Biomedical subjects

Joanna K Sax

Publications and source records attributed to Joanna K Sax.

6 recordsLinked to original sources

PubMed2004

Bnip3L is induced by p53 under hypoxia, and its knockdown promotes tumor growth.

p53-dependent apoptosis is a major determinant of its tumor suppressor activity and can be triggered by hypoxia. No p53 target is known to be induced by p53 or to mediate p53-dependent apoptosis during hypoxia. We report that p53 can directly upregulate expression of Bnip3L, a cell death inducer. During hypoxia, Bnip3L is highly induced in wild-type p53-expressing cells, in part due to increased recruitment of p53 and CBP to Bnip3L. Apoptosis is reduced in hypoxia-exposed cells with functional p53 following Bnip3L knockdown. In vivo, Bnip3L knockdown promotes tumorigenicity of wild-type versus mutant p53-expressing tumors. Thus, Bnip3L, capable of attenuating tumorigenicity, mediates p53-dependent apoptosis under hypoxia, which provides a novel understanding of p53 in tumor suppression.

Animals↗

PubMed2003

Identification and characterization of the cytoplasmic protein TRAF4 as a p53-regulated proapoptotic gene.

The role of p53 in tumor suppression partly relies on its ability to transcriptionally regulate target genes involved in the initiation of cell cycle arrest or the activation of programmed cell death. In recent years many genes have been identified as p53-regulated genes; however, no single target gene has been shown to be required for the full apoptotic effect. We have identified TRAF4 as a p53-regulated gene in a microarray screen using a Murine 11K Affymetrix GeneChip hybridized with cRNA from the p53 temperature-sensitive cell line, Vm10. TRAF4 is a member the TRAF family of adaptor proteins that mediate cellular signaling by binding to various members of the tumor necrosis family receptor superfamily and interleukin-1/Toll-like receptor super-family. In contrast to its other family members, TRAF4 has not been shown to bind to a member of the tumor necrosis factor receptor superfamily in vivo, nor has it been shown to regulate signaling pathways common to its other family members. Therefore the role of TRAF4 in a signaling pathway has not yet been established and requires further study. TRAF4 is specifically regulated by p53 in response to temperature sensitive p53, overexpression of p53 by use of an adenovirus, and stabilization of p53 in response to DNA damage. The murine TRAF4 promoter contains a functional p53 DNA-binding site approximately 1 kilobase upstream of the initiating methionine. TRAF4 localizes to the cytoplasm and appears to remain in the cytoplasm following DNA damage. Interestingly, the overexpression of TRAF4 induces apoptosis and suppresses colony formation. These data suggest a correlation that the orphan adaptor protein TRAF4 may play a role in p53-mediated proapoptotic signaling in the response to cellular stress.

Adenoviridae↗

PubMed2003

p53-induced gene expression analysis.

Researchers in the p53 field have successfully used many high-throughput screening technologies to analyze and characterize p53-induced gene expression. This chapter will focus on one such technology, the Affymetrix GeneChip. DNA-Chip technology has grown rapidly over the last several years. The ability to hybridize RNA from a sample to thousands to tens of thousands of known and unknown cDNAs spotted on a microarray chip has led to the explosion of information ranging from macro-global expression pattern changes to micro-gene-specific expression changes. The relative ease of making a nonradioactive probe from either total RNA or mRNA to be hybridized to a GeneChip makes microarray technology highly attractive.

Animals↗

PubMed2002

BID regulation by p53 contributes to chemosensitivity.

The role of the p53 protein (encoded by TP53) in tumour suppression relies partly on the ability of p53 to regulate the transcription of genes that are important in cell-cycle arrest and in apoptosis. But the apoptotic pathway mediated by p53 is not fully understood. Here we show that BID, a member of the pro-apoptotic Bcl-2 family of proteins, is regulated by p53. BID mRNA is increased in a p53-dependent manner in vitro and in vivo, with strong expression in the splenic red pulp and colonic epithelium of gamma-irradiated mice. Both the human and the mouse BID genomic loci contain p53-binding DNA response elements that bind p53 and mediate p53-dependent transactivation of a reporter gene. In addition, BID-null mouse embryonic fibroblasts are more resistant than are wild-type fibroblasts to the DNA damaging agent adriamycin and the nucleotide analogue 5-fluorouracil, both of which stabilize endogenous p53. Our results indicate that BID is a p53-responsive 'chemosensitivity gene' that may enhance the cell death response to chemotherapy.

Adenoviridae↗

PubMed2002

The cyclin-dependent kinase inhibitor butyrolactone is a potent inhibitor of p21 (WAF1/CIP1 expression).

Butyrolactone I (BL) is a competitive inhibitor of ATP for binding and activation of cyclin-dependent kinases and is a potent inhibitor of cell cycle progression. Treatment of H460 human lung and SW480 human colon cancer cells with doses of BL that exceed the Ki for CDK inhibition but which are much lower than doses required to inhibit MAPK, PKA, PKC, or EGFR lead to a rapid significant reduction of endogenous p21 protein expression. BL-dependent inhibition of p21 expression appears to be p53-independent. BL-dependent p21 degradation was blocked by lactacystin, consistent with the hypothesis that there is accelerated p21 proteasomal degradation in the presence of BL. BL also inhibited the p53-dependent increase of p21 protein expression in cells exposed to the DNA damag-ing agent etoposide, and favored a greater G2/M arrest as compared to the non-BL exposed cells. BL accelerated the degradation of exogenously expressed p21 that was not observed with a C-terminal truncated form of p21. Degradation of exogenous p21 led to a shift to G2 accumulation in the cells exposed to BL. We conclude that BL has effects on the cell cycle beyond its role as a CDK inhibitor and can be used as a novel tool to study the mechanism of p21 degradation and the consequences towards p21- dependent checkpoints.

Acetylcysteine↗

PubMedDate not supplied

Microarray expression profiling of p53-dependent transcriptional changes in an immortalized mouse embryo fibroblast cell line.

The ability of p53 to transcriptionally regulate genes involved with cell cycle progression and apoptosis is critical to its role as a tumor suppressor. Although numerous p53 regulated genes have been identified over the last several years, ablation of any one of these genes cannot account for the full p53-mediated cellular response. Therefore, we performed microarray analysis using two related p53 temperature sensitive cell lines, Val5 and Vm10, to identify novel p53 regulated genes. The Val5 cells undergo p53-mediated cell cycle arrest and the Vm10 cells undergo p53-mediated apoptosis when p53 is in the wild-type conformation. By using these two cell lines, we can compare which genes are regulated by p53 in two different conditions as well as analyze which genes are common to both cell lines. Using the information obtained in the microarray analysis, we confirmed whether a small sub-set of the genes was regulated by p53 using northern blot analysis. By identifying and confirming the regulation of specific genes by p53, we can further characterize biologically why p53 transcriptionally regulates these genes.

Animals↗