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Biomedical subjects

R Kumar

Publications and source records attributed to R Kumar.

At least 325 records · Page 18Linked to original sources

Globus pallidus deep brain stimulation for generalized dystonia: clinical and PET investigation.

Bilateral globus pallidus internus (GPi) deep brain stimulation (DBS) in a patient with severe idiopathic generalized dystonia resulted in immediate improvement of all aspects of dystonia. During joystick movement, GPi DBS reduced PET activation bilaterally in the primary motor, lateral premotor, supplementary motor, anterior cingulate, and prefrontal areas and ipsilaterally in the lentiform nucleus. Altering basal ganglia function with GPi DBS reverses the overactivity of certain motor cortical areas present in dystonia.

Brain↗

Typhoid fever in children aged less than 5 years.

BACKGROUND: Calculation of the incidence of typhoid fever during preschool years is important to define the optimum age of immunisation and the choice of vaccines for public-health programmes in developing countries. Hospital-based studies have suggested that children younger than 5 years do not need vaccination against typhoid fever, but this view needs to be re-examined in community-based longitudinal studies. We undertook a prospective follow-up study of residents of a low-income urban area of Delhi, India, with active surveillance for case detection. METHODS: A baseline census was undertaken in 1995. Between Nov 1, 1995, and Oct 31, 1996, we visited 8172 residents of 1820 households in Kalkaji, Delhi, twice weekly to detect febrile cases. Blood samples were obtained from febrile patients, and those who tested positive for Salmonella typhi were treated with ciprofloxacin. FINDINGS: 63 culture-positive typhoid fever cases were detected. Of these, 28 (44%) were in children aged under 5 years. The incidence rate of typhoid per 1000 person-years was 27.3 at age under 5 years, 11.7 at 5-19 years, and 1.1 between 19 and 40 years. The difference in the incidence of typhoid fever between those under 5 years and those aged 5-19 years (15.6 per 1000 person-years [95% CI 4.7-26.5]), and those aged 19-40 years (26.2 [16.0-36.3]) was significant (p<0.001 for both). The difference between the incidence of typhoid at 5-19 years and the incidence at 19-40 years was also significant (10.6 [6.3-14.8], p<0.001). Morbidity in those under 5 and in older people was similar in terms of duration of fever, signs and symptoms, and need for hospital admission. INTERPRETATION: Our findings challenge the common view that typhoid fever is a disorder of school-age children and of adults. Typhoid is a common and significant cause of morbidity between 1 and 5 years of age. The optimum age of typhoid immunisation and the choice of vaccines needs to be reassessed.

Adolescent↗

Interdomain signaling in a two-domain fragment of the human glucocorticoid receptor.

Studies of individual domains or subdomains of the proteins making up the nuclear receptor family have stressed their modular nature. Nevertheless, these receptors function as complete proteins. Studies of specific mutations suggest that in the holoreceptors, intramolecular domain-domain interactions are important for complete function, but there is little knowledge concerning these interactions. The important transcriptional transactivation function in the N-terminal part of the glucocorticoid receptor (GR) appears to have little inherent structure. To study its interactions with the DNA binding domain (DBD) of the GR, we have expressed the complete sequence from the N-terminal through the DBD of the human GR. Circular dichroism analyses of this highly purified, multidomain protein show that it has a considerable helical content. We hypothesized that binding of its DBD to the cognate glucocorticoid response element would confer additional structure upon the N-terminal domain. Circular dichroism and fluorescence emission studies suggest that additional helicity as well as tertiary structure occur in the two-domain protein upon DNA binding. In sum, our data suggest that interdomain interactions consequent to DNA binding imparts structure to the portion of the GR that contains a major transactivation domain.

Circular Dichroism↗

Comparative effects of unilateral and bilateral subthalamic nucleus deep brain stimulation.

