Ubiquitin-dependent and -independent functions of Myosin VI – Characterization of a molecular motor protein in DNA-replication and -repair and immune signaling

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Unconventional Myosins are actin-based molecular motor proteins responsible for intracellular vesicle transport, structural maintenance and force-generating processes. Myosin VI represents a unique member of the myosin superfamily because it moves in a direction opposite to all other myosins analysed so far. It is involved in various signalling pathways (e.g. endocytosis, secretion, autophagy, etc.) where its deregulation is often correlated with human diseases. In prostate and ovarian carcinoma, myosin VI belongs to the most heavily upregulated genes. Next to its cytoplasmic localization, Myosin VI was also found to be present in the nucleus, although its nuclear functions are poorly characterised.During my first postdoc in the laboratory of Dr. Simona Polo we identified two ubiquitin binding domains (UBDs) within the tail domain of Myosin VI (MIU and MyUb). Insertion of an alternatively spliced element between these two UBDs can lead to the formation of at least three different Myosin VI isoforms. We found that Myosin VI isoforms containing this spliced insert mainly interact with components of the endocytic machinery whereas the isoform without insert binds many nuclear interactors. Interestingly, cancer cells selectively express the short isoform, indicating that mainly nuclear functions of Myosin VI associate with oncogenesis. In the laboratory of Prof. Helle Ulrich (in collaboration with Petra Beli) I confirmed and specified the interactions of the short isoform of Myosin VI with nuclear proteins involved in fundamental genome maintenance pathways such as DNA repair, DNA replication and immune signalling. Furthermore, using cell culture experiments I was able to demonstrate functional importance for Myosin VI in the aforementioned pathways in which I show a DNA dependent Myosin VI localization on filamentous structures in the nucleus.The aim of this project is to investigate the yet poorly understood functions of Myosin VI in the nucleus but also in the cytoplasm with a focus on DNA replication and –repair as well as immune signalling. Characterization of ubiquitin-dependent processes should reveal molecular mechanisms of the Myosin VI regulated pathways. We expect novel insights on how the cytoskeleton interacts with chromatin and its influence on the dynamics of nuclear processes. Results obtained from this project should provide fundamental knowledge to understand the pathological events during oncogenesis in prostate and ovarian carcinomas and hence help to identify new molecular targets for cancer therapy.