Search PubMed⌕ Search

Biomedical subjects

C C Chao

Publications and source records attributed to C C Chao.

At least 217 records · Page 12Linked to original sources
PubMed1987

Loss of inducible photorepair in a frog cell line hypersensitive to solar UV light.

The induction of enzymatic photorepair (EPR) in ICR 2A frog cells and a derived mutant cell line DRP36 hypersensitive to solar UV was studied. Using clonogenic assays, when induced wild-type cells demonstrated an 8-fold increase of EPR the mutant cells displayed a near-background level of inducible EPR. The constitutive EPR in mutant cells, however, was the same as in wild-type cells. A mixed culture of ICR 2A and DRP36 cells showed an intermediate inducible EPR depending upon the cell ratio. Inducible EPR was also detected at the DNA level in wild-type cells, but not in mutant cells.

Animals↗
PubMed1987

Transient induction of photolyase activity in arrested frog cells in response to a short-wave ultraviolet segment of simulated "sunlight".

Induction of photolyase activity was studied in cultured frog cells using clonogenic assays. Exposure of arrested cells to a pre-irradiation (90% survival) of 254 nm ultraviolet light resulted in a transient enhancement of photolyase activity. Cells expressed a decreased level of photolyase activity in response to an equitoxic fluence of simulated "sunlight" wavelengths 280-310 nm. However, no significant increase of enzyme activity was detected in cells following treatment with "sunlight" wavelengths 310-330 nm. In addition, this process depends on newly biosynthesized protein(s).

Animals↗
PubMed1987

Regulation of photorepair in growing and arrested frog cells in response to ultraviolet light.

The constitutive and inducible levels of enzymatic photorepair (EPR) in growing and arrested ICR 2A frog cells were studied using clonogenic assays. Both arrested and growing cells exhibited an equal level of constitutive EPR following ultraviolet irradiation. However, only arrested, but not growing, cells treated with a low fluence of UV (90% survival) developed an enhanced EPR. The induced process developed transiently with a peak 3 days after pre-irradiation, and was totally blocked by a nontoxic concentration of cycloheximide. In addition, the induced EPR is unique to low fluences of UV.

Animals↗
PubMed1987

LH release from dispersed bovine pituitary cells in culture: in vitro effects of estradiol and procedural variables.

Procedures for cell dissociation and in vitro culture were validated to investigate secretion of luteinizing hormone (LH) from bovine anterior lobe (AL) pituitary cells. The concentration of trypsin used for dissociation affected cell yield, cell loss during preincubation, LH secretion, and response to gonadotropin-releasing hormone (GnRH). Optimum results were obtained with trypsin concentrations of 8-16 micrograms/mg fresh tissue. Duration of preincubation and of experimental culture markedly affected LH secretion and response to GnRH. Immediately after dissociation, cells contained relatively low quantities of LH, but they were able to release a substantial proportion of this LH. Basal release of LH and GnRH-induced release of LH were highly correlated with total quantities of LH, and all three parameters increased with time of preincubation until 24 hr. Experimental treatments of 2 hr duration were optimal for investigating GnRH stimulation of LH release, whereas longer treatments may be required to investigate effects of agents that inhibit the release of LH. Preincubation of dissociated AL cells with physiological concentrations of estradiol increased all three LH parameters. Progesterone had no effect either alone or in combination with estradiol. In conclusion, the procedures described for cell dissociation and culture of suspended cells provide a useful tool for studying release of LH from the bovine AL cell.

Animals↗
PubMed1987

Failure of neuropeptide Y to modulate the release of LH and prolactin by cultured bovine pituitary cells.

Possible direct effects of neuropeptide Y (NPY) on dispersed and cultured cells of the anterior lobe (AL) of the bovine pituitary were investigated. AL tissue from steers was enzymatically dissociated into individual cells, preincubated for 18 hr and then incubated in suspension cultures for 2 hr or 24 hr with either NPY, gonadotropin-releasing hormone (GnRH) or both. Release of luteinizing hormone (LH) and prolactin (PRL) into medium was quantified by radioimmunoassay and expressed as hormone released per 100,000 cells. Basal release of LH averaged 38 and 86 ng for 2 hr and 24 hr respectively while that of PRL averaged 118 and 438 ng for the same incubation periods. Addition of NPY did not alter (P greater than .05) basal release of LH or PRL for either duration of incubation. Also, NPY did not affect (P less than .05) release of of LH in response to GnRH. In summary, this study indicated that NPY, at in vitro dosages of .01 to 100 nM, does not modulate the release of LH or PRL at the pituitary level in castrate cattle.

Animals↗
PubMed1987

Posttranslational translocation of influenza virus hemagglutinin across microsomal membranes.

