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Biomedical subjects

V Sundaresan

Publications and source records attributed to V Sundaresan.

50 records · Page 3Linked to original sources
PubMed1991

Neuroendocrine differentiation and clinical behaviour in non-small cell lung tumours.

The present study examines the relationship between neuroendocrine (NE) differentiation and the clinical behaviour of non-small cell lung cancer (NSCLC). Retrospective (n = 315) and prospective (n = 44) cohorts of non-small cell tumours were obtained from surgically treated cases of lung cancer, comprising 218 squamous cell carcinomas, 65 adenocarcinomas, 51 adenosquamous carcinomas, and 25 large cell undifferentiated carcinomas. Paraffin wax embedded and fresh frozen tissue sections were stained for the NE markers neurone specific enolase, creatine kinase-BB, bombesin, neurotensin, chromogranin A, synaptophysin and UJ-13A. The expression of two or more markers was observed in 30% of cases, and was taken to identify NE-NSCLC. A statistically significant correlation between nodal status and NE differentiation (P = 0.05), and disease stage and NE differentiation (P = 0.04) was observed. However, there was no correlation between NE differentiation and survival. These findings suggest that NE-NSCLC, analogous to SCLC is more highly metastatic than non-NE-NSCLC.

Carcinoma, Non-Small-Cell Lung↗
PubMed1989

Frequency and extent of allelic loss in the short arm of chromosome 3 in nonsmall-cell lung cancer.

DNA was prepared from tumour and normal tissue from 48 patients representing all common histological types of nonsmall-cell lung cancer. Using eight DNA probes, which detect nine restriction enzyme fragment length polymorphisms (RFLP) on chromosome 3, we established that among the 44 informative patients 32 had lost alleles on the short arm of one of their copies of chromosome 3. Of these 32, at least 13 had also lost alleles on the long arm of chromosome 3, suggesting that the whole chromosome might be lost. For one patient, cytogenetic analysis indicated that the mechanism of allelic loss was reciprocal translocation followed by chromosomal loss of one of the reciprocal products. Two patients with allelic loss distal to the D3S3 locus (which maps to 3p13-14) retained heterozygosity at that locus. These results indicate that loss of alleles on the short arm of chromosome 3 is a common event in lung tumours of the nonsmall-cell type, that this loss occurs by a variety of chromosomal mechanisms, and that the minimally deleted region is 3p13-14----3pter.

Alleles↗
PubMed1987

An extrachromosomal form of the Mu transposons of maize.

Maize lines known as Robertson's Mutator (Mu) lines generate unstable recessive mutations at high frequencies. These lines carry actively transposing copies of the transposons (Tn) Mu1 and Mu1.7. TnMu1 and TnMu1.7 are approximately 1400 and 1700 base pairs long, respectively, and they have 210-base-pair terminal inverted repeats. We report here extrachromosomal forms of TnMu1 and TnMu1.7. The extrachromosomal Mu1 and Mu1.7 molecules are resistant to alkaline denaturation and to proteinase treatment and have circular restriction maps; therefore, they are probably covalently closed circular DNA. Further, we show that their occurrence is correlated with Mu activity, so they are probably generated during Mu transposition as transposition intermediates or as products of Mu excision. When the total extrachromosomal supercoiled DNA from immature male flowers of a Mu line was examined by electron microscopy, the Mu transposons appeared to constitute a significant fraction of the extrachromosomal DNA circles in Mu lines.

Base Sequence↗
PubMed1987

Abnormal distribution of c-myc oncogene product in familial adenomatous polyposis.

Monoclonal antibodies raised by synthetic peptide immunisation were used to determine the distribution of the protein product of the c-myc gene by immunocytochemical staining of archival wax embedded material from patients with familial adenomatous polyposis. Polyps from 18 cases of familial adenomatous polyposis, 10 of whom had developed malignant change, and 30 normal control colonic biopsy specimens were examined. A consistent staining pattern was observed in normal mucosa; nuclear staining in the basal proliferative zone; mixed nuclear and cytoplasmic staining in the maturation zone; and cytoplasmic localisation in the surface mature zone. In contrast, the polyps and carcinomata showed a mixed pattern of cytoplasmic and nuclear localisation in the basal proliferative zone with nuclear persistence throughout the crypts to the surface mature zone. This abnormal distribution of the c-myc oncogene product may have a role in the evolution of polyps and their subsequent malignant transformation into familial adenomatous polyposis.

Adenomatous Polyposis Coli↗
PubMed1984

A Rhizobium meliloti symbiotic regulatory gene.

