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L H Hansen

Publications and source records attributed to L H Hansen.

At least 37 records · Page 2Linked to original sources
PubMed1997

The role of GH receptor tyrosine phosphorylation in Stat5 activation.

Stimulation of GH receptors leads to rapid activation of Jak2 kinase and subsequent tyrosine phosphorylation of the GH receptor. Three specific tyrosines located in the C-terminal domain of the GH receptor have been identified as being involved in GH-stimulated transcription of the Spi 2.1 promoter. Mutated GH receptors lacking all but one of these three tyrosines are able to mediate a transcriptional response when transiently transfected into CHO cells together with a Spi 2.1 promoter/luciferase construct. Similarly, these GH receptors were found to be able to mediate activation of Stat5 DNA-binding activity, whereas the GH receptor mutant lacking all intracellular tyrosines was not. Synthetic tyrosine phosphorylated peptides corresponding to the GH receptor sequence around the three tyrosines inhibited Stat5 DNA-binding activity while their non-phosphorylated counterparts were ineffective. Tyrosine phosphorylated GST-GH receptor fusion proteins specifically bound to Stat5 in extracts from COS 7 cells transfected with Stat5 cDNA. This binding could be inhibited by tyrosine phosphorylated peptides derived from the GH receptor. This study thus demonstrated that specific GH receptor tyrosine residues, in their phosphorylated state, are involved in transcriptional signaling by directly interacting with Stat5.

Amino Acid Sequence↗
PubMed1997

Identification of differentially expressed genes in chemically induced skin tumors.

Previous studies have demonstrated a role for the fos gene in promoting malignant conversion of mouse skin tumors. In the study reported here, differential display was performed to identify fos- and jun-regulated genes that are differentially expressed during premalignant progression. Total RNA isolated from variants of the papilloma cell line SP-1 transduced with retroviral vectors expressing v-jun and v-fos alone or in tandem was analyzed for the presence of differentially expressed transcripts by using 35 different primer combinations. Differentially expressed clones were rescreened by dot-blot analysis by using cDNA from chemically induced tumors with a high or low risk of malignant conversion. Three differentially displayed fragments were isolated in this analysis. Homology searches indicated that these fragments shared significant homology with the apoptosis inhibitor bcl-2, human alternative splicing factor/splicing factor 2 (ASF/SF2), and a novel gene not present in the GenBank or EMBL databases. In situ hybridization indicated that the expression levels of the bcl-2 homolog increased with malignant potential in chemically derived mouse skin tumors. A similar analysis indicated that expression of the ASF/SF2 homolog was greater in papillomas than in normal skin or in squamous cell carcinomas. Transcripts for this gene were most abundant in the granular layer. The expression pattern of the third differential display fragment was consistent with that of a tumor suppressor gene. This gene was expressed at very high levels in normal skin and benign papillomas but was essentially undetectable in squamous cell carcinomas. Through this approach, we identified known and novel genes that may contribute to malignant progression in epidermal tumors.

Animals↗
PubMed1996

Identification of tyrosine residues in the intracellular domain of the growth hormone receptor required for transcriptional signaling and Stat5 activation.

The binding of growth hormone (GH) to its receptor results in its dimerization followed by activation of Jak2 kinase and tyrosine phosphorylation of the GH receptor itself, as well as Jak2 and the transcription factors Stat1, -3, and -5. In order to study the role of GH receptor tyrosine phosphorylation in intracellular signaling, we constructed GH receptors in which combinations of tyrosines were mutated to phenylalanines. We identified three tyrosine residues at positions 534, 566, and 627 that were required for activation of GH-stimulated transcription of the serine protease inhibitor (Spi) 2.1 promoter. Any of these three tyrosines is able to independently mediate GH-induced transcription, indicating redundancy in this part of the GH receptor. Tyrosine phosphorylation was not required for GH stimulation of mitogen-activated protein (MAP) kinase activity or for GH-stimulated Ca2+ channel activation since these pathways were normal in cells expressing a GH receptor in which all eight intracellular tyrosines were mutated to phenylalanines. Activation of Stat5 by GH was, however, abolished in cells expressing the GH receptor lacking intracellular tyrosines. This study demonstrates that specific tyrosines in the GH receptor are required for transcriptional signaling possibly by their role in the activation of transcription factor Stat5.

Animals↗
PubMed1996

Nurse-conducted smoking cessation with minimal intervention in a lung clinic: a randomized controlled study.