The biosynthesis of influenza virus hemagglutinin (HA) and its translocation across microsomal membranes were studied in a mammalian cell-free system. All forms of HA could be cotranslationally translocated with high efficiency. However, only truncated forms of HA were translocated after protein synthesis has been terminated. The efficiency of this posttranslational translocation was dependent on the extent of the truncation. Posttranslational translocation was ribosome dependent and occurred only in the presence of a functional N-terminal signal sequence. The molecular mechanism of protein targeting and translocation across the membrane of the endoplasmic reticulum is discussed.

Biological Transport↗
PubMed1986

Direct opioid regulation of pituitary release of bovine luteinizing hormone.

Although endogenous opioid peptides (EOP) are thought to alter pituitary release of luteinizing hormone (LH) by modifying the release of gonadotropin-releasing hormone (GnRH) from the brain, EOP may also directly affect the release of LH from pituitary cells. This hypothesis was tested using dispersed cells from the bovine anterior pituitary gland. Pituitaries were enzymatically dissociated, preincubated for 18 h and then cultured for either 2 or 24 h with GnRH, naloxone, methionine-enkephalin (Met-enk) or their combinations. Basal release of LH into media was 18.2 and 38.4 ng/100,000 cells after culture for 2 or 24 h, respectively. When cultured for 2 or 24 h with 10 nM GnRH, LH release was 296% and 131% of the basal release for each culture period. Cellular viability (75% vs 68%) and total (cells + medium) LH (128 vs 134 ng/100,000 cells) did not differ (P greater than .05) between cells cultured for 2 or 24 h. Naloxone (1 microM) increased (P less than .01) basal release of LH by 57% after 2 h of culture but not after 24 h of culture. Naloxone did not augment the amount of LH released in response to 10 nM GnRH. Addition of Met-enk (1 nM to 1 microM) suppressed (P less than .05) basal release of LH (23% to 62%) after 2 h of culture. Similar suppressive effects (8% to 49%) occurred in a dose-dependent manner (0.1 nM to 1 microM) after 24 h of culture. Met-enk (1 and 100 nM) antagonized (P less than .05) the stimulatory effect of naloxone and reduced (P less than .05) the amount of LH released in response to GnRH after 2 h of culture. In summary, the stimulatory effect of naloxone on the basal release of LH suggests that EOP may directly regulate pituitary cell function; the inhibitory effect of physiological concentrations of Met-enk on the basal in vitro release of LH suggests that EOP may directly affect the release of LH in vivo; the antagonism between the stimulatory effect of naloxone and the inhibitory effect of Met-enk is consistent with effects exerted through opioid receptors; and the stimulatory effect of GnRH may be partially reduced by Met-enk. These results are consistent with the hypothesis that opioids may directly modulate the release of LH at the pituitary level.

Animals↗
PubMed1986

The use of metabolic inhibitors to compare the excision repair of pyrimidine dimers and nondimer DNA damages in human skin fibroblasts exposed to 254-nm and sunlamp-produced greater than 310-nm ultraviolet radiation.

Normal human skin fibroblasts were exposed to either 0-5 J/m2 of 254-nm ultraviolet (UV) radiation or 0-50 kJ/m2 of the Mylar-filtered UV (greater than 310 nm) produced by a fluorescent sunlamp. These cells were then incubated for 0-20 min in medium containing 10 mM hydroxyurea (HU) and 0.1 mM 1-beta-D-arabinofuranosyl cytosine (ara C), and the yield of DNA strand breaks was measured by means of the alkaline elution technique. For cells irradiated with 254-nm UV, which results primarily in the formation of cyclobutane pyrimidine dimers, a rapid increase in DNA strand breaks was detected following incubation with these metabolic inhibitors. In contrast, only a low level of strand breaks formed in cells incubated with HU and ara C after irradiation with approximately equitoxic fluences of sunlamp UV greater than 310 nm, which mainly causes the induction of nondimer DNA lesions. Hence, these results are consistent with the conclusion that the pathways involved in the repair of nondimer DNA damages induced by UV wavelengths greater than 310 nm differ from the repair of pyrimidine dimers.

Cells, Cultured↗
PubMed1986

Isolation and preliminary characterization of tear prealbumin from human ocular mucus.

Tear prealbumin was purified from crude tear prealbumin previously isolated from the saline soluble human ocular mucus. Purification was achieved by further column chromatographies on DEAE Sephadex A-25 and Sephadex G-75. Preliminary characterization included amino acid analysis, gel electrophoresis, and isoelectric focusing. Unlike serum prealbumin, the purified tear prealbumin showed a predominance of acidic residues and a trace amount of tryptophan. It exhibited polymorphic nature, with pI values of 4.8 and 4.9. The possibility of a tear prealbumin/retinol complex was also examined. The protein was found to incorporate with 3H retinol. The 3H retinol-incorporated tear prealbumin did not exhibit the characteristic UV spectrum of retinol; however, it did display emission and excitation fluorescence spectra at high concentrations similar to serum retinol-binding protein.

Amino Acids↗