Abstract PTEN functions as a key negative regulator of PI3K-Akt pathway through its lipid phosphatase activity. Mutations or loss of PTEN is frequently observed in brain, breast, prostate and endometrial cancer. PTEN also possesses a PDZ-binding domain (PDZ-BD) at its carboxyl terminus, which can be recruited by PDZ-containing proteins like ZO-1 to cell tight junction. Therefore, PTEN may have a potential role in regulating epithelial tight junction integrity. To study the role of PTEN PDZ-BD in breast epithelial tumorigenesis, a PTEN-ΔPDZ mice lacking this domain was generated and further crossed with MMTV-PyMT breast cancer model. As a result, PTENΔPDZ/MMTV-PyMT mice show enhanced tumor growth and metastasis. To elucidate tumor suppressive mechanisms of PTEN PDZ-BD, three-dimensional cultures of PTENΔPDZ mouse mammary epithelial cells (MMEs) was carried out. Though PTEN-ΔPDZ MMEs spheres have normal morphogenesis in 3D culture, they possess larger diameters than wild-type (WT). Besides, both tight junction (ZO-1) and adherent junction (E-Cadherin) of MMEs were examined in 3D culture, though no major differences in cell junction and polarity was observed between PTEN-ΔPDZ and PTEN-WT. Future work will study signaling activities of PTEN-ΔPDZ/MMTV-PyMT breast cancer cells, morphogenesis, polarity and cell junction of PTEN-ΔPDZ/MMTV-PyMT MMEs in 3D cultures. This work was supported by NIH RO1 (CA133669), Hong Kong Research Grant Council (460713) and Hong Kong PhD Fellowship Scheme (PF12-13584) Citation Format: Mingfei Yan, Penelope Or, Andrew Chan. The role of PTEN PDZ-binding domain in mammary gland tumorigenesis. [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 308. doi:10.1158/1538-7445.AM2015-308