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Biomedical subjects

D J Austin

Publications and source records attributed to D J Austin.

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

A nonnatural transcriptional coactivator.

In eukaryotes, sequence-specific DNA-binding proteins activate gene expression by recruiting the transcriptional apparatus and chromatin remodeling proteins to the promoter through protein-protein contacts. In many instances, the connection between DNA-binding proteins and the transcriptional apparatus is established through the intermediacy of adapter proteins known as coactivators. Here we describe synthetic molecules with low molecular weight that act as transcriptional coactivators. We demonstrate that a completely nonnatural activation domain in one such molecule is capable of stimulating transcription in vitro and in vivo. The present strategy provides a means of gaining external control over gene activation through intervention using small molecules.

Amino Acid Sequence↗
PubMed1997

The transmission dynamics of antibiotic-resistant bacteria: the relationship between resistance in commensal organisms and antibiotic consumption.

We propose a mathematical model of the transmission dynamics of colonization by commensal bacteria within a human community subject to varying levels of antibiotic use designed to control morbidity induced by pathogenic strains of the normally commensal organisms. Colonization is assumed not to induce morbidity in the majority of cases, and antibiotic use is assumed to be related to the arrival and growth of pathogenic strains that give rise to infections including clinical symptoms of disease. In the absence of antibiotic resistance, the model shows how the pattern of antibiotic prescription and use can eliminate the non-pathogenic commensal strains from the host community if the fraction of people taking antibiotics with a defined efficacy exceeds some critical level. The model is extended to take account of the evolution of antibiotic resistance in the commensal population. We assume resistance may be either plasmid-mediated or conferred by selection of low-level pre-existing mutants, and that resistant organisms may experience reduced reproductive fitness. Invasion of the host community by drug-resistant commensals is possible if certain antibiotic prescribing patterns pertain. We calculate these conditions in terms of the transmission parameter of the organism and the level of antibiotic prescription and use. The model is employed to address the issues of how best to use antibiotics in populations harbouring resistant organisms, and when resistant bacteria will out-compete sensitive strains.

Bacterial Infections↗
PubMed1997

Inducible gene expression and protein translocation using nontoxic ligands identified by a mammalian three-hybrid screen.

The natural product rapamycin has been used to provide temporal and quantitative control of gene expression in animals through its ability to interact with two proteins simultaneously. A shortcoming of this approach is that rapamycin is an inhibitor of cell proliferation, the result of binding to FKBP12-rapamycin-associated protein (FRAP). To overcome this limitation, nontoxic derivatives of rapamycin bearing bulky substituents at its C16-position were synthesized, each in a single step. The isosteric isopropoxy and methallyl substituents with the nonnatural C16-configuration abolish both binding to FRAP and inhibition of T cell proliferation. Binding proteins for these derivatives were identified from libraries of cDNAs encoding mutants of the FKBP12-rapamycin-binding (FRB) domain of FRAP by using a mammalian three-hybrid transcription assay. Targeting of the mutations was guided by the structure of the FKBP12-rapamycin-FRB ternary complex. Three compensatory mutations in the FRB domain, all along one face of an alpha-helix in a rapamycin-binding pocket, were identified that together restore binding of the rapamycin derivatives. Using this mutant FRB domain, one of the nontoxic rapamycin derivatives induced targeted gene expression in Jurkat T cells with an EC50 below 10 nM. Another derivative was used to recruit a cytosolic protein to the plasma membrane, mimicking a process involved in many signaling pathways.

Animals↗
PubMed1997

Primary hypothyroidism presenting as severe vaginal bleeding in a prepubertal girl.

We describe a case of acquired primary hypothyroidism in a prepubertal girl who presented with profound bradycardia, precocious puberty, and severe vaginal bleeding. A pelvic ultrasound revealed markedly enlarged ovaries with numerous cysts. Cystic aspiration, in concert with L-thyroxine therapy, appeared to halt vaginal bleeding, and led to resolution of cysts. This is the first reported case of percutaneous cyst aspiration to treat ovarian hyperstimulation caused by hypothyroidism in a child.

Bradycardia↗
PubMed1996

Immunodominance, competition and evolution in immunological responses to helminth parasite antigens.

