PIN: A novel protein involved in IFN-γ accumulation of NOS-1 in neurons

In this study we investigate the role of the protein inhibitor of NOS-1 (PIN) in the interferon-γ (IFN-γ)-mediated posttranscriptional accumulation of nitric oxide synthase-1 (NOS-1) and the anti-vesicular stomatitis virus response in neuronal cells. IFN-γ-induced enhancement of NOS-1 activity is crucial for its antiviral activity in the central nervous system. IFN-γ treatment of neuronal cells results in an increase of total NOS-1 and decrease of total PIN proteins without alteration in their respective mRNA levels. PIN/NOS-1 complexes decreased after IFN-γ treatment. Transfection of cells with small interfering RNA (siRNA) for PIN results in a higher constitutive activity of NOS-1 and inhibition of viral replication. IFN-γ treatment did not change the amount of NOS-1 detectable by Western blot, when PIN is diminished by RNAi treatment. Overexpression of PIN results in lower constitutive NOS-1 expression and activity, and diminishes activation of NOS-1 by IFN-γ. Our findings indicate that in neurons, IFN-γ upregulates NOS-1 through proteasomal degradation of PIN.