Biomedical subjects

Stephen A Murray

Publications and source records attributed to Stephen A Murray.

8 recordsLinked to original sources

PubMed2006

Snail1 gene function during early embryo patterning in mice.

Originally identified as one of two zygotically expressed genes required for gastrulation in Drosophila, the Snail gene and other family members play critical roles in vertebrate development. Functionally, these genes are thought to drive epithelial-mesenchymal transitions at several points during development, and also during the metastatic progression of cancer. Although the Snai2-null mouse is viable and fertile, the early embryonic lethality of Snai1-null mice has precluded the detailed analysis of Snai1 function after gastrulation. We have recently generated a conditional allele of the Snai1 gene and examined its function during the formation of the neural crest and establishment of the left-right axis. We uncovered new details regarding Snai1 function during gastrulation and left-right asymmetry determination, while surprisingly showing that neither the Snai1 nor Snai2 genes are essential for neural crest cell delamination. These results shed new light on the role of Snail family genes in early mouse development, and raise interesting questions concerning the diversity of gene function among vertebrate species.

Alleles↗

PubMed2006

Snail family genes are required for left-right asymmetry determination, but not neural crest formation, in mice.

Snail family genes encode zinc finger transcriptional repressors that are key regulators of epithelial-mesenchymal transitions in vertebrates, including the transitions that generate the mesoderm and neural crest. Here, we show that, contrary to observations in frog and avian embryos, the Snail family genes Snail (Snai1) and Slug (Snai2) are not required for formation and delamination of the neural crest in mice. However, embryos with conditional inactivation of Snai1 function exhibit defects in left-right asymmetry determination. This work demonstrates that although some aspects of Snail family gene function, such as a role in left-right asymmetry determination, appear to be evolutionarily conserved, their role in neural crest cell formation and delamination is not.

Alleles↗

PubMed2006

Generation of a Snail1 (Snai1) conditional null allele.

Members of the Snail gene superfamily, which encode zinc finger transcriptional repressors, play critical roles in the establishment of the vertebrate body plan. The Snail1 (Snai1) gene promotes epithelial-mesenchymal transitions during development and disease progression, and Snai1 null mouse embryos exhibit defects in gastrulation. However, the early embryonic lethality of Snai1 null embryos precludes the study of Snai1 function in other developmental contexts or diseases. To overcome this restriction, we generated a Snai1 conditional null allele by flanking the promoter and first two exons of the Snai1 gene with loxP sites. Cre-mediated deletion of the Snai1(flox) allele generates the Snai1(del2) allele, which behaves genetically as a Snai1 null allele. This conditional null allele will enable investigation of Snai1 function in a variety of developmental and pathological contexts.

Alleles↗

PubMed2005

Increased expression of MDM2, cyclin D1, and p27Kip1 in carcinogen-induced rat mammary tumors.

It is thought that environmental pollutants, such as polycyclic aromatic hydrocarbons (PAH), contribute to human breast tumorigenesis, yet their roles remain incompletely elucidated. The prototypical PAH 7,12-dimethylbenz(alpha)anthracene (DMBA) specifically and effectively induces mammary tumor formation in rodent models. In an attempt to explore the molecular mechanisms by which PAH initiates and promotes mammary tumorigenesis, we examined the expression of several cell cycle regulators in rat mammary tumors induced by DMBA. Expression of cyclin D1, murine double minute-2 (MDM2), and Akt was up-regulated in tumors in comparison to normal mammary glands, as indicated by RT-PCR, Western blot analysis, and immunohistochemical staining. Expression of p27Kip1 protein was also elevated in the tumors with increased cytoplasmic localization. However, RB protein remained hyperphosphorylated. To directly test the effects of DMBA, the MCF-7 human breast cancer cells were treated. DMBA induced MDM2 expression in a dose- and time-dependent fashion in the MCF-7 cells, and this activation appeared to be p53 dependent. These data suggest that activation of cyclin D1, MDM2, and AKT as well as increased expression and cytoplasmic localization of p27Kip1 may play a role in this model of environmental pollutant-induced mammary tumorigenesis.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2003

The MDM2 RING finger is required for cell cycle-dependent regulation of its protein expression.

The MDM2 oncoprotein is overexpressed in many human tumors and cancers. MDM2 functions as an E3 ligase for p53 and for itself. MDM2 also interacts with the retinoblastoma protein (RB) and the transcription factor E2F1 to promote cell cycle S-phase entry. Here, we report that MDM2 protein expression is cell cycle-regulated, which is dependent on its RING finger domain and requires Lys446. We show that MDM2 protein is stabilized at S phase. In addition, overexpression of MDM2 results in stimulation of E2F activity and accumulation of cells in S phase. These data suggest that ubiquitination of MDM2 is cell cycle-regulated and that MDM2 may play a role in cell cycle progression.

Apoptosis↗

PubMed2003

IGF-1 activates p21 to inhibit UV-induced cell death.

The insulin-like growth factor-1 (IGF-1) and its downstream effector Akt have been documented as survival factors in response to a variety of stress signals. In this study, we show that IGF-1 activates p21 protein expression in a p53-dependent manner. Inhibition of PI-3 kinase or ectopic expression of a dominant-negative Akt blocks the effect of IGF-1 on the upregulation of p21 expression. In addition, IGF-1 prevents the UV irradiation-mediated suppression of p21 and MDM2 expression. Furthermore, p21 is important for IGF-1-mediated cell survival upon UV irradiation. Taken together, these data indicate that IGF-1 may activate p21 in executing its survival function upon genotoxic insults.

Animals↗

PubMed2003

Deregulation of Cdc2 kinase induces caspase-3 activation and apoptosis.

Progression of the cell cycle and control of apoptosis are tightly linked processes. It has been reported that manifestation of apoptosis requires cdc2 kinase activity yet the mechanism(s) of which is largely unclear. In an attempt to study the role of human MDM2 (HDM2) in interphase and mitosis, we employed the Xenopus cell-free system to study HDM2 protein stability. Interestingly, HDM2 is specifically cleaved in Xenopus mitotic extracts but not in the interphase extracts. We demonstrate that HDM2 cleavage is dependent on caspase-3 and that activation of cdc2 kinase results in caspase-3 activation in the Xenopus cell-free system. Furthermore, expression of cdc2 kinase in mammalian cells leads to activation of caspase-3 and apoptosis. Taken together, these data indicate that deregulation of cdc2 kinase activity can trigger apoptotic machinery that leads to caspase-3 activation and apoptosis.

Animals↗

PubMed2002

The prolyl isomerase Pin1 is a regulator of p53 in genotoxic response.

p53 is activated in response to various genotoxic stresses resulting in cell cycle arrest or apoptosis. It is well documented that DNA damage leads to phosphorylation and activation of p53 (refs 1-3), yet how p53 is activated is still not fully understood. Here we report that DNA damage specifically induces p53 phosphorylation on Ser/Thr-Pro motifs, which facilitates its interaction with Pin1, a member of peptidyl-prolyl isomerase. Furthermore, the interaction of Pin1 with p53 is dependent on the phosphorylation that is induced by DNA damage. Consequently, Pin1 stimulates the DNA-binding activity and transactivation function of p53. The Pin1-mediated p53 activation requires the WW domain, a phosphorylated Ser/Thr-Pro motif interaction module, and the isomerase activity of Pin1. Moreover, Pin1-deficient cells are defective in p53 activation and timely accumulation of p53 protein, and exhibit an impaired checkpoint control in response to DNA damage. Together, these data suggest a mechanism for p53 regulation in cellular response to genotoxic stress.

Amino Acid Motifs↗