelengths.

Journal Article↗
PubMed1999

2,6-Dichloro-phenol indophenol prevents switch-over of electrons between the cyanide-sensitive and -insensitive pathway of the mitochondrial electron transport chain in the presence of inhibitors.

To evolve a simple oxygen electrode-based method to estimate alternative respiration, one needs to develop a procedure to prevent switch-over of electrons to either pathway upon inhibition by cyanide or salicylhydroxamic acid. It was hypothesized that the inclusion of appropriate electron acceptor, possessing redox potential close to one of the electron transport carriers in between ubiquinone (branch point) and cytochrome a-a3, should be able to stop switch-over of electrons to either pathway by working as an electron sink. To test the hypothesis, 2,6-dichloro-phenol indophenol (DCPIP; redox potential +0.217 V), an artificial electron acceptor having a redox potential quite similar to the site near cytochrome c1 (redox potential +0.22 V) on the cyanide-sensitive pathway, was used with isolated mitochondria and leaf discs in the absence and presence of inhibitors (potassium cyanide, antimycin A, and salicylhydroxamic acid). Polarographic data confirmed electron acceptance by DCPIP only from the inhibited (by cyanide or salicylhydroxamic acid) mitochondrial electron transport chain, hence preventing switch-over of electrons between the cyanide-sensitive and cyanide-insensitive pathway of respiration. Results with antimycin A and reduction status of DCPIP further confirmed electron acceptance by DCPIP from the mitochondrial electron transport chain. Possible implications of the results have been discussed.

2,6-Dichloroindophenol↗
PubMed1999

Breast carcinoma: vascular density determined using CD105 antibody correlates with tumor prognosis.

Angiogenesis is essential for tumor growth and metastasis. There are conflicting reports as to whether microvessel density (IMD) in breast cancers is associated with prognosis. This could be due to the use of different antibodies to endothelial cell markers, variation in tissue pretreatment protocols, and nonstandardized counting methods. We have assessed the IMD in 106 breast carcinomas using a pan-endothelial marker, CD34, and a recently described mAb to CD105, which preferentially reacts with endothelial cell in angiogenic tissues. IMD values (separated as above or below median) for CD105 expression showed a statistically significant correlation with overall (P = 0.0029) and disease-free survival (P = 0.0362). In contrast, blood vessel counts using a panendothelial marker CD34 did not correlate with overall or disease-free survival (P = 0.2912 and P = 03153, respectively). When IMD values were subdivided into quartiles and assessed for their prognostic values, there was a statistically significant difference in the overall survival across CD105, but not CD34, values (P = 0.0017 and P = 0.7997, respectively) and also disease-free survival (P = 0.0431 and P = 0.5066, respectively). Further analysis of IMD values demonstrated that there were no deaths in the lowest quartile for CD105 and it differed from the other three quartiles. However, examination of clinical details of patients in the lowest quartile failed to reveal clustering of patients known to be associated with low-risk factors. Multivariate analysis confirmed that IMD values using CD105 were an independent prognostic factor. These results suggest that the ability to quantitatively distinguish between tumor neovascularization and preexisting vessels may be important in the assessment of tumor angiogenesis, but requires confirmation in a greater number of patients with a longer follow-up.

Adult↗
PubMed1999

Divergence time estimates for the early history of animal phyla and the origin of plants, animals and fungi.

In the past, molecular clocks have been used to estimate divergence times among animal phyla, but those time estimates have varied widely (1200-670 million years ago, Ma). In order to obtain time estimates that are more robust, we have analysed a larger number of genes for divergences among three well-represented animal phyla, and among plants, animals and fungi. The time estimate for the chordate-arthropod divergence, using 50 genes, is 993 +/- 46 Ma. Nematodes were found to have diverged from the lineage leading to arthropods and chordates at 1177 +/- 79 Ma. Phylogenetic analyses also show that a basal position of nematodes has strong support (p > 99%) and is not the result of rate biases. The three-way split (relationships unresolved) of plants, animals and fungi was estimated at 1576 +/- 88 Ma. By inference, the basal animal phyla (Porifera, Cnidaria, Ctenophora) diverged between about 1200-1500 Ma. This suggests that at least six animal phyla originated deep in the Precambrian, more than 400 million years earlier than their first appearance in the fossil record.

Animals↗
PubMed1999

Sequence context effects on mutational properties of cis-opened benzo[c]phenanthrene diol epoxide-deoxyadenosine adducts in site-specific mutation studies.