We have characterized a Rhizobium meliloti regulatory gene required for the expression of two closely linked symbiotic operons, the nitrogenase operon (nifHDK genes) and the "P2" operon. This regulatory gene maps to a 1.8 kb region located 5.5 kb upstream of the nifHDK operon. The regulatory gene is required for the accumulation of nifHDK and P2 mRNA and for the derepression of an R. meliloti nifH-lacZ fusion plasmid during symbiotic growth. The nifH and P2 promoters can be activated in free-living cultures of R. meliloti containing plasmids that produce the Escherichia coli ntrC(glnG) or the Klebsiella pneumoniae nifA regulatory gene products constitutively. The R. meliloti regulatory gene hybridizes to E. coli ntrC(glnG) and, to a lesser extent, to K. pneumoniae nifA DNA. Our results suggest that the R. meliloti regulatory gene acts as a positive transcriptional activator and that it is related to the K. pneumoniae nif regulatory genes.

Escherichia coli↗
PubMed1983

Klebsiella pneumoniae nifA product activates the Rhizobium meliloti nitrogenase promoter.

Bacteria in the genus Rhizobium normally fix nitrogen only when they interact with leguminous plants to produce on the roots a highly differentiated structure, the nodule, within which the bacteria differentiate into nitrogen-fixing bacteroids. By contrast, the enteric bacterium Klebsiella pneumoniae reduces nitrogen in a free-living state in conditions of low oxygen tension and deficiency of fixed nitrogen. In K. pneumoniae, the overall circuitry by which nitrogen-fixation (nif) genes are regulated has been elucidated. In response to ammonia starvation, the product of the glnG gene activates transcription of the nifLA operon; this activation is dependent on the product of glnF (ref. 4). The nifA gene product is in turn required for transcription of all the other nif genes, including the nifHDK operon which codes for the subunits of nitrogenase. In contrast, very little is known about the sequence of events involved in the regulated change in rhizobial nif gene expression associated with bacteroid differentiation. In the work described here, we identify the K. pneumoniae and Rhizobium meliloti nifHDK promoters by mapping the in vivo start points of transcription. By defining and comparing the DNA sequences of these two promoters, we find that they share an unexpected degree of homology. Further, by constructing fusions of each of the two promoters to the lacZ gene from Escherichia coli, we show that both promoters are activated by the product of the K. pneumoniae nifA gene.

Base Sequence↗
PubMed1983

Activation of Klebsiella pneumoniae and Rhizobium meliloti nitrogenase promoters by gln (ntr) regulatory proteins.

We have studied the expression, in different Escherichia coli gln (ntr) mutants, of fusions (constructed in vitro) of the nifHDK (nitrogenase) promoters from Klebsiella pneumoniae and Rhizobium meliloti to E. coli lacZ. Derepression of the K. pneumoniae nifH::lacZ fusion requires the glnF (ntrA) gene product in addition to the K. pneumoniae nifA gene product, indicating that regulation of the K. pneumoniae nif genes is more closely integrated with the overall nitrogen control system than previously demonstrated. Derepression of the R. meliloti nifH::lacZ fusion in E. coli by the K. pneumoniae nifA gene product (which we had previously shown) exhibits the same requirement for glnF. Derepression of the R. meliloti nifH::lacZ fusion, but not the K. pneumoniae nifH::lacZ fusion, can be mediated by the glnG (ntrC) gene product, suggesting that the gln regulatory genes might directly regulate the symbiotic nitrogen fixation genes in Rhizobium.

Bacterial Proteins↗
PubMed1983

Promoters regulated by the glnG (ntrC) and nifA gene products share a heptameric consensus sequence in the -15 region.

We have determined the nucleotide sequences of the Klebsiella pneumoniae nifL (regulation of N2 fixation genes) and the Escherichia coli glnA (glutamine synthetase) promoters. We compared these sequences with the published sequences of three other promoters that, like the nifL and glnA promoters, are activated by the general nitrogen regulators glnF (ntrA) and glnG (ntrC). The three promoters are the argTr (arginine transport) and dhuA (histidine transport) promoters of Salmonella typhimurium and the nifH (nitrogenase) promoter of Rhizobium meliloti. All five sequences (with at most one mismatch) contain the heptameric consensus sequence T-T-T-T-G-C-A. In the R. meliloti nifH and K. pneumoniae nifL promoters, in which the transcription initiation sites have been determined, the consensus sequence is situated in the -15 region. We recently reported that the K. pneumoniae nifA product, which activates nif genes, can substitute for the glnG (ntrC) product in activating promoters of several genes involved in nitrogen assimilation, including the nifL, the glnA, and the R. meliloti nifH promoters. It is likely that nifA also activates the S. typhimurium argTr and dhuA promoters. In contrast, the glnG product cannot substitute for the nifA product in the activation of the K. pneumoniae nifH (nitrogenase) promoter. Consistent with this latter observation, and supporting the conclusion that the T-T-T-T-G-C-A sequence is a regulatory site for glnG product activation, the K. pneumoniae nifH promoter (C-C-C-T-G-C-A) has only partial similarity with the T-T-T-T-G-C-A consensus sequence in the -15 region.

