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Research Description:
Cancer in adults is thought to occur through an accumulation of mutations in a single cell. Mathematical modeling has suggested that 4-7 mutational "hits" are required for the development of most adult tumors. Because time is required for the accumulation of mutations, the incidence of cancer increases with age.
Cancer in children is very different from cancer in adults. For example, children get different types of cancers than adults do. Adult cancers are often genetically unstable, with very abnormal chromosomal complements, while pediatric cancers often have relatively normal karyotypes. Finally, the age distribution of pediatric versus adult tumors is distinct. These and other data raise the possibility that pediatric tumors do not occur as a simple consequence of an accumulation of mutations.
We are focusing on Ewing's sarcoma as a prototypic pediatric cancer. Ewing's sarcoma is a pediatric tumor of uncertain histologic origin that is defined by the presence of a specific chromosomal rearrangement, t(11;22)(q24;q12). This translocation generates the EWS/FLI fusion oncogene. EWS/FLI is an aberrant transcription factor that dysregulates expression of downstream targets. The full complement of these targets, and their roles in the transformation process is unknown. Additionally, while EWS/FLI expression appears to be required for Ewing's sarcoma development, it is unlikely to be the only genetic alteration present in this tumor.
Our research interests involve two main goals: (1) to understand the mechanism of action of EWS/FLI, and (2) to understand what additional genetic events are required in the genesis of Ewing's sarcoma.
We have been using model systems to modulate EWS/FLI expression, and interrogating the transcriptional consequences of EWS/FLI expression using oligonucleotide microarrays. In this way we have identified many genes whose expression is altered by the fusion protein. We have been analyzing these genes for their role in oncogenic transformation using a variety of tools, including knockdown with RNAi, expression of dominant-negatives, and overexpression. Phenotypic consequences are analyzed using a variety of techniques including soft-agar assays and xenografts to assess oncogenic transformation. The ultimate goal of these experiments is to develop a comprehensive understanding of the transcriptional program triggered by EWS/FLI, and how that program leads to cancer.
We have also utilized microarrays to identify putative tumor suppressor pathways that must be abrogated to develop Ewing's sarcoma. As an example, we have identified transcriptional upregulation of the p53 tumor suppressor in response to EWS/FLI in a model system. This suggests that the p53 pathway must be disrupted in the course of development of Ewing's sarcoma. This hypothesis is supported by the finding of mutations in components of the p53 pathway in the majority of Ewing's sarcoma.
In addition to our studies on p53, we have begun to analyze other genes and pathways for their role in cooperating with EWS/FLI to cause Ewing's sarcoma. We have performed mutational screening on various candidate genes in this disease. We plan to analyze the functional consequences of the mutations we've identified, and to assess whether they play a role in tumor development.
We believe that an in-depth understanding of Ewing's sarcoma will help us to understand the mechanisms by which tumors develop in children. Such an understanding will be instrumental in the development of new therapies for these diseases. In this way we hope to make a real impact in the care of children with cancer.
References:
1. Gozani, O, Karuman, P, Jones, DR, Ivanov, D, Cha, J, Lugovskoy, AA, Baird, CL, Zhu, H, Field, SJ, Lessnick, SL, Villasenor, J, Mehrotra, B, Chen, J, Rao, VR, Brugge, JS, Ferguson, CG, Payrastre, B, Myszka, DG, Cantley, LC, Wagner, G, Divecha, N, Prestwich, GD, and Yuan, J. (2003) The PHD Finger of the Chromatin-Associated Protein ING2 Functions as a Nuclear Phosphoinositide Receptor. Cell 114: 99-111.
2. Dolma, S, Lessnick, SL, Hahn, WC, and Stockwell, BR. (2003) Identification of genotype-selective anti-tumor agents using synthetic lethal chemical screening in engineered human tumor cells. Cancer Cell 3:285-296.
3. Widlund, HR, Horstmann, MA, Price, ER, Cui, J, Lessnick, SL, Wu, M, He, X, and Fisher, DE. (2002) b-Catenin-induced melanoma growth requires the downstream target Microphthalmia-associated transcription factor. J Cell Biol 158:1079-1087.
4. Lessnick, SL, Dacwag, CS, and Golub, TR. (2002) The Ewing's sarcoma oncoprotein EWS/FLI induces a p53-dependent growth arrest in primary human fibroblasts. Cancer Cell 1:393-401.
5. Braun BS, Frieden R, Lessnick SL, May WA, Denny CT. (1995) Identification of target genes for the Ewing's sarcoma EWS/FLI fusion protein by representational difference analysis. Mol Cell Biol 15:4623-4630.
6. Lessnick SL, Braun BS, Denny CT, May WA. (1995) Multiple domains mediate transformation by the Ewing's sarcoma EWS/FLI-1 fusion gene. Oncogene 10:423-431.
7. Sorensen PHB, Lessnick SL, Lopez-Terrada D, Liu XF,Triche TJ, Denny CT. (1994) A second Ewing's sarcoma translocation, t(21;22), fuses the EWS gene to another ETS-family transcription factor, ERG. Nature Genet 6:146-151.
8. May WA, Lessnick SL, Braun BS, Klemsz M, Lewis BC, Lunsford LB, Hromas R, Denny CT. (1993) The Ewing's sarcoma EWS/FLI-1 fusion gene encodes a more potent transcriptional activator and is a more powerful transforming gene than FLI-1. Mol Cell Biol 13:7393-7398.
9. May WA, Gishizky ML, Lessnick SL, Lunsford LB, Lewis BC, Delattre O, Zucman J, Thomas G, Denny CT. (1993) Ewing sarcoma 11;22 translocation produced a chimeric tarnscription factor that requires the DNA-binding domain encoded by FLI1 for transformation. Proc Natl Acad Sci USA 90:5752-5756.
Research Keywords:
Cancer Biology, EWS/FLI, Ewing's Sarcoma, Microarrays, Molecular Biology, Oncogenes, Pediatric Cancer, Transcription, Tumor Suppressors