SOCS-1 and SOCS-3 inhibit IFN-alpha-induced expression of the antiviral proteins 2,5-OAS and MxA.
Although the use of IFN-alpha in combination with ribavirin has improved the treatment efficacy of chronic hepatitis C virus (HCV) infection, 20-50% of patients still fail to eradicate the virus depending on the HCV genotype. Recently, overexpression of HCV core protein has been shown to inhibit IFN signaling and induce SOCS-3 expression. Aim of this study was to examine the putative role of SOCS proteins in IFN resistance. By Western blot analysis, a 4-fold induction of STAT-1/3 phosphorylation by IFN-alpha was observed in mock-transfected HepG2 clones. In contrast, IFN-induced STAT-1/3 phosphorylation was considerably downregulated by SOCS-1/3 overexpression. In mock-transfected cells, IFN-alpha induced 2',5'-OAS and myxovirus resistance A (MxA) promoter activity 40- to 80-fold and 10- to 35-fold, respectively, and this effect was abrogated in SOCS-1/3 overexpressing cells. As detected by Northern blot technique, IFN-alpha potently induced 2',5'-OAS and MxA mRNA expression in the control clones. Overexpression of SOCS-1 completely abolished both 2',5'-OAS and MxA mRNA expression, whereas SOCS-3 mainly inhibited 2',5'-OAS mRNA expression. Our results demonstrate that SOCS-1 and SOCS-3 proteins inhibit IFN-alpha-induced activation of the Jak-STAT pathway and expression of the antiviral proteins 2',5'-OAS and MxA. These data suggest a potential role of SOCS proteins in IFN resistance during antiviral treatment.
Vlotides
George
G
Department of Internal Medicine II, Grosshadern, Klinikum der Ludwig, Maximilians-Universität, Munich 81377, Germany.
Sörensen
Astrid S
AS
Kopp
Florian
F
Zitzmann
Kathrin
K
Cengic
Neziha
N
Brand
Stephan
S
Zachoval
Reinhart
R
Auernhammer
Christoph J
CJ
D015088:2',5'-Oligoadenylate Synthetase / Q000378:metabolism*; D000998:Antiviral Agents / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D008113:Liver Neoplasms / Q000378:metabolism*; D064547:Myxovirus Resistance Proteins; D012097:Repressor Proteins / Q000378:metabolism*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014157:Transcription Factors / Q000378:metabolism*
D000998:Antiviral Agents; D002352:Carrier Proteins; D016898:Interferon-alpha; D047908:Intracellular Signaling Peptides and Proteins; C579071:MX1 protein, human; D064547:Myxovirus Resistance Proteins; D012097:Repressor Proteins; C108944:SOCS1 protein, human; C106644:SOCS3 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014157:Transcription Factors; D015088:2',5'-Oligoadenylate Synthetase; D019204:GTP-Binding Proteins