Regulation of activation induced deaminase

Activation Induced Deaminase (AID) belongs to the protein family of DNA deaminases, which catalyse the deamination of the cytosine residues in single stranded DNA, resulting in the formation of deoxy-uracils. The enzymatic activity of AID is required for the immunoglobulin gene modifications by class switch recombination (CSR), somatic hypermutation (SHM) and gene conversion (iGC). While being essential for antibody diversification, the activity of AID can be harmful for the organism due to its direct mutagenic activities and induction of genomic instability. This thesis investigates AID regulation both, on the level of gene expression and its interaction partners, and the DNA repair pathways triggered by AIDmediated DNA deamination. Firstly, I have identified estrogen and progesterone as regulators of AID expression. This is achieved via direct binding of estrogen and progesterone receptors to AID promoter. Estrogen leads to an induction of AID expression and increase in AID-mediated downstream pathways – SHM, CSR as well as oncogenic translocations between Ig and c-myc loci. In contrast, progesterone results in a decrease in AID expression and an attenuation of its downstream pathways. Secondly, by generating DT40 cell lines with endogenously tagged AID, we used co-immunoprecipitation and subsequent mass spectrometry for identifying proteins that form a complex with AID in the cytoplasm, nucleoplasm and chromatin. The results of this approach gave us possible insight into the mechanistic process of AID-mediated DNA deamination in vivo, suggesting that chromatin bound AID resides in a complex with elongating RNA polymerase II. Thirdly, by expressing AID in meiotic recombination deficient fission yeast and nematode, we have established that a meiotic cell can process a base mismatch, using the base excision repair machinery, to give rise to meiotic recombination. This suggests that meiotic cells can process lesions other than Spo-11 induced DSBs for recombination

DNA deaminases: AIDing hormones in immunity and cancer

It is well established that hormones can cause cancer, much less known is how they induce this change in our somatic cells. This review highlights the recent finding that estrogen can exert its DNA-damaging potential by directly activating DNA deaminases. This recently discovered class of proteins deaminate cytosine to uracil in DNA, and are essential enzymes in the immune system. The enhanced production of a given DNA deaminase, induced by estrogen, can lead not only to a more active immune response, but also to an increase in mutations and oncogenic translocations. Identifying the direct molecular link between estrogen and a mutation event provides us with new targets for studying and possibly inhibiting the pathological side-effects of estrogen

Kinetic Theory Approach to Modeling of Cellular Repair Mechanisms under Genome Stress

Under acute perturbations from outer environment, a normal cell can trigger cellular self-defense mechanism in response to genome stress. To investigate the kinetics of cellular self-repair process at single cell level further, a model of DNA damage generating and repair is proposed under acute Ion Radiation (IR) by using mathematical framework of kinetic theory of active particles (KTAP). Firstly, we focus on illustrating the profile of Cellular Repair System (CRS) instituted by two sub-populations, each of which is made up of the active particles with different discrete states. Then, we implement the mathematical framework of cellular self-repair mechanism, and illustrate the dynamic processes of Double Strand Breaks (DSBs) and Repair Protein (RP) generating, DSB-protein complexes (DSBCs) synthesizing, and toxins accumulating. Finally, we roughly analyze the capability of cellular self-repair mechanism, cellular activity of transferring DNA damage, and genome stability, especially the different fates of a certain cell before and after the time thresholds of IR perturbations that a cell can tolerate maximally under different IR perturbation circumstances

Insights into APC/C: from cellular function to diseases and therapeutics

Anaphase-promoting complex/cyclosome (APC/C) is a multifunctional ubiquitin-protein ligase that targets different substrates for ubiquitylation and therefore regulates a variety of cellular processes such as cell division, differentiation, genome stability, energy metabolism, cell death, autophagy as well as carcinogenesis. Activity of APC/C is principally governed by two WD-40 domain proteins, Cdc20 and Cdh1, in and beyond cell cycle. In the past decade, the results based on numerous biochemical, 3D structural, mouse genetic and small molecule inhibitor studies have largely attracted our attention into the emerging role of APC/C and its regulation in biological function, human diseases and potential therapeutics. This review will aim to summarize some recently reported insights into APC/C in regulating cellular function, connection of its dysfunction with human diseases and its implication of therapeutics

Coevolution of the cell cycle and deferred-use cells

The cell cycle and cell fate decisions are interlinked in a broad range of developmental contexts in many organisms. Coordination of stem cell proliferation and differentiation is essential for normal development, organ homeostasis, and tissue repair through a direct interplay between cell cycle progression and differentiation in somatic stem cells in the skin, brain, gut, and hematopoietic system. The connection between cell cycle and cell fate decisions is present across the whole evolutionary tree. Human embryonic stem cells have an interconnection between cell cycle, self-renewal, and differentiation, while they exert a metastable state with heterogeneity at the single cell level. The cell cycle is tightly intertwined with cell fate decisions in diverse species ranging from yeast to human. Particularly important insight to the processes coordinating cell fate and the cell cycle has been derived from pluripotent stem cells

Regulation of activation induced deaminase (AID) by estrogen

Regulation of Activation Induced Deaminase (AID) by the hormone estrogen has important implications for understanding adaptive immune responses as well as the involvement of AID in autoimmune diseases and tumorigenesis. This chapter describes the general laboratory techniques for analyzing AID expression and activity induced by estrogen, focusing on the isolation and preparation of cells for hormone treatment and the subsequent analysis of AID responsiveness to estrogen at the RNA level and for determining the regulation of AID activity via estrogen by analyzing Ig switch circle transcripts and mutations in switch region loci