Metastasis leads to the death of most cancer patients, and basal breast cancer is the most aggressive breast tumor type. Metastasis involves a complex cell migration process dependent on cytoskeletal remodeling such that targeting such remodeling in tumor cells could be clinically beneficial. Here we show that Hormonally Upregulated Neu-associated Kinase (HUNK) is dramatically downregulated in tumor samples and cell lines derived from basal breast cancers. Reconstitution of HUNK expression in basal breast cancer cell lines blocked actin polymerization and reduced cell motility, resulting in decreased metastases in two in vivo murine cancer models. Mechanistically, HUNK overexpression sustained the constitutive phosphorylation and inactivation of cofilin-1 (CFL-1), thereby blocking the incorporation of new actin monomers into actin filaments. HUNK reconstitution in basal breast cancer cell lines prevented protein phosphatase 2-A (PP2A), a phosphatase putatively acting on CFL-1, from binding to CFL-1. Our investigation of HUNK suggests that the interaction between PP2A and CFL-1 may be a target for antimetastasis therapy, particularly for basal breast cancers.M etastasis is a hallmark of cancer and remains the major cause of cancer-related mortality (90%) (1). Currently, there is no FDA-approved drug that specifically blocks metastasis. Metastasis is a multistep process that requires a cancer cell to leave a primary tumor, intravasate, survive in the blood, extravasate, migrate, invade through basement membranes and connective tissues, and establish a viable tumor in a distant site (2). Cytoskeletal reorganization and cell movement underlie all these events (3), and disruption of these processes could therefore constitute an effective anticancer approach.The major subtypes of breast cancer (luminal A/B/C, HER-2, and basal) can be distinguished by their gene expression profiles (4). The basal subtype is the most aggressive, has the worst prognosis, and shows the greatest extent of metastasis (4, 5). To identify molecules whose expression varies by breast cancer subtype and might be linked to metastasis, we screened the online data of Sorlie and colleagues (4) for candidate promoters and suppressors of metastasis. Our hypothesis was that the mRNA expression of kinases involved in cell migration and invasion should be altered in basal breast cancers relative to the mRNA profiles of other breast cancer subtypes. One molecule emerging from this screen was Hormonally Up-regulated Neuassociated Kinase (HUNK), an 80-kDa protein (6). HUNK was down-regulated almost threefold in basal cancer samples compared to the other subtypes. HUNK contains a 260-aa domain predicted to have serine/threonine kinase activity; however, to date, no clear kinase activity, substrates, interacting proteins, or indeed physiological role for HUNK have been identified (6, 7). In normal murine mammary cells, HUNK levels vary with the hormonal cycle (6). With respect to transformed cells, Wertheim et al. recently reported that HUNK is highly express...

The contribution of basal and luminal cells to cancer progression and metastasis is poorly understood. We report generation of reporter systems driven by either keratin-14 (K14) or keratin-8 (K8) promoter that not only express a fluorescent protein but also an inducible suicide gene. Transgenic mice express the reporter genes in the right cell compartments of mammary gland epithelia and respond to treatment with toxins. In addition, we engineered the reporters into 4T1 metastatic mouse tumor cell line and demonstrate that K14+ cells, but not K14− or K8+, are both highly invasive in three-dimensional (3D) culture and metastatic in vivo. Treatment of cells in culture, or tumors in mice, with reporter-targeting toxin inhibited both invasive behavior and metastasis in vivo. RNA sequencing (RNA-seq), secretome, and epigenome analysis of K14+ and K14− cells led to the identification of amphoterin-induced protein 2 (Amigo2) as a new cell invasion driver whose expression correlated with decreased relapse-free survival in patients with TP53 wild-type (WT) breast cancer.