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

Area of Science:

• Molecular Biology
• Cancer Research
• Genetics

Background:

• Cancers utilize telomere maintenance mechanisms (TMMs) for survival, primarily telomerase (85-90%) or the Alternative Lengthening of Telomere (ALT) pathway (10-15%).
• FANCM is known to suppress replication stress and DNA damage at ALT telomeres by disrupting TERRA R-loops.

Purpose of the Study:

• To investigate the role of DNA2 in ALT telomere maintenance.
• To explore the therapeutic potential of targeting DNA2 and FANCM in ALT-positive cancers.

Main Methods:

• Inactivation of DNA2 in ALT-positive (ALT+) and telomerase-positive (TEL+) cells.
• Assessment of replication stress, DNA damage, and ALT properties (TIFs, APBs, C-circles).
• Analysis of TERRA R-loops, replication efficiency, and genetic interactions using co-depletion and single-molecule telomere assay via optical mapping (SMTA-OM).

Main Results:

• DNA2 inactivation in ALT+ cells, but not TEL+ cells, significantly increased replication stress, DNA damage, TERRA R-loops, and ALT properties.
• Co-depletion of DNA2 and FANCM resulted in synthetic lethality specifically in ALT+ cells.
• SMTA-OM revealed genome-wide telomere length increases and chromosome arm-specific telomere changes in DNA2 or FANCM deficient cells.

Conclusions:

• DNA2 plays a crucial role in suppressing replication stress and maintaining telomere integrity in ALT+ cells.
• The synthetic lethality observed upon co-targeting DNA2 and FANCM presents a promising therapeutic strategy for ALT+ cancers.
• Telomeres at different chromosome arms exhibit distinct responses to replication stress, highlighting the complexity of telomere maintenance.