👤 Lixia Zheng

Chylomicrons produced by the human gut contain apolipoprotein (apo) B48, whereas very-low-density lipoproteins made by the liver contain apo B100. To study how these molecules function during lipid absorption, we examined the process as it occurs in apobec-1 knockout mice (able to produce only apo B100; KO) and in wild-type mice (of which the normally functioning intestine makes apo B48, WT). Using the lymph fistula model, we studied the process of lipid absorption when animals were intraduodenally infused with a lipid emulsion (4 or 6 micromol/h of triolein). KO mice transported triacylglycerol (TG) as efficiently as WT mice when infused with the lower lipid dose; when infused with 6 micromol/h of triolein, however, KO mice transported significantly less TG to lymph than WT mice, leading to the accumulation of mucosal TG. Interestingly, the size of lipoprotein particles from both KO and WT mice were enlarged to chylomicron-size particles during absorption of the higher dose. These increased-size particles produced by KO mice were not associated with increased apo AIV secretion. However, we found that the gut of the KO mice secreted fewer apo B molecules to lymph (compared with WT), during both fasting and lipid infusion, leading us to conclude that the KO gut produced fewer numbers of TG-rich lipoproteins (including chylomicron) than the wild-type animals. The reduced apo B secretion in KO mice was not related to reduced microsomal triglyceride transfer protein lipid transfer activity. We propose that apo B48 is the preferred protein for the gut to coat chylomicrons to ensure efficient chylomicron formation and lipid absorption. Show less

Seven single nucleotide polymorphisms (SNPs) were identified by PCR-SSCP and sequencing in the chicken apoA5 gene in F2 chickens from an experimental cross of White Plymouth Rock x Silkies. One SNP(C-169T) located on the 5'-regulatory region, another two in the second exon were transitions of C to T (600) and T to C (635). Four SNPs in the third exon were found, which were C841G, C914T, C1142G, C1394T. The association of the polymorphisms with carcass traits was investigated. The most significant results were yielded from primer apoA3F/R: the abdominal fat weight of CC chickens were significantly higher than that of AA, AB, AC, BB and BC chickens (P<0.05); AC chickens had lower liver weight than that of AA, AB, BB, BC and CC (P<0.05); BC chickens had lower heart weight than that of BB (P<0.05). Show less

Histone deacetylase inhibitor (HDACi) has been shown to demethylate the mammalian genome, which further strengthens the concept that DNA methylation and histone modifications interact in regulation of gene expression. Here, we report that an HDAC inhibitor, depsipeptide, exhibited significant demethylating activity on the promoters of several genes, including p16, SALL3, and GATA4 in human lung cancer cell lines H719 and H23, colon cancer cell line HT-29, and pancreatic cancer cell line PANC1. Although expression of DNA methyltransferase 1 (DNMT1) was not affected by depsipeptide, a decrease in binding of DNMT1 to the promoter of these genes played a dominant role in depsipeptide-induced demethylation and reactivation. Depsipeptide also suppressed expression of histone methyltransferases G9A and SUV39H1, which in turn resulted in a decrease of di- and trimethylated H3K9 around these genes' promoter. Furthermore, both loading of heterochromatin-associated protein 1 (HP1alpha and HP1beta) to methylated H3K9 and binding of DNMT1 to these genes' promoter were significantly reduced in depsipeptide-treated cells. Similar DNA demethylation was induced by another HDAC inhibitor, apicidin, but not by trichostatin A. Our data describe a novel mechanism of HDACi-mediated DNA demethylation via suppression of histone methyltransferases and reduced recruitment of HP1 and DNMT1 to the genes' promoter. Show less

