FANCJ compensates for RAP80 deficiency and suppresses genomic instability induced by interstrand cross-links

Area of Science:

• Molecular Biology
• Genetics
• DNA Repair Mechanisms

Background:

• FANCJ (Fanconi anemia complementation group J) is a DNA helicase essential for repairing DNA interstrand crosslinks (ICLs).
• Its precise role in homologous recombination (HR) repair of DNA double-strand breaks (DSBs) and compensatory mechanisms during FANCJ deficiency are not well understood.
• ICLs are highly toxic DNA lesions that can lead to chromosomal instability and disrupt transcription.

Purpose of the Study:

• To identify genes that, when depleted, sensitize FANCJ-deficient cells to mitomycin C (MMC), a DNA cross-linking agent.
• To investigate the molecular mechanisms underlying DNA repair and chromosomal stability when FANCJ and other DNA damage response proteins are concurrently deficient.
• To elucidate the specific functions of FANCJ's catalytic activity and BRCA1 interaction in response to ICLs.

Main Methods:

• Conducted a siRNA screen to identify DNA damage response/repair genes that enhance sensitivity to MMC in FANCJ knockout cells.
• Utilized genetic complementation experiments to assess the importance of FANCJ's catalytic activity and BRCA1 interaction.
• Analyzed DNA damage levels, cell cycle checkpoint function, and chromosomal instability.
• Examined the formation of RPA and RAD51 foci in response to MMC exposure.

Main Results:

• RAP80 was identified as a key gene whose depletion sensitizes FANCJ-deficient cells to MMC.
• Concomitant loss of FANCJ and RAP80 leads to increased DNA damage, impaired cell cycle checkpoints, and profound chromosomal instability.
• Both FANCJ's catalytic activity and its interaction with BRCA1 are crucial for resistance to ICLs when RAP80 is deficient.
• Elevated RPA and RAD51 foci in co-deficient cells suggest increased single-stranded DNA generation by Mre11 and CtIP nucleases.

Conclusions:

• FANCJ plays a critical role in suppressing toxic joint DNA molecules during the repair of ICL-induced DNA damage.
• The combined deficiency of FANCJ and RAP80 severely compromises DNA repair pathways, leading to genomic instability.
• These findings provide insights into the complex interplay of DNA repair proteins in maintaining genome integrity.