Amino Acid Sequence↗
PubMed1982

Directed transposon Tn5 mutagenesis and complementation analysis of Rhizobium meliloti symbiotic nitrogen fixation genes.

An 18 kb region adjacent to and surrounding the genes for nitrogenase (nif) was cloned from the genome of the symbiotic nitrogen-fixing species Rhizobium meliloti. A total of 31 Tn5 insertions in the nif region were constructed and assayed for their effect on symbiotic nitrogen fixation (Fix phenotype). Fix- insertions were found in two clusters, one 6.3 kb region not containing essential symbiotic genes. The locations of at least three transcription units containing Fix genes were deduced from complementation analysis between genomic nif::Tn5 insertions and nif::Tn5 insertions on mobilizable cloning vectors. The locations of R. meliloti genes nifH, nifD and nifK, which code for the single subunit of the nitrogenase Fe protein and for the two subunits of the nitrogenase MoFe protein respectively, were determined by DNA hybridization to cloned Klebsiella pneumoniae nif genes and by comparison of partial R. meliloti DNA sequences with K. pneumoniae nif gene sequences. R. meliloti nifH, D and K are located in the 6.3 kb fix-::Tn5 cluster and are transcribed in the order nifH, nifD, nifK, which is the same order as in K. pneumoniae.

Base Sequence↗
PubMed1982

Specific protection of nucleotides in the lac operator from DMS methylation and DNase I nicking by crude bacterial cell extracts.

Crude bacterial cell extracts prepared from an Escherichia coli lacIq strain were shown to protect specific nucleotides in the lac operator from methylation by dimethyl sulfate (DMS) or digestion by DNase I, whereas no protection was observed using extracts prepared from a nearly isogenic lacI- strain. These experiments show that it is not necessary to use purified regulatory proteins in experiments designed to localize sequences on DNA which interact with proteins. Therefore, crude cell extracts should be useful in DNA "footprinting" experiments to define regions of DNA which bind to unknown regulatory proteins.

Base Sequence↗
PubMed1981

Nucleotide sequence of the gene coding for the nitrogenase iron protein from Klebsiella pneumoniae.

We report the complete DNA sequence of the Klebsiella pneumoniae nifH gene, the gene which codes for component 2 (Fe protein or nitrogenase reductase) of the nitrogenase enzyme complex. The amino acid sequence of the K. pneumoniae nitrogenase Fe protein is deduced from the DNA sequence. The K. pneumoniae Fe protein contains 292 amino acids, has a Mr = 31,753, and contains 9 cysteine residues. We compare the amino acid sequence of the K. pneumoniae protein with available amino acid sequence data on nitrogenase Fe proteins from two other species, Clostridium pasteurianum and Azotobacter vinelandii. The C. pasteurianum Fe protein, for which the complete sequence is known, shows 67% homology with the K. pneumoniae Fe protein. Extensive regions of strong conservation (90-95%) are found, while other regions show relatively poor conservation (30-35%). It is suggested that these strongly conserved regions are of special importance to the function of this enzyme, and the findings are discussed in the light of evolutionary theories on the origin of nif genes.

Amino Acid Sequence↗
PubMedDate not supplied

Flow cytometric and immunohistochemical analysis of p62c-myc oncoprotein in the bronchial epithelium of lung cancer patients.

The expression of p62c-myc in bronchial resection lines (BRLs) from lung cancer and control patients, has been examined by immunohistochemistry and parallel flow cytometry using antibodies directed against the p62c-myc oncoprotein. Both methods indicated a marked increase in nuclear p62c-myc levels in BRLs from tumour cases as compared to control BRLs. Immunohistochemistry also revealed greater cytoplasmic positivity in BRLs from cancer patients than from control cases. Flow cytometric quantitation of nuclear p62c-myc confirmed the immunohistochemical findings demonstrating that the median level of nuclear p62-myc fluorescence in BRLs from tumour cases was 1919 fluorescence units (FU) (range:216-7367 FU) and 144 FU (range:0-1365 FU) for non-tumour control BRLs. No consistent difference in p62c-myc fluorescence was observed between BRLs from smokers and non smokers. Both methods indicated that in lung tumour cases, nuclear p62c-myc was increased in histologically normal and abnormal BRLs, suggesting that hyperexpression of this protein is an early event preceding detectable morphological change. These results suggest that increased p62c-myc levels may be an early event in the pathogenesis of lung cancer.

Adult↗