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R C Patel

Publications and source records attributed to R C Patel.

At least 19 recordsLinked to original sources
PubMed1996

Specific mutations near the amino terminus of double-stranded RNA-dependent protein kinase (PKR) differentially affect its double-stranded RNA binding and dimerization properties.

The amino-terminal region of the double-stranded (ds) RNA-dependent protein kinase, PKR, has been shown to mediate both dsRNA binding and protein dimerization. To critically examine if PKR dimerization is dependent on dsRNA binding, we generated a series of mutants that are incapable of binding dsRNA. Some, but not all, of these mutants retained the ability to dimerize, as shown by a two-hybrid transcriptional activation assay in vivo and a chemical cross-linking assay in vitro. These mutants were used further to demonstrate that the translational inhibitory activity of PKR in vivo requires dsRNA binding; PKR mutants that dimerized but did not bind dsRNA could not inhibit the translation of a transfected reporter gene.

Amino Acid Sequence↗
PubMed1996

Application of the Roche Amplicor Mycobacterium tuberculosis (PCR) test to specimens other than respiratory secretions.

The ability of the Roche AMPLICOR Mycobacterium tuberculosis (MTB) test to detect M. tuberculosis in specimens other than respiratory secretions was evaluated. A total of 249 specimens from 219 patients were tested. Of these, 12 specimens grew isolates of the M. tuberculosis complex and four grew isolates of the M. avium complex. The AMPLICOR MTB test was positive for 10 of the 12 specimens which grew M. tuberculosis and for three specimens which were culture negative. Two of the latter specimens were from patients with a clinical diagnosis of tuberculosis and with multiple sputum specimens which grew M. tuberculosis. Four specimens grew M. avium complex isolates, and all yielded negative AMPLICOR MTB test results. The sensitivity, specificity, and positive and negative predictive values for the AMPLICOR MTB test were 85.7%, 99.5%, 92.3%, and 99.1%, respectively. Our data indicate that the AMPLICOR MTB test will permit the rapid detection of M. tuberculosis in specimens other than respiratory secretions.

Biopsy↗
PubMed1996

Cardiac involvement in HIV infection.

Cardiac involvement in HIV infection was previously believed to be an unusual manifestation of the disease, but is now being described with increasing frequency. It may be a well-characterized cardiac disease occurring coincidentally in an AIDS patient, a complication of AIDS or its treatment, or possibly a direct result of HIV infection of the heart. In this article, the authors describe the emerging patterns of heart and vascular diseases in HIV-infected patients, pathogenic mechanisms, and implications for treatment.

AIDS-Related Opportunistic Infections↗
PubMed1995

The interferon-inducible double-stranded RNA-activated protein kinase self-associates in vitro and in vivo.

The interferon-inducible double-stranded (ds) RNA-activated protein kinase (PKR) exhibits antiviral, anticellular, and antitumor activities. The mechanisms of its enzymatic activation by autophosphorylation and of the observed transdominant inhibitory phenotype of enzymatically inactive mutants have invoked PKR dimerization. Here we present direct evidence in support of PKR-PKR interaction. We show that radiolabeled PKR can specifically interact with matrix-bound unlabeled PKR in the absence of dsRNA. The self-association activity resides, in part, in the N-terminal region of 170 residues, which also constitutes the dsRNA-binding domain (DRBD). DRBD can bind to matrix-bound PKR or to matrix-bound DRBD. Dimerization of DRBD was directly demonstrated by chemical crosslinking. Affinity chromatography and electrophoretic mobility supershift assays demonstrated that mutants that fail to bind dsRNA can still exhibit protein-protein interaction. The PKR-PKR interaction could also be observed in a two-hybrid transcriptional activation assay in mammalian cells and consequently is likely to be an important feature of PKR activity in vivo.

Biopolymers↗
PubMed1995

Astrocytes synthesize and secrete the lipophilic ligand carrier apolipoprotein D.

Expression of the lipophilic ligand transporter, apolipoprotein D (apoD) by primary astrocyte cultures derived from neonatal mouse brain was investigated. Western blot analysis of cell lysates and media showed that apoD is constitutively secreted by astrocytes with little intracellular storage. The secreted apoD floated primarily at density 1.063-1.21 g ml-1 upon sequential ultracentrifugation indicating its association with lipids. Treatment of astrocytes with the carboxylic ionophore, monensin, resulted in intracellular retention and decreased secretion of apoD that was of slightly reduced M(r). Progesterone, a steroid hormone that binds to apoD with high affinity (10(-6) mol l-1) and the oxysterol, 25-hydroxycholesterol which is a potent regulator of cellular cholesterol homeostasis in mammalian cells, differentially stimulated apoD, but not apoE secretion. These results show that astrocytes synthesize and constitutively secrete apoD and suggest a physiologic role for this lipocalin in cholesterol metabolism in the nervous system.

