Cyclin A1 Expression and Regulation in Hematopoietic and Leukemic Cells

Sammanfattning: Increased expression of the cell cycle regulatory protein cyclin A1 has previously been detected in patients with acute myeloid leukemia (AML) and targeted overexpression of cyclin A1 in a transgenic mouse model initiated AML. The aim of this thesis was to further study the expression and regulation of cyclin A1 in hematopoietic cells. We started with evaluating the subcellular localization of cyclin A1 and found that the protein was localized to the nucleus of normal early hematopoietic cells while it had a cytoplasmic localization in leukemic bone marrow cells as well as in leukemic cell lines. We further found that treatment with all-trans retinoic acid (ATRA) resulted in nuclear localization of cyclin A1 in U-937 cells and in the formation of complex between cyclin A1, CDK1 and RAR?. Our results indicate that the cytoplasmic localization of cyclin A1 correlates with a leukemic phenotype. Next we continued with analyzing the clinical relevance of the increased cyclin A1 expression in 40 AML patients. We found that patients with high levels of cyclin A1 had a significantly worse overall survival and a significantly lower disease-free survival compared to patients with low levels of cyclin A1. We continued with analyzing the correlation between cyclin A1 and drug induced apoptosis. Induction of apoptosis using ATRA, staurosporine and TNF? resulted in significantly increased cyclin A1 protein levels in contrast to decreased levels of other cell cycle regulatory proteins. Interestingly, the increased protein levels did not result from increased protein synthesis but was rather a result from decreased ubiquitination and degradation. Further, upon overexpression of cyclin A1 a significant increased amount of apoptotic cells was found. Our results also suggest that there is an association between the post-translational modifications of cyclin A1 protein and the induction of apoptosis by therapeutic agents.