STAT6 is a cargo of exportin 1: Biological relevance in primary mediastinal B-cell lymphoma

Primary mediastinal B-cell lymphoma (PMBL) is a distinct B-cell lymphoma subtype with unique clinicopathological and molecular features. PMBL cells are characterised by several genetic abnormalities that conduct to the constitutive activation of the Janus kinase 2/signal transducer and activator of transcription 6 (JAK2/STAT6) signalling pathway. Among recurrent genetic changes in PMBL, we previously reported that the XPO1 gene encoding exportin 1 that controls the nuclear export of cargo proteins and RNAs, is mutated (p.E571K) in about 25% of PMBL cases. We therefore hypothesized that STAT6 could be a cargo of XPO1 and that STAT6 cytoplasm/nucleus shuttle could be altered in a subset of PMBL cells. Using immunocytochemistry techniques as well as the proximity ligation assay, we showed that STAT6 bound XPO1 in PBML cell lines and in HEK-293 cells genetically engineered to produce STAT6. Moreover, XPO1-mediated export of STAT6 occurs in cells expressing either a wild-type or the E571K mutated XPO1 protein.