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Biomedical subjects

S Prakash

Publications and source records attributed to S Prakash.

At least 217 records · Page 12Linked to original sources
PubMed1991

Fibroblast stimulation in schistosomiasis. XI. Purification to apparent homogeneity of fibroblast-stimulating factor-1, an acidic heparin-binding growth factor produced by schistosomal egg granulomas.

Liver fibrosis is the most serious complication of infection with Schistosoma mansoni and Schistosoma japonicum and is responsible for severe morbidity and mortality in hundreds of thousands of patients in many Third World nations. The pathogenesis of this condition remains to be elucidated. We proposed that certain cytokines produced by cells that comprise the chronic granulomas that surround the helminth eggs within the liver initiate hepatic fibrogenesis. We now report our successful purification to apparent homogeneity of the egg granuloma-derived fibroblast mitogen. The high affinity of this factor for heparin (elutes from heparin-Sepharose with 1.5 M NaCl) facilitates its purification by a two-step procedure, and identifies the cytokine as a heparin-binding growth factor (HBGF). Furthermore, because it has an isoelectric point approximately equal to 6.2, it has one of the characteristics of a class 1 (acidic) HBGF. We immunized rabbits with the purified factor and observed that the resulting antibodies (IgG) detected the factor but not acidic fibroblast growth factor (the prototypic class 1 HBGF) either by dot-blot ELISA or neutralization of biologic activity. The granuloma product and fibroblast growth factor also differ in target-cell specificity and amino acid composition. On the basis of these distinctions, we have designated the granuloma-derived mitogen fibroblast-stimulating factor-1. With the availability of purified fibroblast-stimulating factor-1 and the future analysis of its amino acid sequence, its structural relationship to other mesenchymal growth factors can be determined.

Animals↗
PubMed1991

Yeast RAD6 encoded ubiquitin conjugating enzyme mediates protein degradation dependent on the N-end-recognizing E3 enzyme.

The RAD6 gene of Saccharomyces cerevisiae encodes a 20 kd ubiquitin conjugating (E2) enzyme that is required for DNA repair, DNA damage-induced mutagenesis, and sporulation. Here, we demonstrate a novel activity of RAD6 protein--its ability to mediate protein degradation dependent on the N-end-recognizing ubiquitin protein ligase (E3). In reaction mixtures containing E1, E3 and the ubiquitin specific protease from rabbit reticulocytes, RAD6 is as effective as mammalian E214k in E3 dependent ubiquitin--protein conjugate formation and subsequent protein degradation. The ubiquitin conjugating activity of RAD6 is required for these reactions as indicated by the ineffectiveness of the rad6 Ala88 and rad6 Val88 mutant proteins, which lack the ability to form a thioester adduct with ubiquitin and therefore do not conjugate ubiquitin to substrates. We also show that the highly acidic carboxyl-terminus of RAD6 is dispensable for the interaction with E3, and that purified S. cerevisiae E2(30k), product of the UBC1 gene, does not function with E3. These findings demonstrate a specific interaction between RAD6 and E3, and highlight the strong conservation of the ubiquitin conjugating system in eukaryotes. We suggest a function for RAD6 mediated E3 dependent protein degradation in sporulation, and discuss the possible role of this activity during vegetative growth.

Animals↗
PubMed1991

Structure-activity relationship studies with mosquito repellent amides.

A series of amide analogues of N,N-diethyl-m-toluamide (DEET) and N,N-diethylphenylacetamide (DEPA) were synthesized to study their mosquito repellency in relation to chemical structure and physical properties. None of these parameters (vapor pressure, lipophilicity, and molecular length) could be related to protection time. However, when the protection time of all five amides derived from the same carboxylic acid was expressed in terms of all three parameters together, excellent correlation was obtained.

Acetamides↗
PubMed1991

N,N-diethylphenylacetamide in treated fabrics as a repellent against Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae).

