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Biomedical subjects

T C Lo

Publications and source records attributed to T C Lo.

At least 73 records · Page 4Linked to original sources
PubMed1984

Mechanism of antibody stimulation of hexose transport in rat myoblasts.

We have recently demonstrated that exposure of rat myoblasts to anti-rat myoblast antiserum results in two- to three-fold activation of hexose transport. The present communication reports the possible mechanism(s) by which specific antibody can bring about such activation. Studies with Fab and Fc fragments indicate that the binding of Fab to specific cell surface component(s) is not sufficient to trigger activation of hexose transport; the immunoglobulin G (IgG) mediated dimerization of membrane components is required for this process. Although cytochalasin D has no effect on hexose transport in control and antibody-treated cells, pretreatment of cells with this inhibitor prevents antibody-mediated activation of hexose transport. It may be inferred from this observation that proper disposition of membrane components is required for the dimerization of membrane receptors. Since this activation of hexose transport is an irreversible process, it is possible that covalent modification of membrane components may have occurred as a result of antibody treatment. Pretreatment of cells with ammonium chloride or methylamine is found to abolish the antibody-mediated activation of hexose transport, even though these inhibitors have no effect on hexose transport in control and antibody-treated cells. These inhibitors may be acting on transglutaminase and (or) on some other proteins involved in the activation process. Several lines of evidence suggest that limited proteolytic cleavage of membrane components may be involved in the antibody-mediated activation of hexose transport. First, pretreatment with several protease inhibitors prevents activation of hexose transport. Second, several cell surface proteins are missing in antibody-treated cells. Third, limited proteolysis of cell surface proteins with trypsin can also bring about activation of hexose transport. In view of the fact that proteolytic activity cannot be detected in various IgG and serum preparations, it seems likely that endogenous membrane associated proteases may be involved in this activation process.

Ammonium Chloride↗
PubMed1984

Hexose transport in plasma membrane vesicles of rat myoblast L6.

To determine the molecular mechanism of hexose transport in rat myoblasts, transport studies were carried out with purified plasma membrane vesicles. Rat myoblasts were homogenized and fractionated by differential and sucrose gradient centrifugation. Six different fractions were obtained. Studies with marker enzymes revealed that two fractions (A and B) were composed of only plasma membrane. These two fractions differed considerably in their physical properties. Fraction A was composed of large multilaminated vesicles, with an intravesicular volume of 50 microL/mg protein, whereas fraction B was composed of membrane fragments and much smaller vesicles, with an intravesicular volume of 7 microL/mg protein. Based on the response of the ouabain-sensitive Na+, K+-ATPase activity to sodium dodecyl sulfate and ionophore treatments, it seemed likely that fraction A was composed of a significant amount of sealed right-side-out vesicles, whereas fraction B was composed of mainly membrane sheets or leaky vesicles. The initial rate of hexose influx into the membrane vesicles was determined by the flow dialysis technique. The optimal conditions for 2-deoxyglucose (2-DG) uptake into the plasma membrane vesicles were either 50 mM phosphate buffer or 10 mM 2-(N-2-hydroxyethylpiperazin-N'-yl)ethanesulfonic acid buffer at pH 7.0. In the presence of 500 microM 2-DG, the initial rates of 2-DG influx were 295 and 49 nmol/min per milligram protein for fractions A and B, respectively. In other words, after 1 min of incubation, the intravesicular concentration of 2-DG was around 6 mM, about 10 times the extravesicular concentration. D-Glucose was taken up to a similar extent (333 nmol/min per milligram protein), whereas L-glucose only equilibrated across the plasma membrane. Analysis of the fate of 2-DG revealed that the substrate was not phosphorylated upon incubation with the vesicles. Transport activity can be abolished either by disruption of the membrane vesicles or by reduction of the electrical potential across the membrane.

Animals↗
PubMed1983

Megavolt electron irradiation in the treatment of recurrent carcinoma of the breast on the chest wall.

Low megavolt electron beam therapy was used to treat 68 women and one man with recurrent carcinoma of the breast on the chest wall. Photon irradiation had been used previously in 53 patients. Of the 63 patients who survived 2 months or longer after electron irradiation, 59 (94%) achieved a complete response. Persistent radiation ulcers developed in only 2 patients (3%). No other late radiation complications were observed. Nineteen patients (28%) survived 3 years after electron irradiation, with a median survival of 54 months. In this group, disease eventually recurred in all patients who received a calculated NSD of less than 1 400 ret; no disease recurred in the patients who received doses greater than 1 400 ret. It is concluded that megavolt electron irradiation is effective in the treatment of chest wall recurrence from carcinoma of the breast and is safe even in patients who have had a previous course of photon irradiation.

