STAT5A stays out of the nucleus (blue) when Rac1 is removed (bottom).
STAT proteins signal downstream of cytokine receptors. These researchers previously reported an association between STAT3 and the GTPase-activating protein MgcRacGAP. Here they report that Rac1 and MgcRacGAP bind STAT5A, and that the association between MgcRacGAP and STAT5A is enhanced by IL-3 signaling. Both Rac1 and MgcRacGAP were necessary for efficient entry of STAT5A into the nucleus, and in semipermeabilized cells a dominant-negative Rac1 prevented binding of STAT5A to importin-α, and thus nuclear entry.
Others have previously shown, using armadillo proteins as import substrates, that Rac1 has a nuclear localization sequence (NLS) that is active when Rac1 is in its active,...