Hepatocyte paraffin 1 (Hep Par 1), a murine monoclonal antibody, is widely used in surgical pathology practice to determine the hepatocellular origin of neoplasms. However, identity of the antigen for Hep Par 1 is unknown. The aim of this study was to characterize the Hep Par 1 antigen. To identify the antigen, immunoprecipitation was used to isolate the protein from human liver tissue, and a distinct protein band was detected at approximately 165 kDa. The protein band was also present in small intestinal tissue, but was not present in several other non-liver tissues nor in three human hepatocellular carcinoma cell lines, Huh-7, HepG2, and LH86. The protein was purified and analyzed by mass spectrometry. It was identified as carbamoyl phosphate synthetase 1 (CPS1). CPS1 is a rate-limiting enzyme in urea cycle and is located in mitochondria. We demonstrated that hepatoid tumors (gastric and yolk sac) were immunoreactive with both Hep Par 1 antibody and anti-CPS1 antibody, further confirming the results of mass spectrometric analysis. We found that the three human hepatocellular carcinoma cell lines do not express either CPS1 RNA or protein. We confirmed that the gene was present in these cell lines, suggesting that suppression of CPS1 expression occurs at the transcriptional level. This finding may have relevance to liver carcinogenesis, since poorly differentiated hepatocellular carcinomas exhibit poor to absent immunoreactivity to Hep Par 1. In conclusion, we have identified the antigen for Hep Par 1 antibody as a urea cycle enzyme CPS1. Our results should encourage further investigation of potential role that CPS1 expression plays in liver pathobiology and carcinogenesis. Show less

The mechanism(s) underlying neurodegeneration-associated activation of ERK1/2 remain poorly understood. We report that in cultured rat cortical neurons, whose basal ERK1/2 phosphorylation required NMDA receptors (NMDAR), the neurotoxic DNA intercalating drug cisplatin increased ERK1/2 phosphorylation via NMDAR despite reducing their activity. The rate of ERK1/2 dephosphorylation was lowered by cisplatin. Cisplatin-treated neurons showed general transcription inhibition likely accounting for the reduced expression of the ERK1/2-selective phosphatases including the dual specificity phosphatase-6 (DUSP6) and the DUSP3 activator vaccinia-related kinase-3 (VRK3). Hence, cisplatin effects on ERK1/2 may be due to the deficient ERK1/2 inhibition by the transcription-regulated phosphatases. Indeed, the transcription inhibitor actinomycin D reduced expression of DUSP6 and VRK3 while inducing the NMDAR-dependent activation of ERK1/2 and the impairment of ERK1/2 dephosphorylation. Thus, cisplatin-mediated transcriptional inhibition of ERK1/2 phosphatases contributed to delayed and long lasting accumulation of phospho-ERK1/2 that was driven by the basal NMDAR activity. Our results provide the first direct evidence for transcriptionally-regulated inactivation of neuronal ERK1/2. Its disruption likely contributes to neurodegeneration-associated activation of ERK1/2. Show less

Epstein-Barr virus (EBV) infection plays a key role in the pathogenesis of nasopharyngeal carcinoma (NPC). This study was to explore the effects of the recurrent infection by EBV reactivation on the genomic expression profile of NPC. The microarray expression data from different cell lines subjected to primary infection of EBV+ vs. EBV- targets in NPC and recurrent EBV reactivation were collected from public data depository. Cross comparison, t-test analysis as well as filtering by flag, expression level and fold change were used to analyze the data and identify differential genes. Moreover, a set of web-based applications, such as DAVID (database for annotation, visualization and integrated discovery), pSTIING (protein, signaling, transcriptional interactions and inflammation networks gateway), GATHER (gene annotation tool to help explain relationships) and TELiS (transcription element listening system), were used to analyze and predict the probable expression profile of the differential genes. As compared with the genes expressed during primary infection of EBV, 25 genes, including DUSP1, TOP1, HOXA9, DEK, PABPC1 and IMPDH2, were differentially expressed during EBV reactivation. Many of them were oncogenic. The differential genes together with related transcriptional factors were interacted mainly through 2 mechanisms: one mainly included TOP1, DUSP1, DUSP6, and RPS28; the other one was a circuit of PITX1, CD9, HOXA9 and IMPDH2. The differential genes might participate in EBV reactivation by changing their expression level through two mechanisms, which contributes to the final development of NPC. Show less

