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Biomedical subjects

C C Liu

Publications and source records attributed to C C Liu.

At least 271 records · Page 15Linked to original sources
PubMed1984

Circulating immune complexes in cervical cancer patients as detected by C1q binding.

In a retrospective study in women with cervical cancer, circulating immune complex levels were measured by radioimmunoprecipitation with 125I-C1q. Sera from 46 patients with cervical cancer and 35 normal controls were examined. Significantly higher levels of immune complexes were detected in cancer patients compared with controls. Mean value of binding capacity in patients was 49.8%, and by contrast, in the controls was 27.4% (two-tail test = 0). Increases in tumor mass were associated with high levels of circulating immune complexes. The presence of immune complexes in circulation statistically correlated with disease activity, however, the assay used still had limited value for diagnosis or aiding in therapeutic decisions. Nevertheless, the future holds promise for such uses.

Antigen-Antibody Complex↗
PubMed1983

Expression of hepatitis B virus surface antigen in yeast.

The structural gene of Hepatitis B virus surface protein (HBsAg) was introduced into a plasmid capable of autonomous replication and selection in both the yeast Saccharomyces cerevisiae and E. coli. In this plasmid transcription of the HBsAg is initiated by the 5'-flanking sequence of the yeast 3-phosphoglycerate kinase (PGK) gene and terminated by the 3'-flanking region of the yeast TRP1 gene. Yeast cells containing this plasmid produce a new major species of mRNA of 1200 nucleotides in length coding for HBsAg. Viral surface antigen is made in nonglycosylated form at a level of about 1-2 percent of total yeast protein. A small fraction of this polypeptide (2-5 percent) is found in aggregated form upon yeast cell disruption by glass beads. This material is similar in size, density, and shape to the 22nm particle, isolated from the plasma of human hepatitis carriers, and induced comparable levels of HBsAg antibodies in mice when compared with the natural particle.

Cysteine↗
PubMed1983

Plasmid-directed synthesis of hepatitis B surface antigen in monkey cells.

We introduced the gene encoding the hepatitis B virus surface antigen (HBsAg) into simian virus 40 (SV40)-based plasmids capable of autonomously replicating in both Escherichia coli and permissive monkey cells. After introduction into monkey cells by transfection, these plasmids directed the synthesis of high levels of HBsAg, as determined by immunofluorescence, radioimmunoassays, and identification by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the polypeptides comprising the antigen. Expression was dependent upon the presence of an SV40 promoter, with both the early and late promoters able to effectively initiate transcription. Using expression of HBsAg to assay promoter function, we demonstrated that an intact copy of the SV40 72-base pair repeat, which constitutes an essential element of the SV40 early promoter during the lytic SV40 cycle and which can enhance the transcriptional activity of heterologous promoters, was not required for HBsAg expression, suggesting that the hepatitis genome contains an enhancer element capable of complementing that provided by the 72-base pair repeat element of SV40. The antigen appears to be glycosylated after synthesis in transfected cells and is apparently secreted, as evidenced by the localization of [35S]cysteine-labeled antigen to the medium of transfected cultures. Using constructions in which the first ATG sequence appearing in HBsAg mRNA was that corresponding to the gene encoding the mature form of the antigen, we demonstrated that these post-translational events could occur without the involvement of a putative precursor peptide suggested by the DNA sequence of the viral genome. In view of the inability of hepatitis B virus to propagate in vitro, this strategy offers a convenient approach for further characterizing the biosynthesis of this antigen and may provide a means to identify additional polypeptides encoded by this virus.

Animals↗
PubMed1982

Studies on the relation of gamma-hydroxybutyric acid (GHB) to gamma-aminobutyric acid (GABA). Evidence that GABA is not the sole source for GHB in rat brain.

The effects of gamma-aminobutyric acid (GABA)-alpha-oxoglutarate aminotransferase (GABA-T) inhibitors, L-glutamic acid decarboxylase (GAD) inhibitors, and antipetit mal anticonvulsants on gamma-hydroxybutyric acid (GHB) and GABA were studied. Treatment with anticonvulsants and GABA-T inhibitors resulted in an increase in steady-state brain levels of both GHB and GABA. GAD inhibitors produced markedly decreased levels of brain GABA but no change in GHB concentrations. Studies of GHB derived exclusively from GABA showed that GABA-T inhibitors which produced an elevation of steady-state levels of GHB in brain also resulted in a decrease in GABA-derived GHB. Intracerebroventricular (i.c.v.) administration of GABA, putrescine, and 1,4-butanediol all produced significant elevations in brain GHB, but GABA-T inhibitors blocked this effect of GABA and putrescine. These data suggest that there may be another source for GHB in brain in addition to GABA and raise the possibility that 1,4-butanediol may be that source.

