Focus on mechanisms of genomic instability
Our laboratory is interested in the molecular mechanisms of cellular immortalization and transformation. We perform in vitro and in vivo analyses in order to understand the molecular and genomic alterations involved in neoplastic transformation. We study mouse models in order to examine early genomic changes during malignant transformation. Furthermore, we study the initiating events of genomic instability and its progression in cancer patients.
c-Myc-dependent genomic instability
A focus of our research has been on the role of the oncoprotein c-Myc in genomic instability. We were the first to demonstrate that the deregulated expression of this oncoprotein is associated with karyotypic and locus-specific genomic instability. We have identified several genes that are targets of c-Myc in genomic instability and these include dihydrofolate reductase (DHFR), cyclin D2, ribonucleotide reductase R2 (R2) and carbamoyl-phosphate synthetase-aspartate transcarbamoyl-dihydroorotase (CAD) genes.
c-Myc-dependent genomic instability has been observed in cell lines of different species and tissue origins, and also in vivo. DHFR gene amplification was found within the first week of pristane-induced c-Myc-dependent plasmacytomas in Balb/c mice. Moreover, we observed the spontaneous c-Myc deregulation in 5-15% of all hematopoietic cells of the fetal liver of p53 nullizygous (p53-/-) embryos as well as in the bone marrow, spleen, thymus, and primary fibroblasts of 4-6 week old p53 nullizygous (p53-/-) mice. The deregulation of c-Myc was associated with the locus-specific amplification of c-Myc target genes. In contrast, age-matched control mice (p53+/+) did not display genomic instability and c-Myc deregulation.
Mechanisms of c-Myc deregulation in translocation-negative plasmacytomas
The activation of the c-myc gene is key to the development of all murine plasmacytomas (PCTs), resulting in deregulated levels of endogenous c-Myc protein expression. In the majority of pristane-induced mouse PCTs, the deregulation of c-myc transcription is achieved by chromosomal translocation that juxtaposes the c-myc/pvt-1 locus on chromosome 15 to one of the immunoglobulin (Ig) loci: on chromosome 12 (IgH), 6(IgK) or 16(IgL).
Several translocation-negative PCTs with deregulated Myc expression have been described. The histological features of such PCTs and the course of disease are indistinguishable from the ones with the typical chromosomal translocations. We have recently studied a translocation-negative mouse plasmacytoma, DCPC21, in great detail (Wiener et al., Proc. Natl. Acad. Sci. (USA) 96: 13967-13972, 1999) (see Fig.1). We have found that c-myc is juxtaposed to IgH on extrachromosomal elements (EEs). These EEs are functional genetic units able to transcribe c-myc as shown in mRNA track studies on the single cell level. This is further supported by the presence of active chromatin on these extrachromosomal DNA molecules. We have shown in addition, that the c-myc/IgH-containing EEs are able to confer c-Myc expression to non-proliferating B cells upon extrachromosomal gene transfer. Interestingly, when introduced into primary B cells, the c-myc/IgH-carrying EEs induce cell death in the majority of the target cells within 24 hours.
Development of novel technologies to study genomic instability
Manitoba Inst Cell Biology
675 McDermot Av
Winnipeg MB CANADA
Tel: 204 787 2135
Fax: 204 787 4125