Role of Pygo1 and Pygo2 in Epithelial Mesenchymal Transition and Tumor Progression

NATALIA RUBINSTEIN.; MEERA SAXENA; CLAUDIO CANTU; KONRAD BASLER; GERHARD CHRISTOFORI

Congreso; 6th TEMTIA Meeting; 2013

Metastasis contributes to most cancer-related mortality and hence forms an important area of investigation. Epithelial to mesenchymal transition (EMT) has been described as an important facilitator of cancer metastasis as it allows the epithelial cells to become migratory and invasive. Pygopus 1 and pygopus 2 (Pygo1 and Pygo2), members of the pygopus protein family were initially described as transcriptional activators of the Wnt/βcat pathway. Later, Pygo2 was also described to be able to directly bind to the histone H3 trimethylated lysine 4. Recently, it has been described that Pygo2?s ability to bind H3 is relevant in mammary stem cell accumulation and regulating tumor-initiating capacity of MMTV-Wnt1-induced mammary gland tumors. However, the role of Pygo1/2 in EMT has not been defined. To investigate the relevance of Pygo in EMT, we first evaluated the expression of Pygo in normal murine mammary gland epithelial cell line (NMuMG-E9) treated with TGFβ over 10 days. Though the expression of Pygo2 was only moderately increased, it showed clear cytoplasm to nuclear translocation on 4 days of EMT induction with TGFβ. To further evaluate if Pygo1/2 are important in the EMT process, we knocked down Pygo1 and Pygo2 in NMuMG-E9 cells using siRNA. Interestingly, while TGFβ treatment of cells in which Pygo1 had been knocked down induced significant apoptosis, knockdown of Pygo2 did not demonstrate such an effect. However, knockdown of Pygo2 impaired the ability of E9 cells to undergo EMT on response to 10 days treatment with TGFβ as assessed by morphology and expression of epithelial (E-cadherin and zona occludens 1) and mesenchymal markers (fibronectin1, Slug, N-cadherin). Further, introduction of a knockin mutation that prevents Pygo2 to bind to histones (Pygo2A342E), in PyMT/FVB mice leads to a decrease in tumor volume as well as number of metastasis as compared to the control PyMT/FVB transgenic mice expressing wild type Pygo2. Collectively, our data indicate that Pygo2 might play an important role in EMT and might potentiate tumorigenesis and metastasis of mammary tumors. Hence, a more detailed study might reveal if Pygo2 might be an attractive therapeutic target for mammary tumors.