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Biochemical reconstitution of temozolomide-induced mutational processes
Mahima R Sanyal1, Tomohiko Sugiyama1
1Department of Biological Sciences, Ohio University, Athens, Ohio, USA; Molecular and Cellular Biology Graduate Program, Ohio University, Athens, Ohio, USA.
Abstract:
Temozolomide (TMZ), a DNA alkylator, is a chemotherapeutic agent for brain tumors, but the treatment induces a distinct pattern of mutations, known as a cancer mutational signature single-base substitution signature 11 (SBS11). Although the correlation between TMZ treatment and SBS11 mutations is very clear, the precise biochemical mechanisms that cause SBS11 have not been elucidated. TMZ can alkylate DNA at several locations, among which O6-methylguanine is believed to be the most toxic. In this study, we reconstituted potential biochemical processes of TMZ-induced mutagenesis in vitro, including TMZ-induced DNA damage and subsequent DNA synthesis by various DNA polymerases. Next-generation sequencing of the DNA products revealed mutations with a similar spectrum to SBS11. Efficient production of the SBS11-like mutation spectra required DNA in double-stranded form and multiple exposures to TMZ. Replicative polymerase δ alone generated SBS11-like mutations on the damaged DNA. Most SBS11-like mutations were sensitive to methyl guanine methyltransferase treatment, indicating that the mutations are formed on O6-methylguanine modifications. Human Pol η reduced the SBS11-like mutations, indicating its suppressive role in TMZ-induced mutagenesis. Yeast Pol ζ and human Pol κ generated distinct mutations unrelated to SBS11.
Insights
Temozolomide (TMZ) chemotherapy causes specific DNA mutations (SBS11) in brain tumors. This study reveals that DNA repair enzyme MGMT and polymerase delta are key to forming these TMZ-induced mutations.
Area of Science:
- Molecular Biology
- Cancer Research
- Genetics
Background:
- Temozolomide (TMZ) is a chemotherapeutic DNA alkylator used for brain tumors.
- TMZ treatment leads to a specific mutational signature known as SBS11.
- The exact biochemical mechanisms underlying SBS11 mutations remain unclear.
Purpose of the Study:
- To investigate the in vitro biochemical mechanisms of TMZ-induced mutagenesis.
- To identify the DNA polymerases and DNA modifications involved in generating SBS11 mutations.
- To explore the role of DNA repair enzymes in modulating TMZ-induced mutagenesis.
Main Methods:
- Reconstitution of TMZ-induced DNA damage and synthesis in vitro.
- Utilizing next-generation sequencing to analyze mutation spectra.
- Testing the activity of various DNA polymerases (Pol δ, Pol η, Pol ζ, Pol κ) on TMZ-damaged DNA.
- Assessing the effect of methyl guanine methyltransferase (MGMT) on mutations.
Main Results:
- In vitro reconstitution generated mutations mirroring the SBS11 spectrum.
- Double-stranded DNA and multiple TMZ exposures were necessary for SBS11-like mutations.
- DNA polymerase delta (Pol δ) alone produced SBS11-like mutations on O6-methylguanine (O6me-G) lesions.
- MGMT treatment reduced SBS11-like mutations, confirming O6me-G as the critical lesion.
- Human polymerase eta (Pol η) suppressed SBS11-like mutations, while yeast Pol ζ and human Pol κ did not.
Conclusions:
- O6-methylguanine is the primary DNA adduct responsible for TMZ-induced SBS11 mutations.
- DNA polymerase delta plays a crucial role in generating SBS11 mutations during replication.
- DNA polymerase eta acts as a suppressor of TMZ-induced mutagenesis, potentially offering therapeutic insights.
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