title: Reciprocal interference between insulin and interferon-alpha signaling in hepatic cells: a vicious circle of clinical significance?
abstract: Insulin resistance (IR) is common in chronic hepatitis C (CHC) and associates with reduced virological response to pegylated-interferon (PEG-IFN)/ribavirin therapy, but the underlying mechanisms are still unclear. We have previously shown that, in CHC patients, insulin plasma levels are inversely related to antiviral effect induced by PEG-IFN. Therefore, we investigated the in vitro effect of insulin on interferon alpha (IFN-α) intracellular signaling as well as that of IFN-α on insulin signaling. HepG2 cells, preincubated with or without insulin, were stimulated with IFN-α2b and messenger RNA (mRNA) and protein expression of IFN-stimulated genes (ISGs) were measured at different timepoints. The role of intracellular suppressors of cytokine signaling 3 (SOCS3) was evaluated with the small interfering RNA (siRNA) strategy. To assess the effect of IFN-α on insulin signaling, HepG2 were preincubated with or without IFN before addition of insulin and cells were then analyzed for IRS-1 and for Akt/PKB Ser473 phosphorylation. Insulin (100 and 1000 nM) significantly reduced in a dose-dependent fashion IFN-induced gene expression of PKR (P=0.017 and P=0.0017, respectively), MxA (P=0.0103 and P=0.00186), and 2'-5' oligoadenylatesynthetase 1 (OAS-1) (P=0.002 and P=0.006). Insulin also reduced IFN-α-induced PKR protein expression. Although insulin was confirmed to increase SOCS3 expression, siRNA SOCS3 did not restore ISG expression after insulin treatment. IFN-α was found to reduce, in a dose-dependent fashion, IRS-1 gene expression as well as Akt/PKB Ser473 phosphorylation induced by insulin.
  
  
  CONCLUSIONS
  These results provide evidence of reciprocal interference between insulin and IFN-α signaling in liver cells. These findings may contribute to understand the role of insulin in CHC: IR might be favored by endogenous cytokines including IFN-α, and the resulting hyperinsulinemia then reduces the antiviral response to exogenous IFN in a vicious circle of clinical significance.
authors.affiliation: Venetian Institute of Molecular Medicine-VIMM, Padova, Italy.
authors.forename: Lisa
authors.initials: L
authors.lastname: Franceschini
authors.forename: Stefano
authors.initials: S
authors.lastname: Realdon
authors.forename: Moira
authors.initials: M
authors.lastname: Marcolongo
authors.forename: Silvia
authors.initials: S
authors.lastname: Mirandola
authors.forename: Gladis
authors.initials: G
authors.lastname: Bortoletto
authors.forename: Alfredo
authors.initials: A
authors.lastname: Alberti
mesh_terms: D002478:Cells, Cultured; D022781:Hepatocytes / Q000187:drug effects* / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000494:pharmacology* / Q000502:physiology*; D000077190:Interferon alpha-2; D016898:Interferon-alpha / Q000187:drug effects* / Q000494:pharmacology* / Q000502:physiology*; D011994:Recombinant Proteins; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D007328:Insulin; D000077190:Interferon alpha-2; D016898:Interferon-alpha; D011994:Recombinant Proteins