OBJECTIVE: To compare the effects of unilateral subthalamic nucleus (STN) deep brain stimulation (DBS) with bilateral STN DBS in advanced PD. METHODS: Our initial 10 consecutive patients with medication-refractory motor fluctuations and levodopa-induced dyskinesias undergoing chronic bilateral STN DBS underwent a standardized evaluation of unilateral and bilateral STN DBS in the medication-off state 6 to 18 months after electrode implantation. RESULTS: Bilateral STN DBS improved the mean total Unified Parkinson's Disease Rating Scale motor score by 54%, whereas unilateral stimulation improved motor scores only 23%. Unilateral STN DBS improved postural stability and gait 14%, other axial motor features 19%, and overall parkinsonism in limbs contralateral to stimulation by 46%, including an 86% improvement in contralateral tremor. However, bilateral STN DBS resulted in greater improvement in each of these domains, including limb function, i.e., the reduction in scores from the limbs on one side was greater with bilateral than with unilateral stimulation of the contralateral STN. CONCLUSIONS: Bilateral STN DBS improves parkinsonism considerably more than unilateral STN DBS; bilateral simultaneous electrode implantation may be the most appropriate surgical option for patients with significant bilateral disability. Unilateral STN DBS results in moderate improvement in all aspects of off-period parkinsonism and improves tremor as much as is typically reported with DBS of the ventral intermedius nucleus of the thalamus (Vim). For this reason, STN DBS may be a more appropriate choice than Vim DBS or thalamotomy for parkinsonian tremor. Some patients with highly asymmetric tremor-dominant PD might be appropriately treated with unilateral instead of bilateral STN DBS.

Aged↗

Redistribution of activated caspase-3 to the nucleus during butyric acid-induced apoptosis.

The colonic epithelial cells near the top of the crypt and in the lumen have been shown to undergo apoptosis. Since butyric acid is the major short-chain fatty acid produced by fermentation of dietary fiber in the large bowel, it has been proposed that it could act as an important regulator of apoptosis in colorectal cancer. Here we report that in cells treated with butyric acid, the cleavage of DNA-PKcs was paralleled or preceded by the induction of activation of caspase-3, and these events were inhibited by Bcl-2 overexpression. We also demonstrated the redistribution of activated caspase-3 to the nuclear compartment where it locally cleaves DNA-PKcs and poly(ADP-ribose) polymerase, and cleaved fragments were released in the cytosolic compartment. The observed activation of caspase-3 and nuclear cleavage of its substrates and their subsequent release into the cytosol were inhibited by a specific caspase-3 inhibitor, the tetrapeptide DEVD-CHO. These findings suggest that relocalization of activated caspase-3 to the nucleus may constitute an important apoptotic signal during butyric acid-induction of apoptosis human colorectal cancer cells.

Apoptosis↗

Association of prokaryotic and eukaryotic chaperone proteins with the human 1alpha,25-dihydroxyvitamin D(3) receptor.

Steroid hormone receptors (SHR) form complexes with heat shock proteins (hsps). The 1alpha,25-dihydroxyvitamin D(3) receptor (VDR) has not been previously shown to interact with hsps. During expression and purification of VDR-glutathione S-transferase (VDR-GST) fusion proteins encompassing full-length, DNA, and ligand-binding domains of the VDR (FL-VDR, DBD-VDR, and LBD-VDR), we observed binding of bacterial hsps with VDR-GST constructs. All VDR constructs bound DnaK in amounts greater than GST alone and bound smaller amounts of DnaJ or GrpE. GroEL bound only to FL-VDR. GroES did not bind to VDR. When VDR-GST constructs were incubated with a reticulocyte lysate system that has been used previously to examine SHR-hsp interactions, eukaryotic hsc70 was detected bound to FL-VDR and DBD-VDR. Binding of hsp90 to VDR was not detected. However, geldanamycin, an hsp90 inhibitor, reduced 1alpha,25-dihydroxyvitamin D(3)-mediated gene activation in osteoblasts. Our data show that the bacterial and eukaryotic hsps associate with the VDR and might be involved in VDR function.

Animals↗

Transcriptional up-regulation of paxillin expression by heregulin in human breast cancer cells.

