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Biomedical subjects

S Lin

Publications and source records attributed to S Lin.

At least 595 records · Page 33Linked to original sources
PubMed1982

The interactions of androgen receptor with poly(A)-containing RNA and polyribonucleotides.

The androgen receptor from mouse kidney cytosol binds not only to DNA but also to RNA as assayed by competition with DNA-cellulose centrifugation or by direct binding with agarose-polynucleotides. The dihydrotestosterone-receptor complex interacts more strongly to poly(A)-containing mRNA than to native natural DNA; it binds much more tightly to synthetic poly(G) than to natural DNA and other homopolyribonucleotides such as poly(U), poly(A), or poly(C). Poly(U) is moderately effective in competing for the complex, whereas poly(A) and poly(C) re not effective. Competition studies with heteropolyribonucleotides show that polymers containing G are most effective on binding to the androgen receptor, whereas those containing U are moderately effective, and those containing only A and C are least effective. Several analogues of poly(G), such as poly(X), poly(I), and poly(m7G) interact very well with the dihydrotestosterone-receptor with some differences in the bindings. A double-stranded polymer, poly(I) . poly(C) competes poorly for the androgen receptor. The observations that the androgen receptor binds to RNA and interacts with polyribonucleotides selectively suggest that androgen receptor-RNA interaction could play important roles in gene regulation.

Animals↗
PubMed1982

Interaction of cytochalasin B with actin filaments nucleated or fragmented by villin.

Villin, a 95,000-dalton protein, is a major component of microvillus cores isolated from intestinal brush borders. In this study, we compared the Ca2+-dependent action of this protein on actin filaments with that of cytochalasin B, a fungal metabolite that binds to the "barbed" end of actin filaments and nuclei. We found that substoichiometric levels of villin inhibit actin filament elongation and self-association in a cytochalasin-like manner. In addition, the protein releases membrane-bound F-actin in the absence of high shear force, probably by severing the filaments. The filament fragments formed in the presence of villin, as well as a nucleating complex consisting of villin and actin, bind stoichiometric amounts of [3H]cytochalasin B with high affinity. The results of this study indicate that both villin and cytochalasin B bind to the same end of actin filaments, yet differ in their binding sites.

Actins↗
PubMed1982

High-affinity interaction of vinculin with actin filaments in vitro.

Immunofluorescence and microinjection experiments have shown that vinculin (molecular weight 130,000) is localized at adhesion plaques of fibroblasts spread on a solid substrate. We found that this protein affects actin filament assembly and interactions in vitro at substoichiometric levels. Vinculin inhibits the rate of actin polymerization under conditions that limit nuclei formation, indicating an effect on the filament elongation step of the reaction. Vinculin also reduces actin filament--filament interactions measured with a low-shear viscometer. Scatchard plot analysis of the binding of 3H-labeled vinculin to actin filaments showed that there is one high-affinity binding site (dissociation constant=20 nM) for every 1,500-2,000 actin monomers. These results suggested that vinculin interacts with a specific site located at the growing ends of actin filaments in a cytochalasin-like manner, a property consistent with its proposed function as a linkage protein between filaments and the plasma membranes.

Actins↗
PubMed1981

Purification and characterization of an inhibitor protein with cytochalasin-like activity from bovine adrenal medulla.

A protein preparation with cytochalasin-like activity has been obtained from bovine adrenal medulla. Analysis by electrophoresis in SDS-polyacrylamide gel and chromatography in a Sephacryl S-200 column indicated that the inhibitor activity coincided with a 90 000 dalton polypeptide. The inhibitor decreased high-affinity binding of [3H]cytochalasin B to actin nuclei, apparently by competing with the drug for the same binding site. At substoichometric levels, the inhibitor had a potent effect on actin filament elongation and on actin-dependent gelation of cell extracts in vitro. These results suggest that the inhibitor may be involved in the control of actin filament assembly and interaction in the adrenal medulla.

Actins↗
PubMed1981

Association of actin with chromaffin granule membranes and the effect of cytochalasin B on the polarity of actin filament elongation.

