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Biomedical subjects

S C Liu

Publications and source records attributed to S C Liu.

At least 127 records · Page 7Linked to original sources
PubMed1985

Demonstration of haemoglobin associated with isolated, purified spectrin from senescent human red cells.

Employing a direct and sensitive radioimmunoassay (RIA) we have confirmed the presence of haemoglobin associated with isolated, purified spectrin from senescent red cells. Haemoglobin associated with spectrin occurs in the highest amount in cells with an MCHC greater than 36 g/dl and is approximately 3% of the total spectrin extract. Spectrin from the young cells had the least haemoglobin, while an intermediate amount was found in unfractionated, whole red cells. The RIA results were in close approximation with estimation of the haemoglobin-spectrin complex obtained by carefully integrating the Coomassie blue stain profiles from 4% SDS PAGE in densitometric scans from isolated spectrin.

Densitometry↗
PubMed1985

Sperm autoimmunity in vasectomized men and its relationship to atherosclerotic coronary artery disease.

A study is reported of sperm autoimmunization in 707 men and its relationship with atherosclerotic coronary artery disease. The following groups were studied: healthy vasectomized men (278), healthy non-vasectomized men (231), vasectomized men with atherosclerotic coronary disease (ACD; 87) and non-vasectomized men with ACD(111). The gelatin agglutination test (GAT), tube slide agglutination test (TSAT) and sperm immobilization test (SIT) were used to detect circulating anti-sperm antibodies. Sperm antibodies developed within 6 months of vasectomy and persisted for more than 20 years. There was no difference in the incidence of antibodies in vasectomized healthy and ACD men. The results of this study provide no evidence for an association between cardiac disease and vasectomy.

Adult↗
PubMed1985

Effect of hydrocortisone on Trichophyton rubrum growth in human epidermal keratinocyte cultures.

A large volume of evidence suggests that topical steroids intensify fungal infections. To verify this observation further, we inoculated Trichophyton rubrum into human epidermal keratinocyte cultures in the presence of hydrocortisone. Our results reveal that hydrocortisone does stimulate mycelium growth. However, it only occurs in the cultures containing human epidermal cells, and the stimulation is greater at a higher concentration of the drug (20 micrograms/ml) than a lower one (2 micrograms/ml).

Cells, Cultured↗
PubMed1984

Hemoglobin enhances the self-association of spectrin heterodimers in human erythrocytes.

Spectrin in isolated erythrocyte membranes is known to undergo tetramer to dimer transformation upon hypotonic incubation at 37 degrees C. In the present study, we detect no such transformation in intact erythrocytes in which hypotonicity is achieved by valinomycin treatment followed by hypotonic swelling. The inhibition of spectrin tetramer to dimer transformation is attributable to intracellular hemoglobin, since the addition of hemoglobin to isolated membranes or spectrin extracts blocks a similar spectrin transformation. However, the inhibitory effect is not limited to hemoglobin; other proteins including heme-containing proteins and basic proteins such as cytochrome c, ribonuclease, and albumin are also effective. The magnitude of their effect is proportional to the increased pI value of these proteins. We conclude that the stabilizing effect of these proteins on spectrin tetramers under hypotonic conditions is partly due to their non-ideality, which excludes water from spectrin and thus increases the effective concentration of spectrin, and to their electrostatic interactions with spectrin. In addition, promotion of spectrin self-association by hemoglobin under hypotonic conditions increases the stability of membrane skeletons against mechanical shearing. More importantly, the hemoglobin effect on spectrin self-association is demonstrable at physiological hemoglobin concentration, pH, and osmolarity, suggesting that in intact red cells the spectrin dimer-dimer association, as well as the membrane skeletal structure, is strengthened by intracellular hemoglobin.

Chromatography, Gel↗
PubMed1984

Oligomeric states of spectrin in normal erythrocyte membranes: biochemical and electron microscopic studies.

We estimated the relative amounts of oligomeric species of spectrin in 0 degrees C red-cell-membrane extracts, including those released from spectrin-actin-polypeptide 4.1 complexes after mild urea treatment. Spectrin dimers, tetramers, and medium-size oligomers were the prominent species, accounting for 5%-10%, 45%-55%, and 25%-35% of spectrin, respectively. When examined by low-angle rotary-shadowing electron microscopy, these medium-size spectrin oligomers (e.g., hexamers, octamers, decamers , dodecamers , and quadecamers ) appeared as polyskelions formed by head-to-head association of three to seven dimers. They were stable species capable of binding to, and subsequent release from, inside-out vesicles without degradation to tetramers or dimers. The data suggest that spectrin tetramers and medium-size oligomers coexist in the normal erythrocyte membrane as the primary native spectrin species.

