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Biomedical subjects

A Molnár

Publications and source records attributed to A Molnár.

At least 19 recordsLinked to original sources
PubMed1999

Development of a monitoring network for the analysis of elements in aerosol samples collected at Lake Balaton.

Determination of different toxic elements in aerosol and precipitation samples collected at Lake Balaton were carried out. A simple sequential leaching procedure was applied for the determination of the distribution of elements. The distribution of elements was determined among environmentally mobile, bound to carbonates and oxides, and bound to silicates and organic matters (environmentally immobile) fractions. Particular attention was paid to distinguish between environmentally mobile and environmentally immobile fractions because these represent the two extreme modes by which the metals are bound to the solid matrices. Aerosol samples were weekly collected in Tihany, Siófok and Keszthely on 5 cm diameter Teflon filters with a membrane pump. While Cd-compounds have been found enormously in the environmentally mobile fractions, As-compounds accumulated almost evenly among portions. The results of sequential leaching give an indication of the mobility of the elements once the aerosol is mixed directly into natural waters on during scavenging of the aerosol by wet deposition. Based upon the data it can be concluded that the effect of anthropogenic sources is minor in this area.

Aerosols↗
PubMed1997

Cdc42Hs, but not Rac1, inhibits serum-stimulated cell cycle progression at G1/S through a mechanism requiring p38/RK.

Antimitogenic stimuli such as environmental or genotoxic stress, transforming growth factor-beta, and the inflammatory cytokines tumor necrosis factor and interleukin-1 activate two extracellular signal-regulated kinase (ERK)-based signaling pathways: the stress-activated protein kinase (SAPK/JNK) pathway and the p38 pathway. Activated p38 phosphorylates transcription factors important in the regulation of cell growth and apoptosis, including activating transcription factor 2 (ATF2), Max, cAMP response element-binding protein-homologous protein/growth arrest DNA damage 153 (CHDP/GADD153). In turn, p38 lies downstream of the Rho family GTPases Cdc42Hs and Rac1, as well as at least three mitogen-activated protein kinase (MAPK)/ERK-kinases (MEKs): MAPK kinases-3, -6, and SAPK/ERK-kinase-1. Although many of the stimuli that activate p38 can also inhibit cell cycle progression, a clear-cut role for the p38 pathway in cell cycle regulation has not been established. Using a quantitative microinjection approach, we show here that Cdc42Hs, but not Rac1 or RhoA, can inhibit cell cycle progression at G1/S through a mechanism requiring activation of p38. These results suggest a novel role for Cdc42Hs in cell cycle inhibition. Furthermore, these results suggest that although both Cdc42Hs and Rac1 can activate p38 in situ, the effects of Cdc42Hs and Rac1 on cell cycle progression are, in fact, quite distinct.

3T3 Cells↗
PubMed1997

Characterization of microtubule-phosphofructokinase complex: specific effects of MgATP and vinblastine.

Phosphofructokinase interacts with both microtubules and microtubules containing microtubule-associated proteins to produce bundling and periodical cross-bridging of tubules. Immunoelectron microscopy using anti-phosphofructokinase antibodies provided direct evidence that the kinase molecules are responsible for the cross-bridging of microtubules. Limited proteolysis by subtilisin, a procedure that cleaves the N-terminal segment of the free enzyme as well as the C-terminal "tails" of tubulin subunits exposed on microtubules, showed that while phosphofructokinase becomes resistant, tubulin retains sensitivity against proteolysis within the heterologous complex. These data suggest that the N-terminal segment of the enzyme, but not the C-terminal "tail" of tubulin subunits, is involved in the interaction between the microtubule and the kinase. The phosphorylation of phosphofructokinase or microtubules containing microtubule-associated proteins by the cAMP-dependent protein kinase did not interfere with the heterologous complex formation. MgATP prevents phosphofructokinase binding to the microtubules, and it can displace the enzyme from the single microtubules. However, the bundled microtubules are apparently resistant to the MgATP dissociation effect. Modelling of the assembly process suggests that the tubulin-kinase complex is able to polymerize as the free tubulin. Vinblastine, an anti-mitotic agent, inhibits tubulin assembly; however, its inhibitory effect is partially suppressed in the presence of phosphofructokinase. Fluorescence anisotropy measurements indicated that kinase and vinblastine compete for tubulin binding with no evidence for ternary complex formation. This competitive mechanism and the ability of the tubulin-enzyme complex to polymerize into microtubules may result in the resistance of the tubulin-enzyme complex against the inhibition of assembly induced by vinblastine. Microtubules formed in the presence of vinblastine plus phosphofructokinase can be visualized by electron microscopy. A molecular model is suggested that summarizes the effects of MgATP and vinblastine on the multiple equilibria in the tubulin/microtubules/phosphofructokinase system.

