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Biomedical subjects

K Lund

Publications and source records attributed to K Lund.

At least 55 records · Page 3Linked to original sources
PubMed1993

Differential expression of non-allelic insulin genes in rodent islet tumour cells.

We have compared the expression patterns of the non-allelic insulin 1 and 2 genes during prolonged in-vitro culture of the mouse islet cell line beta-TC3, where transformation by the SV40 T oncoprotein is targeted to the differentiated beta-cell phenotype, and the rat islet cell line NHI-6F, in which the beta-cell phenotype is induced by transient in-vivo passage. The NHI-6F clone carries, in addition, a single copy of a transfected silent human insulin gene which contains 3 kb of regulatory sequences known to confer beta-cell-specific expression. Insulin gene expression was measured by an assay based on a reverse transcription-polymerase chain reaction, to determine whether the ancestral rodent insulin 2 genes (and the human homologue in the NHI-6F cells) are regulated differently from the duplicated rat and mouse insulin 1 genes. We have shown that activation of insulin gene expression in the NHI-6F cells includes transcriptional activation of all three genes, but that extended propagation of tumour cells in vitro leads to a selective and equal decline in the quantities of transcripts from the rat 2 and human genes relative to transcripts from the rat 1 gene. In the later passages, insulin transcripts were derived almost exclusively from the rat 1 gene. In early in-vitro passages of the mouse endocrine cell line beta-TC3, the expression pattern of the mouse 1 and 2 insulin genes resembled that seen in isolated mouse islets. After more than 45 in-vitro passages, expression of the duplicated mouse 1 gene decreased tenfold when compared with the ancestral mouse 2 gene. As previously shown for NHI-6F cells, the differential expression of non-allelic insulin genes in the beta-TC3 line was also clearly evident at the cellular level, where a subpopulation of cells selectively expressed readily detectable levels of mouse C-peptide 2 immunoreactivity while devoid of C-peptide 1. Our results suggest that the maintenance of insulin gene expression in rodent tumour cells is influenced by enhancer sequences which are not shared by the ancestral and duplicated insulin genes, and that either species-specific conditions or transformation-related differences exist between the rat and mouse cell lines that govern which gene remains active during prolonged in-vitro propagation.

Animals↗
PubMed1992

Implications of epidermal growth factor (EGF) induced egf receptor aggregation.

To investigate the role of receptor aggregation in EGF binding, we construct a mathematical model describing receptor dimerization (and higher levels of aggregation) that permits an analysis of the influence of receptor aggregation on ligand binding. We answer two questions: (a) Can Scatchard plots of EGF binding data be analyzed productively in terms of two noninteracting receptor populations with different affinities if EGF induced receptor aggregation occurs? No. If two affinities characterize aggregated and monomeric EGF receptors, we show that the Scatchard plot should have curvature characteristic of positively cooperative binding, the opposite of that observed. Thus, the interpretation that the high affinity population represents aggregated receptors and the low affinity population nonaggregated receptors is wrong. If the two populations are interpreted without reference to receptor aggregation, an important determinant of Scatchard plot shape is ignored. (b) Can a model for EGF receptor aggregation and EGF binding be consistent with the "negative curvature" (i.e., curvature characteristic of negatively cooperative binding) observed in most Scatchard plots of EGF binding data? Yes. In addition, the restrictions on the model parameters required to obtain negatively curved Scatchard plots provide new information about binding and aggregation. In particular, EGF binding to aggregated receptors must be negatively cooperative, i.e., binding to a receptor in a dimer (or higher oligomer) having one receptor already bound occurs with lower affinity than the initial binding event. A third question we consider is whether the model we present can be used to detect the presence of mechanisms other than receptor aggregation that are contributing to Scatchard plot curvature. For the membrane and cell binding data we analyzed, the best least squares fits of the model to each of the four data sets deviate systematically from the data, indicating that additional factors are also important in shaping the binding curves. Because we have controlled experimentally for many sources of receptor heterogeneity, we have limited the potential explanations for residual Scatchard plot curvature.

Animals↗
PubMed1991

Studies of the topoisomerase II-mediated cleavage and religation reactions by use of a suicidal double-stranded DNA substrate.

