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Biomedical subjects

D Fischer

Publications and source records attributed to D Fischer.

At least 145 records · Page 8Linked to original sources
PubMed1997

Reappraisal of the role of axillary lymph node dissection in the conservative treatment of breast cancer.

PURPOSE: The purpose of this study was (1) to review systemic therapy practice patterns to assess how information regarding nodal status currently influences systemic therapy decisions, and (2) to review long-term outcome of patients who do not undergo axillary dissection compared with patients who do. METHODS AND MATERIALS: For the current practice patterns portion of the study, the records of 292 patients who presented in the past 3 years with invasive breast cancer and underwent conservative surgery were reviewed to determine systemic therapy administered with respect to patient age, primary tumor size, clinical nodal status, and presenting symptoms. For the long-term outcome portion of the study, the records of 955 patients with invasive breast cancer who underwent conservative surgery and radiation therapy before December 1989 were reviewed. Patient characteristics and outcome of those patients who underwent axillary dissection (n = 565, 59%) were compared with a cohort of patients treated during the same era who did not undergo axillary dissection (n = 390, 41%). RESULTS: For the current practice-patterns cohort, information regarding nodal status appeared to influence adjuvant systemic therapy for those patients less than 50 years of age and for those patients with palpable masses who were older than 50. Patients older than 50 with nonpalpable mammographically detected tumors have a low probability of nodal involvement and information regarding nodal status rarely changed therapy in this group of patients. In the long-term outcome study, there were no significant differences in the rates of distant metastasis, disease-free survival, or overall survival between those patients who underwent lymph node dissection and those who did not. CONCLUSION: For selected patients, axillary lymph node dissection appears to have little influence on subsequent management and long-term outcome. These data suggest that it is time to reassess the role of axillary lymph node dissection in patients who undergo conservative surgery and radiation therapy.

Actuarial Analysis↗
PubMed1997

Concerted action of tenascin-C domains in cell adhesion, anti-adhesion and promotion of neurite outgrowth.

We used a new approach to identify domains of chicken tenascin-C required for interaction with cells. Instead of expressing the parts of interest, we deleted them from an otherwise intact tenascin-C molecule and scored for the concomitant change in activity. As a starting point for all mutant constructs we expressed the smallest naturally occurring tenascin-C splice variant in vertebrate cells. The tenascin-C mutants had either deletions of all EGF-like repeats, all fibronectin type III repeats or of the fibrinogen globe. In double mutants the fibronectin type III repeats were deleted together with either the EGF-like repeats or the fibrinogen globe, respectively. All tenascin-C variants assembled correctly to hexameric molecules of the expected molecular characteristics. Intact tenascin-C and the mutant missing the fibrinogen globe did not promote adhesion of chick embryo fibroblasts, whereas both, the hexamers containing solely the fibrinogen globe or the EGF-like repeats were adhesive substrates and even supported cell spreading. When tenascin-C was added to the medium of fibroblasts plated on fibronectin-coated wells, cell adhesion was blocked by intact tenascin-C, but not by mutants missing the fibrinogen globe. In neurite outgrowth assays using dorsal root ganglia, processes formed on all substrates except on the mutant missing only the fibrinogen globe, where the ganglia failed to adhere. The mutants missing the fibronectin type III repeats allowed more rapid neurite outgrowth than all other tenascin-C variants and the mutant consisting essentially of oligomerized EGF-like repeats was as active a substrate for neurite outgrowth as laminin. From the combined data, it is concluded that the activities of intact tenascin-C cannot be mimicked by investigating domain by domain, but the concerted action of several domains leads to the diverse cellular responses.

Animals↗
PubMed1997

Biphasic kinetics of quaternary ammonium glucuronide formation from amitriptyline and diphenhydramine in human liver microsomes.

