Related Experiment Videos
Induction of Jak/STAT signaling by activation of the type 1 TNF receptor
1Department of Microbiology and Immunology and the Walther Oncology Center, Indiana University School of Medicine, Indianapolis 46202, USA.
Abstract:
Cellular responses to TNF are initiated by either of two cell surface receptors, the type 1 TNF receptor (TNFR1) and the type 2 TNF receptor (TNFR2). Although neither receptor contains an intrinsic protein tyrosine kinase, such activity has been implicated in TNF action. In this study, we show that murine TNF induces the tyrosine phosphorylation and activation of the intracellular Janus tyrosine kinases Jak1, Jak2, and Tyk2 in murine 3T3-L1 adipocytes. Activation of Jak kinases by TNF was associated with tyrosine phosphorylation of STAT1, STAT3, STAT5, and STAT6, but not STAT2 or STAT4, showing that TNF acts on a specific subset of these latent cytoplasmic transcription factors in 3T3-L1 adipocytes. Agonist antiserum to TNFR1 induced Jak kinase and STAT protein phosphorylation. Phosphorylation of Jak proteins was also induced by human TNF, which selectively binds to TNFR1 on murine cells. 35S-labeled Jak kinases were precipitated from a cell-free system and from lysates of 3T3-L1 adipocytes by a glutathione S-transferase fusion protein containing the cytoplasmic domain of TNFR1. These results suggest that the cytoplasmic domain of TNFR1 can directly interact with and form signaling complexes with Jak kinases. Jak2 was precipitated from HeLa cells by antiserum to TNFR1, directly demonstrating their association in vivo. Thus, TNF activates a Jak/STAT signal-transduction cascade by acting through TNFR1.
Insights
Tumor necrosis factor (TNF) activates Janus kinases (Jak) and STAT proteins via the tumor necrosis factor receptor 1 (TNFR1) in 3T3-L1 adipocytes. This study reveals TNF signaling through TNFR1 initiates a Jak/STAT cascade.
Area of Science:
- Cellular signaling pathways
- Immunology
- Molecular biology
Background:
- Cellular responses to tumor necrosis factor (TNF) are mediated by two receptors: TNFR1 and TNFR2.
- While neither receptor possesses intrinsic tyrosine kinase activity, tyrosine kinase activity is crucial for TNF signaling.
- The precise mechanisms by which TNF initiates intracellular signaling cascades remain incompletely understood.
Purpose of the Study:
- To investigate the role of Janus kinases (Jak) and Signal Transducer and Activator of Transcription (STAT) proteins in TNF-induced signaling.
- To determine the specific TNF receptor involved in initiating this signaling cascade.
- To elucidate the interaction between TNF receptors and intracellular signaling molecules.
Main Methods:
- Murine TNF was used to stimulate 3T3-L1 adipocytes.
- Tyrosine phosphorylation and activation of Jak kinases (Jak1, Jak2, Tyk2) and STAT proteins (STAT1, STAT3, STAT5, STAT6) were assessed.
- Immunoprecipitation assays were performed using glutathione S-transferase fusion proteins and antisera against TNFR1 and Jak2.
Main Results:
- Murine TNF induced tyrosine phosphorylation and activation of Jak1, Jak2, and Tyk2 in 3T3-L1 adipocytes.
- TNF activated STAT1, STAT3, STAT5, and STAT6, but not STAT2 or STAT4.
- TNFR1 activation led to Jak kinase and STAT protein phosphorylation, and direct interaction between TNFR1 cytoplasmic domain and Jak kinases was demonstrated in vitro and in vivo.
Conclusions:
- TNF activates a Jak/STAT signal-transduction cascade through TNFR1.
- The cytoplasmic domain of TNFR1 directly interacts with Jak kinases, initiating downstream signaling.
- This study identifies a critical mechanism for TNF-mediated cellular responses.