Biology subjects

Matmati, S.

Publications and source records attributed to Matmati, S..

3 recordsLinked to original sources

bioRxiv2025

Rescue from pyridostatin-stabilized telomeric G-quadruplexes by DNA cleavage and microhomology-mediated end joining

G-quadruplexes are four-stranded nucleic acid structures that are formed by guanine rich sequences. They have been implicated to interfere with telomere maintenance, but their effects are not well understood at a molecular level. Here, we treat human cells with the G-quadruplex stabilizer and anti-cancer drug-candidate pyridostatin and characterize its effects on telomere replication and maintenance. We demonstrate that pyridostatin interferes with lagging strand DNA synthesis during semiconservative replication of telomeres. Pyridostatin impedes replication fork progression and triggers telomere cleavage events involving the Flap-endonuclease FEN1 and the nuclease-helicase DNA2. Telomeric protein composition analysis reveals pyridostatin-induced association of LIG3 with telomeres. This enzyme is involved in repair of DNA double strand breaks by microhomology-mediated end joining (MMEJ). Depletion of MMEJ-factors or their chemical inhibition enhances telomere loss events in pyridostatin-treated cells. Altogether, our data reveal a three-step mechanism in which pyridostatin-stabilized G-quadruplexes inhibit replication of lagging strand telomeres, which is overcome by FEN1/DNA2-mediated DNA cleavage and MMEJ-mediated DNA repair. The synthetic effects of pyridostatin and MMEJ inhibition on telomere maintenance may become exploitable in future anti-cancer therapies.

molecular biology↗

bioRxiv2023

Pot1 promotes telomere DNA replication via the Stn1-Ten1 complex in fission yeast

Telomeres are nucleoprotein complexes that protect the chromosome-ends from eliciting DNA repair while ensuring their complete duplication. Pot1 is a subunit of telomere capping complex that binds to the G-rich overhang and inhibits the activation of DNA damage checkpoints. In this study, we explore new functions of fission yeast Pot1 by using a pot1-1 temperature sensitive mutant. We show that pot1 inactivation impairs telomere DNA replication resulting in the accumulation of ssDNA leading to the complete loss of telomeric DNA. Recruitment of Stn1 to telomeres, an auxiliary factor of DNA lagging strand synthesis, is reduced in pot1-1 mutants and overexpression of Stn1 rescues loss of telomeres and cell viability at restrictive temperature. We propose that Pot1 plays a crucial function in telomere DNA replication by recruiting Stn1-Ten1 and Pol-primase complex to telomeres, thus promoting lagging-strand DNA synthesis at stalled replication forks.

genetics↗

bioRxiv2018

SSU72 phosphatase is a telomere replication terminator

Telomeres, the protective ends of eukaryotic chromosomes, are replicated through concerted actions by conventional DNA polymerases and telomerase, though the regulation of this process is not fully understood. Telomere replication requires (C)-Stn1-Ten1, a telomere ssDNA-binding complex that is homologous to RPA. Here, we show that the evolutionarily conserved phosphatase Ssu72 is responsible for terminating the cycle of telomere replication in fission yeast. Ssu72 controls the recruitment of Stn1 to telomeres by regulating Stn1 phosphorylation at S74, a residue that lies within the conserved OB fold domain. Consequently, ssu72{Delta} mutants are defective in telomere replication and exhibit long 3 overhangs, which are indicative of defective lagging strand DNA synthesis. We also show that hSSU72 regulates telomerase activation in human cells by controlling the recruitment of hSTN1 to telomeres. Thus, in this study, we demonstrate a previously unknown yet conserved role for the phosphatase SSU72, whereby this enzyme controls telomere homeostasis by activating lagging strand DNA synthesis, thus terminating the cycle of telomere replication.

cell biology↗