Aberrant WNT signal transduction is involved in many diseases. In colorectal cancer and melanoma, mutational disruption of proteins involved in the degradation of beta-catenin, the key effector of the WNT signaling pathway, results in stabilization of beta-catenin and, in turn, activation of transcription. We have used tandem-affinity protein purification and mass spectrometry to define the protein interaction network of the beta-catenin destruction complex. This assay revealed that WTX, a protein encoded by a gene mutated in Wilms tumors, forms a complex with beta-catenin, AXIN1, beta-TrCP2 (beta-transducin repeat-containing protein 2), and APC (adenomatous polyposis coli). Functional analyses in cultured cells, Xenopus, and zebrafish demonstrate that WTX promotes beta-catenin ubiquitination and degradation, which antagonize WNT/beta-catenin signaling. These data provide a possible mechanistic explanation for the tumor suppressor activity of WTX. Show less

Both G1 and mitotic cyclins have been implicated in regulating Candida albicans filamentous growth. We have investigated the functions of Grr1 whose orthologue in Saccharomyces cerevisiae is known to mediate ubiquitin-dependent degradation of the G1 cyclins Cln1 and Cln2. Here, we report that deleting C. albicans GRR1 causes significant stabilization of two G1 cyclins Ccn1 and Cln3 and pseudohyphal growth. grr1Delta cells are highly heterogeneous in length and many of them fail to separate after cytokinesis. Interestingly, some isolated rod-like G1 cells of similar sizes are present in the grr1Delta culture. Time-lapse microscopy revealed that the rod-shaped G1 cells first grew exclusively in width before budding and then the bud grew exclusively by apical extension until after cytokinesis, yielding rod-like daughter cells. Consistently, actin patches persistently localize to the bud tip until around the time of cytokinesis. Despite the pseudohyphal phenotype, grr1Delta cells respond normally to hyphal induction. Hyperphosphorylated Cln3 isoforms accumulate in grr1Delta cells, indicating that Grr1 selectively mediates their degradation in wild-type cells. grr1Delta pseudohyphal growth requires neither Hgc1 nor Swel, two important regulators of cell morphogenesis. Furthermore, the cellular level of Hof1, a protein having a role in cytokinesis, is also significantly increased in grr1Delta cells. Show less

Human protein kinases make up a large superfamily of homologous proteins, which are related by virtue of their kinase domains (also known as catalytic domains). Here we report the cloning and characterization of a novel human MAST4 (microtubule associated serine/threonine kinase family member 4) gene, which locates on human chromosome 5q13. The MAST4 cDNA is 7587 base pairs in length and encodes a putative protein of 2435 amino acids which contains a serine/threonine kinase domain and a PDZ domain. MAST4 protein has 64%, 63%, 59% and 39% identical aminoacid residues with MAST1, MAST2, MAST3 and MASTL respectively. RT-PCR analysis revealed relatively high expression level of MAST4 in most normal human tissues, with an exception of in testis, small intestine, colon and peripheral blood leukocyte. Show less

To study the genetic control of plant responses to cold stress, Arabidopsis thaliana mutants were isolated by a screen for mutations that impair cold-induced transcription of the CBF3-LUC reporter gene. We report here the characterization and cloning of a mutated gene, atnup160-1, which causes reduced CBF3-LUC induction under cold stress. atnup160-1 mutant plants display altered cold-responsive gene expression and are sensitive to chilling stress and defective in acquired freezing tolerance. AtNUP160 was isolated through positional cloning and shown to encode a putative homolog of the animal nucleoporin Nup160. In addition to the impaired expression of CBF genes, microarray analysis revealed that a number of other genes important for plant cold tolerance were also affected in the mutants. The atnup160 mutants flower early and show retarded seedling growth, especially at low temperatures. AtNUP160 protein is localized at the nuclear rim, and poly(A)-mRNA in situ hybridization shows that mRNA export is defective in the atnup160-1 mutant plants. Our study suggests that Arabidopsis AtNUP160 is critical for the nucleocytoplasmic transport of mRNAs and that it plays important roles in plant growth and flowering time regulation and is required for cold stress tolerance. Show less

