Dicer Expression in Estrogen Receptor Positive versus Triple-Negative Breast Cancer: An Antibody Comparison

Dicer is an RNase III enzyme responsible for cleaving double stranded RNAs into small interfering RNAs and microRNAs, which either target mRNA transcripts for degradation, or inhibit translation. Dicer protein levels have been examined in breast cancer with contradictory results. Our goal was to resolve whether Dicer levels differ in breast cancer versus normal breast epithelium, and between estrogen receptor alpha positive (ER +) or negative (ER-) primary breast cancers. We compared three different Dicer antibodies: Abcam 4 A6, Abcam ab5818, and Sigma HPA000694, using immunohistochemistry and western blot analyses. All three Dicer antibodies detected higher levels of Dicer in ER + breast cancer cell lines versus ER-, and all three recognized exogenous overexpressed Dicer. In clinical specimens, all three antibodies detected higher Dicer in ER + breast cancers versus triple-negative breast cancer (TNBC), but had very different staining patterns by immunohistochemistry on the same tumor samples. Using the optimal antibody, ab5818, selected for its sensitivity and specificity, Dicer protein expression was significantly higher in ER + versus TNBC clinical specimens of primary tumor (p < 0.0001, unpaired t-test). Dicer was also significantly higher in adjacent normal breast epithelium versus TNBC (p < 0.0001, paired t-test, n = 18 pairs). Differences in antibody performance may explain contrasting results observed in the literature regarding Dicer protein in breast cancer. If Dicer becomes more clinically relevant as a prognostic indicator, further antibody optimization and standardization will be critical.