A Rac GTPase-Activating Protein, MgcRacGAP, Is a Nuclear Localizing Signal-Containing Nuclear Chaperone in the Activation of STAT Transcription Factors

作者：Kawashima Toshiyuki^*; Bao Ying Chun; Minoshima Yukinori; Nomura Yasushi; Hatori Tomonori; Hori Tetsuya; Fukagawa Tatsuo; Fukada Toshiyuki; Takahashi Noriko; Nosaka Tetsuya; Inoue Makoto; Sato Tomohiro; Kukimoto Niino Mutsuko; Shirouzu Mikako; Yokoyama Shigeyuki; Kitamura Toshio

来源：Molecular and Cellular Biology, 2009, 29(7): 1796-1813.

DOI：10.1128/MCB.01423-08

In addition to their pleiotropic functions under physiological conditions, transcription factors STAT3 and STAT5 also have oncogenic activities, but how activated STATs are transported to the nucleus has not been fully understood. Here we show that an MgcRacGAP mutant lacking its nuclear localizing signal (NLS) blocks nuclear translocation of p-STATs both in vitro and in vivo. Unlike wild-type MgcRacGAP, this mutant did not promote complex formation of phosphorylated STATs (p-STATs) with importin alpha in the presence of GTP-bound Rac1, suggesting that MgcRacGAP functions as an NLS-containing nuclear chaperone. We also demonstrate that mutants of STATs lacking the MgcRacGAP binding site (the strand beta b) are hardly tyrosine phosphorylated after cytokine stimulation. Intriguingly, mutants harboring small deletions in the C'-adjacent region (beta b-beta c loop region) of the strand beta b became constitutively active with the enhanced binding to MgcRacGAP. The molecular basis of this phenomenon will be discussed, based on the computer-assisted tertiary structure models of STAT3. Thus, MgcRacGAP functions as both a critical mediator of STAT's tyrosine phosphorylation and an NLS-containing nuclear chaperone of p-STATs.

• 出版日期2009-4-1
• 单位河北医科大学