4-Aminobutyrate Transaminase↗
PubMed1982

Acute reduction in osteoclast number during bone repletion.

Growing rats were fed a calcium-deficient diet for 12 days to induce bone loss and were subsequently placed on a calcium-replacement diet for 1 to 3 days to evoke bone repletion. Control animals were fed the calcium-replacement diet continuously. Twelve days of calcium deprivation resulted in a 21-fold increase in the number of endosteal osteoclasts in the tibial diaphysis as compared with controls. These osteoclasts, however, rapidly disappeared from the endosteum after restoration of dietary calcium. Only 14% of these endosteal osteoclasts remained after 1 day, and no osteoclasts were present after 3 days of calcium replenishment. During this time, plump osteoblasts replaced osteoclasts on the endosteal surface. The number of osteoclasts in the marrow space also changed strikingly. An 11-fold increase in the number of osteoclasts in the marrow space occurred during the calcium-deprivation phase. However, the greatest increase (39-fold) was observed during the first day of calcium replenishment. Thereafter, the number of osteoclasts in the marrow space declined and, after 3 days of calcium replenishment, returned to the control level. During calcium replenishment, acid phosphatase-positive fragments in the marrow space appeared concomitantly with osteoclast disintegration and fragmentation. The kinetic changes and acid phosphatase staining of these fragments suggest that the fragments are the products of disintegrating osteoclasts, a finding consistent with the hypothesis that the fate of some osteoclasts in vivo is cell death. At the end of calcium deprivation, serum iPTH levels and the production of 1,25-dihydroxyvitamin D3 from 25-hydroxyvitamin D3 were significantly increased compared to controls. After 3 days of calcium replenishment, serum iPTH had decreased to control levels, but the production of 1,25-dihydroxyvitamin D3 was still elevated. Changes in serum iPTH and the production of 1,25-dihydroxyvitamin D3 cannot, therefore, be totally responsible for the observed decrease in osteoclast number during bone repletion. Bone repair after calcium deprivation may be a locally controlled phenomenon.

Acid Phosphatase↗
PubMed1982

Direct expression of hepatitis B surface antigen in monkey cells from an SV40 vector.

We have developed an SV40-based vector that can be used for the efficient direct expression of foreign genes in permissive monkey cells. The vector lacks the coding sequences for the major SV40 late protein (VP-1) and possesses unique Eco RI and Bam HI restriction sites so that DNA fragments containing the coding sequences of foreign genes bounded by these two restriction sites can be conveniently inserted and directly expressed under the control of the VP-1 transcriptional unit. We have inserted into this vector the gene encoding the surface antigen of hepatitis B virus and observed the synthesis of this protein in monkey cells infected with this vector at a level comparable with that of VP-1. Furthermore, we have shown that the HBsAg synthesized is assembled into and secreted as a complex structure (22-nm particle) indistinguishable from that formed naturally during human infection. These observations enable us to conclude that HBsAg is the only component encoded by HBV that is required for the secretion and assembly of the 22-nm particle and that this process can occur without the involvement of a potential signal peptide suggested by the DNA sequence which precedes the coding region of mature HBsAg.

Animals↗
PubMed1982

Giant-cell tumor of bone: analysis of two hundred and eight cases in Chinese patients.

Giant-cell tumor of bone seems to occur more frequently in Chinese people than in those residing in Western countries. The estimated incidence is about 20 per cent of all primary tumors of bone. Of 208 surgically treated and pathologically proved giant-cell tumors, 194 were benign. We excluded patients with primary or secondary amputation unrelated to recurrence and those followed for less than two years or lost to follow-up. Of the remaining 111 patients who were followed for more than two years, twenty-nine had a recurrence, giving a recurrence rate of 26.1 per cent. The rate of recurrence was highest following curettage and bone-grafting (41.2 per cent) and was much lower in patients who were treated by resection and fusion (7.1 per cent). Since resection of this tumor with reconstructive procedures, either by massive homogenous bone-grafting or artificial joint replacement, is complicated and might cripple the patient if it fails, we propose excision and curettage with bone-grafting as the most suitable method of treatment in the majority of patients with giant-cell tumor of bone.

