Inactive Parp2 causes Tp53-dependent lethal anemia by blocking replication-associated nick ligation in erythroblasts

Area of Science:

• Molecular Biology
• Cancer Biology
• Genetics

Background:

• Poly (ADP-ribose) polymerase inhibitors (PARPi) are effective cancer therapies but cause severe anemia and leukemia.
• The exact mechanisms behind these PARPi-induced hematological toxicities remain unclear.
• PARP inhibitors are known to inhibit enzymatic activity and trap PARP1/2 at DNA lesions.

Approach:

• Investigated the role of PARP2 in erythropoiesis using catalytically inactive Parp2 mutant mice (E534A).
• Analyzed the recruitment and activation of PARP2 at 5'-phosphorylated nicks during DNA replication, particularly in relation to Okazaki fragment ligation.
• Examined the impact of inactive PARP2 on DNA ligase activity and replication fork stability in erythroblasts.

Key Points:

• Catalytically inactive PARP2 (E534A), but not its absence or active form, causes severe erythropoietic failure dependent on Tp53 and Chk2.
• PARP2 is robustly activated by DNA replication and selectively recruited to 5'-phosphorylated nicks, sites typically resolved by Lig1.
• Inactive PARP2 impedes Lig1 and Lig3-mediated ligation, leading to replication fork collapse, especially in erythroblasts with rapid replication forks.

Conclusions:

• The hematological toxicities of PARPi are caused by the presence of inactive PARP2 protein, not impaired enzymatic activity.
• Inactive PARP2 interferes with DNA ligation at Okazaki fragments, causing replication stress and cell death in erythroblasts.
• This study elucidates the mechanism of PARPi-induced anemia and leukemia, particularly in contexts of TP53/CHK2 loss.