Tyrosine kinase inhibitors and antioxidants modulate NF-κB and NOS-II induction in retinal epithelial cells.

Bovine retinal pigmented epithelial (RPE) cells express an inducible nitric oxide synthase (NOS-II) after activation with interferon-γ (IFN-γ) and lipopolysaccharide (LPS). Experiments were performed to investigate the effects of tyrosine kinase inhibitors (genistein and herbimycin A) and antioxidants [pyrrolidine dithiocarbamate (PDTC) and butyl hydroxyanisol] on NOS-II induction. The LPS-IFN-γ-induced nitrite release was inhibited in a concentration-dependent manner by these compounds. Analysis by Northern blot showed that this inhibitory effect correlated with a decrease in NOS-II mRNA accumulation. Analysis by electrophoretic mobility shift assay of the activation of the transcription factor nuclear factor-κB (NF-κB) involved in NOS-II induction demonstrated that LPS alone or combined with IFN-γ induced NF-κB binding. NF-κB activation was not changed by the presence of tyrosine kinase inhibitors but was totally prevented by PDTC pretreatment. Immunocytochemistry experiments confirmed the reduction of the nuclear translocation of NF-κB only by PDTC. Our results demonstrated the existence in retinal pigmented epithelial cells of different intracellular signaling pathways in NOS-II induction, since tyrosine kinase inhibitors blocked NOS-II mRNA accumulation without inhibiting NF-κB activation. Furthermore, the LPS-IFN-γ-induced NOS-II mRNA accumulation was sensitive to cycloheximide, suggesting that, in addition to NF-κB, transcriptional factors that require new protein synthesis are involved in NOS-II induction.