The cleavage and religation reactions of eukaryotic topoisomerase II were studied by use of a 5'-recessed DNA substrate containing a strong recognition sequence for the enzyme. Cleavage of the DNA substrate was suicidal, that is the enzyme was unable to religate the cleaved DNA due to a release of DNA 5' to the cleavage position. With this substrate cleavage products accumulated with time in the absence of protein-denaturing agents, and the cleavage reaction was not reversible with salt. The suicide cleavage complexes contained a kinetically competent topoisomerase II enzyme as determined by the enzyme's ability to perform intermolecular ligation of the cleaved DNA to a free 3'-hydroxyl end on another DNA strand. The efficiency of the religation reaction depended on the ability of the religation substrate to base pair to the DNA in the cleaved enzyme-DNA complex. Higher levels of religation were obtained with dinucleotides than with long DNA substrates. Mononucleotides also were efficiently religated, indicating an ability of the enzyme to mediate religation without making contacts to a long stretch of nucleotides 5' to the cleavage position.

Animals↗
PubMed1990

Characterization of the interaction between topoisomerase II and DNA by transcriptional footprinting.

The interaction between calf thymus topoisomerase II and DNA has been characterized using a transcription assay. A highly preferred recognition sequence for topoisomerase II was inserted in either direction downstream from a promoter specific for a bacteriophage RNA polymerase. The presence of topoisomerase II-DNA complexes on the template provoked blockage of transcription, yielding RNA transcripts terminated 5' to the topoisomerase II binding site. A footprint of topoisomerase II, derived from transcription towards the complex from either side, revealed that eukaryotic topoisomerase II binds a region of 28 base-pairs with a highly protected central core of 22 base-pairs. The binding region was located symmetrically around the topoisomerase II-mediated cleavage site. In agreement with this result, optimal topoisomerase II-mediated cleavage was observed with a DNA substrate consisting of a 28-mer oligonucleotide homologous to the protected region. Stepwise removal of base-pairs from the ends of the 28-mer gradually reduced the level of enzyme-mediated cleavage.

Acetanilides↗
PubMed1990

Minimal DNA requirement for topoisomerase II-mediated cleavage in vitro.

The minimal DNA requirement for topoisomerase II-mediated DNA cleavage in vitro was determined by analyzing the interaction of the enzyme with sets of DNA substrates varying successively by single bases at the 5'- or 3'-end of either strand. A 16-base pair double-stranded region was established as the minimal duplex region required for topoisomerase II cleavage activity. The region was located symmetrically around the 4-base staggered cleavage site. Topoisomerase II-mediated cleavage within the 16-base pair core duplex, however, required single-stranded regions flanking the duplex to either the 5'- or 3'-sides, or an extension at both ends of the duplex with 1 or more base pairs.

Animals↗
PubMed1990

Minimal DNA duplex requirements for topoisomerase I-mediated cleavage in vitro.

The minimal DNA duplex requirements for topoisomerase I-mediated cleavage at a specific binding sequence were determined by analyzing the interaction of the enzyme with sets of DNA substrates varying successively by single nucleotides at the 5'- or 3' end of either strand. Topoisomerase I cleavage experiments showed a minimal region of nine nucleotides on the scissile strand and five nucleotides on the noncleaved strand. On the scissile strand, seven of the nine nucleotides were situated upstream to the cleavage site, while all five nucleotides required on the non-cleaved strand were located to this side. The results suggested that topoisomerase I bound tightly to this region, stabilizing the DNA duplex extensively. On minimal substrates which were partially single-stranded downstream to the cleavage site, cleavage was suicidal, that is, the enzyme was able to cleave the substrates, but unable to perform the final religation.

Base Sequence↗
PubMed1989

Clinical and laboratory features of patients with chronic renal disease at the start of dialysis.

