Abstract BS2-2: Targeting the LIFR-Hippo-YAP pathway as an anti-metastatic strategy

Deregulation of signaling pathways that control organ size, such as the Hippo-YAP pathway, can lead to tumor formation and metastatic progression. Several upstream regulators are known to provide inputs feeding into the core Hippo pathway. However, the cell membrane receptors that activate the MST (the mammalian Hippo homolog)-LATS-YAP phosphorylation cascade are elusive. Although G-protein-coupled receptors have been found to regulate LATS and YAP phosphorylation, they act in a Hippo-independent manner and do not regulate MST. Combining high-throughput RNA sequencing, functional characterization, mechanistic studies, and clinical validation, we identified leukemia inhibitory factor receptor (LIFR) as a novel breast cancer metastasis suppressor downstream of the miR-9 microRNA and upstream of Hippo signaling. We found that LIFR suppresses metastasis by promoting cell membrane localization of the adaptor protein Scribble, leading to activation of a Hippo kinase cascade and functional inactivation of the transcriptional co-activator YAP. We found that LIFR is commonly downregulated in human breast cancer, and that loss of LIFR in non-metastatic stage I-III breast tumors was highly associated with poor metastasis-free, recurrence-free, and overall survival outcomes in approximately 1,000 patients. Recently, we generated Lifr conditional knockout (cKO) mice to determine whether genetic deletion of Lifr in the breast and other organs leads to increased organ size, tumorigenesis, and metastasis. Notably, we confirmed that Hippo signaling is shut down in Lifr-deficient adult mouse tissues and primary mouse embryonic fibroblasts. The phenotypic characterization of these mice is under way. In preliminary analyses, we indeed observed enlarged organs in Lifr cKO mice, which is what is expected from inactivation of Hippo signaling. These results further validated LIFR as a receptor that triggers the Hippo pathway. We aim to make translational advances on this finding. By delineating the appropriate cutoffs, detection of LIFR could be implemented in the clinic as a prognostic marker of metastatic relapse. We are also developing therapeutic agents to target the miR-9-LIFR-Hippo-YAP pathway as new anti-metastatic strategies. miR-9 antagomirs and LIFR ligands (such as LIF) could be useful for tumors with downregulation but not complete loss of LIFR, whereas agents targeting the functional YAP targets, such as CTGF, may be useful for tumors with either downregulation or complete loss of LIFR. Recently, we established collaboration with FibroGen to develop a human CTGF-neutralizing antibody (FG-3019) as an anti-metastatic agent in preclinical models of breast cancer. We will also investigate whether the blood level of CTGF can serve as a prognostic marker for metastatic relapse and a predictive marker to select patients that would benefit from FG-3019 treatment. These studies will likely facilitate biomarker-driven personalization of breast cancer metastasis prevention and treatment. Citation Format: Li Ma. Targeting the LIFR-Hippo-YAP pathway as an anti-metastatic strategy [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr BS2-2.