Adenosine Triphosphate↗
PubMed1997

Involvement of the Sp3 transcription factor in induction of p21Cip1/WAF1 in keratinocyte differentiation.

The cyclin-dependent kinase inhibitor p21 is induced in several in vitro terminal differentiation systems as well as in differentiating tissues in vivo. To determine the mechanism responsible for p21 induction during differentiation of mouse primary keratinocytes, we performed a deletion analysis of the p21 promoter. The minimal region of the p21 promoter required for its induction in keratinocyte differentiation consists of a contiguous stretch of 78 base pairs, which contains a GC-rich region as well as the TATA box. We determined that transcription factors Sp1 and Sp3, present in primary keratinocyte nuclear extracts, bind the GC region concomitantly. Expression studies established that both Sp1 and Sp3 activate the p21 promoter, but showed that only Sp3 overexpression enhances promoter inducibility during differentiation. Furthermore, disruption of the GC-rich region dramatically decreases transcription factor binding as well as promoter activity and inducibility upon differentiation. The overexpression of either Sp1 or Sp3 restores the basal activity of the disrupted promoter, but only Sp3 can restore its inducibility. These findings show that both Sp1 and Sp3 can contribute to the basal activity of the p21 promoter, and establish Sp3 as a specific transcription factor involved in the induction of p21 promoter during keratinocyte differentiation.

Animals↗
PubMed1997

Complete nucleotide sequence of tobacco necrosis virus strain DH and genes required for RNA replication and virus movement.

The complete genome sequence of tobacco necrosis virus strain D (Hungarian isolate, TNV-DH) was determined. The genome (3762 nt) has an organization identical to that reported for TNV-D. Highly infectious synthetic transcripts from a full-length TNV-DH cDNA clone were prepared, the first infectious necrovirus transcript reported. This clone was used for reverse genetic studies to map the viral genes required for replication and movement. Protoplast inoculation with delta 22 and delta 82 mutants revealed that both the 22 kDa and 82 kDa gene products are required for RNA replication. Although the products of three small central genes (p7(1), p7a and p7b) were not essential for RNA replication in protoplasts, mutations in these ORFs prevented infection of plants. In contrast, viral RNA accumulation and cell-to-cell movement were observed in the inoculated, but not the systemically infected, leaves of Nicotiana benthamiana challenged with RNA lacking the intact coat protein (CP) gene. These results strongly suggest that p7(1), p7a, p7b and CP are involved in TNV-DH cell-to-cell and long-distance movement, respectively.

Base Sequence↗
PubMed1997

Comparative studies on potato tuber development using an in vitro tuber induction system.

A method for synchronized in vitro tuber induction in a Hungarian cultivar of Solanum tuberosum designated "Keszthelyi 855" has been developed. It was shown that in this system tuberization and stolon elongation primarily depend on the level of sucrose in the medium. The cytokinin, 6-bensylaminopurine (BAP), also enhances the efficiency of tuber formation, however, only at sucrose concentration above 4% (w/v). The synchronized plant culture provided starting material for isolation of genes specifically expressed in tuberizing Solanum species during the early stage of tuber development. In comparison with the non-tuberizing Solanum brevidens, three types of specific transcripts have been obtained by differential screening. Based on DNA sequence analysis the genes isolated code for the major tuber proteins, patatin and proteinase inhibitors.

Adenine↗
PubMed1996

The Ikaros gene encodes a family of lymphocyte-restricted zinc finger DNA binding proteins, highly conserved in human and mouse.

The Ikaros gene is an essential regulator in the development and homeostasis of the mouse lymphopoietic system. To study the role of the Ikaros gene in the human lymphopoietic system, we cloned and characterized human Ikaros cDNAs. In the human, as in the mouse, differential splicing of Ikaros primary transcripts generates a family of lymphoid-restricted zinc finger DNA binding proteins, highly conserved in sequence composition and relative expression to the mouse homologues. Expression of Ikaros isoforms is highly restricted to the lymphopoietic system and is particularly enriched in maturing thymocytes. The Ikaros gene maps at a syntenic locus located on the short arm of human chromosome 7 and on mouse chromosome 11 next to the epidermal growth factor receptor (Egfr). The high degree of conservation of the Ikaros gene at the genetic and expression levels strongly suggests that it plays a fundamental role in the ontogeny of the lymphopoietic system across species.

