Characterization of cellular proliferation and gene induction by the interferon cytokine

The interferon (IFN) family of cytokines functions in the mediation of cellular immunity and development. IFNs exert changes in cells through the activation of signaling pathways that ultimately result in new gene expression. In this study, evidence is provided that IFN can stimulate the proliferation of primary human endothelial cells. This contrasts with the growth suppressive effect of IFN observed on transformed cells, underscoring the distinctive responses of primary human cells. The growth stimulatory effect of IFN was determined by an increase in DNA synthesis assessed with [3H]-thymidine incorporation, an increase in G2 and M cell cycle phases evaluated by flow cytometric analysis, and an increase in cell number. Distinct cell types including primary human fibroblasts and smooth muscle cells were also growth stimulated by IFN. The signaling pathway of type I IFNs activates the signal transducers and activators of transcription, STAT1 and STAT2. In primary endothelial cells STAT3 and STAT5 were also activated, and these STATs are known to contribute to proliferation. To evaluate effectors of positive growth, DNA microarray analyses were performed to identify genes induced in response to IFN. These results revealed changes in the RNA levels of genes that encode proteins involved in proliferation.; IFN induced expression of antiviral genes is an essential component of the innate immune response. A newly identified IFN induced gene that contributes to an antiviral immune response is cig5. The regulated expression of this gene in response to IFN and Newcastle disease virus was assessed.{09}Kinetic studies of endogenous cig5 mRNA expression revealed an induction within 2.5 hrs of stimulation by IFN or virus.{09}A genomic sequence of 1,257 nt upstream of the cig5 gene was cloned to evaluate the presence of DNA regulatory elements. This sequence conferred responsiveness to both IFN and Newcastle disease virus in transcriptional reporter assays. Analyses with 5′ deletion mutants identified a 71 nt element that was critical for gene induction. Assessment of this sequence revealed the presence of an IFN-stimulated response element in the context of a virus responsive DNA element.