The tricyclic antidepressant amitriptyline and the H1-receptor antagonist diphenhydramine are conjugated in human liver microsomes fortified with UDP-glucuronic acid at their tertiary amino groups with the formation of quaternary ammonium glucuronides. The kinetics of the reactions were found to be biphasic with apparent KM1 and KM2 values of 1.4 microM and 311 microM for amitriptyline and 2.6 microM and 1180 microM for diphenhydramine in four liver samples. Vmax1 values varied between 2 and 17 pmol-mg protein-1.min-1 for the two substrates and Vmax2 values between 80 and 740 pmol-mg protein-1.min-1. A close correlation existed between amitriptyline and diphenhydramine glucuronidation rates in microsomes from seven livers at concentrations corresponding to 10-40% of KM2. At low concentrations, diphenhydramine competitively inhibited the glucuronidation of amitriptyline. Vmax/K(M) values of the high-affinity UDP-glucuronosyltransferase(s) (UGTs) exceed those of the low-affinity enzyme(s) severalfold, such that the former should make the major contribution to N-glucuronidation of the drugs at therapeutic concentrations in vivo.

Amitriptyline↗
PubMed1997

Interleukin-6 receptor-interleukin-6 fusion proteins with enhanced interleukin-6 type pleiotropic activities.

An sIL-6R/IL-6 chimera, directly fusing the natural forms of soluble IL-6 receptor and IL-6, as found in human body fluids, was produced in transfected human cells. The secreted p85 glycoprotein was active at a concentration of 120 pM to produce growth-arrest and spindleoid differentiation of murine melanoma F10.9 cells, which do not respond to IL-6 alone. This fusion protein was as active as the yeast-produced p56 fusion protein containing a shortened sIL-6R, linked through a flexible peptide chain to IL-6 (Hyper IL-6). The concentration of Hyper IL-6 needed to arrest the growth of F10.9 cells was much lower than that needed of a combination of IL-6 and sIL-6R, added separately. Hyper IL-6 was also more active than IL-6 in stimulating growth of murine plasmacytoma T1165 cells, the half maximal stimulation being obtained at 2 pM Hyper IL-6 versus 23 pM for IL-6. In order to evaluate the effect of the fused sIL-6R/IL-6 proteins on human hematopoietic primitive progenitor cells, they were added to suspension cultures of CD34+ cells from human cord blood in addition to both flt3/flk2 ligand (FL) and stem cell factor (SCF). Fused sIL-6R/IL-6 produced a marked stimulation of cell expansion and a marked increase in the number of colony forming units when subsequently plated in semi-solid medium with IL-3, GM-CSF, SCF and erythropoietin. Ex-vivo maintenance and expansion of early progenitor cells in bone marrow transplantation protocols may be a potential application for the sIL-6R/IL-6 chimeric glycoproteins.

Animals↗
PubMed1996

The RNA-binding protein HF-I, known as a host factor for phage Qbeta RNA replication, is essential for rpoS translation in Escherichia coli.

The rpoS-encoded sigma(S) subunit of RNA polymerase in Escherichia coli is a global regulatory factor involved in several stress responses. Mainly because of increased rpoS translation and stabilization of sigma(S), which in nonstressed cells is a highly unstable protein, the cellular sigma(S) content increases during entry into stationary phase and in response to hyperosmolarity. Here, we identify the hfq-encoded RNA-binding protein HF-I, which has been known previously only as a host factor for the replication of phage Qbeta RNA, as an essential factor for rpoS translation. An hfq null mutant exhibits strongly reduced sigma(S) levels under all conditions tested and is deficient for growth phase-related and osmotic induction of sigma(S). Using a combination of gene fusion analysis and pulse-chase experiments, we demonstrate that the hfq mutant is specifically impaired in rpoS translation. We also present evidence that the H-NS protein, which has been shown to affect rpoS translation, acts in the same regulatory pathway as HF-I at a position upstream of HF-I or in conjunction with HF-I. In addition, we show that expression and heat induction of the heat shock sigma factor sigma(32) (encoded by rpoH) is not dependent on HF-I, although rpoH and rpoS are both subject to translational regulation probably mediated by changes in mRNA secondary structure. HF-I is the first factor known to be specifically involved in rpoS translation, and this role is the first cellular function to be identified for this abundant ribosome-associated RNA-binding protein in E. coli.

Allolevivirus↗
PubMed1996

Amino acid pair interchanges at spatially conserved locations.

