Biomedical subjects

Kenneth Fernandes

Publications and source records attributed to Kenneth Fernandes.

3 recordsLinked to original sources

PubMed2006

Tumor susceptibility and apoptosis defect in a mouse strain expressing a human p53 transgene.

Activation of apoptosis is believed to be critical for the role of p53 as a tumor suppressor. Here, we report a new mouse strain carrying a human p53 transgene in the mouse p53-null background. Expression of human p53 in these mice was comparable with wild-type murine p53; however, transactivation, induction of apoptosis, and G(1)-S checkpoint, but not transrepression or regulation of a centrosomal checkpoint, were deregulated. Although multiple functions of p53 were abrogated, mice carrying the human p53 transgene did not show early onset of tumors as typically seen for p53-null mice. In contrast, human p53 in the p53-null background did not prevent accelerated tumor development after genotoxic or oncogenic stress. Such behavior of human p53 expressed at physiologic levels in transgenic cells could be explained by unexpectedly high binding with Mdm2. By using Nutlin-3a, an inhibitor of the interaction between Mdm2 and p53, we were able to partially reconstitute p53 transactivation and apoptosis in transgenic cells. Our findings indicate that the interaction between p53 and Mdm2 controls p53 transcriptional activity in homeostatic tissues and regulates DNA damage- and oncogene-induced, but not spontaneous, tumorigenesis.

Animals↗

PubMed2005

p53 isoforms can regulate p53 transcriptional activity.

The recently discovered p53-related genes, p73 and p63, express multiple splice variants and N-terminally truncated forms initiated from an alternative promoter in intron 3. To date, no alternative promoter and multiple splice variants have been described for the p53 gene. In this study, we show that p53 has a gene structure similar to the p73 and p63 genes. The human p53 gene contains an alternative promoter and transcribes multiple splice variants. We show that p53 variants are expressed in normal human tissue in a tissue-dependent manner. We determine that the alternative promoter is conserved through evolution from Drosophila to man, suggesting that the p53 family gene structure plays an essential role in the multiple activities of the p53 family members. Consistent with this hypothesis, p53 variants are differentially expressed in human breast tumors compared with normal breast tissue. We establish that p53beta can bind differentially to promoters and can enhance p53 target gene expression in a promoter-dependent manner, while Delta133p53 is dominant-negative toward full-length p53, inhibiting p53-mediated apoptosis. The differential expression of the p53 isoforms in human tumors may explain the difficulties in linking p53 status to the biological properties and drug sensitivity of human cancer.

Alternative Splicing↗

PubMed2003

Conservation of IGF2-H19 and IGF2R imprinting in sheep: effects of somatic cell nuclear transfer.

In different mammalian species, in vitro culture and manipulation can lead to aberrant fetal and peri-natal development. It has been postulated that these diverse abnormalities are caused by epigenetic alterations and that these could affect genes that are regulated by genomic imprinting. To explore this hypothesis relative to somatic cell nuclear transfer in sheep, we investigated whether the ovine H19-IGF2 and IGF2R loci are imprinted and analysed their DNA methylation status in cloned lambs. A comparison between parthenogenetic and control concepti established that imprinting at these two growth-related loci is evolutionarily conserved in sheep. As in humans and mice, IGF2R and H19 comprise differentially methylated regions (DMRs) that are methylated on one of the two parental alleles predominantly. In tongue tissue from 12 out of 13 cloned lambs analysed, the DMR in the second intron of IGF2R had strongly reduced levels of DNA methylation. The DMR located upstream of the ovine H19 gene was found to be similarly organised as in humans and mice, with multiple CTCF binding sites. At this DMR, however, aberrant methylation was observed in only one of the cloned lambs. Although the underlying mechanisms remain to be determined, our data indicate that somatic cell nuclear transfer procedures can lead to epigenetic deregulation at imprinted loci.

Alleles↗