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Biomedical subjects

Q Xiao

Publications and source records attributed to Q Xiao.

At least 73 records · Page 4Linked to original sources
PubMed1995

The novel aldehyde dehydrogenase gene, ALDH5, encodes an active aldehyde dehydrogenase enzyme.

The mRNA for the novel aldehyde dehydrogenase 5 (ALDH5) gene was detected in HuH7 hepatoma cells. The cells also expressed cytosolic aldehyde dehydrogenase (ALDH1) mRNA, but no mitochondrial aldehyde dehydrogenase (ALDH2) mRNA. Extracts of the hepatoma cells contained an enzymatic activity with an isoelectric point similar to that of ALDH1. This enzyme activity was insensitive to inhibition by disulfiram, a potent inhibitor of ALDH1. The enzyme was active with short chain aldehydes (acetaldehyde and propionaldehyde) and NAD+, but not with NADP+, and the activity was higher in the mitochondrial pellet than other cell fractions. These studies demonstrate the expression of ALDH5 mRNA in a human hepatoma and suggest that the gene product is enzymatically active and probably resides in the mitochondria.

Aldehyde Dehydrogenase↗
PubMed1995

Regulation of the interferon-inducible protein kinase PKR and (2'-5')oligo(adenylate) synthetase by a catalytically inactive PKR mutant through competition for double-stranded RNA binding.

The interferon-inducible double-stranded RNA-dependent protein kinase PKR has been suggested to function as a tumour suppressor gene product. Catalytically inactive mutants of PKR give rise to a tumorigenic phenotype when overexpressed in NIH-3T3 fibroblasts and this has been attributed to a dominant negative effect on the activity of the wild-type enzyme. Here we show that the mutant with Lys296 replaced by Arg, [K296R]PKR, not only inhibits the protein kinase activity of wild-type PKR but is also inhibitory towards another double-stranded RNA-dependent enzyme, the 40-kDa form of (2'-5')oligo(adenylate) synthetase. Inhibition of both wild-type PKR and (2'-5')oligo(adenylate) synthetase is reversed by adding higher concentrations of double-stranded RNA. These results suggest competition between [K296R]PKR and wild-type PKR or (2'-5')oligo(adenylate) synthetase for limiting amounts of double-stranded RNA. Moreover, the data imply that the tumorigenic effect of this PKR mutant could be due to inhibition of additional pathways requiring low levels of double-stranded RNA for activation and cannot be unambiguously attributed to inhibition of endogenous PKR itself.

2',5'-Oligoadenylate Synthetase↗
PubMed1995

Acute administration of alpha-methyl-para-tyrosine alters levels of norepinephrine transporter mRNA in the rat brainstem.

This study investigated whether rat norepinephrine transporter (NET) mRNA levels would be altered by alpha-methyl-p-tyrosine (alpha-MPT), a tyrosine hydroxylase inhibitor. While NE levels decreased at 1 and 3 days but recovered at 7 days after alpha-MPT, NET mRNA levels decreased at 3 and 7 days but not at 1 day after alpha-MPT. The results indicate that acute treatment with alpha-MPT led to a delayed time response in its effects on NET mRNA and NE levels in the rat brain.

Actins↗
PubMed1995

Hormonal and chemical influences on the expression of class 2 aldehyde dehydrogenases in rat H4IIEC3 and human HuH7 hepatoma cells.

We studied the effect a variety of hormones and chemical stimuli on the activity of low Km aldehyde dehydrogenase (ALDH) in rat H4IIEC3 hepatoma cells and ALDH activity in human HuH7 hepatoma cells. The low Km enzyme in H4IIEC3 cells reflects ALDH2 activity, and the ALDH activity in HuH7 likely represents ALDH5. Of the steroid hormone family, thyroid hormone, progesterone, and dihydrotestosterone increased low Km ALDH activity approximately 50%, whereas dexamethasone and estradiol had little effect. Insulin decreased the activity of low Km ALDH. None of these hormones affected the activity of ALDH in HuH7 cells. Among second messengers, 8-bromo-cAMP and A23187 increased low Km ALDH activity; HuH7 ALDH activity again was unchanged. Exposure of the cells to 22 mM ethanol reduced low Km activity by approximately 20%, whereas hydrogen peroxide, tumor necrosis factor-alpha, and interleukin-1 beta had little effect. Ultraviolet light increased the HuH7 ALDH activity. Retinaldehyde or retinolc acid reduced the HuH7 ALDH activity, but had no effect on low Km ALDH activity. These data suggest that low Km ALDH2 can be regulated by hormones and may not be constitutive as previously thought, and that the HuH7 ALDH is regulated differently.

