| dc.description.abstract | Chromosomal instability (CIN), an unstable genome induced by mitotic dysfunction and unfaithful chromosome segregation, plays a pivotal role in cancer initiation and progression. However, the various upstream events that lead to mitotic dysfunction and how they ultimately result in tumorigenesis are still poorly understood. Prior publications and studies from the laboratory focused on Ewing sarcoma, a pediatric malignant bone cancer caused by a chromosomal translocation which leads to the expression of an aberrant fusion protein (EWS-FLI1). In addition to the well-studied role of EWS-FLI1 as an aberrant transcription factor, EWS-FL1 induces defects in midzone formation during mitosis. The midzone is a midline structure formed between segregating chromosomes during anaphase, and it consists of the central spindle along with associated midzone proteins. Among these midzone proteins, Aurora-B (kinase) was found to be an integral player in phosphorylating various checkpoint molecules involved in cell cycle regulation thus ensuring proper chromosome segregation. The inability of Aurora-B to locate to the midzone in a timely manner during anaphase has been known to cause failure during the process of cytokinesis and results in induction of aneuploidy. Previous studies in the lab had demonstrated that EWS-FLI1 interacted with wildtype EWS and inhibited its function in a dominant negative manner. Wildtype EWS is known to interact with Aurora-B and recruit it to the midzone; therefore, inhibiting its function could result in mitotic defects. Our studies provided insight into the mechanism by which EWS-FLI1 regulates mitosis, which is of importance as mitotic defects can lead to chromosomal instability, aneuploidy and ultimately tumorigenesis. Interestingly, EWS is also fused to a number of different transcription factors and is thought to induce various types of sarcoma. For example, EWS-ATF1 is expressed in clear cell sarcoma, EWS-WT1 is expressed in desmoplastic round cell sarcoma and EWS-SP3 is expressed in undifferentiated round cell sarcoma. Each of these fusions retain the transactivation domain of EWS and are fused to the DNA binding domain of the transcription factor. Since all of the EWS fusion proteins retain the same N terminus region of EWS there could be some mechanisms that are conserved between the fusion proteins. My data suggest that all three EWS fusion proteins (EWS-ATF1, EWS-WT1 and EWS-SP3) induce mis-localization of Aurora-B at the midzone during anaphase. This could lead to uneven distribution of chromosomes in the daughter cells, and result in high incidence of aneuploidy, a hallmark of cancer. Since Aurora-B is known to localize to the chromosome during early stages of mitosis the EWS- fusion proteins may interact with Aurora-B and inhibit its function during early stages of mitosis. To obtain a better mechanistic understanding behind the mis-localization of Aurora-B, the localization patterns of the EWS fusion proteins were analyzed during early stages of mitosis by immunocytochemistry. As a result, all three EWS fusion proteins localized to the chromosome with varying degrees of chromosomal localization; EWS-ATF1 and EWS-FLI1 displayed high level of chromosomal localization, whereas EWS-WT1 and EWS-SP3 displayed low level of chromosomal localization. Despite variation in the degree of the chromosomal localization of EWS fusion proteins, all proteins induced mitotic dysregulation, characterized by mis-localization of Aurora-B during anaphase. Taken together, my study results support a novel mechanism that the molecular pathogenesis of the EWS fusion expressing sarcomas are mediated by a common mechanism of mitotic dysfunction. | |
