Schurse, H. | bioRxiv Science

bioRxiv2025

Unexpected functional role of the transactivation domain for nuclear import of STAT5

Signal transducer and activator of transcription 5 (STAT5) is a key transcriptional regulator acting downstream of hematopoietic cytokines and hormones, such as erythropoietin (Epo), thrombopoietin or prolactin. STAT5-mediated gene regulation involves tyrosine phosphorylation at cytokine receptors and subsequent nuclear import. We studied STAT5 nucleocytoplasmic shuttling via live-cell imaging of fluorescent mutants in STAT5-/- HeLa EpoR cells. Unexpectedly, STAT5 mutants lacking the transactivation domain (TAD) were retained in the cytoplasm following Epo stimulation. Building upon this, we identified a 12-amino-acid stretch in the TAD sufficient to restore nuclear translocation. Further analysis revealed two residues within this 12-amino-acid stretch, D754 and D758, to be essential for nuclear import of phosphorylated full-length STAT5. Importantly, a single intact TAD in the STAT5 dimer is sufficient for nuclear import. Our findings reveal a unique role of the TAD in STAT5 nuclear trafficking distinct from other STATs, providing new mechanistic insight and potential targets for therapeutic intervention in STAT5-driven disease such as myeloproliferative neoplasms and leukemia.

cell biology↗

bioRxiv2025

The V617F mutation in JAK2 renders myeloid cells more sensitive to IL-6-mediated gp130 signaling

The somatic V617F mutation in the pseudokinase domain of JAK2 (JAK2VF) causes various phenotypes of myeloproliferative neoplasms (MPN). By interacting with cytokine receptors such as those for erythropoietin (EPO) or thrombopoietin (TPO), JAK2VF induces ligand-independent dimerization and activation, leading to deregulated blood cell production, cytokine hypersensitivity, and inflammatory cytokine release. Interleukin-6 (IL-6), a key mediator of inflammatory symptoms in MPN, signals via homodimers of the gp130 receptor. We investigated whether JAK2VF alters gp130 dimerization and IL-6 sensitivity. Molecular dynamics simulations demonstrated that the JAK2VF pseudokinase domain forms more stable dimers than wild-type (WT) JAK2, potentially supporting gp130 tetramerization. In cell-based assays, IL-6 stimulation of JAK2VF+ cells induced stronger STAT3 activation than in JAK2-WT cells, reflecting enhanced IL-6 sensitivity. Moreover, JAK2VF expression elevated gp130 surface levels, dependent on the JAK2-binding motif in gp130. These findings indicate that JAK2VF promotes gp130 expression and dimerization, sensitizing mutant cells to IL-6. Thus, JAK2VF-driven amplification of IL-6/gp130 signaling may foster chronic inflammation and disease progression in MPN, representing a potential therapeutic target.

cancer biology↗