Biomedical subjects

Z X Xiao

Publications and source records attributed to Z X Xiao.

At least 19 recordsLinked to original sources

PubMed2001

Vanadate disrupts mammary gland development in whole organ culture.

Protein tyrosine kinases and phosphatases are signaling molecules involved in all aspects of development, including proliferation, differentiation, and apoptosis. How disruption of protein tyrosine phosphatase affects mammary gland development is not entirely clear. We examined the effects of sodium vanadate, which is known to primarily inhibit tyrosine phosphatases, in mouse mammary gland development in whole organ culture. Mammary epithelial differentiation was effectively inhibited by vanadate in a dose-dependent manner as indicated by lack of epithelial alveoli compared to the contralateral non-treated gland controls. Mammary glands in the differentiation medium after four days in the presence of vanadate did not differentiate into alveoli. Instead, they exhibited prominent terminal end buds and lost the distinctive epithelial structures. The inhibitory effect of vanadate on mammary epithelial cell differentiation was irreversible after one day of treatment. Immunohistochemical staining for PCNA (Proliferating Cell Nuclear Antigen) showed that vanadate-treated glands exhibited elevated proliferation signals in the differentiation medium. Expression of beta-casein protein in the vanadate-treated glands decreased dramatically and progressively. Short-term exposure (up to 72 hours) of mammary glands to vanadate resulted in an increase in mammary epithelial cell density and loss of organization of the mammary structures. TUNEL assay of mammary glands with prolonged exposure to vanadate revealed widespread apoptosis. Furthermore, some cells were still proliferating or expressing beta-casein after prolonged exposure to vanadate. Taken together, these data indicate that vanadate treatment blocks mammary epithelial cell differentiation and promotes abnormal proliferation and apoptosis, likely through the inhibition of protein tyrosine phosphatase-mediated signaling.

Animals↗

PubMed1998

p300/MDM2 complexes participate in MDM2-mediated p53 degradation.

Control of p53 turnover is critical to p53 function. E1A binding to p300/CBP translates into enhanced p53 stability, implying that these coactivator proteins normally operate in p53 turnover control. In this regard, the p300 C/H1 region serves as a specific in vivo binding site for both p53 and MDM2, a naturally occurring p53 destabilizer. Moreover, most of the endogenous MDM2 is bound to p300, and genetic analysis implies that specific interactions of p53 and MDM2 with p300 C/H1 are important steps in the MDM2-directed turnover of p53. A specific role for p300 in endogenous p53 degradation is underscored by the p53-stabilizing effect of overproducing the p300 C/H1 domain. Taken together, the data indicate that specific interactions between p300/CBP C/H1, p53, and MDM2 are intimately involved in the MDM2-mediated control of p53 abundance.

Cell Line↗

PubMed1998

Mutagenicity of urine from individuals exposed to LPG combustion products.

The mutagenicity of urine from individuals exposed to the combustion products of liquefied petroleum gas (LPG) was detected with Salmonella typhimurium TA98 and its newly developed derivatives YG1021 (nitroreductase overproducing) and YG1024 (O-acetyltransferase overproducing). The detection showed significantly increased mutagenicity for the two YG strains and increased positive rates for all three strains in the presence of both rat liver S9 and beta-glucuronidase. Further analysis demonstrated that urine samples taken from smoking and non-smoking exposed individuals exhibited significantly higher mutagenic potency (revertants/10 microliters urine concentrate) than their corresponding controls. These results indicate that the increased urine mutagenicity is caused by the exposure to LPG combustion products or smoking. The mutagenic potency of urine samples of all exposed individuals tested with YG1024 was found to be about 7 times higher than with TA98. The difference in mutagenic potency was smaller for the same samples when comparison was made between YG1021 and TA98. This suggests that the mutagenic compounds present in the urine samples contain mainly aromatic compounds as glucuronide conjugates. Our results demonstrate that YG1024 is more sensitive than TA98 in detecting the mutagenicity of these samples. In addition, no significant difference in the mutagenic potency between the 'pure' exposed (non-smokers') and the 'pure' smokers' (unexposed) samples was found in all three tester strains. This might mean that the exposure extent of mutagens/carcinogens in LPG combustion products for exposed individuals roughly corresponds to the smoking level of smokers who smoke 20-40 cigarettes per day. Furthermore, the results also suggest that synergism might exist in the mutagenic effects of exposure to LPG combustion products and cigarette smoking.

Adult↗

PubMed1996

Regulation of the retinoblastoma protein-related protein p107 by G1 cyclin-associated kinases.

p107 is a retinoblastoma protein-related phosphoprotein that, when overproduced, displays a growth inhibitory function. It interacts with and modulates the activity of the transcription factor, E2F-4. In addition, p107 physically associates with cyclin E-CDK2 and cyclin A-CDK2 complexes in late G1 and at G1/S, respectively, an indication that cyclin-dependent kinase complexes may regulate, contribute to, and/or benefit from p107 function during the cell cycle. Our results show that p107 phosphorylation begins in mid G1 and proceeds through late G1 and S and that cyclin D-associated kinase(s) contributes to this process. In addition, E2F-4 binds selectively to hypophosphorylated p107, and G1 cyclin-dependent p107 phosphorylation leads to the dissociation of p107-E2F-4 complexes as well as inactivation of p107 G1 blocking function.