The paper describes the development and analysis of a mathematical framework for the study of the within-host population dynamics of the interaction between macroparasites and the human immune system. Simple models of this interaction based on the proliferation of T cell clones specific to parasite antigen, and the impact of clonal expansion on parasite survival, capture the basic features of age-related changes in worm loads within human communities. The model is generalized to multiple epitopes on a single antigen, and reveals competitive exclusion amongst T cells, with a single clone becoming immunodominant in the absence of cross-reactive responses and genetic variation. The introduction of genetic heterogeneity and concomitant variability in the immunogenicity of specific epitopes induces additional complexity into the dynamical interaction. Most importantly, multiple epitope models with antigenic variation suggest that the immunodominant response may not necessarily be targeted at the epitope at which some strains show the greatest immunogenicity. High immunogenicity at a particular epitope can be masked by genetic variability even though many of the variants are more immunogenic at this epitope by comparison with the epitope to which the immunodominant immunological response is directed.

Animals↗
PubMed1996

RU486 suppresses prolactin production in explant cultures of leiomyoma and myometrium.

OBJECTIVE: To assess the action of RU486 (mifepristone), in the presence and absence of P, on PRL production by explant cultures of leiomyoma and myometrium. DESIGN: Explant cultures using tissue from nine premenopausal women undergoing hysterectomy in the proliferative phase of the menstrual cycle; immunohistochemical staining of tissue sections from five patients for P receptor (PR) subtype. MAIN OUTCOME MEASURES: Prolactin secretion (measured by RIA), lactate dehydrogenase secretion (measured by quantitative colorimetric assay), and immunohistochemistry for PR subtype. RESULTS: Prolactin secretion was decreased in leiomyomas by RU486 at concentrations of 10(-7) M and 10(-5)M when normal serum-containing medium was used. In experiments with all detectable P removed from serum, PRL secretion was suppressed in both leiomyomas and myometrium at an RU486 concentration of 10(-7)M. Immunohistochemistry results suggest that the A form of the PR is the dominant form in both leiomyomas and myometrium. CONCLUSIONS: Prolactin production is suppressed in both leiomyomas and myometrium after treatment with RU486 in vitro, and this suppression may serve as a marker for the clinical effectiveness of agents used in the treatment of leiomyomas.

Culture Media↗
PubMed1995

A general strategy for producing conditional alleles of Src-like tyrosine kinases.

The Src-like tyrosine kinases require membrane localization for transformation and probably for their normal role in signal transduction. We utilized this characteristic to prepare Src-like tyrosine kinases that can be readily activated with the rationally designed chemical inducer of dimerization FK1012. Dimerization of cytoplasmic Src-like tyrosine kinases was not sufficient for signaling, but their recruitment to the plasma membrane led to the rapid activation of transcription factors identical to those regulated by crosslinking the antigen receptor. Moreover, recruitment of activated Src-like kinases to the membrane replaced signaling by the T-lymphocyte antigen receptor complex, leading to the activation of both the Ras/protein kinase C and Ca2+/calcineurin pathways normally activated by antigen receptor signaling. Since these chemical inducers of dimerization are cell permeable, this approach permits the production of conditional alleles of any of the Src-like tyrosine kinases, thereby allowing a delineation of their developmental roles.

Alkaline Phosphatase↗
PubMed1995

Signal transduction in T lymphocytes using a conditional allele of Sos.

While Ras activation has been shown to play an important role in signal transduction by the T-lymphocyte antigen receptor, the mechanism of its activation in T cells is unclear. Membrane localization of the guanine nucleotide exchange factor Sos, but not Vav or Dbl, was sufficient for Ras-mediated signaling in T lymphocytes. Activation of Sos appears to involve membrane recruitment and not allosteric changes, because interaction of Sos with the linking molecule Grb-2 was not required for Ras activation. To extend this analysis, we constructed a modified Sos that could be localized to the membrane inducibly by using a rationally designed chemical inducer of dimerization, FK1012. The role of Grb-2 in signaling was mimicked with this technique, which induced the association of a modified Sos with the membrane, resulting in rapid activation of Ras-induced signaling. In contrast, inducible localization of Grb-2 to the membrane did not activate signaling and suggests that the interaction of Grb-2 with Sos in T cells is subject to regulation. This conditional allele of Sos demonstrates that membrane localization of Sos is sufficient for Ras activation in T cells and indicates that the role of Grb-2 is to realize the biologic advantages of linker-mediated dimerization: enhanced specificity and favorable kinetics for signaling. This method of generating conditional alleles may also be useful in dissecting other signal transduction pathways regulated by protein localization or protein-protein interactions.