Glucagon-like peptide 1 (GLP-1) is a gastrointestinal hormone secreted in response to meal ingestion by enteroendocrine L cells located predominantly in the lower small intestine and large intestine. GLP-1 inhibits the secretion and motility of the upper gut and has been suggested to play a role in the "ileal brake." In this study, we investigated the effect of recombinant GLP-1-(7-36) amide (rGLP-1) on lipid absorption in the small intestine in intestinal lymph duct-cannulated rats. In addition, the effects of rGLP-1 on intestinal production of apolipoprotein (apo) B and apo A-IV, two apolipoproteins closely related to lipid absorption, were evaluated. rGLP-1 was infused through the jugular vein, and lipids were infused simultaneously through a duodenal cannula. Our results showed that infusion of rGLP-1 at 20 pmol.kg(-1).min(-1) caused a dramatic and prompt decrease in lymph flow from 2.22 +/- 0.15 (SE) ml/h at baseline (n = 6) to 1.24 +/- 0.06 ml/h at 2 h (P < 0.001). In contrast, a significant increase in lymph flow was observed in the saline (control) group: 2.19 +/- 0.20 and 3.48 +/- 0.09 ml/h at baseline and at 6 h of lipid infusion, respectively (P < 0.001). rGLP-1 also inhibited intestinal triolein absorption (P < 0.05) and lymphatic apo B and apo A-IV output (P < 0.05) but did not affect cholesterol absorption. In conclusion, rGLP-1 dramatically decreases intestinal lymph flow and reduces triglyceride absorption and apo B and apo A-IV production. These findings suggest a novel role for GLP-1 in lipid absorption. Show less

The recently discovered apolipoprotein A5 ( APOA5 ) gene has been shown to be important in determining plasma triglyceride levels, a major cardiovascular disease risk factor. We searched for possible associations of the APOA5 gene polymorphisms S19W and -1131T>C with coronary heart disease (CHD) in a Chinese population. A total of 483 Chinese CHD patients and 502 control non-CHD subjects were genotyped by polymerase chain reaction-restriction fragment length polymorphism for these 2 single nucleotide polymorphisms. We found that the minor allele 19W was observed only in CHD patients and not in controls, with allelic frequencies of 0.047 and 0.000, respectively ( P < .000001), and the minor allele -1131C was significantly higher in CHD patients than in controls (0.391 vs 0.299, P < .0001). These results suggest that both the S19W and -1131T>C variations in the APOA5 gene are associated with the CHD and appear to be 2 genetic risk factors for CHD susceptibility in Chinese. Moreover, we found that triglyceride levels were significantly higher in -1131C carriers than in -1131T subjects of the control group and that high-density-lipoprotein cholesterol was decreased in -1131C carriers among CHD patients. Show less

In addition to controlling a switch to glycolytic metabolism and induction of erythropoiesis and angiogenesis, hypoxia promotes the undifferentiated cell state in various stem and precursor cell populations. Here, we show that the latter process requires Notch signaling. Hypoxia blocks neuronal and myogenic differentiation in a Notch-dependent manner. Hypoxia activates Notch-responsive promoters and increases expression of Notch direct downstream genes. The Notch intracellular domain interacts with HIF-1alpha, a global regulator of oxygen homeostasis, and HIF-1alpha is recruited to Notch-responsive promoters upon Notch activation under hypoxic conditions. Taken together, these data provide molecular insights into how reduced oxygen levels control the cellular differentiation status and demonstrate a role for Notch in this process. Show less

To investigate the single nucleotide polymorphism 4 (SNP4) of the apolipoprotein A5 (APOA5) gene possible association with coronary heart disease(CHD) and its distribution of in Chinese Han population. APOA5 SNP4 genotyping was performed using polymerase chain reaction and Hae III restriction fragment length polymorphism analysis. APOA5 allelic frequencies of T, C were 0.435, 0.565 and 0.374, 0.626 in CHD group and control group, respectively. There is significant difference in allele and genotype frequencies between CHD group and control group (P<0.05). The levels of plasma high density lipoprotein in CHD patients with CC genotype were higher than those in CHD patients with other genotypes (P<0.01). The frequencies of T allele and C allele in Chinese was significantly different from those in Caucasians (0.374 vs 0.663, 0.626 vs 0.337, P<0.01). The C allele was much more common in Chinese population. The association is found between the Hae III polymorphism and CHD, There is a significant correlation between the CC genotype of the APOA5 and the levels of plasma high density lipoprotein-cholosteal in the CHD group. Show less

