Regulation of the interferon-inducible PKR kinase gene: the KCS element is a constitutive promoter element that functions in concert with the interferon-stimulated response element.

The RNA-dependent protein kinase PKR plays important roles in the antiviral and antiproliferative actions of IFN. The IFN-inducible promoter of the human PKR gene contains a 15-bp DNA element designated KCS. The KCS element is located 4 bp upstream of the interferon-stimulated response element (ISRE) and is required for both basal and IFN-inducible transcription. We have examined the effect of insertion mutations between the KCS and the ISRE elements, as well as altered orientation of the KCS element relative to the ISRE element, to assess a possible functional interaction between them. Large insertions (>or=93 bp) between the KCS and ISRE elements significantly reduced both basal and IFN-inducible promoter activity. The function of the KCS element was dependent on the orientation of KCS relative to the ISRE element. Multimerization of the KCS element increased both basal and IFN-inducible transcription. Electrophoretic mobility shift analyses (EMSA) identified IFN-inducible protein complex formation that required both the KCS and the ISRE DNA element sequences. The novel IFN-inducible protein complexes contained the transcription factor STAT1, as shown by supershift analyses and by their presence in extracts prepared from STAT1 wild-type but not from STAT1-/- null cells. These results, taken together, strongly suggest that the KCS and ISRE elements of the human PKR promoter represent a functional unit.