Chromatography, Gel↗
PubMed1984

A molecular defect of spectrin in a subset of patients with hereditary elliptocytosis. Alterations in the alpha-subunit domain involved in spectrin self-association.

Hereditary elliptocytosis (HE) is a clinically and biochemically heterogenous group of diseases characterized by elliptically shaped erythrocytes and an autosomal dominant mode of inheritance. Whereas the self-association of spectrin heterodimers to tetramers is defective in a subpopulation of HE patients, designated HE[SpD-SpD], it is normal in others. We have examined the peptide pattern produced by limited tryptic digestion of spectrin extracts from patients with HE[SpD-SpD] to determine if the functional defects in spectrin self-association could be correlated with structural changes in the spectrin molecule. Although the peptide pattern produced by limited tryptic digestion of spectrin extracts from those HE patients with normal spectrin self-association was indistinguishable from the pattern from control normal volunteers, digestion of the spectrin extracts from the HE[SpD-SpD] patients showed a reproducible diminution in the 80,000-D domain of the alpha-subunit, which is involved in spectrin dimer self-association. The decrease in the 80,000-D fragment was associated with an increase in a 74,000-D fragment in eight of nine families, or, in one family, with an increase of fragments at 46,000 and 17,000 D. These atypical peptide patterns were similar to those previously reported in two variants of hereditary pyropoikilocytosis (HPP), which also had defective self-association of spectrin. These data indicate that two distinct structural variants of spectrin alpha-subunit are associated with the defective spectrin heterodimer self-association in a subpopulation of HE patients.

Electrophoresis, Polyacrylamide Gel↗
PubMed1983

The effect of copper on the binding of prostaglandin E1 to NMU-induced rat mammary carcinoma membranes.

Mammary carcinomata were induced by administration of nitrosomethyl urea to female Buffalo rats. Specific binding of PGE1 to the 15,000 xg membranes obtained from these tumors was maximal after approximately 60 minutes of incubation at 15 degrees C. An excess of unlabeled PGE1 dissociated 50% of the [3H]PGE1 from the membrane within 15 minutes. The binding of [3H]PGE1 was inhibited by various prostaglandins in a concentration-dependent manner, the order of potency being PGE1 greater than PGE2 greater than PGA2 greater than PGF2 alpha greater than PGB2. High affinity receptor sites were not definable by Scatchard analysis until 5mM CuCl2 was added. This resulted in the detection of both high and low affinity receptors (Kd = 1.01 nM and 21 microM) having binding capacities of 29 and 357 fmole/mg protein, respectively. Addition of CaCl2 or MgCl2 did not result in a significant increase in the specific binding of PGE1 to the receptors. These studies provide a means by which high affinity prostaglandin E1 receptors can be detected in neoplastic tissue and suggest a mechanism by which copper ions can increase the effect of PGE1 in tissues.

Alprostadil↗
PubMed1983

Serial cultivation of epidermal keratinocytes from psoriatic plaques.

Using the combined techniques of Rheinwald and Green, and Liu and Karasek, large quantities of proliferative keratinocytes from involved (PP) or uninvolved (PN) skin of psoriatic patients and from normal skin of non-psoriatic donors (NN) can be obtained. Primary cultures, initiated from a 6-mm punch biopsy, are grown on a 3T3 feeder layer seeded on a collagen surface and fed with Dulbecco's Modified Eagle's Medium containing 20% fetal calf serum, hydrocortisone, epidermal growth factor, and cholera toxin. To test the hypothesis that the mechanism(s) responsible for the abnormal proliferation of psoriatic keratinocytes may be located within the cells themselves, primary cultures are passaged onto collagen surfaces without a feeder layer and maintained with medium plus serum, but no additional supplements, and the growth profiles of the 3 cell populations compared. No difference in morphology among these cells is observed in either primary or passaged cultures. In primary cultures, PP keratinocytes, especially those isolated from active lesions, seem to initiate growth at a slower rate than do PN and NN keratinocytes. The difference in the growth rate, as determined by cell number, DNA content, and mitotic activity, is insignificant among passaged PP, PN, and NN cells. Waves observed in the mitotic index and the metabolic activity of the passaged keratinocytes from all 3 sources suggest that the cells are synchronized during subculturing. The cells have high metabolic and mitotic activities during the first week after subculturing, indicative of an initial population of actively dividing cells. We have not found the characteristic feature of hyperproliferation seen in psoriatic keratinocytes in situ, in the cultured cells; however, it is too early to reach the definite conclusion that the mechanism(s) responsible for psoriasis does not exist in the keratinocyte itself. These 3 cell types may respond differently to agents that either enhance or inhibit cell growth and, by using the culture system outlined in this report, we may study these factors and their potential role in psoriasis.

