Mechanisms of human LINE-1 retrotransposition and DNA repair

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LINE-1 elements (L1) represent about 17% of the human genome and play a major part in shaping the mammalian genome, not only through their own expansion but also through the mobilization of non-L1 sequences. Despite the clearly demonstrated impact this group of active, mobile elements has on structure, organization and stability of mammalian genomes and the diseases that are caused by their action, only few laboratories investigate the biology of L1 retrotransposition worldwide. We want to elucidate the mechanisms of human LINE-1 retrotransposition and identify the components that are involved in this genome shaping process. The process of L1 integration can be devided into "Target-Primed Reverse Transcription" (TPRT), which describes the initiating step of L1 replication, integration and minus-strand synthesis, and plus-strand synthesis that is not understood so far. Our first goal is to determine L1-encoded gene products and host factors that are involved in the insertion of a new L1 copy into the genome and shed light on the mechanism of L1 integration. We will attempt to reveal details about the mechanism of plus-strand synthesis of L1 retrotransposition by analysis of target site duplications from L1- and Alu insertions, preexisting in the genome of human cells. Since DNA damage caused by L1-specific endonuclease activity is repaired by the host as part of the L1 integration process, we want to identify those factors of the host´s repair mechanisms that take part in Double-Strand Break repair linked to L1 retrotransposition. If the host´s DNA repair mechanism is impaired, L1 activity is causing chromosomal damage. Furthermore, first indications exist for an upregulation of L1 expression in tumor cells. Therefore, it is our second goal to systematically characterize the expression of functional L1 elements in cancer cell lines and evaluate the effect of L1 retrotransposition on large-scale genome rearrangements underlying cancerogenic events.