Poly(ADP-ribose) polymerase null mouse cells synthesize ADP-ribose polymers

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Poly(ADP-ribose) polymerase (PARP) is crucial for DNA repair and genomic stability.
• PARP synthesizes ADP-ribose polymers from NAD+ in response to DNA strand breaks.
• PARP-deficient mice exhibit sensitivity to DNA-damaging agents.

Purpose of the Study:

• To investigate ADP-ribose polymer synthesis in cells lacking functional PARP.
• To determine if DNA damage can induce polymer formation in the absence of PARP.

Main Methods:

• Utilized PARP-/- mouse embryo cells and 3T3 cells.
• Treated cells with the DNA-damaging agent N-methyl-N'-nitro-N-nitrosoguanidine.
• Analyzed synthesized ADP-ribose polymers using boronate resin, enzymatic digestion (snake venom phosphodiesterase, alkaline phosphatase, recombinant poly(ADP-ribose) glycohydrolase), and nucleoside analysis.

Main Results:

• ADP-ribose polymers were synthesized in PARP-/- cells following DNA damage, despite the absence of detectable PARP protein.
• The synthesized polymers exhibited characteristics identical to those from wild-type cells, including binding to boronate resin and yielding ribosyladenosine upon enzymatic digestion.
• Recombinant poly(ADP-ribose) glycohydrolase specifically digested the polymers from PARP-/- cells.

Conclusions:

• ADP-ribose polymer formation occurs in a DNA damage-dependent manner even in the absence of PARP.
• These findings indicate the existence of a previously unrecognized enzymatic activity responsible for ADP-ribose polymer synthesis in PARP-null cells.
• Suggests alternative pathways for DNA damage response and genomic integrity maintenance.