Adult↗
PubMed1981

Use of a nonpenetrating substrate analogue to study the molecular mechanism of the outer membrane dicarboxylate transport system in Escherichia coli K12.

We have recently demonstrated that a cell-surface dicarboxylate-binding protein (DBP) is involved in the outer membrane dicarboxylate transport system in Escherichia coli K12. The present report deals with our findings relating to the mode of action of this protein, and the identity and properties of the outer membrane integral protein which is involved in the translocation of dicarboxylic acids across the hydrophobic regions of the outer membrane. By the use of a nonpenetrating succinate analogue, aspartate-dextran, and through reconstitution studies with purified DBP, the cell-surface DBP is found to play an important role in succinate influx but not efflux. Transport studies with major outer membrane protein mutants indicate that the matrix protein (also referred to as protein I or porin) is the only outer membrane integral protein actively involved in the outer membrane dicarboxylate transport system. In the absence of a functional DBP, porin translocates succinate in a relatively less efficient and nonspecific manner. A tentative working model is proposed for this transport system. In this model, the cell-surface DBP is depicted as the substrate recognition component of the otherwise nonspecific porin channel. Together, this "DBP-porin channel complex" forms an efficient, specific transport channel for dicarboxylic acids.

Biological Transport↗
PubMed1981

Megavolt electron irradiation for localized mycosis fungoides.

A retrospective analysis was carried out to evaluate the effectiveness of small field megavolt electron irradiation for localized mycosis fungoides. Only local field electron beam therapy was employed for limited disease reserving total skin electron irradiation for multiple lesions or diffuse disease covering at least 25 per cent of the entire body surface. Of the 14 patients with limited disease treated between 1964 and 1973 with the local field technique, 10 patients (71 per cent) are alive without evidence of disease at a minimum of 5 years. In contrast, of 200 patients with extensive cutaneous disease who received total skin electron irradiation, only 16 (8 per cent) were considered cured. It is concluded that early localized mycosis fungoides is potentially curable, and that limited field electron beam therapy with a relatively low total dose is adequate to obtain excellent response.

Humans↗
PubMed1980

Radiotherapy for Kaposi's sarcoma.

Between 1954 and 1976, 60 patients with Kaposi's sarcoma were treated in the Department of Radiotherapy of the Lahey Clinic Foundation at the High Voltage Research Laboratory of Massachusetts Institute of Technology. Only 2 patients were free of clinical disease in the lower extremities at the time of initial presentation, and 40 patients (69%) had cutaneous lesions involving areas extending above the knees. Eight patients (13%) also presented with mucous membrane involvement in addition to skin disease. Twenty-one patients were treated only with megavoltage electrons during the initial course of radiotherapy, and 12 patients were treated with supervoltage photons alone. The remaining 27 patients were treated with a combination of electrons and photons; in 17 patients, the same tumor sites were irradiated with both modalities. Eleven patients received whole-body surface electron irradiation. The choice of treatment modalities was based on the extent and distribution of cutaneous disease and depth of the lesions. The overall response rate was 93% after a single fractionated course of radiotherapy. Twenty-five patients achieved complete regression and 18 were in remission for 2-13 years. Response rates were also analyzed with respect to the three subgroups in terms of treatment modalities. A single dose of 800 to 1200 rads or its equivalent was required to control local cutaneous lesions. Widespread visceral metastasis was the most common cause of failure and death; the incidence of second malignancies was increased. Trial of systemic chemotherapy and immunotherapy would seem to be a reasonable therapeutic adjunct.

Adult↗
PubMed1980

Localization of the dicarboxylate binding protein in the cell envelope of Escherichia coli K12.

Examination of the localization of the dicarboxylate binding protein (DBP) in the cell envelope of Escherichia coli K12 reveals that this protein is present on the cell surface, and also in the inner and outer regions of the periplasmic space. The cell surface DBP is release by treating the cells with EDTA. This protein can be surface labeled by lactoperoxidase radioiodination, and by diazo[125I]iodosulfanilic acid in whole cells. It also binds tightly, but not covalently, to lipopolysaccharide. The DBP located in the outer region of the periplasmic space is released when the outer membrane is dissociated by EDTA-osmotic shock treatment. The DBP located in the inner region of the periplasmic space is released only when the EDTA-osmotic shocked cells are subjected to lysozyme treatment. At the moment, it is not certain whether this protein is bound to or trapped by the peptidoglycan network. This protein cannot be surface labeled in whole cells or in EDTA-osmotic shock treated cells; and it is not associated with lipopolysaccharide. Analysis of transport mutants indicates that these DBP are coded by the same gene.