3T3 Cells↗
PubMed1995

Anti-calmodulin potency of indol alkaloids in in vitro systems.

We have demonstrated that bis-indol Vinca alkaloids of anti-mitotic activities (vinblastine, vincristine, and navelbine) bind to calmodulin in a Ca(2+)-dependent manner. We designed direct binding tests (fluorescence energy transfer and circular dichroism measurements) to quantify the interactions of bis-indol derivatives with calmodulin. The dissociation constants of calmodulin-navelbine and calmodulin-vinblastine complexes with 1:1 stoichiometry are 0.5 microM and 3 microM, respectively. These values indicate that the binding affinities of these Vinca alkaloids to calmodulin and tubulin are comparable. Immunological, enzyme kinetic and fluorescence anisotropy measurements showed that bis-indol alkaloids inhibit the interactions of calmodulin with target proteins. The results of indirect enzyme-linked immunosorbent assay showed that bis-indol alkaloids effectively antagonize with anti-calmodulin antibody for calmodulin binding (IC50 = 90 microM, 400 microM, and 430 microM for navelbine, vincristine and vinblastine, respectively). According to the fluorescence anisotropy and enzyme kinetic measurements, vinblastine, vincristine and vinblastine, similarly to trifluoperazine, the classic calmodulin antagonist, compete with target enzyme [phosphofructokinase (ATP: D-fructose 6-phosphate 1-phosphotransferase, EC 2.7.1.11)] for an inhibitory effect either on immunocomplex formation or on calmodulin-enzyme interaction. Navelbine appeared in our tests as the most potent drug in inhibiting the association of calmodulin to target proteins in comparison to other bis-indol derivatives. Since navelbine and vinblastine possess identical vindoline moiety, although they differ in the catharantine part, the difference in anti-calmodulin potencies is suggested to reside predominantly on this portion of the molecules. These findings might establish the pharmacological importance of these activities in the specificity and toxicity of the drugs.

Animals↗
PubMed1995

[Experiences at the regional stroke centrum of the Erzsébet Hospital].

The authors describe the organizational structure, starting-up procedure and the experiences gained during the first half year run of a regional stroke center deserving 3 districts of Budapest. The neurological ward of the Erzsébet hospital has became active from 1. january 1993, as a first step in the implementation of the capital stroke project. They report the history, circumstances of hospitalisation, type and course of disease of 160 cerebrovascular patients and the diagnosis leading to death of 31 patients.

Adult↗
PubMed1995

Characterization of tubulin-alkaloid interactions by enzyme-linked immunosorbent assay.

An indirect enzyme-linked immunosorbent assay has been developed to characterize the interactions of drugs (bisindol alkaloids and colchicine) with immobilized tubulin. The binding of polyclonal antibodies raised in rabbits to tubulin heterodimers and monoclonal antibodies against the C-terminal regions of alpha- and beta-tubulin subunits is tested at various concentrations of the drugs. The results of the displacement experiments showed that (i) the monomeric alkaloids compete with neither polyclonal nor monoclonal antibodies for tubulin binding; (ii) the dimer alkaloids displace the polyclonal but not the monoclonal antibodies from tubulin; and (iii) the inhibitory potencies of the bisindol alkaloids of different chemical structures are different. A new semisynthetic derivative of bisindol alkaloids, KAR-2, was found to be a powerful ligand in inhibiting both tubulin polymerization and immunocomplex formation. Colchicine did not inhibit binding of the antibodies to the immobilized tubulin. Competitive-displacement experiments were also designed to test the anti-tubulin activity of drugs in solution. The results suggest that while bisindol alkaloids interact with tubulin bound on surface or in solution, colchicine binds exhaustively to tubulin in solution and enhances the affinity of polyclonal antibodies probably via long-distance interactions between the binding domains in tubulin.

Alkaloids↗
PubMed1995

[Hiatal hernia associated with mitral prolapse in childhood].

Authors examined 17 cases of hiatal hernia, out of which 13 proved to have mitral valve prolapse. The diagnosis was based on auscultation, ECG and echocardiographic examination. The incidence of mitral valve prolapse (76.5%) found in this study in considerably high. Up to now no such relationship has been reported in the literature. At the moment it could not be stated that similar aetiological factors may play any role in the developmental of both hiatal hernia and mitral valve prolapse. At the same time it can not be excluded either, that the hiatal hernia and mitral valve prolapse are not a part of a connective tissue disorder. Authors plan to follow up the patients.

