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

Area of Science:

• Molecular Biology
• Genetics
• Cancer Biology

Background:

• Poly (ADP-ribose) polymerase inhibitors (PARPi) show promise in cancer therapy but are associated with severe anemia and leukemia.
• PARPi function by inhibiting PARP1/2 enzymatic activity and trapping PARP proteins at DNA lesions.

Purpose of the Study:

• To investigate the underlying mechanisms of PARPi-induced anemia and leukemia.
• To elucidate the specific roles of PARP2 catalytic activity and DNA lesion binding in erythropoiesis.

Main Methods:

• Utilized Parp2 knockout and catalytically inactive Parp2 mutant mice (Parp2^EA/EA).
• Analyzed erythropoiesis, DNA replication, and DNA damage response pathways.
• Investigated the interaction of PARP2 with DNA ligases (Lig1 and Lig3) at 5'-phosphorylated nicks.

Main Results:

• Mice with inactive PARP2 (Parp2^EA/EA) exhibited TP53- and Chk2-dependent erythropoietic failure, unlike Parp2^-/- mice.
• PARP2 is robustly activated during DNA replication and specifically recruited to 5'-phosphorylated nicks, including Okazaki fragment junctions.
• Inactive PARP2, but not its absence or active form, interferes with Lig1 and Lig3 activity, leading to replication fork collapse in erythroblasts.

Conclusions:

• PARP2 possesses a critical structural function at 5'-phosphorylated nicks, essential for DNA ligation during replication.
• PARP2 inactivation, particularly its catalytic inactivity, disrupts erythropoiesis and explains PARPi-induced anemia.
• The findings highlight the role of TP53 and CHK2 in mediating the detrimental effects of PARP2 dysfunction and suggest a mechanism for the selection of TP53/CHK2 loss in cancer treatment.