1. A GTPase-activating protein binds STAT3 and is required for IL-6-induced STAT3 activation and for differentiation of a leukemic cell line.
- Author
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Tonozuka Y, Minoshima Y, Bao YC, Moon Y, Tsubono Y, Hatori T, Nakajima H, Nosaka T, Kawashima T, and Kitamura T
- Subjects
- Cell Line, Tumor, DNA-Binding Proteins genetics, GTPase-Activating Proteins genetics, GTPase-Activating Proteins physiology, Humans, Protein Binding, Protein Structure, Tertiary, STAT3 Transcription Factor, Trans-Activators genetics, Transcriptional Activation, Transfection, rac1 GTP-Binding Protein metabolism, Cell Differentiation drug effects, DNA-Binding Proteins metabolism, GTPase-Activating Proteins metabolism, Interleukin-6 pharmacology, Leukemia pathology, Trans-Activators metabolism
- Abstract
We previously identified a guanosine triphosphatase (GTPase)-activating protein (GAP) male germ cell Rac GAP (MgcRacGAP) that enhanced interleukin-6 (IL-6)-induced macrophage differentiation of murine M1 leukemia cells. Later, MgcRacGAP was found to play crucial roles in cell division. However, how MgcRacGAP enhanced IL-6-induced differentiation remained elusive. Here we show that MgcRacGAP enhances IL-6-induced differentiation through enhancement of signal transducer and activator of transcription-3 (STAT3) activation. MgcRacGAP, Rac, and STAT3 formed a complex in IL-6-stimulated M1 cells, where MgcRacGAP interacted with Rac1 and STAT3 through its cysteine-rich domain and GAP domain. In reporter assays, the wild-type MgcRacGAP enhanced transcriptional activation of STAT3 while a GAP-domain deletion mutant (DeltaGAP) did not significantly enhance it, suggesting that the GAP domain was required for enhancement of STAT3-dependent transcription. Intriguingly, M1 cells expressing DeltaGAP had no effect on the differentiation signal of IL-6, while forced expression of MgcRacGAP rendered M1 cells hyperresponsive to the IL-6-induced differentiation. Moreover, knockdown of MgcRacGAP by RNA interference profoundly suppressed STAT3 activation, implicating MgcRacGAP in the STAT3-dependent transcription. All together, our data not only reveal an important role for MgcRacGAP in STAT3 activation, but also demonstrate that MgcRacGAP regulates IL-6-induced cellular differentiation in which STAT3 plays a pivotal role.
- Published
- 2004
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