Alcoholism↗
PubMed1995

The aldehyde dehydrogenase ALDH2*2 allele exhibits dominance over ALDH2*1 in transduced HeLa cells.

Individuals heterozygous or homozygous for the variant aldehyde dehydrogenase (ALDH2) allele (ALDH2*2), which encodes a protein differing only at residue 487 from the normal protein, have decreased ALDH2 activity in liver extracts and experience cutaneous flushing when they drink alcohol. The mechanisms by which this allele exerts its dominant effect is unknown. To study this effect, the human ALDH2*1 cDNA was cloned and the ALDH2*2 allele was generated by site-directed mutagenesis. These cDNAs were transduced using retroviral vectors into HeLa and CV1 cells, which do not express ALDH2. The normal allele directed synthesis of immunoreactive ALDH2 protein (ALDH2E) with the expected isoelectric point. Extracts of these cells contained increased aldehyde dehydrogenase activity with low Km for the aldehyde substrate. The ALDH2*2 allele directed synthesis of mRNA and immunoreactive protein (ALDH2K), but the protein lacked enzymatic activity. When ALDH2*1-expressing cells were transduced with ALDH2*2 vectors, both mRNAs were expressed and immunoreactive proteins with isoelectric points ranging between those of ALDH2E and ALDH2K were present, indicating that the subunits formed heteromers. ALDH2 activity in these cells was reduced below that of the parental ALDH2*1-expressing cells. Thus, the ALDH2*2 allele is sufficient to cause ALDH2 deficiency in vitro.

Aldehyde Dehydrogenase↗
PubMed1994

Lipofectin-aided cell delivery of ribozyme targeted to human urokinase receptor mRNA.

A 37-mer hammerhead ribozyme has been designed to efficiently cleave the 1.4 kb mRNA of the urokinase plasminogen activator receptor (uPAR). Under in vitro conditions, the chemically synthesized ribozyme cleaved uPAR mRNA and inhibited its translation in a concentration-dependent fashion. The ribozymes were 5'-[35S]thiophosphorylated and used as a model to analyze conditions for RNA delivery in a cultured human osteosarcoma cell system. Ribozymes degraded immediately in cell-conditioned medium but ribozymes complexed with lipofectin were protected from RNases for up to 22 h. Lipofectin rapidly transported ribozyme into the cell, where it accumulated almost exclusively in the cytoplasm. Thus, lipofectin dramatically enhances stability and cytoplasmic delivery of ribozymes, potentially enabling targeting of mRNA in vivo.

Base Sequence↗
PubMed1994

The La antigen inhibits the activation of the interferon-inducible protein kinase PKR by sequestering and unwinding double-stranded RNA.

The La (SS-B) autoimmune antigen is an RNA-binding protein that is present in both nucleus and cytoplasm of eukaryotic cells. The spectrum of RNAs that interact with the La antigen includes species which also bind to the interferon-inducible protein kinase PKR. We have investigated whether the La antigen can regulate the activity of PKR and have observed that both the autophosphorylation of the protein kinase that accompanies its activation by dsRNA and the dsRNA-dependent phosphorylation of the alpha subunit of polypeptide chain initiation factor eIF-2 by PKR are inhibited in the presence of recombinant La antigen. This inhibition is partially relieved at higher concentrations of dsRNA. Once activated by dsRNA the protein kinase activity of PKR is insensitive to the La antigen. We have demonstrated by a filter binding assay that La is a dsRNA binding protein. Furthermore, when recombinant La is incubated with a 900 bp synthetic dsRNA or with naturally occurring reovirus dsRNA it converts these substrates to single-stranded forms. We conclude that the La antigen inhibits the dsRNA-dependent activation of PKR by binding and unwinding dsRNA and that it may therefore play a role in the regulation of this protein kinase in interferon-treated or virus-infected cells.

Amino Acid Sequence↗
PubMed1994

[The clinical role of appendectomy in surgical procedures for ovarian cancer].

