The HXY Box Regulatory Element Modulates Expression of the Murine I A Antigen-Associated Invariant Chain in L Fibroblasts

Abstract

The murine invariant chain (Ii) gene has been shown to be interferon-γ (IFN-γ)-inducible in a number of nonlymphoid cell types. In mouse L cells, steady-state levels of Ii mRN A are barely detectable in untreated cells but increase sharply upon IFN-γ treatment. In IFN-γ treated L cells, transcription starts 23, 28, 38, and 40 bases downstream of the TATA box. To identify cis-acting elements regulating expression of the Ii gene, reporter plasmids containing deletions of the Ii promoter have been constructed and transfected into mouse L cells. Deletion of the H box results in a 50-100% increase in basal expression. Deletion of both the H and X boxes increases basal expression by 200-300% above that seen in constructs containing all three elements. A 25% decrease in basal level expression is seen for constructs that lack the Y-box element when compared to constructs containing the Y-box element but not the H- and X-box elements. DNase I footprinting analysis demonstrates protection of the H, X, and Y boxes as well as a nonconserved region between the H and X boxes. Mobility-shift experiments detect a factor specifically interacting with the Y box. Although the H-, X-, and Y-box elements interact with nuclear protein and are regulatory elements in L cells, these elements do not appear to play a role in IFN-γ induction suggesting that other regulatory mechanisms must account for IFN-γ's induction of the Ii in L cells.