Induced mutagenesis by the DNA cytosine deaminase APOBEC3H Haplotype I protects against lung cancer

The DNA cytosine deaminases APOBEC3A, APOBEC3B, and APOBEC3H Haplotype I can induce mutations in cells that lead to cancer evolution. The database of cancer biomarkers in DNA repair genes (DNArCdb) identified a single nucleotide polymorphism (rs139298) of APOBEC3H Haplotype I that is involved in lung cancer. Here, we show that this single nucleotide polymorphism causes the destabilization of APOBEC3H Haplotype I. Computational analysis suggests that the resulting K121E change affects the structure of APOBEC3H leading to active site disruption and destabilization of the RNA-mediated dimer interface. A K117E mutation in a K121E background stabilized the APOBEC3H Haplotype I, enabled biochemical study, and showed that the K121E affected catalytic activity, single-stranded DNA binding, and oligomerization on single-stranded DNA. That the destabilization of a DNA mutator would be associated with lung cancer suggests that too much mutation could result in immune recognition or death of tumor cells, suggesting that multiple APOBEC3s would not be expressed in the same tumor cells. In support of this hypothesis, stably expressed APOBEC3H Haplotype I caused a high amount of double-stranded DNA breaks in a lung cancer cell line that endogenously expressed APOBEC3B. Altogether, the data support the model that high APOBEC3 mutations in tumors are protective.