Adolescent↗
PubMed1983

DNA repair in cultured keratinocytes.

Most of our understanding of DNA repair mechanisms in human cells has come from the study of these processes in cultured fibroblasts. The unique properties of keratinocytes and their pattern of terminal differentiation led us to a comparative examination of their DNA repair properties. We have examined the relative repair capabilities of the basal cells and the differentiated epidermal keratinocytes as well as possible correlations of DNA repair capacity with respect to age of the donor. In addition, since portions of human skin are chronically exposed to sunlight, we have assessed the repair response to ultraviolet (UV) irradiation (254 nm) when the cells are conditioned by chronic low-level UV irradiation. The methods of Liu and Karasek were used to grow pure keratinocytes on collagen gels following their isolation from abdominal skin of newborns and adults at autopsy. Density labeling with 5-bromodeoxyuridine was used to resolve repair replication from the semiconservative mode. We found similar repair characteristics in human epidermal keratinocytes to those previously reported for cultured fibroblasts. However, the DNA repair response in basal cells was much greater than that in differentiated cells from the same skin preparation. Our comparative studies of DNA repair in keratinocytes from infant and aged donors have revealed no significant age-related differences for repair of UV-induced damage to DNA. Sublethal UV conditioning of cells from infant skin had no appreciable effect on either the repair or normal replication response to higher, challenge doses of UVL. However, such conditioning resulted in attenuated repair in keratinocytes from adult skin after UV doses above 25 J/m2. In addition, a surprising enhancement in replication was seen in conditioned cells from adult following challenge UV doses.

Cell Differentiation↗
PubMed1983

Molecular heterogeneity of hereditary pyropoikilocytosis: identification of a second variant of the spectrin alpha-subunit.

In hereditary pyropoikilocytosis (HPP), the red cell membrane skeletons exhibit a mechanical instability that can be correlated to defective self-association of spectrin heterodimers. To determine the underlying molecular defect, we have subjected HPP spectrin to limited tryptic digestion, followed by one- and two-dimensional separations of the peptides. Two of the HPP kindreds exhibited a marked decrease in 80,000-dalton peptide (previously identified as the spectrin dimer-dimer contact domain of the alpha-subunit) and a concomitant increase of the 74,000-dalton polypeptide (presumably derived from the 80,000-dalton domain) and a decrease in a 22,000-dalton polypeptide. We now report tryptic digests of two other HPP kindred that are characterized by a decrease or complete absence of the 80,000-dalton tryptic fragment, with a concomitant increase in fragments at 46,000 and 17,000 daltons. The 46,000-dalton fragment separated into multiple spots on isoelectric focusing, ranging in isoelectric point from 5.25 to 5.35, and the 17,000-dalton fragment focused to a single spot at 5.4. Minor fragments at 56,000 and 22,000 daltons were also decreased, while a 38,000-dalton fragment increased. Limited tryptic digestion of the separated alpha- and beta-subunits revealed that the 74,000-dalton fragment in the first group of patients and the 46,000-dalton fragment in the second group of patients were derived from the alpha-subunit. Both subtypes exhibited a similar defect of spectrin self-association, with 30%-38% of spectrin dimers in O degrees C extracts. The results indicate that at least two distinct forms of structurally defective spectrin may give rise to the clinical presentation of HPP.

Adolescent↗
PubMed1982

Prostaglandin synthesis and binding is increased in regressing NMU mammary carcinoma.

Mammary tumors induced in Buffalo rats by treatment with nitrosomethyl urea will regress after oophorectomy. Their ability to synthesize and bind prostaglandins E and F2 alpha was studied in the growing and regressing states. Prostaglandins present in suspension of 100,000 xg tumor membranes after 2 hr incubation at 37 degrees C +/- 5x10(-4)M indomethacin were partially purified by silica gel column chromatography before assay by specific PG RIA. The amounts of PGE and F2 alpha synthesized rose from 0.13 and 10.5 ng/mg protein in the growing tumors to a maximum of 1.2 and 26.5 ng/mg protein 5 days after oophorectomy. Specific binding of 3H-PGE2 ad 3H-PGF2 alpha to 15,000 xg tumor membranes was achieved during a 45 min incubation at 23 degrees C +/- excess unlabelled PG. Free and bound prostaglandins were separated by filtration. Binding reached equilibrium after 30 min, was saturable and reversible. Scatchard analysis revealed high affinity binding of PGF2 alpha but only low affinity PGE2 binding in membranes obtained from growing tumors. A 2-3-fold increase in specific binding of PGE2 and PGF2 alpha was noted at 4 days after oophorectomy which represented an increase in the number of PGF2alpha receptors. PGE2 binding retained a low affinity character. The elevated PGF2 alpha synthesis rates observed in the regressing tumors coupled with a regression-associated increase in receptor number suggests that PGF2 alpha plays a significant role in hormone-dependent mammary tumor regression.