To assess the clinical role of appendectomy in the surgical procedures for ovarian cancer. We have evaluated retrospectively 96 cases of epithelial ovarian cancer treated from Aug. 1986 to Aug. 1993. In 19 cases the appendiceal involvement was pathologically confirmed (19.8%). All of the patients with appendiceal metastases were found in stages III-IV, with an incidence of 33.3%. There was no significant statistical difference between either the histologic type of ovarian cancer or the side (left or right) of the ovarian involvement and the incidence of metastasis in the appendix. We conclude, with these results, that the appendix was not a primary site involved in the early stages. Appendectomy is not to be regarded as a routine surgical procedures in the early I-II stages of ovarian cancer, but it may help to reduce residual disease in advanced patients.

Adenocarcinoma, Mucinous↗
PubMed1994

[Effects of beta-endorphin on blood pressure and heart rate in rats].

The present work was undertake to investigate the mechanism of changes of blood pressure and heart rate induced by beta-endorphin (beta-End) after microinjection into the Nucleus Amygdaloideus Centralis (AC) of anaesthetized rats. The results were as follows: (1) beta-End (100, 250 pg/microliters) injected into AC decreased both blood pressure and heart rate. (2) Both these effects could be antagonized by naloxone and beta-End anti-serum. (3) The effects of beta-End could also be reversed by phentolamine and propranolol. The results showed that the cardiovascular effects on beta-End were mediated by opioid receptors and through the intervention of adrenergic neurons.

Amygdala↗
PubMed1993

The primary structure of phosphofructokinase from Lactococcus lactis.

The primary amino acid sequence of phosphofructokinase (EC2.7.1.11) from Lactococcus lactis, obtained by Edman analysis of peptides obtained from proteolytic digestions, is MKRIAVLTSGGDAPGMNAAIRAVVRKAISEGIEVYGINHGYAGMVAGDIF PLTSASVGDKIGRGGTFLYSARYPEFAQVEGQLAGIEQLKKFGIEGVVVI GGDGSYHGAMRLTEHGFPAVGLPGTIDNDIVGTDFTIGFDTAVSTVVDAL DKIRDTSSSHNRTFVVEVMGRNAGDIALNAGIAAGADDISIPELEFKFEN VVNNINKGYEKGKNHHIIIVAEGVMTGEEFATKLKEAGYKGDLRVSVLGH IQRGGSPTARDRVLASRMGARAVELLRDGIGGVAVGIRNEELVESPILGT AEEGALFSLTTEGGIKVNNPHKAGLELYRLNSALNNLNL.

Amino Acid Sequence↗
PubMed1993

Reversal of the double-stranded-RNA-induced inhibition of protein synthesis by a catalytically inactive mutant of the protein kinase PKR.

The interferon-inducible double-stranded-RNA(dsRNA)-dependent protein kinase PKR has been implicated in both the antiviral and cell growth-regulatory effects of the interferons. Over-expression of the wild-type form of this protein inhibits cell proliferation, whereas over-expression of inactive mutant forms transforms cells to a tumourigenic phenotype. It has been suggested that mutant PKR exerts a dominant negative effect on the activity of the wild-type protein kinase. We have investigated this possibility using the rabbit reticulocyte cell-free translation system in which protein synthesis is inhibited by dsRNA due to activation of PKR and phosphorylation of initiation factor eIF-2. Addition of a highly purified inactive PKR mutant, synthesised in a baculovirus-infected insect cell system, rescues protein synthesis from inhibition by low concentrations of dsRNA in a dose-dependent manner. The PKR mutant has no effect on protein synthesis in the absence of dsRNA or in the presence of another inhibitory protein kinase, the haem-controlled repressor. Inhibition of translation can be re-established in the presence of the mutant PKR by adding a higher concentration of dsRNA. These results suggest that inactive mutant PKR does exert a dominant negative effect on wild-type PKR and that this may be due to competition for dsRNA binding.

Animals↗
PubMed1993

Changes in the glucose-6-phosphatase complex in hepatomas.