Activation of heregulin (HRG) signaling has been implicated in the development of aggressive phenotype in breast cancer cells. The mechanisms through which HRG regulates the progression of breast cancer cells to a more invasive or motile phenotype are currently unknown. Because the process of cell migration must involve dynamic changes in the formation of new focal adhesions at the leading edge and dissolution of preexisting focal points, we explored the potential HRG regulation of paxillin, a major component of focal adhesion. Here, we report that HRG stimulation of noninvasive breast cancer MCF-7 cells resulted in the up-regulation of paxillin mRNA and protein. The observed HRG stimulation of paxillin mRNA expression was completely blocked by actinomycin D (a transcriptional inhibitor) as well as by cycloheximide (a protein synthesis inhibitor), suggesting the involvement of an inducible protein factor(s) and transcriptional regulation of paxillin mRNA by HRG. Extension of these observations to other HRG-responsive human cell lines also demonstrated that HRG has a significant capacity to up-regulate the paxillin expression. Furthermore, the levels of paxillin expression were closely linked with the coexpression of human epidermal growth factor receptor 2 (HER2)/HER3 receptors in breast cancer cell lines and in grade III human breast tumors. This study is the first demonstration of regulation of paxillin expression by a polypeptide growth factor, and it suggests a potential role for paxillin in the HER2 pathway in breast cancer.

Breast Neoplasms↗

Purification and characterization of a major zinc binding protein from renal brush border membrane of rat.

In spite of the fact that zinc is an essential trace element, mechanisms that contribute to zinc homeostasis in mammals are poorly understood. An attempt has been made to identify and purify zinc binding components from renal brush border membrane (BBM), which could be involved in the binding of zinc and the subsequent translocation across the BBM. A 40 kDa major zinc binding protein has been identified and purified from renal BBM, which showed a dissociation constant (Kd) of 211 microM and maximal binding (Bmax) of 207 nmol/mg protein. 8 g zinc atoms could interact with 1 mol of protein. Specificity of the protein for zinc was checked by metal displacement and UV-absorption assay. It was found that only Cd2+ could displace the zinc bound to the protein. Other metals tested (Cu2+, Mg2+, Ca2+) did not show any interaction with the protein. These data indicated that purified protein is highly specific and has a high affinity for zinc. The carbohydrate content was found to be 7.85 mg% in the purified protein. Immunofluorescence localization of this protein in kidney sections revealed that this major zinc binding protein is exclusively localized in the proximal convoluted tubules. These results suggested that the 40 kDa major zinc binding transmembrane glycoprotein is highly specific for zinc and has a high affinity for zinc.

Animals↗

Catalytic mechanism of nucleoside diphosphate kinase investigated using nucleotide analogues, viscosity effects, and X-ray crystallography.

Nucleoside diphosphate (NDP) kinases display low specificity with respect to the base moiety of the nucleotides and to the 2'-position of the ribose, but the 3'-hydroxyl is found to be important for catalysis. We report in this paper the enzymatic analysis of a series of derivatives of thymidine diphosphate (TDP) where the 3'-OH group was removed or replaced by fluorine, azido, and amino groups. With Dictyostelium NDP kinase, kcat decreases 15-200-fold from 1100 s-1 with TDP, and (kcat/Km)NDP decreases from 12 x 10(6) to 10(3) to 5 x 10(4) M-1 s-1, depending on the substrate. The poorest substrates are 3'-deoxyTDP and 3'-azido-3'-deoxyTDP, while the best modified substrates are 2',3'-dehydro-3'-deoxyTDP and 3'-fluoro-3'-deoxyTDP. In a similar way, 3'-fluoro-2',3'-dideoxyUDP was found to be a better substrate than 2',3'-dideoxyUDP, but a much poorer substrate than 2'-deoxyUDP. (kcat/Km)NDP is sensitive to the viscosity of the solution with TDP as the substrate but not with the modified substrates. To understand the poor catalytic efficiency of the modified nucleotides at a structural level, we determined the crystal structure of Dictyostelium NDP kinase complexed to 3'-fluoro-2',3'-dideoxyUDP at 2.7 A resolution. Significant differences are noted as compared to the TDP complex. Substrate-assisted catalysis by the 3'-OH, which is effective in the NDP kinase reaction, cannot occur with the modified substrate. With TDP, the beta-phosphate, which is the leaving group when a gamma-phosphate is transferred to His122, hydrogen bonds to the 3'-hydroxyl group of the sugar; with 3'-fluoro-2',3'-dideoxyUDP, the beta-phosphate hydrogen bonds to Asn119 and moves away from the attacking Ndelta of the catalytic His122. Since all anti-AIDS nucleoside drugs are modified at the 3'-position, these results are relevant to the role of NDP kinase in their cellular metabolism.

