Biology subjects

Abid, H. Z.

Publications and source records attributed to Abid, H. Z..

3 recordsLinked to original sources

bioRxiv2026

The function of human PIF1 in G quadruplex formation and replication stress response at ALT telomeres

Cancers maintain their telomeres through two telomere maintenance mechanisms: 85-90% of cancers rely on telomerase (TEL+), while 10-15% of cancers adopt the Alternative Lengthening of Telomeres (ALT) pathway. The Break-Induced Replication (BIR) pathway plays a critical role in maintaining telomere length in the ALT+ cells. In both yeast and human, PIF1, a 5' to 3' helicase, is required for the robust activity of BIR. However, the extent of human PIF1 (hPIF1) involvement in the ALT pathway remains unknown. Here we showed that hPIF1 can be recruited to damaged telomeres in ALT+ cells. In addition, we demonstrated that inhibition of hPIF1 induced DNA damage and G quadruplex (G4) accumulation at ALT telomeres, leading to a moderate reduction of the mean telomere length. Most interestingly, we demonstrated that inhibition of hPIF1 also attenuates checkpoint activation, BLM recruitment, single-stranded DNA (ssDNA) formation, DNA damage, and G4s at telomeres in the FANCM deficient ALT+ cells. Finally, we showed that inactivation of hPIF1 affects the viability of both ALT+ and TEL+ cancers, suggesting that hPIF1 is a potential drug target for cancer therapy.

molecular biology↗

bioRxiv2025

DNA2 and FANCM function in two distinctive pathways in disrupting TERRA R-loops and suppressing replication stress at ALT telomeres

Cancers maintain their telomeres through two main telomere maintenance mechanisms (TMMs): 85-90% of cancers rely on telomerase, while 10-15% of cancers adopt the Alternative Lengthening of Telomere (ALT) pathway. Previously, we and others reported that FANCM, one of the Fanconi Anemia proteins, plays a critical role in suppressing replication stress and DNA damage at ALT telomeres by actively disrupting TERRA R-loops [1-4]. Here, we showed that inactivation of DNA2 in ALT-positive (ALT+) cells, but not in telomerase-positive (TEL+) cells, induces a robust increase of replication stress and DNA damage at telomeres, which leads to a pronounced increase of many ALT properties, including telomere dysfunction-induced foci (TIFs), ALT-associated PML bodies (APBs), and C-circles. We further demonstrated that depletion of DNA2 induces a pronounced increase of TERRA R-loops and a decrease in replication efficiency at ALT telomeres. Most importantly, we uncovered a strong additive genetic interaction between DNA2 and FANCM in the ALT pathway. Furthermore, co-depletion of DNA2 and FANCM causes synthetic lethality in ALT+ cells, but not in TEL+ cells, suggesting that targeting DNA2 and FANCM could be a viable strategy to treat ALT+ cancers. Finally, utilizing the single-molecule telomere assay via optical mapping (SMTA-OM) technology, we thoroughly characterized genome-wide changes in DNA2 deficient cells and FANCM deficient cells and found that most chromosome arms manifested increased telomere length. Unexpectedly, we uncovered many chromosome arm-specific telomere changes in those cells, suggesting that telomeres at different chromosome arms may regulate and respond to replication stress differently. Collectively, our study not only shed new light on the molecular mechanisms of the ALT pathway, but also discovered a new strategy for targeting ALT+ cancer.

cancer biology↗

bioRxiv2019

Comprehensive Analysis of Human Subtelomeres by Whole Genome Mapping

Detailed comprehensive knowledge of the structures of individual long-range telomere-terminal haplotypes are needed to understand their impact on telomere function, and to delineate the population structure and evolution of subtelomere regions. However, the abundance of large evolutionarily recent segmental duplications and high levels of large structural variations have complicated both the mapping and sequence characterization of human subtelomere regions. Here, we use high throughput optical mapping of large single DNA molecules in nanochannel arrays for 154 human genomes from 26 populations to present a comprehensive look at human subtelomere structure and variation. The results catalog many novel long-range subtelomere haplotypes and determine the frequencies and contexts of specific subtelomeric duplicons on each chromosome arm, helping to clarify the currently ambiguous nature of many specific subtelomere structures as represented in the current reference sequence (HG38). The organization and content of some duplicons in subtelomeres appear to show both chromosome arm and population-specific trends. Based upon these trends we estimate a timeline for the spread of these duplication blocks.\n\nAuthor SummaryThe ends of human chromosomes have caps called telomeres that are essential. These telomeres are influenced by the portions of DNA next to them, a region known as the subtelomere. We need to better understand the subtelomeric region to understand how it impacts the telomeres. This subtelomeric region is not well described in the current references. This is due to large variations in this region and portions that are repeated many times, making current sequencing technologies struggle to capture these regions. Many of these variations are evolutionary recent. Here we use 154 different samples from the 26 geographic regions of the world to gain a better understanding of the variation in these regions. We found many new haplotypes and clarified the haplotypes existing in the current reference. We then examined population and chromosome specific trends.

genomics↗