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Biomedical subjects

M S Swanson

Publications and source records attributed to M S Swanson.

At least 37 records · Page 2Linked to original sources
PubMed1999

hnRNP complexes: composition, structure, and function.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are predominantly nuclear RNA-binding proteins that form complexes with RNA polymerase II transcripts. These proteins function in a staggering array of cellular activities, ranging from transcription and pre-mRNA processing in the nucleus to cytoplasmic mRNA translation and turnover. Recent studies suggest that several fundamental characteristics of hnRNPs account for their involvement in multiple regulatory pathways.

Animals↗
PubMed1999

Co-ordination of legionella pneumophila virulence with entry into stationary phase by ppGpp.

Legionella pneumophila survives in aquatic environments, but replicates within amoebae or the alveolar macrophages of immunocompromised individuals. Here, the signal transduction pathway that co-ordinates L. pneumophila virulence expression in response to amino acid depletion was investigated. To facilitate kinetic and genetic studies, a phenotypic reporter of virulence was engineered by fusing flaA promoter sequences to a gene encoding green fluorescent protein. When subjected to amino acid depletion, L. pneumophila accumulated ppGpp and converted from a replicative to a virulent state, as judged by motility and sodium sensitivity. ppGpp appeared to initiate this response, as L. pneumophila induced to express the Escherichia coli RelA ppGpp synthetase independently of nutrient depletion accumulated ppGpp, exited the exponential growth phase and expressed flaAgfp, motility, sodium sensitivity, cytotoxicity and infectivity, five traits correlated with virulence. Although coincident with the stationary phase, L. pneumophila virulence expression appeared to require an additional factor: mutant Lp120 accumulated ppGpp and acquired two stationary phase traits but none of six virulence phenotypes analysed. We propose that, when nutrients are limiting, ppGpp acts as an alarmone, triggering the expression of multiple traits that enable L. pneumophila to escape its spent host, to survive and disperse in the environment and to re-establish a protected intracellular replication niche.

Amino Acids↗
PubMed1999

Comparative analysis of Legionella pneumophila and Legionella micdadei virulence traits.

While the majority of Legionnaire's disease has been attributed to Legionella pneumophila, Legionella micdadei can cause a similar infection in immunocompromised people. Consistent with its epidemiological profile, the growth of L. micdadei in cultured macrophages is less robust than that of L. pneumophila. To identify those features of the Legionella spp. which are correlated to efficient growth in macrophages, two approaches were taken. First, a phenotypic analysis compared four clinical isolates of L. micdadei to one well-characterized strain of L. pneumophila. Seven traits previously correlated with the virulence of L. pneumophila were evaluated: infection and replication in cultured macrophages, evasion of phagosome-lysosome fusion, contact-dependent cytotoxicity, sodium sensitivity, osmotic resistance, and conjugal DNA transfer. By nearly every measure, L. micdadei appeared less virulent than L. pneumophila. The surprising exception was L. micdadei 31B, which evaded lysosomes and replicated in macrophages as efficiently as L. pneumophila, despite lacking both contact-dependent cytopathicity and regulated sodium sensitivity. Second, in an attempt to identify virulence factors genetically, an L. pneumophila genomic library was screened for clones which conferred robust intracellular growth on L. micdadei. No such loci were isolated, consistent with the multiple phenotypic differences observed for the two species. Apparently, L. pneumophila and L. micdadei use distinct strategies to colonize alveolar macrophages, causing Legionnaire's disease.

Animals↗
PubMed1998

Control of cleavage site selection during mRNA 3' end formation by a yeast hnRNP.

Endonucleolytic cleavage of pre-mRNAs is the first step during eukaryotic mRNA 3' end formation. It has been proposed that cleavage factors CF IA, CF IB and CF II are required for pre-mRNA 3' end cleavage in yeast. CF IB is composed of a single polypeptide, Nab4p/Hrp1p, which is related to the A/B group of metazoan heterogeneous nuclear ribonucleoproteins (hnRNPs) that function as antagonistic regulators of 5' splice site selection. Here, we provide evidence that Nab4p/Hrp1p is not required for pre-mRNA 3' end endonucleolytic cleavage. We show that CF IA and CF II devoid of Nab4p/Hrp1p are sufficient to cleave a variety of RNA substrates but that cleavage occurs at multiple sites. Addition of Nab4p/Hrp1p prevents these alternative cleavages in a concentration-dependent manner, suggesting an essential and conserved role for some hnRNPs in pre-mRNA cleavage site selection.

