Small Cajal body-associated RNA 2 and RNA-binding protein WRAP53β in DNA repair and Hoyeraal-Hreidarsson syndrome

Sammanfattning: The DNA in our cells can be damaged through many different mechanisms and correct repair of DNA lesions is of utmost importance to ensure genomic integrity and prevent alteration in the genetic code contributing to diseases such as cancer, neurodegenerative disorders and premature aging. Non-coding RNAs were for a long time considered as non-functional transcriptional byproducts. This view has changed dramatically over the last decades where numerous functions have been assigned to non-coding RNAs including regulation of gene expression, genome organization and DNA repair to mention only a few. In paper I we show that mutations in the RNA-binding protein WD40 repeat-containing antisense to p53 b (WRAP53b) can cause Hoyeraal-Hreidarsson syndrome, a disease presenting itself by progressive telomere shortening, skin abnormalities, bone marrow failure and brain defects. Characterization of the disease-causing mutations reveal that they affect interactions between WRAP53b, Cajal body components and the telomerase complex as well as alter the cellular localization of this protein and its normal function in the DNA damage response. In paper II we study the role of small Cajal-body associated RNA2 (scaRNA2) in the repair of DNA double-strand breaks, showing that removal of scaRNA2 from cells causes defects in repair by homologous recombination while at the same time increasing the activity of the non-homologous end joining pathway. We show that scaRNA2 can bind directly to DNAdependent protein kinase catalytic subunit (DNA-PKcs) and inhibit its activation, while WRAP53b on the other hand can bind and sequester scaRNA2 away from DNA-PKcs, allowing repair to be carried out by non-homologous end joining. Taken together, the results in this thesis highlight the role of WRAP53b in telomere biology, Cajal body maintenance and DNA repair and show that mutations in this protein can disrupt all above-mentioned functions and thereby cause Hoyeraal-Hreidarsson syndrome. We also introduce scaRNA2 as a novel regulator of DNA repair pathway choice, a regulation that is modulated by scaRNA2 being bound and sequestered by WRAP53b.