Reduced expression of Jak-1 and Tyk-2 proteins leads to interferon resistance in hepatitis C virus replicon.
BACKGROUND
Alpha interferon in combination with ribavirin is the standard therapy for hepatitis C virus infection. Unfortunately, a significant number of patients fail to eradicate their infection with this regimen. The mechanisms of IFN-resistance are unclear. The aim of this study was to determine the contribution of host cell factors to the mechanisms of interferon resistance using replicon cell lines.


RESULTS
HCV replicons with high and low activation of the IFN-promoter were cultured for a prolonged period of time in the presence of interferon-alpha (IFN-alpha2b). Stable replicon cell lines with resistant phenotype were isolated and characterized by their ability to continue viral replication in the presence of IFN-alpha. Interferon resistant cell colonies developed only in replicons having lower activation of the IFN promoter and no resistant colonies arose from replicons that exhibit higher activation of the IFN promoter. Individual cell clones were isolated and nine IFN resistant cell lines were established. HCV RNA and protein levels in these cells were not altered by IFN- alpha2b. Reduced signaling and IFN-resistant phenotype was found in all Huh-7 cell lines even after eliminating HCV, suggesting that cellular factors are involved. Resistant phenotype in the replicons is not due to lack of interferon receptor expression. All the cell lines show defect in the JAK-STAT signaling and phosphorylation of STAT 1 and STAT 2 proteins were strongly inhibited due to reduced expression of Tyk2 and Jak-1 protein.


CONCLUSIONS
This in vitro study provides evidence that altered expression of the Jak-Stat signaling proteins can cause IFN resistance using HCV replicon cell clones.
Hazari
Sidhartha
S
Department of Pathology and Laboratory Medicine, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, USA. shazari@tulane.edu
Taylor
Lizeth
L
Haque
Salima
S
Garry
Robert F
RF
Florman
Sander
S
Luftig
Ronald
R
Regenstein
Frederic
F
Dash
Srikanta
S
D000998:Antiviral Agents / Q000276:immunology* / Q000494:pharmacology; D002460:Cell Line; D016174:Hepacivirus / Q000187:drug effects* / Q000276:immunology*; D006801:Humans; D016898:Interferon-alpha / Q000276:immunology* / Q000494:pharmacology; D053613:Janus Kinase 1 / Q000096:biosynthesis* / Q000276:immunology; D010766:Phosphorylation; D012367:RNA, Viral / Q000096:biosynthesis / Q000187:drug effects; D050794:STAT1 Transcription Factor / Q000378:metabolism; D050795:STAT2 Transcription Factor / Q000378:metabolism; D053634:TYK2 Kinase / Q000096:biosynthesis* / Q000276:immunology; D014764:Viral Proteins / Q000096:biosynthesis / Q000187:drug effects
D000998:Antiviral Agents; D016898:Interferon-alpha; D012367:RNA, Viral; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D014764:Viral Proteins; D053613:Janus Kinase 1; D053634:TYK2 Kinase; C070139:TYK2 protein, human