Base Sequence↗
PubMed1998

Influence of socioeconomic and cultural factors on racial differences in late-stage presentation of breast cancer.

CONTEXT: Breast cancer mortality is higher among African American women than among white women in the United States, but the reasons for the racial difference are not known. OBJECTIVE: To evaluate the influence of socioeconomic and cultural factors on the racial difference in breast cancer stage at diagnosis. DESIGN: Case-control study of patients diagnosed as having breast cancer at the University Medical Center of Eastern Carolina from 1985 through 1992. SETTING: The major health care facility for 2 rural counties in eastern North Carolina. SUBJECTS: Five hundred forty of 743 patients with newly diagnosed breast cancer and 414 control women from the community matched by age, race, and area of residence. MAIN OUTCOME MEASURES: Breast cancer stage at diagnosis. RESULTS: Of the 540 patients, 94 (17.4%) presented with TNM stage III or IV disease. The following demographic and socioeconomic factors were significant predictors of advanced stage: being African American (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.9-4.7); having low income (OR, 3.7; 95% CI, 2.1-6.5); never having been married (OR, 2.9; 95% CI, 1.4-5.9); having no private health insurance (OR, 2.5; 95% CI, 1.6-4.0); delaying seeing a physician because of money (OR, 1.6; 95% CI, 1.1-2.5); or lacking transportation (OR, 2.0; 95% CI, 1.2-3.6). Univariate analysis also revealed a large number of cultural beliefs to be significant predictors. Examples include the following beliefs: air causes a cancer to spread (OR, 2.8; 95% CI, 1.8-4.3); the devil can cause a person to get cancer (OR, 2.1; 95% CI, 1.2-3.5); women who have breast surgery are no longer attractive to men (OR, 1.9; 95% CI, 1.1-3.5); and chiropractic is an effective treatment for breast cancer (OR, 2.4; 95% CI, 1.4-4.4). When the demographic and socioeconomic variables were included in a multivariate logistic regression model, the OR for late stage among African Americans decreased to 1.8 (95% CI, 1.1 -3.2) compared with 3.0 (95% CI, 1.9-4.7) for race alone. However, when the belief measures were included with the demographic and socioeconomic variables, the OR for late stage among African Americans decreased further to 1.2 (95% CI, 0.6-2.5). CONCLUSIONS: Socioeconomic factors alone were not sufficient to explain the dramatic effect of race on breast cancer stage; however, socioeconomic variables in conjunction with cultural beliefs and attitudes could largely account for the observed effect.

Adult↗
PubMed1998

Normal fetal cardiac dimensions obtained by perpendicular imaging.

This study provides normal fetal cardiac dimensional data in a large patient group over a wide range of gestational ages. Perpendicular imaging decreased lateral resolution error, resulting in normal values with narrower confidence limits than in prior studies.

Aorta, Thoracic↗
PubMed1998

A new paradigm for type 2 diabetes mellitus: could it be a disease of the foregut?

