Negative Regulation by Protein Tyrosine Phosphatase of IFN-γ-Dependent Expression of Inducible Nitric Oxide Synthase

Abstract

Abstract Treatment of cultured peritoneal macrophages with IFN-γ resulted in tyrosine phosphorylation of IκBα and IκBβ, NF-κB activation, and expression of inducible NO synthase (iNOS). Since tyrosine phosphorylation of IκBα is sufficient to activate NF-κB in Jurkat cells, macrophages were treated with the protein tyrosine phosphatase inhibitor peroxovanadate (POV), which elicited an intense tyrosine phosphorylation of both IκB. However, this phosphorylation failed to activate NF-κB. Treatment with POV of macrophages stimulated with IFN-γ or LPS potentiated the degradation of IκBα and IκBβ, the activation of NF-κB, and the expression of iNOS. Analysis of the iNOS gene promoter activity corresponding to the 5′-flanking region indicated that POV potentiates the cooperation between IFN-γ-activated transcription factors and NF-κB. These results indicate that tyrosine phosphorylation of IκB is not sufficient to activate NF-κB in macrophages and propose a negative role for protein tyrosine phosphatase in the expression of iNOS in response to IFN-γ.