Animals↗
PubMed1995

Activation of interferon-inducible 2'-5' oligoadenylate synthetase by adenoviral VAI RNA.

2'-5' oligoadenylate (2-5(A)) synthetase and protein kinase, RNA activated (PKR) are the only two known enzymes that bind double-stranded RNA (dsRNA) and get activated by it. We have previously identified their dsRNA binding domains, which do not have any sequence homology. Here, we report a profound difference between the two enzymes with respect to the structural features of the dsRNA that are required for their activation. The adenoviral virus-associated type I (VAI) RNA cannot activate PKR, although it binds to the protein and thereby prevents its activation by authentic dsRNA. In contrast, we observed that VAI RNA can both bind and activate 2-5(A) synthetase. Mutations in VAI RNA, which removed occasional mismatches present in its double-stranded stems, markedly enhanced its 2-5(A) synthetase-activating capacity. These mutants, however, are incapable of activating PKR. Other mutations, which disrupted the structure of the central stem-loop region of the VAI RNA, reduced its ability to activate 2-5(A) synthetase. These debilitated mutants could bind to the synthetase protein, although they fail to bind to PKR.

2',5'-Oligoadenylate Synthetase↗
PubMed1995

Rapid diagnosis of pulmonary tuberculosis by using Roche AMPLICOR Mycobacterium tuberculosis PCR test.

A rapid PCR-based test for the diagnosis of pulmonary tuberculosis, the Roche AMPLICOR Mycobacterium tuberculosis test (AMPLICOR MTB), was evaluated. Results from AMPLICOR MTB were compared with culture results and the final clinical diagnosis for each patient. A total of 985 specimens from 372 patients were tested. When AMPLICOR MTB results were compared with resolved results, i.e., a specimen grew M. tuberculosis or was obtained from a patient with a clinical diagnosis of tuberculosis, the sensitivity, specificity, positive predictive value, and negative predictive value for the AMPLICOR MTB test were 66.7, 99.6, 91.7, and 97.7%, respectively. These results were comparable to those obtained from culture. Test results were available approximately 6.5 h after specimen receipt in the laboratory. Our data demonstrate that AMPLICOR MTB will provide rapid, valuable information for the diagnosis and control of tuberculosis.

Bacteriological Techniques↗
PubMed1994

25-Hydroxycholesterol induces reorganization of lysosomes in normal but not Niemann-Pick disease type C astrocytes.

25-hydroxycholesterol (25-OHC), an oxysterol that potently regulates cellular cholesterol metabolism, induced formation of novel fibrillar structures in normal mouse astrocytes as observed by fluorescence microscopy with the cholesterol probe, filipin. These fibrils were identified as lysosomes by their immunoreactivity for the lysosome associated membrane glycoprotein (LAMP). In contrast, astrocytes derived from the Niemann-Pick disease type C (NPC) mutant mouse were resistant to this oxysterol-induced lysosomal reorganization. NPC astrocytes have abnormal intracellular cholesterol storage as observed by brightly positive filipin staining of their lysosomes. These results show that lysosomal cholesterol storage in NPC astrocytes is associated with a block in oxysterol-mediated fibrillar reorganization of lysosomes.

Animals↗
PubMed1994

Role of the amino-terminal residues of the interferon-induced protein kinase in its activation by double-stranded RNA and heparin.

We have previously reported that the amino-terminal residues 1-34 of the interferon-induced protein kinase (RNA-activated) (PKR) are necessary for its binding to and activation by double-stranded RNA (dsRNA) (Patel, R. C., and Sen, G. C. (1992) J. Biol. Chem. 267, 7671-7676). Here, we report that the amino-terminal 24 residues are indispensable for these properties of the enzyme. The replacement of these residues with 14 unrelated residues fully restored the protein's dsRNA binding activity, but only partially restored the enzyme activity. Mutation of residues 18 and 19 revealed their importance in determining the affinity of PKR for dsRNA and its ability to phosphorylate eukaryotic initiation factor 2 alpha. These mutations, however, did not affect PKR's autophosphorylation activity. Deletion mutants that failed to bind to and be activated by dsRNA could be fully activated by the alternative activator, heparin. Thus, activation of PKR by dsRNA and heparin is mediated through different mechanisms that require different domains of the protein.