Diastereomeric N6-substituted dAdo adducts (cis B[c]PhDE-2/1R and cis B[c]PhDE-2/1S) that correspond to cis-opening at C-1 of the enantiomeric benzo[c]phenanthrene 3,4-diol 1,2-epoxides in which the epoxide oxygen and the benzylic hydroxyl group are trans (DE-2) were synthetically incorporated into oligonucleotide 16-mers. Each adduct was placed at the fourth nucleotide from the 5'-end of each of two different oligonucleotide sequences derived from the E. coli supF gene. Each adduct was also placed in two additional oligonucleotide sequences that were constructed by interchanging the adduct site and the immediately adjacent nucleotides between the two original sequences. These oligonucleotides were designed for use in site-specific mutation studies, with a single-stranded bacteriophage M13mp7L2 vector, to determine if the effects of sequence context on types and frequencies of base substitution mutations are attributable only to nucleotides immediately adjacent to these polycyclic aromatic hydrocarbon diol epoxide-dAdo adducts, or whether more distant nucleotide residues also affect the mutagenic response. In SOS-induced Escherichia coli SMH77, total base substitution mutation frequencies for the cis B[c]PhDE-2/1R-dAdo adduct were relatively low (0.62-5.6%) compared with those for the cis B[c]PhDE-2/1S-dAdo adduct (11.9-56.5%). Depending on sequence context, cis B[c]PhDE-2/1R-dAdo gave predominantly A-->T or a more equal distribution of A-->T and A-->G mutations whereas cis B[c]PhDE-2/1S-dAdo gave either predominantly A-->T or predominantly A-->G base substitutions. Our results clearly indicate that nucleotides that are distal as well as those that are proximal to the adduct site are capable of influencing both the mutation frequency and the distribution of base substitution mutations.

Bacteriophage M13↗
PubMed1999

TL1, a novel tumor necrosis factor-like cytokine, induces apoptosis in endothelial cells. Involvement of activation of stress protein kinases (stress-activated protein kinase and p38 mitogen-activated protein kinase) and caspase-3-like protease.

TL1 is a recently discovered novel member of the tumor necrosis factor (TNF) cytokine family. TL1 is abundantly expressed in endothelial cells, but its function is not known. The present study was undertaken to explore whether TL1 induces apoptosis in endothelial cells and, if so, to explore its mechanism of action. Cultured bovine pulmonary artery endothelial cells (BPAEC) exposed to TL1 showed morphological (including ultrastructural) and biochemical features characteristic of apoptosis. TL1-induced apoptosis in BPAEC was a time- and concentration-dependent process (EC50 = 72 ng/ml). The effect of TL1 was not inhibited by soluble TNF receptors 1 or 2. TL1 up-regulated Fas expression in BPAEC at 8 and 24 h after treatment, and significantly activated stress-activated protein kinase (SAPK) and p38 mitogen-activated protein kinase (p38 MAPK). The peak activities of SAPK and p38 MAPK in TL1-treated BPAEC were increased by 9- and 4-fold, respectively. TL1-induced apoptosis in the BPAEC was reduced by expression of a dominant-interfering mutant of c-Jun (62.8%, p < 0.05) or by a specific p38 inhibitor, SB203580 (1-10 microM) dose-dependently. TL1 also activated caspases in BPAEC, and TL1-induced apoptosis in BPAEC was significantly attenuated by the caspase inhibitor, ZVAD-fluromethyl-ketone. The major component activated by TL1 in BPAEC was caspase-3, which was based on substrate specificity and immunocytochemical analysis. These findings suggest that TL1 may act as an autocrine factor to induce apoptosis in endothelial cells via activation of multiple signaling pathways, including stress protein kinases as well as certain caspases.

Animals↗
PubMed1999

Expectant management of stage A-1 (T1a) prostate cancer utilizing serum PSA levels: a preliminary report.

BACKGROUND AND OBJECTIVES: The natural history of stage A-1 (Tla) prostate cancer remains unpredictable. Although stage A-1 (Tla) was traditionally considered an indolent lesion, recent reports have documented the potential progression of stage A-1 (Tla) cancer. METHODS: Eight men aged 65 to 76 years at the time of diagnosis with stage A-1 (Tla) prostate cancer received no therapy. These men have been followed from 3 to 9.5 years (mean, 6.25 years). During this period, the patients have been followed with periodic rectal examinations and prostate-specific antigen (PSA) levels. RESULTS: The PSA levels of five of the eight patients remain in the normal range and no patient has had a change in his rectal examination. In the three patients who had elevated PSA levels, there was no evidence of metastatic disease. No patient has died from prostate cancer; one patient died from cerebrovascular causes. CONCLUSIONS: Patients with stage A-1 (Tla) prostate cancer have an unpredictable natural history. PSA levels can be used to monitor disease progression and identify those patients where observation is no longer appropriate.

Aged↗
PubMed1999

Regulatory light chain phosphorylation and the assembly of myosin II into the cytoskeleton of microcapillary endothelial cells.

