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H O Li

Publications and source records attributed to H O Li.

10 recordsLinked to original sources
PubMed2001

Interaction of Myc-associated zinc finger protein with DCC, the product of a tumor-suppressor gene, during the neural differentiation of P19 EC cells.

Expression of the DCC (deleted in colorectal cancer) protein is strongly induced during the neural differentiation of mouse P19 embryonal carcinoma (EC) cells that occurs when these cells are treated with retinoic acid (RA). Myc-associated zinc finger protein (MAZ) is a DNA-binding protein that is widely expressed and functions in human, mouse and hamster cells as an activator, an initiator or a terminator of transcription. However, the biological functions of MAZ remain elusive. We report here that MAZ associates with the cytoplasmic domain of the DCC protein in vivo and in vitro. Yeast two-hybrid assays confirmed this association. An immunofluorescence study demonstrated that DCC protein is expressed at elevated levels in neuron-like P19 EC cells, in particular in axons, in which the MAZ protein is also expressed. We found that MAZ was translocated from the nucleus to the cytoplasm during the RA-induced terminal differentiation of P19 EC cells with resultant loss of the ability of MAZ to bind to the ME1a1 site of the c-myc promoter. Taken together, our observations imply that the DCC protein might play a critical role as a signaling molecule in the regulation of the transcriptional activity of MAZ during the neural differentiation of P19 EC cells.

Active Transport, Cell Nucleus↗
PubMed2000

A cytoplasmic RNA vector derived from nontransmissible Sendai virus with efficient gene transfer and expression.

We have recovered a virion from defective cDNA of Sendai virus (SeV) that is capable of self-replication but incapable of transmissible-virion production. This virion delivers and expresses foreign genes in infected cells, and this is the first report of a gene expression vector derived from a defective viral genome of the Paramyxoviridae. First, functional ribonucleoprotein complexes (RNPs) were recovered from SeV cloned cDNA defective in the F (envelope fusion protein) gene, in the presence of plasmids expressing nucleocapsid protein and viral RNA polymerase. Then the RNPs were transfected to the cells inducibly expressing F protein. Virion-like particles thus obtained had a titer of 0.5 x 10(8) to 1. 0 x 10(8) cell infectious units/ml and contained F-defective RNA genome. This defective vector amplified specifically in an F-expressing packaging cell line in a trypsin-dependent manner but did not spread to F-nonexpressing cells. This vector infected and expressed an enhanced green fluorescent protein reporter gene in various types of animal and human cells, including nondividing cells, with high efficiency. These results suggest that this vector has great potential for use in human gene therapy and vaccine delivery systems.

Animals↗
PubMed1997

MAZ, a Myc-associated zinc finger protein, is essential for the ME1a1-mediated expression of the c-myc gene during neuroectodermal differentiation of P19 cells.

To investigate whether MAZ (Myc-associated zinc finger protein) affects the expression of the c-myc gene during the retinoic acid-induced (RA-induced) neuroectodermal differentiation of P19 embryonal carcinoma (EC) cells, we introduced a CAT reporter construct, human c-myc promoter/CAT (pMyc2CAT), and a mutant CAT derivative that lacked an ME1a1 site (pMyc1CAT) into P19EC cells to monitor the promoter activity of the c-myc gene. The expression of CAT in pMyc2CAT-transformed cells declined fivefold after 24 h in the presence of RA, returned to the normal level within 48 h, and decreased again to below 20% of the normal level after 96 h. By contrast, the expression of CAT in pMyc1CAT-transformed cells did not return to the normal level after 48 h in the presence of RA. In addition, an electrophoretic mobility shift assay (EMSA) with ME1a1 DNA as probe demonstrated that the kinetics of the DNA-binding activity of MAZ were closely correlated with the changes in the expression of CAT from the c-myc promoter/CAT gene during the differentiation of P19EC cells. Taken together, these results suggest that MAZ plays a key role in the transient increase in the expression of the c-myc gene after 48 h of exposure to RA during the neuroectodermal differentiation of P19EC cells.

Animals↗
PubMed1996

Specific regulation of gene expression by antisense nucleic acids: a summary of methodologies and associated problems.

Gene therapy based on gene-specific nucleic acids has moved from theory to a practical possibility in a very short time. The new DNA and RNA therapeutic reagents are intended to stop the growth of cancerous cells or the production of viruses. At the practical level, the efficacy of antisense oligomers as therapeutic reagents has been carefully examined in various clinical contexts. For the efficient use of antisense nucleic acids as pharmaceutical agents, a complete analysis of their mechanisms of action is necessary. The use of antisense oligomers always involves the following problems: basepair specificity, stereoisomer specificity, stability and resistance to nucleases of sense-antisense duplexes, permeability of the cell membrane and targeting of the oligomer, safety, and the preparation of large amounts of oligomer. Herein, we review the basic concepts and problems associated with the exploitation of antisense technology. We have identified a new transcription factor triple-helix-binding zinc-finger protein-1 (THZif-1) induced by antisense c-myc RNA in the antisense-transformed HL60 cells. The encoded protein functions as the repressor of c-myc to achieve the reduction of the endogenous expression of c-myc gene. Therefore, the introduction of THZif-1 gene into HL60 cells in conjunction with antisense c-myc oligomers may result in the efficient repression of the expression of the c-myc gene. The molecular features of this factor are herein discussed.