Adaptor Proteins, Signal Transducing↗
PubMed1994

Proximity versus allostery: the role of regulated protein dimerization in biology.

Regulated dimerization of proteins is increasingly understood to be important in many cellular processes, including signaling, transciption and protein degradation. Organic molecules that induce dimerization may offer as much potential to regulate biological processes as those that allosterically induce conformational change.

Animals↗
PubMed1994

An analysis of referral routes and diagnostic accuracy in cases of suspected glaucoma.

Over a nine-month period two hundred and thirteen referrals to the Department of Ophthalmology of the Leicester Royal Infirmary, England, for suspicion of glaucoma were examined by a single ophthalmologist. Ninety-nine percent of referrals resulted from the findings at an optometric visit. Despite this, less than 32% were confirmed as having glaucoma and less than 23% had ocular hypertension. Twenty-nine percent showed no abnormality. Of those with glaucoma 19% showed advanced field loss in their worse eye. The guidelines relating to referral practices as a result of optometric examinations need to be reviewed and agreed upon by ophthalmologists, optometrists and general practitioners.

Adult↗
PubMed1986

Carotid endarterectomy for cerebrovascular insufficiency: long-term results in 592 patients followed up to thirteen years.

Seven hundred forty-eight carotid endarterectomies were performed on 592 patients with cerebrovascular insufficiency during a 13-year period. Overall operative procedure mortality was 2.7%. In the last 6 years, using a shunt routinely and avoiding operation on acute strokes, mortality was 1.47%. In frank strokes it was 3.7%; in transient ischemia, 0.77%; and zero for chronic ischemia and asymptomatic bruits. Incidence of operation-related deficits among transient ischemia and asymptomatic bruit patients was 0.9% for transient weakness and 2% for permanent deficits. Of 172 long-term deaths, 23 were due to cerebral causes, or 3.9% of the entire series. Among frank stroke survivors, 30.2% are normal and 58.7% improved. In transient ischemia survivors 81% are normal and 15.7% improved. In 65 asymptomatic bruit patients operated upon electively, two had strokes during follow-up, one mild and one severe. Among 37 asymptomatic bruit control patients, 24 or 65% developed symptoms of transient ischemia or frank strokes. Of 118 totally occluded carotid arteries explored, flow was restored in 48 (40.7%) but could not be restored in 70 (59.3%). For cerebral protection during carotid endarterectomy the routine use of a temporary inlying bypass shunt with general anesthesia is advocated for all partial occlusions. Endarterectomy is most useful for transient ischemia and selected patients with mild frank strokes and asymptomatic bruits. Acute profound and rapidly progressing strokes should not be operated upon as an emergency, but allowed to stabilize for several weeks and then be considered for possible operation.

Acute Disease↗
PubMed1984

Treatment of chalazions with injection of a steroid suspension.

A trial was conducted to compare the efficacy of the treatment of chalazions by injection of triamcinolone acetonide with conventional incision and curettage. Of the 39 injected cases 77% resolved completely, though 54% of the injected cases required a second injection. Of the 30 surgically treated cases 90% resolved, but 27% required a second operation. Injection of chalazions with a steroid suspension is a convenient and reasonably effective alternative to the standard surgical management of this common condition.

Adult↗
PubMed1981

Treatment of radiation retinopathy.

A case of radiation induced retinopathy with neovascularisation arising from the optic disc and retina was treated with panretinal argon laser photocoagulation. Complete regression of the new vessels was observed within 2 weeks of therapy. The pathogenesis of neovascularisation in this condition is discussed.

Fluorescein Angiography↗