During the crawling movements of non-muscle cells, myosin II-containing structures assemble and disassemble with a high degree of spatial and temporal heterogeneity. In order to understand how this is controlled, we examined factors that influence the association of myosin II with detergent-resistant cytoskeletons of cultured endothelial cells. Treatment of cells with 0.05% Triton X-100 in an actin-stabilizing buffer released approximately 42% of the myosin II from the cytoplasm. Most remaining myosin II was dissociated from the cytoskeleton by treatment with ATP or AMPPNP, but not ADP, suggesting that myosin II is retained as ATP-sensitive filaments or via rigor-like binding to F-actin. Disruption of actin filaments with cytochalasin or latrunculin prior to detergent permeabilization sharply decreased the amount of myosin II retained, suggesting the latter type of association. Because phosphorylation of myosin II affects filament assembly and actin binding in vitro, phosphorylation levels in soluble and cytoskeletal myosin II were measured. Phosphorylation of myosin heavy chains was not significantly different between the two fractions, but regulatory light chains of cytoskeletal myosin II were 5 times more phosphorylated than in soluble myosin II. Tryptic-peptide mapping showed that cytoskeletal light chains were phosphorylated predominantly at serine 19/threonine 18, which regulates myosin II assembly in vitro, whereas soluble light chains were not phosphorylated or were phosphorylated at threonine 9. Treating cells with the kinase inhibitor, staurosporine, prior to permeabilization decreased light-chain phosphorylation with concomitant reduction in myosin retention. These observations suggest that assembly of myosin II into cytoskeletal structures, where it can generate and resist forces, is regulated in vivo by phosphorylation of myosin light chains at serine 19/threonine 18.

Actins↗
PubMed1999

Fine-needle aspiration biopsy of orbital meningioma.

Fine-needle aspiration was performed on an orbital mass in a 53-yr-old woman. The cytologic diagnosis was meningioma, which was later confirmed by histologic study of biopsy material. The cytologic features of the aspirated material (nuclear pseudoinclusions, psammoma bodies, and cells arranged in syncytial sheets and whorls) allowed a rapid, reliable, outpatient diagnosis to be formulated. The cytologic features are discussed and the literature is reviewed. Diagn. Cytopathol. 1999;21:402-404.

Biopsy, Needle↗
PubMed1999

Cervical radiculopathies: relationship between symptom duration and spontaneous EMG activity.

The purpose of this multicenter study was to prospectively examine whether denervation in paraspinal muscles (PSM) and in other major proximal and distal muscles is related to symptom duration in cervical radiculopathies (CRs). Information was collected on 93 electrodiagnostically confirmed CRs using standardized history, physical examination, and electromyographic (EMG) screens. Multivariate, maximum-likelihood estimates showed no evidence of correlation between PSM spontaneous activity and symptom duration. Symptom duration was also nonsignificant in eight of the remaining nine upper limb muscles analyzed. We conclude that the probability of spontaneous activity is not related to symptom duration. Clinicians, therefore, should refrain from interpreting electrodiagnostic findings based upon duration of symptoms.

Adolescent↗
PubMed1999

Relative roles of T-cell receptor ligands and interleukin-2 in driving T-cell proliferation.

Stimulation of T cells by the T-cell receptor (TCR)/CD3 complex results in interleukin-2 (IL-2) synthesis and surface expression of the IL-2 receptor (IL-2R), which in turn drive T-cell proliferation. However, the significance of the requirement of IL-2 in driving T-cell proliferation, when TCR stimulation itself delivers potential mitogenic signals, is unclear. We show that blocking of IL-2 synthesis by Cyclosporin A (CsA) suppressed both the Concanavalin A (Con A)- and phorbol myristate acetate (PMA)/ionomycin-induced proliferation of T cells. The latter is also inhibited by anti-IL-2R. Kinetic studies showed that T-cell proliferation begins to become resistant to CsA inhibition by about 12 h and became largely resistant by 18 h of stimulation. PMA, the protein kinase C activator, enhanced Con A-induced T-cell proliferation if added only within first 12 h of stimulation, and not after that. Given the fact that, in the present study, TCR is downregulated within 2 h of Con A stimulation and T cells entered the S phase of cell cycle by about 18 h of stimulation, the above results suggest that TCR stimulation provides the initial trigger to the resting T cells, which allows the cells to traverse the first two third portions of G1 phase of cell cycle and become proliferation competent. IL-2 action begins afterward, delivering the actual proliferation signal(s), allowing the cells to traverse the rest of G1 phase and enter the S phase of the cell cycle.

Animals↗
PubMed1999

Inhibition of keratinocyte growth by different Nepalese zanthoxylum species.

A total of 11 methanol extracts obtained from four different Nepalese Zanthoxylum species were screened for their antiproliferative activity against the growth of human keratinocytes (HaCaT cells). The extract obtained from Z. armatum barks was highly active with an IC50 value of 11 micrograms/mL. Also, the extracts obtained from Z. oxyphyllum barks and roots with IC50 values of 53 and 57 micrograms/mL, respectively, showed potent activity. Their antiproliferative activity was not due to cytotoxic effects on cell membranes, as documented by the activity of lactate dehydrogenase released from the cytoplasm of keratinocytes, which did not exceed that of the control value. Rather, they also protected against radical-induced damage to model membranes stimulated with 2,2'-azo-bis(2-amidinopropane) dihydrochloride.

Cell Division↗