The efficacy of fabrics impregnated with N,N-diethylphenylacetamide (DEPA), a new repellent, was studied in the laboratory and field against Aedes aegypti (L.) and Culex quinquefasciatus Say. DEPA-treated polyester cotton and cotton fabrics provided repellency for 30 and 36 d and had a half-life of 11 and 5 d, respectively. The repellent could not be applied at a rate of greater than 15% of fabric weight. DEPA-treated fabric patches were found to be a practical and novel approach and were effective for 90 d in the laboratory against Ae. aegypti and 77 d in the field against Cs. quinquefasciatus.

Acetamides↗
PubMed1991

Single small enhancing CT lesions in Indian patients with epilepsy: clinical, radiological and pathological considerations.

Thirty consecutive Indian patients with focal or generalised seizures and single, small (less than 10 mm), enhancing lesions on CT scans (SSECTL) were studied. Five patients (Group A) were treated with anticonvulsants alone and did not have a biopsy. In ten patients (Group B) a CT guided stereotaxic biopsy of the lesion was carried out and in the remainder (15-Group C) and excision biopsy of the lesion was carried out following CT guided stereotaxic localisation. In all patients in Group B the lesion were reported as "chronic nonspecific inflammation". In seven of 15 patients in Group C the lesions showed a cysticercus with a granuloma and in a further five the pathology was that of a "parasitic granuloma" but the parasite could not be identified. Biopsy did not reveal a tuberculoma or neoplasm in any of the patients. The lesions studied are the same as "disappearing" CT lesions reported in Indian patients, as in 12 of 15 patients in Groups A and B, who could be followed up for more than three months, the lesions had spontaneously disappeared or left calcific residues. It is concluded that in Indian epileptic patients with SSECTL cysticercosis is the commonest aetiology. A treatment protocol for these patients is suggested on the basis of the findings.

Biopsy↗
PubMed1991

Alterations in influence of granuloma-derived cytokines on fibrogenesis in the course of murine Schistosoma mansoni infection.

Schistosomiasis is the main cause of hepatic fibrosis worldwide, yet its pathogenesis remains unknown. We previously reported that conditioned medium from cultures of hepatic egg granulomas (isolated from mice acutely infected with Schistosoma mansoni) can stimulate fibroblast proliferation and matrix production in vitro. We have proposed that initiation of hepatic fibrosis in this infection might be under the control of granuloma-derived cytokines. We now report that conditioned medium from cultures of schistosomal egg granulomas isolated from liver of chronically infected mice has reduced fibrogenic activity compared with medium from cultures of granulomas obtained from more acutely infected mice. In related studies, we adoptively transferred splenocytes from infected mice and examined the fibrogenic activity in culture supernatants of hepatic egg granulomas isolated from the recipients. Those prepared from recipients of splenocytes from chronically infected mice contained substantially less fibrogenic activity than did those from recipients of splenocytes of acutely infected mice. These findings suggest that the fibrogenic influence of schistosomal egg granuloma products decreases during the course of chronic murine S. mansoni infection. Furthermore, our preliminary findings suggest that immunoregulatory cells may be responsible for the down-regulation of this influence. Previous observations indicating that in murine schistosomiasis hepatic collagen and hyaluronate synthesis and deposition are elevated in acute but not chronic infection might be explained on the basis of our observations.

Animals↗
PubMed1991

In vivo experimental model to evaluate the insect repellent N-N, diethylphenylacetamide in Periplaneta americana Linn.

The responsiveness of insect antennae to bornyl acetate (BA), a sex pheromone mimic and N,N-diethyl phenylacetamide (DEPA), a multi-insect repellent has been studied. Electrical activity from the antennal lobe was quantified to observe the alterations in power and frequency spectrum in P. americana Linn. following exposure to these chemicals. Two distinct patterns of responses were exhibited on exposure to BA and DEPA, the former producing a marked excitation and the latter inhibition of electrical discharge during the exposure to these compounds at a concentration of 200 micrograms.