We examined clinical and laboratory features retrospectively in 402 patients at the start of chronic hemodialysis in order to define better the "uremic syndrome" in the dialysis era. The information gathered included demographic data, renal diagnoses, uremic symptoms, biochemical values, and prevalences of hypertension (69%), diabetes mellitus (23%) and ischemic heart disease (16%). Unexpected findings were the wide ranges of serum creatinine levels (3.5 to 35 mg/dl) and blood urea nitrogen levels (35 to 345 mg/dl), and the frequency of hyponatremia (27%), hypoalbuminemia (52%), and anion gaps above 25 mg/dl (5%). There were higher hematocrits in males and diabetics, lower serum creatinine levels in females, diabetics and older patients, and lower blood urea nitrogen levels in blacks. The time interval from diagnosis of diabetes mellitus to initiation of dialysis in patients with diabetic nephropathy due to juvenile-onset diabetes mellitus (20.6 +/- 6.8 years) was twice that in adult onset diabetes mellitus (10.3 +/- 8.3 years).

Acid-Base Equilibrium↗
PubMed1988

Isolated aneurysms of the iliac artery: what are the chances of rupture?

Sixteen patients with 22 isolated aneurysms of the common or external iliac artery were treated between 1974 and 1986. There were ten men and six women with a median age of 69 years. The aneurysm was discovered incidentally in seven patients; and in nine patients it was diagnosed upon rupture. A pulsating abdominal tumour was palpable in 12 patients seven of whom had a ruptured aneurysm. Common symptoms included urological and neurological problems and abdominal pain. Of the seven patients in whom the diagnosis was confirmed prior to rupture, three were operated upon successfully and four were not. Of the latter, two died within 3 months due to coexisting disease while two remain alive after one and 6 years. Of the nine patients with a ruptured aneurysm only four survived. The high risk of rupture justifies elective operation of an aneurysm of the iliac artery in the majority of cases.

Adult↗
PubMed1987

Purification and properties of phosphoserine aminotransferase from bovine liver.

L-Phosphoserine aminotransferase was purified from bovine liver to apparent homogeneity as judged by nondenaturing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, analytical ultracentrifugation, and immunochemical analysis. The purification procedure described involves the specific elution of the enzyme from Cibacron blue-agarose by micromolar concentrations of its substrate, phosphohydroxypyruvate. The purified enzyme had a specific activity of approximately 13 mumol of phosphohydroxypyruvate formed min-1 mg-1 of protein at 38 degrees C. Determinations of the native molecular weight and the subunit molecular weight indicated that the phosphoserine aminotransferase from bovine liver was a dimer composed of two subunits with identical molecular weights of 43,000.

Animals↗
PubMed1987

An integration of the DSM-III and ICD-8 by global severity assessments for measuring multidimensional outcomes in general hospital psychiatry.

A multiaxial classification system has been developed in which three ICD-8 derived axes of psychiatric syndromes, personality disorders and somatic syndromes, and two DSM-III axes of psychosocial stressors and social functioning have been included. Global assessment scales were annexed the three ICD-8 axes. This DSM-III/ICD-8 system was used for registration of 880 consequetively admitted psychiatric patients in a general hospital setting. The results showed that six psychiatric syndromes (substance use disorders, schizophrenia, manic-depressive psychosis, reactive psychosis, neurosis, and adjustment reactions) were responsible for 80% of the diagnostic variance. Of these syndromes, manic-depressive psychosis had the highest improvement rate both concerning symptoms and social functioning. Manic-depressive psychosis had also the lowest coefficient of variation in the stay in hospital indicating a high degree of homogeneity in accordance to the diagnose-related group system. However, patients within the categories of reactive psychosis and neurosis who received antidepressants also had a low coefficient of variation, although the neurotics were significantly more depressed than the manic-depressives at discharge from hospital.

Adolescent↗
PubMed1987

Breast cancer incidence subsequent to surgical reduction of the female breast.

The incidence of breast cancer was determined in 1245 women who were treated surgically for breast hypertrophy in Copenhagen, Denmark, between 1943 and 1971. Breast cancer cases were identified by a linkage to the Danish Cancer Registry. The expected number of breast cancers was estimated from age and calendar-time specific incidence rates in the Danish female population. A total of 18 breast cancers developed compared to 30.28 expected, yielding a relative risk (RR) of 0.59 (95% confidence interval (CI) 0.35-0.94). The greatest risk reduction was observed ten or more years after the plastic surgery operation in women who had 600 g or more of breast tissue removed (RR = 0.27; 95% CI 0.03-0.99). This suggests that the number of potential foci are important for cancer development in the breast.

