Stat5B shuttles between cytoplasm and nucleus in a cytokine-dependent and -independent manner.
In response to cytokine stimuli, Stats are phosphorylated and translocated to the nucleus to activate target genes. Then, most are dephosphorylated and returned to the cytoplasm. Using Ba/F3 cells, we found that the nuclear export of Stat5B by cytokine depletion was inhibited by leptomycin B (LMB), a specific inhibitor of nuclear export receptor chromosome region maintenance 1. Interestingly, LMB treatment in the absence of cytokine led to the accumulation of Stat5B in the nucleus, suggesting that Stat5B shuttles between the nucleus and the cytoplasm as a monomer without cytokine stimulation. This notion is supported by the observation that LMB-induced accumulation of Stat5B in the nucleus was also observed with Stat5B having a mutated tyrosine 699, which is essential for dimer formation. Using a series of mutant Stat5Bs, we identified a part of the coiled coil domain to be a critical region for monomer nuclear import and a more N-terminal region to be critical for the cytokine stimulation dependent import of Stat5B. Taken together, we propose a model in which Stat5B shuttles between the nucleus and cytoplasm by two different mechanisms, one being a factor-independent constitutive shuttling by monomeric form, and the other, a factor stimulation-dependent one regulated by tyrosine phosphorylation and subsequent dimerization.
Zeng
Rong
R
Department of Molecular and Developmental Biology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Aoki
Yutaka
Y
Yoshida
Minoru
M
Arai
Ken-ichi
K
Watanabe
Sumiko
S
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D016207:Cytokines / Q000494:pharmacology*; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D007377:Interleukin-3 / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D008894:Milk Proteins; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D017434:Protein Structure, Tertiary; D050799:STAT5 Transcription Factor; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018909:src Homology Domains
D016207:Cytokines; D004268:DNA-Binding Proteins; D005231:Fatty Acids, Unsaturated; D007377:Interleukin-3; D008894:Milk Proteins; D050799:STAT5 Transcription Factor; C494096:Stat5b protein, mouse; D015534:Trans-Activators; D019000:Phosphotyrosine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; C038753:leptomycin B