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

A 12-amino-acid stretch within the STAT5 transactivation domain is essential for its nuclear import, with residues D754 and D758 being critical for this process.

• Why it matters: Understanding STAT5 nuclear translocation is crucial because it underpins gene regulation in hematopoietic signaling and is linked to diseases like myeloproliferative neoplasms and leukemia.
• What they did: Live-cell imaging of fluorescent STAT5 mutants in STAT5 -/- HeLa EpoR cells revealed that mutants lacking the transactivation domain are retained in the cytoplasm after Epo stimulation, and identified a specific 12-amino-acid segment necessary for nuclear import.
• The result: A single intact TAD in the STAT5 dimer suffices for nuclear import, highlighting a unique role of the TAD in STAT5 trafficking that may inform therapeutic strategies for STAT5-related diseases.