Here we study the pattern of amino acid interchanges at spatially, locally conserved regions in globally dissimilar and unrelated proteins. By using a method which completely separates the amino acid sequence from its respective structure, this work addresses the question of which properties of the amino acids are the most crucial for the stability of conserved structural motifs. The proteins are taken from a structurally non-redundant dataset. The spatially conserved substructural motifs are defined as consisting of a "large enough" number of Calpha atoms found to provide a geometric match between two proteins, regardless of the order of the Calpha atoms in the sequence, or of the sequence composition of the substructures. This approach can apply to proteins with little or no sequence similarity but with sufficient structural similarity, and is unique in its ability to handle local, non-topological matches between pairs of dissimilar proteins. The method uses a computer-version based algorithm, the Geometric Hashing. Since the Geometric Hashing ignores sequence information it lends itself to answer the question posed above. The interchanges at geometrically similar positions that have been obtained with our method demonstrate the expected behaviour. Yet, a closer inspection reveals some distant characteristics, as compared with interchanges based upon sequence-order based techniques, or from energy-contact-based considerations. First, a pronounced division of the amino acids into two classes is displayed: Lys, Glu, Arg, Gln, Asp, Asn, Pro, Gly, Thr, Ser and His on the one hand, and Ile, Val, Leu, Phe, Met, Tyr, Trp, Cys and Ala on the other. These groups further cluster into subgroups: Lys, Glu, Arg, Gln; Asp Asn; Pro, Gly; Ile, Val, Leu, Phe. The other amino acids stand alone. Analysis of the conservation among amino acids indicates proline to be consistently, by far, the most conserved. Next are Asp, Glu, Lys and Gly. Cys is also highly conserved. Interestingly, oppositely charged amino acids are interchanged roughly as frequently as those of the same charge. These observations can be explained in terms of the three-dimensional structures of the proteins. Most of all, there is a clear distinction between residues which prefer to be on the protein surfaces, compared to those frequently buried in the interiors. Analysis of the interchanges indicates their low information content. This, together with the separation into two groups, suggest that the predictive value of the spatial positions of the Calpha+ atoms is not much greater than the sequence alone, aside from their hydrophobicity/hydrophillicity classification.

Amino Acid Sequence↗
PubMed1996

The response regulator RssB controls stability of the sigma(S) subunit of RNA polymerase in Escherichia coli.

The rpoS-encoded sigma(S) subunit of RNA polymerase is a central regulator in a regulatory network that governs the expression of many stationary phase-induced and osmotically regulated genes in Escherichia coli. sigma(S) is itself induced under these conditions due to an increase in rpoS transcription (only in rich media) and rpoS translation as well as a stabilization of sigma(S) protein which in growing cells is subject to rapid turnover. We demonstrate here that a response regulator, RssB, plays a crucial role in the control of the cellular sigma(S) content. rssB null mutants exhibit nearly constitutively high levels of sigma(S) and are impaired in the post-transcriptional growth phase-related and osmotic regulation of sigma(S). Whereas rpoS translational control is not affected, sigma(S) is stable in rssB mutants, indicating that RssB is essential for sigma(S) turnover. RssB contains a unique C-terminal output domain and is the first known response regulator involved in the control of protein turnover.

Bacterial Proteins↗
PubMed1996

Analysis of topological and nontopological structural similarities in the PDB: new examples with old structures.

We have developed a new method and program, SARF2, for fast comparison of protein structures, which can detect topological as well as nontopological similarities. The method searches for large ensembles of secondary structure elements, which are mutually compatible in two proteins. These ensembles consist of small fragments of C alpha-trace, similarly arranged in three-dimensional space in two proteins, but not necessarily equally-ordered along the polypeptide chains. The program SARF2 is available for everyone through the World-Wide Web (WWW). We have performed an exhaustive pairwise comparison of all the entries from a recent issue of the Protein Data Bank (PDB) and report here on the results of an automated hierarchical cluster analysis. In addition, we report on several new cases of significant structural resemblance between proteins. To this end, a new definition of the significance of structural similarity is introduced, which effectively distinguishes the biologically meaningful equivalences from those occurring by chance. Analyzing the distribution of sequence similarity in significant structural matches, we show that sequence similarity as low as 20% in structurally-prealigned proteins can be a strong indication for the biological relevance of structural similarity.

