[A novel molecular mechanism of interferon alpha-regulated expression of retinoic acid-induced gene G].
OBJECTIVE
To investigate the molecular mechanisms by which IFN-alpha regulated retinoic acid-induced gene G (RIG-G) expression.


METHODS
The expression of STAT1, p-STAT1 and RIG-G in IFN-alpha-treated NB4 cells was detected by Western blot. The roles of STAT1, STAT2 and IRF-9 in IFN-alpha-induced RIG-G expression were analyzed in STAT1-null U3A cells by cell transfection, reporter gene assay, co-immunoprecipitation and chromatin immunoprecipitaion.


RESULTS
In U3A cells, only when STAT2 and IRF-9 were co-transfected, the luciferase activities of RIG-G promoter-containing reporter gene could be highly increased about 8-fold compared with that in the control group. Moreover, in the absence of IFN-alpha, similar effects were observed in either IRF-9 co-transfected with wild type or mutant form of STAT2, whereas IFN-alpha could increase the transactivation activity of wild type STAT2 and IRF-9 by 6-fold compared with that without IFN-alpha, but had no effect on mutant STAT2. In addition, STAT2 could interact with IRF-9 and bind to the RIG-G promoter.


CONCLUSIONS
STAT2 may interact with IRF-9 in a STAT1-independent manner. The complex STAT2/IRF-9 is the key factor mediating the expression of RIG-G gene regulated by IFN-alpha. This is a novel signal transduction cascade for IFN which is different from the classical JAK-STAT pathway.
Lou
Ye-jiang
YJ
Shanghai Institute of Hematology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, China.
Pan
Xiao-rong
XR
Jia
Pei-min
PM
Li
Dong
D
Zhang
Zhang-lin
ZL
Xu
Gui-ping
GP
Tong
Jian-hua
JH
D045744:Cell Line, Tumor; D005354:Fibrosarcoma / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D047468:Immunoprecipitation; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit / Q000235:genetics / Q000378:metabolism*; D016898:Interferon-alpha / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation; D010957:Plasmids; D050794:STAT1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D050795:STAT2 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
C116468:IFIT3 protein, human; C494227:IRF9 protein, human; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D016898:Interferon-alpha; D047908:Intracellular Signaling Peptides and Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human