Melanoma-Derived DNA Polymerase Theta Variants Exhibit Altered DNA Polymerase Activity

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• DNA polymerase theta (Pol θ/POLQ) is crucial for DNA double-strand break repair via microhomology-mediated end joining (MMEJ/TMEJ).
• Pol θ is considered error-prone but essential for cell survival.
• Melanoma tumors present opportunities to study cancer-associated DNA repair gene variants.

Purpose of the Study:

• To identify and characterize POLQ gene variants in human melanoma.
• To assess the functional impact of these variants on DNA polymerase activity, including nucleotide incorporation and accuracy.
• To explore the potential role of aberrant Pol θ in melanoma progression, metastasis, and drug resistance.

Main Methods:

• Identification of POLQ gene variants from human melanoma tumor samples.
• In vitro assays to measure polymerization rates and nucleotide selection accuracy of wild-type (WT) and variant Pol θ.
• Comparative analysis of variant polymerase activity against WT Pol θ.

Main Results:

• Several POLQ gene variants were identified in human melanoma tumors.
• Variants exhibit significantly reduced nucleotide incorporation efficiency (30-fold lower) compared to WT Pol θ.
• Variants demonstrate markedly decreased accuracy in nucleotide selection (up to 70-fold lower) during DNA repair.
• Aberrant Pol θ shows impaired DNA repair capabilities and potentially increased mutagenesis.

Conclusions:

• Mutated Pol θ in melanoma cells has compromised DNA repair functions.
• These Pol θ variants may contribute to increased mutagenesis, potentially driving tumor evolution.
• The presence of Pol θ variants in established tumors suggests a role in promoting cancer metastasis and therapeutic resistance.