Previously, we have shown that mammary-specific loss of E-cadherin is causal to the formation of invasive lobular carcinoma and induces metastatic disease and anoikis resistance in mouse models for human ILC (mILC). Loss of E-cadherin has differential consequences for the associated catenins; while β-catenin is readily degraded, p120-catenin (p120) remains stable in the cytosol where it mediates anoikis resistance through MRIP-dependent indirect activation of Rho/ROCK signaling. In addition, p120 has the intrinsic capability to shuttle between the nucleus and the cytosol. Evidence for a functional role of nuclear p120 emerged when the transcriptional repressor Kaiso was discovered as a novel p120 interactor. Using a Kaiso-specific reporter, we have shown that basal Kaiso repression is significantly reduced in mILC cell lines compared to E-cadherin-proficient cell lines. In addition, overexpression of p120 in E-cadherin-proficient cells relieved Kaiso repression showing a causal role for p120 in modulating Kaiso activity.
While p120/Kaiso signaling has been relatively well-studied in the context of developmental biology, limited data exists on the function and relevance of this pathway in cancer biology. To identify novel Kaiso target genes specifically involved in the context of breast cancer biology, we combined genome-wide expression profiling and computational analysis approaches. RNA was harvested from eight independent mILC cell lines cultured in both anchorage-independent and adherent setting and subsequently differentially displayed against itself. This approach yielded a subset of genes that showed upregulation in an anchorage-independent context and therefore could represent genes with a regulatory function in anoikis resistance. Computational analysis of the promoter region of these genes revealed 33 potential Kaiso target genes including the known Kaiso target Wnt11. First, binding of Kaiso to the Wnt11 promoter was confirmed using ChIP. Genetic ablation of Wnt11 significantly reduced survival in anchorage-independent mILC cell lines revealing a regulatory role for Wnt11 signaling in anoikis resistance. In addition, knockdown of Wnt11 reduced cell migration indicating a broad role for Wnt11 signaling in cancer invasion. Furthermore, RhoA levels were reduced upon Wnt11 knockdown suggesting that Wnt11-driven anoikis resistance and migration is driven through modulation of this GTPase.
We hypothesize that loss of E-cadherin and subsequent nuclear shuttling of p120 in ILC relieves Kaiso-mediated transcriptional repression of multiple target genes including Wnt11. Autocrine Wnt11 signaling mediates anoikis resistance and migration through regulation of RhoA activity in ILC. Our future research will focus on delineating the p120/Kaiso pathway and identification and functional characterization of novel Kaiso target genes in invasive breast cancer.
Citation Format: Robert A.H. van de Ven, Milou Tenhagen, Wouter Meuleman, Patrick W.B. Derksen. Identification and characterization of novel p120/Kaiso target genes in invasive breast cancer. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr C50.