This study aimed to evaluate the effect of a motivational, minimal intervention approach to smoking cessation in an open, randomized design conducted by nurses as routine work in a lung clinic. Subjects who smoked less than 10 cigarettes x day(-1), and subjects who smoked > or = 10 cigarettes x day(-1) and who had refused to participate in a smoking cessation trial with nicotine replacement therapy, were randomly allocated to a motivational approach to smoking cessation or to a control group. The motivational approach consisted of a nurse-conducted 5 min consultation concerning reasons to quit smoking, brochures about smoking cessation and advice about how to quit. After 4-6 weeks, subjects in the motivational group received a letter encouraging them to quit smoking. After 1 year, all subjects were contacted by phone and smoking status reported. Subjects claiming to be abstinent attended the clinic for carbon monoxide verification. A total of 507 subjects were enrolled, 254 in the motivational group and 253 in the control group. The mean age of the motivational group was 51 yrs, 50% were males and they smoked a mean of 13 cigarettes x day(-1). The mean age of the control group was 53 yrs, 61% were males and they smoked a mean of 12 cigarettes x day(-1). At the 1 year follow-up, the success rate for point prevalence (no smoking at 1 year and during the preceding month) was 8, 7% in the motivational group versus 3.6% in the control group (p=0.025). The 12 months sustained success rate (no smoking at all during the year) was 3.1 versus 1.2% (p=0.22). The point prevalence for light smokers (<10 cigarettes x day(-1)) was 13.9% in the motivational group versus 6.3% in control group (p=0.12), and for heavy smokers (10 or more cigarettes x day(-1)) 5.2% versus 1.9% (p=0.20). In conclusion, the effect of this nurse-conducted, minimal intervention, motivational approach seems promising as the quit rate at 1 year follow-up had doubled.

Adult↗
PubMed1996

The Gly40Ser mutation in the human glucagon receptor gene associated with NIDDM results in a receptor with reduced sensitivity to glucagon.

The pancreatic islet hormone, glucagon, stimulates hepatic glucose production and has also been shown to potentiate glucose-induced insulin secretion. Because glucagon is a key regulator of glucose homeostasis, its receptor, which mediates the actions of glucagon, was considered a candidate gene involved in the pathogenesis of NIDDM. We have previously reported that a single heterozygous missense mutation in exon 2 of the glucagon receptor gene, which changes a glycine to a serine (Gly40Ser), is associated with NIDDM in a French population. In the present study, the signaling properties of this mutant receptor were examined in baby hamster kidney cells and rat insulinoma cells (RIN-5AH) stably transfected with either the wild type or Gly40Ser mutant human glucagon receptor cDNAs. Competition assays using (125)I-labeled glucagon were performed, and in both cell types, the Gly40Ser mutant receptor was found to bind glucagon with an approximately threefold lower affinity compared with the wild type receptor. In both cell types, the production of cAMP in response to glucagon was decreased in cells expressing the mutant receptor compared with those expressing the wild type. Finally, glucagon-stimulated insulin secretion by RIN cells expressing the mutant receptor was decreased such that the dose-response curve was shifted to the right in comparison to that obtained with cells expressing the wild type receptor. These results indicate that this single-point mutation located in the extracellular region of the glucagon receptor decreases the sensitivity of target tissues to glucagon.

Amino Acid Sequence↗
PubMed1995

Pseudoknot in domain II of 23 S rRNA is essential for ribosome function.

The structure of domain II in all 23 S (and 23 S-like) rRNAs is constrained by a pseudoknot formed between nucleotides 1005 and 1138, and between 1006 and 1137 (Escherichia coli numbering). These nucleotides are exclusively conserved as 1005C.1138G and 1006C.1137G pairs in all Bacteria, Archaea and chloroplasts, whereas 1005G.1138C and 1006U.1137A pairs occur in Eukarya. We have mutagenized nucleotides 1005C-->G, 1006C-->U, 1137G-->A and 1138G-->C, both individually and in combinations, in a 23 S rRNA gene from the bacterium E. coli. The ability of 23 S rRNA to support cell growth is reduced when either of these base-pairs is disrupted, and it is completely abolished upon disruption of both base-pairs. Each mutant 23 S rRNA is assembled into 50 S subunits, but the mutant subunits do not stably interact with 30 S to engage in protein synthesis. Enzymatic and chemical probing of ribosomal particles reveals increased accessibility in the rRNA structure close to the sites of the mutations. The degree to which the mutations increase rRNA accessibility correlates with the severity of their phenotypic effects. Nucleotide 1131G is extremely reactive to dimethyl sulphate modification in wild-type subunits and ribosomes, but is rendered unreactive when either the pseudoknot is broken or when the r-proteins are removed. The structure of the pseudoknot region is possibly influenced by interaction of an r-protein at or close to the pseudoknot. Re-establishing the pseudoknot Watson-Crick interactions with one "eukaryal" (1005G.1138C or 1006U.1137A) pair and one "bacterial" C.G pair largely restores the structure and function of the rRNA. Bacterial ribosomes containing both these eukaryal pairs also participate in protein synthesis, although at much reduced efficiency, and the structure of their pseudoknot region is partially open and accessible.

Base Sequence↗
PubMed1995

Glucagon receptor mRNA distribution in rat tissues.