Adolescent↗
PubMed1995

Seasonal changes in sperm parameters of British milk rams.

Seasonal changes in the sperm parameters of British Milk rams were studied at weekly intervals over a period of 12 months. By comparing the seasonal averages of the test parameters, significant differences were determined in several cases. Substantial differences were found in the averages of quantitative parameters between autumn and the other seasons. As regards the qualitative parameters, the results obtained in summer and autumn were significantly different from those measured in winter and spring. The ratio of deformed spermatozoa was outstandingly high (22.72%) in August. A close negative correlation was established between sperm motility and the incidence of acrosomal defects (r = -0.52; P < 0.1%). The length of natural daylight and daily average temperature were found to exert an influence on the sperm parameters. In autumn, the combined effect of the two weather parameters shows a significant correlation with the concentration of spermatozoa (r = -0.62; P < 0.1%). As British Milk rams show well-balanced sperm production throughout the year with only minor fluctuations, they can be used for reproduction all the year round.

Animals↗
PubMed1994

Ligand-modulated cross-bridging of microtubules by phosphofructokinase.

The interaction of phosphofructokinase and microtubules results in mutual effects: decreases overall activity of the kinase and alters the ultrastructural organization of microtubules. Electron microscopic studies provide direct evidence for the periodical cross-bridges of microtubules by the kinase. 3-4 closely aligned tubules are connected by rows of highly periodic lateral arms about 13 nm long and 12 nm wide. The bundling activity of the enzyme seems to be specific since aldolase, which also interacts with microtubules, does not cross-link tubules, but it impedes the binding of the kinase to tubules. ATP, ADP and fructose bisphosphates inhibit the cross-bridges of microtubules by phosphofruktokinase to a different extent and concentration dependent manner. The kinase complexed with specific metabolites inducing distinct conformers does not interact with tubules. Microtubules cross-linked by the kinase became partly resistant to the depolymerizing action of vinblastine.

Ligands↗
PubMed1994

The Ikaros gene encodes a family of functionally diverse zinc finger DNA-binding proteins.

We previously described the lymphocyte-restricted Ikaros gene encoding a zinc finger DNA-binding protein as a potential regulator of lymphocyte commitment and differentiation. Here, we report the isolation of four additional Ikaros transcripts, products of alternate splicing that encode functionally diverse proteins. The Ikaros proteins contain unique combinations of zinc finger modules that dictate their overall sequence specificity and affinity. The Ik-1 and Ik-2 proteins can both bind, albeit with different affinities, to the same recognition sequences present in a number of lymphocyte-specific regulatory elements. The Ik-3 and the Ik-4 proteins interact only with a subset of these motifs. The Ik-1 and Ik-2 proteins can strongly stimulate transcription, whereas Ik-3 and Ik-4 are weak activators. Significantly, the transcription activation potential of the Ikaros proteins correlates with their subcellular localization. Upon ectopic expression of the Ikaros isoforms in nonlymphoid cells, Ik-1 and Ik-2 localize to the nucleus, whereas Ik-3 and Ik-4 are predominantly found in the cytoplasm. The Ikaros isoforms are expressed differentially in lymphocytes: Ik-1 and Ik-2 mRNAs are the predominating forms, and Ik-4 is present in significant amounts only in early T-cell progenitors, whereas Ik-3 and Ik-5 transcripts are expressed at relatively low levels throughout lymphocyte development. The ability of the Ikaros gene to generate functionally diverse proteins that may participate in distinct regulatory pathways substantiates its role as a master regulator during lymphocyte development.

Alternative Splicing↗
PubMed1992

[Mitochondrial myopathy (mono- and multisystem mitochondrial diseases)].

Four mitochondrial myopathy cases are reported. In addition to complaints, clinical and laboratory findings the changes in number, size, shape and in structure of the mitochondria in skeletal muscles are detailed. In three of their cases the disease is monosystemic, one case seems to be multisystemic in character: beside the morphologically proven muscle and liver changes it is likely that cardiac muscle and the central nervous system is also affected on the base of the clinical symptoms.

Adolescent↗
PubMed1991

Identification of ATGCAT sequence at sites of SmuC I restriction endonuclease by computer and physical mapping of adenovirus type 1 DNA.

Physical mapping of adenovirus type 1 DNA was carried out in order to analyze the recognition sequence of a novel Streptococcus restriction endonuclease. In addition to the new map and homology data on this poorly analyzed serotype, the result offers the definite evidence for the ATGCAT recognition sequence on adenovirus DNA and the physical map of cleavage points.

Adenoviridae↗