Abstract The developmental Wnt/planar cell polarity (PCP) pathway is the most recently described branch of the Wnt signaling pathways and is strongly implicated in cancer development at early and late stages (PMID: 28718442 and PMID: 30952630). Upregulation of the Wnt/PCP components is observed in many cancers and is associated with cancer progression. However, how their molecular functions are regulated remains an open question. Recent data from our laboratory showed that Prickle1 and Vangl2, two core Wnt/PCP components, are overexpressed in Triple Negative Breast Cancers (TNBC) and associated with poor prognosis (PMID: 27184734 and 26754771). Prickle1 is a cytoplasmic protein phosphorylated by the serine/threonine kinase Mink1, which triggers Prickle1 localization at the plasma membrane and regulates its activity (PMID: 22037766). Activation of this axis contributes to breast cancer cell motility and metastatic spreading in vitro and in vivo (PMID: 27184734). To extend our knowledge of the Mink1 substrates, we carried out a phosphoproteomic strategy and identified LL5β. LL5β is a membrane scaffold molecule that anchors microtubules (MTs) at the cell cortex through its association with CLASP, a plus-end MT protein, to trigger focal adhesion disassembly. We found that LL5β is a prominent member of the Prickle1-associated protein complex and harbors a consensus motif for Mink1 phosphorylation. At the molecular level, we demonstrated a two-step phosphorylation cascade carried out by Mink1 that phosphorylates sequentially Prickle1 to mediate its association with LL5β, then LL5β to promote its interaction with CLASP. Finally, analysis of gene expression data suggests that the concomitant up-regulation of Prickle1 and LL5β mRNA levels is associated with a poor metastasis-free survival for TNBC patients. In an effort to counteract the Mink1-Prickle1-LL5β prometastatic pathway, we selected a Mink1 inhibitor that recapitulates all the phenotypes observed following the knockdown of Mink1 expression. This chemical compound is currently under investigation in preclinical assays using xenografted TNBC cell lines and patient-derived xenografts in nude mice. Citation Format: Avais Daulat, Monica Silveira Wagner, Malgorzata Kowalczewska, Pascal Finetti, Rémy Castellano, Stéphane Audebert, François Bertucci, Luc Camoin, Jean-Paul Borg. The serine-threonine kinase Mink1 as a potential therapeutic target in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2290.