Abstract LB-193: APOBEC3 catalyzed genomic mutations in breast cancer

Abstract

Abstract In this work, we present evidence that an endogenous DNA mutating protein, APOBEC3, is massively overexpressed in a high proportion of breast cancers and that this overexpression may be responsible for the genetic variability seen in these cancers. Multiple driver mutations are required for cancer development and recent genome-wide approaches have revealed that many cancers, including breast, harbor staggering numbers of mutations, both point mutations as well as gross chromosomal rearrangements. The molecular origins of most of these somatic aberrations remain unclear. In this work, we test the hypothesis that APOBEC3, an endogenous DNA mutator, is a causative factor driving these mutations. One clue derives from the fact that C/G-to-T/A transition mutations, both within and outside of methyl-C-p-G dinucleotide motifs, predominate in subsets of many tumor types, including breast cancer. We demonstrate that APOBEC3, a DNA cytosine deaminase, is a likely endogenous source of mutation in breast cancer. We show, using quantitative reverse transcriptase PCR (qRT-PCR), that APOBEC3 is overexpressed in a majority of commonly available breast cancer cell lines (34/44) when compared to MCF-10A and hTERT-HMEC control lines. This overexpression phenotype persists when examining primary breast tumors (24/37) using patient-matched normal tissues as controls. APOBEC3 is predominantly localized to the nuclear compartment when overexpressed, as seen using fluorescently tagged APOBEC3. Additionally, its catalytic DNA cytosine to uracil deamination activity is dramatically elevated in this compartment in multiple breast cancer cell lines, as quantified using a FRET-based DNA oligonucleotide cleavage assay. This presentation will discuss the potential impact of this potent endogenous mutagen on the breast cancer genome and the implications for tumor evolution and therapy resistance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-193. doi:10.1158/1538-7445.AM2011-LB-193