Cell Line↗

PubMed1995

Interaction between the retinoblastoma protein and the oncoprotein MDM2.

Inactivation of tumour-suppressor genes leads to deregulated cell proliferation and is a key factor in human tumorigenesis. Both p53 and retinoblastoma genes are frequently mutated in human cancers, and the simultaneous inactivation of RB and p53 is frequently observed in a variety of naturally occurring human tumours. Furthermore, three distinct DNA tumour virus groups--papovaviruses, adenoviruses and human papillomaviruses--transform cells by targeting and inactivating certain functions of both the p53 and retinoblastoma proteins. The cellular oncoprotein, Mdm2, binds to and downmodulates p53 function; its human homologue, MDM2, is amplified in certain human tumours, including sarcomas and gliomas. Overproduction of Mdm2 is both tumorigenic and capable of immortalizing primary rat embryo fibroblasts. Here we show that MDM2 interacts physically and functionally with pRB and, as with p53, inhibits pRB growth regulatory function. Therefore, both pRB and p53 can be subjected to negative regulation by the product of a single cellular protooncogene.

Carrier Proteins↗

PubMed1995

Functional interaction between the CSE2 gene product and centromeres in Saccharomyces cerevisiae.

The cse2-1 allele was identified through a genetic screen for mutations affecting chromosome segregation in Saccharomyces cerevisiae. This mutation confers cold and temperature sensitivity and causes increases in mitotic chromosome non-disjunction and loss. The CSE2 gene encodes a 17 kDa protein with a basic region-leucine zipper motif. Disruption of CSE2 is not lethal but results in the accumulation of large-budded cells. Here, we report that disruption of CSE2 results in a significant increase in chromosome missegregation, slower growth and defective meiosis. The combination of the CSE2 disruption and a mutant centromere results in a synergistic effect on both cell growth and cell viability. These data suggest a functional interaction between the CSE2 protein and the yeast centromere.

Centromere↗

PubMed1995

A neuron model based on brain biochemical principles.

The electrical activity and excitation of the brain is based on certain biochemical processes, particularly, the activity of transmitter-receptor-ion channel system and the DNA-RNA-Pr (Pr:protein) system. There have already been some neuron models relating to the ion channel, but the kinds and numbers of transmitters, receptors, and ion channels are directly or indirectly conditioned by the DNA-RNA-Pr system. To reflect these facts, we present a new neuron model based on the important biochemical chains of the brain. This model is applied to both the simulation research of electrical activity and the information processing function of the brain. In this demonstration, we will introduce: 1) How to express the connection between the neuron excitation and the transmitter-receptor-ion channel system; 2) How to express the connection between the transmitter-receptor-ion channel system of neuron and the DNA-RNA-Pr system; 3) How to express the connection among 16,000 artificial neurons on the basis of the above-mentioned points; 4) The time and the state of the excitation passing through a particular neuron in a group of neurons.

Brain↗

PubMed1994

Analysis of potential functional regions using local degeneracy: mutational hotspots in human factor IX are localized in high-degeneracy regions.

To study the relationship between the potential functional regions with the primary amino acid sequence, we introduced a new factor termed local degeneracy to analyze the degree of the degeneracy in a given segment of the protein. Using the defined local degeneracy, we have analyzed the human coagulation Factor IX (Christmas factor) which is an essential component of the clotting cascade. The mutational hotspots in Factor IX are primarily distributed in the high-degeneracy regions, suggesting a direct correlation of the functional regions with high degree of the degeneracy. This method may be useful to predict and to evaluate potential functional domains of a protein.

Animals↗

PubMed1994

E2F-4, a new member of the E2F transcription factor family, interacts with p107.

The E2F family of transcription factors has been implicated in the regulation of cell proliferation, and E2F-binding sites are present in the promoters of several growth-regulating genes. E2F family members are functionally regulated, in part, by complex formation with one or more members of the nuclear pocket protein family, RB, p107, and p130. Pocket protein regulation of E2F likely contributes to normal cellular growth control. While the three cloned species of E2F, E2F-1, E2F-2, and E2F-3, are known to be targets of RB interaction, no E2F species has yet been shown to be a specific p107 or p130 target. Here, we describe the cloning of a new member of the E2F family, E2F-4, which forms heterodimers with a member(s) of the DP family and, unlike some family members, is present throughout the cell cycle and appears to be a differentially phosphorylated p107-binding partner. p107 binding not only can be linked to the regulation of E2F-4 transcriptional activity, but also to suppression of the ability of E2F-4 to transform an immortalized rodent cell line.

Adenovirus E2 Proteins↗

PubMed1988