Animals↗

Trimethylamine N-oxide-induced cooperative folding of an intrinsically unfolded transcription-activating fragment of human glucocorticoid receptor.

A number of biologically important proteins or protein domains identified recently are fully or partially unstructured (unfolded). Methods that allow studies of the propensity of such proteins to fold naturally are valuable. The traditional biophysical approaches using alcohols to drive alpha-helix formation raise serious questions of the relevance of alcohol-induced structure to the biologically important conformations. Recently we illustrated the extraordinary capability of the naturally occurring solute, trimethylamine N-oxide (TMAO), to force two unfolded proteins to fold to native-like species with significant functional activity. In the present work we apply this technique to recombinant human glucocorticoid receptor fragments consisting of residues 1-500 and residues 77-262. CD and fluorescence spectroscopy showed that both were largely disordered in aqueous solution. TMAO induced a condensed structure in the large fragment, indicated by the substantial enhancement in intrinsic fluorescence and blue shift of fluorescent maxima. CD spectroscopy demonstrated that the TMAO-induced structure is different from the alpha-helix-rich conformation driven by trifluoroethanol (TFE). In contrast to TFE, the conformational transition of the 1-500 fragment induced by TMAO is cooperative, a condition characteristic of proteins with unique structures.

Circular Dichroism↗

The gain-of-function Chinese hamster ovary mutant LEC11B expresses one of two Chinese hamster FUT6 genes due to the loss of a negative regulatory factor.

The LEC11 Chinese hamster ovary (CHO) gain-of-function mutant expresses an alpha(1,3)fucosyltransferase (alpha(1,3)Fuc-T) activity that generates the LeX, sialyl-LeX, and VIM-2 glycan determinants and has been extensively used for studies of E-selectin ligand specificity. In order to identify regulatory mechanisms that control alpha(1,3)Fuc-T expression in mammals, mechanisms of FUT gene expression were investigated in LEC11 cells and two new, independent mutants, LEC11A and LEC11B. Northern and ribonuclease protection analyses, using probes that span the coding region of a cloned CHO FUT gene, detected transcripts in each LEC11 mutant but not in CHO cells or other gain-of-function CHO mutants that express a different alpha(1,3)Fuc-T activity. Coding region sequence analysis and alpha(1,3)Fuc-T acceptor specificity comparisons with recombinant human Fuc-TV and Fuc-TVI showed that the cloned FUT gene is orthologous to the human FUT6 gene. Southern analyses identified two closely related FUT6 genes in the Chinese hamster, whose evolutionary relationships are discussed. The blots showed that rearrangements had occurred in LEC11A and LEC11 genomic DNA, consistent with a cis mechanism of FUT6 gene activation in these mutants. By contrast, somatic cell hybrid analyses revealed that LEC11B cells express FUT6 gene transcripts due to the loss of a trans-acting, negative regulatory factor. Sequencing of reverse transcriptase-polymerase chain reaction products identified unique 5'- and 3'-untranslated region sequences in FUT6 gene transcripts from each LEC11 mutant. Northern and Southern analyses with gene-specific probes showed that LEC11A cells express only the cgFUT6A gene (where cg is Cricetulus griseus), whereas LEC11 and LEC11B cells express only the cgFUT6B gene. In LEC11A x LEC11B hybrid cells, the cgFUT6A gene was predominantly expressed, as predicted if a trans-acting negative regulatory factor functions to suppress cgFUT6B gene expression in CHO cells. This factor is predicted to be a cell type-specific regulator of FUT6 gene expression in mammals.

Amino Acid Sequence↗

Effects of ischemia on discontinuous action potential conduction in hybrid pairs of ventricular cells.