SUMMARY BACKGROUND DATA: We previously reported, in a study of 608 patients, that the gastric bypass operation (GB) controls type 2 diabetes mellitus in the morbidly obese patient more effectively than any medical therapy. Further, we showed for the first time that it was possible to reduce the mortality from diabetes; GB reduced the chance of dying from 4.5% per year to 1% per year. This control of diabetes has been ascribed to the weight loss induced by the operation. These studies, in weight-stable women, were designed to determine whether weight loss was really the important factor. METHODS: Fasting plasma insulin, fasting plasma glucose, minimal model-derived insulin sensitivity and leptin levels were measured in carefully matched cohorts: six women who had undergone GB and had been stable at their lowered weight 24 to 30 months after surgery versus a control group of six women who did not undergo surgery and were similarly weight-stable. The two groups were matched in age, percentage of fat, body mass index, waist circumference, and aerobic capacity. RESULTS: Even though the two groups of patients were closely matched in weight, age, percentage of fat, and even aerobic capacity, and with both groups maintaining stable weights, the surgical group demonstrated significantly lower levels of serum leptin, fasting plasma insulin, and fasting plasma glucose compared to the control group. Similarly, minimal model-derived insulin sensitivity was significantly higher in the surgical group. Finally, self-reported food intake was significantly lower in the surgical group. CONCLUSIONS: Weight loss is not the reason why GB controls diabetes mellitus. Instead, bypassing the foregut and reducing food intake produce the profound long-term alterations in glucose metabolism and insulin action. These findings suggest that our current paradigms of type 2 diabetes mellitus deserve review. The critical lesion may lie in abnormal signals from the gut.

Adult↗
PubMed1998

Expression of Legionella pneumophila virulence traits in response to growth conditions.

In nature, Legionella pneumophila replicates exclusively as an intracellular parasite of amoebae, but it also persists in the environment as a free-living microbe. Studies of how this opportunistic pathogen recognizes and responds to distinct extracellular and intracellular environments identified a link between the growth phase and expression of traits previously correlated with virulence. When cultured in broth, only post-exponential-phase L. pneumophila was sodium sensitive, cytotoxic, osmotically resistant, competent to evade macrophage lysosomes, infectious, and motile. Likewise, the L. pneumophila phenotype changed during growth in macrophages. During the intracellular replication period, this bacterium was sodium resistant and lacked flagella; concomitant with macrophage lysis, L. pneumophila became sodium sensitive and flagellated. Expression of the virulent phenotype was a response to starvation, since exponential-phase L. pneumophila became cytotoxic, sodium sensitive, and motile after incubation in broth from stationary-phase cultures, except when it was supplemented with amino acids. Together, these data indicate that while nutrients are plentiful, intracellular L. pneumophila organisms are dedicated to replication; when amino acids become limiting, the progeny express virulence factors to escape the spent host, to disperse and survive in the aquatic environment, and to reestablish a protected intracellular niche favorable for growth.

Animals↗
PubMed1997

Altered phosphorylation and intracellular distribution of a (CUG)n triplet repeat RNA-binding protein in patients with myotonic dystrophy and in myotonin protein kinase knockout mice.

Myotonic dystrophy (DM) is associated with expansion of CTG repeats in the 3'-untranslated region of the myotonin protein kinase (DMPK) gene. The molecular mechanism whereby expansion of the (CUG)n repeats in the 3'-untranslated region of DMPK gene induces DM is unknown. We previously isolated a protein with specific binding to CUG repeat sequences (CUG-BP/hNab50) that possibly plays a role in mRNA processing and/or transport. Here we present evidence that the phosphorylation status and intracellular distribution of the RNA CUG-binding protein, identical to hNab50 protein (CUG-BP/hNab50), are altered in homozygous DM patient and that CUG-BP/hNab50 is a substrate for DMPK both in vivo and in vitro. Data from two biological systems with reduced levels of DMPK, homozygous DM patient and DMPK knockout mice, show that DMPK regulates both phosphorylation and intracellular localization of the CUG-BP/hNab50 protein. Decreased levels of DMPK observed in DM patients and DMPK knockout mice led to the elevation of the hypophosphorylated form of CUG-BP/hNab50. Nuclear concentration of the hypophosphorylated CUG-BP/hNab50 isoform is increased in DMPK knockout mice and in homozygous DM patient. DMPK also interacts with and phosphorylates CUG-BP/hNab50 protein in vitro. DMPK-mediated phosphorylation of CUG-BP/hNab50 results in dramatic reduction of the CUG-BP2, hypophosphorylated isoform, accumulation of which was observed in the nuclei of DMPK knockout mice. These data suggest a feedback mechanism whereby decreased levels of DMPK could alter phosphorylation status of CUG-BP/hNab50, thus facilitating nuclear localization of CUG-BP/hNab50. Our results suggest that DM pathophysiology could be, in part, a result of sequestration of CUG-BP/hNab50 and, in part, of lowered DMPK levels, which, in turn, affect processing and transport of specific subclass of mRNAs.

