All organisms need to propagate their genomes to their descendants completely and accurately. A correct genome is crucial for the organism's maintenance so that genes necessary for any stage of its life cycle are expressed properly.
DNA helicases and topoisomerases are enzymes involved in many genetic interactions such as replication, transcription, and repair. If these proteins do not function properly they can have profound effects on the outcome of functions of the cell. DNA helicases unwind double-stranded DNA or other DNA structures, such as G-quadruplexes (G4), so that DNA can be accessed by DNA and RNA polymerases for replication and transcription.
Topoisomerases resolve topological structures produced due to underwinding or overwinding of DNA during replication or transcription. In this study we showed that certain sequences of S. pombe form G4 structures and that they can be resolved by the Pfh1 helicase. We showed that Pfh1 moves with the DNA replication machinery and is not just recruited to its sites of action whenever it is needed. Additionally, we studied the effects of absence of Pfh1 together with Top1 and determined how the transcriptome and DNA replication of these cells are affected.
Generally, cells were more affected when Pfh1 was absent compared to only Top1. However, coupling Top1 absence to Pfh1 absence decreased the growth rate synergistically. DNA topoisomerases and helicases are highly conserved in eukaryotes and are popular targets for developing drugs against cancer and other diseases. While they usually are studied separately, our findings show that targeting these two proteins simultaneously can increase the chances of activating programmed cell death. This may be used specially in treating diseases like cancer that dysregulate cell proliferation towards a higher rate and increased DNA replication. These findings shall be further investigated in human cells to further understand the mechanisms of inhibiting Top1 and Pif1 (Pfh1 homolog) in humans.
The studies are performed both in vitro and in vivo, with biochemical, molecular, and bioinformatics methods. Protein purification, helicase assay, mass spectrometry, RNA-sequencing, DNA fiber stretching, Chromatin immunoprecipitation (ChIP) and ChIP-sequencing. The experiments have been performed with participation of a total of thirteen authors.
Parham Pourbozorgi Langroudi was born in Rasht - Iran, finished junior and high school in NODET. Then earned a bachelor's degree in biology at Azad University and master's degree in molecular biology at Umeå University.
Om dipsutationen
Parham Pourbozorgi Langroudi, Institutionen för medicinsk kemi och biofysik, försvarar fredag 8 juni sin avhandling med titeln: Studier av funktionen av det essentiella Pfh1 DNA-helikaset i både cellkärnans och mitokondriens arvsmassa. (Engelsk titel: Insights into the Roles of the Essential Pfh1 DNA helicase in the Nuclear and Mitochondrial Genomes) Fakultetsopponent: Professor Per Sunnerhagen, Institutionen för kemi och molekylärbiologi, Göteborgs universitet. Huvudhandledare: Nasim Sabouri. Tid: 13.00 - 16.00. Plats: KBC-huset, Karl Kempe-salen.