Adolescent↗
PubMed1981

Characterization of the DNA-dependent GTPase activity of T4 gene 41 protein, an essential component of the T4 bacteriophage DNA replication apparatus.

The product specified by T4 bacteriophage gene 41 is known from genetic analyses to be essential for phage DNA replication in vivo. Correspondingly, the purified gene 41 protein is an essential component of an efficient in vitro DNA replication system reconstructed from seven purified T4 replication proteins; it is required both for the synthesis of short RNA primers (in conjunction with the T4 gene 61 protein) and for the rapid unwinding of the double-helical DNA template at a replication fork. The purified gene 41 protein exhibits a DNA-dependent GTPase (and ATPase) activity. In this report, we have used this associated GTPase activity as a biochemical probe for the analysis of the interactions between DNA and the 41 protein. Our results suggest that, upon binding GTP, the 41 protein monomer is induced to form a dimer, which can them form a tight complex with single-stranded DNA. Driven by the repeated hydrolysis of GTP molecules, the 41 protein dimer appears to run rapidly along the bound DNA chain. Studies with the synthetic GTP analogue, GTP gamma S, suggest that GTP hydrolysis is required for this 41 protein movement, but that it is not essential for the function of the 41 protein in RNA primer synthesis. In sum, our observations suggest that a 41 protein dimer runs along the lagging strand template at a DNA replication fork; from this position, it functions as a DNA helicase and simultaneously interacts with the T4 gene 61 protein to make the pentaribonucleotide primers which initiate Okazaki pieces at specific primer initiation sites.

DNA Replication↗
PubMed1981

Characterization of RNA primer synthesis in the T4 bacteriophage in vitro DNA replication system.

In the presence of any natural single-stranded DNA, the bacteriophage T4 gene 41 and gene 61 proteins catalyze the synthesis of a group of pentaribonucleotides. These RNA molecules are homogeneous in chain length, but heterogeneous in sequence. In the presence of the other five T4 replication proteins, these pentaribonucleotides are utilized with high efficiency as primers for de novo DNA chain initiations on the lagging strand in the T4 DNA replication process. By using a two-dimensional fractionation system plus a variety of enzymatic analyses, the pentaribonucleotides are found to have either a unique pppApC dinucleotide or a pppG as their starting residue, followed in both cases by many different sequences. However, when natural T4 DNA containing glucosylated 5-hydroxylmethyl cytosine is used as template, only the pppApC-initiated class of RNA primers is made. Alone, the gene 41 protein exhibits a DNA-dependent GTPase (and ATPase) activity, with nucleoside diphosphate and inorganic phosphate as products. By blocking this GTPase activity with the synthetic GTP analogue, GTP gamma S, we show that limited RNa primer synthesis can occur without this nucleotide hydrolysis by the 41 protein, but that prolonged RNA primer synthesis requires such hydrolysis. This result, viewed in the light of the observations presented in the accompanying paper, suggests that the gene 41 protein acts as a "mobile promoter," perhaps leaving the gene 61 protein to perform the actual polymerization and chain termination functions in the synthetic process.

DNA Replication↗
PubMed1981

Stability and sterility of cimetidine admixtures frozen in minibags.

The stability and sterility of cimetidine hydrochloride admixtures after freezing for extended periods were investigated. Cimetidine hydrochloride, 300 mg, was added to each of six 50-ml minibags containing 5% dextrose injection. The cimetidine concentration was determined and the bags were frozen for up to 30 days. After freezing for the appropriate length of time, the bags were thawed. Cimetidine concentrations were determined by high-pressure liquid chromatography immediately and then daily for eight days while the admixtures were refrigerated. Sterility tests were carried out throughout the study. Data were analyzed by least-squares linear regression to test for trends. The cimetidine hydrochloride admixtures were stable while frozen for up to 30 days and for at least eight days following thawing when kept under refrigeration. Sterility of the admixture was maintained throughout the study period.

