EphB6 Regulates TFEB-Lysosomal Pathway and Survival of Disseminated Indolent Breast Cancer Cells

Simple Summary A large number of estrogen receptor-positive breast cancer patients show relapses at the metastatic site up to 20 years after the removal of the primary tumor. This phenomenon, called "metastatic dormancy", is a particularly dangerous aspect of cancers, as it affects patients considered healed. A metastatic relapse after years since mastectomy implies that disseminated cells could survive in the metastatic organ for a long period of time. Our goal was to better understand the signals supporting the survival of the disseminated cancer cells with the aim of killing them before the relapse. We found a molecule, called EphB6, that supports the persistence of disseminated dormant cancer cells thanks to the activation of a cellular process, the lysosomal-flux, that is a central hub for nutrient sensing and recycling of the cell. Late relapse of disseminated cancer cells is a common feature of breast and prostate tumors. Several intrinsic and extrinsic factors have been shown to affect quiescence and reawakening of disseminated dormant cancer cells (DDCCs); however, the signals and processes sustaining the survival of DDCCs in a foreign environment are still poorly understood. We have recently shown that crosstalk with lung epithelial cells promotes survival of DDCCs of estrogen receptor-positive (ER+) breast tumors. By using a lung organotypic system and in vivo dissemination assays, here we show that the TFEB-lysosomal axis is activated in DDCCs and that it is modulated by the pro-survival ephrin receptor EphB6. TFEB lysosomal direct targets are enriched in DDCCs in vivo and correlate with relapse in ER+ breast cancer patients. Direct coculture of DDCCs with alveolar type I-like lung epithelial cells and dissemination in the lung drive lysosomal accumulation and EphB6 induction. EphB6 contributes to survival, TFEB transcriptional activity, and lysosome formation in DDCCs in vitro and in vivo. Furthermore, signaling from EphB6 promotes the proliferation of surrounding lung parenchymal cells in vivo. Our data provide evidence that EphB6 is a key factor in the crosstalk between disseminated dormant cancer cells and the lung parenchyma and that the TFEB-lysosomal pathway plays an important role in the persistence of DDCCs.