Abstract 34: Identification of a phosphorylation cascade triggering Wnt/planar cell polarity signaling in breast cancer cells

Abstract

Abstract The developmental Wnt/planar cell polarity (PCP) pathway is the most recently described branch of Wnt signaling strongly implicated in cancer development at early and late stages. Upregulation of Wnt/PCP components and signaling is indeed observed in many cancers, this event being mostly associated with cancer progression. However, how the function of this signaling is remains presently an open question. Recent work in our laboratory found that Prickle1 and Vangl2, two core Wnt/PCP components, are overexpressed in triple negative breast cancers and associated with poor prognosis. Prickle1 is a cytoplasmic PET/LIM-containing protein phosphorylated by the serine/threonine kinase Mink1 which triggers Prickle1 localization at the plasma membrane and regulates its activity. Activation of the Prickle1-Mink1 axis promotes breast cancer cell motility and metastatic spreading in the mouse by promoting β1-integrin turn-over, focal adhesion dynamics and cytoskeleton remodeling. However, Prickle1 is probably not the unique substrate of Mink1 in breast cancer cells. Through a combination of protein purification and mass spectrometry analysis, we identified novel partners of the Prickle1-Mink1 complex which includes LL5β, a PH domain containing protein involved in β1-integrin turn-over. In parallel, by an independent approach looking for Mink1 substrates in breast cancer cells, we identified LL5β as a potential substrate for this poorly described protein kinase. Using recombinant LL5β and Prickle1, we confirmed that Mink1 can directly phosphorylate both proteins in in vitro kinase assays. We also defined that, in breast cancer cells, Mink1 associates with and phosphorylates LL5β, controlling its subcellular localization, a key step for cancer cell motility. Our data provide novel insights on the regulation of the prometastatic Wnt/PCP pathway by characterizing an yet unknown multi-step phosphorylation cascade with promising targeting potential. Citation Format: Jean-Paul Borg. Identification of a phosphorylation cascade triggering Wnt/planar cell polarity signaling in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 34.