Adult↗
PubMed1986

Purification and subunit structure of phosphoglycerate dehydrogenase from rabbit liver.

D-3-Phosphoglycerate dehydrogenase (EC 1.1.1.95) was purified from rabbit liver by (NH4)2SO4 fractionation, DEAE-Sephacel chromatography, affinity chromatography on AMP-agarose and molecular-sieve h.p.l.c. The purified enzyme was homogeneous as judged by SDS/polyacrylamide-slab-gel electrophoresis. On the basis of molecular-sieve h.p.l.c. and SDS/polyacrylamide-gel electrophoresis, the enzyme is a tetramer composed of subunits of Mr 60,000.

Animals↗
PubMed1986

The reactions of the phosphorylated pathway of L-serine biosynthesis: thermodynamic relationships in rat liver in vivo.

The effect of the induction of the enzymes of the phosphorylated pathway of L-serine biosynthesis on the thermodynamic relationships among the reactions has been determined in rat liver in vivo. The mass action ratios of the reactions involved were calculated from the concentrations of appropriate metabolites in freeze-clamped liver from animals fed normal and low-protein diets for 2 weeks. These ratios were compared with the equilibrium constants of the same reactions previously determined under physiological conditions and the results previously obtained in the rabbit. The thermodynamic relationships in the pathway were different between the normal rat and rabbit as might have been expected, because of the significantly lower activities of the L-serine biosynthetic enzymes in the former animal. Although the delta G for the overall pathway is nearly identical in the rat and rabbit (-5.8 versus -5.5 kcal/mol, respectively), the distribution of delta G among the reactions is different. The disequilibrium in the pathway in rat liver is nearly equally divided between the L-phosphoserine phosphatase (EC 3.1.3.3) step and the other two reactions [D-3-phosphoglycerate dehydrogenase (EC 1.1.1.95) and L-phosphoserine aminotransferase (EC 2.6.1.52)], whereas in rabbit the phosphatase reaction accounts for nearly the entire delta G. Feeding the rat a low protein diet, however, induced the activity of D-3-phosphoglycerate dehydrogenase 12-fold, that of L-phosphoserine aminotransferase 20-fold, and that of L-phosphoserine phosphatase 2-fold. With the induction of the pathway, L-phosphoserine appeared in the tissue, there was a more than 3-fold rise in L-serine in the liver, and the pattern of delta G in the rat liver approached that in the rabbit.

Animals↗
PubMed1986

Synthesis of mitochondrial macromolecules in herpes simplex type 1 virus infected Vero cells.

How viral infections affect host cell mitochondrial functions is largely unknown. In this study, uptake of radiolabeled precursors was used to assess how a herpes simplex virus type 1 (HSV 1) infection influences synthesis of macromolecules comprising Vero cell mitochondria. Total macromolecular synthesis in infected cells was determined for comparative purposes. Mitochondrial and total cellular DNA syntheses were approximately halved at 1-2.5 h postinfection (PI). Mitochondrial DNA synthesis in infected cells then rose to 3.5-fold that in control cells at 3-4.5 h PI. Total DNA synthesis in infected cells also rose, but more slowly, reaching threefold that for control cells at 5-6.5 h PI. Mitochondrial and total RNA synthesis in infected cells were both decreased by approximately 40% at 1-3 h PI. Over the next 4 h, total RNA synthesis in infected cells slowly continued to decrease, while that in mitochondria recovered to control levels. Synthesis of mitochondrial proteins in infected cells decreased progressively, dropping to about 60% of control levels by 5-6.5 h PI. With the metabolic inhibitors ethidium bromide and cycloheximide, it was determined that nuclear DNA and mitochondrial DNA and mitochondrial DNA directed synthesis of mitochondrial proteins were each partially inhibited in infected cells. Total cellular protein synthesis was decreased by 30% at 1-2.5 h PI and then recovered to control levels by 5-6.5 h PI. Finally, phospholipid synthesis in mitochondria from infected cells was elevated 2.3-fold at 1-5 h PI, but dropped to 14% below control levels during 4-8 h PI.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