BACKGROUND: Acute ischemia often occurs in cardiac tissue that has prior injury, resulting in spatially inhomogeneous distributions of membrane properties and intercellular coupling. Changes in action potential conduction with ischemia, which can be associated with release of catecholamines, may be particularly important in tissue that has discontinuous conduction resulting from prior infarction, hypertrophy, or myopathy. METHODS AND RESULTS: Isolated guinea pig ventricular myocytes were electrically coupled by a coupling-clamp circuit to a comprehensive computer model of a guinea pig ventricular myocyte to assess alterations in the critical value of coupling conductance required for action potential conduction from the real cell to the model cell when the real cell was exposed to a solution that included hypoxia, acidosis, and an elevated extracellular potassium concentration to simulate acute ischemia. The "ischemic" solution increased critical coupling conductance from 6.2+/-0.1 to 7.4+/-0.2 nS and decreased the associated maximum conduction delay from 31+/-1 to 23+/-1 ms (mean+/-SEM, n=11). The ischemic solution plus 1 micromol/L norepinephrine decreased critical coupling conductance from 5.9+/-0.2 to 5.0+/-0.1 nS and increased maximum conduction delay from 31+/-2 to 54+/-4 ms (mean+/-SEM, n=8). CONCLUSIONS: The release of catecholamines with ischemia, in a setting of partially uncoupled cells, may play a major role in producing long conduction delays, which may allow reentrant pathways.

Action Potentials↗

Identification of 1 alpha,25-dihydroxyvitamin D3 response elements in the human transforming growth factor beta 2 gene.

Transforming growth factor-beta (TGF-beta) is one of the most abundant growth factors secreted by bone cells, and regulation of TGF-beta expression is crucial for bone development and growth. Previous studies from our laboratory demonstrated that 1 alpha, 25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) inhibits human osteoblast and keratinocyte growth by increasing TGF-beta2 secretion and synthesis. To examine the mechanism by which 1 alpha,25(OH)2D3 regulates TGF-beta 2 transcription in osteoblasts, we ligated segments of the human TGF-beta 2 promoter 5' of a growth hormone reporter gene in a growth hormone reporter plasmid and examined the effects of 1 alpha,25(OH)2D3 administration on the expression of growth hormone in cells transfected with such chimeric promoter-reporter plasmids. The promoter region extending from -973 to +68 bp of the transcription start site elicited a 7-fold increase in reporter gene activity in transiently transfected osteoblasts after 1 alpha,25(OH)2D3 treatment, whereas the region from -553 to +68 bp of the transcription start site showed no response following 1 alpha,25(OH)2D3 treatment. Transfection of osteoblasts with reporter plasmids containing TGF-beta 2 promoter DNA from -869 to -658 bp revealed a 3.8-fold increase in reporter gene activity. DNA fragments from this region (-743 to -676 bp and -786 to -728 bp) ligated into reporter plasmids also showed increases in reporter activity. Gel retardation assay experiments showed that DNA fragments from -774 to -735 bp and -714 to -675 bp both formed a DNA-protein complex with bacterially expressed human retinoic acid X receptor alpha (RXR alpha) and vitamin D receptor (VDR) and with nuclear extracts from human bone cells. Addition of a vitamin D receptor antibody to reactions containing the aforesaid DNA fragments and bone cell nuclear extract resulted in further retardation of the mobility of the DNA-protein complex (super-shifting). Removal of two putative direct repeat DNA fragments in this region abolished VDR-RXR alpha-vitamin D response element complex formation. The TGF-beta 2 promoter contains two imperfect direct repeat DNA sequences: TGTAGAACAAGTAGA and AATGAAGTTGGTGGA that mediate the effect of 1 alpha,25(OH)2D3.

Base Sequence↗

Fibrin-dependent platelet procoagulant activity requires GPIb receptors and von Willebrand factor.

Thrombin generation in platelet-rich plasma (PRP) involves complex interactions between platelets and coagulation proteins. We previously reported that the addition of fibrin to PRP enhances tissue-factor initiated thrombin generation by approximately 40%, and the current studies were designed to assess the mechanism(s) underlying thrombin generation in the absence and presence of fibrin. Blocking platelet GPIIb/IIIa + alphavbeta3 receptors with a monoclonal antibody (MoAb) inhibited basal thrombin generation, but did not affect the enhancement produced by fibrin. In contrast, blocking GPIb with any of three different MoAbs had no effect on basal thrombin generation, but essentially eliminated fibrin enhancement of thrombin generation. When thrombin generation was tested in PRP deficient in von Willebrand factor (vWF), both basal and fibrin-enhanced thrombin generation were markedly reduced, and the addition of factor VIII did not normalize thrombin generation. Botrocetin, which induces the binding of vWF to GPIb, enhanced thrombin generation. In all studies, the ability of PRP to support thrombin generation correlated with the production of platelet-derived microparticles and serum platelet-derived procoagulant activity. Thus, two separate mechanisms, both of which depend on vWF, appear to contribute to platelet-derived procoagulant activity: one is independent of fibrin and relies primarily on GPIIb/IIIa, but with a minor contribution from alphavbeta3; and the other is fibrin-dependent and relies on GPIb. These data may have implications for understanding the mechanisms of the abnormalities in serum prothrombin times reported in Bernard-Soulier syndrome, hemorrhage in von Willebrand disease (vWD), and the increased risk of thrombosis associated with elevated vWF levels.