Animals↗
PubMed1996

Identification of a (CUG)n triplet repeat RNA-binding protein and its expression in myotonic dystrophy.

Myotonic dystrophy (DM) is an autosomal dominant neuromuscular disease that is associated with a (CTG)n repeat expansion in the 3'-untranslated region of the myotonin protein kinase (Mt-PK) gene. This study reports the isolation and characterization of a (CUG)n triplet repeat pre-mRNA/mRNA binding protein that may play an important role in DM pathogenesis. Two HeLa cell proteins, CUG-BP1 and CUG-BP2, have been purified based upon their ability to bind specifically to (CUG)8 oligonucleotides in vitro. While CUG-BP1 is the major (CUG)8-binding activity in normal cells, nuclear CUG-BP2 binding activity increases in DM cells. Both CUG-BP1 and CUG-BP2 have been identified as isoforms of a novel heterogeneous nuclear ribonucleoprotein (hnRNP), hNab50. The CUG-BP/hNab50 protein is localized predominantly in the nucleus and is associated with polyadenylated RNAs in vivo. In vitro RNA-binding/photocrosslinking studies demonstrate that CUG-BP/hNab50 binds to RNAs containing the Mt-PK 3'-UTR. We propose that the (CUG)n repeat region in Mt-PK mRNA is a binding site for CUG-BP/hNab50 in vivo, and triplet repeat expansion leads to sequestration of this hnRNP on mutant Mt-PK transcripts.

Amino Acid Sequence↗
PubMed1996

Analysis of the intracellular fate of Legionella pneumophila mutants.

L. pneumophila is a model organism for investigating the mechanisms by which intracellular pathogens acquire the metabolites needed for replication while evading the microbicidal mechanisms of the macrophage. We determined that intracellular L. pneumophila replicate in close association with the endoplasmic reticulum and suggest that L. pneumophila exploits the macrophage autophagy pathway to establish this specialized vacuole. To identify the bacterial factors required at this step as well as the factors important for other stages of the intracellular pathway, we isolated a collection of bacterial mutants that are defective for growth in macrophages. The ability of the mutant strains to evade fusion with the lysosomes and to establish replication vacuoles was examined by fluorescence microscopic localization of markers for the late endosomes (lgp 120), lysosomes (Texas Red-ovalbumin), endoplasmic reticulum (BiP), and L. pneumophila. By this approach, we identified mutants with distinct intracellular fates; one type does not evade the endocytic pathway, another forms replication vacuoles less efficiently than does wild-type, and a third type forms replication vacuoles but replicates poorly. These mutants are likely to facilitate identification and characterization of the bacterial factors required by L. pneumophila to establish a protected niche for intracellular replication.

Animals↗
PubMed1996

Pregnancy outcomes among active and sedentary primiparous women.

OBJECTIVE: To describe the relationship between exercise during the last trimester of pregnancy and physiologic outcomes of mothers and newborns to determine whether differences exist between active and sedentary exercise patterns on these variables. DESIGN: Nonexperimental, descriptive. SETTING: Physicians' offices, Lamaze classes, and hospitals. PARTICIPANTS: One hundred one primiparous women (48 sedentary and 53 active), 20-30 years of age, with no medical complications, whose length of gestation was at least 32 weeks. OUTCOME MEASURES: Weight gain, weeks of gestation, length of labor, common discomforts of pregnancy, occurrence of cesarean section, birth weight, and Apgar scores. RESULTS: Brisk walking was the preferred physical activity among 47% of the participants. Regular, active exercise had no significant effect on maternal weight gain or neonate birth weight. Twenty-five percent of the women in the active exercise group reported five or fewer discomforts compared with 6% of the women in the sedentary group (X2 = 7.45, p < 0.01). For the discomforts of swelling, leg cramps, fatigue, and shortness of breath, 44% of the women in the active group reported having only one or two of them, compared with 21% of the women in the sedentary group (X2 = 6.15, p = 0.01). CONCLUSION: Women who engaged in active exercise during the last trimester of pregnancy had fewer of the common discomforts associated with pregnancy.

