Recent studies by our group and others demonstrated a required and conserved role of Stim in store-operated Ca ²⁺ influx and Ca ²⁺ release-activated Ca ²⁺ (CRAC) channel activity. By using an unbiased genome-wide RNA interference screen in Drosophila S2 cells, we now identify 75 hits that strongly inhibited Ca ²⁺ influx upon store emptying by thapsigargin. Among these hits are 11 predicted transmembrane proteins, including Stim , and one, olf186-F , that upon RNA interference-mediated knockdown exhibited a profound reduction of thapsigargin-evoked Ca ²⁺ entry and CRAC current, and upon overexpression a 3-fold augmentation of CRAC current. CRAC currents were further increased to 8-fold higher than control and developed more rapidly when olf186-F was cotransfected with Stim . olf186-F is a member of a highly conserved family of four-transmembrane spanning proteins with homologs from Caenorhabditis elegans to human. The endoplasmic reticulum (ER) Ca ²⁺ pump sarco-/ER calcium ATPase (SERCA) and the single transmembrane-soluble N -ethylmaleimide-sensitive (NSF) attachment receptor (SNARE) protein Syntaxin5 also were required for CRAC channel activity, consistent with a signaling pathway in which Stim senses Ca ²⁺ depletion within the ER, translocates to the plasma membrane, and interacts with olf186-F to trigger CRAC channel activity.

Tenascin C is an extracellular matrix protein previously linked to breast cancer metastasis. Here the authors uncover how tenascin C promotes the fitness of metastasis-initiating cells by sustaining the stem and survival signaling pathways NOTCH and Wnt through specific regulation of Msi1 and Lgr5, respectively. We report that breast cancer cells that infiltrate the lungs support their own metastasis-initiating ability by expressing tenascin C (TNC). We find that the expression of TNC, an extracellular matrix protein of stem cell niches, is associated with the aggressiveness of pulmonary metastasis. Cancer cell–derived TNC promotes the survival and outgrowth of pulmonary micrometastases. TNC enhances the expression of stem cell signaling components, musashi homolog 1 (MSI1) and leucine-rich repeat–containing G protein–coupled receptor 5 (LGR5). MSI1 is a positive regulator of NOTCH signaling, whereas LGR5 is a target gene of the WNT pathway. TNC modulation of stem cell signaling occurs without affecting the expression of transcriptional enforcers of the stem cell phenotype and pluripotency, namely nanog homeobox (NANOG), POU class 5 homeobox 1 (POU5F1), also known as OCT4, and SRY-box 2 (SOX2). TNC protects MSI1-dependent NOTCH signaling from inhibition by signal transducer and activator of transcription 5 (STAT5), and selectively enhances the expression of LGR5 as a WNT target gene. Cancer cell–derived TNC remains essential for metastasis outgrowth until the tumor stroma takes over as a source of TNC. These findings link TNC to pathways that support the fitness of metastasis-initiating breast cancer cells and highlight the relevance of TNC as an extracellular matrix component of the metastatic niche.