Alkaline Phosphatase↗
PubMed1979

The transfer of a bacterial transmembrane function to eukaryotic cells.

This communication reports our preliminary studies on the reconstitution of the bacterial dicarboxylate transport system into rat myoblasts and mouse L-cells. Purified dicarboxylate membrane transport components (SBP 1 and SBP 2) from Escherichia coli K12 were added to rat myoblasts and mouse L-cells. These components were readily incorporated into the cell membranes. The rat myoblasts, as well as the mouse L-cells, were unable to transport succinate by themselves, or in the presence of either one of the transport components. However, when both components were added to the cells, the latter acquired the ability to transport succinate. There was a direct relationship between the amount of transport components added and the rate of succinate uptake. The newly acquired dicarboxylate transport system exhibited similar substrate affinity and specificity as the E. coli dicarboxylate transport system. The above findings suggest that it is possible to transfer a bacterial transmembrane function into eukaryotic cell membrane, and that these proteins can function normally in a foreign environment.

Biological Transport, Active↗
PubMed1979

Dicarboxylic acid transport in Escherichia coli K12: involvement of a binding protein in the translocation of dicarboxylic acids across the outer membrane of the cell envelope.

We have previously found that the dicarboxylate transport system in Escherichia coli K12 is an active transport system and that at least one binding protein and two cytoplasmic membrane transport components are involved in the uptake of dicarboxylic acids. Recently, through surface labelling studies, some dicarboxylate binding proteins were found to be exposed on the cell surface. In the present paper, we demonstrate that the dicarboxylate transport component located in the outer membrane can be inactivated by two different kinds of nonpenetrating inhibitors, viz. proteases, and diazosulfanilic acid. These inhibitors seem to act on the dicarboxylate binding protein. By adding this protein to inactivated cells or to transport-negative mutants, we have succeeded in reconstituting the dicarboxylate transport system. These findings suggest that the dicarboxylate binding protein found on the cell surface plays an essential role in the translocation of dicarboxylic acids across the outer membrane.

Biological Transport, Active↗
PubMed1979

Whole body surface electron irradiation in the treatment of mycosis fungoides. An evaluation of 200 patients.

The records of 200 patients with generalized cutaneous mycosis fungoides treated with whole body surface electron irradiation were reviewed. Type of skin lesion appeared to be the most important factor with respect to both survival and generalized skin disease-free interval. High-dose irradiation did not seem to influence prognosis significantly compared with a relatively conservative dose. The "cure" rate for the entire group was 7%. For a more homogeneous dose distribution, the eight-field technique is now used instead of the original four-field method. A new formula is proposed to standardize the reporting of doses.

Adolescent↗
PubMed1979

Dose considerations in total skin electron irradiation for mycosis fungoides.

Two hundred patients with generalized cutaneous mycosis fungoides were treated with total skin electron irradiation (TSEI) in the Lahey Clinic Radiotherapy Department-MIT High Voltage Research Laboratory between 1964 and 1973. None of the patients had any clinical evidence of extracutaneous disease at presentation. The 3-year absolute survival rate was 54% (107 patients). Analysis of these 107 long-term survivors evaluated the relation between incidence of generalized cutaneous recurrence and total treatment dose given during the initial course of TSEI. Results indicated that in patients with erythroderma, the need for a second course of TSEI was inversely related to the total dose given during the first course. However, the curve seemed to flatten at about 1,500 cGy (rad). In plaque disease, the percentage of patients who received repeated courses of TSEI seemed to be relatively constant independent of total dose given during the initial course (65%-80%). In patients with tumor lesions, the incidence of generalized cutaneous recurrence was directly proportional to total dose. The optimal dose of TSEI for patients with mycosis fungoides may vary depending on types of skin lesions. Total dose during the initial course of TSEI should be kept relatively conservative, particularly in patients with generalized plaques where relapse rate is high allowing reserve of normal tissue tolerance for further TSEI when indicated.

Dermatitis, Exfoliative↗
PubMed1979

Treatment of carcinoma of base of tongue with radiation therapy and 5-fluorouracil. Potential for optimization with 18F-FU.

The treatment of advanced base of tongue carcinoma with concurrent radiation therapy and 5-fluorouracil versus radiation therapy alone is compared. Although the results are inconclusive, it is noteworthy that all the 5-year survivors were patients given combined treatment. Important questions regarding optimization of time-dose relationships with combined therapy were generated. Accordingly, 18F-5 fluorouracil was synthesized in an attempt to answer some of these questions.

