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

• Published in: Blood 2004-12, Vol.104 (12), p.3550-3557
• Main Authors: Tonozuka, Yukio, Minoshima, Yukinori, Bao, Ying Chun, Moon, Yuseok, Tsubono, Yohei, Hatori, Tomonori, Nakajima, Hideaki, Nosaka, Tetsuya, Kawashima, Toshiyuki, Kitamura, Toshio
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cell Differentiation - drug effects; Cell differentiation, maturation, development, hematopoiesis; Cell Line, Tumor; Cell physiology; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Fundamental and applied biological sciences. Psychology; GTPase-Activating Proteins - genetics; GTPase-Activating Proteins - metabolism; GTPase-Activating Proteins - physiology; Hematologic and hematopoietic diseases; Humans; Interleukin-6 - pharmacology; Leukemia - pathology; Leukemias. Malignant lymphomas. Malignant reticulosis. Myelofibrosis; Medical sciences; Molecular and cellular biology; Protein Binding; Protein Structure, Tertiary; rac1 GTP-Binding Protein - metabolism; STAT3 Transcription Factor; Trans-Activators - genetics; Trans-Activators - metabolism; Transcriptional Activation; Transfection
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2004-03-1066

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 (ΔGAP) did not significantly enhance it, suggesting that the GAP domain was required for enhancement of STAT3-dependent transcription. Intriguingly, M1 cells expressing ΔGAP 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.