Animals↗
PubMed1982

Defective spectrin dimer-dimer association with hereditary elliptocytosis.

We examined erythrocytes from 18 patients with hereditary elliptocytosis. Spectrin from eight patients (referred to as type 1) was defective in dimer-dimer association as demonstrated in two ways. First, there was an increased amount of spectrin dimer with a concomitant decrease in tetramer as measured in erythrocyte membrane preparations extracted at 0 degrees C under low-salt conditions (the amount of spectrin dimer was 15-33% of total spectrin species compared with a normal range of 3-7%). Second, the equilibrium constants of spectrin dimer-dimer association were decreased in both solution and in situ membrane. Spectrin from the remaining 10 patients (referred to as type 2) showed normal dimer-dimer association. Membrane skeletons, produced from ghosts of both types of hereditary elliptocytosis by Triton X-100 extraction, were unstable when mechanically shaken. Because spectrin tetramers, but not dimers, can crosslink actin, we postulate that the defective spectrin dimer-dimer association in type 1 diminishes actin crosslinking and thus is responsible for membrane skeletal instability. A defective protein-protein association in type 2, however, remains to be identified.

Elliptocytosis, Hereditary↗
PubMed1982

DNA repair response in human epidermal keratinocytes from donors of different age.

We have compared the excision-repair and growth properties of epidermal keratinocytes from humans of different ages. Keratinocytes isolated from newborn and adult abdominal skin at autopsy were cultured on collagen gels. Repair replication was assayed by the 5-bromodeoxyuridine density-labeling method following ultraviolet (UV) irradiation (254 nm) of the cultures. The keratinocytes from newborn donors proliferated more rapidly and attained a higher concentration at confluence than did those from aged donors. Semiconservative DNA replication was inhibited by UV radiation to an equal extent in cell cultures from newborns and adults. After a UV dose of 13 J/m2, the time course of DNA repair was similar for the respective cultures. Furthermore, there were no significant differences in the time course of repair for keratinocytes in the proliferative or the plateau phase of growth. The dose-response curves for repair replication in cells from both young and old donors maximized at about 50 J/m2 but the attenuation in repair at higher doses appeared somewhat greater in cells from older donors. We conclude that no significant age-related differences exist in the rate and extent of the repair-replication response of human epidermal keratinocytes to UV-radiation damage in DNA. However, it remains to be determined whether other cellular recovery responses to damaged DNA are also relatively unrelated to age.

Adult↗
PubMed1982

Molecular defect of spectrin in hereditary pyropoikilocytosis. Alterations in the trypsin-resistant domain involved in spectrin self-association.

In hereditary pyropoikilocytosis (HPP) the erythrocyte membrane skeleton exhibits mechanical instability that can be correlated to defective self-association of spectrin heterodimers. To detect structural changes in the functional domains of HPP spectrin we have examined the peptide pattern produced by limited tryptic digestion of spectrin extracts from two families that contain three HPP patients. Limited tryptic digestion of all three HPP patients revealed a similar and reproducible decrease in the staining intensity of an 80,000-, and 22,000-, and an 88,000-dalton polypeptide with a concomitant increase in a 74,000- and a 90,000-dalton polypeptide as compared with controls. Only changes in the 80,000-, and 74,000-, and 22,000-dalton polypeptides could be correlated to defective spectrin self-association and the amount of spectrin dimers in 0 degrees C extracts of the HPP patients and their affected kindred. Similar results were obtained when the tryptic digests were analyzed by two-dimensional isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis with the affected 74,000- and 80,000-dalton polypeptides focusing into multiple spots ranging in isoelectric point from 5.3-5.4. When HPP spectrin dimers and tetramers were separated and subjected to trypsin digestion, changes in the 80,000-, 74,000-, and 22,000-dalton polypeptides were found predominantly in the spectrin dimer pool. Similar results were obtained for spectrin from two of the probands' mother, whom we have identified as an HPP carrier. We conclude that these HPP patients contain a population of normal, (principally tetrameric) and mutant (principally dimeric) spectrin. The latter is characterized by a defective spectrin dimer self-association due to conformational changes that affect the 80,000-dalton domain.

Electrophoresis, Polyacrylamide Gel↗