Carcinoma, Squamous Cell↗
PubMed1978

The molecular mechanisms of dicarboxylic acid transport in Escherichia coli K12. The role and orientation of the two membrane-bound dicarboxylate binding proteins.

Previous communications from this laboratory have indicated that dicarboxylic acid transport in Escherichia coli is an active process, and that at least three genes are responsible for this transport system. In attempts to identify the transport components, one periplasmic binding protein and two membrane integral proteins (SBP 1 and SBP 2) were implicated to participate in the transport system in vivo. In the present communication, we demonstrate, through biochemical analysis of the transport mutants, that the two membrane transport genes, dctA and dctB, are responsible for the two membrane-bound dicarboxylate binding proteins, SBP 2 and SBP 1, respectively. We also find that the substrate recognition sites of SBP 1 and SBP 2 are exposed to the inner and outer surfaces of the membrane, respectively. This may have important implications for the role of SBP 1 and SBP 2 in the translocation process.

Biological Transport, Active↗
PubMed1977

The molecular mechanism of dicarboxylic acid transport in Escherichia coli K 12.

It is the purpose of this communication to review the properties of the dicarboxylic acid transport system in Escherichia coli K 12, in particular the role of various dicarboxylate transport proteins, and the disposition of these components in the cytoplasmic membrane. The dicarboxylate transport system is an active process and is responsible for the uptake of succinate, fumarate, and malate. Membrane vesicles prepared from the EDTA, lysozyme, and osmotic shock treatment take up the dicarboxylic acids in the presence of an electron donor. Genetic analysis of various transport mutants indicates that there is only one dicarboxylic acid transport system present in Escherichia coli K 12, and that at least 3 genes, designated cbt, dct A, and dct B, are involved in this transport system. The products corresponding to the 3 genes are: a periplasmic binding protein (PBP) specified by cbt, and 2 membrane integral proteins, SBP 1 and SBP 2, specified by dct B and dct A, respectively. Components SBP 1 and SBP 2 appear to be exposed on both the inner and outer surfaces of the membrane, and lie in close proximity to each other. The substrate recognition sites of SBP 2 and SBP 1 are exposed on the outer and inner surfaces of the membrane respectively. The data presently available suggest that dicarboxylic acids may be translocated across the membrane via a transport channel. A tentative working model on the mechanism of translocation of dicarboxylic acids across the cell envelope by the periplasmic binding protein, and the 2 membrane carrier proteins is presented.

Binding Sites↗
PubMed1976

Combined radiation therapy and 5-fluorouracil for advanced squamous cell carcinoma of the oral cavity and oropharynx: a randomized study.

In 1961, a randomized study was begun at the University of Wisconsin Medical Center in which the treatment of advanced squamous cell carcinoma of the head and neck with radiation therapy was compared with combined treatment with radiation therapy and 5-Fluorouracil. One hundred and thirty-six patients with primary lesions in the oral cavity, the base of the tongue, and the oropharynx were analyzed. Both local control and survival were better in the combined treatment group than in the group with radiation therapy alone. However, in only the oral cavity patient population was the difference statistically significant. Both acute and late complications were also increased in this group of patients who received combined treatment.

Carcinoma, Squamous Cell↗
PubMed1976

Radiation therapy for testicular tumors metastasizing to the lungs.

Records of 63 cases of testicular tumors treated at the Hunter Radiation Therapy Center, Yale-New Haven Hospital from 1962 through 1971 were reviewed. One hundred percent cure rate was obtained in the 36 Stage I and II pure seminoma (Group I) patients. For Stage I, the para-aortic and homolateral iliac lymph nodes were irradiated to a dose of 3,000 to 3,500 rads in three to four weeks. Elective irradiation of the mediastinum and supraclavicular areas was omitted. For Stage II, such extended field irradiation was employed to a dose of 2,000 to 3,000 rads in two to three weeks. Six (or 43 percent) of the 14 embryonal carcinoma (Group II) patients are alive for a minimum of three to a maximum of eleven years. Both teratoma (Group III) patients are alive at five and seven years as well. All eight Stage I teratocarconoma (Group IV) patients are alive with no evident disease at three to ten years. Our data indicate the difference in prognosis between patients who subsequently developed localized lung metastases and those who initially presented with pulmonary disease. We conclude that intensive combined efforts of both radiation and medical oncologists can salvage a considerable number of patients with metachronous onset of pulmonary metastases.

Adolescent↗