Apolipoprotein AIV (apo AIV) is a satiety protein secreted by the small intestine. We demonstrate for the first time that apo AIV protein and apo AIV mRNA are present in rat hypothalamus, a site intimately involved in the integration of signals for regulation of food intake and energy metabolism. We further characterized the regulation of hypothalamic apo AIV mRNA levels. Food-deprived animals showed a pronounced decrease in gene expression of apo AIV in the hypothalamus, with a concomitant decrease in the jejunum. Refeeding fasted rats with standard laboratory chow for 4 h evokes a significant increase of apo AIV mRNA in jejunum but not in hypothalamus. However, lipid refeeding to the fasted animals restored apo AIV mRNA levels both in hypothalamus and jejunum. Intracerebroventricular administration of apo AIV antiserum not only stimulated feeding, but also decreased apo AIV mRNA level in the hypothalamus. These data further confirm the central role of apo AIV in the regulation of food intake. Show less

We cloned and characterized a full-length cDNA of mouse actin cross-linking family 7 (mACF7) by sequential rapid amplification of cDNA ends-PCR. The completed mACF7 cDNA is 17 kb and codes for a 608-kD protein. The closest relative of mACF7 is the Drosophila protein Kakapo, which shares similar architecture with mACF7. mACF7 contains a putative actin-binding domain and a plakin-like domain that are highly homologous to dystonin (BPAG1-n) at its NH(2) terminus. However, unlike dystonin, mACF7 does not contain a coiled-coil rod domain; instead, the rod domain of mACF7 is made up of 23 dystrophin-like spectrin repeats. At its COOH terminus, mACF7 contains two putative EF-hand calcium-binding motifs and a segment homologous to the growth arrest-specific protein, Gas2. In this paper, we demonstrate that the NH(2)-terminal actin-binding domain of mACF7 is functional both in vivo and in vitro. More importantly, we found that the COOH-terminal domain of mACF7 interacts with and stabilizes microtubules. In transfected cells full-length mACF7 can associate not only with actin but also with microtubules. Hence, we suggest a modified name: MACF (microtubule actin cross-linking factor). The properties of MACF are consistent with the observation that mutations in kakapo cause disorganization of microtubules in epidermal muscle attachment cells and some sensory neurons. Show less

Apolipoprotein (apo) A-IV is a protein synthesized, in humans, only by the small intestine. It has a molecular weight of 46 000 Da. This paper summarizes the evidence supporting its role as a satiety factor following the ingestion of fat. This function of apo A-IV is unique and not shared by other apolipoproteins, including apo A-I. The satiety effect of apo A-IV is centrally mediated. The mechanism of how apo A-IV inhibits food intake is not clear but it probably acts by inhibiting both gastric acid secretion as well as gastric motility. Lipid absorption stimulates apo A-IV synthesis and secretion by the jejunum. In addition to lipid feeding, there is evidence that a factor which is released as a result of lipid absorption in the distal small intestine also stimulates the synthesis and release of apo A-IV by the jejunum. This factor is probably PYY. Show less

The translocation t(10;11)(p13;q14) is a recurring chromosomal abnormality that has been observed in patients with acute lymphoblastic leukemia as well as acute myeloid leukemia. We have recently reported that the monocytic cell line U937 has a t(10;11)(p13;q14) translocation. Using a combination of positional cloning and candidate gene approach, we cloned the breakpoint and were able to show that AF10 is fused to a novel gene that we named CALM (Clathrin Assembly Lymphoid Myeloid leukemia gene) located at 11q14. AF10, a putative transcription factor, had recently been cloned as one of the fusion partners of MLL. CALM has a very high homology in its N-terminal third to the murine ap-3 gene which is one of the clathrin assembly proteins. The N-terminal region of ap-3 has been shown to bind to clathrin and to have a high-affinity binding site for phosphoinositols. The identification of the CALM/AF10 fusion gene in the widely used U937 cell line will contribute to our understanding of the malignant phenotype of this line. Show less