In addition to glucagon's role in regulating glucose production from the liver, a number of extrahepatic effects of glucagon have been reported. We have therefore examined various rat tissues for glucagon receptor mRNA expression. In liver, kidney, heart, adipose tissue, spleen, pancreatic islets, ovary, and thymus, glucagon receptor mRNA expression was found to be relatively abundant whereas lower levels were detected in stomach, small intestine, adrenal gland, thyroid, and skeletal muscle. The presence of glucagon receptor mRNA in tissues known to be responsive to glucagon suggests that these effects are mediated by specific glucagon receptors. Furthermore, the finding of glucagon receptor mRNA in the spleen, thymus, thyroid, adrenal gland, ovary, and skeletal muscle, where glucagon is not generally considered to act, indicates that there may be novel actions of glucagon that have yet to be determined.

Animals↗
PubMed1995

Development and testing of improved suicide functions for biological containment of bacteria.

We have developed very efficient suicide functions for biological containment based on the lethal Escherichia coli relF gene. The suicide functions are placed in duplicate within a plasmid and arranged to prevent inactivation by deletion, recombination, and insertional inactivation. The efficiency of this concept was tested in a plasmid containment system that prevents transfer of plasmids to wild-type bacteria. Protection against plasmid transfer was assayed in test tubes and in rat intestine. Protection was efficient and refractory to inactivation by mutation and transposons. The efficiency of the suicide system was also tested in soil and seawater. We show that unprecedented suicide efficiency can be achieved in soil and seawater after suicide induction by IPTG (isopropyl-beta-D-thiogalactopyranoside). More than 7 orders of magnitude reduction in suicide bacteria was achieved.

Animals↗
PubMed1995

The conformation of 23S rRNA nucleotide A2058 determines its recognition by the ErmE methyltransferase.

The ErmE methyltransferase confers resistance to MLS antibiotics by specifically dimethylating adenine 2058 (A2058, Escherichia coli numbering) in bacterial 23S rRNA. To define nucleotides in the rRNA that are part of the motif recognized by ErmE, we investigated both in vivo and in vitro the effects of mutations around position A2058 on methylation. Mutagenizing A2058 (to G or U) completely abolishes methylation of 23S rRNA by ErmE. No methylation occurred at other sites in the rRNA, demonstrating the fidelity of ErmE for A2058. Breaking the neighboring G2057-C2611 Watson-Crick base pair by introducing either an A2057 or a U2611 mutation, greatly reduces the rate of methylation at A2058. Methylation remains impaired after these mutations have been combined to create a new A2057-U2611 Watson-Crick base interaction. The conformation of this region in 23S rRNA was probed with chemical reagents and it was shown that the A2057 and U2611 mutations alone and in combination alter the reactivity of A2058 and adjacent bases. However, mutagenizing position G-->A2032 in an adjacent loop, which has been implicated to interact with A2058, alters neither the ErmE methylation at A2058 nor the accessibility of this region to the chemical reagents. The data indicate that a less-exposed conformation at A2058 leads to reduction in methylation by ErmE. Nucleotide G2057 and its interaction with C2611 maintain the conformation at A2058, and are thus important in forming the structural motif that is recognized by the ErmE methyltransferase.

Base Sequence↗
PubMed1979

Bowel cancer.

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Adult↗
PubMed1979

Reproductive efficiency and incidence of MMA after controlled farrowing using a prostaglandin analogue, cloprostenol.

In a herd of sows 106 sows having 4.3 litters on aver., were over a period of 10 weeks treated on Thursdays with 0.175 mg of cloprostenol on the 111th to 114th day of gestation; 93--95% of the sows treated on the 112th and 113th day farrowed within 33 hours after treatment, 73% after treatment on the 111th day (Table I); the mean period of gestation after treatment was 113.4 +/- 0.9 days. 8 sows that only farrowed 2--5 days after the treatment, had on 21 previous farrowings proved to have significantly longer mean periods of gestation, 115.6 days, than the 112 sows in the control group, having 3.6 litters on average, that farrowed in the same period and section of the piggery as the sows treated with cloprostenol. In total 32 weekend-farrowings occurred in the observation period including 7 farrowings after a period of gestation of 110--113 days, 6 cases of unsuccessfully induced parturition and 19 farrowings on the 114th to 119th day that could have been programmed to occur on Fridays; the number of weekend-farrowings, which for this herd in connection with the weaning procedure normally accounted for about 40--45% of farrowings, could thus be reduced to 7% of farrowings (Table II). Cloprostenol treatment on the 111th day resulting in farrowing on the 112th day leads to a significantly higher rate of piglet mortality after 3 weeks compared with the results after farrowing for control sows that farrowed on the 112th day (Table III); this category of control sows had on previous farrowings proved to have a significantly shorter mean period of gestation, 112.7 days, than that of the sows in the cloprostenol group farrowing on the 112th day which had been 114.3 days on previous farrowings. Farrowing and weaning results after induced parturition resulting in farrowing on the 113th to 115th day showed no significant differences from the results for control sows farrowing spontaneously on the 112th to 115th day of gestation. The incidence of MMA (Table II) was not influenced by the cloprostenol treatment, nor by the number of litters, the length of the period of gestation, or by the piling of farrowings on Fridays.

Animals↗