Algorithms↗
PubMed1996

Protein fold recognition using sequence-derived predictions.

In protein fold recognition, one assigns a probe amino acid sequence of unknown structure to one of a library of target 3D structures. Correct assignment depends on effective scoring of the probe sequence for its compatibility with each of the target structures. Here we show that, in addition to the amino acid sequence of the probe, sequence-derived properties of the probe sequence (such as the predicted secondary structure) are useful in fold assignment. The additional measure of compatibility between probe and target is the level of agreement between the predicted secondary structure of the probe and the known secondary structure of the target fold. That is, we recommend a sequence-structure compatibility function that combines previously developed compatibility functions (such as the 3D-1D scores of Bowie et al. [1991] or sequence-sequence replacement tables) with the predicted secondary structure of the probe sequence. The effect on fold assignment of adding predicted secondary structure is evaluated here by using a benchmark set of proteins (Fischer et al., 1996a). The 3D structures of the probe sequences of the benchmark are actually known, but are ignored by our method. The results show that the inclusion of the predicted secondary structure improves fold assignment by about 25%. The results also show that, if the true secondary structure of the probe were known, correct fold assignment would increase by an additional 8-32%. We conclude that incorporating sequence-derived predictions significantly improves assignment of sequences to known 3D folds. Finally, we apply the new method to assign folds to sequences in the SWISSPROT database; six fold assignments are given that are not detectable by standard sequence-sequence comparison methods; for two of these, the fold is known from X-ray crystallography and the fold assignment is correct.

Amino Acid Sequence↗
PubMed1996

A molecular anatomical analysis of mosaic trisomy 16.

A one-month-old child presenting with an aortic coarctation was found to have a left single transverse palmar crease and proportionate growth delay on physical examination, prompting a peripheral blood chromosome analysis. This showed a mosaic trisomy of chromosome 16, subsequently observed to decrease with the passage of time. As her phenotype was relatively benign, further analysis was performed to define more precisely the extent of her mosaicism given the supposedly lethal nature of the aneuploid cell line. Fluorescence in situ hybridisation and CA repeat polymorphism studies demonstrated the aneuploidy in multiple tissues, including the structurally affected aorta. Molecular analysis showed both maternal chromosomes 16 to be present in the trisomic cells, but maternal heterodisomy was not present in the diploid cells. Given the increasing number of individuals described with aneuploid mosaicism, we suggest that the study of multiple tissues is a necessary approach, the eventual goal being the appreciation of the relationship between the characteristics of a somatic mosaicism and the phenotype it imparts.

Alleles↗
PubMed1996

A study of combined structure/sequence profiles.

BACKGROUND: For genome sequencing projects to achieve their full impact on biology and medicine, each protein sequence must be identified with its three-dimensional structure. Fold assignment methods (also called profile and threading methods) attempt to assign sequences to known protein folds by computing the compatibility of sequence to fold. RESULTS: We have extended profile methods for the detection of protein folds having structural similarity but low sequence similarity to sequence probes. Our extension combines sequence substitution tables with structural properties to form a combined profile. The structural properties used in this study include distances between residues, exposed areas, areas buried by polar atoms, and properties of the original three-dimensional profile method. We compared the performance of these combined profiles with different sequence matrices and with the original three-dimensional profile method. To determine the optimal gap penalties and weights used with these profiles, we employed a genetic algorithm. The performance of these combined profiles was tested by cross validation using independent test and training sets. CONCLUSIONS: These studies show that the combined profiles perform better than profiles based on either structural or sequence information alone.

Algorithms↗
PubMed1996

Assigning amino acid sequences to 3-dimensional protein folds.