Hepatomas tend to have a decreased glucose-6-phosphatase activity. We have observed phenotypic stability for this change in Morris hepatomas transplanted in rats. To determine if this decrease is selective for translocase functions or the hydrolase activity associated with glucose-6-phosphatase, we have compared activities in liver and hepatomas with glucose-6-phosphate or mannose-6-phosphate as substrates and with intact or histone-disrupted microsomes. In five out of seven subcutaneously transplanted rat hepatoma lines, the microsomal mannose-6-phosphatase activity was lower than in preparations from liver of normal or tumor-bearing rats. With liver microsomes and with most hepatoma microsomes, preincubation with calf thymus histones caused a greater increase in mannose-6-phosphatase than in glucose-6-phosphatase activity. In studies with liver and hepatoma microsomes there were similar increases in mannose-6-phosphatase activity with total calf thymus histones and arginine-rich histones. A smaller increase was seen with lysine-rich histones. The effect of polylysine was similar to the action of lysine-rich histones. There was only a small effect with protamine at the same concentration (1 mg/ml). Rat liver or hepatoma H1 histones gave only about half the activation seen with core nucleosomal histones. Our data suggested that microsomes of rat hepatomas tend to have decreased translocase and hydrolase functions of glucose-6-phosphatase relative to activities in untransformed liver.

Animals↗
PubMed1993

Inhibitory effects of tea extracts and (-)-epigallocatechin gallate on DNA synthesis and proliferation of hepatoma and erythroleukemia cells.

Polyphenols extracted from green or black tea with ethyl acetate were strongly inhibitory for DNA synthesis in HTC rat hepatoma cells and DS19 mouse erythroleukemia cells at concentrations of 0.1-0.2 mg/ml. There was less inhibition with a subsequent black tea fraction extracted with butanol and with the residual water-soluble fraction. Although cell proliferation was inhibited by (-)-epigallocatechin gallate and the tea extracts, there were only marginal effects on differentiation of DS19 cells as judged by hemoglobin synthesis.

Animals↗
PubMed1993

Inhibitory effect of arginine restriction on hepatoma growth.

The potential effects of arginine depletion on promotion of hepatocarcinogenesis and the proliferation of hepatoma cells was investigated. A promotional effect of an arginine-free diet on tumor incidence in liver and kidney was not detected in rats and mice treated with N-nitrosodimethylamine. Inhibitory effects of an arginine-deficient diet on the growth of transplanted hepatomas were observed. Relative to the effect on body weight, the inhibition was greater in mice than rats. The inhibitory effects of an arginine-deficient diet were not correlated with the arginase activity in the tumors. Studies with hepatoma cells treated with polyethyleneglycol-modified arginase indicated that the inhibitory effects of arginine-deprivation on DNA synthesis need not be related to depletion of polyamine precursors.

Animals↗
PubMed1993

[Clinical significance of changes in plasma renin-angiotensin aldosterone system in patients with high altitude pulmonary edema].

Plasma levels of renin activity, angiotensin II and aldosterone were determined in 16 patients with high altitude pulmonary edema (HAPE) with radioimmunoassay and compared with those in the controls including 9 patients with high altitude acute response (HAAR) and 14 health subjects. All of them arrived recently in Lhasa, a place with an altitude of 3,658 m. The results showed that the concentration of plasma renin activity, angiotensin II, and aldosterone was significantly increased (P < 0.05-0.001) in patients with HAPE and higher than that in the controls. It is suggested that the increase plays a role in the development of pulmonary edema in patients with HAPE.

Adolescent↗
PubMed1993

[Efficacy of pyquiton in the treatment of Echinochasmus liliputanus infection].

Two hundred cases of Echinochasmus liliputanus infection were randomly divided into three groups and treated with pyquiton at a single dose of 10.5 and 2.5 mg/kg, respectively. As assessed one month after treatment the egg negativity rates were 100%, 98.7% and 96.5%, respectively. The symptoms such as abdominal pain, distension, diarrhea and anorexia relieved. The results suggest that pyquiton is effective against Echinochasmus liliputanus infection.

Adolescent↗
PubMed1992

dUTP pyrophosphatase and uracil-DNA glycosylase in rat liver and hepatomas.

1. The activity of dUTP pyrophosphatase (dUTPase) was similar in rat liver and hepatomas of slow or moderate growth rate but was increased several fold in three rapidly growing hepatomas. 2. There was an approx three-fold increase in the activity of uracil-DNA glycosylase in Morris hepatoma 7800 but there was little change in activity in other hepatomas that were examined. 3. The activities of dUTPase and uracil-DNA glycosylase were not significantly affected by two diets that may be promotional for hepatocarcinogenesis, a high orotate diet and an arginine-deficient diet.

Animals↗