Acetamides↗
PubMed1990

Transcript levels of the Saccharomyes cerevisiae DNA repair gene RAD23 increase in response to UV light and in meiosis but remain constant in the mitotic cell cycle.

The RAD23 gene of Saccharomyces cerevisiae is required for excision-repair of UV damaged DNA. In this paper, we determine the location of the RAD23 gene in a cloned DNA fragment, identify the 1.6 kb RAD23 transcript, and examine RAD23 transcript levels in UV damaged cells, during the mitotic cell cycle, and in meiosis. The RAD23 mRNA levels are elevated 5-fold between 30 to 60 min after 37 J/m2 of UV light. RAD23 mRNA levels rise over 6-fold during meiosis at a stage coincident with high levels of genetic recombination. This response is specific to sporulation competent MATa/MAT alpha diploid cells, and is not observed in asporogenous MATa/MATa diploids. RAD23 mRNA levels, however, remain constant during the mitotic cell cycle.

Cloning, Molecular↗
PubMed1990

Regulated expression of the Saccharomyces cerevisiae DNA repair gene RAD7 in response to DNA damage and during sporulation.

The RAD7 gene of Saccharomyces cerevisiae affects the proficiency of excision repair of DNA damaged by UV light. Here, we report our studies on the regulation of the RAD7 gene in response to UV irradiation and during sporulation. RAD7 transcript levels increased 6-fold within 40 min of exposure of cells to 37 J/m2 of UV light. Higher UV doses also elicited rapid increases in the level of RAD7 mRNA. RAD7 mRNA levels increased in sporulating MATa/MAT alpha diploid cells, but not in the asporogenous MATa/MATa strain exposed to sporulation conditions. The increase in RAD7 mRNA level in MATa/MAT alpha cells was 15-fold after 6 h and 9-fold after 7 h in sporulation medium; thereafter, RAD7 mRNA levels declined. Periodic transcription of RAD7 during sporulation suggests a role for RAD7 in this process.

DNA Damage↗
PubMed1990

Expression of the Saccharomyces cerevisiae DNA repair gene RAD6 that encodes a ubiquitin conjugating enzyme, increases in response to DNA damage and in meiosis but remains constant during the mitotic cell cycle.

The RAD6 gene of Saccharomyces cerevisiae encodes a ubiquitin-conjugating (E2) enzyme and is required for the repair of damaged DNA, mutagenesis, and sporulation. Here, we report our studies on the regulation of RAD6 gene expression after UV damage, during the mitotic cell cycle, in meiosis, and following heat shock and starvation. RAD6 mRNA levels became elevated in cells exposed to UV light, and at all UV doses the increase in mRNA levels was rapid and occurred within 30 min after exposure to UV. RAD6 mRNA levels also increased in sporulating MATa/MAT alpha cells, and the period of maximal accumulation of RAD6 mRNA during meiosis is coincident with the time during which recombination occurs. However, RAD6 mRNA levels showed no periodic fluctuation in the mitotic cell cycle, were not elevated upon heat shock, and fell in cells in the stationary phase of growth. These observations suggest that RAD6 activity is required throughout the cell cycle rather than being restricted to a specific stage, and that during meiosis, high levels of RAD6 activity may be needed at a stage coincident with genetic recombination. The observation that RAD6 transcription is not induced by heat and starvation, treatments that activate stress responses, suggests that the primary role of RAD6 is in the repair of damaged DNA rather than in adapting cells to stress situations.

DNA Damage↗
PubMed1990

Fibroblast stimulation in schistosomiasis. IX. Schistosomal egg granulomas from congenitally athymic mice are deficient in production of fibrogenic factors.