Amino Acid Sequence↗
PubMed1995

Induction by adenovirus-5 E1A of the differentiation phenotype of F9 teratocarcinoma cells involves a conserved region (CR1) of E1A.

The effects of the E1A protein of adenovirus-5 on the differentiation program of F9 teratocarcinoma cells were examined by the stable introduction of plasmids that expressed wild-type or mutated forms of E1A. Constitutive expression of plasmids for most of the mutant E1As induced loss of expression of the cell-surface antigen SSEA-1 and the enhanced expression of genes specific for the differentiated phenotype of F9 cells, such as genes for laminin B1, tissue-type plasminogen activator (tPA) and type IV collagen, as well as the altered cell morphology that is associated with the differentiated state. However, such changes were not observed in the case of genes for mutant proteins from which a conserved region (CR1) of E1A had been deleted. Furthermore, no significant induction of expression of the c-jun gene or transactivation of the c-jun-CAT reporter gene were observed when the sequence that encodes CR1 of E1A had been deleted. A palindromic sequence element (DRE) of the c-jun promoter was essential for the E1A-mediated up-regulation of the c-jun gene. These results imply that CR1 is required for activation of the c-jun gene and that it is implicated in the growth arrest, expression of parietal endoderm-specific functions and the orderly differentiation of F9 cells.

Adenovirus E1A Proteins↗
PubMed1995

Cooperatively between an upstream TATA-like sequence and a CAA repeated element mediates E1A-dependent negative repression of the H-2Kb class I gene.

In primary rodent cells transformed by the E1A region of the highly oncogenic adenovirus type 12, repression of transcription mediated by the far upstream TATA-like element was observed only in conjunction with either possible juxtaposition of a CAA repeated element in the presence of E1A and was dependent upon the relative arrangement of both the TATA-like and CAA repeated motifs in both homologous and heterologous promoter constructs. A gel shift competition study demonstrated that the TATA-binding protein (TBP) or a TBP-like protein can bind to both the upstream TATA-like sequence and the regular TATA box on the H-2Kb basal promoter. Moreover, employing immunoselection and cyclic amplification and selection of targets (CASTing) methods with nuclear extracts derived from Ad12-E1A transformants, we have identified a high affinity binding site in the H-2Kb class I promoter for E1A-associated DNA-binding proteins. The sequences of the binding sites were identified and were found to contain both the upstream TATA-like motif and the CAA repeated motifs. Our results suggest that the TATA-like sequence in the far upstream region of the H-2Kb gene is one of the elements that is required for Ad12-E1A-mediated negative repression.

Adenovirus E1A Proteins↗
PubMed1994

DNA fingerprinting involving fluorescence-labeled termini of any enzymatically generated fragments of DNA.

We have developed a new fluorescence-based method for DNA fingerprinting that does not require a fluorescent linker or a synthetic oligonucleotide primer, both of which are normally used for labeling of DNA. Cosmid DNAs are digested with appropriate restriction enzymes and the 3' termini of DNA fragments are labeled with the corresponding, fluorescent dye-conjugated dideoxynucleotide triphosphate terminator (dye-ddNTP) by the Klenow fragment of DNA polymerase I from Escherichia coli, which has 3'-->5' exonuclease and replacement activities as well as its main 5'-->3' polymerase activity. Samples are separated on a DNA-sequencing gel and data are analyzed by application of both the Version 0.3.8a mapper program (Applied Biosystem Inc., Foster City, CA) and our Overlap I program that facilitate rapid analysis of the frequency of overlapping of cosmid DNAs. Using this method we have determined the overlap frequency of DNA fragments of each cosmid clone from the mouse MHC class I gene cluster.

Animals↗
PubMed1993

A mathematically designed STS primer without any mismatches for direct sequencing of cosmid DNA clones.

We report here a new method for the direct sequencing of large DNA inserts of cosmid clones from human chromosomes using STS primers of 14 nucleotides without any mismatches, which are designed from results of a mathematical analysis. It is clear that STS primer of 14 nucleotides is optimum for direct sequencing of cosmid recombinant DNA clones. We also provide examples of direct sequencing of cosmid clones of human chromosome 21 using these STS primers.

Animals↗