Priming does not change promoter sequence requirements for IFN induction or correlate with the expression of IFN regulatory factor-1.

Pretreatment of L929 cells with IFN enhances Sendai virus-mediated induction of IL-6, TNF-alpha, and IFNA and IFNB genes. The priming effect could be demonstrated at both the RNA and protein levels and the former did not require cellular protein synthesis. Priming increased the Sendai virus-mediated induction of a murine IFNA4 promoter-chloramphenicol acetyltransferase gene hybrid plasmid (A4CAT) in transiently transfected cells, and deletion analysis showed that the identical DNA sequence was required for the inducibility in primed and unprimed cells. Cotransfection of A4CAT plasmid with interferon regulatory factor-1 (IRF-1) expression plasmid increased CAT expression, however, the IRF-1-mediated expression was further enhanced by priming. These results show that the identical inducible element present in the promoter region of IFNA4 gene is required for both the inducibility and the priming effect; however, no direct correlation between the enhancement of expression of the IRF-1 gene and enhancement of expression of IFN, IL-6, and TNF-alpha genes in the primed cells was observed. We suggest that priming facilitates inducer-mediated posttranscriptional modulation of various transcriptional factors that play a role in stimulation of transcription of these genes.