Updated project metadata. B cell receptor (BCR) signaling and oncogenic tyrosine kinases that mimic BCR-signaling in B-lineage leukemia and lymphoma depend on assembly of membrane proximal signaling complexes. Signalosomes in normal BCR- and oncogene (e.g. BCR-ABL1, RAS-pathway lesions) signal transduction are recruited to phospholipid anchors in lipid rafts. The robustness of these complexes depends on cholesterol accumulation in lipid rafts. Here we identified the interferon-induced transmembrane protein IFITM3 as a central regulator of cholesterol in lipid rafts.