Abstract LB-200: Loss of the scaffold protein Kibra in a mouse model of triple-negative breast cancer

Abstract

Abstract Introduction: Targeted therapies in breast cancer rely on tumor cell expression of Estrogen and/or HER2 receptors. Triple negative breast cancers (TNBCs), lacking these receptors, have no targeted therapies. We have developed a preclinical murine model expressing a naturally occurring oncogenic variant of the Met receptor in the mammary gland combined with loss of function of the tumour suppressor p53 (MMTV-Met;Trp53fl/+;Cre). This model recapitulates many features of TNBC at the level of gene expression, pathological markers and genomic alterations. Notably, this model spontaneously undergoes loss of a genomic region syntenic with human chromosome 5q which is lost in up to 70% of human TNBCs (Turner et al., 2010). This provides an opportunity for us to identify and study potential driver genes for this breast cancer subtype. Experimental procedures: Approximately 80% of MMTV-Met;Trp53fl/+;Cre mammary tumors have a mesenchymal pathology that recapitulates key features of TNBC. Array CGH profiling showed a consistent loss of chromosome 11:31.35-58.2Mb, syntenic with human 5q31.1 and 5q33.1-35.3. Analysis of mouse model expression profiling data confirmed decreased expression of 83 genes within this region. Comparison with human breast cancers within the TCGA dataset further highlighted 14 of these genes with significantly decreased expression in humans with the TNBC subtypes ‘Basal’ and ‘Claudin-low’. One of these genes, WWC1, undergoes heterozygous deletion in 49% of human Basal breast cancers (TCGA, Nature 2012) and has also been associated with Claudin-low cancers (Moleirinho et al., 2013). WWC1, also known as Kibra, encodes a scaffold protein that positively regulates the Hippo tumor suppressor pathway. We used both Kibra knockdown and over-expression to understand the functional consequences of Kibra-loss. Results: MMTV-Met solid carcinoma cells retain both Kibra expression and epithelial characteristics typical of human luminal breast cancers (Ponzo et al., 2009). Kibra depletion by siRNA in these cells led to weakening of cell-cell junctions and colony dispersal, as well as decreased cortical actin and increased membrane protrusions, consistent with epithelial-to-mesenchymal transition (EMT). Mice injected with Kibra shRNA-tumor cells developed secondary lesions at sites distant to the mammary gland. By comparison, re-expression of Kibra in MMTV-Met;Trp53fl/+ cell lines and human TNBC cells led to morphological changes consistent with an EMT reversal, including loss of actin rich protrusions. Furthermore, re-expressing Kibra impaired proliferation in vitro and decreased tumorigenicity in vivo. Globally, our results strongly suggest that Kibra loss plays a significant role in TNBC development and metastasis and is a candidate driver gene for Chr5q loss. Citation Format: Jennifer France Knight, Tina Gruosso, Danielle Angeline de Verteuil, Sadiq Saleh, Robert Lesurf, Hong Zhao, Ryan Davis, Dongmei Zuo, Robert Cardiff, Jeffrey Gregg, Michael Hallett, Morag Park. Loss of the scaffold protein Kibra in a mouse model of triple-negative breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-200. doi:10.1158/1538-7445.AM2015-LB-200