With the advent of genome sequencing projects, the amino acid sequences of thousands of proteins are determined every year. Each of these protein sequences must be identified with its function and its 3-dimensional structure for us to gain a full understanding of the molecular biology of organisms. To meet this challenge, new methods are being developed for fold recognition, the computational assignment of newly determined amino acid sequences to 3-dimensional protein structures. These methods start with a library of known 3-dimensional target protein structures. The new probe sequence is then aligned to each target protein structure in the library and the compatibility of the sequence for that structure is scored. If a target structure is found to have a significantly high compatibility score, it is assumed that the probe sequence folds in much the same way as the target structure. The fundamental assumptions of this approach are that many different sequences fold in similar ways and there is a relatively high probability that a new sequence possesses a previously observed fold. We review various approaches to fold recognition and break down the process into its main steps: creation of a library of target folds; representation of the folds; alignment of the probe sequence to a target fold using a sequence-to-structure compatibility scoring function; and assessment of significance of compatibility. We emphasize that even though this new field of fold recognition has made rapid progress, technical problems remain to be solved in most of the steps. Standard benchmarks may help identify the problem steps and find solutions to the problems.

Algorithms↗
PubMed1996

Ipsilateral breast tumor recurrence as a predictor of distant disease: implications for systemic therapy at the time of local relapse.

PURPOSE: To evaluate the prognostic significance of ipsilateral breast tumor recurrence (IBTR) with respect to the subsequent development of distant metastasis. MATERIALS AND METHODS: Between January 1970 and December 1989, 973 patients with invasive breast cancer were treated with conservative surgery and radiation therapy at Yale-New Haven Hospital. The median follow-up time as of December 1993 was 8.6 years. A number of prognostic factors were tested as possible predictors of distant metastases, including whether a patient experienced IBTR. IBTRs were broken down by time to recurrence to determine whether the breast recurrence-free interval had any prognostic relevance with respect to the development of distant metastasis. RESULTS: As of December 1993, out of the entire population of 973 patients, 73 patients had developed IBTR and 134 had developed distant metastases. The overall actuarial survival rate at 10 years was .71 +/- .02, with a 10-year actuarial breast recurrence-free rate of .84 +/- .02 and a 10-year distant metastasis-free rate of .77 +/- .02. The overall distant metastasis rate was higher in patients who experienced IBTR compared with patients who had never experienced IBTR. Furthermore, the time to IBTR had a significant effect on distant metastases. Of 32 patients who developed an IBTR within 4 years of original diagnosis, 16 (50%) developed distant metastases. In contrast, of 41 patients who developed later breast relapses (> 4 years from original diagnosis), only seven (17%) developed distant metastases (P < .01). Of 32 patients who developed early breast relapse, the 5-year survival rate following breast relapse was .50 +/- .01, compared with a 5-year post-breast relapse survival rate of .78 +/- .10 among 41 patients with later breast relapses (P < .05). CONCLUSION: It appears that early IBTR is a significant predictor for distant metastases. Whether early breast tumor relapse is a marker for or cause of distant metastases remains a controversial and unresolved issue. Implications for adjuvant systemic therapy at the time of breast relapse are discussed.

Adult↗
PubMed1996

Repairing fractured porcelain: how surface preparation affects shear force resistance.

This article reports on a study of the shear bond strength of porcelain repaired with any of several currently available dentin bonding systems and composite resin. The authors describe the benefits of the use of silane and the decrease in shear bond strength values after thermocycling. The results should be helpful to any practitioner confronted with a restoration that is a candidate for intraoral repair of fractured porcelain.

Analysis of Variance↗
PubMed1996

Chlamydia trachomatis antibodies in serum and ejaculate of male patients without acute urethritis.

In a prospective study, the prevalence of specific antibodies against Chlamydia trachomatis in serum and seminal plasma evaluated by a genus specific immunofluorescence test in 101 men without acute urethritis was investigated. The results were compared to the clinical diagnosis, cell culture of urethral swabs, demonstration of DNA particles by Polymerase Chain Reaction (PCR) in the ejaculate and signs of genital inflammation by counting peroxidase-positive leukocytes and elastase level in semen. The objective was to evaluate the significance of chlamydial antibodies in genital infection. Serum specific IgG and IgA antibodies were found in 26% and 15%, respectively; seminal IgG and IgA antibodies were present in 6% and 7%, respectively. Serum specific antibodies were not associated with the clinical diagnosis of infection nor with C. trachomatis cell culture, PCR findings, peroxidase positive leukocytes or PMN-elastase level. It is concluded that serum antibodies are not useful in detecting a chlamydial infection. Seminal plasma antibodies were not correlated with the clinical diagnosis of infection, positive cell culture, PMN-elastase levels and leukocytes in semen. However, a significant correlation was found for positive PCR in the ejaculate (p < 0.001 for IgG, p < 0.05 for IgA, p < 0.001 when combined). Though seminal antibodies may be more useful in detecting ascended or occult chlamydial infection, their significance remains unclear, their absence does not exclude chlamydial infection. In particular, the biological significance of locally derived IgA needs further evaluation.