Membranes of chromaffin granules isolated from bovine adrenal medulla are shown to bind dihydrocytochalasin B with high affinity. These membranes also bound [3H]actin in a time- and Mg2+-dependent manner and electron microscopy showed the presence of membrane-attached actin filaments following addition of exogenous actin. Binding of [3H]actin was partially inhibited by cytochalasin B. Electron microscopic analysis of heavy meromyosin-decorated, membrane-attached filaments showed terminally (end-on) attached filaments with both possible polarities (i.e., filaments with arrowheads pointing both towards and away from the membranes). Treatment of samples with cytochalasin B preferentially inhibited growth of filaments with their 'barbed' ends pointing away from membranes. These results are discussed with respect to the role of actin in secretory granule function and the mechanism of cytochalasin action.

Actins↗
PubMed1981

Cost analysis of the Auto Microbic system urine identification card.

The AutoMicrobic system (Vitek Systems, Inc., Hazelwood, Mo.) is a fully automated, computerized instrument. One of the most thoroughly studied aspects of the system is its ability to identify and quantify of nine most common urinary tract pathogens. The major advantages of the AutoMicrobic system are that the results of urine cultures are available in a fraction of the time required by conventional methods and that samples can be processed with fewer man-hours. Although the specificity, sensitivity, and reliability of the system have been amply described in the literature, only one study combines these aspects with a cost analysis (D. P. Nicholson and J. A. Koepke, J. Clin. Microbiol. 10:823-833, 1979). Because one of the major considerations that microbiology laboratory directors must face is the cost-effectiveness of instruments, we studied the relative cost of the system as compared with that of conventional methods. Our findings indicated that the instrument provided valuable savings in technologist and turnaround time. These advantages were most easily realized in processing positive urine specimens. For negative urine specimens, the savings in technologist time were cancelled by the cost of the consumable supplies, which greatly exceeded the cost of supplies for conventional methods. This disadvantage might be ameliorated by efficient and effective screening methods to exclude those urine specimens that are most probably negative.

Autoanalysis↗
PubMed1981

Correlation of the biologic effects and binding of cytochalasins to human polymorphonuclear leukocytes.

Treatment of human PMNs with cytochalasins (CE, CD, CB, and H2CB) results in alteration of cell morphology and inhibition of cell motility. Morphological changes are similar to those reported for nonamoeboid fibroblasts--rounding, zeiosis, and arborization. Mean cell velocity of PMNs, as measured by quantitative analysis of time-lapse videotape recordings, was reduced to 0.1 micron/min (control, 7.3 +/- 4.2 micron/min). Phagocytosis by PMNs, as measured by phagocytosis of latex beads, was inhibited by 75%. The relative potency of the cytochalasins for inducing morphological change or for inhibiting locomotion and phagocytosis is similar to their relative potencies for affecting non-amoeboid cells: CE greater than CD greater than CB greater than or equal to H2CB. Quantitative binding of 3H-CB to purified PMNs under equilibrium conditions reveal two types of specific CB binding sites: high-affinity sites (KD approximately 3 x 10(-7) M, 3 x 10(6) sites/cell) and low affinity sites (KD approximately 2 x 10(-6) M). The relative affinities of the cytochalasins for the high-affinity and low-affinity CB binding sites parallel their relative potencies for inducing biologic effects (i.e. CE greater than CD greater than CB greater than or equal to H2CB).

Cell Movement↗
PubMed1980

Cytochalasins block actin filament elongation by binding to high affinity sites associated with F-actin.

We have found that addition of a small amount of filamentous muscle actin (F-actin) to a solution of globular actin (G-actin) in a low ionic strength medium resulted in rapid polymerization of the G-actin. This reaction was inhibited by substoichiometric levels of cytochalasins (relative potency: cytochalasin D greater than cytochalasin E approximately equal to cytochalasin B greater than dihydrocytochalasin B). Binding experiments show that F-actin, but not G-actin, contains high affinity binding sites for [3H]cytochalasin B; the number of sites detected was on the order of about one per actin filament (one site/500 actin monomers). This number remained unchanged when the actin (prepared by polymerization-depolymerization cycles) was further purified by ion exchange and gel filtration chromatography. Competitive displacement experiments showed that the relative affinity of several cytochalasins for these sites corresponds to their relative effectiveness in inhibiting actin polymerization induced by F-actin. These results suggest that actin filaments can accelerate the rate of polymerization of G-actin in low ionic strength medium by providing sites onto which actin monomers can be added, and that cytochalasins inhibit actin filament elongation by binding to high affinity sites located at the polymerization end of the filaments.

Actins↗