期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：46
页码：13015-13020
DOI：10.1073/pnas.1611228113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceSTAT6 is a transcription factor and plays a predominant role in IL-4/IL-13 and virus-mediated signaling pathways. Extensive studies have linked malfunctions of STAT6 to pathological features of asthma and cancer. Targeting the function of STAT6 has become an attractive therapy. Understanding the molecular mechanisms of STAT6 transcriptional regulation is still scarce. Here, we report the atomic-level structures of the phosphorylated STAT6 core fragment homodimer, both in DNA-free and complexed with N4 or N3 site DNA, uncovering both a larger dimer interface intersection angle and the unique residue H415 of STAT6 as important factors for discrimination of N4 from N3 site DNA. This study uncovers a dramatic conformational change in STAT6 dimer for recognizing and preferring N4 site DNA. STAT6 participates in classical IL-4/IL-13 signaling and stimulator of interferon genes-mediated antiviral innate immune responses. Aberrations in STAT6-mediated signaling are linked to development of asthma and diseases of the immune system. In addition, STAT6 remains constitutively active in multiple types of cancer. Therefore, targeting STAT6 is an attractive proposition for treating related diseases. Although a lot is known about the role of STAT6 in transcriptional regulation, molecular details on how STAT6 recognizes and binds specific segments of DNA to exert its function are not clearly understood. Here, we report the crystal structures of a homodimer of phosphorylated STAT6 core fragment (STAT6CF) alone and bound with the N3 and N4 DNA binding site. Analysis of the structures reveals that STAT6 undergoes a dramatic conformational change on DNA binding, which was further validated by performing molecular dynamics simulation studies and small angle X-ray scattering analysis. Our data show that a larger angle at the intersection where the two protomers of STAT meet and the presence of a unique residue, H415, in the DNA-binding domain play important roles in discrimination of the N4 site DNA from the N3 site by STAT6. H415N mutation of STAT6CF decreased affinity of the protein for the N4 site DNA, but increased its affinity for N3 site DNA, both in vitro and in vivo. Results of our structure-function studies on STAT6 shed light on mechanism of DNA recognition by STATs in general and explain the reasons underlying STAT6s preference for N4 site DNA over N3.
关键词：STAT6 ; N4 site DNA recognition ; JAK-STAT pathway ; antiviral innate immunity ; crystal structure
