Immunohistochemical Study of Hace1 in Wilms' Tumor and Breast Cancer Suggests a Pro-Tumorigenic Role for Its Nuclear Isoform
T Ng, F Zhang, J Mathers, B Rotblat, D Fink, V Friedrich, A Li, H Joensuu, P Sorensen. BC Cancer Research Centre, Vancouver, BC, Canada; University of British Columbia, Vancouver, BC, Canada; Helsinki University Central Hospital, Helsinki, Finland
Background: Hace1 is a cytoplasmic HECT E3 ubiquitin ligase we identified by cloning the 6q21 breakpoint of a translocation targeting the Hace1 locus in Wilms' tumor (WT). Subsequent studies showed that Hace1 is frequently inactivated epigenetically in WT, and decreased expression by RT-PCR was seen in multiple tumor types relative to patient-matched normal tissue. Also, Hace1 null mice developed diverse spontaneous tumors. However, studies into the significance of Hace1 protein expression in primary tumors are needed.
Design: Using a mouse monoclonal antibody we developed, immunohistochemistry (IHC) was performed on ten WT cases along with matched normal kidney. We also performed Hace1 IHC on a tissue microarray (TMA) of 1378 interpretable breast cancer cases with associated prognostic data, including median follow-up time for non-relapsed patients of 9.5 years. Hace1 expression was scored separately for cytoplasmic and nuclear staining (0=negative; 1+=weak or <10% positive cells, 2+=strong >10% of cells, 3+=intense in >50% cells).
Results: Hace1 IHC of normal kidney showed strong 2+ cytoplasmic and nuclear staining of the tubular epithelium, while paired WT samples showed markedly less staining overall, with consistently negative cytoplasmic staining. However, in contrast to in vitro expression studies, 7/10 cases showed 2+ nuclear staining. Hace1 IHC of the breast cancer TMA showed widely variable levels of both cytoplasmic and nuclear Hace1 staining. Neither cytoplasmic nor nuclear Hace1 levels correlated with disease-free survival when analyzing all cases combined. However, when basal-like triple-negative cases (HER2-/ER-/PR-) were isolated, strong nuclear Hace1 (2-3+) showed a trend towards decreased disease-free survival (n=169, RR=1.68, p=0.086). Preliminary in vitro studies suggest that a truncated alternative transcript of Hace1 exists which localizes to the nucleus, the biological function of which is yet unknown.
Conclusions: An unexpected nuclear localization of Hace1 was observed in this IHC study of WT and breast cancer, and suggests a pro-tumorigenic role based on an association with poor prognosis in basal-like breast cancer. Further studies using a larger cohort of the basal-like subtype is needed, and in vitro studies are needed to determine the biological role of nuclear Hace1.
Tuesday, March 10, 2009 1:00 PM
Poster Session IV # 202, Tuesday Afternoon