SLX4IP limits replication stress globally and at ALT telomeres.

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• Faithful DNA replication is crucial for genome stability.
• Replication forks are susceptible to stress, and Bloom syndrome helicase (BLM) activity is vital for their integrity.
• However, excessive BLM activity can paradoxically induce replication stress.

Purpose of the Study:

• To identify regulators of Bloom syndrome helicase (BLM) that maintain replication fork stability.
• To investigate the role of SLX4IP in genome-wide regulation of replication stress.
• To explore SLX4IP's function at ALT telomeres and its implications for ALT-positive cancers.

Main Methods:

• Chromatin localization studies of SLX4IP under replication stress.
• Analysis of replication fork speed, replisome remodeling, and DNA gap formation upon SLX4IP loss.
• Assessment of ATR signaling, telomere fragility, and ALT-associated PML bodies in SLX4IP-deficient cells.
• Genetic interaction studies involving SLX4IP, FANCM, and BLM in ALT-positive cells.

Main Results:

• SLX4IP is a genome-wide regulator that restrains BLM activity, thereby maintaining replication fork stability.
• Loss of SLX4IP leads to slower replication forks, replisome alterations, and increased single-stranded DNA gaps.
• At ALT telomeres, SLX4IP deficiency activates ATR signaling and causes telomere fragility, functioning in parallel with FANCM to control BLM.
• Co-depletion of SLX4IP and FANCM is synthetically lethal in ALT-positive cells, a phenotype rescued by BLM loss.

Conclusions:

• SLX4IP acts as a critical negative regulator of BLM-dependent replication stress, safeguarding genome-wide replication fork integrity.
• SLX4IP plays a key role at ALT telomeres, collaborating with FANCM to restrain BLM.
• SLX4IP deficiency represents a potential therapeutic vulnerability in ALT-positive cancers.