Acute Disease↗
PubMed1996

Assessing the performance of fold recognition methods by means of a comprehensive benchmark.

Recently there has been an explosion of methods for fold recognition. These methods seek to align a protein sequence to a three-dimensional structure and measure the compatibility of the sequence to the structure. In this work, we present a benchmark to assess the performance of such methods. The benchmark consists of a set of protein sequences matched by superposition to known structures. This set covers a wide range of protein families, and includes matching proteins with insignificant sequence similarity. To demonstrate the usefulness of this benchmark, we apply it here to compare different fold-recognition methods developed through the years in our group as well as several sequence-sequence substitution matrices. The results show that "global-local" alignments are superior to either local or global alignments. The most effective sequence-sequence matching matrix is the Gonnet table. The best performance overall is obtained by a method which combines the 3D-1D profiles of Bowie et al. with a substitution matrix and takes into account residue pairwise interactions.

Amino Acid Sequence↗
PubMed1995

Subareolar breast cancer: long-term results with conservative surgery and radiation therapy.

PURPOSE: It has been suggested that patients presenting with breast cancers within 2 cm of the nipple areolar complex represent a relative contraindication to conservative management due to either a compromised cosmetic result associated with sacrifice of the nipple areolar complex, reluctance to include the entire nipple areolar complex in the conedown field, or increased risk of multicentricity. We have reviewed our experience of conservatively treated patients with specific reference to the subset of patients presenting with tumors within 2 cm of the nipple areolar complex. METHODS AND MATERIALS: Between January 1970 and December 1989, 1014 patients with early stage breast cancer were treated at Yale-New Haven Hospital by excisional biopsy with or without axillary lymph node dissection. Of the 1014 charts reviewed, a total of 98 patients fulfilled the criteria of having a central/ subareolar breast cancer. Reexcision was performed on only 16 patients. Following conservative surgery, patients were treated with radiation therapy to the intact breast to a total median dose of 48 Gy with conedown to a total of 64 Gy. adjuvant systemic therapy and regional nodal irradiation were administered as clinically indicated. RESULTS: As of December 1993, the median follow-up for the 98 patients in this study was 9.03 years. The majority of patients had presented with either a palpable mass or a mammographically detected lesion. Three patients presented with Paget's disease, five with nipple discharge, and seven with nipple inversion. Ten of the 98 patients had the nipple areolar complex sacrificed at the time of surgery, while the remaining 88 patients had the entire nipple areolar complex included in the conedown field. Four of these 88 patients had the nipple partially blocked during the electron conedown. There were no significant complications associated with including the entire nipple areolar complex within the conedown field to a median dose of 64 Gy. Six of the 98 patients experienced a local recurrence, three experienced a regional recurrence, and nine experienced distant metastasis. The actuarial 10-year survival (0.79 +/- 0.06), distant disease-free survival (0.88 +/- 0.04) and breast recurrence-free survival (0.84 +/- 0.07) were not significantly different from those patients who presented with cancers in other parts of the breast. CONCLUSIONS: Patients presenting with subareolar breast cancers within 2 cm of the nipple areolar complex are suitable candidates for conservative surgery and radiation therapy. In the majority of patients in this study, the nipple areolar complex did not need to be sacrificed and could be safely included in the electron conedown field with acceptable complications and cosmesis. A subareolar breast cancer does not represent a relative contraindication to conservative management in patients with early stage breast cancer.

Breast Neoplasms↗