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The DNA cytosine deaminase APOBEC3H haplotype I likely contributes to breast and lung cancer mutagenesis

View Article: PubMed Central - PubMed

ABSTRACT

Cytosine mutations within TCA/T motifs are common in cancer. A likely cause is the DNA cytosine deaminase APOBEC3B (A3B). However, A3B- breast tumours still have this mutational bias. Here we show that APOBEC3H haplotype I (A3H-I) provides a likely solution to this paradox. A3B- tumours with this mutational bias have at least one copy of A3H-I despite little genetic linkage between these genes. Although deemed inactive previously, A3H-I has robust activity in biochemical and cellular assays, similar to A3H-II after compensation for lower protein expression levels. Gly105 in A3H-I (versus Arg105 in A3H-II) results in lower protein expression levels and increased nuclear localization, providing a mechanism for accessing genomic DNA. A3H-I also associates with clonal TCA/T-biased mutations in lung adenocarcinoma suggesting this enzyme makes broader contributions to cancer mutagenesis. These studies combine to suggest that A3B and A3H-I, together, explain the bulk of ‘APOBEC signature' mutations in cancer.

No MeSH data available.


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A3H haplotype I has greater nuclear localization than haplotype II.(a) Representative images of A3H-I (untagged), A3H-II (untagged), A3B-HA and A3G-HA in SK-BR-3, HeLa and U2OS cells. The 20 μm scale applies to all images. (b) Whisker plots quantifying the subcellular localization data as nuclear-to-cytoplasmic ratios for n>50 cells per condition. The average is shown, the error box represents the first and third quartiles, and the whiskers extend to the highest value within 1.5 × the interquartile range (P values determined by two-tailed Welch's t-test).
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f5: A3H haplotype I has greater nuclear localization than haplotype II.(a) Representative images of A3H-I (untagged), A3H-II (untagged), A3B-HA and A3G-HA in SK-BR-3, HeLa and U2OS cells. The 20 μm scale applies to all images. (b) Whisker plots quantifying the subcellular localization data as nuclear-to-cytoplasmic ratios for n>50 cells per condition. The average is shown, the error box represents the first and third quartiles, and the whiskers extend to the highest value within 1.5 × the interquartile range (P values determined by two-tailed Welch's t-test).

Mentions: To clarify and advance this important point, we used immunofluorescent microscopy to quantify the localization of untagged A3H-I versus A3H-II in cell lines with varying endogenous A3B levels (, SK-BR-3; low, HeLa; high, U2OS)7. A3B-HA and A3G-HA were used as controls for predominantly nuclear and cytoplasmic localization, respectively (Fig. 5). We found the overall subcellular distributions of A3H-I and A3H-II to be consistent in all cell types, regardless of endogenous A3B levels, with the former enzyme invariably appearing more nuclear than the latter (representative images, Fig. 5a; quantification, Fig. 5b). These data show that A3H-I is proficient at entering the nuclear compartment, and advance the general model in which Gly105 disrupts a cytoplasmic retention mechanism and enables the A3H-I enzyme to breach the nuclear compartment and mutagenize genomic DNA.


The DNA cytosine deaminase APOBEC3H haplotype I likely contributes to breast and lung cancer mutagenesis
A3H haplotype I has greater nuclear localization than haplotype II.(a) Representative images of A3H-I (untagged), A3H-II (untagged), A3B-HA and A3G-HA in SK-BR-3, HeLa and U2OS cells. The 20 μm scale applies to all images. (b) Whisker plots quantifying the subcellular localization data as nuclear-to-cytoplasmic ratios for n>50 cells per condition. The average is shown, the error box represents the first and third quartiles, and the whiskers extend to the highest value within 1.5 × the interquartile range (P values determined by two-tailed Welch's t-test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036005&req=5

f5: A3H haplotype I has greater nuclear localization than haplotype II.(a) Representative images of A3H-I (untagged), A3H-II (untagged), A3B-HA and A3G-HA in SK-BR-3, HeLa and U2OS cells. The 20 μm scale applies to all images. (b) Whisker plots quantifying the subcellular localization data as nuclear-to-cytoplasmic ratios for n>50 cells per condition. The average is shown, the error box represents the first and third quartiles, and the whiskers extend to the highest value within 1.5 × the interquartile range (P values determined by two-tailed Welch's t-test).
Mentions: To clarify and advance this important point, we used immunofluorescent microscopy to quantify the localization of untagged A3H-I versus A3H-II in cell lines with varying endogenous A3B levels (, SK-BR-3; low, HeLa; high, U2OS)7. A3B-HA and A3G-HA were used as controls for predominantly nuclear and cytoplasmic localization, respectively (Fig. 5). We found the overall subcellular distributions of A3H-I and A3H-II to be consistent in all cell types, regardless of endogenous A3B levels, with the former enzyme invariably appearing more nuclear than the latter (representative images, Fig. 5a; quantification, Fig. 5b). These data show that A3H-I is proficient at entering the nuclear compartment, and advance the general model in which Gly105 disrupts a cytoplasmic retention mechanism and enables the A3H-I enzyme to breach the nuclear compartment and mutagenize genomic DNA.

View Article: PubMed Central - PubMed

ABSTRACT

Cytosine mutations within TCA/T motifs are common in cancer. A likely cause is the DNA cytosine deaminase APOBEC3B (A3B). However, A3B- breast tumours still have this mutational bias. Here we show that APOBEC3H haplotype I (A3H-I) provides a likely solution to this paradox. A3B- tumours with this mutational bias have at least one copy of A3H-I despite little genetic linkage between these genes. Although deemed inactive previously, A3H-I has robust activity in biochemical and cellular assays, similar to A3H-II after compensation for lower protein expression levels. Gly105 in A3H-I (versus Arg105 in A3H-II) results in lower protein expression levels and increased nuclear localization, providing a mechanism for accessing genomic DNA. A3H-I also associates with clonal TCA/T-biased mutations in lung adenocarcinoma suggesting this enzyme makes broader contributions to cancer mutagenesis. These studies combine to suggest that A3B and A3H-I, together, explain the bulk of ‘APOBEC signature' mutations in cancer.

No MeSH data available.


Related in: MedlinePlus