Adult↗
PubMed1996

Identification of Legionella pneumophila mutants that have aberrant intracellular fates.

After uptake by macrophages, Legionella pneumiophila evades phagosome-lysosome fusion and replicates in a compartment associated with the endoplasmic reticulum. A collection of bacterial mutants defective for growth in macrophages were isolated, and the intracellular fate of each mutant strain was analyzed by fluorescence microscopy. To measure intracellular replication, bacteria inside macrophages were stained with the DNA dye 4',6-diamidino-2-phenylindole (DAPI). Evasion of the endocytic pathway was quantified by immunofluorescence localization of lp120 [correction of IgpI20] (LAMP-1), a membrane protein of late endosomes and lysosomes, or by measuring colocalization of bacteria with a fluorescent tracer, Texas red-ovalbumin, preloaded into lysosomes. Replication vacuoles were quantified by immunofluorescence localization of BiP, an endoplasmic reticulum protein. By these approaches, four phenotypic groups of mutants were classified. One class formed replication vacuoles less efficiently than the wild type did; another formed replication vacuoles, but replication was abortive; in another class, most phagosomes containing bacteria acquired markers of the endocytic pathway but a minority formed replication vacuoles and the bacteria replicated; finally, a fourth class, the one most defective for intracellular growth, occupied vacuoles that acquired markers of the endocytic pathway.

Animals↗
PubMed1996

Skeletal muscle content of membrane glycoprotein PC-1 in obesity. Relationship to muscle glucose transport.

Membrane glycoprotein PC-1, an inhibitor of insulin signaling, produces insulin resistance when overexpressed in cells transfected with PC-1 cDNA. In the present study, we determined whether PC-1 plays a role in the insulin resistance of skeletal muscle in obesity. Rectus abdominus muscle biopsies were taken from patients undergoing elective surgery. Subjects included both NIDDM patients (n = 14) and nondiabetic patients (n = 34) across a wide range of BMI values (19.5-90.1). Insulin-stimulated glucose transport was measured in incubated muscle strips, and PC-1 content, enzymatic activity, and insulin receptor content were measured in solubilized muscle extracts. Increasing BMI correlated with both an increase in the content of PC-1 in muscle (r = 0.55, P < 0.001) and a decrease in insulin stimulation of muscle glucose transport (r = -0.58, P = 0.008). NIDDM had no effect on either PC-1 content or glucose transport for any given level of obesity. Insulin stimulation of muscle glucose transport was negatively related to muscle PC-1 content (r = -0.68, P = 0.001) and positively related to insulin receptor content (r = 0.60, P = 0.005). Multivariate analysis indicated that both skeletal muscle PC-1 content and insulin receptor content, but not BMI, were independent predictors of insulin-stimulated glucose transport. Muscle PC-1 content accounted for 42% and insulin receptor content for 17% of the variance in glucose transport values. These studies raise the possibility that increased expression of PC-1 and a decreased insulin receptor content in skeletal muscle may be involved in the insulin resistance of obesity.

Adult↗
PubMed1995

Lgn1, a gene that determines susceptibility to Legionella pneumophila, maps to mouse chromosome 13.

The intracellular pathogen Legionella pneumophila is unable to replicate in macrophages derived from most inbred mouse strains. Here, we report the mapping of a gene, called Lgn1, that determines whether mouse macrophages are permissive for the intracellular replication of L. pneumophila. Although Lgn1 has been previously reported to map to mouse chromosome 15, we show here that it actually maps to chromosome 13, between D13Mit128 and D13Mit70. In the absence of any regional candidates for Lgn1, this map position will facilitate positional cloning attempts directed at this gene.

Animals↗