Amino Acid Sequence↗
PubMed1994

EDTA and the absorption of iron from food.

Iron EDTA is an effective fortificant in meals of low iron bioavailability. Na2EDTA, added to food to prevent oxidation, enhances iron bioavailability by chelating added iron. This study examines the optimal ratio of EDTA to iron causing enhanced iron absorption. Iron absorption from a rice-based meal of low iron bioavailability containing increasing molar ratios of EDTA to iron, was compared in 127 women volunteers by using standard double isotope techniques. Iron deficiency was present in 38% of the women. Mean standardized absorptions, at EDTA-iron ratios of 0.25, 0.5, and 1, were 11.3%, 13.5%, and 8.8%, respectively, compared with 3.8% when no Na2EDTA was present. In meals of high iron bioavailability, Na2EDTA (EDTA:Fe, 1.0) produced little enhancement (potato-based meal) nor inhibited iron absorption (apple-based meal). Na2EDTA added to meals with molar ratios of EDTA to iron between 1.0 and 0.25 significantly increases iron absorption provided the meal is of low iron bioavailability.

Diet↗
PubMed1994

Characterization of the interactions between double-stranded RNA and the double-stranded RNA binding domain of the interferon induced protein kinase.

The interferon-inducible protein kinase, PKR, requires double-stranded (ds) RNA for its activation. We have previously mapped its dsRNA-binding domain (DRBD) to the amino terminal 170 residues (Patel and Sen, 1992). In the present study, we have characterized in detail the interactions between dsRNA and DRBD. For this purpose, DRBD was produced in bacteria as a polyhistidine-tagged protein and purified by affinity chromatography. A polyclonal antibody was raised against purified DRBD. For studying dsRNA-DRBD interactions, a Northwestern assay and an electrophoretic mobility shift assay (EMSA) using a radiolabeled in vitro transcribed 82 bp dsRNA probe was developed. The antiserum reacted with both DRBD and PKR but did not prevent their interactions with dsRNA. DRBD, on the other hand, blocked the activation of PKR by dsRNA. DRBD and the dsRNA probe formed multimeric complexes which were separable by EMSA. The antibody could interact with these complexes and supershift their mobility. Competition with unlabeled dsRNA revealed that the dimeric DRBD-dsRNA complex was much more stable than the monomeric complex. Similar competition assays using 11 different synthetic and natural RNA molecules revealed that only authentic dsRNA molecules could effectively compete with the probe for binding DRBD in a sequence-independent fashion.

Amino Acid Sequence↗
PubMed1993

Fulminant amyloid cardiomyopathy.

Within a 3-month period, a 71-year-old man went from an asymptomatic, active existence to intractable heart failure and death. Widespread amyloid deposition was noted on the histologic examination of endomyocardial biopsy samples. The historical and laboratory features of this patient's rapidly devastating clinical course form the basis of this report.

Aged↗
PubMed1992

Identification of the double-stranded RNA-binding domain of the human interferon-inducible protein kinase.

The interferon-inducible double-stranded (ds) RNA-activated protein kinase (p68 kinase) is a physiologically important enzyme that regulates the rate of cellular and viral protein synthesis by phosphorylating and thereby inactivating the peptide chain initiation factor 2. We have generated a cDNA clone of the human p68 kinase by polymerase chain reaction cloning using the recently published sequence of this enzyme. Active enzyme was synthesized by in vitro transcription-translation of the cDNA clone. This system was used for mapping the dsRNA-binding domain of the enzyme. Progressive deletions from the carboxyl terminus were introduced by digesting the cDNA with suitable restriction enzymes. Expression of proteins harboring deletions from the amino terminus was achieved by cloning DNA fragments into appropriately constructed expression vectors. Affinity of the truncated proteins for dsRNA was examined by testing their capacity to bind to dsRNA-agarose beads. Our results demonstrated that the dsRNA-binding domain lies at the amino terminus of the protein. A truncated protein containing the first 170 amino acid residues from the amino terminus could bind to dsRNA. However, deletion of 34 residues from the amino terminus or 41 residues from the carboxyl terminus of this truncated protein eliminated its dsRNA-binding activity. Comparison of the primary structure and the secondary structure of this region of p68 kinase and the corresponding region of 2'-5'-oligoadenylate synthetase revealed no apparent similarity.

