Functional characterization of the nucleoporin CAN and CAN-derived leukemia-specific fusion proteins

Chromosome translocations are cytogenetically visible genetic abnormalities that are often associated with specific tumors. Characterization of the genes at the chromosome breakpoints can give insights into the processes that transform normal cells to tumor cells. The (6;9) translocation, associated with acute myeloid leukemia and myelodysplastic syndrome, fuses the DEK gene to CAN and results in the expression of a chimeric DEK-CAN gene. In a second chromosome rearrangement, found in one patient with acute undifferentiated leukemia, CAN is fused to SET. Knowledge of the normal functions of the proteins encoded by the fusion partners is indispensable in understanding the mechanisms by which DEK-CAN and SET-CAN contribute to leukemogenesis. The aim of the research described here is to define the functions of CAN, which was identified as a nuclear pore complex component (nucleoporin), and of the CAN-derived fusion proteins. This thesis starts out with an introduction about chromosome aberrations in hematopoietic malignancies, that result in the generation of fusion genes. The DEK, SET, and CAN proteins are introduced, and a number of molecular mechanisms in oncogenic transformation by fusion proteins are highlighted with examples (Chapter 1). The chapters that follow describe our experimental work concerning the functions of CAN and DEK-CAN. First, we studied the consequences of loss of CAN function after disruption of the mouse CAN gene by homologous recombination (Chapter 2). Second, the effects of CAN and DEK-CAN expression on the growth, differentiation and survival of myeloid precursor cells were investigated (Chapter 3). Third, we studied the localization of the CAN protein within the nuclear pore complex using immunoelectron microscopy (Chapter 4). An additional approach to unravel the function of CAN was to identify CAN-interacting proteins by coimmunoprecipitation (Chapter 5). Lastly, sensitive molecular detection of the (6;9) translocation was applied towards the diagnosis and follow-up of an acute myeloid leukemia patient (Chapter 6). CAN emerges from these studies as an essential factor involved in both nuclear protein import and mRNA export through the nuclear pore. These findings have implications for the possible molecular mechanism of leukemogenic transformation by the CAN-derived fusion proteins (Chapter 7).