A GTPase-activating protein binds STAT3 and is required for IL-6-induced STAT3 activation and for differentiation of a leukemic cell line.

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.

• Authors: Yukio Tonozuka, Yukinori Minoshima, Ying Chun Bao, Yuseok Moon, Yohei Tsubono, Tomonori Hatori, Hideaki Nakajima, Tetsuya Nosaka, Toshiyuki Kawashima, Toshio Kitamura
• Journal: Blood (Blood) Vol. 104 Issue 12 Pg. 3550-7 (Dec 01 2004) ISSN: 0006-4971 [Print] United States
• PMID: 15284113 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA-Binding Proteins
• GTPase-Activating Proteins
• Interleukin-6
• STAT3 Transcription Factor
• STAT3 protein, human
• Trans-Activators
• mgcRacGAP
• rac1 GTP-Binding Protein

Topics

• Cell Differentiation (drug effects)
• Cell Line, Tumor
• DNA-Binding Proteins (genetics, metabolism)
• GTPase-Activating Proteins (genetics, metabolism, physiology)
• Humans
• Interleukin-6 (pharmacology)
• Leukemia (pathology)
• Protein Binding
• Protein Structure, Tertiary
• STAT3 Transcription Factor
• Trans-Activators (genetics, metabolism)
• Transcriptional Activation
• Transfection
• rac1 GTP-Binding Protein (metabolism)