Interdomain interaction of Stat3 regulates its Src homology 2 domain-mediated receptor binding activity.
Activation of Stat proteins by cytokines is initiated by their Src homology 2 (SH2) domain-mediated association with the cytokine receptors. Previously, we identified an essential role of the coiled-coil domain of Stat3 in binding of the receptor peptides derived from the interleukin-6 receptor subunit, gp130. In this study, we further investigated the molecular basis of this regulation. We found that the C-terminal domain of Stat3 negatively regulates its receptor binding activity only in the absence of the first alpha-helix of the coiled-coil domain, which leads to a hypothesis of intramolecular interaction. Physical interactions between the coiled-coil domain and the C-terminal domain, as well as the SH2 domain, were indeed detected. Furthermore, a sub-region of the C-terminal domain (amino acids 720-740), which is also involved in the interaction with the coiled-coil domain, was demonstrated to be critical for the regulation of the receptor binding. Correspondingly, phosphorylation on Ser-727 within this region inhibits this interaction. In agreement with the peptide binding results, both the coiled-coil domain and the C-terminal sub-region are necessary for the functional recruitment of Stat3 to the cellular gp130 in response to interleukin-6, suggesting that the interdomain interaction is a prerequisite for the SH2-mediated receptor binding in interleukin-6 signaling.
Zhang
Tong
T
Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609.
Seow
Kah Tong
KT
Ong
Chin Thing
CT
Cao
Xinmin
X
D000818:Animals; D015703:Antigens, CD / Q000502:physiology; D050822:Cytokine Receptor gp130; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000502:physiology; D008956:Models, Chemical; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D050796:STAT3 Transcription Factor; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000737:chemistry / Q000502:physiology*; D018909:src Homology Domains / Q000502:physiology*
D015703:Antigens, CD; D004268:DNA-Binding Proteins; C494199:IL6ST protein, human; C494201:Il6st protein, rat; D008562:Membrane Glycoproteins; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494088:Stat3 protein, rat; D015534:Trans-Activators; D050822:Cytokine Receptor gp130