Schistosomal egg granulomas spontaneously secrete fibrogenic factors, suggesting that there exists a molecular link between granulomatous inflammation and hepatic fibrosis in schistosomiasis. To further assess this possibility, we compared elaboration of fibrogenic factors by egg granulomas isolated from Schistosoma mansoni-infected euthymic mice that develop substantial liver fibrosis, with those elaborated by similarly infected congenitally athymic mice that develop minimal fibrosis. Conditioned medium from cultures of granulomas from euthymic mice stimulated fibroblast proliferation, chemotaxis, and synthesis of collagen, collagenase, tissue inhibitor of metalloproteinases, and hyaluronate, whereas those prepared from cultures of granulomas isolated from athymic mice were relatively or absolutely deficient in such activities. These observations provide a correlation between the presence of fibrosis in vivo and the production of fibrogenic factors and reinforce our hypothesis that granuloma-derived fibrogenic factors play a role in the pathogenesis of liver fibrosis in schistosomiasis. Furthermore, the results of this study suggest a central role of T lymphocytes in the fibrogenic process.

Animals↗
PubMed1990

The rhp6+ gene of Schizosaccharomyces pombe: a structural and functional homolog of the RAD6 gene from the distantly related yeast Saccharomyces cerevisiae.

The RAD6 gene of Saccharomyces cerevisiae encodes a ubiquitin conjugating enzyme and is required for DNA repair, DNA-damage-induced mutagenesis and sporulation. Here, we show that RAD6 and the rhp6+ gene from the distantly related yeast Schizosaccharomyces pombe share a high degree of structural and functional homology. The predominantly acidic carboxyl-terminal 21 amino acids present in the RAD6 protein are absent in the rhp6(+)-encoded protein; otherwise, the two proteins are very similar, with 77% identical residues. Like rad6, null mutations of the rhp6+ gene confer a defect in DNA repair, UV mutagenesis and sporulation, and the RAD6 and rhp6+ genes can functionally substitute for one another. These observations suggest that functional interactions between RAD6 (rhp6+) protein and other components of the DNA repair complex have been conserved among eukaryotes.

Amino Acid Sequence↗
PubMed1990

A nondenaturing solid phase pharmaceutical carrier comprised of surface-modified nanocrystalline materials.

Numerous carrier systems have been developed for the controlled delivery of biologically active molecules such as drugs and diagnostic agents. The biophysical interactions between the biologically active molecules and their carriers, however, may denature the former and lead to reduced biological activity. In this study, a model nondenaturing carrier comprised of a nanocrystalline (10 -7 m) tin oxide core and a surface-charge-reducing organic bonding layer (GF292) was synthesized. A subsequently bound protein (human transferrin) showed significant retained conformation by immunoelectron microscopy. In the synthesis of targeted drug systems and vaccines, nanocrystalline cores treated with appropriate surface-modifying agents may be suitable carriers.

Crystallins↗
PubMed1990

Mutation of cysteine-88 in the Saccharomyces cerevisiae RAD6 protein abolishes its ubiquitin-conjugating activity and its various biological functions.

The RAD6 gene of Saccharomyces cerevisiae is required for DNA repair, DNA damage-induced mutagenesis, and sporulation. RAD6 protein is a ubiquitin-conjugating enzyme (E2) that has been shown to attach multiple molecules of ubiquitin to histones H2A and H2B. We have now examined whether the E2 activity of RAD6 is involved in its various biological functions. Since the formation of a thioester adduct between E2 and ubiquitin is necessary for E2 activity, the single cysteine residue (Cys-88) present in RAD6 was changed to alanine or valine. The mutant proteins were overproduced in yeast cells and purified to near homogeneity. We show that the rad6 Ala-88 and rad6 Val-88 mutant proteins lack the capacity for thioester formation with ubiquitin and, as a consequence, are totally devoid of any E2 activity. The rad6 Ala-88 and rad6 Val-88 mutations confer a defect in DNA repair, mutagenesis, and sporulation equivalent to that in the rad6 null allele. We suggest that the biological functions of RAD6 require its E2 activity.

Alanine↗