Base Sequence↗
PubMed1992

Cis-acting sequences in the 5'-untranslated region of the ribosomal protein A1 mRNA mediate its translational regulation during early embryogenesis of Drosophila.

The rate of ribosomal (r)-protein synthesis in the early Drosophila embryo is low despite the presence of abundant, maternally supplied r-protein mRNAs. This low rate is due to specific repression of r-protein mRNA translation. In contrast to r-protein mRNAs, most other mRNAs are efficiently translated in the early embryo. Here we report on the identification of cis-acting sequences that mediate translational repression of the r-protein A1 (rpA1) mRNA. Chimeric genes containing sequences from the translationally regulated rpA1 mRNA fused to the constitutively translated alpha-tubulin mRNA were constructed and transformed into the Drosophila germ line. Translation of the corresponding hybrid mRNAs was measured in ovaries and embryos of the transgenic flies. The results indicated that a 89-nucleotide sequence in the untranslated rpA1 mRNA leader is by itself sufficient to confer full translational regulation to a heterologous mRNA.

Animals↗
PubMed1992

Construction and expression of an enzymatically active human-mouse chimeric double-stranded RNA-dependent protein kinase.

The interferon (IFN)-inducible double-stranded (ds) RNA-activated protein kinase (p68 kinase) is a physiologically important enzyme that regulates the rate of cellular and viral protein synthesis by phosphorylating and thereby inactivating the peptide chain initiation factor 2. We have generated a partial cDNA clone, which probably represents the murine p68 kinase, by reverse transcription-polymerase chain reaction (RT-PCR) using sequence information of the human p68 kinase. The 725-bp cDNA clone encoded the carboxyl-terminal 238 amino acid residues of the mouse kinase. It has 67% overall identity with the corresponding region of the human kinase. All the protein kinase catalytic domains are conserved in the mouse protein. Moreover, there are additional stretches of residues that are totally conserved between the two proteins. The functional equivalence of the two proteins was tested by constructing a chimeric cDNA that encoded a protein whose amino-terminal 364 residues were of human origin and carboxyl-terminal 187 residues were of mouse origin. The chimeric protein was as efficient as the human p68 kinase in binding to the dsRNA, autophosphorylating and phosphorylating exogenous substrate.

Amino Acid Sequence↗
PubMed1990

Overproduction and translational regulation of rp49 ribosomal protein mRNA in transgenic Drosophila carrying extra copies of the gene.

During Drosophila early development the translation of ribosomal protein mRNAs is regulated specifically and coordinately. In this study we assayed for changes of ribosomal protein rp49 gene expression in flies transformed with extra copies of the gene. RNA blot analysis revealed that the rp49 transcript was overrepresented in most of the transformed fly lines: flies carrying three times more genes than the wild type contained up to seven times more mRNA. The abundance of other ribosomal protein mRNAs was not affected. Despite the large differences in rp49 mRNA content, the proportion of the rp49 mRNA which was associated with polysomes during oogenesis and early embryogenesis did not differ significantly from the wild type, implying that rp49 protein is overproduced in the transgenic flies. The results indicate that the basis for coordinate r-protein gene expression lies in the intrinsic properties of r-protein genes, rather than in a dynamic system that separately modulates the expression of individual genes.

Animals↗
PubMed1990

Effects of sequential doses of parenteral terbutaline on plasma levels of potassium and related cardiopulmonary responses.

beta-agonist bronchodilator drugs are known to cause hypokalemia; nevertheless, successive parenteral doses are recommended for the treatment of status asthmaticus. The metabolic and cardiopulmonary effects of sequential, subcutaneous doses of terbutaline were studied in eight stable adult asthmatic patients. Each subject received terbutaline, 0.25 mg subcutaneously, followed 30 min later either by a second subcutaneous dose of terbutaline (sequential) or normal saline (single) in a randomized, double-blind, crossover fashion. Maximum reductions in plasma potassium from baseline were significantly greater (p less than 0.05) following sequential treatment compared to single treatment (-1.1 versus -0.6 mEq/L, respectively). Improvements in forced expiratory volume in 1 s were temporally related to changes in serum potassium and were significantly greater (p less than 0.01) following sequential terbutaline treatment. Prolongation of the QTc interval occurred following both treatment regimens. The change in QTc was statistically significant only following sequential treatment, increasing from 377 +/- 21 to 441 +/- 39 ms (p less than 0.05). Sequential doses of parenterally administered terbutaline result in clinically significant reductions in plasma potassium that are temporally related to changes in pulmonary function and associated with important electrocardiographic alterations.

Adult↗