Animals↗

Regulation of cyclooxygenase-2 pathway by HER2 receptor.

Emerging lines of evidence suggest that in addition to growth factors, the process of colorectal tumorigenesis may also be driven by the upregulation of the inducible form of cyclooxygenase-2 (COX-2), an enzyme responsible for the conversion of arachidonic acid to PGEs. The present study was undertaken to investigate the expression and activation of the HER family members, and to explore the regulation of COX-2 expression by the HER2 pathway in human colorectal cancer cells. Here, we report that human colorectal cancer cell lines express abundant levels of HER2 and HER3 receptors, and are growth-stimulated by recombinant neu-differentiation factor-beta 1 (NDF). NDF-treatment of colorectal cancer cells was accompanied by increased tyrosine phosphorylation and heterodimerization of HER3 with HER2. In addition, we demonstrated that HER2 and HER3 receptors in colorectal cancer cells are constitutively phosphorylated on tyrosine residues and form heterodimeric complexes in the absence of exogenous NDF. Inhibition of HER2/HER3 signaling by an anti-HER3 mAb against the ligand binding site resulted in a decrease in the levels of constitutively activated HER2/ HER3 heterodimers, and the unexpected reduction of COX-2 expression. Activation of the HER2/HER3 pathway by NDF induced the activation of COX-2 promoter, expression of COX-2 mRNA, COX-2 protein and accumulation of prostaglandin E2 in the culture medium. Finally, we demonstrated that NDF promotes the ability of colorectal cancer cells to survive in an extracellular matrix milieu, such as Matrigel, and also to invade through a 8 microm porous membrane. These biological activities of NDF and its stimulation of cell proliferation are blocked by a specific inhibitor of COX-2. Taken together, our findings provide the first biochemical evidence of a possible role of the COX-2 pathway in the mitogenic action of NDF in colorectal cancer cells where it may be constitutively upregulated due to the autocrine/paracrine activation of HER2/ HER3 heterodimers.

3T3 Cells↗

On-line sample clean-up and chromatography coupled with electrospray ionization mass spectrometry to characterize the primary sequence and disulfide bond content of recombinant calcium binding proteins.

We have used on-line sample clean-up, concentration, and chromatography with electrospray ionization mass spectrometry (ESI-MS), to characterize and determine the presence of disulfide bonds in recombinant full-length rat brain calbindin D28K and two deletion mutants of the protein, one lacking EF-hand 2 (calbindin delta 2) and the other lacking EF-hands 2 and 6 (calbindin delta 2,6). The molecular weights of the expressed proteins dissolved in biological buffers were determined with high accuracy using a low-flow, pressurized chamber infusion system, that allows on-line protein clean-up by removing buffers/salts incompatible with ESI-MS. The molecular weight determinations showed that the amino-terminal methionine residues had been cleaved during the expression and isolation of the recombinant proteins. Approximately 85-90% of the protein sequences were confirmed by on-line HPLC-ESI-MS analysis of peptides generated by a lysyl endoproteinase C digestion. Comparisons of ESI-MS spectra of native and reduced calbindin D28K and delta 2 show that the full length- and delta 2 mutant-protein contain one disulfide bond. Molecular mass determinations of calbindin delta 2,6 showed that this protein contains a highly active cysteine residue that covalently binds a mercaptoethanol group, or forms a homodimer via a disulfide bond. The results show surprising differences amongst the deletion mutants of calbindin D28K with respect to the formation of disulfide bonds. These differences are not readily detected by other techniques and show that ESI-MS is a powerful, rapid method by which to detect disulfide linkages for intact proteins.

Amino Acid Sequence↗