Cimetidine↗
PubMed1981

Intakes of vitamins and minerals by pregnant women with selected clinical symptoms.

Toxemia in pregnancy is characterized by a combination of at least two of the following clinical symptoms: hypertension, edema, and proteinuria. In this study the dietary intakes of young pregnant women attending a Maternal and Infant Care Program at Tuskegee Institute were evaluated for selected vitamins and minerals. Women with toxemia were identified, and women without toxemia served as controls. The toxemia group generally consumed lesser amounts of vitamins and minerals than the controls. However, both groups were deficient (less than two-thirds RDA) in calcium, magnesium, vitamin B6, vitamin B12, and thiamin. Milk, meat, and grains supplied an appreciable proportion of each vitamin except vitamin A, which was found primarily in the two vegetable groups. Meat and grains contained the greatest quantities of minerals, but milk provided a relatively good proportion of potassium, calcium, magnesium, and phosphorus. Anemia was not related to the incidence of toxemia. Women exhibiting anemia consumed smaller amounts of vitamins studied than did women without anemia.

Diet↗
PubMed1980

A Palladium-palladium oxide miniature pH electrode.

A wire-form miniature palladium-palladium oxide electrode has been fabricated for pH measurement. The electrode exhibits a super-Nernstian behavior and gives a mean pH response of 71.4 millivolts per [pH] (standard deviation, 5.2 millivolts). Uncorrected zero current potential values can be used to determine the pH value of the medium to within 0.012 pH. The electrode should find applications in biological, medical, and clinical studies.

Buffers↗
PubMed1980

Type II DNA topoisomerases: enzymes that can unknot a topologically knotted DNA molecule via a reversible double-strand break.

The T4 DNA topoisomerase is a recently discovered multisubunit protein that appears to have an essential role in the initiation of T4 bacteriophage DND replication. Treatment of double-stranded circular DNA with large amounts of this topoisomerase in the absence of ATP yields new DNA species which are knotted topological isomers of the double-stranded DNA circle. These knotted DNA circles, whether covalently closed or nicked, are converted to unknotted circles by treatment with trace amounts of the T4 topoisomerase in the presence of ATP. Very similar ATP-dependent enzyme activities capable of unknotting DNA are present in extracts of Drosophila eggs. Xenopus laevis eggs and mammalian tissue culture cells. The procaryotic enzyme, DNA gyrase, is also capable of unknotting DNA. We propose that these unknotting enzymes constitute a new general class of DNA topoisomerases (type II DNA topoisomerases). These enzymes must act via mechanisms that involve the concerted cleavage and rejoining of two opposite DNA strands, such that the DNA double helix is transiently broken. The passage of a second double-stranded DNA segment through this reversible double-strand break results in a variety of DNA topoisomerization reactions, including relaxation:super-coiling; knotting:unknotting and catenation:decatenation. In support of this type of mechanism, we demonstrate that the T4 DNA topoisomerase changes the linking number of a covalently closed double-stranded circular DNA molecule only by multiples of two. We discuss the possible roles of such enzymes in a variety of biological functions, along with their probable molecular mechanisms.

Animals↗
PubMed1980

Pentaribonucleotides of mixed sequence are synthesized and efficiently prime de novo DNA chain starts in the T4 bacteriophage DNA replication system.

In the presence of single-stranded DNA, the bacteriophage T4 gene 41 and gene 61 proteins catalyze the synthesis of a group of pentaribonucleotides which are homogeneous in chain length but heterogeneous in nucleotide sequence. When single-stranded T4 DNA is used as template, a unique dinucleoside sequence, pppApC, is found at the 5' end of these pentaribonucleotides with the general sequence pppApCpNpNpN. In the presence of the remaining five T4 replication proteins, the pentaribonucleotides can be utilized with high efficiency to prime de novo DNA chain starts; as a result, the vast majority of them can be detected at the 5' end of newly made DNA molecules in an unaltered form. There are multiple, but specific, sites at which new DNA chains are primed in this way on a natural single-stranded DNA. Because identical RNA primers have been isolated from the 5' end of the Okazaki fragments made in T4-infected cells, we suggest that the T4 gene 41 and gene 61 proteins also make the pentaribonucleotides that prime de novo T4 DNA chain starts in vivo during lagging strand DNA synthesis.

Base Sequence↗